Evaluation of CHROMagar Acinetobacter and MacConkey media for the recovery of Acinetobacter baumannii from soil samples

Abstract

The opportunistic pathogen Acinetobacter baumannii occupies niches in human and veterinary clinics and other environments. This comparative study was designed to assess the recovery rate of Ac. baumannii from 20 soil samples collected in Germany (from which Ac. baumannii had been previously isolated) on selective CHROMagar Acinetobacter (CMA) and MacConkey Agar (MCA). Suspected Ac. baumannii were confirmed by detection and sequencing of blaOXA-51-like genes. Overall, the recovery rate of Ac. baumannii from both media was similar. Out of the 20 soil samples enriched in mineral salt medium (MM) plus 0.2% acetate for 5 h, Ac. baumannii was recovered from 12 (60%) on CMA and 11 (55%) on MCA, and from 14 (70%) with both selective media after enrichment for 24 h. Typical and distinct colonies of Ac. baumannii were more often observed on CMA with soil enriched in MM for 5 h, while on MCA distinct colonies were more obvious after 24 h. In five soil samples (25%), strains harbouring different OXA-51-like variants were recovered on MCA. Late lactose fermentation (48 h) was observed on MCA. The study suggests that no single growth medium would efficiently recover Ac. baumannii from all soil samples.