micro E3

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micro E3
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  1. Aerobic Gram-negative Cocci
    Genus Neisseria

    General
    Presumptive identifications of Neisseria gonorrhoeae and N. meningitidis are based on their gram reaction, cellular morphology and cellular arrangement. These gram-negative cocci are arranged in pairs.
  2. Aerobic Gram-negative Cocci
    Genus Neisseria

    Pathogenic Neisseria Species
    • N. gonorrhoeae causes human gonorrhoeae. It is a human-adapted pathogen.
    • N. meningitidis causes human meningococcal meningitis. It is a human-adapted pathogen.
  3. Aerobic Gram-negative Cocci
    Genus Neisseria

    Habitat and Ecology
    Neisseria species are transient flora of mucous membranes.
  4. Aerobic Gram-negative Cocci
    Genus Neisseria

    Cellular Characteristics
    Neisseria species are gram-negative cocci arranged in pairs.
  5. Aerobic Gram-negative Cocci
    Genus Neisseria

    Cultural Characteristics
    • Neisseria species are obligate aerobes with fastidious atmospheric and nutritional growth requirements.
    • Neisseria species can be cultured on chocolate agar under capnophilic conditions at 37C.
  6. Aerobic Gram-negative Cocci
    Genus Neisseria

    Biochemical Characteristics
    Neisseria species are oxidase-positive and saccharolytic.
  7. Aerobic Gram-negative Cocci
    Genus Neisseria

    Human Gonorrhea
    • Gonorrhea is a sexually transmitted disease that primarily affects heterosexuals. The disease is transmitted during intercourse with 2 to 8 day incubation period. Infection of mucous membranes of the genitalia produces suppurative exudate.
    • In females, clinical signs (burning, increased frequency of urination and abnormal vaginal discharge) are characteristic. Infertility due to scarring of the Fallopian tubes is a common complication. Many women with gonorrhea are asymptomatic.
    • In males, clinical signs (yellow purulent urethral discharge) are characteristic. About 10% of men are asymptomatic. Clinical diagnoses are based on signs of a reproductive tract infection and the presence of gram-negative cocci arranged in pairs in gram stained exudate.
    • Diagnoses are confirmed by culture and biochemical identification of N. gonorrhoeae.
  8. Aerobic Gram-negative Cocci
    Genus Neisseria

    Human Meningococcal Meningitis
    • Meningococcal meningitidis primarily occurs in children from 6 to 24 months-of-age and young adults from 10 to 20 years-of-age. Inhalation is the primary mode of transmission. Adults that are nasal pharyngeal carriers are the primary source and reservoir of N. meningitidis. The bacteria enter via upper respiratory tract, disseminate via blood and induce lesions in various organs and tissues (meninges). Lesions are largely confined to meninges, but pharyngeal lesions can be observed. Clinical meningococcal meningitis cases have a high mortality rate.
    • Clinical diagnoses are based on signs of meningitis and the presence of gram-negative cocci arranged in pairs in Gram stained smears prepared from spinal fluids.
    • Diagnoses are confirmed by the cultural isolation and biochemical identification of N. meningitidis.
  9. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Aerobic Genera
    Citrobacter, Enterobacter, Escherichia, Klebsiella, Proteus, Salmonella, Yersinia
  10. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genera with Human Enteric Pathogens
    Selected members of the genera Escherichia, Salmonella, Shigella and Yersinia cause enteric infections in humans.
  11. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genera with Animal Enteric Pathogens
    Selected members of the genera Escherichia and Salmonella cause enteric infections in selected domestic animals.
  12. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genera with Human and Animal Extraintestinal Pathogens
    Selected members of the genera Citrobacter, Enterobacter, Escherichia, Klebsiella, Proteus, Salmonella and Yersinia cause extraintestinal infections in humans and selected domestic animals.
  13. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Habitat and Ecology
    • Many Enterobacteriaceae are normal or transient enteric flora. Natural habitat of these microorganisms is the lower gastrointestinal tract (ileum and large intestine). From a few hours after birth and throughout life, successions of different Enterobacteriaceae colonize the gastrointestinal tracts of humans and animals.
    • Enterobacteriaceae, which are facultative anaerobes, comprise one percent of intestinal microflora and obligate anaerobic bacteria comprise 99% of intestinal microflora.
    • Escherichia coli is the most prevalent facultative anaerobic species in gastrointestinal tracts of healthy humans and animals.
