Salmonella Infection, Prevention, and Control in the Food Industry
A Common Foodchain Contaminant Frequently Isolated From Foodborne Infection
WHAT IS SALMONELLA SPP.?
Salmonella is a normally motile, Gram-negative, rod-shaped bacterium belonging to the family Enterobacteriaceae. The genus Salmonella is divided into two species that can cause illness in humans (salmonellosis), S. enterica and S. bongori.
Salmonella enterica, which is of the greatest public health concern (WHO, 2015), is comprised of six subspecies, namely enterica, salamae, arizonae, diarizonae,
houtenae and indica.
Salmonella species (spp.) and subspecies can be distinguished based on differential biochemical characters (Grimont P. & Weill F.X., 2007).
Salmonella isolates are further subdivided into serotypes according to the Kauffmann-White classification based on their flagellar (H) and somatic (O) antigens (Grimont P. & Weill F.X., 2007) or using genome-based serotyping approaches (Banerji S. et al., 2020). Salmonella spp. are commonly referred to by their serotype names.
Over 2500 Salmonella serotypes have been referenced (Ibrahim GM and Morin PM, 2018); However, only a few of them, such as Enteritidis and Typhimurium, have proven to be consistent isolates along the food chain and responsible for significant foodborne human infections (EFSA & ECDC, 2021; CDC, 2021). In fact, chromosomal or plasmid-borne virulence and regulatory factors often associated to antimicrobial resistance determinants (Cadel-six S. et al., 2021) confer upon them striking fitness for survival and spread (Chen R.A. et al., 2019; Huang X. et al., 2019; Guillén, S. et al., 2021) within animal feeds, farm animals, food industries, foodstuffs and human beings.
WHAT ARE THE RISKS FOR THE CONSUMERS?
Healthy persons infected with Salmonella often experience fever, diarrhea, nausea, vomiting and abdominal pain. In rare circumstances, bloodstream infections can produce more severe illnesses especially in young children or elderly people, and others with weakened immune systems.
Mortality is generally less than 1%; However, fatality rate associated to specific serotypes such as S. Enteritidis can surge up to 3.6% with the elderly being particularly affected. (FDA, 2012). Multidrug resistant Salmonella infections have more serious health outcomes (EFSA & ECDC, 2021b).
Key figures:
- In 2020, EU Salmonella reporting recorded the lowest number of human cases since 2007 owing to the impacts of both the withdrawal of the United Kingdom from the EU and the COVID-19 pandemic.
- The number of confirmed cases of human salmonellosis was 52,702, corresponding to an EU notification rate of 13.7 per 100,000 population. This was a decrease of 29.7% and 32.8% compared with the rate in 2019 (19.5 and 20.4 per 100,000 population) with and without the data from the United Kingdom, respectively. Notwithstanding, the overall trend for salmonellosis in 2016–2020 did not show any statistically significant increase or decrease (EFSA-ECDC, 2021).
- The proportion of hospitalized cases was 29.9%, which was lower than in 2019, with an EU case fatality rate of 0.19%.
- The top five Salmonella serovars involved in human infections overall were S. Enteritidis (48.7%), S. Typhimurium (12.4%), monophasic S. Typhimurium (1,4, [5],12:i:-) (11.1%), S. Infantis (2.5%) and S. Derby (1.2%).
- In total, 694 foodborne outbreaks of Salmonella were reported causing 3,686 illnesses, 812 hospitalizations and seven deaths. Salmonella caused 22.5% of all EU foodborne outbreaks in 2020. The majority (57.9%) of the reported foodborne outbreaks of Salmonella were caused by S. Enteritidis.
- In the US, during 2020 (CDC, 2021), 26% fewer infections were reported for all pathogens compared with the average annual number reported during 2017–2019. As in the EU, the widespread 2020 interventions associated to the covid-19 pandemic as well as other changes to daily life and hygiene behaviors, including increased handwashing, have likely changed exposures to foodborne pathogens.
- The overall 2020 Salmonellosis incidence in the US was 13.3 per 100,000; The proportion of hospitalized cases was 29 % and the fatality rate, 0,7 %. The seven most common serotypes were Enteritidis (1.6 per 100,000 population), Newport (1.5), Javiana (1.0), Typhimurium (0.9), I 4,[5],12: i: - (0.5), Hadar (0.4), and Infantis (0.3). Most (73%) of the outbreak-associated Salmonella infections during 2020 were caused by three serotypes: Newport (35%), Hadar (21%), and Enteritidis (17%).
