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PubMed2006

Listeria: A foodborne pathogen that knows how to survive.

The foodborne pathogen Listeria is the causative agent of listeriosis, a severe disease with high hospitalization and case fatality rates. Listeria monocytogenes can survive and grow over a wide range of environmental conditions such as refrigeration temperatures, low pH and high salt concentration. This allows the pathogen to overcome food preservation and safety barriers, and pose a potential risk to human health. This review focuses on the key issues such as survival of the pathogen in adverse environments, and the important adaptation and survival mechanisms such as biofilm formation, quorum sensing and antimicrobial resistance. Studies on the development of technologies to prevent and control L. monocytogenes contamination in foods and food processing facilities are also discussed.

Adaptation, Physiological↗

PubMed2001

Evaluation of thin agar layer method for recovery of acid-injured foodborne pathogens.

The thin agar layer (TAL) method of Kang and Fung was used to enumerate acid-injured foodborne pathogens. This method involves overlaying 14 ml of nonselective medium (tryptic soy agar [TSA]) onto a prepoured and solidified pathogen-specific, selective medium in a petri dish. After surface plating, injured cells resuscitated and grew on TSA during the first few hours of incubation; then, the selective agents from the selective medium diffused to the top layer, interacted with the recovered microorganisms, and started to produce typical reactions. Foodborne pathogens were exposed to 2% acetic acid for 1, 2, or 4 min, and the recovery rate with the TAL method was compared with the rate of TSA and pathogen-specific, selective media. No significant difference occurred between TSA and TAL (P > 0.05) for enumeration of acid-injured Escherichia coli O157:H7, Salmonella Typhimurium, Staphylococcus aureus, and Yersinia enterocolitica, and both recovered significantly higher numbers than the selective medium for each respective pathogen (P < 0.05). For recovery of acid-injured Listeria monocytogenes, no difference (P > 0.05) occurred among TSA, TAL, and selective media. However, fewer cells were recovered in the selective media. The TAL method is a one-step, convenient procedure for recovery of acid-injured cells.

Acids↗

PubMed2005

Human health consequences of antimicrobial drug-resistant Salmonella and other foodborne pathogens.

There are several clinical and public health consequences associated with antimicrobial drug resistance in non-Typhi Salmonella species and other foodborne pathogens. If bacteria acquire resistance to clinically important antimicrobial drugs, early empirical treatment may fail, and there will be limitations in the choices of treatment after the establishment of microbial diagnosis. Drug-resistant gastrointestinal pathogens preferentially cause illness in persons receiving antimicrobial drugs for any medical condition. Consequently, emerging resistance in foodborne pathogens may result in increased burdens of illness and outbreaks in settings where patients are treated with antimicrobial drugs. Finally, resistance may be associated with increased virulence, and several epidemiological studies have demonstrated that infections with drug-resistant non-Typhi Salmonella serotypes and Campylobacter species are associated with excess mortality and morbidity. Mitigation of drug resistance in foodborne bacteria is likely to be of benefit for human health.

Anti-Bacterial Agents↗

PubMedDate not supplied

Quantitative assessment of hard surface disinfectant activity against the foodborne pathogen Listeria monocytogenes.

Listeria monocytogenes is an important foodborne pathogen that must be controlled to ensure food safety. For the years 2003 and 2004, L. monocytogenes caused 20 deaths per 100 listeriosis cases and was responsible for most food recalls for pathogen contamination. The objective of this work was to develop a quantitative method to assess disinfectant activity against L. monocytogenes. Standard procedures for testing disinfectants against 3 bacteria are described in the AOAC Official Methods of Analysis as use-dilution methods. No standard methods are provided for L. monocytogenes. In this study, preliminary efficacy of a quaternary ammonium compound with hydroperoxide ion was determined for 25 bacterial strains. The zones of inhibition ranged from 7.0 to 12.5 mm, and the minimum inhibitory concentration ranged from 5 to 250 ppm. For final efficacy, stainless steel carriers were contaminated with L. monocytogenes and tested separately for 5, 10, and 15 min in disinfectant or phenol. After exposure, the carriers were placed into 2 series of D/E neutralization broth. For 3 replications with duplicate samples, the phenol coefficient was 3.3. This research presents a technique-sensitive method that provides quantitative data for comparison and analysis of disinfectant activity against L. monocytogenes.

Bacteria↗

PubMed2003

Proteolytic fungi isolated from decayed and damaged raw tomatoes and implications associated with changes in pericarp pH favorable for survival and growth of foodborne pathogens.

