Assessment of Listeria monocytogenes contamination in retail fresh pork in the post-COVID-19 era

Abstract:

[Background] The outbreak of corona virus disease 2019 (COVID-19) at the end of 2019 posed a major challenge to food safety. [Objective] To assess the contamination of Listeria monocytogenes in commercial fresh pork in Nanjing in the post-COVID-19 era. [Methods] We collected the fresh pork samples from different locations and in different packages and quarters during 2020-2021, and then analyzed the contamination rate and level of L. monocytogenes and the epidemiological characteristics of the isolates. [Results] The contamination rate of L. monocytogenes in fresh pork was 15.28% (77/504). The contamination rates of pork from open-air market and pork direct-sale stores were higher than that from supermarkets. Among different packaging methods, pre-package and simple package had higher contamination rate than bulk package. Further, the contamination rate varied significantly among different quarters, being the highest (27.78%) in the third quarter. Quantitative results demonstrated that 40.26% of the positive samples had the contamination level exceeding 10 MPN/g (MPN: most probable number). In particular, the contamination level of three samples exceeded 100 MPN/g. The results of serotyping showed that 1/2a-3a (48.05%) and 1/2c-3c (44.16%) were the main serotypes. Moreover, 19.50% of the isolates were multi-antibiotic resistant, and 2 isolates (2.60%) were sensitive to all the test antibiotics. Among the 77 isolates, 68 (88.30%), 46 (59.70%), and 45 (58.40%) were resistant to oxacillin, ampicillin, and cefotaxime, respectively. [Conclusion] In the post-COVID-19 era, the L. monocytogenes contamination of fresh pork varied among different locations, packaging methods, and quarters. A few products had high contamination levels, and the serotype distribution and resistance characteristics were diverse. Therefore, it is essential to strengthen food safety supervision to reduce the occurrence of foodborne diseases.