Kieran Jordan | Teagasc, Irish Agriculture and Food Development Authority (original) (raw)

Papers by Kieran Jordan

Journal of Applied Microbiology, 2003

Aim: To study stress resistance mechanisms in Campylobacter spp. Methods and Results: Campylobact... more Aim: To study stress resistance mechanisms in Campylobacter spp. Methods and Results: Campylobacter strains were grown to the appropriate phase in Brucella broth. The cells were diluted into either cell-free spent medium (obtained by filtration of a grown culture) or a freshly prepared medium and the pH reduced to 4AE5, a lethal pH value. At suitable time intervals survivors were enumerated on Campylobacter blood free selective agar base. The cell-free spent medium from mid-exponential and stationary phase had a protective effect on acid and thermal stress in Campylobacter jejuni CI 120, a natural isolate. The protective effect of the extracellular compound was not significantly inactivated by boiling, but was inactivated by proteinase. Conclusions: The present study suggests that a protein (or proteins) accumulated by C. jejuni CI 120 during growth may play an active role in the induction of stress responses and that this protein is heat stable. Significance and Impact of the Study: The results indicate that C. jejuni CI 120, a natural isolate, has the ability to use extracellular signalling mechanisms to induce tolerance to stress factors. This is a major advancement in the understanding of the physiological basis for survival of C. jejuni in the environment.

Staphylococcal enterotoxin type C (SEC) is one of the classical enterotoxins implicated in staphy... more Staphylococcal enterotoxin type C (SEC) is one of the classical enterotoxins implicated in staphylococcal food poisoning. Staphylococcus aureus strains isolated from bovine unpasteurised milk and associated cheese samples produced the SECbovine sub-type. The objectives of this study were to determine the cell numbers required for SECbovine production in milk and to determine if SECbovine was produced by S. aureus during cheesemaking. To predict the point at which toxin production begins, SEC production was modelled against cell numbers of S. aureus (at different controlled pH/temperature combinations) in sterile reconstituted milk using a biphasic model fitted using the Solver routine in Excel. Under the conditions tested, the average cell number required for SECbovine production was log 8.43 ± 0.39 in sterile reconstituted milk. A semi-soft cheese was manufactured using milk inoculated with either washed (to remove any pre-formed toxin) or unwashed (containing toxin) S. aureus at 105 and 107 cfu.mL−1. An enzyme-linked immunosorbent assay was used to quantify toxin production and Baird-Parker agar to quantify S. aureus. Cheese made with washed and unwashed cells showed a one log increase in S. aureus cell numbers during cheesemaking. In cheese made with washed cells, no SEC was detected. With unwashed cells, the SEC concentration remained constant throughout cheesemaking. The results show that SECbovine is not formed in milk or cheese at <108 cfu.mL−1, and therefore, the risk-associated with SECbovine in cheese is low.

SpringerBriefs in Food, Health, and Nutrition, 2015

Journal of Dairy Science, 1994

... SYMPOSIUM: THE DAIRY LEUCONOSTOC Metabolism of Leuconostoc Bacteria TIMOTHY M. COGAN and KIER... more ... SYMPOSIUM: THE DAIRY LEUCONOSTOC Metabolism of Leuconostoc Bacteria TIMOTHY M. COGAN and KIERAN N. JORDAN National Dairy Products Research centre ... However, the internal pH (PHIn) of cells is much higher than the external pH (pile,,), making this unlikely. ...

Genome Announcements, 2015

Listeria monocytogenes is responsible for the rare disease listeriosis, which is associated with ... more Listeria monocytogenes is responsible for the rare disease listeriosis, which is associated with the consumption of contaminated food products. We report here the complete genome sequences of vB_LmoS_188 and vB_LmoS_293, phages isolated from environmental sources and that have host specificity for L. monocytogenes strains of the 4b and 4e serotypes.

International journal of food microbiology, Jan 2, 2015

Studies on the heat resistance of dairy pathogens are a vital part of assessing the safety of dai... more Studies on the heat resistance of dairy pathogens are a vital part of assessing the safety of dairy products. However, harmonized methodology for the study of heat resistance of food pathogens is lacking, even though there is a need for such harmonized experimental design protocols and for harmonized validation procedures for heat treatment studies. Such an approach is of particular importance to allow international agreement on appropriate risk management of emerging potential hazards for human and animal health. This paper is working toward establishment of a harmonized protocol for the study of the heat resistance of pathogens, identifying critical issues for establishment of internationally agreed protocols, including a harmonized framework for reporting and interpretation of heat inactivation studies of potentially pathogenic microorganisms.