HOW ARE SALMONELLA SPP. TRANSMITTED?
Salmonella can colonize the intestinal tracts of vertebrates, including livestock, wildlife, domestic pets, and humans. They can also survive for long times in diverse environments (Chen G. et al., 2021).
It is spread through the fecal-oral route and through contact with contaminated water. It may then contaminate meat, irrigation water (thus contaminating Produce in the field), soil and insects, factory equipment, hands, kitchen surfaces and utensils (FDA, 2012).
Salmonellosis is mostly foodborne (94 % - Scallan E. et al., 2011) but direct contact with live animals and environmental transmission have been identified as potential sources (Pires S.M. et al., 2011).
WHAT ARE THE FOOD INDUSTRIES AFFECTED BY SALMONELLA SPP.?
Salmonella is a significant and objectionable concern for most of the food sectors (primary productions and the downstream corresponding food industries). In the US (IFSAC, 2021), more than 75% of Salmonella illnesses were attributed to seven food categories i.e. chicken, fruits, pork, seeded vegetables (such as tomatoes), other Produce (such as nuts), turkey and eggs. In the EU, the three food vehicles most involved in foodborne salmonellosis outbreaks were ‘eggs and egg products’, followed by pork and bakery products (EFSA & ECDC, 2021).
Some key serotypes such as Enteritidis or Typhimurium has been more closely associated respectively with laying hens (Pires S.M. et al., 2011) and with the pig reservoir (Pires S.M. et al., 2011; Munk et al., 2020; Arnold et al., 2021).
HOW CAN SALMONELLA SPP. BE PREVENTED AND CONTROLLED IN THE FOOD INDUSTRY?
Food business operators along the food chain must consider their business specificities, design and implement their tailor-made HACCP- based control systems and Good Hygiene & Manufacturing practices as required by US and EU regulations (FDA 21CFR 1 et al., 2015; 9CFR304 et al., 1996; EU 852/2004).
Salmonella spp. which is consistently a hazard more than reasonably likely to occur shall be part of most of the food industries’ HACCP or food safety plans to prevent the adulteration of foodstuffs (EU 178/2002; Federal Food, Drug & Cosmetic Act, 1938; FDA-FSMA, 2011). Additional regulatory measures for the control of the most public-health significant Salmonella serotypes such as Enteritidis and Typhimurium have been set up in the EU and in the US (read the specific article: Salmonella Enteritidis and Typhimurium factsheet).
HOW CAN THE PRESENCE OF SALMONELLA SPP. BE DETECTED IN THE FOOD INDUSTRY?
EU and US regulations specifically require that food business operators perform microbiological testing as appropriate when they are validating and verifying the effectiveness of their HACCP and GHP -based control systems (EU 852/2004; FDA, 2011).
Salmonella spp. monitoring is specifically put in place i) by regulatory agencies for compliance and surveillance purposes (EU 625/2017; FDA, 2011) and ii) within concerned food sectors by business partners primarily for customer protection but also for the prevention of both mandatory product recall (FDA, 2011; EU 178/2002) and legal prosecution.
Different microbiological methods either traditional or molecular (PCR or Whole Genome sequencing) for the detection of Salmonella spp and/or serotyping of Salmonella Enteritidis or Typhimurium have been described, notably:
- Standardized reference methods,
- the FDA-BAM, 2021
- the USDA NPIP standard, 2019
- the MLG 4.11, 2021
- the ISO 6579-1:2017 and 2020 amendment, ISO TR 6579-3:2014 (serotyping), ISO/DTS 6579-4 (1,4,[5],12, i:-).
- AOAC or EN ISO 16140-2:2016 or ISO 16140-6:2019 validated alternative methods. Compared to the standard methods, these rapid methods usually bring ease of use as well as reduced times to results which add flexibility to the management of the analytical and business flows.
bioMérieux provides the food safety managers with proven standardized or validated methods for the management of Salmonella spp. or S. Enteritidis & S. Typhimurium along the Food Chain.
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References:
Arnold M. et al. Bayesian Source attribution of Salmonella Typhimurium isolates from human patients and farm animals in England and Wales. 2021. Front. Microbiol. 12:579888.
Banerji S. et al. Genome-based Salmonella serotyping as the new gold standard. Nature Research, 2020, 10:4333.
Cadel-Six S. et al. The Spatiotemporal Dynamics and Microevolution Events That Favored the Success of the Highly Clonal Multidrug-Resistant Monophasic Salmonella Typhimurium Circulating in Europe. Front. Microbiol. 2021, 12:651124.
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