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PubMed2002

Listeria monocytogenes virulence and pathogenicity, a food safety perspective.

Several virulence factors of Listeria monocytogenes have been identified and extensively characterized at the molecular and cell biologic levels, including the hemolysin (listeriolysin O), two distinct phospholipases, a protein (ActA), several internalins, and others. Their study has yielded an impressive amount of information on the mechanisms employed by this facultative intracellular pathogen to interact with mammalian host cells, escape the host cell's killing mechanisms, and spread from one infected cell to others. In addition, several molecular subtyping tools have been developed to facilitate the detection of different strain types and lineages of the pathogen, including those implicated in common-source outbreaks of the disease. Despite these spectacular gains in knowledge, the virulence of L. monocytogenes as a foodborne pathogen remains poorly understood. The available pathogenesis and subtyping data generally fail to provide adequate insight about the virulence of field isolates and the likelihood that a given strain will cause illness. Possible mechanisms for the apparent prevalence of three serotypes (1/2a, 1/2b, and 4b) in human foodborne illness remain unidentified. The propensity of certain strain lineages (epidemic clones) to be implicated in common-source outbreaks and the prevalence of serotype 4b among epidemic-associated stains also remain poorly understood. This review first discusses current progress in understanding the general features of virulence and pathogenesis of L. monocytogenes. Emphasis is then placed on areas of special relevance to the organism's involvement in human foodborne illness, including (i) the relative prevalence of different serotypes and serotype-specific features and genetic markers; (ii) the ability of the organism to respond to environmental stresses of relevance to the food industry (cold, salt, iron depletion, and acid); (iii) the specific features of the major known epidemic-associated lineages; and (iv) the possible reservoirs of the organism in animals and the environment and the pronounced impact of environmental contamination in the food processing facilities. Finally, a discussion is provided on the perceived areas of special need for future research of relevance to food safety, including (i) theoretical modeling studies of niche complexity and contamination in the food processing facilities; (ii) strain databases for comprehensive molecular typing; and (iii) contributions from genomic and proteomic tools, including DNA microarrays for genotyping and expression signatures. Virulence-related genomic and proteomic signatures are expected to emerge from analysis of the genomes at the global level, with the support of adequate epidemiologic data and access to relevant strains.

Consumer Product Safety↗

PubMed2007

Attachment of Shiga toxigenic Escherichia coli to stainless steel.

Shiga toxigenic Escherichia coli (STEC) are important foodborne pathogens causing gastrointestinal disease worldwide. Bacterial attachment to food surfaces, such as stainless steel may lead to cross contamination of foods and subsequent foodborne disease. A variety of STEC isolates, including E. coli O157:H7/H- strains, were grown in planktonic (broth) and sessile (agar) culture, following which initial attachment to stainless steel was determined using epifluorescence microscopy. Experiments were performed to determine whether the number of bacteria attached to stainless steel differed between STEC strains and between the two modes of growth. No relationship was found between STEC strains and the number of bacteria attached to stainless steel. Five STEC strains, including one non-toxigenic O157 isolate, attached in significantly greater (p<0.05) numbers to stainless steel following growth in planktonic culture compared to sessile culture. In contrast, two clinical strains of O157:H7 attached in significantly greater (p<0.05) numbers following growth in sessile culture compared to planktonic culture. Thirteen out of twenty E. coli strains showed no significant difference (p>0.05) in attachment when grown in planktonic or sessile culture. The change of interfacial free energy between the bacterial strains and stainless steel was calculated and the influence of free energy in attachment was determined. Although a significant variation (p<0.05) in free energy values was found between STEC strains, no correlation was found between free energy values and bacterial counts on stainless steel. In addition, no correlation was also found between bacterial hydrophobicity and surface charge values or production of surface structures (type I fimbriae or flagella) (previously determined) with the number of bacteria attached to stainless steel. The results of this study suggest that different growth conditions (planktonic and sessile) can influence the attachment of STEC to stainless steel. Factors other than bacterial physicochemical properties and these surface structures may also influence STEC attachment to stainless steel.

Bacterial Adhesion↗

PubMed2006

The process of systematic review and its application in agri-food public-health.

