Family Enterobacteriaceae

  • enterics

  • large family of small, non-spore-forming gram-negative rods

  • enterobacterial common antigen (ECA)

  • many members inhabit soil, water, decaying matter, and are common occupants of large bowler of animals including humans

  • most frequent cause of diarrhea through enterotoxins

  • most diseases usually outside GI tract

  • enterics, along with pseudomonas sp., account for almost 50% of nosocomial infections

  • facultative anaerobes, grow best in air

  • all ferment glucose, reduce nitrates to nitrites, oxidase negative and catalase positive

  • divided into coliforms (lactose fermenters - E. coli, kelbsiella, enterobacter, cirtobacter, serratia) and non-coliforms (non-lactose fermenters- salmonella, shigella, yersinia)

  • enrichment, selective and differential media utilized for screening samples for pathogens

  • some have peritrichous flagella

Antigenic Structures and Virulence Factors

  • complex surface antigens contribute to pathogenicity and trigger immune response:

    • H - flagellar Ag

    • K - capsule and/or fimbrial Ag

    • type III secretion - like syringe insert into host cell

    • siderophores - iron binding

    • O - somatic or cell wall Ag - all have

    • endotoxin (LPS - heat stable)

    • exotoxins

    • serotype: O and H (e.g., E Coli O157:H7)

Escherichia Coli: the most prevalent enteric bacillus

  • most common aerobic and non-fastidious bacterium in gut

  • clinical disease: UTIs, neonatal meningitis, septicemia, gastroenteritis

  • 150 strains; O antigen > 150; H antigen > 50

  • opportunistic infection - some have developed virulence through plasmid transfer, others are opportunists

Pathogenic Strains of E. coli: adhesion or toxin

  • enterotoxin E. coli (ETEC); 2 exotoxins (LTI, II< STA) causes severe diarrhea due to heat-lable (LTI, II) toxin and heat-stable toxin (STA) - stimulate secretion and fluid loss (traveler’s diarrhea); also has fimbriae

  • enteraggregative - EAEC - aggregrative adherence fimbriae, stacked brick appearance; stimulate mucus secretion - protect, toxins similar to ETEC

  • enteroinvasive E. coli (EIEC); rare-O123, O143, O164; (invasive plasmid antigen and hemolysin A) invade mucosa, lyse vacuole; causes inflammatory disease of the large intestine

  • enteropathogenic E. coli (EPEC): bind and destroy microvilli, intimin+ receptor- actin; linked to wasting form infantile diarrhea

  • enterohemorrhagic E. coli (EHEC), O157: H7 strain, shiga like toxin for eukaryotic ribosomes (STEC); AB toxin; toxin binds to intestinal villi and renal cells; bloody diarrhea; causes hemolytic uremic syndrome and kidney damage

Escherichia coli

  • pathogenic strains frequent agents of infantile diarrhea - greatest cause of mortality among babies

  • causes ~70% of traveler’s diarrhea

  • causes 50-80% UTI- adhesins and hemolysins important

  • neonatal meningitis- K1 especially; similar to neural cell adhesion molecule

  • coliform count - indicator of fecal contamination in water

    • large numbers, fast and easy to detect, fairly resistant

Opportunistic Coliforms

  • patients with cancer, diabetes, on steroids, COPD

  • klebsiella pneumoniae - normal inhabitant of nasopharynx, never on skin has large capsule

  • cause of nosocomial pneumonia, meningitis, bacteremia, wound infections, and UTIs (new superbug-Carbapenem resistant)

  • klebsiella granulomatis - genital granulomas,

    • subcutaneous nodule

    • may be an STI

    • 3 weeks macrolides

  • enterobacter sp. - UTIs, surgical wounds, motile

  • citrobacter sp. - opportunistic UTIs and meningitis in neonates bacteremia

  • serratia marcescens - motile; produces a red pigment; causes UTIs, pneumonia, burn and wound infections, septicemia and meningitis

Noncoliform Lactose-Negative Enterics

  • proteus, moragnella, providencia-opportunists

  • salmonella and shigella - true pathogens

Opportunists: Proteus and Its Relatives

  • ordinarily harmless saprobes in soil, manure, sewage, polluted water, commensals of humans and animals

    • proteus sp. swarm on surface of moist agar in a concentric pattern and are involved in UTI, wound infections, pneumonia, septicemia, and infant diarrhea

    • resistant to many antibiotics

    • morganella morganii and providencia sp. involved in similar infections

Salmonella and Shigella

  • well-developed virulence factors, primary pathogens, not normal human flora

  • salmonelloses and shigelloses

    • some gastrointestinal involvement and diarrhea but often affect other systems

Typhoid Fever and Other Salmonelloses: Salmonella enterica

  • salmonella typhi - most serious pathogen of the genus; cause of typhoid fever; human host