International Journal of Food Microbiology, 2015

Sporeforming bacteria are a significant concern for the international dairy industry. Spores pres... more Sporeforming bacteria are a significant concern for the international dairy industry. Spores present in milk survive heat treatments and can persist during downstream processing. If they are present in sufficient numbers in dairy products they can cause spoilage or lead to illness as a result of toxin production. While many reviews have highlighted the threat posed by spores of aerobic bacteria to the dairy industry, few have focused on problems caused by the array of different species of anaerobic sporeformers (Clostridium and related genera) that can be found in milk. This is despite of the fact that members of these bacteria are found throughout the dairy farm environment, and can be toxigenic, neurotoxigenic or spoilage bacteria. This makes the possible presence of Clostridium and related spores in bulk tank milk (BTM) important from both a financial and a public health perspective. In this review dairy associated anaerobic sporeformers are assessed from a number of perspectives. This includes the taxonomy of this group of bacteria, the important subgroup of this genus the &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;sulphite reducing clostridia&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; (SRC), how these bacteria are detected in milk products, the epidemiological data regarding pathogenic species and strains within the SRC group as well as the influence of farming practices on the presence of SRC in BTM.

International Dairy Journal, 2014

Frontiers in Cellular and Infection Microbiology, 2014

Surface-ripened cheeses are matured by means of manual or mechanical technologies posing a risk o... more Surface-ripened cheeses are matured by means of manual or mechanical technologies posing a risk of cross-contamination, if any cheeses are contaminated with Listeria monocytogenes. In predictive microbiology, primary models are used to describe microbial responses, such as growth rate over time and secondary models explain how those responses change with environmental factors. In this way, primary models were used to assess the growth rate of L. monocytogenes during ripening of the cheeses and the secondary models to test how much the growth rate was affected by either the pH and/or the water activity (a w ) of the cheeses. The two models combined can be used to predict outcomes. The purpose of these experiments was to test three primary (the modified Gompertz equation, the Baranyi and Roberts model, and the Logistic model) and three secondary (the Cardinal model, the Ratowski model, and the Presser model) mathematical models in order to define which combination of models would best predict the growth of L. monocytogenes on the surface of artificially contaminated surface-ripened cheeses. Growth on the surface of the cheese was assessed and modeled. The primary models were firstly fitted to the data and the effects of pH and a w on the growth rate (μ max ) were incorporated and assessed one by one with the secondary models. The Logistic primary model by itself did not show a better fit of the data among the other primary models tested, but the inclusion of the Cardinal secondary model improved the final fit. The a w was not related to the growth of Listeria. This study suggests that surface-ripened cheese should be separately regulated within EU microbiological food legislation and results expressed as counts per surface area rather than per gram.

Journal of food protection, 2014

Building a comprehensive knowledge base of the association of Listeria monocytogenes isolates acr... more Building a comprehensive knowledge base of the association of Listeria monocytogenes isolates across national food chains, clinical cases, and environments can play a key role in helping control the incidence of listeriosis. Today, many food chains cross national borders and are often shared by neighboring countries. This study characterized L. monocytogenes isolated from food samples in Northern Ireland and investigated whether similarities in the population and associations of L. monocytogenes strains exist in the neighboring countries of Northern Ireland and the Republic of Ireland, which together constitute the island of Ireland. Listeria monocytogenes isolates were characterized using serotyping and pulsed-field gel electrophoresis subtyping. This data was then interrogated against existing data for the Republic of Ireland, to identify any shared trends in the ecology and contamination patterns of L. monocytogenes strains. The results of this study indicated that contaminated f...

