One. General characteristics of Enterobacteriaceae
One. General characteristics of Enterobacteriaceae
. Largest and most medically important family of gram-negative bacilli.
. More than ninety percent of medically important isolates belong to just a few genera.
. Found worldwide and part of the normal microbiota of all animals.
. Common cause of nosocomial infections.
. All members ferment glucose, reduce nitrates to nitrites, and are oxidase negative; the PPT notes Plesiomonas as an oxidase-positive exception and says phylogenetic studies place it close to Proteus.
. Antigens include O/somatic antigen, H/flagellar antigen, and K/capsular antigen.
. Commonly present in the large intestine.
. Facultatively anaerobic; non-sporing; non-acid-fast; gram-negative bacilli.
. Complex family: some are nonpathogenic, a few are highly pathogenic, and commensals can become pathogenic.
. Motile except Shigella and Klebsiella.
. Non-capsulated except Klebsiella.
. Non-fastidious.
. Grow on bile-containing media such as MacConkey agar.
Two. Selective/differential media and lactose fermentation
Two. Selective/differential media and lactose fermentation
. Important media listed in the PPT: MacConkey agar, Eosin Methylene Blue agar, Salmonella-Shigella agar, and Triple Sugar Iron agar.
. MacConkey agar is selective and differential for Enterobacteriaceae.
. MacConkey components listed: bile salts, crystal violet, lactose, and neutral red.
. Bile salts and crystal violet inhibit gram-positive bacteria and provide selectivity.
. Lactose fermentation produces acid; neutral red is the pH indicator.
. Lactose fermenters appear pink; non-lactose fermenters appear colorless.
. Method given: streak inoculate MacConkey agar and incubate at thirty-seven degrees Celsius for twenty-four hours.
. Example lactose fermenter: E. coli, pink colonies.
. Example non-lactose fermenter: Shigella, colorless colonies.
. Basic classification in the PPT: lactose fermenters/coliforms (E. coli, Escherichia, Klebsiella); late lactose fermenter (Shigella sonnei); non-lactose fermenters (Salmonella, Shigella).
. The PPT notes Shigella sonnei is pronounced 'son-ya' and Shigella flexneri 'flex-ne-ra'.
. Lactose fermenter is also called 'para colons' in the PPT.