Emerging foodborne diseases

Noroviruses: agents in outbreaks of acute gastroenteritis

Noroviruses are the most common cause of acute gastroenteritis in the United States and are believed to be the most common cause of food borne illnesses.1 Noroviruses have avoided attention for years due to the difficulty of detection and inability to be cultured. Norovirus outbreaks have major implications for health care workers as they can occur in nursing homes and hospitals. To further complicate the picture, these viruses can infect persons of all ages which is a feature that distinguishes noroviruses from other agents. Factors that contribute to the significant impact of noroviruses include a large human reservoir, low infection dose, and the ability to be transmitted by various routes. This article provides an overview of noroviruses particularly as it relates to health care workers.

A mortalidade por doenças infecciosas no início e no final do século XX no Município de São Paulo

A melhora das condições de vida do homem durante o século XX contribuiu para transformações da estrutura demográfica e para mudanças dos padrões de morbi-mortalidade. Com o objetivo de discutir essas mudanças, pretende-se comparar os dados de mortalidade do Município de São Paulo em 1901, 1960 e 2000. As causas de morte foram obtidas das seguintes fontes: Anuários Estatísticos da FSEADE, para 1901; Anuário de 1961 do Departamento de Estatística do Estado e CD-ROM de Mortalidade do Ministério da Saúde, para o ano de 2000. Os demais dados - de população, de nascidos vivos, coeficientes de mortalidade geral e infantil - foram obtidos do CD-ROM "500 anos de Divisão territorial e 100 anos de Estatísticas Demográficas Municipais" da FSEADE. Do início até o final do século XX, a população do Município de São Paulo aumentou 36 vezes, o número de nascimentos quase 24 e o número de óbitos 13,6 vezes. No entanto, as taxas de mortalidade diminuíram, a mortalidade geral foi 2,6 vezes menor no ano 2000 e a mortalidade infantil 11,3 vezes menor. A proporção de óbitos por doenças infecciosas declina de 45,7% do total de óbitos em 1901 para 9,7% em 2000. Em 1901, entre as 10 principais causas de morte no Município, 5 eram doenças infecciosas, correspondendo a 37% das mortes; em 1960, apareciam nesta lista apenas 3 doenças infecciosas (16,1% dos óbitos), e em 2000 apenas a pneumonia constava entre as principais causas de morte. Doenças como tétano, difteria, coqueluche, sarampo e escarlatina mostraram-se controladas no final do período. No entanto, a pneumonia, a tuberculose, a septicemia e a aids ainda se situam entre as que merecem especial atenção na área de saúde pública.

Consumer food-handling behaviors associated with prevention of 13 foodborne illnesses

To be effective in reducing the incidence of foodborne illness, consumers and food safety educators need information about behaviors that will decrease exposure to foodborne pathogens. A four-round Delphi technique was used to survey nationally recognized experts in food microbiology, epidemiology, food safety education, and food safety policy with the aim of identifying and ranking food-handling and consumption behaviors associated with 13 major foodborne pathogens. The food safety experts ranked behaviors related to keeping foods at safe temperatures as of primary importance in preventing illness caused by Bacillus cereus and Clostridium perfringens and of secondary importance in preventing illness caused by Staphylococcus aureus. The use of a thermometer to cook foods adequately was ranked as of primary importance for the prevention of illness caused by Campylobacter jejuni, Salmonella species, Escherichia coli O157:H7, Toxoplasma gondii, and Yersinia enterocolitica, with the avoidance of cross-contamination being ranked as of secondary importance for most of these pathogens. Hand washing was the top-ranked behavior for the prevention of shigellosis. The avoidance of certain foods that are likely to be contaminated was the top-ranked behavior for the prevention of illnesses caused by Listeria monocytogenes, Noroviruses, and Vibrio species. The expert panel's ranking of behaviors for the reduction of the risk of illness caused by major foodborne pathogens can enable consumers to make informed choices about food consumption and handling behaviors and can guide food safety educators in prioritizing their educational efforts.

Molecular subtyping to detect human listeriosis clusters

We analyzed the diversity (Simpson's Index, D) and distribution of Listeria monocytogenes in human listeriosis cases in New York State (excluding New York City) from November 1996 to June 2000 by using automated ribotyping and pulsed-field gel electrophoresis (PFGE). We applied a scan statistic (p<or=0.05) to detect listeriosis clusters caused by a specific Listeria monocytogenes subtype. Among 131 human isolates, 34 (D=0.923) ribotypes and 74 (D=0.975) PFGE types were found. Nine (31% of cases) clusters were identified by ribotype or PFGE; five (18% of cases) clusters were identified by using both methods. Two of the nine clusters (13% of cases) corresponded with investigated multistate listeriosis outbreaks. While most human listeriosis cases are considered sporadic, highly discriminatory molecular subtyping approaches thus indicated that 13% to 31% of cases reported in New York State may represent single-source clusters. Listeriosis control and reduction efforts should include broad-based subtyping of human isolates and consider that a large number of cases may represent outbreaks.

Isolation of Escherichia coli O157:H7 from dung beetles Catharsius molossus

In an epidemiological survey, Escherichia coli O157:H7 was isolated from the intestine 4 of 113 dung beetle Catharsius molossus captured below ground at Tongshan County, Jiangsu Province of China. In parallel, 10 strains of E. coli O157:H7 were isolated from fecal samples of 383 diarrhea patients from the same region. Most importantly, using pulsed field gel electrophoresis (PFGE) of chromosomal DNA restriction fragments and PCR method, we found that the PFGE pattern and virulence genes of beetle isolates were identical to those of the human isolates, such as Shiga-toxins (stx) and enterohemorrhagic Escherichia coli hemolysin A (EHEC-hlyA). Therefore, dung beetle might acquire pathogenic E. coli O157:H7 through contact with feces of domestic animals.

Detection and quantification of Escherichia coli O157:H7 in environmental samples by real-time PCR

AIMS

To apply the real-time Polymerase chain reaction (PCR) method to detect and quantify Escherichia coli O157:H7 in soil, manure, faeces and dairy waste washwater.