    • Many Enterobacteriaceae are found ubiquitously in the environment as fecal contaminants. These bacteria can survive for days or weeks under ideal conditions.
  14. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Cellular Characteristics
    • Enterobacteriaceae are gram-negative bacilli.
    • Klebsiella and Shigella species are nonmotile.
    • Citrobacter, Enterobacter and Proteus species are motile with peritrichous flagella. Most Escherichia coli serovars and mammalian-adapted Salmonella serovars are motile with peritrichous flagella, but some E. coli serovars and avian-adapted Salmonella serovars are nonmotile.
    • Y. enterocolitica and Y. pseudotuberculosis are motile with peritrichous flagella at 20C and below and nonmotile at 37C.
    • Y. pestis is nonmotile.
  15. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Cultural Characteristics
    • Enterobacteriaceae are facultative anaerobes and can be cultured on blood agar and MacConkey agar under aerobic conditions at 37C.
    • On blood agar, colonies of E. coli can be hemolytic or nonhemolytic, but other Enterobacteriaceae are nonhemolytic.
    • On MacConkey agar, lactose-positive bacteria form red colonies and lactose-negative bacteria form colorless colonies.
  16. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Biochemical Characteristics
    • Enterobacteriaceae are oxidase-negative and saccharolytic.
    • Identification to species level, except Salmonella, is based on biochemical test criteria.
  17. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Extraintestinal Infections
    • In humans and domestic animals, Enterobacteriaceae are isolated from over fifty percent of opportunistic infections. These infections can be primary or secondary to other disease causing agents.
    • Extraintestinal infections can be caused by only one bacterial species, but many infections are polymicrobial with 2 or more bacterial species. Enterobacteriaceae are commonly found in mixed culture with other facultative anaerobes and/or obligate anaerobes.
    • Because of fecal contamination, Enterobacteriaceae can be involved in infections anywhere in the body (genital tract, respiratory tract, urinary tract, mastitis, septicemias and wounds).
    • From extraintestinal infections, E. coli and Klebsiella pneumoniae subspecies pneumoniae are the most commonly isolated pathogens.
    • From urinary tract infections, E. coli and Proteus species are the most commonly isolated pathogens.
  18. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Citrobacter
    Citrobacter species are isolated from opportunistic extraintestinal infection and are usually isolated in mixed culture.
  19. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Enterobacter
    Enterobacter species are isolated from opportunistic extraintestinal infections and are usually isolated in mixed culture.
  20. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    E. coli is a common cause of enteric and extraintestinal infections.
  21. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    Enteric Infections
    • In humans and domestic animals, colibacillosis is a group of diseases where the primary site of infection is the intestine. All ages are affected, but colibacillosis is primarily a disease of the young.
    • In humans, cattle and swine, enterotoxigenic E. coli are commonly isolated from clinical diseases and are serotyped using their fimbrial (F) antigens.
    • In humans, clinical significance of enterohemorrhagic E. coli, enteroinvasive E. coli and enteropathogenic E. coli is well documented.
    • In domestic animals, clinical significance of enterohemorrhagic E. coli, enteroinvasive E. coli and enteropathogenic E. coli is poorly documented.
    • Enterohemorrhagic E. coli, enteroinvasive E. coli and enteropathogenic E. coli pathotypes are serotyped using capsular (K), flagellar (H) and somatic (O) antigens.
  22. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    Extraintestinal Infections
    • Two theories of E. coli in extraintestinal infections are presented.
    • Prevalence theory is based on the premise that E. coli serovars frequently found in various extraintestinal diseases are the same as those found to be most prevalent in feces.
    • Special pathogenicity theory is based on the premise that selected E. coli serovars have a special affinity to induce various extraintestinal diseases (cystitis and meningitis).
    • Current data suggest validity for each theory depending on the disease condition.
  23. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    Serovars
    Over 3,500 E. coli serovars are based on their H, K and O antigens.
  24. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Klebsiella
    Klebsiella species are isolated from opportunistic extraintestinal infections and are commonly isolated in pure culture (cystitis, mastitis and metritis). Because of their potent endotoxin, endotoxemia and endotoxic shock are commonly observed in these infections.
  25. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Proteus
    Proteus species are isolated from opportunistic extraintestinal infections and are usually isolated in mixed culture. In humans and domestic animals, urinary tract infections are common.
  26. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Motile Mammalian-Adapted Salmonella Serovars
    Over 2,500 motile Salmonella serovars and are identified based on H and O antigens. In humans and domestic animals, selected Salmonella serovars are enteric pathogens and numerous Salmonella serovars are isolated from extraintestinal infections.
