• Facultative anaerobic, nonencapsulated Gram-negative rod [M. morganii].
    • Non-lactose fermenter in the same family as Proteus.
    • Environmentally ubiquitous, part of normal colonic flora.
    • "Urea splitter," but stones are seen less frequently than Proteus due to less effective urease enzyme.
  • Morganella only has a single member in its genus M. morganii and two subspecies: M. morganii and M. sibonii, which differ only in trehalose fermentation.
  • Antimicrobial susceptibility:
    • Naturally resistant to penicillin, ampicillin, first- and second-generation cephalosporins, fosfomycin, and macrolides.
    • Beta-lactamase is inducible, AmpC type but less commonly seen than with Enterobacter and Serratia.
    • Tigecycline is not reliably effective due to the ArcAB efflux pump, although it may show synergy in vitro with other antimicrobials[9].

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Last updated: February 7, 2023