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What is the "general" virulence factor found in enterics?
LPS (although it's antigenic)
What is an enteric?
- Gram negative rods
- Facultative anaerobes
- Found in intestine
- Typically transmitted via fecal contamination
List the enteric genera and if they cause disease in or out of the GI tract
- Both: Escherichia, Salmonella, Yersinia, Camplybacter
- Gastrointestinal: Shigella, Helicobacter, Vibrio
- Extraintestinal: Enterobacter, Klebsiella, Serratia, Proteus
Properties of E. coli (aeration, unique metabolic reactions/biochemical tests)
- Facultative anaerobe
- Ferments glucose
- Can reduce nitrates to nitrites in absence of O2
- Oxidase negative (no cytochrome C, uses quinol oxidases to reduce O2 to H2O)
Describe the serotyping of E. coli in detail
- Based on differences in three structural antigens
- O antigens: polysaccharide portion of LPS
- H antigens: flagella
- K antigens: capsule (less commonly fimbriae)
- Specific serotypes are associated with particular diseases
What is the "famous" dangerous strain of E. coli and what does it cause?
E. coli O157:H7 causes severe hemorrhagic colitis and hemolytic uremic syndrome (HUS) (bloody diarrhea and kidney failure)
What are the five types of E. coli pathogens, their general disease, and which are most important.
- *Enterotoxigenic E. coli (ETEC): Watery diarrhea
- *Enteropathogenic E. coli (EPEC): Watery diarrhea of long duration (typically infants)
- *Enterohemorrhagic E. coli (EHEC): Hemmorhagic colitis and hemolytic uremic syndrome (HUS)
- Enteroinvasive E. coli (EIEC): Bloody diarrhea
- Enteroaggregative E. coli (EAEC): Persistant watery diarrhea in immunocompromised
Describe ETEC in detail. Disease? Transmission? Site of colonization? What causes the disease state (details)?
- Traveler's diarrhea
- Contaminated food/water, person-to-person contact, fomites
- Colonizes small intestine mucosa (pili facilitate binding)
- Enterotoxins mediate hypersecretion of Cl- and H2O by mucosal cells results in watery diarrhea for several days
What are the enterotoxins of ETEC, and how do they affect the mucosal cells?
- Heat-stable toxin (ST): elevates cyclic guanosine monophosphate (cGMP)
- Heat-liable toxin (LT): elevates cytlic adenosine monophosphate (cAMP)
Give detailed information about structure and function of heat-labile toxin in ETEC.
- More sensitive to heat than most toxins
- Action identical to Vibrio enterotoxin
- Subunit B: binds to epithelial cells
- Subunit A: increases cAMP levels, activating ion transport systems. Cell secretes large amounts of fluids and electrolytes leading to severe diarrhea.
Describe EPEC in detail. Disease? Transmission? Site of colonization? What causes the disease state?
- Diarrhea in infants in developing countries
- Newborn infected during birth or in utero
- Attach to mucosal cells in small intestine and cause a lesion called attaching and effacing (A/E).
- A/E lesions categorized by microvilli destruction, intimate adherence of bacteria, pedestal formation, and aggregation of cytoskeleton elements at site of attachment.
Describe EHEC in detail. Transmission? Site of colonization? What causes the disease state? Disease?
- Cow is primary reservoir
- Transmitted primarily through uncooked meat and unpasteurized milk
- Can be transmitted from vegetables in contact with infected cow feces
- Bind to cells in the large intestine
- Production of exotoxin (verotoxin AKA Shiga-like toxin) causes hemorrhagic colitis and Hemolytic uremic syndrome
Describe the actions of Shiga toxins in EHECs.
- AKA verotoxin
- 1. Directly inhibit protein biosynthesis of commensal bacteria in the gut (giving competitive advantage to E. coli)
- 2. Induce apoptosis in mucosal epithelia, leading to bloody diarrhea (also provides iron and other nutrients to bacteria)
Describe the laboratory identification of E. coli
- Intestinal disease: detection difficult due to being normal flora
- EHEC do not ferment sorbitol (or do so slowly) and can be detected on MacConkey sorbitol agar
- Extraintestinal disease: Isolation from normally sterile body sites (bladder or CSF) onto MacConkey agar
What is MacConkey agar designed for? Components and purpose?
- To grow gram negatives AND differentiate them for lactose fermentation.