Raw and minimally processed high-acid fruits and vegetables are considered to be at low or no risk for supporting growth of foodborne pathogens. The potential increase in the pH of tissues as a result of fungal growth, however, may enhance the potential for survival and growth. We examined 77 decayed and 138 damaged, raw, ripe tomatoes for the presence of yeasts and molds that produce proteolytic enzymes and other metabolites that can potentially increase the pH of pulp tissue. The pH of decayed and sound radial pericarp tissues (pulp) of decayed tomatoes ranged from 4.7 to 7.8 (mean = 6.2) and 4.3 to 5.8 (mean = 5.0), respectively, whereas the pH of damaged and sound pericarp of damaged tomatoes ranged from 4.2 to 7.8 (mean = 5.2) and 4.2 to 8.0 (mean = 4.9), respectively. The pH of sound pericarp of 8.5% of decayed tomatoes and 3.4% of damaged tomatoes, respectively, was > 5.41. In contrast, the pH of 70% of the decayed tissue and 18% of the damaged tissue was > 5.41. Fungal isolates (n = 371) recovered from decayed and damaged tomatoes on dichloran rose bengal chloramphenicol agar were examined for proteolytic activity on gelatin agar and standard methods caseinate agar. One hundred eight (29%) of the isolates exhibited proteolytic activity on one or both differential media; 96 (89%) were molds, and 12 (11%) were yeasts. The pH of both media increased at the edge of proteolytic fungal colonies. Growth of proteolytic isolates from decayed tomatoes on tomato juice agar (pH = 4.3) and on the surface of tomato juice (pH = 4.1) caused an increase in mean pH values at the colony/medium interface to 7.2 and 6.4, respectively. Results show that some fungi capable of infecting raw tomatoes, as well as the mycoflora incident on tomato surfaces, can increase the pH of pericarp and juice to levels favorable for growth of most foodborne pathogenic bacteria.

Bacteria↗

PubMed2002

Subtyping of bacterial foodborne pathogens.

Phenotype-based and DNA-based subtyping methods allow for differentiation of bacterial isolates beyond the species and subspecies level. Bacterial subtyping methods not only have improved our ability to detect and track foodbome disease outbreaks, but also represent tools to track sources of bacterial contamination throughout the food system. The use of subtyping methods furthermore provides an opportunity to better understand the population genetics, epidemiology, and ecology of different foodbome pathogens. The last 5 years have seen tremendous advancement in the development of sensitive, rapid, automated, and increasingly easy-to-use molecular subtyping methods for a variety of different bacterial foodborne pathogens. This review will highlight key aspects of different subtyping methods for bacterial foodborne pathogens and provide examples of their applications in public health, food safety, epidemiology, and population genetics. Molecular subtyping and characterization methods may also facilitate the development of a novel framework for tracking, preventing, and regulating foodborne bacterial diseases, which is based on evolutionary relationships and genetic characteristics rather than traditional species definitions.

Bacterial Typing Techniques↗

PubMed2004

Temperature and biological soil effects on the survival of selected foodborne pathogens on a mortar surface.

The survival of three foodborne pathogens (Listeria monocytogenes, Yersinia enterocolitica, and Salmonella) attached to mortar surfaces, with or without biological soil (porcine serum) and incubated at either 4 or 10 degrees C in the presence of condensate, was evaluated. Soiled and unsoiled coupons were inoculated by immersion into a five-strain cocktail (approximately 10(7) CFU/ml) of each organism type and evaluated. Coupons were incubated at 25 degrees C for 2 h to allow attachment of cells, rinsed to remove unattached cells, and incubated at either 4 or 10 degrees C at high humidity to create condensate on the surface. Sonication was used to remove the attached cells, and bacteria (CFU per coupon) was determined at 9 to 10 sampling periods over 120 h. Yersinia populations decreased more than 5 log units in the presence of serum in a 24-h period. Listeria and Salmonella had better survival on mortar in the presence of serum than Yersinia throughout the 120-h incubation period. Populations of L. monocytogenes declined more rapidly at 10 than at 4 degree C after 24 h. In general, differences in temperature did not affect the survival of Salmonella or Yersinia. Serum had a protective effect on the survival of all three organisms, sustaining populations at significantly (P < or = 0.05) higher numbers over time than on corresponding unsoiled coupons. There were no significant differences (P > 0.05) among the mean number (CFU per coupon) of L. monocytogenes, Y. enterocolitica, or Salmonella on initial attachment onto the mortar surfaces (unsoiled). The results indicate relatively rapid destruction of selected pathogenic bacteria on unsoiled mortar surfaces compared with those that contained biological soil, thus highlighting the need for effective cleaning to reduce harborage of these microbes in the food factory environment.

