Comparative Analysis of Antibiotic Resistance and Biofilm Characteristics of Two Major Enterococcus Species from Poultry Slaughterhouses in South Korea

The spread of antibiotic-resistant <i>Enterococcus</i> in the poultry industry poses significant public health challenges due to multidrug resistance and biofilm formation. We investigated the antibiotic resistance profiles and biofilm characteristics of <i>E. faecalis</i> and <i>E. faecium</i> isolates from chicken meat in poultry slaughterhouses in South Korea. Ninety-six isolates (forty-eight each of <i>E. faecalis</i> and <i>E. faecium</i>) were collected between March and September 2022. Both species were analyzed using MALDI-TOF, PCR, antibiotic susceptibility testing, and biofilm assays. A high level of multidrug resistance was observed in <i>E. faecalis</i> (95.8%) and <i>E. faecium</i> (93.8%), with <i>E. faecium</i> exhibiting a broader range of resistance, particularly to linezolid (52.1%) and rifampicin (47.9%). All <i>E. faecalis</i> isolates formed biofilm in vitro, showing stronger biofilm formation than <i>E. faecium</i> with a significant difference (<i>p</i> < 0.001) in biofilm strength. Specific genes (<i>cob</i>, <i>ccf</i>, and <i>sprE</i>) were found to be correlated with biofilm strength. In <i>E. faecium</i> isolates, biofilm strength was correlated with resistance to linezolid and rifampicin, while a general correlation between antibiotic resistance and biofilm strength was not established. Through analysis, correlations were noted between antibiotics within the same class, while no general trends were evident in other analyzed factors. This study highlights the public health risks posed by multidrug-resistant enterococci collected from poultry slaughterhouses, emphasizing the complexity of the biofilm-resistance relationship and the need for enhanced control measures.