  27. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Nonmotile Avian-Adapted Salmonella Serovars
    The 2 nonmotile Salmonella serovars that are avian-adapted pathogens are identified based on O antigens. In chickens, S. Gallinarium causes foul typhoid and S. Pullorum causes pullorum disease.
  28. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Host-Adapted Salmonella Serovars
    Some Salmonella serovars are host-adapted to humans or one animal or avian species. Numerous Salmonella serovars have a broad host range and can infect humans and numerous animal and avian species.
  29. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Enteric Infections
    Most Salmonella infections cause an enterocolitis and commonly occur in humans, cattle, horses and swine. An enterocolitis involves both the small intestine and large intestine. In humans, S. Typhi causes typhoid.
  30. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Extraintestinal Infections
    Salmonella serovars are occasionally isolated from extraintestinal infections of humans and domestic animals.
  31. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Shigella
    Enteric Infections
    • Shigella species are human-adapted pathogens and do not cause infections in domestic animals.
    • S. dysenteriae causes human bacillary dysentery and is the most commonly isolated species.
    • Selected serovars of other Shigella species cause human diarrhea.
  32. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Yersinia
    General
    • Y. enterocolitica and Y. pseudotuberculosis are facultative intracellular pathogens and infect macrophages and monocytes.
    • Y. enterocolitica, Y. pestis and Y. pseudotuberculosis are the most commonly isolated species.
  33. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Yersinia
    Enteric Infections
    • In humans, Y. enterocolitica causes diarrhea, lymphadenitis and septicemia.
    • In domestic animals, Y. enterocolitica has rarely been incriminated in clinical enteric infections.
  34. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Yersinia
    Extraintestinal Infections
    • Y. pestis causes plague in humans, cats and dogs. Most Y. pestis infections are reported in the southwestern United States where the organism is endemic in desert areas (Arizona, California and New Mexico). Fleas or ingestion of infected rodents transmits plague.
    • In humans and selected domestic animals, Y. pseudotuberculosis is an opportunistic pathogen and the lesions are characterized by caseous necrosis.
  35. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    General
    In humans and domestic animals, Escherichia coli is the most prevalent facultative anaerobic bacterium in the gastrointestinal tract.
  36. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    Pathogenic Escherichia Species
    E. coli is the only species isolated from enteric infections of humans and domestic animals and is the most commonly isolated species from extraintestinal infections.
  37. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    Habitat and Ecology
    • E. coli is enteric flora of humans, animals and birds.
    • E. coli comprises one percent or less of enteric flora, but is the most numerous facultative anaerobe in gastrointestinal tracts of healthy humans and animals. From a few hours after birth and throughout life, successions of different E. coli strains colonize the gastrointestinal tract.
    • E. coli is ubiquitous in the environment from fecal contamination.
  38. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    Cellular Characteristics
    • E. coli is a gram-negative bacillus.
    • Most E. coli strains are motile with peritrichous flagella, but some strains are nonmotile.
  39. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    Cultural Characteristics
    • E. coli is a facultative anaerobe and can be cultured on blood agar and MacConkey agar under aerobic conditions at 37C.
    • On blood agar, most pathogenic E. coli strains produce complete hemolysis, but some strains are nonhemolytic.
    • On MacConkey agar, E. coli is lactose-positive and forms red-colored colonies.
  40. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    Biochemical Characteristics
    • E. coli is oxidase-negative and saccharolytic.
    • E. coli has an oxidative metabolism when grown under aerobic conditions and a fermentative metabolism when grown under anaerobic conditions.
  41. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    Escherichia coli Serovars
    • There are over 3,500 E. coli serovars that are identified based their somatic (O), capsular (K) and flagellar (H) antigens. This includes the enterohemorrhagic E. coli, enteroinvasive E. coli and enteropathogenic E. coli.
    • The enterotoxigenic E. coli strains are identified based on their fimbrial (F) antigens.
    • Somatic antigens are present on all E. coli serovars, but capsular and flagellar antigens are present only on serovars with capsules and flagella. Somatic antigens are based on antigenicity of lipopolysaccharide O-side chain carbohydrates.
    • Capsular antigens are composed of carbohydrate.
    • Fimbrial and flagellar antigens are composed of protein.
    • Nonmotile strains are designated NM.
  42. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    Antigenic Formulas
  43. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    Serotyping Antigens for Enterotoxigenic E. coli
    • E. coli isolates from enteric infections are occasionally serotyped.
