MICROBIOLOGY

• Gram-negative non-fermenting, motile bacillus [Fig 1]; known for blue-green pus due to pyocyanin and pyoverdin pigments.
• Non-fastidious organism; it can inhabit a variety of environments including soil and water (hot tubs, sinks, water faucets, respirators, disinfectants, and contact lens cleaning solutions).
• Grows on a wide variety of media. Clinical isolates usually render smooth colonies on plates [Fig 2].
• Produces biofilm, toxins and proteases.
• Drug resistance mechanisms include multiple pathways: chromosomal and inducible beta-lactamases, active efflux pumps, acquired genes and plasmid-mediated ESBLs (TEM, SHV, CTX-M), and altered permeability.[11]
  • Carbapenem resistance mechanisms include:
    • Loss of outer membrane porin D (OprD) results in resistance to carbapenems, specifically imipenem.[14]
    • The combined loss of OprD in combination with another mechanism, i.e., overexpression of AmpC beta-lactamase OR overexpression of efflux pumps, is a major determinant of resistance to carbapenems.[10]
    • Production of carbapenemases, esp. Ambler class B metallo-beta-lactamases (NDM, VIM, IMP).[3]
  • Clinical utility of rapid molecular diagnostic platforms to detect genotype resistance to beta-lactam/beta-lactamase inhibitor combinations is limited by the complexity of nontested determinants of beta-lactam resistance, such as OprD changes and drug efflux systems.[6]