Chromium/cadmium plays a pivotal role to emerge amoxicillin resistant Staphylococcus aureus

Rationale The rapid emergence of resistant bacteria is occurring worldwide, endangering the efficacy of antimicrobials. Apart from horizontal gene transfer and plasmid mediated antimicrobial resistance (AMR) acquisition, co-exposure of heavy metals and antibiotics cause to emerge AMR Enterobacteriaceae. Heavy metals and antimicrobials co-exist in many environmental settings. We hypothesized that heavy metals and lower dose of antibiotic co-exposure may alter levels of antimicrobial susceptibility and facilitate to emerge AMR bacteria. Methods The growth kinetics of antimicrobial susceptible Staphylococcus aureus ST80 was carried out in the presence of chromium/cadmium salt and a lower dose of antibiotics. Subsequently, the antimicrobials susceptibility patterns of heavy metals pre-exposed for 48 hours Staphylococcus aureus ST 80 was determined by Kirby-Bauer disc diffusion method. Results The antimicrobial susceptibility profile revealed that the zone of inhibition (ZOI) for ampicillin, amoxicillin, ciprofloxacin and doxycycline significantly decreased in chromium pre-exposed Staphylococcus compared to unexposed bacteria. However, cadmium pre-exposed bacteria only showed significant decreased ZOI for amoxicillin. Moreover, the MIC of amoxicillin was increased by 8-fold in chromium and 32-fold in cadmium with a low-dose of amoxicillin co-exposed bacteria. Besides, the RT-qPCR data demonstrated that chromium and a low-dose of amoxicillin pre-exposed significantly increased the mRNA expression of femX (25-fold), mepA (19-fold) and norA (17-fold) in S. aureus. In essence, minimum levels of chromium/cadmium and a MIC of amoxicillin exposure induced efflux pumps, which might responsible to emerge amoxicillin resistant S. aureus. ### Competing Interest Statement The authors have declared no competing interest.