    • E. coli isolates from extraintestinal infections are rarely serotyped.
    • Some E. coli serovars are commonly isolated from various extraintestinal infections.
  44. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    Disease Overview
    Human and Domestic Animal Infections
    • E. coli is a common cause of enteric and extraintestinal infections.
    • Colibacillosis is a group of diseases where the primary site of infection is the intestine. Humans and all species and ages of domestic animals are affected, but it is primarily a disease of the young.
    • Enterotoxigenic E. coli are commonly isolated from enteric diseases of humans, cattle, sheep and swine.
    • Enterohemorrhagic E. coli, enteroinvasive E. coli and enteropathogenic E. coli cause clinical enteric infections in humans. However, the clinical significance of these pathotypes in domestic animals is poorly understood.
    • E. coli is commonly isolated from a variety of extraintestinal infections of humans and animals.
  45. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    Disease Overview
    Human Enteric Infections
    • E. coli causes a number of distinct enteric diseases collectively referred to as colibacillosis.
    • Each E. coli pathotype with virulence factors causes a distinct enteric infection.
    • Enterohemorrhagic E. coli primarily affect the lower small intestine where the infection causes a bloody diarrhea. Some infections can cause severe kidney damage and death. Shigalike toxins I and II are responsible for the pathological effects on the kidneys. The most commonly isolated serovar is O157:H7.
    • Enteroinvasive E. coli produce enteric infections very similar to bacillary dysentery (Shigella dysenteriae). These infections affect the large intestines and colon. Virulence factors and pathogenesis of enteroinvasive E. coli are very similar to Shigella species. These pathogens are nonmotile.
    • Enteropathogenic E. coli produce an enterocolitis very similar to enterocolitis caused by selected Salmonella serovars. These pathogens produce enterotoxins and shigalike toxins.
    • Enterotoxigenic E. coli have specific fimbriae (CFA-I, CFA-II, CFA-III and CFA-IV) for colonizing the small intestine and produce heat-labile enterotoxin and heat-stable enterotoxins A and B. These enterotoxins cause a loss of fluid and electrolytes into intestinal lumen.
    • Fimbriae, heat-labile enterotoxin and heat-stable enterotoxins are often encoded on plasmids.
  46. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Escherichia
    Disease Overview
    Porcine Edema Disease
    E. coli strains, which produce a variant of shigalike toxin, cause edema disease. The toxigenic strains are inhabitants of the lower intestinal tract and during periods of stress (nutritional or physical conditions) produce the cytotoxin. The toxin is absorbed from the intestine and subsequently attaches to endothelial cells of the small arterioles. Edema disease is characterized by subcutaneous and subsersosal edema. In weaned pigs, acute disease is usually fatal.
  47. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Enterotoxigenic Escherichia coli Infections
    General
    Enterotoxigenic Escherichia coli strains with fimbrial (F) antigens for colonizing intestines cause enterotoxigenic colibacillosis.
  48. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Enterotoxigenic Escherichia coli Infections
    Etiology
    E. coli is an aerobic gram-negative bacillus.
  49. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Enterotoxigenic Escherichia coli Infections
    Transmission
    • E. coli is a normal enteric flora and is found in the environment as a fecal contaminant. Pathogenic E. coli strains can be part of the normal intestinal microflora and proliferate within the intestinal tract to attain an infective dose level, or they can be acquired by ingestion of fecal contaminated material (food and water).
    • Two mechanisms help control the population of E. coli in intestinal tract: 1) competitive antagonistic interactions with other bacterial species as well as between E. coli strains help restrict proliferation of pathogenic strains, and 2) intestinal immunity helps prevent colonization of intestinal epithelial cells.
    • At birth, the gastrointestinal tract is sterile, but it is colonized from the mouth and rectum. The initial microflora is acquired from the mother’s vaginal and perianal flora as well as from the environmental microbiota. Within hours after birth, the gastrointestinal tract is colonized with coliforms, lactobacilli and obligate anaerobes. The balance of the gastrointestinal flora is controlled by acid secreted in the stomach, ingestion of immunoglobulins and other protective factors in colostrum and milk and establishment of lactobacilli as the dominant organisms in the stomach and upper small intestine. Obligate anaerobic bacteria comprise the majority of the flora of the ileum and large intestine. Lactobacilli are normal intestinal flora. They produce high levels of lactic acid that results in a decreased pH in the small intestine. Low pH inhibits the growth of E. coli in the upper small intestine and helps prevent diarrhea.
