Transmission in the community of clonal Proteus mirabilis carrying VIM-1 metallo-beta-lactamase

Several infections among patients attending our outpatient clinic were caused by imipenem-resistant Proteus mirabilis that were phenotypically metallo-beta-lactamase (MBL)-positive. The aim of the study was to investigate this extrahospital dissemination and the mechanisms of resistance to carbapenems.

During a 1 year period (December 2005-December 2006), the characteristics of the outpatients with infections caused by isolates of P. mirabilis with reduced susceptibility to imipenem (MIC > 4 mg/L) were prospectively collected. The isolates were tested by agar dilution MICs, phenotypic MBL testing and enterobacterial repetitive intergenic consensus PCR. PCR assays and nucleotide sequencing were used for the identification of bla gene types and mapping of the integron carrying the MBL gene. The location of the MBL allele was investigated by mating experiments, plasmid analysis and hybridization of the Southern-blotted plasmid extract with a bla(VIM-1) probe.

During the study, 12 MBL-positive P. mirabilis isolates were recovered from urinary tract infections of community patients. In all cases, the patients had a previous hospitalization in a Greek regional hospital and had received fluoroquinolones and/or aminoglycosides and beta-lactams. MICs of imipenem ranged from 32 to >128 mg/L, whereas those of meropenem ranged from 1 to 8 mg/L and those of ertapenem ranged from 0.5 to 4 mg/L. The isolates originated from the same clonal strain and harboured a bla(VIM-1) gene in a common integron structure. Conjugation experiments, plasmid analysis and hybridization assays indicated the chromosomal location of the bla(VIM-1) gene.

This is the first study that documents transmission in the extrahospital setting of acquired MBL-producing Gram-negatives causing community-onset infections.