Molecular epidemiology of acquired-metallo-β-lactamase-producing bacteria in Poland

We have analyzed 40 metallo-beta-lactamase (MBL)-producing isolates of Pseudomonas aeruginosa (n = 38), Pseudomonas putida (n = 1), and Acinetobacter genospecies 3 (n = 1) from 17 hospitals in 12 cities in Poland that were identified in 2000 to 2004. Pulsed field gel electrophoresis typing classified the P. aeruginosa isolates into eight types, with two types differentiated further into subtypes. Each of the types was specific either to a given center or to several hospitals of the same or neighboring geographic area. Almost all of the organisms produced beta-lactamase VIM-2; the only exceptions were several P. aeruginosa isolates from two centers which expressed VIM-4. The bla(VIM) genes resided exclusively within class 1 integrons, and these were located in either chromosomal or plasmid DNA. PCR-restriction fragment length polymorphism study of the variable regions of the integrons, followed by DNA sequencing, revealed the presence of eight different, mostly novel gene cassette arrays, six of which contained bla(VIM-2) and two of which contained bla(VIM-4). The occurrence of the integron variants correlated well with the geographic distribution of the MBL-producing organisms, and this suggested that their emergence in particular parts of the country had been likely due to a number of independent events. The following regional dissemination of MBL producers could be attributed to various phenomena, including their clonal spread, horizontal transmission of resistance determinants, or both. All of the data collected in this study revealed that even at this early stage of detection, the epidemiological situation concerning MBL producers in Poland has already been complex and very dynamic.