METHODS AND RESULTS

Soil samples were spiked with E. coli O157:H7 and subjected to a single enrichment step prior to multiplex PCR. Other environmental samples suspected of harbouring E.coli O157:H7 were also analysed. The sensitivity of the primers was confirmed with DNA from E.coli O157:H7 strain 3081 spiked into soil by multiplex PCR assay. A linear relationship was measured between the fluorescence threshold cycle (C T ) value and colony counts (CFU ml(-1)) in spiked soil and other environmental samples. The detection limit for E.coli O157:H7 in the real-time PCR assay was 3.5 x 10(3) CFU ml(-1) in pure culture and 2.6 x 10(4) CFU g(-1) in the environmental samples. Use of a 16-h enrichment step for spiked samples enabled detection of <10 CFU g(-1) soil. E. coli colony counts as determined by the real-time PCR assay, were in the range of 2.0 x 10(2) to 6.0 x 10(5) CFU PCR (-1) in manure, faeces and waste washwater.

CONCLUSIONS

The real-time PCR-based assay enabled sensitive and rapid quantification of E. coli O157:H7 in soil and other environmental samples.

SIGNIFICANCE AND IMPACT OF THE STUDY

The ability to quantitatively determine cell counts of E.coli O157:H7 in large numbers of environmental samples, represents considerable advancement in the area of pathogen quantification for risk assessment and transport studies.

Analysis of molecular epidemiology of Chilean Salmonella enterica serotype enteritidis isolates by pulsed-field gel electrophoresis and bacteriophage typing

Human Salmonella enterica serotype Enteritidis infections emerged in Chile in 1994. S. enterica serotype Enteritidis phage type 1 isolates predominated in the north, and phage type 4 isolates predominated in the central and southern regions. A study was planned to characterize this epidemic using the best discriminatory typing technique. Research involved 441 S. enterica serotype Enteritidis isolates, including clinical preepidemic samples (n = 74; 1975 to 1993) and epidemic (n = 199), food (n = 72), poultry (n = 57), and some Latin American (n = 39) isolates. The best method was selected based on a sample of preepidemic isolates, analyzing the discriminatory power (DP) obtained by phage typing and randomly amplified polymorphic DNA and pulsed-field gel electophoresis (PFGE) analysis. The highest DP was associated with BlnI PFGE-bacteriophage typing analysis (0.993). A total of 38 BlnI patterns (B patterns) were identified before the epidemic period, 19 since 1994, and only 4 in both periods. Two major clusters were identified by phylogenetic analysis, and the predominant B patterns clustered in the same branch. Combined analysis revealed that specific B pattern-phage type combinations (subtypes) disappeared before 1994, that different genotypes associated with S. enterica serotype Enteritidis phage type 4 had been observed since 1988, and that strain diversity increased before the expansion of S. enterica serotype Enteritidis in 1994. Predominant subtype B3-phage type 4 was associated with the central and southern regions, and subtype B38-phage type 1 was associated with the north (P < 0.0001). Food and poultry isolates matched the predominant S. enterica serotype Enteritidis subtypes, but isolates identified in neighboring countries (Peru and Bolivia) did not match S. enterica serotype Enteritidis subtypes identified in the north of Chile. The results of this work demonstrate that genetic diversity, replacement, and expansion of specific S. enterica serotype Enteritidis subtypes were associated with epidemic changes.

Short and long term mortality associated with foodborne bacterial gastrointestinal infections: registry based study

OBJECTIVES

To determine the excess mortality associated with infections with Salmonella, Campylobacter, Yersinia enterocolitica, and Shigella and to examine the effect of pre-existing illness.

DESIGN

Registry based, matched cohort study.

SETTING

Denmark.

PARTICIPANTS

48 857 people with gastrointestinal infections plus 487 138 controls from the general population.

MAIN OUTCOME MEASURE

One year mortality among patients with gastrointestinal infections compared with controls after adjustment for comorbidity.

RESULTS

1071 (2.2%) people with gastrointestinal infections died within one year after infection compared with 3636 (0.7%) controls. The relative mortality within one year was 3.1 times higher in patients than in controls. The relative mortality within 30 days of infection was high in all four bacterial groups. Furthermore, there was excess mortality one to six months after infection with Yersinia enterocolitica (relative risk 2.53, 95% confidence interval 1.38 to 4.62) and from six months to one year after infection with Campylobacter (1.35, 1.02 to 1.80) and Salmonella (1.53, 1.31 to 1.79).

CONCLUSIONS

Infections with all these bacteria were associated with an increased short term risk of death, even after pre-existing illnesses were taken into account. Salmonella, Campylobacter, and Yersinia enterocolitica infections were also associated with increased long term mortality.

Pathogens and manure management systems: a review

There has been an increasing concern about the effects of pathogens that are present in animal manure on humanand animal health. In recent years, outbreaks of food-borne diseases associated with the consumption of animal products havereceived much attention from the media in North America and Europe, leading to increased consumer concerns about the safety of their food supply. The health risks associated with animal operations depend on various factors. The most important ones appear to be related to the animal species being reared and the concentration of pathogenic microorganisms in animal manure. The ability of the pathogens to survive for long periods and through treatment to remain infective in the environment until ingested by human or animal host is an added concern. On the other hand, the role of livestock in most waterborne bacterial outbreaks has often been difficult to clarify since both humans and various wildlife species can shed the same microorganisms and thereby serve as sources of infection. This paper summarizes existing information on the main microbial pathogens present in livestock wastes, and discusses the impact of livestock wastes and agricultural drainage on microbiological quality of water, as well as available management and treatment technologies to minimize the prevalence of pathogens in animal wastes. Despite the fact that most disease outbreaks have been associated with food poisoning by cross-contamination during meat or milk processing and during finished product storage this review shows that a number of best management practices and technical solutions have been developed in the last few years that can be effective tools in minimizing the spread of pathogens from livestock operations in the environment.

