Abstract
The rapid spread of carbapenemase-producing strains has led to increased levels of resistance among Gram-negative bacteria, especially enterobacteria. The current study aimed to collect and genetically characterize the colistin- and carbapenem-resistant isolates, obtained in one of the biggest hospitals (Military Medical Academy) in Sofia, Bulgaria. Clonal relatedness was detected by RAPD and MLST. Carbapenemases, ESBLs, and mgrB were investigated by PCR amplification and sequencing, replicon typing, and 16S rRNA methyltransferases with PCRs. Fourteen colistin- and carbapenem-resistant K. pneumoniae isolates were detected over five months. Six carbapenem-resistant and colistin-susceptible isolates were also included. The current work revealed a complete change in the spectrum of carbapenemases in Bulgaria. bla(NDM-5) was the only NDM variant, and it was always combined with bla(OXA-232). The coexistence of bla(OXA-232) and bla(NDM-5) was observed in 10/14 (72%) of colistin- and carbapenem-resistant K. pneumoniae isolates and three colistin-susceptible isolates. All bla(NDM-5)- and bla(OXA-232)-positive isolates belonged to the ST6260 (ST101-like) MLST type. They showed great mgrB variability and had a higher mortality rate. In addition, we observed bla(OXA-232) ST14 isolates and KPC-2-producing ST101, ST16, and ST258 isolates. The colistin- and carbapenem-resistant isolates were susceptible only to cefiderocol for bla(NDM-5)- and bla(OXA-232)-positive isolates and to cefiderocol and ceftazidime/avibactam for bla(OXA-232)- or bla(KPC-2)-positive isolates. All bla(OXA-232)-positive isolates carried rmtB methylase and the colE replicon type. The extremely limited choice of appropriate treatment for patients infected with such isolates and their faster distribution highlight the need for urgent measures to control this situation.