Lecture 11: Enterobacteriaceae
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Name the largest group of medically important Gm- rods
Where can enterobacteriaceae be found?
enterobacteriaceae are ubiquitous and can be found in the soil, water, vegetation and intestinal flora.
What percentage of bacteremia does enterobacteriaceae cause. What percentage of UTIs does enterobacteriaceae cause?
- causes 30-35% of all bacteremia
- causes more than 70% of all UTI infections
What disease does Enterobacteriaceae cause?
- intestinal infections
What are the two possible sources that Enterobacteriaceae can originate from?
- Animal reservoirs (mostly salmonella species & Yersenia species)
- Human Carriers ( shigella species and some salmonella
Describe the physiology and structure of enterobacteriaceae
Enterobacteriaceae are Gm- rods and can either be motile or non-motile. They do not form spores and are facultative anaerobes. They are not fastidious. Test results show that enterobacteriaceae are catalase positive and oxidase negative. LPS is a major cell wall antigen in enterobacteriaceae. Peritrichous flagella & fimbriae are also present.
Describe the 3 antigens found in enterobacteriaceae
- O polysaccharides: present in each genus. detected by agglutination with specific antibodies
- Capsular K antigens: heat-labile. can interfere with O polysaccharide typing
- Flagellar H proteins: heat-labile flagellin proteins. not always present. can undergo antigenic variation
Name two qualities of enterobacteriaceae that allows it to be distinguishable
- fermenation of lactose
- resistance to bile salts
What characteristics of enterobacteriaceae allow it to be pathogenic?
- the release of its endotoxin causes many symptoms of disease
- the capsule protects the sell from phagocytosis
- the antigenic phase variation expresses the capsular K and flagellar H antigens and protects the cell from antibody-mediated death
- the type III secretion systems deliver virulence factors into the host cell. Without TTSS, bacteria loses virulence
- the sequestration of iron produces siderophones or iron-chelating compounds. Releases iron from host cells using hemolysins
Name the five virotypes of Escherichia coli
- Entertoxigenic E. coli (ETEC)
- Enteropathogenic E. Coli (EPEC)
- Enteroaggregative E. Coli (EAEC)
- Enteroinvasive E. Coli (EIEC)
- Enterohemorrhagic E. Coli (EHEC)
Where and amongst whom is Entertoxigenic E. coli (ETEC) most common? (class of country and which demographic) Why?
Entertoxigenic E. coli (ETEC) is most common in developping countries and among children because it is spread through the fecal-oral route
How is Entertoxigenic E. coli (ETEC) spread?
Entertoxigenic E. coli (ETEC) is spread through he fecal-oral route but requires high inoculum, thus there is no person to person spread. The bacteria then adhere to the intestinal mucosa, but arouses no inflamation or intestinal changes
What two classes of enterotoxins are produced by Entertoxigenic E. coli (ETEC) ? What symptoms do these enterotoxins cause?
- Result in secretion of fluids and electrolytes into bowel
In what demographic (persons and place) do Enteropathogenic E. Coli (EPEC) cause diarrhea? What are the general symptoms?
- Enteropathogenic E. Coli (EPEC) typically causes diarrhea in infants in impoverished nations
- Symptoms include watery diarrhea (severe and extended), fever and vomiting
How is Enteropathogenic E. Coli (EPEC) spread?
Enteropathogenic E. Coli (EPEC) is spread through person to person contact since only a low infectious dose is needed.
How does Enteropathogenic E. Coli (EPEC) attach itself to its host?
the bacteria attach to the epithelial cells of the small intestine and destroy microvilli due to the formation of pedestals of actin under the site of attachement. This results in the aggregation of bacteria on the epithelial surface mediated by plasmid-encoded pili.
What process is undergone in order to secrete proteins into the host cells of Enteropathogenic E. Coli (EPEC)?
TTSS initiates the secretion of proteins into the host cell. Tir inserts into the epithelial cell and functions as receptor for the outer membrane adhesin, intimin. The intimin-Tir binding results in the polymerization of actin and the accumulation of cytoskeletal elements beneath the attached bacteria. The cell then loses surface integrity and dies
Describe the pathogenesis of enteroaggragative E. Coli (EAEC)
- EAEC binds small intestinal cells into small aggregates. The bacteria is non invasive and causes no intestinal changes.
