Prevalence and genetic characterization of Gram-positive bacteria carrying linezolid resistance genes in vegetables

Abstract Background Linezolid resistance poses an ecological threat to the health of humans, animals, and the environment. Vegetable may serve as reservoirs for resistance genes, yet its prevalence remain underexplored. Therefore, this study aims to investigate the prevalence of linezolid resistance gene-positive Gram-positive bacteria in vegetables, and to explore the genetic relatedness between linezolid resistance gene reservoirs from vegetables and various niches. Result In this study, 70 Gram-positive bacteria carrying linezolid resistance genes were isolated from 115 samples, with Enterococcus as the main host bacteria (45/70). Among them, Enterococcus casseliflavus was most frequently identified (26/70), followed by Lactococcus lactis (18/70). Phylogenetic analysis revealed that the genetic backgrounds of these strains were significantly different from the linezolid resistance gene reservoirs in other niches. The results of the antimicrobial susceptibility test showed that these strains had high resistance rates of chloramphenicol, erythromycin, and tetracycline, and the resistance rate of linezolid was 37.1%. The overall carriage rate of linezolid resistance genes was 30.4% (95% CI 21.4–39.4%). The optrA was the most common linezolid resistance gene, with a carriage rate of 29.7% (34/115), followed by poxtA, cfr, and cfr(D) gene, with carriage rates of 2.6% (3/115), 1.7% (2/115), and 0.9% (1/115), respectively. No strains were positive for cfr(B), cfr(C), or cfr(E) genes. Among the 68 strains carrying the optrA gene, a total of 18 variants were identified. The KLDP variant was the most common (n = 25), followed by EDD (n = 10) and EDM (n = 10). Some strains also exhibited multiple OptrA variant carriage. The flanking structures of the optrA gene showed diversity, with IS1216E-fexA-optrA-Δerm(A) and Tn558-araC-optrA being the most common. Conclusion This study highlighted a high prevalence of the optrA gene in vegetables. E. casseliflavus was the predominant host for linezolid resistance genes, followed by L. lactis. Significant differences in genetic background were found in the linezolid resistance gene reservoirs from vegetables when compared to those from humans, animals, and the environment.