Tularemia Outbreak, Bulgaria, 1997–2005

The 1997–2005 tularemia outbreak in Bulgaria affected 285 people. Ten strains were isolated from humans, a tick, a hare, and water. Amplified fragment length polymorphism typing of the present isolates and of the strain isolated in 1962 suggests that a new genetic variant caused the outbreak

Detection of different colistin resistance mechanisms among multidrug resistant Klebsiella pneumoniae isolates in Bulgaria

The more frequent usage of colistin resulted in an increase of colistin resistance due to lipopolysaccharide modifications. The aim of this study was to reveal the prevalence and mechanisms of colistin resistance among multidrug-resistant Klebsiella pneumoniae isolates collected in Bulgaria. One hundred multidrug resistant K. pneumoniae isolates were collected in a period between 2017 and 2018. Among them, 29 colistin resistant and 8 heteroresistant isolates were observed and further investigated. Clonal relatedness was detected by RAPD and MLST. Carbapenemases, two component system phoQ/phoP, pmrA/B, and mgrB were investigated by PCR amplification and Sanger sequencing. Among 37 colistin nonsusceptible isolates, we detected 25 NDM-1 producers. The isolates belonged mainly to ST11 (80%), and also to ST147, ST35, ST340, ST219 (1-2 members per clone). Nine colistin resistant isolates showed changes in mgrB. IS903B-like elements truncated mgrB in five isolates. In two isolates, premature stopcodon (Q30stopcodon) was observed and another two isolates did not amplify mgrB, possibly due to bigger deletion or insertion. No isolates showed phoQ/phoP and pmrA/B mutations except for pmrB (four isolates had R256G). All isolates with IS903B insertions belonged to ST11 clone. The mgrB alterations play major role in colistin resistance in K. pneumoniae isolates studied in the current work. We report truncation of mgrB by IS903 like element in colistin resistant NDM-1 producing K. pneumoniae ST11 clone in Bulgaria

ANTIBIOTIC COMBINATIONS WITH COLISTIN AGAINST CARBAPENEM-RESISTANT Klebsiella pneumoniae - in vitro ASSESSMENT

Purpose: The treatment of infections, caused by highly resistant strains of Gram-negative bacteria is extremely difficult. A potentially valuable option is combination antibiotic therapy. The aim of this study was to evaluate three different in vitro methods for synergy testing and to assess the effect of different combinations with colistin against carbapenem-resistant K. pneumoniae strains. Material/methods: A screening test for synergy with colistin (developed in the laboratory) and the microdilution method of El-Azizi were used on 50 carbapenem-resistant strains of K. pneumoniae. Additionally, time-kill assays (TKA) were performed for one antibiotic combination. Results: A total of 16 combinations were tested with the screening test. Synergy and probable synergy with colistin were observed mainly with azithromycin (18% of the isolates), rifampicin (16%), meropenem (14%) and doxycycline (12.8%). The combinations colistin-rifampicin, colistin-meropenem and colistin-gentamicin, were synergistic in 36%, 8% and 20%, respectively, according to the microdilution method of El-Azizi. The observed synergy was detected mainly against some of the colistin resistant strains. Agreement between the two methods was found in 80% for the combinations colistin-rifampicin and colistin-meropenem and in 84% for colistin-gentamicin. Agreement between the three methods used was observed for four strains (80%). Conclusions: The screening test may represent a rapid and cost effective screening of a large number of combinations with colistin. The microdilution method of El-Azizi may provide an opportunity for rapid testing of three double and one triple antibiotic combinations in one plate. There is an urgent need for standardization of the methods for synergy testing and guidelines for diagnostic laboratories