Presence of Pseudomonas putida Strains Harboring Plasmids Bearing the Metallo-β-Lactamase Gene bla _IMP in a Hospital in Japan

Abstract

To determine the persistence and spread of antibiotic-resistant strains in Gunma University Hospital, 83 Pseudomonas putida strains (each from a different patient) were isolated from January 1997 through December 2001. Of the 83 strains isolated, 27 were resistant to carbapenems. All 27 produced metallo-␤-lactamase and were found to be PCR positive for the bla IMP gene. Most (22 strains) were primarily isolated from the wards (W7 [9 strains] and W4 [8 strains]). Another five bla IMP -positive P. putida strains from wards W7 and W4 were obtained by swabbing around the water pipes. A total of 32 bla IMP -positive P. putida strains were assessed by pulsed-field gel electrophoresis (PFGE) and testing of drug susceptibility to 10 chemotherapeutic agents. Both PFGE and MIC patterns revealed that there were long-term resident strains among inpatients and hospital environments. The bla IMP genes of 22 of 32 strains were all transferable to a recipient strain of Pseudomonas aeruginosa by conjugation or transformation and conferred resistance to carbapenems and cephems. The bla IMP plasmids were conjugally transmissible among P. aeruginosa strains and mediated resistance to amikacin as well as ␤-lactams. Ten of the 22 plasmids mediated additional resistance to gentamicin and tobramycin. Plasmids with identical DNA and drug resistance patterns were found in P. putida strains with identical PFGE patterns and with different PFGE patterns. We presumed that P. putida was one of the resident species in inpatients and especially in hospital environments, spreading drug resistance genes via plasmids among P. putida strains and supplying them to more pathogenically important species, such as P. aeruginosa.Carbapenem-hydrolyzing metallo-␤-lactamases, especially IMP-type and VIM-type metallo-␤-lactamases, are clinically important, because these enzymes effectively hydrolyze almost all ␤-lactam antibiotics except monobactams, conferring resistance to penicillins and cephems in addition to carbapenems on pathogenic bacteria (12,13,18,21,23,32). Since genes encoding these metallo-␤-lactamases (bla IMP and bla VIM ) and their variant genes have become easy to detect using the PCR method, dissemination of these genes in clinical isolates has been widely observed in gram-negative bacteria, especially in Pseudomonas aeruginosa and other non-glucose-fermenting bacteria (3, 4, 6, 8-10, 26-30, 34, 35). Recently, nosocomial infections of Pseudomonas putida producing VIM-type metallo-␤-lactamase were reported in Italy (15). The bla VIM gene was plasmid-borne but was not transferable to either P. aeruginosa or Escherichia coli. We also observed metallo-␤-lactamase-producing P. putida strains in Gunma University Hospital, but the responsible gene was bla IMP , not bla VIM , and it was plasmid-borne in most of the isolates. In this paper, we report the existence of multiple-drug-resistant P. putida strains that harbored bla IMP plasmids easily transmissible to P. aeruginosa in Gunma University Hospital. MATERIALS AND METHODSBacterial strains. A to...

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