Foodborne illness is an important public-health concern. Livestock operations represent the original source of many foodborne pathogens. Policy- and decision-makers in the area of agri-food public-health need dependable information on interventions to reduce foodborne diseases. While individual studies might be weak or reach contradictory conclusions, the body of information contained in all studies might reveal a clearer picture of the state of knowledge. A formal process has been developed for conducting systematic reviews of the human healthcare literature. Systematic reviews differ from traditional narrative reviews in that systematic reviews follow a structured research protocol to reduce sources of bias at all stages of the review. This includes the objective, the literature search, the identification of relevant literature, quality assessment of relevant studies, summarization or statistical analysis of data, and conclusions. To date, systematic reviews have not been widely used in agri-food public-health. Existing systematic reviews on agri-food public-health topics revealed a scarcity of rigorously conducted intervention research, indicating a need for additional high quality primary studies. The specific protocols used to conduct systematic reviews in agri-food public-health need to accommodate the use of challenge studies and observational studies, the lack of randomized controlled trials, and the clustering of animal populations.

Animals↗

PubMed2004

Purification of antilisterial bacteriocins.

In recent years, numerous contamination outbreaks, involving various pathogens (i.e., Listeria and Salmonella), have increased concern over food preservation. Research efforts have focused on the discovery of new molecules targeting such foodborne pathogens and therefore able to inhibit and or kill them. Lactic acid bacteria (LAB) extensively used in fermented foods for thousands of years not only improve their flavor and texture but also inhibit pathogenic and spoilage microorganisms. LAB inhibitory activity is primarily owing to pH decrease and competition for substrates. Antagonistic activity of LAB also depends on secreted antimicrobial compounds with a poor selectivity, such as metabolic compounds (i.e., hydrogen peroxide, acetoin, and others) or more specific ones like bacteriocins. The latter are proteinaceous compounds, ribosomally synthesized and subsequently secreted by Gram-positive as well as Gram-negative bacteria. Their antimicrobial activity is generally restricted to strains phylogenetically related to the producers.A classification of bacteriocins produced by LAB was first proposed by Klaenhammer in 1993 and was modified by Nes et al. in 1996; class I and class II bacteriocins are the most abundant and thoroughly studied. Bacteriocins from both classes exhibit antilisterial activity. Class I bacteriocins, namely, lantibiotics, have been widely studied, and among them, nisin is used in many countries as a preservative in food products. These bacteriocins are characterized by the presence, in their primary structure, of post-translationally modified amino acid residues (i.e., lanthionine and methylanthionine) that are formed. Class II bacteriocins, containing three subclasses, consist of small peptides that do not bear any modified amino acid residue. The most studied subclass corresponds to class IIa, also termed anti-Listeria bacteriocins. These peptides share strong structural homologies in their N-terminal domain, with the presence of one disulfide bond and a net positive charge. Their C-terminal domain is more variable but appears quite hydrophobic. Moreover, some of these bacteriocins, namely, sakacin G, pediocin PA-1, enterocin A, coagulin, and divercin V41, are characterized by the presence of a second disulfide bond in the C-terminal region.

Amino Acid Sequence↗

PubMed2001

Salmonella, Shigella and growth potential of other food-borne pathogens in Ethiopian street vended foods.

OBJECTIVE: To evaluate the bacteriological safety of food items sold by street vendors with regard to Salmonella and Shigella and to assess the growth potential of some foodborne pathogens in some street foods. DESIGN: Collection of street-vended foods and laboratory based microbiological analysis. SETTING: Microbiology Laboratory, Department of Biology, Addis Ababa University, Addis Ababa, Ethiopia. RESULTS: Most of the street food samples had aerobic mesophilic counts >10(7) cfu/g. Nine "kitfo" and one "egg sandwich" samples yielded Salmonella. Shigella was isolated from three "macaroni" samples. The Salmonella isolates were sensitive to all ten drugs tested but the Shigella isolates had multiple resistance against five drugs. In a challenge study, Salmonella typhimurium, Shigella flexneri and Staphylococcus aureus grew in street-vended food samples to hazardous levels within eight to twelve hours. CONCLUSION: Street foods are heavily contaminated with micro-organisms and are potential sources of food borne infections. Health hazards from street foods may be significantly minimised by consumption within four hours of preparation.