Frontiers in Microbiology, 2014

Listeria monocytogenes is a virulent food-borne pathogen most often associated with the consumpti... more Listeria monocytogenes is a virulent food-borne pathogen most often associated with the consumption of "ready-to-eat" foods. The organism is a common contaminant of food processing plants where it may persist for extended periods of time. A commonly used approach for the control of Listeria monocytogenes in the processing environment is the application of biocides such as quaternary ammonium compounds. In this study, the transcriptomic response of a persistent strain of L. monocytogenes (strain 6179) on exposure to a sub-lethal concentration of the quaternary ammonium compound benzethonium chloride (BZT) was assessed. Using RNA-Seq, gene expression levels were quantified by sequencing the transcriptome of L. monocytogenes 6179 in the presence (4 ppm) and absence of BZT, and mapping each data set to the sequenced genome of strain 6179. Hundreds of differentially expressed genes were identified, and subsequent analysis suggested that many biological processes such as peptidoglycan biosynthesis, bacterial chemotaxis and motility, and carbohydrate uptake, were involved in the response of L. monocyotogenes to the presence of BZT. The information generated in this study further contributes to our understanding of the response of bacteria to environmental stress. In addition, this study demonstrates the importance of using the bacterium's own genome as a reference when analysing RNA-Seq data. (2014) Transcriptome analysis of Listeria monocytogenes exposed to biocide stress reveals a multi-system response involving cell wall synthesis, sugar uptake, and motility. Front. Microbiol. 5:68.

Journal of the Science of Food and Agriculture, 2014

Foodborne illness continues as a considerable threat to public health. Despite improved hygiene m... more Foodborne illness continues as a considerable threat to public health. Despite improved hygiene management systems and increased regulation, pathogenic bacteria still contaminate food, causing sporadic cases of illness and disease outbreaks worldwide. For many centuries, microbial antagonism has been used in food processing to improve food safety. An understanding of the mode of action of this microbial antagonism has been gained in recent years and potential applications in food and feed safety are now being explored. This review focuses on the potential opportunities presented, and the limitations, of using microbial antagonism as a biocontrol mechanism to reduce contamination along the food chain; including animal feed as its first link.

Journal of Dairy Research, 1988

ABSTRACT

Journal of Dairy Research, 2013

High fat dairy products, such as butter and margarine can be contaminated during the milk product... more High fat dairy products, such as butter and margarine can be contaminated during the milk production process with a residue called Trichloromethane (TCM), which results from the use of chlorine based detergent solutions. Although, TCM concentrations in Irish products are not at levels that are a public health issue, such contamination can cause marketing difficulties in countries to which Irish products are being exported. In an attempt to reduce such milk residues, a template procedure was developed, tried and tested on 43 farms (from 3 processing companies). This involved identifying farms with high TCM milk, applying corrective action in the form of advice and recommendations to reduce TCM and re-measuring milks from these farms. Trichloromethane in milk was measured by head-space gas chromatography with electron capture detector. The TCM reduction strategy proved successful in significantly reducing the levels in milk in the farms tested, e.g. TCM was reduced from 0.006 to the target of 0.002 mg/kg (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.05). The strategy was then applied to farms who supplied milk to six Irish dairy processors with the objective of reducing TCM in those milks to a level of ≤ 0.002 mg/kg. Initially, milk tankers containing milks from approximately 10-15 individual farms were sampled and analysed and tankers with high TCM (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;0.002 mg/kg) identified. Individual herd milks contributing to these tankers were subsequently sampled and analysed and farms supplying high TCM identified. Guidance and advice was provided to the high TCM milk suppliers and levels of TCM of these milk supplies were monitored subsequently. A significant reduction (minimum P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.05) in milk TCM was observed in 5 of the 6 dairy processor milks, while a numerical reduction in TCM was observed in the remaining processor milk.

Journal of Dairy Research, 2014

Each cheese producer is responsible by the legislation for the number of Listeria monocytogenes i... more Each cheese producer is responsible by the legislation for the number of Listeria monocytogenes in cheese and is required to prove that numbers will not exceed 100 cfu/g throughout the shelf-life of the cheese. Even in the case of hard-cheese such as Cheddar cheese, the absence of growth of List. monocytogenes during ripening has to be demonstrated to comply with EU legislation. Studies dedicated to assessing List. monocytogenes growth throughout cheese shelf-life are generally based on artificially contaminated cheeses. Contrary to the majority of works, the current study focused on the growth of List. monocytogenes in naturally contaminated raw milk farmhouse Cheddar cheeses during a five-month ripening period. List. monocytogenes growth was assessed by direct count and its presence was detected by enrichment in two naturally contaminated cheese batches. In order to track routes of contamination, 199 processing environment samples from inside and outside the processing facility were taken, and their analysis for the presence of List. monocytogenes was performed on four occasions over a 9-month period. List. monocytogenes isolates were differentiated using PFGE and serotyping. List. monocytogenes never exceeded 20 cfu/g in the cheeses and could not be detected after five months of ripening. Eleven pulsotypes were identified. One pulsotype was found in the yard outside the processing facility, in a vat, on the processing area floor and in a cheese. This indicated that the outside environment constitutes a potential source of contamination of the processing environment and of the cheese. These results demonstrate that this farmhouse Cheddar cheese does not support List. monocytogenes growth and suggests that the efforts to reduce processing environment contamination are worthwhile.