Bacterial Adhesion↗

PubMed2000

Interactions of high hydrostatic pressure, pressurization temperature and pH on death and injury of pressure-resistant and pressure-sensitive strains of foodborne pathogens.

The objective of this study is to determine the interactions between high hydrostatic pressure, pressurization temperature, time and pH during pressurization on death and injury of pressure-resistant and pressure-sensitive strains of four foodborne pathogens: Staphylococcus aureus 485 and 765, Listeria ,monocytogenes CA and OH2, Escherichia coli O157:H7 933 and 931, Salmonella enteritidis FDA and Salmonella typhimurium E21274. Among these strains S. aureus 485, L. monocytogenes CA, E. coli O157:H7 933 and S. enteritidis FDA were reported to be more pressure-resistant than the respective strain of the same species (Alpas et al., 1999). In general, viability loss of all pathogens was enhanced significantly as the level of pressure and temperature were increased (P < 0.05). All the strains except S. aureus 485 demonstrated more than 8 log cycle reduction when pressurized at 345 MPa at 50 degrees C for 5 min. This strain seemed to be the most pressure-resistant strain within the conditions of the study. Pressurization in the presence of either citric or lactic acid increased the viability loss by an additional 1.2-3.9 log cycles at pH 4.5 for both acids at 345 MPa. This study has indicated that high hydrostatic pressure applied in conjunction with mild heat and acidity can be an effective method for inactivating pressure-resistant and pressure-sensitive strains of four foodborne pathogens in organic acid solutions. This combination treatment indicates possible pressure pasteurization applications to liquid foods that have low pH. reserved.

Analysis of Variance↗

PubMed2004

Irrigation water as source of foodborne pathogens on fruit and vegetables.

Awareness is growing that fresh or minimally processed fruit and vegetables can be sources of disease-causing bacteria, viruses, protozoa, and helminths. Irrigation with poor-quality water is one way that fruit and vegetables can become contaminated with foodborne pathogens. Groundwater, surface water, and human wastewater are commonly used for irrigation. The risk of disease transmission from pathogenic microorganisms present in irrigation water is influenced by the level of contamination; the persistence of pathogens in water, in soil, and on crops; and the route of exposure. Groundwater is generally of good microbial quality, unless it is contaminated with surface runoff; human wastewater is usually of very poor microbial quality and requires extensive treatment before it can be used safely to irrigate crops; surface water is of variable microbial quality. Bacteria and protozoa tend to show the poorest survival outside a human host, whereas viruses and helminths can remain infective for months to years. Guidelines governing irrigation water quality and strategies to reduce the risk of disease transmission by foodborne pathogens in irrigation are discussed.

Consumer Product Safety↗

PubMedDate not supplied

Identifying and controlling emerging foodborne pathogens: research needs.

Systems for managing the risks associated with foodborne pathogens are based on detailed knowledge of the microorganisms and the foods with which they are associated--known hazards. An emerging pathogen, however, is an unknown hazard; therefore, to control it, key data must be acquired to convert the pathogen from an unknown to a known hazard. The types of information required are similar despite the identity of the new agent. The key to rapid control is rapid mobilization of research capabilities targeted at addressing critical knowledge gaps. In addition, longer-term research is needed to improve our ability to respond quickly to new microbial threats and help us become more proactive at anticipating and preventing emergence. The type of contingency planning used by the military in anticipating new threats serves as a useful framework for planning for new emergence.

Food Microbiology↗

PubMed2003

Interaction of a free-living soil nematode, Caenorhabditis elegans, with surrogates of foodborne pathogenic bacteria.

