Module 5.5 Gram Negative Aerobic Rods Lactose Fermenters Flashcards
List some key characteristics of Enterobacterales (order) as a whole
- gram negative (pink)
- short rods
- aerobes, facultative anaerobes
- intestinal inhabitants
- often ID using MacConkey agar which identifies lactose fermenters (pink) from NLF (white)
- MacConkey Agar inhibits the growth of GP and fungi
What are the main 3 enterobacterales that are lactose fermenters?
Escherichia, Klebsiella, Enterobacter
Escherichia coli 1-PR/OPP-Z
- found as a commensal in the intestine (large bowel)
- it is a dominant aerobe
- many serotypes found in the outer membrane (flagellum = H, capsule = K, LPS = O, Fimbria/Pili = F)
What are the enteric pathogenic E. coli strains?
ETEC, EPEC, STEC
What is ETEC?
Enterotoxigenic strain of E coli. causing diarrhea, adhesin on the pili allowing it to attach, produces enterotoxins
What is EPEC?
Enteropathogenic strain of E coli causing diarrhea, adhesin (intimin and A/E protein)
What is STEC?
Shiga toxin producing E coli
What are the 2 strains of STEC?
EHEC and Porcine STEC
What is EHEC?
- a strain of STEC
- Enterohemorrhagic E coli
- produces diarrhea, systemic disease, adhesin (intimin and pili) and produces Shiga toxin
What is Porcine STEC?
- Porcine Shiga toxin producing E coli
- neonatal scours
- PWD
- Edema disease
Case Report:
- Veal calf with severe scours, dehydrated, off feed
- treated with oral electrolytes, found collapsed, cold extremities, died
- Agglutination test and PCR for adhesin and enterotoxin
What is a likely cause given this information?
Enterotoxigenic Escherichia coli (ETEC)
Enterotoxigenic E. coli ETEC 1-PR
- very host specific
- usually watery neonatal diarrhea (pigs and calves)
- absence of local inflammation (no lesions)
- enterotoxins act on epithelial cells of small intestine
Pathogenicity of ETEC?
- ETEC proliferates in the small intestine
- Adherence by Pili/Fimbriae (adhesin)
- Production of enterotoxins
- diarrhea is mainly seen in calves and post-weaning piglets
What are the main ETEC enterotoxins?
- STI = increases cGMP
- STII = increase in Ca
- LT = increases cAMP, irreversible
- fluid will follow and can be fatal
How do we treat and control ETEC?
- symptomatic treatment (rehydration)
- antibiotics after damaged intestinal cells are replaced
- good colostrum, hygiene, there is a vaccine but not overly effective
Shiga toxin producing E. coli (STEC)
- two strains: Porcine STEC and EHEC
Enterohemorrhagic E. coli (EHEC) 1-PR-Z
- generally E. coli is not zoonotic but EHEC is the exception
- found in large bowel NOT small intestine
- inflammatory diarrheal illness
- severe disease in humans
Pathogenesis of EHEC?
- bacteria is ingested
- attaches to the colon via intimin and pili
- produces Shiga toxin causing bloody diarrhea, toxemia, kidney failure
Diagnosis and treatment of EHEC?
- hemorrhagic diarrhea
- PCR is the big one for virulence factors
- symptomatic treatment, antibiotics not recommended
- in general EHEC is not a significant cause of illness for animals rather they are a reservoir for humans, infectious does for humans is extremely low
- it is important we have slaughter hygiene because of it
Enteropathogenic E. coli (EPEC) 2-PR
- EHEC without the Shiga toxin
- ingested, attaches to the colon and causes diarrhea, no systemic or toxemia phase
Case Report:
- four days after calving, cow off feed
- two quarters hot and swollen, slightly painful
- thin milk
- found down, shivering, trembling, depressed
- fever, tachycardia, watery diarrhea, dehydration
- milk turned thin, yellow, serous, small flakes and then she died
- typing of isolates (agglutination and PCR for adhesin and endotoxin)
- high somatic cell count, positive for coliform mastitis
What could have happened?
She had coliform mastitis caused by enterotoxigenic E. coli and died of endotoxic shock
Extraintestinal E. coli (ExPEC) 1-OPP-Z
- adhesins and other virulence factors like LPS
- seen in dogs and cats
- predisposing factors like fecal contamination followed by ascending infection
Avian pathogenic E. coli (APEC) 1-OPP-Z
- respiratory route infection
- septicemia and death
- septicemia E. coli from predisposing factors causing agammaglobulinemia which prevents the body from producing antibodies
ExPEC Virulence factors?
- LPS = endotoxin
- siderophores = iron scavenging
- capsule (antiphagocytic)
Explain the concepts of endotoxic shock and the factors (LPS and endotoxin) that cause it.
- gram negative bacteria release a toxin into the bloodstream triggering a severe inflammatory response
- LPS is an endotoxin, the main component of the outer wall of the gram negative bacteria