Characterization of antimicrobial resistance among Escherichia coli O111 isolates of animal and human origin

Fifty isolates of Escherichia coli serogroup O111 recovered from humans and various animal species over a 24-year period (1976-1999) were examined for typical virulence-associated factors and susceptibilities to antimicrobials of human and veterinary significance. Nine H (flagellar) types were identified including nonmotile (n = 24), 32 (n = 12), negative (n = 5), and 56 (n = 3). Thirty-five (70%) isolates possessed at least one Shiga-toxin-producing E. coli (STEC)-associated virulence determinants (eae, stxl, stx2, hlyA) via PCR analysis. Of these 35 isolates, 20 possessed eae, stxl, and hlyA genes, whereas three isolates possessed eae, stxl, stx2, and hylA genes. Multiple antibiotic resistance was observed in 70% of the 50 E. coli O111 isolates. The majority of isolates displayed resistance to streptomycin, sulfamethoxazole, tetracycline, and kanamycin. Bacterial resistance to ampicillin, gentamicin, chloramphenicol, trimethoprim and apramycin was also observed. Integrons were identified in 23 (46%) of the E. coli isolates assayed, with a 1-kb amplicon being most frequently observed. DNA sequencing of these integrons revealed the presence of the aadA gene, encoding resistance to streptomycin. Two integrons of 1.5 and 2 kb contained the aadA2 and either dfrI or dfrXII genes, encoding resistance to streptomycin and trimethoprim, respectively. Integrons were also identified from isolates dating back to 1982. Isolates were further genetically characterized via ribotyping, which identified 15 distinct ribogroups, with 62% of isolates clustering into four major ribogroups. Certain riboprint patterns from different animal species, including humans, were observed in isolates spanning the 24-year collection period, suggesting the dissemination of specialized pathogenic O111 clones.

Green-leaf-derived C6-aroma compounds with potent antibacterial action that act on both Gram-negative and Gram-positive bacteria

All eight C6-aliphatic alcohol and aldehyde compounds in naturally occurring green leaves showed bacteriostatic effects against Staphylococcus aureus IFO 12732, methicillin-resistant S. aureus, Escherichia coli IFO 3301, E. coli O157:H7, and Salmonella enteritidis, with bacteriostatic activities of less than 12.5 microg mL(-1). In this study, the susceptibility of Gram-positive bacteria tested was observed to be greater than that of Gram-negative bacteria. The bactericidal action of the aldehyde compounds was found to be much stronger than that of the alcohol compounds under both liquid and gaseous conditions. The most effective compound was (3E)-hexenal at concentrations of 0.1 and 1 microg mL(-1), which killed 2.1 x 10(5) cfu mL(-1) of S. aureus IFO 12732 and 1.4 x 10(5) cfu mL(-1) of E. coli IFO 3301, respectively, by direct contact with the compound. Lethality of (3E)-hexenal against S. aureus IFO 12732 and E. coli IFO 3301 was also observed as a result of gaseous contact at concentrations of 3 and 30 microg mL(-1), respectively. The bactericidal effects of 30 microg mL(-1) (3E)-hexenal were thoroughly maintained throughout periods of 2 days and 1 day against S. aureus IFO 12732 and E. coli IFO 3301, respectively, by a complex formation with alpha-cyclodextrin.

A emergência das doenças emergentes e as doenças infecciosas emergentes e reemergentes no Brasil

O artigo discute a emergência do conceito de doenças infecciosas emergentes e reemergentes. Postula-se que o conceito surge frente às limitações da teoria da transição epidemiológica em explicar as tendências recentes da morbidade e mortalidade. São discutidas as bases da teoria da transição epidemiológica e as razões de sua superação. Em seguida, são apresentados o conceito de doenças emergentes e reemergentes, os fatores relacionados à emergência das doenças infecciosas e as principais ocorrências no Brasil. Por fim, são abordados os desafios colocados pela emergência e reemergência das doenças infecciosas, e propostas para o seu enfrentamento.

An outbreak of febrile gastroenteritis associated with delicatessen meat contaminated with Listeria monocytogenes

In June 2001, the Los Angeles County Department of Health Services/Public Health conducted a cohort study of an outbreak of acute febrile gastroenteritis among 16 of 44 healthy attendees of a catered party. The median age of the attendees who became ill was 15.5 years. Symptoms included body aches (in 88% of attendees), fever (81%), headache (81%), diarrhea (63%), and vomiting (56%). Illness was associated with ingestion of precooked, sliced turkey (P=.000004). Six stool specimens yielded Listeria monocytogenes. Leftover turkey yielded L. monocytogenes, 1.6x10(9) cfu/g. All isolates were serotype 1/2a and had matching molecular fingerprints. Clusters of suspect cases were identified among attendees at 2 other catered events, but no additional cases were confirmed. This is only the third reported outbreak of L. monocytogenes-associated gastroenteritis in the United States. In cases of febrile gastroenteritis for which routine cultures for enteric pathogens are negative, clinicians should suspect listeriosis and should consider asking laboratories to retain stool specimens to expedite testing for Listeria organisms.

Characterization of a novel intracellularly activated gene from Salmonella enterica serovar typhi

A Salmonella enterica serovar Typhi gene that is selectively up-regulated upon bacterial invasion of eukaryotic cells was characterized. The open reading frame encodes a 298-amino-acid hydrophobic polypeptide (30.8 kDa), which is predicted to be an integral membrane protein with nine membrane-spanning domains. The protein is closely related (87 to 94% reliability) to different transport and permease systems. Gene expression under laboratory conditions was relatively weak; however, sevenfold induction was observed in a high-osmolarity medium (300 mM NaCl). The growth pattern in a laboratory medium of a serovar Typhi strain Ty2 derivative containing a 735-bp in-frame deletion in this gene, named gaiA (for gene activated intracellularly), was not affected. In contrast, the mutant was partially impaired in intracellular survival in murine peritoneal macrophages, as well as in human monocyte-derived macrophages. However, in the case of human macrophages, this survival defect was modest and evident only at late infection times (24 h). Despite the distinct intracellular survival kinetics displayed in macrophages of different species, the gaiA null mutant was significantly affected in its potential to trigger apoptosis in both murine and human macrophages. Provision of the gaiA gene in trans resulted in complementation of these phenotypes. Interestingly, the absence of a functional gaiA gene caused a marked attenuation in the mouse mucin model, as shown by the increase (3 orders of magnitude) in the 50% lethal dose of the mutant strain over that of the parental strain Ty2 (P Collapse

