Category Archives: Serotype

Research – Human Salmonellosis: A Continuous Global Threat in the Farm-to-Fork Food Safety Continuum

Posted on May 1, 2023 by | Leave a comment

MDPI

Abstract

Salmonella is one of the most common zoonotic foodborne pathogens and a worldwide public health threat. Salmonella enterica is the most pathogenic among Salmonella species, comprising over 2500 serovars. It causes typhoid fever and gastroenteritis, and the serovars responsible for the later disease are known as non-typhoidal Salmonella (NTS). Salmonella transmission to humans happens along the farm-to-fork continuum via contaminated animal- and plant-derived foods, including poultry, eggs, fish, pork, beef, vegetables, fruits, nuts, and flour. Several virulence factors have been recognized to play a vital role in attaching, invading, and evading the host defense system. These factors include capsule, adhesion proteins, flagella, plasmids, and type III secretion systems that are encoded on the Salmonella pathogenicity islands. The increased global prevalence of NTS serovars in recent years indicates that the control approaches centered on alleviating the food animals’ contamination along the food chain have been unsuccessful. Moreover, the emergence of antibiotic-resistant Salmonella variants suggests a potential food safety crisis. This review summarizes the current state of the knowledge on the nomenclature, microbiological features, virulence factors, and the mechanism of antimicrobial resistance of Salmonella. Furthermore, it provides insights into the pathogenesis and epidemiology of Salmonella infections. The recent outbreaks of salmonellosis reported in different clinical settings and geographical regions, including Africa, the Middle East and North Africa, Latin America, Europe, and the USA in the farm-to-fork continuum, are also highlighted.

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Posted in Decontamination Microbial, food bourne outbreak, Food Micro Blog, Food Microbiology, Food Microbiology Blog, Food Microbiology Research, Food Microbiology Testing, Food Pathogen, foodborne outbreak, foodbourne outbreak, microbial contamination, Microbial growth, Microbiological Risk Assessment, Microbiology, Microbiology Investigations, Microbiology Risk, outbreak, Pathogen, pathogenic, Salmonella, Serotype

Research – Use of a phage cocktail to reduce the numbers of seven Escherichia coli strains belonging to different STEC serogroups applied to fresh produce and seeds

Posted on February 2, 2023 by | Leave a comment

Wiley Online

Abstract

The aims of this research were to evaluate the effectiveness of a phage cocktail at reducing seven Shiga toxigenic Escherichia coli (STEC) serogroups on different food matrixes: mung bean sprouts (MBP), lettuce, and mung bean seeds (MBS) and to test the phage cocktail effectiveness to reduce E. coli O157 on Romaine and iceberg lettuce. To study the effect of the type of food matrix on the STEC phage cocktail effectiveness, a mixture of seven highly sensitive STEC strains designated as phage propagation strains (PPS) were used to adulterate Romaine lettuce, MBP, and MBS matrixes at a concentration of 105 logs CFU/g. A subsample of the treated MBS was germinated to assess STEC survival. Recovered STEC strains were confirmed using latex agglutination and PCR. To test the phage cocktail effectiveness to reduce E. coli O157:H7 on Romaine and iceberg lettuce, a mixture of four STEC strains (different than phage propagation strains, non-PPS) at both low (103 CFU/g) and high (105 CFU/g) concentrations were used to spike the samples in scaled up trials for the purpose of potential commercialization. Phage treatments including a combination of STEC phage cocktail and chlorinated water treatment were then applied to lettuce in a simulated scaled-up trial. STEC was assessed on the treated samples at different storage time and temperatures (0, 24, 48, and 72 hr at 2, 10 and 25°C). In the food matrix trial, the combination of STEC phage cocktail and chlorinated water-reduced PPS (p < 0.001) STEC on lettuce by 2.1 log10 CFU/g and on MBP by 2.2 log10 CFU/g. However, isolates from all 7 STEC serogroups remained viable after phage treatment in both lettuce and MBP; particularly those associated with serogroup O111, O121, O103, and O145, while only a few colonies of serogroup O26, O45, and O157 were detected. Lettuce adulterated with low levels of 4 non-PPS E. coli O157:H7 (103 CFU/g) achieved a reduction of 2.6–3.2 logs. While a reduction 1.7–2.3 logs was achieved by the phage cocktail when lettuce was inoculated with 105 CFU/g. Overall phage performance was more effective at 2 and 10°C and improved over storage time up to 72 hr. However, for MBS, the phage cocktail was not able to kill any of the STEC populations as all of them recovered during germination.

