Abstract

Antimicrobial resistance (AMR) is an escalating global public health concern, with aquatic environments acting as important reservoirs of multidrug-resistant (MDR) bacteria. In this study, a Staphylococcus haemolyticus (S. haemolyticus) isolate (CGPA) was recovered from the intestinal tract of Catla catla (C. catla) obtained from a retail fish market in Punjab, India, and characterized using phenotypic and genomic approaches. Antimicrobial susceptibility testing using the Kirby–Bauer disk diffusion method (Clinical and Laboratory Standards Institute guidelines) revealed resistance to β-lactam agents (amoxicillin and imipenem), fluoroquinolones, macrolides, tetracyclines, and phenicols, confirming its MDR phenotype. Molecular identification using 16S ribosomal RNAs gene sequencing showed ≥99% nucleotide identity with S. haemolyticus (100% query coverage; E-value ≈ 0), which was further validated by whole-genome-based phylogenetic analysis and average nucleotide identity (>99%). Whole-genome sequencing (MGI DNBSEQ-G400, 2 × 150 bp) generated a 2.57 Mb draft genome (177 contigs; N50: 38,787 bp; Guanine–Cytosine content: 32.71%) with 100% completeness. Genome annotation identified 2,608 protein-coding genes and 59 RNA genes. Key AMR genes included mecA, APH(3′)-IIIa, ANT(4′)-Ia, tet(45), tet(K), tet(L), erm(C), qacA, vgaALC, and catA8, along with the virulence-associated gene clpP. The detection of mecA indicates the genetic potential for methicillin resistance; however, phenotypic confirmation using cefoxitin or oxacillin susceptibility testing was not performed. Although no complete plasmid sequence was resolved, plasmid replicon-associated sequences were detected, suggesting the potential for horizontal gene transfer. Phylogenetic analysis clustered CGPA within the S. haemolyticus clade, and PathogenFinder predicted a high probability (0.97) of human pathogenicity. These findings demonstrate that S. haemolyticus recovered from a market-sold freshwater fish can harbor diverse AMR determinants and may have potential public-health relevance. The results highlight the importance of continued genomic surveillance of AMR in aquatic food systems within a One Health framework.

Key words: Catla catla, Multidrug resistance, Public health relevance, Staphylococcus haemolyticus, Whole-genome sequencing