# Efflux pump-associated antimicrobial resistance genes in Staphylococcus spp. from dairy and meat samples

## TL;DR

This study examines antibiotic resistance genes in Staphylococcus bacteria from dairy and meat, finding that efflux pumps play a key role in resistance to antibiotics and biocides.

## Contribution

The study identifies and validates the role of efflux pump genes in antimicrobial resistance among Staphylococcus spp. in food samples.

## Key findings

- Reserpine reduced MIC values in cefuroxime-resistant isolates, indicating efflux pump involvement.
- Common efflux pump genes like smr, efrA, and mdeA were frequently detected in the isolates.
- Resistance to tetracycline and cefuroxime was most prevalent among the tested isolates.

## Abstract

This study aimed to investigate the phenotypic resistance and distribution of efflux pump-associated antimicrobial resistance genes in Staphylococcus spp. isolated from dairy and meat samples. Antimicrobial resistance in foodborne bacteria increases with antibiotic exposure and biocides, particularly through efflux mechanisms. Thus, monitoring potential genetic reservoirs in the food chain is very important.

A total of 132 dairy and meat samples were collected for the study, and Staphylococcus spp. were isolated using Mannitol salt phenol red agar. Antimicrobial susceptibility was evaluated using the Clinical and Laboratory Standards Institute’s microdilution method. Twenty-six resistant isolates were identified by 16S rDNA sequencing. The effect of reserpine on MIC values was evaluated using microdilution tests to assess the role of efflux pumps in antibiotic resistance and biocide tolerance. Antibiotic resistance and efflux pump genes were detected using real-time PCR with specific primers.

Of the 77 isolates evaluated, 26 (33.8%) were resistant to at least one antibiotic. Resistance to tetracycline (69.2%) and cefuroxime (38.5%) were the most common. The administration of reserpine reduced minimum inhibitory concentration (MIC) values across all cefuroxime-resistant isolates and in a subset of tetracycline- and nitrofurantoin-resistant strains, suggesting the potential involvement of efflux pumps. It also lowered MICs for triclosan (46.7%) and povidone-iodine (32%). The most frequently detected efflux pump genes were smr (88.5%), efrA (84.6%), efrB (80.8%), mdeA (84.6%), and norE (80.8%). qacA/B was not detected in any isolate.

Genes encoding efflux pump proteins were commonly found in Staphylococcus spp. isolated from dairy and meat samples. Reserpine inhibition tests confirmed the phenotypic effects of these genes. These results suggest efflux-mediated resistance can significantly impact antibiotic tolerance and biocides in foodborne isolates. Continued surveillance and control strategies are essential to limit the spread of these resistance genes in the food chain.