Processing plant and machinery sanitation and hygiene practices associate with Listeria monocytogenes occurrence in ready-to-eat fish products

Revisiting old friends: updates on the role of two-component signaling systems in Listeria monocytogenes survival and pathogenesis

Listeria monocytogenes is well recognized for both its broad resistance to stress conditions and its ability to transition from a soil bacterium to an intracellular pathogen of mammalian hosts. The bacterium's impressive ability to adapt to changing environments and conditions requires the rapid sensing of environmental cues and the coordinated response of gene products that enable bacterial growth and survival. Two-component signaling systems (TCSs) have been long recognized for their ability to detect environmental stimuli and transmit those signals into transcriptional responses; however, often the precise nature of the stimulus triggering TCS responses can be challenging to define. L. monocytogenes has up to 16 TCSs that have been recognized based on homology and included in this list are several whose functions remain poorly described. This review highlights the current understanding of the breadth and scope of L. monocytogenes TCS as relates to stress resistance and pathogenesis. Precise signals still often remain elusive, but the gene networks associated with TCSs are providing clues into possible functions.

Prevalence of Listeria monocytogenes and other Listeria species in fish, fish products and fish processing environment: A systematic review and meta-analysis

Fish and seafood products are one of the most common causes of listeriosis in humans. A systematic review and meta-analysis were conducted using scientific literature to summarize available data on the prevalence of Listeria monocytogenes and Listeria sp. in fish, fish products and fish processing environment. Meta-analysis models were used to estimate the mean prevalence of the pathogen and to compare prevalence among the most popular fishes. Data from a total of 14,496 samples were analysed. Pooled prevalence of L. monocytogenes and Listeria sp. in raw fish was 5.8 % (95 % CI: 4.7-6.9) and 12.2 % (95 % CI: 8.9-15.5) respectively. Significantly higher results were observed for ready-to-eat products, occurrence of L. monocytogenes and Listeria sp. was 14.5 % (95 % CI: 11.1-18.0) and 21.7 % (95 % CI: 11.8-31.6) respectively. Moreover, meta-regression was performed to investigate changes in L. monocytogenes and Listeria sp. occurrence over the years and it shows a downward trend for both raw fish and RTE products. The results of the present study provide useful epidemiological information about the contamination level and distribution of Listeria sp. and L. monocytogenes among raw fish, fish products and fish processing environment.

Invasive listeriosis in Finland: surveillance and cluster investigations, 2011-2021

Foodborne pathogen Listeria monocytogenes may cause serious, life-threatening disease in susceptible persons. We combined data from Finnish national listeriosis surveillance, patient interview responses, and laboratory data of patient samples and compared them to listeria findings from food and food production plants collected as part of outbreak investigations during 2011-2021. The incidence of invasive listeriosis in Finland (1.3/100000 in 2021) is higher than the EU average (0.5/100000 in 2021), and most cases are observed in the elderly with a predisposing condition. Many cases reported consuming high-risk foods as well as improper food storage. Since ongoing patient interviews and whole genome sequencing were introduced, several listeriosis outbreaks were detected and food sources identified. Recommendations about high-risk foods for listeriosis and proper food storage should be better communicated to susceptible people. In Finland, patient interviews and typing and comparing listeria isolates in foods and patient samples are crucial in solving outbreaks and determining measures to control invasive listeriosis.

Food handlers' knowledge, attitudes and self-reported practices regarding safe food handling in charitable food assistance programmes in the eThekwini District, South Africa: cross-sectional study

OBJECTIVE

This study aimed to assess food handlers' knowledge, attitudes and self-reported practices towards safer donated foods.

DESIGN

This cross-sectional study was conducted from January to May 2021.

SETTING

This study was conducted in the eThekwini District, South Africa.

PARTICIPANTS

A convenience sampling-based cross-sectional survey of food handlers (n=252) served as the study's main source of data. A total of eight study sites across five municipal planning regions of eThekwini District were visited. The principal investigator administered the validated structured standardised questionnaire, using participants' language of choice, which was either English or isiZulu. All the questions in the questionnaire were asked in exactly the same manner, following the same flow, in order to avoid bias and ensure consistency. Furthermore, the close-ended nature of questions in the questionnaire mitigated the risks of question manipulation. The questionnaire was adapted from the WHO's five keys to a safer food manual.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary outcome was the knowledge, attitudes and self-reported practices towards safer donated foods. The secondary outcomes were the sanitary conditions of infrastructure and facilities, food handlers' observed food handling behaviour and nutritional information/labelling.

