Genomic characterisation of Pseudomonas asiatica as an emerging mastitis pathogen in dairy cows with resistance and virulence implications.

OBJECTIVE

Mastitis, a major concern in the dairy industry, is often caused by multidrug-resistant (MDR) pathogens, making treatment more challenging. This study aimed to elucidate the prevalence, antimicrobial resistance (AMR), antibiotic resistance genes (ARGs) and virulence genes (VGs) profiles of Pseudomonas asiatica strains isolated from milk, faeces, and farm soils of dairy cows diagnosed with clinical mastitis (CM).

METHODS

Forty-five milk and 35 faeces samples from cows with CM, as well as 30 soil samples were collected from 30 small-holding dairy farms in Gazipur district, Bangladesh. P. asiatica was identified using culture-based methods, VITEK-2, and 16S rRNA sequencing. AMR profile was determined using disc diffusion method. Whole-genome sequencing (WGS) of four MDR P. asiatica isolates was performed for phylogenetic analysis, ARGs and VGs prediction.

RESULTS

The overall prevalence of P. asiatica in the investigated dairy farms in this study was 37.27%, with rates of 29.27% in milk, 34.15% in faeces, and 36.59% in soil. All P. asiatica isolates were MDR, exhibiting highest resistance to imipenem, ampicillin, oxacillin, sulfonamides, nitrofurantoin, azithromycin, tetracycline, and cefoxitin. WGS revealed close phylogenetic ties between P. asiatica isolates (2M1, 2F1, 2F2, 2S1) and global Pseudomonas strains. Each of the four P. asiatica strains harbored 11 ARGs imparting resistance to multiple antibiotics, and 30 VGs linked to motility, alginate/pyoverdine synthesis, and regulatory systems.

CONCLUSIONS

This study identifies P. asiatica as an emerging MDR mastitis pathogen with significant environmental persistence. These findings highlight for species-specific diagnostics, and tailored antimicrobial strategies to improve mastitis control in dairy farming systems.