- Bile salt: inhibits most gram+
- Crystal violet dye: inhibits gram+
- Neutral red dye: stains lactose fermentors
- lactose and peptone: aid in growth
Describe treatment for E. coli disease
- Maintenance of fluid and electrolyte balance during diarrhea
- Antibiotic resistance is widespread, rarely used for gastrointestinal disease
- Extraintestinal diseases require antibiotics, and sensitivity testing on isolates is necessary before drug is chosen
Describe E. coli extraintestinal disease (source of infection, diseases and description)
- Often the patient's own flora has made it to a normally sterile site
- Urinary tract infections: E. coli is most common cause of UTI
- Uropathogenic strains characterized by P fimbriae, hemolysin, and colicin V
- Neonatal meningitis: K1 (capsular) antigen is particularly associated
- Nosocomial infections: include sepsis/bacteremia, endotoxic shock, and pneumonia
Information about Salmonella (variety of disease, current classification, Biochemical reactions)
- From gastroenteritis (salmonellosis) and enteric (typhoid) fever
- All strains are grouped into a single species (S. enterica) that has ~2500 different serotypes/serovars
- Most are Lac- and produce acid and gas during glucose fermentation
- Produce H2S gas from sulfur containing amino acids (M and C)
- 98% identical to E. coli (although Salmonella are Lac-)
Most important Salmonella human pathogens with brief description
- S. enterica subsp. enterica serovar Typhimurium (Salmonella Typhimurium): Salmonellosis (gastroenteritis)
- The most common serotype isolated in the US
- S. enterica subsp. enterica serovar Typhi (Salmonella Typhi): Typhoid fever
- exclusively human pathogen
Describe transmission of Salmonella Typhimurium
- Poultry meat: bacteria from intestine can contaminate carcass during slaughter
- Eggs: contaminated on outside and inside of the shell (increase in number when left at room temperature)
- Reptiles and amphibians
Describe the symptoms of Salmonellosis (time to appearance, symptoms, severity, infectious time period)
- Caused by Salmonella Typhimurium
- Appear within 6-24 hours after ingestion
- nausea and vomiting followed by abdominal pain, diarrhea, and fever
- Severity ranges from mild pain to bloody diarrhea
- Continue to excrete bacteria for up to 3 months after symptoms subside
- Enters bloodstream in very small amount of people causing septic shock (LPS endotoxin)
Describe the pathogensis of Salmonella (site of colonization, steps of infection)
- Invade epithelial cells of small intestine (Typhimirium)
- Facultative intracellular parasites that survive in phagocytic cells and are disseminated (Typhi)
- 1. Ingestion of contaminated food or beverage
- 2. Salmonella cross the epithelial barrier (active or passive)
- 3. Taken up by macrophages and transported into lymphatic system and disseminate
- 4. Presence of intracellular Salmonella may lead to apoptosis
Describe transmission of Salmonella Typhi
- Asymptomatic carriers (~3% of infected), especially as food handlers
- *Typhoid Mary
- In some people S. Typhi persists in gallbladder and can shed bacteria in feces
S. Typhi symptoms (incubation period, steps of infection, symptoms)
- Week to a month after ingestion (longer than S. Typhimurium)
- Colonize intestine, enter lymphatic and move to spleen/liver, multiply in spleen and liver, released to bloodstream (high fever, flushed appearance, anorexia), move from liver to gallbladder and shed back into intestine
- Severe ulceration of intestinal mucosa (likely fatal at this stage)
Describe prevention of S. Typhi
- Typhoid vaccines (3) for those living in or traveling to high risk areas, the military
- Killed whole bacteria: (injected) side effects due to LPS
- Vi vaccine: (injected) consists of capsular material
- Attenuated S. Typhi Ty21a: (oral) live, but avirulent due to mutation
Describe treatment of S. Typhi
- Antibiotics are essential part of treatment for patients AND to clear carriers
- Cephalosporins, fluoroquinolones, etc
Describe the diagnosis of Salmonella (options with description)
- Traditional: (3-5 days) sample (stool or food) cultured onto selective agar media
- Rapid detection: (<48 hours)
- Immunochromatography - anti-antibody causes color production on strip
- PCR-based assay
- Confirmation/ID: confirmed using classical biochemical and serological testing
- Probabilistic indicator - battery of biochemical tests performed simultaneously (eg enterotube)
- API 20e strip: battery of biochemical tests fermentation of variety of C sources and products