RESULTS

The results show that the food handlers had good knowledge, positive attitude and acceptable behaviours towards safe food handling and general hygiene, with mean scores (SD) of 62.8 (14.6), 92.5 (14.1) and 80.4 (13.3), respectively. Significant correlations were found between knowledge and attitudes (p=0001), knowledge and practices (p<0001), and attitudes and practices (p=0.02). However, the correlations between knowledge versus attitude and attitude versus practice were poor (Spearman's r<0.3), and the association between knowledge versus practice was moderate (0.3-0.7). The majority of food handlers (92.5%) did not understand the value of thorough cooking and temperature control. About 53% of respondents acknowledged to never adequately reheating cooked meals, 5% did not see the significance of preventing cross-contamination and 5% were unsure.

CONCLUSIONS

Despite the relatively positive knowledge, attitude and practice levels of the food handlers, safe food handling and hygiene practices, such as thorough cooking and temperature control, properly reheating cooked meals and taking precautions to prevent cross-contamination, require some emphasis.

Comparison of Selected Phenotypic Features of Persistent and Sporadic Strains of Listeria monocytogenes Sampled from Fish Processing Plants

(1) Background: The main source of transmission of Listeria monocytogenes is contaminated food, e.g., fish and meat products and raw fruit and vegetables. The bacteria can remain for 13 years on machines in food processing plants, including fish plants. (2) Methods: A total of 720 swabs were collected from a salmon filleting line. The research material consisted of 62 (8.6%) L. monocytogenes isolates. Pulsed Field Gel Electrophoresis (PFGE) allowed detecting a pool of persistent strains. All persistent strains (n = 6) and a parallel group of strains collected sporadically (n = 6) were characterized by their ability to invade HT-29 cells, biofilm formation ability, and minimum bactericidal concentrations (MBC) of selected disinfectants. (3) Results: Among the obtained isolates, 38 genetically different strains were found, including 6 (15.8%) persistent strains. The serogroup 1/2a-3a represented 28 strains (73.7%), including the persistent ones. There were no significant differences in invasiveness between the persistent and sporadic strains. The persistent strains tolerated higher concentrations of the tested disinfectants, except for iodine-based compounds. The persistent strains initiated the biofilm formation process faster and formed it more intensively. (4) Conclusions: The presence of persistent strains in the food processing environment is a great challenge for producers to ensure consumer safety. This study attempts to elucidate the phenotypic characteristics of persistent L. monocytogenes strains.

Antibiotic Resistance Patterns of Listeria Species Isolated from Broiler Abattoirs in Lusaka, Zambia

L. monocytogenes is a public health threat linked to fast foods such as broiler chickens. This study aimed to verify the occurrence of Listeria species in chickens from abattoirs and evaluate their antimicrobial resistance. In total, 150 broiler carcass swabs distributed as cloacal (n = 60), exterior surface (n = 60), and environmental (n = 30) were collected. Listeria species were characterized using biochemical tests and PCR. We conducted antibiotic resistance tests using the disc diffusion and Etest (Biomerieux, Durham, NC, USA) methods. Overall isolation of Listeria species was 15% (23/150) 95% CI (10.16–22.33), 2% (3/150) 95% CI (0.52–6.19) and 13% (20/150) 95% CI (8.53–20.08) came from environmental swabs and carcass swabs, respectively. Proportions of positive Listeria isolates were L. monocytogenes 74% (17/23), L. welshimeri 22% (5/23), and L. innocua 4% (1/23). Listeria species from the exterior carcass swabs was 61% (14/23), cloacal swabs 26% (6/23), and environmental swabs 3% (3/23). L. monocytogenes had the greatest resistance percentage to the following antibiotics: clindamycin (61%, 10/23), tetracycline 30% (7/23), and erythromycin 13%, (3/23). Isolation of L. monocytogenes in relatively high numbers, including the antimicrobial profiles, suggests a potential risk of the pathogen remaining viable in the food continuum and a public health risk to would-be consumers.

Incidence and genetic diversity of multi-drug resistant Listeria monocytogenes isolates recovered from fruits and vegetables in the Eastern Cape Province, South Africa