Free-living nematodes may harbor, protect, and disperse bacteria, including those ingested and passed in viable form in feces. These nematodes are potential vectors for human pathogens and may play a role in foodborne diseases associated with fruits and vegetables eaten raw. In this study, we evaluated the associations between a free-living soil nematode, Caenorhabditis elegans, and Escherichia coli, an avirulent strain of Salmonella Typhimurium, Listeria welshimeri, and Bacillus cereus. On an agar medium, young adult worms quickly moved toward colonies of all four bacteria; over 90% of 3-day-old adult worms entered colonies within 16 min after inoculation. After 48 h, worms moved in and out of colonies of L. welshimeri and B. cereus but remained associated with E. coli and Salmonella Typhimurium colonies for at least 96 h. Young adult worms fed on cells of the four bacteria suspended in K medium. Worms survived and reproduced with the use of nutrients derived from all test bacteria, as determined for eggs laid by second-generation worms after culturing for 96 h. Development was slightly slower for worms fed gram-positive bacteria than for worms fed gram-negative bacteria. Worms that fed for 24 h on bacterial lawns formed on tryptic soy agar dispersed bacteria over a 3-h period when they were transferred to a bacteria-free agar surface. The results of this study suggest that C. elegans and perhaps other free-living nematodes are potential vectors for both gram-positive and gram-negative bacteria, including foodborne pathogens in soil.

Animals↗

PubMed2002

Essential oil constituents and in vitro antimicrobial activity of Decalepis hamiltonii roots against foodborne pathogens.

Hydrodistillation of Decalepis hamiltonii roots yielded an essential oil (0.33% v/w) that contained 2-hydroxy-4-methoxybenzaldehyde (37.45%), 2-hydroxybenzaldehyde (31.01%), 4-O-methylresorcylaldehyde (9.12%), benzyl alcohol (3.16%), and alpha-atlantone (2.06%) as major constituents, with aromatic aldehydes constituting the main fraction of this root's essential oil. The oil was tested for its antimicrobial activity against foodborne pathogens responsible for food spoilage and human pathologies using standard antimicrobial assays. It exhibited strong antimicrobial activity against Bacillus cereus, Bacillus megaterium, Candida albicans, Escherichia coli, Micrococcus luteus, Micrococcus roseus, and Staphylococcus aureus at a concentration range of 1:0 with inhibitory activities of 27, 23, 16, 19, 22, 19, and 23 mm, respectively, which are comparable to those of the standards. The roots of D. hamiltonii, therefore, may be considered as an inexpensive source of an essential oil rich in antimicrobial compounds against foodborne pathogens.

Anti-Bacterial Agents↗

PubMed2005

Use of oligonucleotide array for identification of six foodborne pathogens and Pseudomonas aeruginosa grown on selective media.

Identification of presumptive foodborne pathogens grown on selective media may take one to several days and requires a different battery of biochemical tests for each microorganism. A molecular identification method was developed in which universal primers were used to amplify the 16S to 23S rDNA intergenic spacer of target microorganisms, and PCR products were hybridized to a panel of species-specific oligonucleotides that were immobilized on a nylon membrane. The seven target microorganisms were Bacillus cereus, Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella, Staphylococcus aureus, and Vibrio parahaemolyticus. After testing a large collection of target bacteria (29 to 51 strains) and nontarget bacteria (> 500 strains), the performances (sensitivity and specificity) of the oligonucleotide array were as follows: B. cereus (100 and 77%), E. coli (100 and 100%), L. monocytogenes (100 and 90%), P. aeruginosa (100 and 100%), Salmonella (100 and 100%), S. aureus (100 and 100%), and V. parahaemolyticus (100 and 94.2%). Other species in the B. cereus group cross-hybridized to the probes used for identification of B. cereus, and positive results should be confirmed by additional morphological observation of colonies. Listeria innocua cross-reacted with probes used to identify L. monocytogenes, but a simple hemolysis test was used to differentiate the two species. Some strains of Vibrio harveyi and Vibrio mimicus cross-hybridized with probes used for identification of V. parahaemolyticus and caused false-positive reactions. The advantage of the array is that a common protocol was used to identify the seven target microorganisms and multiple different microorganisms could be simultaneously identified on a single array.

Bacillus cereus↗

PubMed2004

Antibacterial effect of water-soluble tea extracts on foodborne pathogens in laboratory medium and in a food model.