International Journal of Food Microbiology, 2013

The involvement of the pathogenic Shiga-toxin-producing Escherichia coli (STEC; also called veroc... more The involvement of the pathogenic Shiga-toxin-producing Escherichia coli (STEC; also called verocytotoxicproducing E. coli or VTEC) in sporadic cases and disease outbreaks is presently increasing. Infrequent cases are due to ingestion of milk and dairy products. As ruminants are healthy carriers of STEC and most dairy products may provide these bacteria with favourable conditions for their growth, milk and dairy products are a potential source of STEC. But not all STEC serotypes are pathogens; only relatively small numbers in the entire family of STEC are pathogenic. This review focuses on the recent advances in understanding of STEC and their significance in milk and dairy products. It is intended to gather the information that is needed to understand how these bacteria are described, detected and characterised, how they contaminate milk and grow in dairy products, and how the dairy industry can prevent them from affecting the consumer.

Foodborne Pathogens and Disease, 2011

Adaptation to sublethal stress can confer increased survival capability on foodborne pathogens. I... more Adaptation to sublethal stress can confer increased survival capability on foodborne pathogens. In this article, we report on the adaptive response of Cronobacter spp. to heat and compare the survival of heat adapted to unadapted Cronobacter spp. Five different isolates, representing at least three different Cronobacter spp., were adapted at 46°C for 30 min and subjected to a lethal stress at 52°C. All showed increased survival upon adaptation. Survival was greater in milk-grown cells, but broth-grown cells showed a higher degree of adaptation. The survival potential acquired following adaptation was not transferred to survival in a dry environment or to survival during reconstitution of artificially contaminated milk powder by conventional or microwave heat. The ratio of membrane unsaturated to saturated fatty acids decreased, possibly resulting in a more rigid membrane in adapted cells. Heat-adapted cells showed increased survival potential to lethal heat stress, but not to dry stress. Alterations in the ratio of fatty acids in the membrane may explain this adaptation.

Foodborne Pathogens and Disease, 2014

Cross-contamination via equipment and the food-processing environment has been implicated as the ... more Cross-contamination via equipment and the food-processing environment has been implicated as the main cause of Listeria monocytogenes transmission. The aim of this study, therefore, was to determine the occurrence and potential persistence of L. monocytogenes in 19 European cheese-processing facilities. A sampling approach in 2007-2008 included, respectively, 11 and two industrial cheese producers in Austria and the Czech Republic, as well as six Irish on-farm cheese producers. From some of the producers, isolates were available from sampling before 2007. All isolates from both periods were included in a strain collection consisting of 226 L. monocytogenes isolates, which were then typed by serotyping and pulsed-field gel electrophoresis (PFGE). In addition, metabolic fingerprints from a subset of isolates were obtained by means of Fourier-transform infrared (FTIR) spectroscopy. PFGE typing showed that six processing environments were colonized with seven persistent PFGE types of L. monocytogenes. Multilocus sequence typing undertaken on representatives of the seven persisting PFGE types grouped them into distinct clades on the basis of country and origin; however, two persistent strains from an Austrian and an Irish food processor were shown to be clonal. It was concluded that despite the fact that elaborate Hazard Analysis and Critical Control Point concepts and cleaning programs are applied, persistent occurrence of L. monocytogenes can take place during cheese making. L. monocytogenes sanitation programs could be strengthened by including rapid analytical tools, such as FTIR, which allow prescreening of potentially persistent L. monocytogenes contaminants.

Food Microbiology, 2009

Food safety is a critical factor in the production of farmhouse cheese. In Ireland the varieties ... more Food safety is a critical factor in the production of farmhouse cheese. In Ireland the varieties of farmhouse cheese produced reflect a much broader range than those produced commercially and some of these cheese varieties are associated with greater microbiological risk. These include cheese produced from unpasteurised milk and soft ripened cheese such as mould or smear-ripened cheeses which have high pH and relatively short ripening times. The aim of this study was to determine the microbiological quality of farmhouse cheeses in Ireland.