Enteric Bacteria Overview

Question 1

Are enteric bacteria gram positive or gram negative and what antigenic structures do they possess?

Answer 1

Gram Negative Possess LPS

Question 2

What are the four most important pathogens of the Enterobacteriaceae family?

Answer 2

E. coli Shigella Salmonella Yersinia

Question 3

What are the three important enteric pathogens that are not members of family Enterobacteriaceae?

Answer 3

Campylobacter Vibrionaceae Helicobacter

Question 4

What are the three components of LPS?

Answer 4

Lipid A - toxic part of LPS (endotoxin), a similar but not identical structure amongst all Gram negatives. The lipid (fatty acid portion) forms the outer half of the lipid bilayer of the outer membrane. Core polysaccharides - constant region of LPS within a genus—different between genera. O antigens - repeating subunits of oligosaccharides (up to 40) of LPS- variable within a genus; helps species identification (e.g. Shigella sonnei vs. Shigella dysenteriae) or antigenic types as in Salmonella or E. coli.

Question 5

What are H antigens?

Answer 5

“H” antigens are flagellar protein antigens associated with motile organisms. Not all enteric have this antigen.

Question 6

What are K antigens?

Answer 6

“K” antigens in the enterics consist of capsular polysaccharide. It is not found on all strains. When it is, it is usually associated with increased virulence. Capsules are most significant when the organism produces extraintestinal infections (eg. bacteremias).

Question 7

What are the three primary antigenic structures on enteric bacteria?

Answer 7

LPS H antigen K antigen

Question 8

What pathogens are non-invasive?

Answer 8

V Chol ETEC EHEC EPEC

Question 9

What are the invasive pathogens?

Answer 9

Shigella E coli more on slides

Question 10

What are the characteristics and likely bacterial causes of watery diarrhea?

Answer 10

Copious, watery, no blood or pus. No tissue invasion. Involves small intestine. Most likely causes: ETEC, EPEC, Campylobacter

Question 11

What are the characteristics and likely bacterial causes of dysentery?

Answer 11

Scant volume, blood, pus, or mucus present. Tissue invasion. Involves large intestine. Most likely causes: Shigella, EIEC, Campylobacter

Question 12

What are the characteristics and likely bacterial causes of protracted diarrhea?

Answer 12

Any diarrhea lasting more than 14 days. Most likely cause: EPEC

Question 13

What are the characteristics and likely bacterial causes of bloody, watery diarrhea?

Answer 13

Copious volume, some blood, pus, invasion. Involves ileum and colon. Most likely causes: Salmonella, Campylobacter, Yersiniae

Question 14

What are the characteristics and likely bacterial causes of hemorrhagic colitis?

Answer 14

Copious, like liquid, blood, no leukocytes, or invasion. Involves large intestine. Likely cause: EHEC

Question 15

What are the two basic mechanisms of pathogenicity?

Answer 15

TOXIGENIC - Vibrio cholerae, ETEC, EHEC INVASIVE - Salmonella. or both mechanisms used (Shigella dysenteriae).

Question 16

Name and describe three types of toxins produced by enteric bacteria

Answer 16

Exotoxin - usually a protein secreted out of the cell by the organism. Enterotoxin - an exotoxin that has specific effects on the intestine. Endotoxin - lipopolysaccharide (LPS) - lipid A + O antigen.

Question 17

How are disease characteristics influenced by location of infection?

Answer 17

Site of infection - determines disease outcome - generally small intestine = secretory diarrhea large intestine = inflammatory diarrhea. Stomach - Helicobacter pylori. Small intestine - V. cholerae, ETEC, Salmonella, Yersinia, Campylobacter. Large intestine (colon) Shigella, EHEC.

Question 18

What is the most important factor influencing the relative infectivity of different bacteria? What are the minimal infective quantities for Shigella, Salmonella, and Vibrio/ETEC?

Answer 18

Sensitivity to stomach acid. Organisms that are more sensitive to acid (e.g. vibrios) have higher infective doses. These organisms are more likely to be transmitted by food or water, whereas those that have low infective doses are more likely to be transmitted directly from person to person. Shigella - as low as 10^1-10^2 Salmonella - 10^5 but may be as low as 10^2 Vibrio, ETEC- 10^8 but this may be reduced to 10^4 by foods that neutralize stomach acidity