The microbial inhibition of foodborne pathogens was determined in brain heart infusion broth with 10% (wt/vol) water-soluble extracts of green, jasmine, black, dungglre, and oolong tea against Escherichia coli O157:H7, Salmonella enterica serovar Enteritidis, Listeria monocytogenes, and Staphylococcus aureus. The mixed culture (approximately 6.0 log CFU/ml), which was composed of the four pathogens, was inoculated into brain heart infusion broth with and without tea extracts. After incubation at 35 degrees C for 0, 1, 3, and 5 days, proper dilution of each sample was spiral plated on each selective agar. Viable cell counts were performed after incubation at 35 degrees C for 24 to 36 h. Green, jasmine, and black tea exhibited an approximately 5.0 log suppression of S. aureus compared with the control from days 1 to 5. Green and jasmine tea also suppressed the growth of L. monocytogenes by approximately 3.0 log CFU/ml on day 5. In contrast, no tea extracts inactivated E. coli O157:H7 and Salmonella Enteritidis. Based on the result in liquid medium, green and jasmine teas of 0.1% (vol/wt) were individually evaluated for their antimicrobial activity against L. monocytogenes and S. aureus in a food model (ground beef) stored at 7 degrees C for 0, 1, 3, 5, and 7 days. Viable cell counts of total bacteria, L. monocytogenes, and S. aureus in ground beef were not significantly different among green and jasmine tea and the control.

Anti-Bacterial Agents↗

PubMed2002

Human diseases caused by foodborne pathogens of animal origin.

Many lines of evidence link antimicrobial-resistant human infections to foodborne pathogens of animal origin. Types of evidence reviewed include: (1) direct epidemiologic studies; (2) temporal evidence; (3) additional circumstantial evidence; (4) trends in antimicrobial resistance among Salmonella isolates; and (5) trends in antimicrobial resistance among other pathogens, such as Campylobacter jejuni. Commensal microorganisms in animals and humans may contribute to antimicrobial resistance among pathogens that cause disease among humans. For instance, enterococci of food-animal origin, particularly strains that are vancomycin resistant, have been linked to strains found in the human gastrointestinal tract. The latent period between the introduction of a given antimicrobial and emergence of resistance varies considerably, but once the prevalence in a population reaches a certain level, control becomes extremely difficult.

Animals↗

PubMed2002

The physiology of Campylobacter species and its relevance to their role as foodborne pathogens.

Campylobacter jejuni and C. coli are recognised as the leading causes of bacterial foodborne diarrhoeal disease throughout the development world. While most foodborne bacterial pathogens are considered to be relatively robust organisms, as a consequence of the necessity to survive the inimical conditions imposed by food processing and preservation, Campylobacter species have uniquely fastidious growth requirements and an unusual sensitivity to environmental stress. Campylobacters also lack many of the well characterised adaptive responses that can be collated with resistance to stress in other bacteria. The aim of this review is to outline the unusual physiology of campylobacters (C. jejuni and C. coli) and to describe how this influences their role as foodborne pathogens.

Campylobacter↗

PubMed2006

Bactericidal effects of CaO (scallop-shell powder) on foodborne pathogenic bacteria.

This study was investigated the bactericidal effects of calcium oxide (CaO) on three common foodborne pathogenic bacteria: Escherichia coli, Listeria monocytogenes, and Salmonella typhimurium. Each bacteria level was determined in a CaO solution (0.01, 0.03, 0.05, 0.10, 0.15, and 0.20% [w/v]) exposed for either 15 sec, 30 sec, 1 min, 2 min, 3 min, 5 min, 10 min, or 30 min. All three bacteria were not greatly affected by CaO solutions at concentrations of 0.01 and 0.03%, however, the decline of E. coli (99%; 2.78 log10 CFU/mL), L. monocytogens (45%; 1.44 log10 CFU/mL), and S. typhimurium (70%; 2.08 log10 CFU/mL) was greatest when they were exposed to 0.05% CaO solution for 10 min. Moreover, the bactericidal action of CaO was maintained for at least 24 h of storage. The results of this study provide evidence that CaO, as a substitute for synthetic chemical substances has potential for use in the disinfection and sanitization of foods and food processing equipment.

Calcium Compounds↗

PubMed2006

Antibacterial activity of bioconverted eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) against foodborne pathogenic bacteria.

The antimicrobial activity of bioconversion extracts of EPA and DHA against a range of foodborne pathogenic bacteria was investigated. The bioconverted EPA and DHA exhibited antibacterial activities against four gram-positive bacteria, Bacillus subtilis, Listeria monocytogenes, Staphylococcus aureus (ATCC 6538) and S. aureus (KCTC 1916) and seven gram-negative bacteria, Enterobacter aerogenes, Escherichia coli, E. coli O157:H7, E. coli O157:H7 (human), Pseudomonas aeruginosa, Salmonella enteritidis and S. typhimurium. The growth inhibition by both bioconverted EPA and DHA was similar against gram-positive bacteria, while the bioconverted extract of DHA was more effective than EPA against gram-negative bacteria as determined by minimum inhibitory concentration.

Colony Count, Microbial↗