Listeria monocytogenes persistence in ready-to-eat sausages and in processing plants

Abstract

<i>Listeria monocytogenes</i> is of major concern in the fermented meat products and is able to persist in their processing environments. The aim of the present work was to evaluate the virulence profile and the persistence capacity of <i>L. monocytogenes</i> strains isolated in Sardinian fermented sausages processing plants. Food (ground meat, sausages at the end of acidification and ripening stage) and environmental samples (a total of n. 385), collected from 4 meat processing plants located in Sardinia (Italy), were examined to detect <i>L. monocytogenes</i> presence. All the <i>L. monocytogenes</i> isolates were identified by polymerase chain reaction (PCR) method. A subset of strains was also characterised by multiplex PCR-based serogrouping, using the <i>lmo0737</i>, <i>lmo1118</i>, <i>ORF2819</i> and <i>ORF2110</i> genes. Three different multiplex PCRs were used to obtain the virulence profiles by the <i>rrn</i>, <i>hlyA</i>, <i>actA</i>, <i>prfA</i>, <i>inlA</i>, <i>inlB</i>, <i>iap</i>, <i>plcA</i>, <i>plcB</i> and <i>mpl</i> marker genes. Furthermore, <i>in vitro</i> biofilm forming ability and resistance to disinfectants were carried out on microtiter plate. The overall prevalence was 31.5% in food, and 68.5% in environmental samples. The prevalent serotype resulted 1/2c (43%), followed by 1/2a (40%), 4b (8.6%), and 1/2b (8.6%). The amplification products of the virulence genes were found in all the isolates with the following prevalence: 77.1% <i>hlyA</i>; 100% <i>rrn</i>; 100% <i>prfA</i>; 97.1% <i>iap</i>; 65.7% <i>inlB</i>; 88.6% <i>inlA</i>; 100% <i>plcA</i>; 100% <i>plcB</i> and 74.3% <i>mpl</i>. As for biofilm forming ability, 37.1% of the strains were positive and resulted weak producer, but all the isolates were sensible to disinfectants showing a reduction of <i>L. monocytogenes</i> growth after each incubation time. More appropriate technologies and application of measures of hygienic control should be implemented to prevent the <i>L. monocytogenes</i> growth and cross-contamination in <i>salsiccia sarda</i> processing plants.