Abstract
Listeria monocytogenes is the etiologic agent of listeriosis, which remains a significant public health concern in many countries due to its high case-fatality rate. The constant risk of L. monocytogenes transmission to consumers remains a central challenge in the food production industry. At present, there is very little known about L. monocytogenes contamination in ready-to-eat (RTE) processing plants in China. In this study, L. monocytogenes in an RTE meat processing plant in Shanghai municipality was characterized using pulsed-field gel electrophoresis (PFGE) and whole genome sequencing (WGS). Furthermore, the biofilm formation ability of the pathogen was also tested. Results revealed that L. monocytogenes isolates were present in 12 samples out of the 48 samples investigated. Most of them (66.7%, 8/12) were identified from the processing facilities irrespective of observed hygiene levels of aerobic plate count (APC) and coliforms. Coliforms were present in only one processing area. ST5 (1/2b) isolates were predominant (83.3%, 10/12) and were identified in two dominant pulsotypes (PTs) (three in PT3 and seven in PT4, respectively). Results of the core-genome multi-locus sequence typing (cgMLST) showed that ST5 in three PTs (PT1, PT3, and PT4) had 0–8 alleles, which confirmed that clonal transmission occurred in the RTE meat processing facilities. In addition, the biofilm formation test confirmed that the isolates from the processing facilities could form biofilms, which helped them colonize and facilitate persistence in the environment. These results indicated that common sanitation procedures regularly applied in the processing environment were efficient but not sufficient to remove L. monocytogenes isolates, especially biofilm of L. monocytogenes. Furthermore, the ST5 isolates in this study exhibited 12 alleles with one ST5 clinical isolate, which contributes to the understanding of the potential pathogenic risk that L. monocytogenes in RTE meat processing equipment posed to consumers. Therefore, strong hygienic measures, especially sanitation procedures for biofilms eradication, should be implemented to ensure the safety of raw materials. Meanwhile, continuous surveillance might be vital for the prevention and control of listeriosis caused by L. monocytogenes.
Highlights
Listeria monocytogenes is an important foodborne pathogen, which can cause severe human listeriosis, in older adults, newborns, pregnant women, and immune-compromised individuals (Lomonaco et al, 2009)
In the United States, L. monocytogenes must not present in RTE foods at any point (USDA FSIS, 2003)
A similar requirement in China is that L. monocytogenes is not detectable in 25 g or 25 ml RTE food according to GB29921 (GB29921-2013, 2013)
Summary
Listeria monocytogenes is an important foodborne pathogen, which can cause severe human listeriosis, in older adults, newborns, pregnant women, and immune-compromised individuals (Lomonaco et al, 2009). Listeriosis remains a significant public health concern due to the high case-fatality rate (Thomas et al, 2015). Especially ready-to-eat (RTE) meat products, are often vehicles of listeriosis outbreaks (Currie et al, 2015; Jensen et al, 2016; Thomas et al, 2020). A risk assessment report from the United States in 2003 attributed 90% of listeriosis cases to the consumption of contaminated RTE deli meats (Richard Whiting, 2003). In the United States, L. monocytogenes must not present in RTE foods at any point (USDA FSIS, 2003). A similar requirement in China is that L. monocytogenes is not detectable in 25 g or 25 ml RTE food according to GB29921 (GB29921-2013, 2013)
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