We investigated the prevalence, genetic diversity and antibiogram profiles of Listeria monocytogenes (Lm) recovered from fruits and vegetables sourced from three District Municipalities in the Eastern Cape Province, South Africa after the recent listeriosis outbreak in the country. The procedure outlined by the International Organization for Standardization EN ISO 11290:2017 Parts 1 and 2 was adopted for the isolation of Lm from 140 vegetable samples. Molecular detection of the pathogen and the presence of 10 virulence-associated markers were assessed. Lm was detected in 42.86% of all the vegetable samples tested. Highest prevalence was recorded in tomato (65.52%) followed by spinach (56.67%), cabbage (38.10%), apple (36.84%), mushroom (29.41%) and carrot (10%). The virulence determinants including the inlA, inlC, prfA and plcA, hly, plcB genes were detected in all Lm isolates whereas, inlJ (88.35%), inlB (86.41%), mpl (92.23%) and actA (84.55%) respectively. High susceptibility (> 50) was observed to all antibiotics tested except for sulfamethoxazole (17.48%), streptomycin (38.84%), amoxicillin (41.75%) and erythromycin (43.69%). However, high resistance against sulfamethoxazole (80.58%), amoxicillin (58.25%) and erythromycin (49.52%) were observed. About 85.44% of Lm isolates showed multidrug-resistance phenotypes against the test antibiotics. Furthermore, twenty (20) resistance genes encoding tetracyclines, sulphonamides, phenicols, aminoglycosides, β-lactamases, and variants of the extended-spectrum of β-lactamases (ESBLs) resistance were detected among the Lm isolates. The sul2 (90.81), tetM (68.42%) sul1 (45.98%) were more prevalent among the resistant strains. The dendrogram signatures generating seven clades is an indication of the high genetic diversity among the isolates. We conclude that the presence of Lm in fruits and vegetables is a potential threat to the consumers and a potential public health hazard, particularly to the high-risk group of the population.

Potassium Lactate as a Strategy for Sodium Content Reduction without Compromising Salt-Associated Antimicrobial Activity in Salami

Reformulating recipes of ready-to-eat meat products such as salami to reduce salt content can mitigate the negative health impacts of a high salt diet. We evaluated the potential of potassium lactate (KL) as a sodium chloride (NaCl) replacer during salami production. NaCl and KL stress tolerance comparisons showed that four food-derived Listeria innocua isolates were suitable as biologically safe Listeria monocytogenes surrogates. Effects of the high salt (4% NaCl) concentration applied in standard salami recipes and a low salt (2.8% NaCl) plus KL (1.6%) combination on product characteristics and growth of contaminating Listeria and starter culture were compared. Simulated salami-ripening conditions applied in meat simulation broth and beef showed that the low salt plus KL combination retained similar to superior anti-Listeria activity compared to the high salt concentration treatment. Salami challenge tests showed that the low NaCl plus KL combination had comparable anti-Listeria activity as the high NaCl concentration during ripening and storage. No significant differences were detected in starter culture growth profiles and product characteristics between the high NaCl and low NaCl plus KL combination treated salami. In conclusion, KL replacement enabled a 30% NaCl reduction without compromising the product quality and antimicrobial benefits of high NaCl concentration inclusion.

β-Phenylethylamine as a Natural Food Additive Shows Antimicrobial Activity against Listeria monocytogenes on Ready-to-Eat Foods

Listeria monocytogenes is an important foodborne pathogen and a major cause of death associated with bacterial foodborne infections. Control of L. monocytogenes on most ready-to-eat (RTE) foods remains a challenge. The potential use of β-phenylethylamine (PEA) as an organic antimicrobial against L. monocytogenes was evaluated in an effort to develop a new intervention for its control. Using a collection of 62 clinical and food-related isolates we determined the minimum inhibitory concentration (MIC) of PEA against L. monocytogenes in different broth and agar media. Bologna type sausage (lyoner) and smoked salmon were used as food model systems to validate the in vitro findings. PEA had a growth inhibitory and bactericidal effect against L. monocytogenes both in in vitro experiments as well as on lyoner and smoked salmon. The MIC’s ranged from 8 to 12.5 mg/mL. Furthermore, PEA also inhibited L. monocytogenes biofilm formation. Based on good manufacturing practices as a prerequisite, the application of PEA to RTE products might be an additional hurdle to limit L. monocytogenes growth thereby increasing food safety.

Growth Potential of Listeria monocytogenes in Three Different Salmon Products

Cold smoked salmon and sushi salmon have been implicated in outbreaks of listeriosis. We performed challenge tests and a durability study with Listeria monocytogenes on different salmon products to determine the growth potential of this important food-borne pathogen. Data from the challenge test showed a significant growth potential of L. monocytogenes on all of the tested salmon products, with faster growth in sushi salmon than in cold smoked salmon. In identical products that were naturally contaminated at low levels, the durability study did not confirm a high growth potential, possibly due to interactions with competing microflora. The injection of sodium lactate (NaL) at a high concentration (30%) into cold smoked salmon significantly reduced the growth potential of L. monocytogenes. In addition to good manufacturing practices, the injection of higher concentrations of NaL may therefore be a useful additional hurdle to prevent growth of L. monocytogenes to high numbers in the tested salmon products.