Virulence Potential, Biofilm Formation, and Antibiotic Susceptibility of Listeria monocytogenes Isolated from Cattle Housed in a Particular Gaushala (Cattle Shelter) and Organized Farm.

OBJECTIVES

The occurrence of Listeria monocytogenes was studied by using cultural and serological methods in cattle housed in a particular gaushala (cattle shelter) and organized dairy farm.

MATERIALS AND METHODS

A total of 1201 samples from cattle comprising blood (n = 207), milk (n = 203), vaginal swabs (n = 210), and serum (n = 207) from an organized farm (n = 210) and blood (n = 100), milk (n = 74), vaginal swabs (n = 100), and serum (n = 100) from a gaushala (n = 100) were collected and analyzed for L. monocytogenes. All samples excluding serum were analyzed for isolation and identification of L. monocytogenes, while the serum samples were screened for seropositivity. The isolates were further subjected to assess their virulence potential (in vitro and in vivo), biofilm formation ability, and antibiotic susceptibility patterns.

RESULTS

Four L. monocytogenes strains were isolated from the cattle; three (0.48%) from the organized farm and one (0.36%) from the gaushala. On serological screening of cattle from the organized dairy farm, 16.42% were found to be positive for antibodies against listeriolysin O, while cattle from the gaushala revealed 36% seropositivity. Furthermore, on characterization of the isolates for their pathogenic potential and biofilm-forming ability, all were found to be pathogenic by both in vitro and in vivo assays and were weak to moderate biofilm formers. The minimum inhibition concentration (MIC) of recovered isolates revealed resistance for ampicillin by two L. monocytogenes isolates (MIC >256 μg/mL), whereas three L. monocytogenes isolates were intermediately resistant (MIC >4 μg/mL) and one resistant against amoxicillin (MIC >8 μg/mL). However, all four isolates were susceptible to gentamicin, cotrimoxazole, and erythromycin.

CONCLUSIONS

Isolation of virulent and antibiotic-resistant strains of L. monocytogenes warrants the need for epidemiological surveillance, antimicrobial susceptibility, and implementation of control measures to combat the occurrence of L. monocytogenes infection in animals as well as humans.