Which organism is lactose fermenting, non-motile, and indole positive?

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Multiple Choice

Which organism is lactose fermenting, non-motile, and indole positive?

This set of traits points to Klebsiella oxytoca. Lactose fermentation is typical for Klebsiella species, so you’d see acid production with pink colonies on lactose-containing media. Being non-motile means it lacks flagella, so a motility test would show no movement. The indole test being positive is a distinctive feature of Klebella oxytoca (unlike Klebsiella pneumoniae, which is indole negative). Among the other organisms, Enterobacter cloacae also ferments lactose but is motile and indole negative, so it doesn’t fit all three traits; Citrobacter freundii can be lactose fermenter but is motile and has variable indole reaction; Providencia rettgeri typically does not ferment lactose. The combination of lactose fermentation, non-motility, and indole positivity best matches Klebsiella oxytoca.

This set of traits points to Klebsiella oxytoca. Lactose fermentation is typical for Klebsiella species, so you’d see acid production with pink colonies on lactose-containing media. Being non-motile means it lacks flagella, so a motility test would show no movement. The indole test being positive is a distinctive feature of Klebella oxytoca (unlike Klebsiella pneumoniae, which is indole negative). Among the other organisms, Enterobacter cloacae also ferments lactose but is motile and indole negative, so it doesn’t fit all three traits; Citrobacter freundii can be lactose fermenter but is motile and has variable indole reaction; Providencia rettgeri typically does not ferment lactose. The combination of lactose fermentation, non-motility, and indole positivity best matches Klebsiella oxytoca.

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