  • S. cholerae-suis - zoonosis of swine

  • S. enteritidis - includes 1,700 different serotypes based on variation on O, H, and Vi

  • flagellated; survive outside the host

  • pathogenicity islands: type 3 secretion systems (injects invasion proteins); stimulate cAMP (watery diarrhea); inflammatory

  • resistant to chemicals - bile and dyes

Typhoid Fever

  • bacillus enters with ingestion of fecally contaminated food or water; occasionally spread by close personal contact

  • asymptomatic carriers; some chronic carriers shed bacilli from gallbladder

  • bacilli adhere to small intestine- invade through M cells, cause invasive diarrhea that leads to septicemia

    • ulceration, abscesses in liver, peritonitis

  • diagnosis- preliminary: hisory, symptoms, Abs, definitive requires culture

  • treat with chloramphenicol or sulfatrimethoprim

  • 2 vaccines for temporary protection

    • live oral 4 doses, 2 weeks before travel, ,in. age 6, lasts 5 years

    • Ag injection - 1 dose, 2 weeks before travel, min. age 2, lasts 2 years

Animal Salmonelloses

  • salmonelloses other than typhoid fever are called enteric fevers (bacteremia), salmonella food posioning, and gastroenteritis

  • caused by one of many (>2500) serotypes of salmonella enterica; all zoonotic in origin but humans can become carriers

    • cattle, poultry, rodents, reptiles, animal, and dairy products

    • fomites contaminated with animal intestinal flora

  • usually less severe than typhoid fever but more prevalent

    • 6-72 hours incubation, lasts 2-7 days

    • severe treat like typhoid fever

    • milder- supportive therapy

    • salmonella = most common food-borne cause of hospitalizations and deaths

Shigella and Bacillary Dysentery

  • shigellosis - incapacitating dysentery = lower abdominal cramping + bloody, mucoid, diarrhea, seizures under 2

    • four main types: S. dysenteriae, S. sonnei, S. flexneri, and S. boydii

  • species vary incidence/ severity, non-motile, no capsule (e.g. Shigella dysenteriae)

    • human parasites; ID: 50-200 bacterial cells

    • 1-3 days incubation

    • replicate in small intestine: evade phagocytic killing; replicate in phagocytes, propel through cytoplasm to adjacent cells

    • shiga toxin (AB toxin) and exotoxin causes diarrhea

    • then invades villus of large intestine, does not perforate intestine or invade blood

    • enters peyer’s patches instigate inflammatory response; endotoxin and exotoxins

    • treatment- fluid replacement and ciprofloxacin and sulfatrimethoprim

Avoiding GI Infections

  • modes of transmission - thw 5 Fs (plus one W)

    • feces, fingers, flies, food, fomites, water (fluid?)

  • prevention

    • at home

      • sanitation, proper storage, and sufficient temperatures (refrigeration and cooking)

        • the 5 Bs while traveling (generally safe): bread, bananas, beer, bottled beverages, boiled water (no ice) [alternative B- bring your own]

        • CDC says boil it, cook it, peel it or forget it

The Enteric Yersinia Pathogens

  • Yersinia enterocolitica - domestic and wild animals, fish, fruits, vegetables, and water

    • bacteria enter small intestinal mucosa, some enter lymphatic and survive in phagocytes; inflammation of ileum; pain can mimic appendicitis

  • Y. pseudotuberculosis - infection similar to Y. enterocolitica, more lymph node inflammation

Nonenteric Yersinia pestis and Plague

  • nonenteric

  • tiny, gram-negative rod, unusual bipolar staining and capsules

  • virulence factors - capsular and envelope proteins protect against phagocytosis and allow intracellular growth

    • coagulase

    • endotoxin

    • murine toxin

    • vascular failure

    • type III secretion system

    • plasminogen activator protease- degrades C3b and C5a

Yersinia pestis

  • zoonotic

  • human develop plague through contact with wild animals (sylvatic plague) or domestic or semidomestic animals (urban plague) or infected humans

  • found in 200 species of mammals - rodents, without causing disease

  • flea vectors - bacteria replicates in gut, coagulase causes blood clotting that blocks the esophagus; flea becomes ravenous

Pathology of Plague

  • ID 3-50 bacilli

  • bubonic - bacillus multiplies in flea bite, enters lymph, causes necrosis and swelling called a bubo in lymph nodes

    • swollen tender nodes, fever, headache, weakness

  • septicemic - progression to massive bacterial growth; virulence factors cause intravascular coagulation subcutaneous hemorrhage and purpura - black plague

  • pneumonic - infection localized to lungs, highly contagious; fatal without treatment; pneumonia may be bloody

Diagnosis, Treatment and Prevention of Plague

  • diagnosis depends on history, symptoms, and lab findings from aspiration of buboes

  • treatment: streptomycin, tetracycline, or chloramphenicol

  • killed or attenuated vaccine available

  • prevention by quarantine and control of rodent population in human habitats