    • Colostrum and milk can contain antibodies specific for a pathogenic E. coli strain as well as other nonspecific factors that inhibit the growth of E. coli within the intestinal tract. These factors can prevent E. coli from colonizing the intestinal epithelium and help restrict the bacterium to intestinal tract.
    • Dietary changes can alter the digestive tract physiology and provide conditions for the proliferation of E. coli.
    • Various stress factors can predispose humans to clinical infections.
  50. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Enterotoxigenic Escherichia coli Infections
    Clinical Features
    • Enterotoxigenic colibacillosis is caused by enterotoxigenic E. coli strains. These enteric pathogens possess specific F antigens for colonization of small intestine and heat-labile and heat-stable enterotoxins that cause a loss of fluid and electrolytes into intestinal lumen by active hypersecretion.
    • Enterotoxigenic colibacillosis is characterized by watery diarrhea with dehydration and deaths are caused by dehydration and electrolyte imbalances.
    • Stomach and small intestine are distended with fluids and gas. In uncomplicated infections, inflammation is not present in the gastrointestinal tract.
  51. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Enterotoxigenic Escherichia coli Infections
    Pathogenesis
    Fimbriae
    Enterotoxigenic E. coli strains colonize the mucosal surface of the epithelial cells of the small intestine and produce enterotoxins. Genetic determinants controlling the production of fimbriae and enterotoxins are often carried on plasmids, which can be transferable via conjugation. Plasmids can simultaneously carry genes for fimbriae and enterotoxins. Fimbrial antigens bind to the villous bases of intestinal epithelial cell receptors. This prevents expulsion of bacteria from the small intestine.
  52. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Enterotoxigenic Escherichia coli Infections
    Pathogenesis
    Enterotoxins
    Enterotoxins are responsible for the physiological loss of electrolytes and water into the lumen of the small intestine. Heat-labile enterotoxin is destroyed at 56C for 30 minutes, but heat-stable enterotoxins A and B are stable at 56C for 30 minutes. A given strain of E. coli can produce 1 or more enterotoxins.
  53. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Enterotoxigenic Escherichia coli Infections
    Pathogenesis
    Heat-Labile Enterotoxin
    Heat-labile enterotoxin with molecular weight 85,000 is a holotoxin with 1 A subunit and 5 B subunits. The B subunits are responsible for binding to the Gm1 ganglioside of epithelial cells of small intestine and the A subunit carries out ADP-ribosylation of an ATP-binding protein with concomitant activation of adenylate cyclase with a subsequent increase in cAMP levels in intestinal cells. Increased level of cAMP inhibits the absorption of Na+ and increases Na+ secretion with a subsequent loss of Cl- and water.
  54. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Enterotoxigenic Escherichia coli Infections
    Pathogenesis
    Heat-Stable Enterotoxins A and B
    Modes of action of heat-stable enterotoxins A and B are distinct. These enterotoxins with molecular weight two thousand are nonantigenic polypeptides. Heat-stable enterotoxin A activates guanylate cyclase with a subsequent increase in cGMP levels in the intestinal cells. The mechanism by which cGMP leads to a net secretion of electrolytes and water has not been clearly delineated. The mode of action of heat-stable enterotoxin B may be anti-absorptive.
  55. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Enterotoxigenic Escherichia coli Infections
    Pathogenesis
    Hemolysin and Lipopolysaccharide
    Hemolysin and lipopolysaccharide are is not required for disease.
  56. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Enterotoxigenic Escherichia coli Infections
    Pathogenesis
    Genetics of Virulence Factors
    Production of enterotoxins is relevant in the induction of diarrhea only when E. coli has proliferated sufficiently to produce a high local concentration of enterotoxins in the small intestine. Fimbrial antigens are required for intestinal colonization and enterotoxins are required for intestinal hypersecretion. Genes for enterotoxins, fimbriae and hemolysin can be encoded on a plasmid, the chromosome or both. These plasmid-mediated virulence factors can be transferred via conjugation between E. coli strains.
  57. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Enterotoxigenic Escherichia coli Infections
    Pathology
    Patients are dehydrated and intestines are distended with fluid and gas.
  58. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Enterotoxigenic Escherichia coli Infections
    Diagnosis
    • Presumptive diagnoses are based on clinical signs of a watery diarrhea and dehydration.