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MESH Headings

• Amino Acid Sequence
• Animals
• Apoptosis
• Bacterial Proteins/genetics
• Bacterial Proteins/physiology
• Base Sequence
• DNA, Bacterial/genetics
• Gene Expression Regulation, Bacterial
• Genes, Bacterial
• Humans
• Macrophages/microbiology
• Macrophages/pathology
• Membrane Proteins/genetics
• Membrane Proteins/physiology
• Mice
• Molecular Sequence Data
• Mutation
• Salmonella Infections/etiology
• Salmonella Infections/microbiology
• Salmonella Infections/pathology
• Salmonella typhi/genetics
• Salmonella typhi/pathogenicity
• Virulence/genetics
• Virulence/physiology

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Affiliation(s)

Holger Basso Division of Microbiology, GBF-German Research Centre for Biotechnology, D-38124 Braunschweig, Germany
Faiza Rharbaoui
Lothar H Staendner
Eva Medina
Francisco García-Del Portillo
Carlos A Guzmán

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Predictive microbiology: providing a knowledge-based framework for change management

This contribution considers predictive microbiology in the context of the Food Micro 2002 theme, "Microbial adaptation to changing environments". To provide a reference point, the state of food microbiology knowledge in the mid-1970s is selected and from that time, the impact of social and demographic changes on microbial food safety is traced. A short chronology of the history of predictive microbiology provides context to discuss its relation to and interactions with hazard analysis critical control point (HACCP) and risk assessment. The need to take account of the implications of microbial adaptability and variable population responses is couched in terms of the dichotomy between classical versus quantal microbiology introduced by Bridson and Gould [Lett. Appl. Microbiol. 30 (2000) 95]. The role of population response patterns and models as guides to underlying physiological processes draws attention to the value of predictive models in development of novel methods of food preservation. It also draws attention to the paradox facing today's food industry that is required to balance the "clean, green" aspirations of consumers with the risk, to safety or shelf life, of removing traditional barriers to microbial development. This part of the discussion is dominated by consideration of models and responses that lead to stasis and inactivation of microbial populations. This highlights the consequence of change on predictive modelling where the need is now to develop interface and non-thermal death models to deal with pathogens that have low infective doses for general and/or susceptible populations in the context of minimal preservation treatments. The challenge is to demonstrate the validity of such models and to develop applications of benefit to the food industry and consumers as was achieved with growth models to predict shelf life and the hygienic equivalence of food processing operations.

Verotoxigenic Escherichia coli (VTEC): a major public health threat in Canada

BACKGROUND

Verotoxigenic Escherichia coli (VTEC) was first described in Canada during the 1980s as an emerging foodborne disease in association with morbidity and mortality in outbreaks of hemorrhagic colitis caused by E coli O157:H7.

OBJECTIVE

To describe the surveillance activities and epidemiological laboratory markers of VTEC that are used at the National Laboratory for Enteric Pathogens (NLEP) to investigate sporadic cases and outbreaks of E coli O157:H7 and non-O157 VTEC in Canada.

METHODS

Passive surveillance was conducted by obtaining data on laboratory confirmed cases of VTEC from the Provincial Laboratories of Public Health across Canada. The laboratory epidemiological markers generated for isolates of VTEC included biotyping, serotyping, phage typing, toxin detection and characterization, and molecular typing using pulsed-field gel electrophoresis.

RESULTS

Major outbreaks of VTEC O157:H7 disease have been associated with ground beef, unpasteurized apple juice, salami and untreated water. In 1999 and 2000, a total of 46 outbreaks of E coli O157:H7 disease were investigated. Among those, one outbreak was associated with contact at a petting zoo and a second with the consumption of salami. An outbreak in 2000 in Ontario was associated with water and resulted in more than 1000 cases of human illness, with six deaths. The NLEP has also identified more than 100 non-O157 VTEC serotypes from cattle and meat products. At least 23 VTEC serotypes found in humans were also identical to those found in cattle and meat products.

CONCLUSIONS

The laboratory-based information that is generated is used to define the incidence, sources of infection, risk factors, trends, distribution and transmission of VTEC to humans from food, water and animal sources. Prevention and control of outbreaks are high-priority health concerns.

Rapid and specific identification of Shiga toxin-producing Escherichia coli in faeces by multiplex PCR

AIMS

The object of this study was to develop a multiplex PCR system for rapid and specific identification of Shiga toxin-producing Escherichia coli (STEC) in faeces.

METHODS AND RESULTS

A multiplex PCR (mPCR) protocol was developed using a primer pair specific for genes that are involved in the biosynthesis of the O157 E. coli antigen, and primers that identify the sequences of Shiga toxin 1 and 2 (stx 1 and stx1) and the intimin protein (eaeA). The mPCR assay was used for amplification of STEC genes in bacteria directly (after enrichment) in faeces. The test was very sensitive and could detect between 9 and 1 bacterial cells per gram of faeces. The mPCR was used for the examination of 69 bovine faecal samples derived from healthy cattle. The results indicated that 62 x 3% of the samples were positive, generating at least one PCR amplicon of the expected size.

CONCLUSIONS

The method can be applied for rapid and specific identification of STEC bacteria in faecal samples, and for differentiation of their main virulence marker genes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The ability to sensitively detect Shiga toxin-producing E. coli directly in faeces within a short time represents a considerable advancement over more time-consuming and less sensitive methods for identification and characterization of STEC bacteria.

