Διερεύνηση νέων β-λακταμασών σε στελέχη gram-αρνητικών βακτηρίων στην κοινότητα

Abstract

The aim of the study was to investigate the dissemination in the community of carbapenem-resistant gram-negative bacteria and the mechanisms of acquired resistance.Patients who were referred to the outpatient department of Serres General Hospital with community-onset infections due to carbapenem-resistant gram-negative bacteria during a 3 year period (2005-2008) were included in this study. The selected isolates were tested by determination of agar dilution MICs, phenotypic carbapenemase testing and molecular typing methods. PCR and sequencing analyses were employed for identification of bla genes and mapping of the integron carrying the metallo-β-lactamase (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 blaVIM probe. The demographic and clinical characteristics of the outpatients were prospectively collected.During the study period 12 Proteus mirabilis, 97 Pseudomonas aeruginosa and 24 Klebsiella pneumoniae isolates with reduced susceptibility to imipenem and/or meropenem were recovered from urinary tract infections of 12, 45 and 12 outpatients, respectively. As many as 64 of the outpatients had a history of previous hospitalization or visit to the healthcare facilities in the preceding year while the remaining 5 outpatients with urinary tract infections due to P. aeruginosa carbapenem-resistant isolates had not been hospital admission in the preceding year.In 18 outpatients infected with P. aeruginosa and 6 outpatients infected with K. pneumoniae the carbapenem-resistant organisms caused recurrent community-onset infections, while in three outpatients P. aeruginosa isolates were also implicated in community-onset bacteremic episodes. Diabetes mellitus, prostatic hyperplasia and infection with an MBL-producing strain during a previous hospitalization were significantly associated with recurrent infections in the community setting.Recurrent infections were not detected among patients infected with MBL-producing P. mirabilis isolates. Among P. mirabilis isolates imipenem, meropenem and ertapenem MICs ranged from 32 to >128 mg/L, 1 to 8 mg/L and 0.5 to 4 mg/L, respectively. The isolates originated from the same clonal strain and harbored a blaVIM-1 gene in a common integron structure. Conjugation experiments, plasmid analysis and hybridization assays indicated the chromosomal location of blaVIM-1 gene. All 45 single-patient P. aeruginosa isolates harbored the blaVIM-2 MBL gene in a common class 1 integron structure. They belonged to one predominant pulsed-field gel electrophoresis type and three sporadically detected types; two of the sporadic clonal types were identified among outpatients without previous exposure to health care facilities, while the predominant clonal type was also identified to cause infections in hospitalized patient. The integron carrying the MBL gene was located on the bacterial chromosome.For the K. pneumoniae isolates imipenem, meropenem and ertapenem MICs ranged from 8 to 64mg/L, 4 to 32mg/L and 8 to 128mg/L, respectively. All studied isolates as well as those two recovered during previous hospitalization belonged to a single PFGE clone. They harbored a plasmid-mediated blaVIM-1 gene in an integron structure that has been previously described among clinical isolates from Greek hospitals.This is the first study to document the dissemination of MBL-producing P. mirabilis, P. aeruginosa and K. pneumoniae isolates in the community. Present clinical and molecular data provided evidence that MBL-producing strains could easily disseminated in the community from patients colonized during a previous hospitalization. Increased awareness and intensified infection control practices in the hospital as well as the community setting are the keys to curtailing the spread of these alarming carbapenem resistant pathogens.