Gram-Negative Enteric Rods – Part 1

These set of notes are done in a similar fashion to the virus lectures. Try and answer the following questions, and look at the paragraph answers provided. Try and know the main species each family of enteric gram –ve rods.

General information

1. What are the main families of the enteric gram negative rods?

Enteric gram negative rods have three major families, with the fourth one being those of the commensals in the gut. These are: Enterobacteriaceae, Vibrioncaeae, Pseduomanodoceae. The 4^th group is Bacteroidaceae.

Enterobacteriaceae

• Describe the general properties of this family of bacteria. Name some of the species (major ones).

• Describe some of the characteristics of Enterobacteriaceae. Elaborate on each one.

Enterobacteriaceae form the major family of gram negative enteric rods. They are gram –ve, have a high degree of motility due to presence of petrichous flagella, grow well on artificial media, oxidase –ve, asporogenous, bacilli, anaerobic/facultative aerobes. Most of the Enterobacteriaceae are commensals found in the gut – part of normal gut flora but some others are very pathogenic causing: typhoid, shiga dysentery, + plaque. Haemolytic uraemic syndrome is caused by food/water borne species.

Some of the characteristics of this family of bacteria include:

• Motility: some species are highly motile, while others are non-motile. Generally, Enterobacteriaceae are highly motile. Swarming proteus is motile, whilst Shigella + Klebsiella are non-motile.

• Antigenic structure: the bacteria contain three antigens namely: O, H, K. O is found on the cell surface, H is found on the flagella, and K is a capsular antigen over the H antigen.

• Endotoxin: LPS/cell wall: cause pyrogenicity, comsumption of complement, shock.

• Exotoxin: These include cytotonic + cytotoxic enterotoxins, neurotoxins, verotoxins, haemolysins.

• Bacteriocins

• Drug resistance: due to overuse of antibiotics, great problem, resistance plasmids transmit the resistance from one bacteria to another.

Category: Microbiology Notes