Characterization of Listeria monocytogenes isolated from human clinical cases

Abstract

Listeria monocytogenes is an emerging foodborne pathogen and causative agent of listeriosis. It is one of the cause of spontaneous abortions and meningitis. The study determines the incidences of L. monocytogenes from human cases of spontaneous abortions or having a history of spontaneous abortions and meningitis. A total of 481 samples from humans having a history of spontaneous abortions and meningitis were analyzed. Isolation of the pathogen was attempted employing two step enrichment followed by plating on selective media. Characterization of the isolates was based on biochemical tests, haemolysis on blood agar, CAMP test, phosphatidyl inositolspecific phospholipase C assay, multiplex PCR to detect virulence-associated genes (hlyA, actA and iap) and serotyping by conventional and PCR based method. Of the 481 samples analysed, 7 (1.45 percent) samples from abortion cases were found positive, while no CSF sample from meningitis cases was positive for L. monocytogenes. All the isolates showed in-vitro virulence characteristics such as hemolysis on 5 percent sheep blood agar, positive CAMP test and showed hallow formation on ALOA medium. All the isolates showed the presence of the hly, actA and iap genes. Conventional serotyping as well as PCR based serotyping revealed the isolates to be of 4b, 1/2b and 4e serotypes. Antibiotic sensitivity assay showed that the isolates were sensitive to trimethoprim, however, the isolates were least sensitive to meropenem. The study highlights the incidence of L. monocytogenes in humans with spontaneous abortions.