Association between a case study of asymptomatic ovine listerial mastitis and the contamination of soft cheese and cheese processing environment with listeria monocytogenes in portugal
Association between a case study of asymptomatic ovine listerial mastitis and the contamination of soft cheese and cheese processing environment with listeria monocytogenes in portugal
For 5 months, the udders of milking ewes, raw ewe’s milk, cheese, and the plant and environment of a cheese
manufacturer in Portugal were investigated using standard methods for the presence of Listeria spp. An association between subclinical mastitis and Listeria monocytogenes in a single lactating sheep was investigated by
visual inspection of udders for signs of inflammation, application of somatic cell counts, the California mastitis
test, pH measurement to milk, and culture of L. monocytogenes and Staphylococcus spp. To track the routes of
contamination by L. monocytogenes, 103 isolates were characterized by molecular serotyping and amplified
fragment length polymorphism, and a selection was further tested by pulsed-field gel electrophoresis. This study
provides molecular and epidemiological evidence tracking the persistence of a single L. monocytogenes strain
causing a subclinical udder infection without obvious inflammation in a single ewe. This infection was the
likely source of contamination of raw milk that was subsequently used to produce unpasteurised milk cheese
and resulted in a single strain of this bacterium colonizing the processing environment and the final cheese
product. info:eu-repo/semantics/publishedVersion