Colony Count, Microbial↗

PubMed2001

Consumers and foodborne diseases: knowledge, attitudes and reported behavior in one region of Italy.

A survey was conducted to investigate knowledge, attitudes and related behavior on foodborne diseases and food-handling practices among consumers in one region of Italy. A self-administered questionnaire was offered to a random sample of mothers of children attending public schools. Of the 394 responding mothers, 36% knew about all the six foodborne pathogens investigated but only 11.1% correctly indicated six related different food vehicles; education level was a predictor of this knowledge. A positive attitude towards foodborne disease control, significantly higher in older and more educated women, was reported by the great majority, who agreed that improper storage of food represents a health hazard (95.7%), that washing hands before handling unwrapped raw or cooked food reduces the risk of food poisoning (93.2%), and that the awareness of the temperature of the refrigerator is crucial in reducing risk of food poisoning (90.1%). Only 53.9% reported washing hands before and after touching raw or unwrapped food and 50.4% reported using soap to wash hands. A total of 75.6% clean kitchen benches after every use and 81.1% use hot water and soap for this purpose. Only 25.6% thaw food in the refrigerator and 49.9% put leftovers in the refrigerator soon after meals. Washing hands before and after touching unwrapped food was significantly higher in women living in larger families and who had been informed by physicians about foodborne diseases. Educational programs and the counseling efforts of physicians, particularly focused to less educated subjects, are greatly needed.

Adult↗

PubMedDate not supplied

[Molecular typing by amplified fragment length polymorphism and PCR-restriction fragment length polymorphism , biotyping and antimicrobial susceptibility of Campylobacter jejuni].

Molecular typing systems have provided invaluable information for tracking infectious agents through the food chain. These tools have been essential for understanding the epidemiology of gastrointestinal infectious diseases, therefore providing essential and evidence-based information for appropriate interventions and preventative measures. Two such molecular typing techniques based on the polymerase chain reaction (PCR) that have been applied to the epidemiology of foodborne pathogens are, amplified fragment length polymorphism (AFLP) and restriction fragment length polymorphism (RFLP) analysis. Campylobacter is responsible for one of the most common bacteria foodborne gastrointestinal infections affecting humans, especially in developed countries. The object of this paper is to apply AFLP and RFLP analysis of the flagellin (flaA) gene to 18 isolates of Campylobacter jejuni from human sporadic cases in Italy. Results of these analyses were compared to the phenotypes of these isolates based on biotyping and antimicrobial resistance determinations. All isolates were typable by the four methods. The RFLP procedure was performed with DdeI and HinfI enzymes, and 12 and 8 distinct profiles respectively were recognised. AFLP analysis was more discriminatory, and recognised 16 different profiles. Results from AFLP were reproducible and applicable for definitive characterisation of C. jejuni isolated from different outbreaks. PCR-RFLP of the flaA gene represents a useful tool only to compare isolates within a single outbreak.

Anti-Bacterial Agents↗

PubMed2000

Augmentation of antibiotic resistance in Salmonella typhimurium DT104 following exposure to penicillin derivatives.

Antibiotic resistance in pathogenic bacteria has been a problem in both developed and developing countries. This problem is especially evident in Salmonella typhimurium, one of the most prevalent foodborne pathogens. While performing in vitro gentamicin protection-based invasion assays, we found that certain isolates of multiresistant S. typhimurium can be 'induced' to exhibit new resistance profiles. That is, bacteria become resistant to a wider range of antibiotics and they also exhibit quantitative increases in MIC values for antibiotics that were part of their pre-induction antibiograms. This 'induction' process involves growing the bacteria to stationary phase in the presence of antibiotics such as ampicillin, amoxicillin or ticarcillin. Since the isolates studied exhibited resistance to ampicillin, amoxicillin and ticarcillin prior to exposing the bacteria to these antibiotics, the observed phenomenon suggests that resistant Salmonella not only have a selective advantage over non-resistant Salmonella but their resistance phenotypes can be accentuated when an inappropriate antibiotic is used therapeutically.

Ampicillin Resistance↗

PubMed2002

Aeromonas species in foods.

