Biofilms contain microbial cells which are protected by a self-produced matrix and they firmly attach themselves to many different food industry surfaces. Due to this protection, microorganisms within biofilms are much more difficult to eradicate and therefore to control than suspended cells. A bacterium that tends to produce these structures and persist in food processing plants is Listeria monocytogenes. To this effect, many attempts have been made to develop control strategies to be applied in the food industry, although there seems to be no clear direction on how to manage the risk the bacteria poses. There is no standardized protocol that is applied equally to all food sectors, so the strategies for the control of this pathogen depend on the type of surface, the nature of the product, the conditions of the food industry environment, and indeed the budget. The food industry performs different preventive and corrective measures on possible L. monocytogenes-contaminated surfaces. However, a critical evaluation of the sanitization methods applied must be performed to discern whether the treatment can be effective in the long-term. This review will focus on currently used strategies to eliminate biofilms and control their formation in processing facilities in different food sectors (i.e., dairy, meat, fish, chilled vegetables, and ready-to-eat products). The technologies employed for their control will be exemplified and discussed with the objective of understanding how L. monocytogenes can be improved through food safety management systems.

https://www.mdpi.com/2076-2607/9/1/181/pdf

Listeria monocytogenes Biofilms in the Food Industry: Is the Current Hygiene Program Sufficient to Combat the Persistence of the Pathogen?

This study aimed to investigate the prevalence and molecular characteristics of Listeria monocytogenes in cooked products in Zigong City, China The overall occurrence of the L monocytogenes in the ready-to-eat (RTE) shops and mutton restaurants surveyed was 162% (141/873) An occurrence of 135% was observed in RTE pork, 65% in RTE vegetables, and more than 240% in either cooked mutton or cooked haggis Serotype 1/2b (454%), 1/2a (333%), and 1/2c (142%) were the predominant types By comparing the clonal complexes (CCs) based on multilocus sequence typing (MLST) of the L monocytogenes from cooked foods in Zigong City and 33 listeriosis cases from different districts of China, CC87, CC9, CC8, and CC3 were showed to be prevalent in cooked products and CC87 and CC3 were the first two frequent types in the 33 clinic-source strains All CC87 stains harbored the newly reported Listeria pathogenicity island 4 (LIPI-4) gene fragment ptsA, and all CC3 strains possessed the Listeria pathogenicity island 3 (LIPI-3) gene fragment llsX These may increase the occurrence of the strains belonging to CC87 and CC3 in listeriosis cases in China and also underline the risk of infection owing to the consumption of the cooked products from Zigong ST619 (serotype 1/2b) harbored both llsX and ptsA, indicating a potential hypervirulent sequence type in Zigong

Prevalence and molecular characteristics of Listeria monocytogenes in cooked products and its comparison with isolates from listeriosis cases.

Listeria monocytogenes is a pathogen mostly associated with consumption of ready-to-eat foods and can cause severe disease and death. It can be introduced to food chains from raw materials, but often the contamination source is the food production environment where certain clones can persist for years. In the meat chain, ST9 is one of the most commonly encountered L. monocytogenes sequence types, and for effective source tracking, the divergence and spread of ST9 must be understood. In this study, WGS was used to characterize and track 252 L. monocytogenes ST9 isolates collected from four Norwegian meat processing plants between 2009 and 2017. The isolates formed distinct clusters relative to genomes found in public databases, and all but three isolates clustered into two major clonal populations. Different contamination patterns were revealed, e.g.: Evidence of contamination of two factories with a clone diverged from its ancestor in the late 19909s through a common source of raw materials; breach of hygienic barriers within a factory leading to repeated detection of two clones in the high-risk zone during a 4-6 year period; entry through purchase and installation of second-hand equipment harboring a previously established clonal population; and spreading and diversification of two clones from two reservoirs within the same production room over a nine year period. The present work provides data on the diversity of ST9 which is crucial for epidemiological investigations and highlights how WGS can be used for source tracking within food processing factories. IMPORTANCEListeria monocytogenes is a deadly foodborne pathogen that is widespread in the environment, and certain types establish in food factories. The sequence type ST9 dominates in meat processing environments, and this work was undertaken to obtain data needed for tracking of this subtype. By using whole genome sequencing (WGS) we could reveal the presence of cross-contamination routes between meat factories as well as within a single factory, including the spread from different reservoirs within the same room. It was also possible to estimate the timeframe of persistence in the factory, as well as when and how new clones had entered. The present work contributes with valuable information about the diversity of ST9 and exemplifies the potential power of WGS in food safety management, allowing determination of relationships between strains both in an international context and locally between and within factories.

