Detection and molecular characterization of Listeria monocytogenes and Listeria spp. isolates recovered from cattle farms in Mpumalanga Province, South Africa

Abstract

This study determined the prevalence, characteristics and factors associated with isolating L. monocytogenes and other Listeria species (Listeria spp.) from samples collected from cattle farms in Mpumalanga province, South Africa. A total of 475 samples comprising fresh faeces, pooled environmental faeces, silage, feeds and water were collected from 25 farms (feedlot, cow–calf operations and communal) in three districts (Bronkhorstspruit, Emalahleni and Middleburg). Standard bacteriological and molecular assays were used to isolate, identify and characterize Listeria isolates. The prevalence of L. monocytogenes and other Listeria spp. in farm samples was 2.5% (12/475) and 9.2% (44/475) (p < 0.05), respectively. The highest prevalence of isolation of L. monocytogenes and Listeria spp. was 5.9% (5/85) and 16.7% (5/30) in faeces and silage, respectively. Farm size was the only factor significantly (p < 0.05) associated with detecting L. monocytogenes; the only serotype detected was 1/2a, and all the isolates were positive for virulence genes hlyA and inlJ. The overall prevalence of L. monocytogenes in samples collected from cattle farms (2.5%) across the province, the detection of serotype 1/2a associated with human listeriosis and the positivity of all strains for one or more virulent genes all pose significant public health and food safety risks from the sources assessed. There is a need to implement measures to reduce or eliminate carriage or contamination by L. monocytogenes on cattle farms to avoid the entry of the pathogen into the human food chain in South Africa.