Enterobacteriaceae

Basics

Facultative gram (-) enteric bacilli found in soil, water, decaying matter, and large intest of humans, animals, insects

Non-spore forming and resist bile salts

Have flagella all over body (peritrichous flagella) Þ motile (exception: Shigella and Klebsiella are non-motile)

Some have capsules (Klebsiella) while others do not

Members of this family (> 80 species): Salmonella, Shigella, Escherichia, Yersinia Þ intestinal infections Þ diarrhea

Others include opportunistic pathogens at other sites Þ urinary tract, peritoneum, lungs, meninges, wounds, blood

Produce endotoxins and exotoxins which play roles in pathogenesis of infections by these organisms

classification

metabolic capabilities
Antigenic tests: K antigen (capsular), H antigen (flagellar), O antigen (on outermost extension of LPS)
Diagnostic tests at level of DNA (more useful in future years)

with all enterics, secondary bacteremia is always a concern

Clinical Findings

Escherichia coli: most common, causing UTI and wound infections, pneumonia, meningitis, septicemia, intestinal infections

glossary: ETEC (enterotoxigenic E. Coli), EIEC (enteroinvasive E. Coli), EHEC = STEC = VTEC (enterohemorrhagic or Shiga-toxin producing or Verotoxin producing E. coli), EPEC (enteropathogenic E. Coli), EAEC (enteroaggregative E. Coli), EEC (catch all term = enterovirulent E. Coli) Þ syllabus.meds.cwru.edu/textbooks/sherris/tables/t20_20.htm

E. Coli which cause UTI: express pap pili which target urinary epithelium

EPEC: pedistles Þ diarrhea; problem in infants and young children (Tir secreted, acts as receptor for intimin)

Salmonella and Shigella Þ refer to D3J-1BBD-189 Microbial Virulence: Adherence and Invasion

Klebsiella: Pneumonia, UTI, other opportunistic infections; encapsulated strains more virulent than unencapsulated

Enterobacter: associated with nosocomial infections, notably UTI

Proteus –Morganella – Providencia: cause UTI; Providencia is resistant to many standard antibiotics

Citrobacter: opportunistic pathogen at variety of sites, most commonly encountered in UTI; agent of neonatal meningitis

Toxins

Endotoxin – the LPS of the cell wall (lipid A specifically)

stimulates overproduction of various cytokines which along with their downstream effects, mediates toxic shock (sepsis)

Exotoxin – secreted toxin that may be entero- (causes diarrhea) or cyto- (kills cells they interact with)

Toxins characterized by sensitivity to inactivation by heating

LT (heat labile) Þ inactivate upon heating; utilizes a complex mechanism Þ long protein

ST (heat stable toxin) Þ not inactivated upon heating; utilizes a simple mechanism Þ short protein

cytotoxin examples:

Cholera toxin Þ refer to D3J-1BBD-222 Microbial Virulence III: Bacterial Exotoxins – increases cAMP

Shigella dysenteriae type I Þ shiga toxin; and EHEC ("SLT-1, "verotoxin 1") Þ shiga-like toxin I

Local: Pentamer of B subunits organized with A1 (RNA-adenine N glycosylase) subunit Þ B subunits bind to Gb₃ (found on erythrocytes, platelets, endothelial cells, kidney cells) Þ A1 enters cell and cleaves a single adenine residue from 28S rRNA Þ blocks protein synthesis Þ kills cell

Systemic: dysentery, hemorrhagic colitis, and hemolytic-uremic syndrome

enterotoxins have been noted in Salmonella, Shigella, Escherichia, Klebsiella, Citrobacter, Yersinia, Enterobacter

enterotoxin examples:

bind to (activate) guanyulate cyclase (GC-C) in apical memb throughout gut Þ Ý cGMP Þ Ý Cl secretion or inhibits NaCl absorption Þ excess fluid retention in bowel Þ diarrhea

GC-C more prominent in infants so are more susceptible

similar to cholera toxin but not as effective Þ refer to D3J-1BBD-222 Microbial Virulence III: Bacterial Exotoxins

Other Factors Related to Pathogenesis: capsule (anti-phagocytic); pili or fimbriae (mediate attachment and invasion)