In depth longitudinal study of Listeria monocytogenes ST9 isolates from meat processing industry: Resolving diversity and transmission patterns using WGS

Listeria monocytogenes consists of four lineages that occupy a wide variety of ecological niches. Sequence type (ST) 87 (serotype 1/2b), belonging to lineage I, is one of the most common STs isolated from food products, food associated environments and sporadic listeriosis in China. Here, we performed a comparative genomic analysis of the L. monocytogenes ST87 clone by sequencing 71 strains representing a diverse range of sources, different geographical locations and isolation years. The core genome and pan genome of ST87 contained 2667 genes and 3687 genes respectively. Phylogenetic analysis based on core genome SNPs divided the 71 strains into 10 clades. The clinical strains were distributed among multiple clades. Four clades contained strains from multiple geographic regions and showed high genetic diversity. The major gene content variation of ST87 genomes was due to putative prophages, with eleven hotspots of the genome that harbor prophages. All strains carry an intact CRISRP/Cas system. Two major CRISPR spacer profiles were found which were not clustered phylogenetically. A large plasmid of about 90 Kb, which carried heavy metal resistance genes, was found in 32.4% (23/71) of the strains. All ST87 strains harbored the Listeria pathogenicity island (LIPI)-4 and a unique 10-open read frame (ORF) genomic island containing a novel restriction-modification system. Whole genome sequence analysis of L. monocytogenes ST87 enabled a clearer understanding of the population structure and the evolutionary history of ST87 L. monocytogenes in China. The novel genetic elements identified may contribute to its virulence and adaptation to different environmental niches. Our findings will be useful for the development of effective strategies for the prevention and treatment of listeriosis caused by this prevalent clone.

/pdf/genomic-dissection-of-the-most-prevalent-listeria-1aimc66nx4.pdf

Genomic dissection of the most prevalent Listeria monocytogenes clone, sequence type ST87, in China

Listeria monocytogenes can contaminate various foods via food processing environments and contamination of raw materials. There is a limited understanding of L. monocytogenes transmission in retail market and the role of insects in L. monocytogenes transmission in the retail environments. To better understand the risk factors of raw pork contamination, the prevalence of L. monocytogenes was examined in raw pork, retail environments and insects in a retail market over a 6-month period from March to August in 2016 in Beijing, China. A total of 2,789 samples were collected, including 356 raw pork samples, 1,392 meat contact surface swabs (MCS), 712 non-meat contact surface swabs (NMCS) and 329 insect samples. Overall, 424 (15.20%) of the samples were found to be contaminated by L. monocytogenes. Analyzed by serotyping, multilocus sequence typing and pulsed-field gel electrophoresis, the 424 L. monocytogenes isolates were divided into three serotypes (1/2c, 1/2a and 3a), 15 pulsotypes (PTs) and nine sequence types (STs), 1/2c/PT4/ST9 (244/424, 58%) was the most prevalent type of L. monocytogenes strains. The raw pork, MCS of the environments and insects were contaminated with higher levels of L. monocytogenes than NMCS of the environments, which suggested that cross contamination of L. monocytogenes between raw pork and the environment existed in the retail market, and long-term contaminated surfaces and vector insects would act as high risk factors to transmit L. monocytogenes to raw pork. Thus more effective strategies are needed to reduce the risk of retail pork meat contamination by L. monocytogenes and prevent foodborne human listeriosis.

/pdf/risk-factors-and-level-of-listeria-monocytogenes-h8yu5unjrv.pdf

Risk Factors and Level of Listeria monocytogenes Contamination of Raw Pork in Retail Markets in China.

A 12-month longitudinal study of Listeria monocytogenes contamination and persistence in pork retail markets in China

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A 12-month longitudinal study of Listeria monocytogenes contamination and persistence in pork retail markets in China