In 2003-04 first five VIM-2 metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa (MPPA) isolates with an In4-like integron In461 (aadB–blaVIM-2–aadA6) on conjugative plasmids were identified in three hospitals in Poland. In 2005-15 MPPA much expanded in the country, and as many as 80 isolates in a collection of 454 MPPA (~18%) had In461, being one of two most common MBL-encoding integrons. The organisms occurred in 49 hospitals in 33 cities of 11/16 main administrative regions. PFGE and MLST classified them into 55 pulsotypes and 35 STs, respectively, revealing their remarkable genetic diversity overall, with only a few small clonal clusters. The S1 nuclease/hybridization assays and mating of 63 representative isolates showed that ~85% of these had large In461-carrying plasmids of ~350-550 kb, usually self-transmitting with high efficiency (~10–1-10–2 per donor cell). The plasmids fr om 19 isolates were sequenced, and subjected to structural and SNP-based phylogenetic analysis. These formed a subgroup within a family of IncP-2-type megaplasmids, observed worldwide in pseudomonads from various environments and conferring resistance/tolerance to multiple stress factors, including antibiotics. Their microdiversity in Poland arose mainly from acquisition of different accessory fragments, as well as new resistance genes and multiplication of these. Short-read sequence and/or PCR mapping confirmed the In461-carrying plasmids in the remaining isolates to be the IncP-2 types. The study demonstrated a large-scale epidemic spread of multi-drug resistance plasmids in P. aeruginosa populations, creating an epidemiological threat. It contributes to the knowledge on IncP-2 types, which are interesting research objects in resistance epidemiology, environmental microbiology and biotechnology.
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