Emergence of and Positive Colistin- and Carbapenem-Resistant in a Bulgarian Hospital.

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 were investigated by PCR amplification and sequencing, replicon typing, and 16S rRNA methyltransferases with PCRs. Fourteen colistin- and carbapenem-resistant 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. was the only NDM variant, and it was always combined with . The coexistence of and was observed in 10/14 (72%) of colistin- and carbapenem-resistant isolates and three colistin-susceptible isolates. All - and -positive isolates belonged to the ST6260 (ST101-like) MLST type. They showed great variability and had a higher mortality rate. In addition, we observed ST14 isolates and KPC-2-producing ST101, ST16, and ST258 isolates. The colistin- and carbapenem-resistant isolates were susceptible only to cefiderocol for - and -positive isolates and to cefiderocol and ceftazidime/avibactam for - or -positive isolates. All -positive isolates carried 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.