engleski

Colistin-Resistant Acinetobacter baumannii Recovered from Wastewaters in Croatia

Background: Due to growing antimicrobial resistance rates of clinical isolates of Acinetobacter baumannii, colistin is now considered as a last resort antibiotic for treatment of A. baumannii infections. Although colistin-resistant clinical isolates have been sporadically reported in Croatia, our monitoring of A. baumannii outside hospitals suggested the presence of colistin-resistant isolates in Croatian wastewaters. In this study, colistin- resistant A. baumannii recovered from hospital and urban wastewater are reported. Material/methods: Hospital wastewater (HW) was collected at the central manhole of Special Hospital for Pulmonary Diseases in Zagreb in August and October 2015. HW is released into the urban sewage system without pre-treatment, reaches the central wastewater treatment plant (WWTP), where it is treated by the technology of activated sludge. The activated sludge and treated effluent wastewater were collected from September 2015 to March 2016. Samples were aseptically collected and analysed within 2h. A. baumannii was isolated on CHROMagar Acinetobacter supplemented with CR102 and 15 mg/L of cefsulodin after incubation at 42 °C/48h. A. baumannii was identified by routine bacteriological techniques and MALDI-TOF MS. MLST alleles (Oxford/Pasteur) were determined. Susceptibility to clinically relevant antibiotics was determined by MICs values obtained by Vitek2 system. Colistin resistance was confirmed by gradient dilution E- test and broth microdilution method. Results: Three isolates of A. baumannii were recovered from untreated HW, one from activated sludge and two from WWTP effluent. All isolates were ST- 2pas, five were ST-195ox, while one isolate from HW was ST-451ox. These STs correlate with international clonal lineage 2 (IC2). Four isolates were extensively drug-resistant, while two isolates from WWTP effluent were pandrug- resistant. Identification of colistin susceptibility by Vitek2 system gave the false negative result for two of six isolates tested. By using the E-test and broth microdilution all isolates were confirmed resistant to colistin. Conclusions: Colistin-resistant A. baumannii were present in untreated HW and WWTP. The findings suggest the need to disinfect HW and WWTP effluent prior to its discharge into the environment in order to mitigate the propagation of colistin-resistant A. baumannii.

Acinetobacter baumannii, colistin resistance, wastewater

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