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

Gram Negative Possess LPS


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

E. coli Shigella Salmonella Yersinia


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

Campylobacter Vibrionaceae Helicobacter


What are the three components of LPS?

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.


What are H antigens?

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


What are K antigens?

"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).


What are the three primary antigenic structures on enteric bacteria?

LPS H antigen K antigen


What pathogens are non-invasive?



What are the invasive pathogens?

Shigella E coli more on slides


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

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


What are the characteristics and likely bacterial causes of dysentery?

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


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

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


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

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


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

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


What are the two basic mechanisms of pathogenicity?

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


Name and describe three types of toxins produced by enteric bacteria

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.


How are disease characteristics influenced by location of infection?

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.


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?

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