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Posted in Decontamination Microbial, E.coli, Food Micro Blog, Food Microbiology, Food Microbiology Blog, Food Microbiology Research, Food Microbiology Testing, microbial contamination, Microbial growth, Microbiological Risk Assessment, Microbiology, Microbiology Investigations, Microbiology Risk, Serotype, STEC, STEC E.coli

UK – Salmonella Serotyping

Posted on May 4, 2021 by | Leave a comment

New Food Magazine

Traditionally, Salmonella isolates are separated into serotypes based on structural differences on the surface of the cells (O antigens) and thread‑like portions of the flagella (H antigens), using the Kauffman-White classification scheme. In this technique, antibodies are prepared against these specific antigens in a blood serum known as antiserum. Confirmed Salmonella sp. isolates are then tested with this antisera and are observed for agglutination reactions.

Through testing unknown samples against a series of antisera, the specific serotype of an isolate can be discerned. As previously discussed, there are a great number of serological variants of Salmonella and so this process can be very long and labour intensive, requiring highly experienced staff with a vast library of antisera at their disposal. Because of this, the Kauffman-White serotyping method is often only carried out by reference laboratories, with routine microbiology laboratories only stocking a small number of antisera.

As an example, at ALS Rotherham we stock the antisera for our in-house control strain, Salmonella enterica subsp. enterica ser. Nottingham, which enables us to distinguish our strain from others using the antisera O16, Henz15 and Hd. This serotype is recommended by the health protection agency in the UK for use as a control strain, due to being a very rare serotype and thus very unlikely to be isolated as a wild type. Historically, when further analysis was required for one of our samples, the isolates would be subcontracted to a reference laboratory capable of full serological testing. For a plethora of reasons, this type of analysis all too often had a lengthy turnaround time which, while accurate, was often too little too late and unhelpful in making a practical difference to our client, the FBO (food business operator).

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Posted in ALS, Food Microbiology Research, Food Technology, Research, Salmonella, Serotype, Technology

Research – Relationship of growth conditions to desiccation tolerance of Salmonella enterica, Escherichia coli, and Listeria monocytogenes

Posted on April 24, 2021 by | Leave a comment

Journal of Food Protection

Growth on solid media as sessile cells is believed to increase the desiccation tolerance of Salmonella enterica . However, the reasons behind increased resistance have not been well explored. In addition, the same effect has not been examined for other foodborne pathogens such as pathogenic Escherichia coli or Listeria monocytogenes . The purpose of this research was two-fold: first, to determine the role of oxygenation during growth on the desiccation resistance of S. enterica , E. coli , and L. monocytogenes , and second, to determine the effect of sessile versus planktonic growth on the desiccation resistance of these pathogens. Three different serotypes each of Salmonella , E. coli , and L. monocytogenes were cultured in trypticase soy broth with 0.6% yeast extract (TSBYE), with (aerobic) shaking or on TSBYE with agar (TSAYE) under either aerobic or anaerobic conditions and harvested in stationary phase. After adding cell suspensions to cellulose filter disks, pathogen survival was determined by enumeration at 0 and after drying for 24 h. Results showed statistical differences in harvested initial populations prior to drying (0 h). For Salmonella , a correlation was found between high initial population and greater survival on desiccation (p = 0.05). In addition, statistical differences (p ≤ 0.05) between survival based on growth type were identified. However, differences found were not the same for the three pathogens, or between their serotypes. In general, Salmonella and E. coli desiccation resistance followed the pattern of aerobic agar media ≥ liquid media ≥ anaerobic agar media. For L. monocytogenes serotypes, resistance to desiccation was not statistically different based on mode of growth. These results indicate growth on solid media under aerobic conditions is not always necessary for optimal desiccation survival but may be beneficial when the desiccation resistance of the test serotype is unknown.

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Posted in E.coli, Food Micro Blog, Food Microbiology, Food Microbiology Blog, Food Microbiology Research, Food Microbiology Testing, Listeria monocytogenes, microbial contamination, Microbiological Risk Assessment, Microbiology, Research, Salmonella, Serotype