    • Culture and biochemical identification of pathogenic E. coli strains are used to confirm the diagnoses. On aerobic blood agar cultures, most pathogenic strains produce complete hemolysis. Pathogens are present in high numbers in the small intestine and are frequently isolated in pure culture. E. coli isolates are serotyped to determine their F antigens.
    • To detect the enterotoxins in culture supernatants of the enterotoxigenic E. coli, several methods have been developed. Tests for the heat-labile enterotoxin include ligated ileal loops of live rabbits and tissue culture methods using Y1 mouse adrenal cells or Chinese hamster ovary cells. Methods for detecting heat-stable enterotoxins A and B include the infant mouse test.
    • Ligated ileal loops of rabbits are injected with culture supernatants of the enterotoxigenic E. coli. This test cannot distinguish the heat-labile enterotoxin from the heat-stable enterotoxins unless the culture supernatants are heat treated at 56C for 30 minutes to inactivate the heat-labile enterotoxin. A positive test is indicated by the accumulation of fluid in a ligated loop.
  59. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Enterotoxigenic Escherichia coli Infections
    Diagnosis
    Rabbit Ileal Loup Test
    • Filtrate of the E. coli culture is heated at 56C for 30 minutes.
    • Fluid: +++++ = large amounts, +++ = moderate amounts, + = small amounts, and - = none.
    • Y1 mouse adrenal cells or Chinese hamster ovary cells are used for the detection of the heat- labile enterotoxin. With these tests, tissue culture cells are exposed to culture supernatants. When enterotoxin is present, intracellular level of cAMP are increased leading to a morphological response of the eucaryotic cells that can be seen microscopically.
    • Infant mouse test is used for detection of the heat-stable enterotoxins. With this test, culture supernatants are injected directly into the stomach of infant mice. After 4 hours, their intestines are examined for dilation due to fluid accumulation.
  60. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    General
    • Salmonella enterica serovar Typhi and S. enterica serovar Typhimurium are designated as S. Typhi and S. Typhimurium, respectively,
    • There are 2,500 Salmonella enterica serovars, but fewer than 100 serovars have been incriminated as enteric pathogens.
  61. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Pathogenic Salmonella Serovars
    • S. Choleraesuis causes pneumonia and septicemia in pigs. It is porcine-adapted pathogen.
    • S. Typhi causes typhoid in humans. It is a human-adapted pathogen.
    • Selected Salmonella serovars cause enterocolitis and extraintestinal infections in humans and selected domestic animals.
  62. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Host Ranges of Selected Salmonella Serovars
    • Various Salmonella serovars are host-adapted to humans or to 1 or 2 animal species, but some Salmonella serovars are found in a large number of mammals.
    • In humans and domestic animals, numerous Salmonella serovars with a broad host range have been isolated from enteric infections. Commonly isolated serovars are classified in serogroups A, B, C, D and E (S. Agona, S. Albany, S. Anatum, S. Choleraesuis, S. Derby, S. Dublin, S. Enteritidis, S. Heidelberg, S. Paratyphi A and S. Typhimurium).
    • Salmonella serovars with a restricted host range include S. Choleraesuis in swine and S. Typhi in humans.
  63. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Habitat and Ecology
    • Salmonellae are transient enteric flora of humans and animals. Their presence can be a transient change in flora with no apparent illness, or at the other extreme, salmonellosis can be a persistent disease with high mortality.
    • Salmonellae are found in soil and water as fecal contaminants.
  64. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Cellular Characteristics
    • Salmonella serovars are gram-negative bacilli.
    • Salmonella serovars from humans and animals are motile with peritrichous flagella except for nonmotile mutants.
  65. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Cultural Characteristics
    Salmonella serovars are facultative anaerobes and can be cultured on blood agar and MacConkey agar under aerobic conditions at 37C. Colonies are nonhemolytic on blood agar and colorless on MacConkey agar.
  66. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Biochemical Characteristics
    Salmonella serovars are oxidase-negative and saccharolytic.
  67. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Salmonellae Serogroups and Serovars
    • Salmonella serovars are based on an antigenic formula for different somatic (O) and flagellar (H) antigens. Arabic numbers designate O antigens. Small letters designate H phase 1 antigens, which are shared by a few serovars. Arabic numbers designate H phase 2 antigens, which are shared by many serovars. Selected serovars (S. Dublin, S. Typhi and S. Paratyphi A) have virulence (VI) carbohydrate capsular antigen. Vi antigen is not utilized in serotyping the encapsulated serovars.
    • Serovars are classified in serogroups based on antigenic similarities of their O antigens.
