engleski

Multidrug resistant Proteus mirabilis in nursing homes

Background: An increased frequency of Proteus mirabilis isolates resistant to expanded-spectrum cephalosporins was observed recently in a long-term care facility in Zagreb The aim of this study was the molecular characterization of resistance mechanisms to expanded-spectrum cephalosporins in P. mirabilis isolates from this nursing home. Material and methods: Twenty strains collected from 2013-2014 showing reduced susceptibility to ceftazidime were investigated. Antibiotic susceptibilities were determined by broth microdilution method. Inhibitor-based tests were performed to detect ESBLs extended-spectrum AmpC β-lactamases. Transfer of ceftazidime was tested by conjugation (broth mating method) using E. coli resistant to rifampicin. AmpC β-lactamases were characterized by PCR and sequencing of blaampC genes. Quinolone resistance determinants (qnr genes) were characterized by PCR. Plasmids were characterized by PCR-based replicon typing (PBRT). Results: Presence of an AmpC β-lactamase was confirmed in all strains by combined-disk test with phenylboronic acid. The strains were phenotypically negative for ESBLs. All strains were resistant to amoxicillin alone and combined with clavulanate, cefotaxime, ceftriaxone, cefoxitin, and ciprofloxacin, but susceptible to combination of ceftazidime with clavulanic acid, piperacillin/tazobactam, cefoxitin, imipenem, and meropenem. Ceftazidime resistance was not transferred to E. coli recipient strain. PCR and sequencing using primers targeting blacmy genes revealed CMY-16 β-lactamase. Blacmy-16 in three isolates was carried by a non-conjugative plasmid which did not belong to any known PBRT. Conclusions: This is the first report of multidrug resistant P. mirabilis in a nursing home in Croatia. Cephalosporin resistance was due to plasmid-mediated AmpC β-lactamase CMY-16.

CMY-16; Proteus mirabilis; Amp C β-lactamases; conjugative plasmid; clonal dissemination

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