Enterobacteriaceae
General: Composed of numerous genera of Gram- bacilli, about 9 of which are of common clinical significance. Typical flora of the gastrointestinal tract, but may cause both GI and extra-GI (esp. urinary, respiratory, wound, & bloodstream) infections. Include both motile and nonmotile species, but never form spores.
Clinical:
- Normal:
- Abnormal:
Resistance: Some species carry chromosomally encoded beta-lactamase, which must be induced in order to be expressed, unlike with plasmid encoded beta-lactamases; i.e., it's possible that usual susceptibility testing will erroneously categorize them as susceptible.
Morphology: Gram- bacilli or coccobacilli, usually short and plump, ranging from 0.5-2.0 x 2-4um.
Growth characteristics: Grow well after 18-24hrs at 35C under aerobic conditions on routine blood agar as well as differential MacConkey agar or selective differential Hektoen or xylose-lysine-deoxycholate agar. Usually medium to large, dry or mucoid/glistening, gray colonies, and some are beta-hemolytic or motile; see specific genera or species as some have more distinct morphology. Ferment glucose and other carbohydrates, are oxidase-, catalase+, and reduce nitrate to nitrite. Commonly identified with indole, methyl red, Voges-Proskauer, and citrate screen, also known as the IMViC tests.
Common/important pathogens: By genus:
- Escherichia sp.
- Enterobacter sp.
- Klebsiella sp.
- Pantoea sp.
- Proteus sp.
- Citrobacter sp.
- Serratia sp.
- Salmonella sp.
- Shigella sp.
- Yersinia sp.