    • Most pathogenic Salmonella serovars are classified in serogroups A, B, C, D and E.
    • For identification of serogroups, group-specific antisera for salmonellae groups A through I are available for slide agglutination tests. To test a Salmonella isolate, it is first reacted with polyvalent O serum for serogroups A to I. If the isolate has an agglutination-positive reaction, tests are conducted with the individual serogroup antisera.
  68. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Antigenic Formulas
  69. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Disease Overview
    Human and Domestic Animal Infections
    • Salmonellae are occasionally isolated from extraintestinal infections where they are opportunistic pathogens.
    • Selected pathogenic Salmonella serovars are facultative intracellular pathogens and are commonly isolated from enteric infections. Ingestion of fecal contaminated material (feed and water) is the primary mode of transmission. Two primary sources are clinically affected humans and animals and asymptomatic carriers. Minimum infective dose for most serovars in healthy humans and animals is about 108 bacteria. Since most serovars tend to be host-specific, it takes a larger dose of a serovar to infect an unusual host. Severity of salmonellosis is largely determined by age and immunological status of the host and by various types of stress. Predominant types of salmonellosis include enterocolitis and/or septicemia.
  70. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Disease Overview
    Human Infections
    S. Typhi causes typhoid and is a host-adapted pathogen of humans and selected primates. Most infections result from ingestion of food and water that have been contaminated with feces from clinically affected individuals or intestinal carriers. An affected individual exhibits clinical signs of a gram-negative septicemia with a high fever and gastrointestinal symptoms.
  71. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Disease Overview
    Bovine Infections
    S. Dublin and S. Typhimurium are the most commonly isolated serovars. These serovars cause an acute enterocolitis with bloody diarrhea. Clinical infections occur most frequently in feedlot cattle and calves that have been shipped.
  72. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Disease Overview
    Canine Infections
    Salmonellosis occurs primarily in pups where disease is manifested as acute or subacute enteritis. The disease is often associated with dogs housed in overcrowded unsanitary conditions. Enteric infections are occasionally seen in adult dogs. These infections tend to be self-limiting and are probably due to their eating habits.
  73. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Disease Overview
    Equine Infections
    • S. Typhimurium and other selected serovars cause outbreaks of enterocolitis, which are often stress related with high mortality. Stress reduces the minimum infective dose and causes the activation of a quiescent infection (worming, general anesthesia, surgery and transportation).
    • Antibiotic induced salmonellosis is common in horses where oral and systemic therapy with tetracyclines alters the normal bacterial flora. The altered flora allows salmonellae to become established and cause enterocolitis.
    • Salmonellosis in foals is manifested as an acute enterocolitis and septicemia. Common sequelae are bacterial localization in brain (meningitis), lungs (pneumonia) and joints (arthritis).
  74. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Genus Salmonella
    Disease Overview
    Porcine Infections
    • S. Choleraesuis is host-adapted for swine and causes an acute septicemia with an endotoxemia, fever and high mortality rate or chronic pneumonia. With both types of infection, clinical signs of enteritis are seldom manifested.
    • S. Typhimurium and numerous other serovars cause catarrhal to mucohemorrhagic enterocolitis. These infections can become chronic.
  75. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Typhoid
    General
    Typhoid is infrequently diagnosed in the United States, but commonly diagnosed in many undeveloped countries with poor sanitation facilities.
  76. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Typhoid
    Etiology
    Salmonella Typhi is an aerobic gram-negative bacillus and a host-adapted human pathogen.
  77. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Typhoid
    Transmission
    Most infections are acquired from ingestion of food or water that has been contaminated with feces from clinically affected individuals or intestinal carriers.
  78. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Typhoid
    Clinical Features
    An affected individual exhibits clinical signs of a gram-negative septicemia with high fever and gastrointestinal symptoms.
  79. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Typhoid
    Pathogenesis
    Capsular Vi antigen of S. Typhi is a significant virulence factor. Other virulence factors are similar to those of other Salmonella serovars that cause enterocolitis in humans and animals.
  80. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Typhoid
    Pathology
    Gross and microscopic lesions are associated with the gastrointestinal tract and septicemia.
  81. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Human Typhoid
    Diagnosis
    • S. Typhi can be cultured on blood agar and MacConkey agar under aerobic conditions at 37C. The bacterium is nonhemolytic on blood agar and lactose-negative on MacConkey agar.
    • In a glucose broth culture, S. Typhi produces is anaerogenic, but other pathogenic Salmonella serovars are aerogenic.