Aeromonas species have been recognized as potential or emerging foodborne pathogens for more than 20 years. Aeromonads are estuarine bacteria and are ubiquitous in fresh water, fish and shellfish, meats, and fresh vegetables. Actual sourced foodborne outbreaks are few, but epidemiological evidence suggests that the bacterium can cause self-limiting diarrhea, with children being the most susceptible population. Most aeromonads are psychrotrophic and can grow in foods during cold storage. Aeromonads are not resistant to food processing regimes and are readily killed by heat treatment. A host of virulence factors are present, but the exact role of each in human disease has not been fully elucidated.

Aeromonas↗

PubMed2000

Economic cost to New Zealand of foodborne infectious disease.

AIMS: To estimate the annual economic cost to New Zealand of foodborne infectious disease. METHODS: Annual incidence rates were combined with unit cost data to derive estimates of the annual economic cost to society of each foodborne infectious disease. Market prices and wages were used as proxies for the unit costs of resource utilisations. A decision analytic model was developed to estimate the costs of each disease and to undertake sensitivity analysis. RESULTS: There are an estimated 119 320 episodes of foodborne infectious disease per year in New Zealand (3241 per 100 000 population). The total cost of these cases was $55.1 million ($462 per case) made up of direct medical costs of $2.1 million, direct non-medical costs of $0.2 million, indirect cost of lost productivity of $48.1 million, and intangible cost of loss of life of $4.7 million. Campylobacteriosis generated most of the costs. Lost productivity was the major cost component for all diseases. The total cost of potentially foodborne infectious disease was estimated to be $88.8 million. Broad estimates of additional costs due to cases of infectious intestinal diseases caused by non-foodborne pathogens or for which no pathogen is identified could raise the cost to $215.7 million. CONCLUSION: The findings imply that resources of $55 million could be devoted to prevention of foodborne infectious disease. Efforts should focus on lowering the incidence of campylobacteriosis as this disease accounts for most of foodborne illness costs.

Disease Outbreaks↗

PubMed1998

Inactivation of Listeria monocytogenes in milk by pulsed electric field.

Pasteurized whole, 2%, and skim milk were inoculated with Listeria monocytogenes Scott A and treated with high-voltage pulsed electric field (PEF). The effects of milk composition (fat content) and PEF parameters (electric field strength, treatment time, and treatment temperature) on the inactivation of the bacterium were studied. No significant differences were observed in the inactivation of L. monocytogenes Scott A in three types of milk by PEF treatment. With treatment at 25 degrees C, 1- to 3-log reductions of L. monocytogenes were observed. PEF lethal effect was a function of field strength and treatment time. Higher field strength or longer treatment time resulted in a greater reduction of viable cells. A 4-log reduction of the bacterium was obtained by increasing the treatment temperature to 50 degrees C. Results indicate that the use of a high-voltage PEF is a promising technology for inactivation of foodborne pathogens.

Animals↗

PubMed1997

Long-term sequelae to foodborne disease.

Most of the concern about foodborne disease has been focused on the immediate effects of acute infection. Recent information has shown that many of these foodborne infections also have long-term sequelae with serious health effects and a significant economic impact. To increase the awareness of animal health professionals to these sequelae, the authors discuss two groups of sequelae which are strongly associated with preceding infection (reactive arthritides, including Reiter's syndrome, and the Guillain-Barré syndrome) as well as the possible association between Crohn's disease and Mycobacterium paratuberculosis. The discussion includes a description of the disease syndromes along with epidemiological and economic information. More reliable epidemiologial and economic data on chronic sequelae to foodborne disease will be needed for future evaluation of the cost-effectiveness of mitigation strategies to reduce the occurrence of foodborne pathogens.

Animals↗

PubMed2004

Efficacy of chlorine dioxide gas as a sanitizer of lettuce leaves.

