ACINETOBACTER BAUMANNII RECOVERED FROM TREATED MUNICIPAL WASTEWATER IS RELATED TO CLINICAL ISOLATES

Over the last decade hospital-acquired infections due to Acinetobacter baumannii are increasing worldwide. Clinical isolates of A. baumannii are usually multi-drug resistant (MDR), with resistance to carbapenems increasing drastically in Croatia. The most important mechanism of carbapenem resistance in A. baumannii is the enzymatic hydrolysis mediated by oxacillinases encoded by blaOXA genes. Although A. baumannii has been isolated from patients and hospital environment during outbreaks, its epidemiology remains incompletely understood. Here we report the finding of MDR carbapenem resistant A. baumannii in treated municipal wastewater related to clinical isolates. The isolate of A. baumannii named EF2 was recovered from the secondary treated municipal wastewater of the City of Zagreb. The isolation was performed at 42°C/48h on CHROMagar Acinetobacter supplemented with CR102 and cefsulodin sodium salt hydrate. By phenotypical analyses and Vitek 2 system the isolate was determined as A. calcoaceticus-baumannii complex. MALDI-TOF MS analysis gave the reliable score value of 2.352 identifying it as A. baumannii. Phylogenetic analysis of the RNA polymerase β-subunit (rpoB) gene fragment confirmed the identity as A. baumannii species and showed 100% sequence ID to the clinical isolates. According to MIC values determined by Vitek 2 system or E-test and interpreted according to EUCAST criteria, isolate was susceptible to amikacin, trimethoprim- sulfamethoxazole and colistin, but resistant to carbapenems (imipenem, meropenem), fluoroquinolones (ciprofloxacin, levofloxacin), aminoglycosides (gentamicin, tobramycin) and therefore could be classified as MDR. Multiplex PCR and sequencing confirmed the presence of both intrinsic blaOXA-51 and acquired blaOXA-23 genes. Phylogenetic analyses of blaOXA genes from environmental isolate showed association with those previously described from clinical isolates. Isolate multiplied in the batch system containing autoclaved water from which it was recovered up to 50 days of monitoring at 16.7°C, when its number was 9% higher than initial number. These results suggest that MDR A. baumannii recovered from treated municipal wastewater is most probably of clinical origin and is able to survive in environment outside hospital.