  82. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Porcine Salmonellae Enterocolitis
    General
    Over 50 Salmonella serovars have been associated with enterocolitis in swine. The disease is characterized by bloody diarrhea with or without a concurrent septicemia.
  83. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Porcine Salmonellae Enterocolitis
    Etiology
    • Pathogenic Salmonella serovars are aerobic gram-negative bacilli and facultative intracellular pathogens.
    • Of the numerous Salmonella serovars that cause enterocolitis, S. Typhimurium is the most frequently isolated serovar.
    • S. Typhimurium has a broad host range in humans, birds and domestic animals.
  84. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Porcine Salmonellae Enterocolitis
    Transmission
    • Ingestion of contaminated feed and water is the primary mode of transmission.
    • Most epidemics result from oral ingestion of feces contaminated with salmonellae from clinically affected or asymptomatic carrier swine.
    • Adult swine can become asymptomatic carriers for indefinite periods of time.
    • Salmonellae can persist in low numbers in the intestine and be excreted in feces, or feces can be seeded intermittently from the gall bladder, which serves as a habitat for the bacteria.
    • Salmonellae can persist in the regional lymph nodes of the alimentary tract, but these organisms are not excreted in the feces.
    • Salmonellae can survive in the environment for 1 year or more.
  85. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Porcine Salmonellae Enterocolitis
    Clinical Features
    • Swine of all ages can be affected, but clinical disease most frequently occurs in pigs from 8 to 16 weeks-of-age.
    • Infections are characterized by anorexia, fever, mucohemorrhagic diarrhea, progressive emaciation and eventually death.
  86. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Porcine Salmonellae Enterocolitis
    Pathogenesis
    • Pathogenesis has 4 sequential stages (ingestion, infection and invasion of gastrointestinal tract, proliferation in intestinal wall and regional lymph nodes and a bacteremia or septicemia). Infections are acquired by ingestion of fecal contaminated feed and water. Some infections can result from recrudescence of the intestinal carrier states.
    • Bacteria invade mucous membranes of alimentary tract and colonize lymphoid tissues. The major route of invasion is from intestinal lumen into the lamina propria and Peyer's patches of ileum, cecum and colon. Bacteria that invade the gastrointestinal mucosa proliferate within the mucosa and elicit an inflammatory reaction. Neutrophils are the predominant cell type in these initial infectious foci in lamina propria. Numerous phagocytes migrate into intestinal lumen with invasion and destruction of epithelial cells and reticuloendothelial cells in intestinal wall. This results in mucosal and serosal hemorrhages followed by thrombosis, necrosis and ulceration of mucous membranes. These lesions occur primarily in ileum, cecum and colon, which have high concentrations of lymphoid tissues.
    • Salmonellae invade the regional lymph nodes via the lymphatics where affected lymph nodes have a lymphadenopathy with hemorrhages.
    • Following a period of proliferation in regional lymph nodes, bacteria invade the bloodstream via the lymphatics and cause a transient bacteremia or septicemia. Some infections remain confined at their primary foci of infection and do not disseminate. The resulting clinical manifestations are an enterocolitis with or without a septicemia.
    • Salmonella serovars possess a variety of virulence factors that play a major role in the pathogenesis of salmonellosis (cytotoxins, heat-labile enterotoxin, heat-stable enterotoxins and lipopolysaccharide.
    • Cytotoxins are similar to those of the enterohemorrhagic, enteroinvasive and enteropathogenic E. coli and enterotoxins are similar to those of the enterotoxigenic E. coli.
  87. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Porcine Salmonellae Enterocolitis
    Pathology
    Intestinal lesions occur in the colon, cecum and ileum. Lymphadenopathy, hepatomegaly and splenomegaly are common. Encephalitis, meningitis and pneumonia are often complications of septicemias.
  88. Aerobic Gram-negative Cocci
    Family Enterobacteriaceae

    Porcine Salmonellae Enterocolitis
    Diagnosis
    • Clinical signs and gross pathology are used for the presumptive diagnosis of salmonellosis.
    • Culture and serologic identification of the infective serovar is used to confirm the diagnosis.
    • Salmonella serovars can be cultured on blood agar and MacConkey agar under aerobic conditions at 37C. Colonies on blood agar are nonhemolytic and colonies on MacConkey agar are colorless.
    • Most Salmonella serovars associated with enteric infections are members of serogroups B, C, D and E. An enteric Salmonella isolate can be identified as a member of a serogroup utilizing agglutination tests with serogroup-specific antisera.

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