PCR-Based Screening for mcr-7, mcr-8, and mcr-9 in Acinetobacter baumannii–Acinetobacter calcoaceticus Complex Isolates from Veterinary and Environmental Sources

Background/Objectives: The Acinetobacter baumannii–calcoaceticus (Acb) complex comprises opportunistic pathogens of increasing relevance in human and veterinary medicine due to their capacity to acquire multidrug resistance. colistin, a last-resort antimicrobial for carbapenem-resistant A. baumannii (CRAB), is increasingly challenged by the emergence of resistance determinants, including those encoded by the mobilized colistin resistance (mcr) gene family. This study aimed to screen for mcr genes in Acb complex isolates recovered from animal and environmental sources in Rio de Janeiro State, Brazil. Methods: Thirty-five isolates obtained from dogs, cats, horses, and soil between 2018 and 2020 were genotypically identified using multiplex PCR. Of these, 23 successfully recovered isolates were screened for mcr variants (mcr-1 to mcr-9) by multiplex PCR. Results: Five isolates (21.7%) yielded amplicons of expected sizes consistent with the presence of mcr-associated determinants, including two consistent with mcr-7, one with mcr-8, and two with mcr-9. Because amplicon sequencing and phenotypic colistin susceptibility testing were not performed, these findings should be interpreted as preliminary molecular screening results. Conclusions: These findings indicate the presence of PCR-detectable mcr-associated genetic targets in isolates from animal and environmental sources, highlighting the need for further molecular characterization and integrated surveillance under a One Health framework.