Acinetobacter baumannii detected on mCCDA medium in a waste stabilisation pond

Acinetobacter baumannii survives for prolonged periods under a wide range of environmental conditions. In a larger study investigating the efficacy of pathogen removal in a waste stabilization ponds (WSP), we cultivated microbes from wastewater samples on mCCDA agar containing selective and recommended supplements for the growth of Campylobacter. This bacterium is a recommended reference pathogen for the verification and validation of water recycling schemes in Australia and other parts of the world. A high number of colonies characteristic of Campylobacter grew on the selective media but this did not correlate with qPCR data. Using primers targeting the16S rRNA gene, and additional confirmatory tests such as detection of VS1, ompA, blaOXA-51-like, blaOXA-23-like genes, we tested eight random colonies from eight samples (64 colonies in total) and identified them as A. baumannii. Wastewater grab samples taken three times over 6 months throughout the WSP system showed removal of A. baumannii in the WSP atrates similar to E. coli. In contrast, further intensive sampling from the inlet and the outlet of the WSP using a refrigerated auto-sampler showed that the number of A. baumannii in most sampling rounds did not differ significantly between the inlet and outlet of the WSP and that there was high variation between replicates at the outlet only. Resistance genes were detected in most A. baumannii isolated from the waste stabilisation pond and may potentially be a source of antibiotic resistance for environmental strains.