Module 5.5 Gram Negative Aerobic Rods Lactose Fermenters

Question 1

List some key characteristics of Enterobacterales (order) as a whole

Answer 1

• 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

Question 2

What are the main 3 enterobacterales that are lactose fermenters?

Answer 2

Escherichia, Klebsiella, Enterobacter

Question 3

Escherichia coli 1-PR/OPP-Z

Answer 3

• 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)

Question 4

What are the enteric pathogenic E. coli strains?

Answer 4

ETEC, EPEC, STEC

Question 5

What is ETEC?

Answer 5

Enterotoxigenic strain of E coli. causing diarrhea, adhesin on the pili allowing it to attach, produces enterotoxins

Question 6

What is EPEC?

Answer 6

Enteropathogenic strain of E coli causing diarrhea, adhesin (intimin and A/E protein)

Question 7

What is STEC?

Answer 7

Shiga toxin producing E coli

Question 8

What are the 2 strains of STEC?

Answer 8

EHEC and Porcine STEC

Question 9

What is EHEC?

Answer 9

• a strain of STEC
• Enterohemorrhagic E coli
• produces diarrhea, systemic disease, adhesin (intimin and pili) and produces Shiga toxin

Question 10

What is Porcine STEC?

Answer 10

• Porcine Shiga toxin producing E coli
• neonatal scours
• PWD
• Edema disease

Question 11

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?

Answer 11

Enterotoxigenic Escherichia coli (ETEC)

Question 12

Enterotoxigenic E. coli ETEC 1-PR

Answer 12

• very host specific
• usually watery neonatal diarrhea (pigs and calves)
• absence of local inflammation (no lesions)
• enterotoxins act on epithelial cells of small intestine

Question 13

Pathogenicity of ETEC?

Answer 13

• ETEC proliferates in the small intestine
• Adherence by Pili/Fimbriae (adhesin)
• Production of enterotoxins
• diarrhea is mainly seen in calves and post-weaning piglets

Question 14

What are the main ETEC enterotoxins?

Answer 14

• STI = increases cGMP
• STII = increase in Ca
• LT = increases cAMP, irreversible
• fluid will follow and can be fatal

Question 15

How do we treat and control ETEC?

Answer 15

• symptomatic treatment (rehydration)
• antibiotics after damaged intestinal cells are replaced
• good colostrum, hygiene, there is a vaccine but not overly effective

Question 16

Shiga toxin producing E. coli (STEC)

Answer 16

• two strains: Porcine STEC and EHEC

Question 17

Enterohemorrhagic E. coli (EHEC) 1-PR-Z

Answer 17

• 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

Question 18

Pathogenesis of EHEC?

Answer 18

• bacteria is ingested
• attaches to the colon via intimin and pili
• produces Shiga toxin causing bloody diarrhea, toxemia, kidney failure

Question 19

Diagnosis and treatment of EHEC?

Answer 19

• 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

Question 20

Enteropathogenic E. coli (EPEC) 2-PR

Answer 20

• EHEC without the Shiga toxin
• ingested, attaches to the colon and causes diarrhea, no systemic or toxemia phase

Question 21

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?

Answer 21

She had coliform mastitis caused by enterotoxigenic E. coli and died of endotoxic shock

Question 22

Extraintestinal E. coli (ExPEC) 1-OPP-Z

Answer 22

• adhesins and other virulence factors like LPS
• seen in dogs and cats
• predisposing factors like fecal contamination followed by ascending infection

Question 23

Avian pathogenic E. coli (APEC) 1-OPP-Z

Answer 23

• respiratory route infection
• septicemia and death
• septicemia E. coli from predisposing factors causing agammaglobulinemia which prevents the body from producing antibodies

Question 24

ExPEC Virulence factors?

Answer 24

• LPS = endotoxin
• siderophores = iron scavenging
• capsule (antiphagocytic)

Question 25

Explain the concepts of endotoxic shock and the factors (LPS and endotoxin) that cause it.

Answer 25

• 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