- The bacteria causes watery diarrhea with dehydration, and usually occurs in infants.
What occurs during autoagglutination?
Aggregative adherence fimbriae (adhesins) adheres to the intestinal surface, stimulates mucus secretion and leads to the formation of thick biofilm
Name the two groups of toxins associated with enteroaggregative e. coli.
- Enteroaggregative heat stable toxin
- Plasmid encoded toxin
What vehicles usually transmit enterohemorrhagic e. coli to the human host? What is the organ that EHEC typically infects
- the consumption of contaminated foods such as: undercooked meat, water, unpasteurized milk or fruit juice and uncooked vegetables and fruits
- EHEC usually infects the large intestine
- *usually requires very low inoculum and so can be spread person to person
Describe the symptoms of EHEG
- Watery diarrhea followed by grossly bloody diarrhea with adominal cramps.
- little to no fever usually occurs
- can sometimes progress to hemolytic uremic syndrome
describe the characteristics of hemolytic uremic syndrome (HUS)
- acute renal failure
- can be fatal
Describe the pathogenesis of EHEC
- infection is mediated by cytotoxi Shiga toxins which disrupt protein synthesis.
- causes attaching/effacing lesions with destruction of intestinal microvilli that results in decreased absorption
Which other bacteria species is Enteroinvasive E. Coli closely related to? In what way are they alike?
Shigella. symptoms from EIEC are often indistinguishable from from shigellosis, which is usually less severe.
Describe the pathogenesis of EIEC
- Invasion & destruction of epithelial cells lining the colon is plasmid mediated.
- After invasion of the colonic epithelium, the bacteria lyse the vacuoule, replicate in the cytoplasm and spread to adjacent cells.
- can cause colonic ulceration
Describe the clinical disease manifestations of EIEC
- develops mainly in the large intestine and causes fever, cramping & watery diarrhea.
- may progress to dysentry (inflammation of intestine) with scant, bloody stools
Describe the cause, symptoms and treatment of gastroenteritis
- caused by : salmonella
- symptoms: nausea, vomiting, non-bloody diarrhea, fever, abdominal cramps, myalgias (muscle pain) & headache
What bacteria causes typhoid/enteric fever?
Salmonella enterica serovar. Typhi
10 to 14 days after ingestion of a certain bacteria, a patient experiences gradually increasing fever with nonspecific complaints of headache, myalgias, malaise and anorexia. The symptoms persist for a week or longer and are followed by gastrointestinal symptoms. What disease does the patient have and what is the cause? How can this be treated?
- The patient is suffereing from typhoid/enteric fever that is caused by Salmonella Typhi.
- Infection is treated with an effective antibiotic such as fluoroquinolones, chloramphenicol, trimethoprimsulfamethoxazole or a broad-specturm cephalosporing
Why is antibiotic treatment not recommended for salmonella-induced enteritis?
It is not recommended because it may prolong the duration of the disease
name the 4 species of shigella
- shigella dysenteriae
- shigella flexneri
- shigella boydii
- shigella sonnei Technically, all shigella species are sub-groups of E. Coli
This disease can often be endemic in male homosexuals and households with infected children and is spread by person-to-person contact with contaminated hands (fecal-oral route). Is characterized by abdominal cramps, diarrhea, fever and bloody stools that appear one to three days after the bacteria are ingested.
Describe the recommended treatment for shigellosis
antibiotic therapy, although not necessary to recovery, is recommended in order to shorten the course of symptomatic disease and fecal shedding.
This species of enterobacteria is resistant to phagocytic killing due to Type III Secretion Systems
Yersinia pestis cause which 2 types of infection?
- Bubonic (urban) plague: spread by fleas and rats
- Pneumatic (sylvatic) plague: spread by squirrels, rabbits, rats and cats
Which species of yersinia lives within pigs, rodents, livestock and rabbits and causes inflammation of the intestine (enterocolitis) in cool areas
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