Iranian Journal of Medical Microbiology

Background: Listeria monocytogenes is a facultative intracellular pathogen that causes listeriosis which has extensive clinical manifestations. Infections with L. monocytogenes are a serious threat to immunocompromised persons. The aim of this study was to determine the frequency of L. monocytogenes strains recovered from clinical and non-clinical samples using phenotypic methods and confirmed by PCR.

Materials and Methods: In this study, 617 specimens were analyzed. All specimens were cultured in the specific PALCAM agar. Colonies were initially identified by routine biochemical tests. Finally, PCR assays using primers specific for inlA gene were performed.

Results: In all, 46 (8.2%) L. monocytogenes isolates were recovered from 617 specimens. Fourteen (8.2%) strains, including 4 (7.5%), 2 (5.7%), 5 (14.2%) and 3 (8.5%) isolates were obtained from placental tissue, urine, vaginal and rectal swabs, respectively. In addition, 9 (7.4%) strains of L. monocytogenes which were isolated from 107 different dairy products originated from cheese 5 (7.1%), cream 2 (10%) and kashk 2 (11.7%), respectively. Among 11 (5.2%) strains isolated from 210 different meat products, 5 (5.5%), 4 (7.2%) and 2 (3%) strains belonged to sausage, meat and poultry extracts, respectively. Finally, 12 (9.2%) Listeria strains were recovered from 130 animal specimens that included 6 (10%), 4 (8%) and 2 (10%) strains from goat, sheep and cattle, respectively. Furthermore, all Listeria isolates (100%) were found to be carriers of  inlA gene in PCR assay.

Conclusion: The present study showed that the clinical and non-clinical specimens were contaminated with L. monocytogenes. So, it seems necessary to use a simple and standard technique such as PCR for rapid detection of this organism from various sources.