MedMicroTest3EntericRods

LPS (although it's antigenic)

• Gram negative rods
• Facultative anaerobes
• Found in intestine
• Typically transmitted via fecal contamination

• Both: Escherichia, Salmonella, Yersinia, Camplybacter
• Gastrointestinal: Shigella, Helicobacter, Vibrio
• Extraintestinal: Enterobacter, Klebsiella, Serratia, Proteus

• 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)

• 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

E. coli O157:H7 causes severe hemorrhagic colitis and hemolytic uremic syndrome (HUS) (bloody diarrhea and kidney failure)

• *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

• 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

• Heat-stable toxin (ST): elevates cyclic guanosine monophosphate (cGMP)
• Heat-liable toxin (LT): elevates cytlic adenosine monophosphate (cAMP)

• 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.

• 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.

• 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

• 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)

• 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

• 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

• 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

• 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

• 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-)

• 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

• 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

• 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)

• 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

• 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

• 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)

• 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

• Antibiotics are essential part of treatment for patients AND to clear carriers
• Cephalosporins, fluoroquinolones, etc

• 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