Foodborne illness: new developments concerning an old problem

Foodborne illnesses continue to cause substantial morbidity and mortality in the United States, primarily as gastroenteritis but occasionally as other syndromes as well. Most of these illnesses are caused by a variety of widely known infectious agents, principally viruses, and are probably the result of common mistakes in food handling in the home or in restaurants. The epidemiology of foodborne illness is evolving. Major changes in food production, distribution, and consumption have created opportunities for new pathogens to emerge and for old ones to reemerge, and the potential for widespread outbreaks is increasing. Antibiotic resistance in bacterial pathogens resulting from the widespread use of antimicrobial agents in animal husbandry is also an important concern. Clinicians must be aware of the changing epidemiology of foodborne illness to recognize and manage these conditions in the clinical setting. In addition, clinicians are critical in the reporting of recognized or suspected foodborne illness, so that public health authorities are able to investigate, understand, and ultimately better control them. A number of new techniques have been employed, and others under development will improve our ability to recognize and cope with foodborne diseases.

Diarrhea associated acute renal failure in a patient with Salmonella enteritidis sepsis

Salmonella enteritidis infection occurs primarily in animals and often results in self-limited gastroenteritis in accidental cross contamination in human. However, the acute renal failure could be a rare but serious complication of the S. enteritidis infection. We report one case of acute renal failure from severe dehydration caused by S. enteritidis food poisoning. The acute renal failure completely recovered after hydration and antibiotic treatment.

Mechanisms contributing to hypochlorous acid resistance of a Salmonella isolate from a poultry-processing plant

AIMS

We have recently reported the isolation of Salmonella that have acquired tolerance to hypochlorous acid (HOCl) (Mokgatla et al. 1998). The aim of this work was to investigate possible protective mechanisms involved in the increased tolerance to HOCl of a selected resistant strain.

METHODS AND RESULTS

One resistant (Salmonella 104) and one sensitive (Salmonella 81) isolate in exponential phase were exposed to HOCl at a final active concentration of 28 mg l(-1). Cultures were assayed for superoxide dismutase and catalase activity, as well as for four membrane-bound dehydrogenases (malate, lactate, glutamate and glucose-6-phosphate dehydrogenase). The degree of single-strand breaks in genomic DNA was analysed and lipopolysaccharide profiles determined. The resistant Salmonella isolate differed from the sensitive isolate in a number of ways. It responded within 10 min of exposure by producing catalase and decreasing the activity levels of four membrane-bound dehydrogenases. This combination would lead to lower levels of hydroxyl radicals and singlet oxygen, moieties thought to be integrally involved in the antibacterial action of HOCl. Furthermore, the resistant strain did not display the same degree of DNA damage as did the sensitive strain.

CONCLUSIONS

Strain 104 is believed to grow in the presence of 28 mg l(-1) HOCl by protecting itself against HOCl by decreasing the levels of species that could react with HOCl to generate toxic reactive oxygen radicals and by improved DNA damage repair mechanisms.

SIGNIFICANCE AND IMPACT OF THE STUDY

The occurrence of Salmonella able to grow in the presence of 28 mg l(-1) HOCl is of relevance to the food-processing and drinking water treatment industries as these strains would survive sanitation regimes.

Ecological factors influencing survival and growth of human pathogens on raw fruits and vegetables

Outbreaks of human infections associated with consumption of raw fruits and vegetables have occurred with increased frequency during the past decade. Factors contributing to this increase may include changes in agronomic and processing practices, an increase in per capita consumption of raw or minimally processed fruits and vegetables, increased international trade and distribution, and an increase in the number of immuno-compromised consumers. A general lack of efficacy of sanitizers in removing or killing pathogens on raw fruits and vegetables has been attributed, in part, to their inaccessibility to locations within structures and tissues that may harbor pathogens. Understanding the ecology of pathogens and naturally occurring microorganisms is essential before interventions for elimination or control of growth can be devised.

From farm to table to brain: foodborne pathogen infection and the potential role of the neuro-immune-endocrine system in neurotoxic sequelae

The American diet is among the safest in the world; however, diseases transmitted by foodborne pathogens (FBPs) still pose a public health hazard. FBPs are the second most frequent cause of all infectious illnesses in the United States. Numerous anecdotal and clinical reports have demonstrated that central nervous system inflammation, infection, and adverse neurological effects occur as complications of foodborne gastroenteritis. Only a few well-controlled clinical or experimental studies, however, have investigated the neuropathogenesis. The full nature and extent of neurological involvement in foodborne illness is therefore unclear. To our knowledge, this review and commentary is the first effort to comprehensively discuss the issue of FBP induced neurotoxicity. We suggest that much of this information supports the role of a theoretical model, the neuro-immune-endocrine system, in organizing and helping to explain the complex pathogenesis of FBP neurotoxicity.

Salmonella spp. shedding by alberta beef cattle and the detection of Salmonella spp. in ground beef

Breeder cows, cattle recently arrived at feedlots, and cattle about to be shipped for slaughter were tested for Salmonella spp. No Salmonella spp. were detected in fecal samples from breeding cows. Nineteen of 1,000 (1.9%) fecal samples from recently arrived feedlot cattle were positive for Salmonella spp. compared to only 2 of 1,000 (0.2%) fecal samples taken within 2 weeks of slaughter. The positive fecal samples were collected in 5 of 50 (10%) "recent arrival" pens tested and in 1 of 50 (2%) pens tested within 2 weeks of slaughter. The serotypes isolated were Salmonella Agona, Salmonella Enteritidis, Salmonella Typhimurium DT104, and Salmonella 4,5,12:i:-. Ground beef samples purchased from retail outlets throughout Alberta were processed for Salmonella spp. Thirteen of 1,002 (1.3%) samples were positive for Salmonella spp. The serotypes isolated from ground beef were Salmonella Anatum, Salmonella Heidelberg, Salmonella Montevideo, Salmonella Typhimurium, Salmonella Typhimurium var. Copenhagen, and Salmonella Rough-O:i:1,2. The antibiotic resistance and pulsed-field electrophoresis gel macrorestriction patterns of all isolates were compared.

