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Tracking Listeria monocytogenes contamination and virulence-associated characteristics in the ready-to-eat meat-based food products industry according to the hygiene level

https://doi.org/10.1016/j.ijfoodmicro.2016.11.020Get rights and content

Highlights

  • Diverse L. monocytogenes PFGE types in industries with good hygiene level

  • Specific audit requisites related with the presence of the most common human disease-associated L. monocytogenes serogroups.

  • Improvement of route-cause analysis is needed in industries where L. monocytogenes is detected.

Abstract

Listeria monocytogenes isolates collected from final products and food contact surfaces of 10 ready-to-eat meat-based food products (RTEMP) producing industries were analyzed to relate their virulence-associated characteristics and genetic profiles with the hygiene assessment of those industries. Together with sample collection, an audit was performed to evaluate the implemented food safety management system and to investigate the specific audit requisites more associated to the occurrence of those L. monocytogenes serogroups frequently related with human disease. L. monocytogenes was present in 18% of the samples. The isolates (n = 62) were serogrouped and detection of virulence-associated genes inlA, inlB, inlC and inlJ, and also plcA, hlyA, actA and iap was done by multiplex PCR. After this initial characterization, selected isolates (n = 31) were submitted to antibiotic resistance testing by the disk diffusion method for the currently most used human and veterinary antibiotics and resistance was low. These isolates were also subtyped by pulsed-field gel electrophoresis. Genotyping and serogrouping of L. monocytogenes isolates revealed a genetically diverse population. Our data indicate that contamination of final products does not seem to be uniquely related to the sampled food surfaces. The occurrence of those L. monocytogenes serogroups more commonly associated with human disease in industries with a high hygienic audit classification could be the result of a previous identification of the pathogen, with an enforcement of the hygiene program without recognizing the real source of contamination. This reinforces the importance of a conjoined diagnosis using audit data and microbiological testing. Food safety management systems of those industries need improvement, particularly in cleaning and sanitizing operations, analytical control, preventive maintenance, personal hygiene and root cause analysis.

Introduction

In ready-to-eat food (RTE) industry, hygiene procedures are crucial to prevent microbial contamination of the processing environment, especially by Listeria monocytogenes (Muhterem-Uyar et al., 2015). To verify and monitor control measures, food and food environment microbiological sampling is commonly used. Auditing also plays an important role in the food safety management systems (FSMS), and should be based on good hygiene and manufacturing practices (GHMP) and hazard analysis and critical control points (HACCP) principles (Fraqueza and Barreto, 2015). To have a more comprehensive insight of the FSMS performance, a conjoined diagnosis using microbiological data and audit results should be adopted (Luning et al., 2011).

Over the last years, ready-to-eat meat-based food products (RTEMP) are among the foods most commonly associated with L. monocytogenes (EFSA and ECDC, 2015). There are several ways by which RTEMP can be contaminated by L. monocytogenes, namely by post-listericidal treatment recontamination due to contact with processing equipment or surfaces, in operations such as slicing, cutting and weighing (Henriques and Fraqueza, 2015, Muhterem-Uyar et al., 2015).

Because of the importance of L. monocytogenes to human health and the notable diversity in the pathogenicity among its strains (Borucki et al., 2003), subtyping and virulence characterization are of upmost importance. The main objectives of this work were (i) to characterize the potential virulence of L. monocytogenes isolates by genotypic and phenotypic methods, (ii) to identify the likely sources of contamination of final products by using the PFGE typing method, (iii) to relate the isolates virulence-associated characteristics and genetic profile with the hygiene assessment level of the RTEMP industries and (iv) to investigate the audit requisites with the highest relation with the occurrence of L. monocytogenes serogroups most frequently associated with human disease.

Section snippets

Industries characterization

Ten industrial units producing RTEMP located in the central region of Portugal were assessed using a GHMP and HACCP questionnaire with 82 closed-ended questions (yes or no answer), structured in six sections: industrial typology, standard operating procedures (SOP), analytical control, personal hygiene, hygiene program and food-processing technology, as described in Henriques et al. (2014). Each audit included: a) an on-site visit for procedure verification; b) a documental assessment regarding

Audit data

All the studied industries produce RTEMP using pork, veal and/or poultry meat as raw materials and diverse manufacturing practices and hygio-sanitary conditions, as described by Henriques et al. (2014). The technological processing included cooking, fermenting, drying, smoking or baking. In 8 of the 10 industries the final product was cut, shredded or diced before packaging in aerobic or modified atmosphere. All the establishments were above 50% of conformity in the audit so no plant was

Conclusion

Genotyping of L. monocytogenes isolates from the RTEMP industry revealed a genetically diverse population with low resistance to commonly used antibiotics. Subtyping revealed that contamination of final products does not seem to be uniquely related with the sampled direct food contact surfaces.

Enhancement of the FSMS in those industries is also needed. Industries with a high hygienic audit classification revealed higher probability to present L. monocytogenes serogroups more commonly associated

Acknowledgments

The authors gratefully acknowledge the participating industries, Maria Helena Fernandes, Maria José Fernandes, Maria Paula Silva and CIISA-Project UID/CVT/00276/2013. This work was supported by Project “Portuguese traditional meat products: strategies to improve safety and quality” (PTDC/AGR-ALI/119075/2010), Project PRODER-PA No13017, MAMAOT-IFAP, I. P. and FCT PhD research grant SFRH/BD/70711/2010.

References (24)

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