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Investigating the prevalence of Listeria monocytogenes within food manufacturing sites across the UK using whole genome sequencing. Determination of biocide and antimicrobial resistance towards recommendations of contamination control

   Cardiff School of Health Sciences

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  Dr J Blaxland  No more applications being accepted  Funded PhD Project (UK Students Only)

About the Project

Listeria monocytogenes is a Gram positive, facultative anaerobic, motile, opportunistic pathogen. With the ability to grow at temperatures below 5 degrees Celsius chilled, ready to eat (RTE) food products are most at risk of supporting the growth of this microorganism. Those most at risk of listeriosis, the disease caused by L. monocytogenes, include those whom are pregnant, elderly or immunocompromised. An intracellular pathogen, L. monocytogenes can cross the blood brain barrier and placenta. Listeriosis is a rarely reported disease in the UK with around 3 cases per million each year. However, amongst cases, the outcome in pregnancy remains severe with a third resulting in miscarriage or stillbirth, and a mortality rate of 24.6% amongst non-pregnancy related cases this is despite antibiotics being available (Swaminathan and Gerner-Smidt, 2007) 

Being a preventable foodborne infection, the identification of risk factors, diagnosis, control and treatment is imperative for the future of food safety. In the UK during 2019, there were 23 deaths among 117 non-pregnancy cases reported to surveillance (19.7%), compared to an average of 43 deaths among reported cases in the preceding 6 years (2013 to 2018). Of the 23 deaths, 15 were known to have a clinical manifestation of invasive L. monocytogenes infection recorded as a cause of death. This represented a case fatality rate of 12.8%, compared to 8.5% in the previous year. 

The emergence of microorganisms exerting resistance to biocides is a challenge within food manufacturing and production environments. Bacteria can be intrinsically resistant to biocides, but resistance can also be acquired by adaptation to their sub-lethal concentrations, these resistance determinants, which are related to antibiotic resistance, could lead to co-selection during disinfection practices along the food chain, and select cross-resistant foodborne pathogens. 

Conficoni and colleagues (2016) evaluated a total of 45 strains collected from meat processing environments in Northeast Italy, the authors found that there were a number of genetic links to biocide resistance which were further expressed by a using sub lethal or indeed a high concentration of certain biocides (Conficoni et al., 2016). This further confirms that the following of certain disinfection procedures may select for more biocide/antimicrobial tolerant strains.  

Listeria monocytogenes are a genetically diverse species of bacteria. These bacteria can be divided into clonal complexes (CC) based on the sequence of DNA within the genome. Studies have identified hypervirulent (more dangerous) CC’s and hypovirulent (less dangerous) CC’s when linked to clinical outcome (Maury et al., 2016). Recent work from France identified hypervirulent L. monocytogenes belonging to CC1, CC2, CC4 and CC6 are predominantly associated with dairy products, whereas the hypovirulent isolates, CC9 and CC121, are associated with meat products (Maury et al., 2019). Although hypovirulent strains are less lethal, they seem to be more adapted to survival within food processing environments with greater survival to cleaning agents containing benzalkonium chloride. By understanding the prevalence of specific CC present within food processing facilities, and associated tolerance to cleaning agents, this may help to inform changes in practice to help reduce transmission into the food chain. To date, the prevalence of hypervirulent or hypovirulent clones in the UK is poorly understood. 

In instances where L. monocytogenes establishes an infection within a human host, there are a number of treatment options, but this can be compromised due to the presence of antimicrobial resistance (AMR). A recent review by Olaimat and colleagues highlighted AMR can be as high as 38% in countries such as Greece (Olaimat et al., 2018), with AMR isolates having been identified in UK clinical and food isolates, albeit at a reassuringly low prevalence (Threlfall, Skinner and McLauchlin, 1998). There is a need to monitor AMR among food isolates within the UK, to give further reassurance and confidence in UK food products. It has been over 25 years since the last report on AMR among L. monocytogenes in the UK food products, therefore a more recent prevalence study of AMR among UK isolates, is overdue.  

The potential candidate will be based within the ZERO2FIVE Food Industry Centre and the Cardiff School of Sport and Health Sciences at Cardiff Metropolitan University. The candidate will be expected to liaise with food manufacturing companies across the UK and travel to a range of sites. Candidates will have an excellent knowledge and understanding of microbiology, specifically Listeria identification and growth, genetic techniques and antimicrobial resistance. We offer a fully funded PhD Studentship with the opportunity to work closely with industry; encouraged attendance at national and international conferences as well as self-development and future career support.

This study will have the following broad aims:

1.          Identify the prevalence of Listeria spp. across food manufacturing sites in the UK. Specifically, industries related to dairy, ice cream, dips, pate, RTE products and cooked meats as these can be considered the most ‘at risk’. 

2.          Whole genome sequencing of isolates. – this will highlight the diversity of collected isolates.

3.          Identification of biocide and antibiotic resistance profile to the isolated microorganisms

4.          Development of novel decontamination methodologies. Cardiff Met is home to a large bioaerosol chamber which can be used for surface and aerosol decontamination testing of category 2 microorganisms such as L. monocytogenes.

Applications are sought from potential candidates with a class 2:1 honours degree or above in microbiology or a closely related subject. Candidates without this qualification may still be considered if they have an MSc in a microbiology or closely related subject.

Applicants are requested to email an expression of interest and CV to Dr James Blaxland, [Email Address Removed] before the 1st of October 2021; we anticipate interviews to take place from the 11th of October with a view for the candidate to start in January 2022. 

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