Listeria monocytogenes: clinical and experimental update

Listeria monocytogenes, a small gram-positive bacillus, causes sepsis and meningitis in immunocompromised patients and a devastating maternal/fetal infection in pregnant women. Recent outbreaks demonstrated that L. monocytogenes can cause gastroenteritis in otherwise healthy individuals and more severe invasive disease in immunocompromised patients. Centralized processing in the food industry may be the cause of these large-scale listeriosis outbreaks. The mouse model of listeriosis, which was developed in the 1960s, has been extraordinarily useful for studying T cell-mediated immunity. Contrary to the original concept that macrophages are the principal effector cells in listeriosis, we found that immigrating neutrophils play the predominant role in early liver defenses. At later time points, CD8(+) T cells lyse infected hepatocytes by both perforin- and Fas-L/Fas--dependent mechanisms. Of interest, nonclassical major histocompatibility complex (MHC) class Ib--restricted cytolytic activity is expressed early during primary infection, whereas MHC class Ia--restricted activity is predominant through late primary and secondary infections.

Flow-injection electrospray ionization mass spectrometry of crude cell extracts for high-throughput bacterial identification

Flow-injection electrospray ionization mass spectrometry (FI-ESI-MS) of unfractionated cell-free extracts obtained from bacterial cells suspended in a solvent mixture was investigated as a rapid analytical method for reproducible, high-throughput bacterial identification. Five bacterial strains (two Escherichia coli, two Bacillus spp. and one Brevibacillus laterosporus) were studied in this investigation. Axenically grown bacterial cells were suspended in an acidic organic solvent and the cell-free extract was sequentially injected into a solvent flow stream that was sprayed into the ionization chamber of the ESI-MS. The spectra produced contained reproducible information, which was useful for discriminating between the bacteria. Tandem mass spectrometry was used to characterize further the peaks, and at least three classes of macromolecules, namely phospholipids, glycolipids, and proteins, were found to contribute most to the spectral information. Bacterial extracts stored under different conditions gave very similar mass spectra for each of the five bacterial strains, indicating that the extracts were stable even at room temperature for up to 24 h, with no loss of information content, which has obvious implications for automated high-throughput analysis. An analysis of the components of the extracting solvent mixture and their effects on the spectral information showed that acetonitrile contributes most significantly to the extraction process and hence to the information content of the spectra.

Inactivation of Escherichia coli O157:H7, Salmonella enteritidis, and Listeria monocytogenes on apples, oranges, and tomatoes by lactic acid with hydrogen peroxide

The objective of this study was to develop a practical and effective method for inactivating or substantially reducing Escherichia coli O157:H7, Salmonella Enteritidis, and Listeria monocytogenes on apples, oranges, and tomatoes. Apples, oranges, and tomatoes were spot-inoculated with five-strain mixtures of E. coli O157:H7, Salmonella Enteritidis, and L. monocytogenes near the stem end and were submerged in sterile deionized water containing 1.5% lactic acid plus 1.5% hydrogen peroxide for 15 min at 40 degrees C. Inoculated samples treated with sterile deionized water at the same temperature and for the same duration served as controls. The bacterial pathogens on fruits subjected to the chemical treatment were reduced by >5.0 log10 CFU per fruit, whereas washing in deionized water decreased the pathogens by only 1.5 to 2.0 log10 CFU per fruit. Furthermore, substantial populations of the pathogens survived in the control wash water, whereas no E. coli O157:H7, Salmonella Enteritidis, or L. monocytogenes cells were detected in the chemical treatment solution. The sensory and qualitative characteristics of apples treated with the chemical wash solution were not adversely affected by the treatment. It was found that the treatment developed in this study could effectively be used to kill E. coli O157:H7, Salmonella Enteritidis, and L. monocytogenes on apples, oranges, and tomatoes at the processing or packaging level.

Enterotoxigenic potential of Staphylococcus intermedius

Staphylococcal food poisoning (SFP) caused by enterotoxigenic staphylococci is one of the main food-borne diseases. In contrast to Staphylococcus aureus, a systematic screening for the enterotoxins has not yet been performed on the genomic level for the coagulase-positive species S. intermedius. Therefore, the enterotoxigenic potential of 281 different veterinary (canine, n = 247; equine, n = 23; feline, n = 9; other, n = 2) and 11 human isolates of S. intermedius was tested by using a multiplex PCR DNA-enzyme immunoassay system targeting the staphylococcal enterotoxin genes sea, seb, sec, sed, and see. Molecular results were compared by in vitro testing of enterotoxin production by two immunoassays. A total of 33 (11.3%) S. intermedius isolates, including 31 (12.6%) canine isolates, 1 equine isolate, and 1 human isolate, tested positive for the sec gene. In vitro production of the respective enterotoxins was detected in 30 (90.9%) of these isolates by using immunological tests. In contrast, none of 65 veterinary specimen-derived isolates additionally tested and comprising 13 (sub)species of coagulase-negative staphylococci were found to be enterotoxigenic. This study shows on both molecular and immunological levels that a substantial number of S. intermedius isolates harbor the potential for enterotoxin production. Since evidence for noninvasive zoonotic transmission of S. intermedius from animal hosts to humans has been documented, an enterotoxigenic role of this microorganism in SFP via contamination of food products may be assumed.

Salmonella DNA adenine methylase mutants elicit protective immune responses to homologous and heterologous serovars in chickens

Salmonella DNA adenine methylase (Dam) mutants that lack or overproduce Dam are highly attenuated for virulence in mice and confer protection against murine typhoid fever. To determine whether vaccines based on Dam are efficacious in poultry, a Salmonella Dam(-) vaccine was evaluated in the protection of chicken broilers against oral challenge with homologous and heterologous Salmonella serovars. A Salmonella enterica serovar Typhimurium Dam(-) vaccine strain was attenuated for virulence in day-of-hatch chicks more than 100,000-fold. Vaccination of chicks elicited cross-protective immune responses, as evidenced by reduced colonization (10- to 10,000-fold) of the gastrointestinal tract (ileum, cecum, and feces) and visceral organs (bursa and spleen) after challenge with homologous (Typhimurium F98) and heterologous (Enteritidis 4973 and S. enterica O6,14,24: e,h-monophasic) Salmonella serovars that are implicated in Salmonella infection of poultry. The protection conferred was observed for the organ or the maximum CFU/tissue/bird as a unit of analysis, suggesting that Dam mutant strains may serve as the basis for the development of efficacious poultry vaccines for the containment of Salmonella.

