Molecular Characterization, Antibiogram, and Virulence Gene Profiling of <i>Proteus vulgaris</i> Isolated From Cattle With Bovine Respiratory Disease in Bangladesh

This study aimed to molecularly characterize Proteus vulgaris, assess its antibiotic susceptibility and profile virulence genes in isolates from cattle showing clinical signs of bovine respiratory disease (BRD) in Bangladesh. A total of 61 samples, including nasal swabs and lung tissues, were collected from cattle of varying ages and sexes between January and June 2024. Samples were cultured in sterile nutrient broth and streaked onto nutrient agar, blood agar, and MacConkey agar. Identification was performed through Gram staining, biochemical assays and molecular techniques, including PCR and partial gene sequencing. Antibiotic susceptibility was evaluated using the disc diffusion method, and virulence genes were detected by PCR. The isolates exhibited swarming motility and hemolytic, greyish colonies on blood agar; small, circular, pale-to-yellow colonies with a fishy odour on MacConkey agar; and appeared as small, pink-stained coccobacilli (singly or in pairs) under Gram staining. Biochemical testing showed positive reactions for catalase, methyl red, indole and Voges-Proskauer tests, and negative results for lactose fermentation and oxidase. PCR confirmed P. vulgaris in 11 samples (18%). Partial sequencing and phylogenetic analysis revealed 100% identity with strains reported in Germany and the USA. All isolates were sensitive to ceftriaxone and levofloxacin but showed complete resistance to penicillin, erythromycin, ampicillin and tetracycline. PCR analysis also identified the presence of the virulence genes luxS and rsbA. This is the first report of P. vulgaris associated with respiratory infections in cattle in Bangladesh.