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<p>Antimicrobial resistance (AMR) in livestock production systems represents a major One Health concern due to the potential transfer of resistant bacteria and resistance genes along the food chain and into the environment. This study investigated the occurrence of multidrug-resistant bacteria and associated antibiotic resistance genes (ARGs) in a pig production farm in Portugal. Samples were collected from slurry, animal skin swabs, feed, soil, and processed meat across three production batches. Enterobacteriaceae, <i>Staphylococcus</i>, and <i>Enterococcus</i> isolates were recovered using selective media, identified by 16S rRNA gene sequencing, and assessed for antimicrobial susceptibility using the disk diffusion method. ARGs were detected by multiplex PCR. Thirty-two isolates were identified, including <i>Escherichia coli</i>, <i>Enterobacter</i> spp., <i>Kosakonia cowanii</i>, <i>Staphylococcus haemolyticus</i>, <i>Staphylococcus borealis</i>, <i>Staphylococcus devriesei</i>, <i>Staphylococcus pasteuri</i>, <i>Enterococcus faecalis</i>, and <i>Enterococcus faecium</i>. Tetracycline resistance was widespread across all genera, with frequencies of 56.3% in Enterobacteriaceae, 77.8% in <i>Staphylococcus</i>, and 66.7% in <i>Enterococcus</i>. Among <i>E. coli</i>, <i>bla</i><sub>TEM</sub> variants and <i>tet</i>(A) were the most frequently detected resistance genes, alongside occasional sulfonamide (<i>sul</i>1, <i>sul</i>2) and AmpC (<i>CIT</i>) determinants. <i>Staphylococcus</i> isolates exhibited high rates of resistance to clindamycin, erythromycin, and chloramphenicol, supported by the presence of <i>erm</i>B,&#xa0;<i>erm</i>C, and <i>bla</i>Z. <i>Enterococcus</i> isolates carried <i>pbp</i>5 and <i>erm</i> genes. Overall, 76.6% of isolates showed Multiple Antibiotic Resistance Index values above 0.2, indicating high selective pressure within the farm environment. These findings demonstrate the circulation of multidrug-resistant bacteria and clinically relevant ARGs across the animal-environment interface, emphasizing the need for improved sanitation, responsible antibiotic use, and strengthened antimicrobial stewardship within pig production systems.</p>

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Assessment of multidrug-resistant bacteria and antibiotic resistance genes in pig production system

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月23日

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  • Cátia Salamandane,
  • Celso Chaves,
  • Gomes Cahango,
  • Acácio Salamandane

摘要

Antimicrobial resistance (AMR) in livestock production systems represents a major One Health concern due to the potential transfer of resistant bacteria and resistance genes along the food chain and into the environment. This study investigated the occurrence of multidrug-resistant bacteria and associated antibiotic resistance genes (ARGs) in a pig production farm in Portugal. Samples were collected from slurry, animal skin swabs, feed, soil, and processed meat across three production batches. Enterobacteriaceae, Staphylococcus, and Enterococcus isolates were recovered using selective media, identified by 16S rRNA gene sequencing, and assessed for antimicrobial susceptibility using the disk diffusion method. ARGs were detected by multiplex PCR. Thirty-two isolates were identified, including Escherichia coli, Enterobacter spp., Kosakonia cowanii, Staphylococcus haemolyticus, Staphylococcus borealis, Staphylococcus devriesei, Staphylococcus pasteuri, Enterococcus faecalis, and Enterococcus faecium. Tetracycline resistance was widespread across all genera, with frequencies of 56.3% in Enterobacteriaceae, 77.8% in Staphylococcus, and 66.7% in Enterococcus. Among E. coli, blaTEM variants and tet(A) were the most frequently detected resistance genes, alongside occasional sulfonamide (sul1, sul2) and AmpC (CIT) determinants. Staphylococcus isolates exhibited high rates of resistance to clindamycin, erythromycin, and chloramphenicol, supported by the presence of ermB, ermC, and blaZ. Enterococcus isolates carried pbp5 and erm genes. Overall, 76.6% of isolates showed Multiple Antibiotic Resistance Index values above 0.2, indicating high selective pressure within the farm environment. These findings demonstrate the circulation of multidrug-resistant bacteria and clinically relevant ARGs across the animal-environment interface, emphasizing the need for improved sanitation, responsible antibiotic use, and strengthened antimicrobial stewardship within pig production systems.