Gastrointestinal infections

Advances in public health have reduced the risk of contracting certain enteric diseases, but many remain, and new pathogens have emerged and/or recently have been discovered. The pathogenic agents are varied and consist of a variety of bacteria and select viruses and parasites. Selected use of microbiologic assays to detect these pathogens is encouraged. When tests are ordered non-judiciously, costs rapidly accrue. The age of the patient, time of year, travel history, and clinical presentation all provide clues to the etiologic agent. Microbiologic assays should be used judiciously to confirm or exclude the likely infectious agents.

Combination of immunomagnetic separation and polymerase chain reaction for the simultaneous detection of Listeria monocytogenes and Salmonella spp. in food samples

A method that combined the immunomagnetic separation (IMS) technique and the multiplex polymerase chain reaction (PCR) method (i.e., the IMS-mPCR method) was developed for simultaneous detection of Listreria monocytogenes and Salmonella spp. in food samples. When only the multiplex PCR method was used, it was found that if cell numbers of each of the two target organisms (L. monocytogenes and Salmonella spp.) were above the detection limit, but differed by more than 2 logs-e.g., n x 10(7) to n x 10(4) or n x 10(6) to n x 10(3)--the organism presenting the lower numbers might go undetected. Following the enrichment step with universal preenrichment (UP) broth, if an IMS method using equal quantities of anti-Listeria and anti-Salmonella immunomagnetic beads was performed prior to PCR, both pathogens could be detected unambiguously. Such results could be obtained for target organisms in food samples, such as milk, dairy, and meat products, if similar enrichment and IMS steps were performed prior to PCR.

Pseudomonas fluorescens as a potential pathogen: adherence to nerve cells

In order to determine the infectious potential of the psychrotrophic bacterium Pseudomonas fluorescens, a species closely related to the opportunistic pathogen P. aeruginosa, we investigated the binding activity of this bacterium on primary cultures of rat neonate cortical neurons and glial cells, adrenal paraneurons and NG108-15 neuroblastoma cells. Incubated at concentrations of 10(6) and 10(8) CFU/mL, P. fluorescens MF37 exhibited a high binding activity on neurons in the same range as that of P. aeruginosa PAO1. A significant, but lower, adherence of P. fluorescens was also detected on glial cells and adrenal paraneurons. In contrast, when P. fluorescens MF37 or P. aeruginosa PAO1 were incubated with neuroblastoma cells, no binding was observed. In neurons, the association of P. fluorescens with the plasma membrane occurred both on neurites and cell body. Leakage of the cytoplasmic content was frequently noted. Studies performed using the fluorescent probe Hoechst 33258 revealed that in 10% of neurons, P. fluorescens induced the appearance of densely stained clusters of DNA that was typical of an early step of apoptosis. In glial cells exposed to P. fluorescens, marked changes in the morphology of the nucleus, including fragmentation into lobular structures and aggregation of DNA, were also reminiscent of the existence of a possible apoptotic mechanism. Taken together, these results reveal that P. fluorescens can bind to nerve cells and affect their physiology and, in agreement with recent clinical observations, suggest that P. fluorescens could behave as a pathogen.

Survival of salmonellae on and in tomato plants from the time of inoculation at flowering and early stages of fruit development through fruit ripening

The fate of salmonellae applied to tomato plants was investigated. Five Salmonella serotypes were used to inoculate tomato plants before and after fruits set, either by injecting stems with inoculum or brushing flowers with it. Ripe tomato fruits were subjected to microbiological analysis. Peptone wash water, homogenates of stem scar tissues, and homogenates of fruit pulp were serially diluted and plated on bismuth sulfite agar before and after enrichment. Presumptive Salmonella colonies were confirmed by serological tests, PCR assay using HILA2 primers, and enterobacterial repetitive intergenic consensus PCR. Of 30 tomatoes harvested from inoculated plants, 11 (37%) were positive for Salmonella. Of the Salmonella-positive tomatoes, 43 and 40%, respectively, were from plants receiving stem inoculation before and after flower set. Two of eight tomatoes produced from inoculated flowers contained Salmonella. Higher percentages of surface (82%) and stem scar tissue (73%) samples, compared to pulp of Salmonella-positive tomatoes (55%), harbored the pathogen. Of the five serotypes in the inoculum, Montevideo was the most persistent, being isolated from tomatoes 49 days after inoculation, and Poona was the most dominant, being present in 5 of 11 Salmonella-positive tomatoes. Results suggest that Salmonella cells survive in or on tomato fruits from the time of inoculation at flowering through fruit ripening. Tomato stems and flowers are possible sites at which Salmonella may attach and remain viable during fruit development, thus serving as routes or reservoirs for contaminating ripened fruit.

Efficacy of commonly used disinfectants for the inactivation of calicivirus on strawberry, lettuce, and a food-contact surface

Norwalk and Norwalk-like viruses (NLVs) are important causes of foodborne gastroenteritis in restaurant-related outbreaks. Efficacy of common disinfection methods against these viruses on food-contact surfaces and fresh produce is not known partially because of their nonculturability. Seven commercial disinfectants for food-contact surfaces and three sanitizers for fruits and vegetables were tested against cultivable feline calicivirus (FCV). Disks of stainless steel, strawberry, and lettuce were contaminated with known amounts of FCV. The disinfectants were applied at one, two, and four times the manufacturer's recommended concentrations for contact times of 1 and 10 min. The action of disinfectant was stopped by dilution, and the number of surviving FCVs was determined by titration in cell cultures. An agent was considered effective if it reduced the virus titer by at least 3 log10 from an initial level of 10(7) 50% tissue culture infective dose. None of the disinfectants was effective when used at the manufacturer's recommended concentration for 10 min. Phenolic compounds, when used at two to four times the recommended concentration, completely inactivated FCV on contact surfaces. A combination of quaternary ammonium compound and sodium carbonate was effective on contact surfaces at twice the recommended concentration. Rinsing of produce with water alone reduced virus titer by 2 log10. On artificially contaminated strawberry and lettuce, peroxyacetic acid and hydrogen peroxide was the only effective formulation when used at four times the manufacturers' recommended concentration for 10 min. These findings suggest that FCV and perhaps NLVs are very resistant to commercial disinfectants. However, phenolic compounds at two to four times their recommended concentrations appear to be effective at decontaminating environmental surfaces and may help control foodborne outbreaks of calicivirus in restaurants.