Aqueous solutions of sodium hypochlorite or hypochlorous acid are typically used to sanitize fresh fruits and vegetables. However, pathogenic organisms occasionally survive aqueous sanitization in sufficient numbers to cause disease outbreaks. Chlorine dioxide (ClO2) gas generated by a dry chemical sachet was tested against foodborne pathogens on lettuce leaves. Lettuce leaves were inoculated with cocktail of three strains each of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium and treated with CLO2 gas for 30 min, 1 h, and 3 h in a model gas cabinet at room temperature (22 +/- 2 degrees C). After treatment, surviving cells, including injured cells, were enumerated on appropriate selective agar or using the overlay agar method, respectively. Total ClO2, generated by the gas packs was 4.3, 6.7, and 8.7 mg after 30 min, 1 h, and 3 h of treatment, respectively. Inoculated lettuce leaves exposed to ClO2 gas for 30 min experienced a 3.4-log reduction in E. coli, a 4.3-log reduction in Salmonella Typhimurium, and a 5.0-log reduction in L. monocytogenes when compared with the control. After 1 h. the three pathogens were reduced in number of CFU by 4.4. 5.3, and 5.2 log, respectively. After 3 h, the reductions were 6.9, 5.4, and 5.4 log, respectively. A similar pattern emerged when injured cells were enumerated. The ClO2, gas sachet was effective at killing pathogens on lettuce without deteriorating visual quality. Therefore, this product can be used during storage and transport of lettuce to improve its microbial safety.

Chlorine Compounds↗

PubMed2003

Growths kinetics comparison of clinical and seafood Listeria monocytogenes isolates in acid and osmotic environment.

Comparison of pathogenic bacterial strains of clinical origin with strains of the same species isolated from the environment may be a valuable tool for microbial risk assessment, especially for foodborne pathogens. Thus, a number of Listeria monocytogenes strains responsible for human cases of listeriosis, in relation to the consumption of contaminated seafood, have been compared with "natural" L. monocytogenes strains isolated from similar seafood products. Complete factorial designs were used to assess quantitatively the growth abilities of four clinical and four seafood isolates of L. monocytogenes placed in various environmental conditions. The cells were submitted to acid and osmotic stress as they were in stationary phase (constant condition) or in exponential phase (dynamic condition). The effects and interactions of pH (5-7) and NaCl concentration (0.5-8% v/v) were studied at two growth temperatures (10 and 20 degrees C). Growth parameters (lag and generation times calculated with Gompertz equation) were used to compare the behavior of the strains with respect to the conditions of culture. The results indicated an overall weak effect of acid stress alone, whereas osmotic stress clearly affected bacterial growth and a synergic effect between these two factors was observed. Clinical strains displayed better adaptation than seafood strains in stationary phase, however, this difference was not verified in exponential phase. Low temperature (10 degrees C) usually confirmed the observations at 20 degrees C, and the differences between clinical and food strains were more pronounced. Finally, a classification of the eight strains, based on the collected data, showed three groups: (i) seafood strains, (ii) three clinical strains and (iii) the last clinical strain, alone due to its high resistance to adverse conditions.

Food Contamination↗

PubMed2002

Effect of organic acids and temperature on survival of Shigella flexneri in broth at pH 4.

The survival of bacterial pathogens in acidified foods depends not only on the hydrogen ion concentration, but also on the type of acid and the storage temperature. Shigella flexneri is a foodborne pathogen that is acid tolerant. The survival of S. flexneri 5348 in brain heart infusion broth supplemented with 0.04 M acetic, citric, lactic, malic, or tartaric acid and adjusted to pH 4 with HCI or NaOH was studied. The control medium was brain heart infusion broth adjusted to pH 4 with HCI. Stationary-phase cells were inoculated into media at initial populations of 6 to 7 log10 CFU/ml and incubated at 4, 19, 28, and 37 degrees C. A two-phase linear inactivation model was applied to plate count data to derive lag times (tL) and slopes of the curves, from which D-values and time required for a 4-log10 decrease in population (T4D) were calculated. In all cases, survival increased with decreasing temperature. For each acid, tL, the D-value, and T4D increased with decreasing temperature. All acids inhibited S. flexneri to some extent but to differing degrees as follows: lactic acid, acetic acid > citric acid, malic acid, tartaric acid > HCl. The T4D values for the control medium and for media containing acetic, citric, lactic, malic, and tartaric acids were 64, 47, 50, 34, 58, and 52 h, respectively, at 37 degrees C and 2,607, 1,498, 1,905, 1,346, 1,726, and 2,134 h, respectively, at 4 degrees C. The results of this study indicate that organic acids may aid in the inactivation of Shigella. However, these data also suggest that foods stored at or below room temperature containing low levels (< 1%) of acids could cause illness if contaminated with Shigella.

Acids↗

PubMed2004

Modeling growth and reduction of microorganisms in foods as functions of temperature and time.

Food safety objectives (FSOs) are established in order to minimize the risk of foodborne illnesses to consumers, but these have not yet been incorporated into regulatory policy. An FSO states the maximum frequency and/or concentration of a microbiological hazard in a food at the time of consumption that provides an acceptable level of protection to the public and leads to a performance criterion for industry. However, in order to be implemented as a regulation, this criterion has to be achievable by the affected industry. In order to determine an FSO, the steps to produce and store that food need to be known, especially where they have an impact on contamination, growth, and destruction. This article uses existing models for growth of Listeria monocytogenes in conjunction with calculations of FSOs to approximate the outcome of more than one introduction of the foodborne organism throughout the food-processing path from the farm to the consumer. Most models for the growth and reduction of foodborne illnesses are logarithmic in nature, which fits the nature of the growth of microorganisms, spanning many orders of magnitude. However, these logarithmic models are normally limited to a single introduction step and a single reduction step. The model presented as part of this research addresses more than one introduction of food contamination, each of which can be separated by a substantial amount of time. The advantage of treating the problem this way is the accommodation of multiple introductions of foodborne pathogens over a range of time durations and conditions.

Food Handling↗

PubMed2000

Food handlers and foodborne diseases: knowledge, attitudes, and reported behavior in Italy.

The purpose of this study was to evaluate knowledge, attitudes, and behavior concerning foodborne diseases and food safety issues among food handlers in Italy. Face-to-face interviews were conducted within a random sample using a structured questionnaire. Of the 411 food handlers responding, 48.7% knew the main foodborne pathogens (Salmonella spp., Staphylococcus aureus, Vibrio cholerae or other Vibrio spp., Clostridium botulinum, hepatitis A virus), and this knowledge was significantly greater among those with a higher education level, in practice from a longer period of time, and who had attended education courses (P < 0.05). A vast majority (90.4%) correctly indicated those foods classified as common vehicles for foodborne diseases, and only 7.1% of food handlers were able to name five different food vehicles, each of which transmit one of the five pathogens. The proportion of those who were able to specify a food vehicle that transmitted hepatitis A virus was significantly higher for those with a higher educational level and with a longer food-handling activity. A positive attitude toward foodborne diseases control and preventive measures was reported by the great majority of food handlers, and it was more likely achieved by those who had attended education courses. This attitude was not supported by some of the self-reported safe practices observed for hygienic principles, because only 20.8% used gloves when touching unwrapped raw food, and predictors of their use were educational level and attending education courses. Results strongly emphasize the need for educational programs for improving knowledge and control foodborne diseases.

Adolescent↗

PubMed1999

Resistance responses of microorganisms in food environments.

Food borne microorganisms display a broad spectrum of resistance responses to naturally occurring and intentionally added antimicrobial agents. Resistance may be conferred by innate structural features of the bacterial strain such as an impermeable outer membrane or a mechanism for antibiotic-inactivation. Bacteria previously susceptible to an antimicrobial compound can acquire resistance through mutation or through genetic transfer processes such as transformation, transduction, and conjugation. Resistance can also be conferred by biofilm formation on food processing surfaces as an adaptive response to protect colonies from cleaning and sanitation. Resistant pathogens are a global problem, facilitated by international trade of raw and processed foods. Cross resistance between clinical and nonclinical antimicrobials can exist and is of concern. The development of resistant foodborne pathogens has been attributed to increased antibiotic use in hospitals, outpatient facilities, and veterinary applications. Resistant microorganisms can also develop as a result of physical processes used in food preservation, such as acid treatments and irradiation processes. Strategies to effectively counter resistance development include: changing current practices of antibiotic usage, developing new antibiotics, applying hurdle preservation approaches, preventing bacterial adhesion, and utilizing competitive exclusion. This paper presents an overview of problems arising from the development of microbial resistance, and explores possible solutions for detecting and defeating the adaptive changes of microorganisms.

Drug Resistance, Microbial↗