Discrimination of aerobic endospore-forming bacteria via electrospray-lonization mass spectrometry of whole cell suspensions

Direct injection electrospray ionization mass spectrometry (ESI-MS) without prior analyte separation was investigated for the analysis of whole cell suspensions of bacteria. Thirty-six strains of aerobic endospore-forming bacteria, consisting of six Bacillus species and one Brevibacillus species, were studied

Effect of different levels of beef bacterial microflora on the growth and survival of Escherichia coli O157:H7 on beef carcass tissue

The influence of various levels of endogenous beef bacterial microflora on the growth and survival of Escherichia coli O157:H7 on bovine carcass surface tissue was investigated. Bacterial beef microflora inoculum was prepared by enriching and harvesting bacteria from prerigor lean bovine carcass tissue (BCT) and was inoculated onto UV-irradiated prerigor BCT at initial levels of 10(5), 10(4), 10(3), and <10(3) CFU/cm2. Additional control BCT was inoculated with sterile H2O. E. coli O157:H7 was inoculated onto all tissues at an initial level of 10(2) CFU/cm2. Following a 48-h incubation at 4 degrees C, BCT was incubated up to 14 days at 4 or 12 degrees C, either aerobically or vacuum packaged. Regardless of the microflora level, there was no substantial growth of E. coli O157:H7 on BCT during storage at 4 degrees C under either aerobic or vacuum-packaged conditions. Instead, viable cell numbers at 4 degrees C remained constant, with no reduction in numbers associated with the different beef microflora levels. E. coli O157:H7 grew on all BCT stored at 12 degrees C, regardless of microflora inoculation treatment, reaching higher populations on aerobic samples than on vacuum-packaged samples in 10 days. However, the presence of the beef microflora did appear to delay the onset of growth or slow the growth of the pathogen, and E. coli O157:H7 counts on BCT without added microflora were generally higher following 7 to 10 days of 12 degrees C storage than those counts on BCT inoculated with beef microflora. These data demonstrate the importance of temperature control during meat handling and storage to prevent the outgrowth of this pathogen and indicate that proper sanitation and processing practices that prevent and reduce contamination of carcasses with E. coli O157:H7 are essential, regardless of background microflora levels.

Microarray analysis of microbial virulence factors

Hybridization with oligonucleotide microchips (microarrays) was used for discrimination among strains of Escherichia coli and other pathogenic enteric bacteria harboring various virulence factors. Oligonucleotide microchips are miniature arrays of gene-specific oligonucleotide probes immobilized on a glass surface. The combination of this technique with the amplification of genetic material by PCR is a powerful tool for the detection of and simultaneous discrimination among food-borne human pathogens. The presence of six genes (eaeA, slt-I, slt-II, fliC, rfbE, and ipaH) encoding bacterial antigenic determinants and virulence factors of bacterial strains was monitored by multiplex PCR followed by hybridization of the denatured PCR product to the gene-specific oligonucleotides on the microchip. The assay was able to detect these virulence factors in 15 Salmonella, Shigella, and E. coli strains. The results of the chip analysis were confirmed by hybridization of radiolabeled gene-specific probes to genomic DNA from bacterial colonies. In contrast, gel electrophoretic analysis of the multiplex PCR products used for the microarray analysis produced ambiguous results due to the presence of unexpected and uncharacterized bands. Our results suggest that microarray analysis of microbial virulence factors might be very useful for automated identification and characterization of bacterial pathogens.

The future impact of societal and cultural factors on parasitic disease -- some emerging issues

A variety of societal and cultural factors will increase host exposure or susceptibility to infectious agents, particularly parasites. Such factors have already had a major impact on the emergence of infectious diseases and the situation is likely to worsen further as we enter the new millennium. The changes that are enhancing the spread and transmission of parasitic diseases, as well as those which are adversely affecting host responsiveness, are examined with reference to specific parasites.

The emerging nosocomial pathogens Cryptosporidium, Escherichia coli O157:H7, Helicobacter pylori, and hepatitis C: epidemiology, environmental survival, efficacy of disinfection, and control measures

New and emerging infectious diseases pose a threat to public health and may be responsible for nosocomial outbreaks. Cryptosporidium parvum and Escherichia coli are gastrointestinal pathogens that have caused nosocomial infections via person-to-person transmission, environmental contamination, or contaminated water or food. Helicobacter pylori has been transmitted via inadequately disinfected endoscopes. Finally, hepatitis C may be acquired by healthcare personnel by percutaneous or mucous membrane exposure to blood or between patients by use of contaminated blood products or via environmental contamination. Rigorous adherence to Standard Precautions, Contact Precautions for patients with infectious diarrhea, disinfection of environmental surfaces, and appropriate disinfection of endoscopes are adequate to prevent nosocomial acquisition of these pathogens.

Standardized laboratory-scale preparation of mayonnaise containing low levels of Salmonella enterica serovar Enteritidis

Salmonella enterica serovar Enteritidis PT4 and PT6 are associated with food poisoning outbreaks and are often found in food only in low concentrations. In this study a reproducible laboratory-scale procedure for preparation of mayonnaise is presented. The mayonnaise that simulates a naturally low-level contaminated product can be used for validation of new methods and is also suitable to study the behavior of low numbers of food pathogenic spoilage microorganisms in a food environment. During processing, liquid egg was artificially contaminated with low levels of S. enterica serovar Enteritidis that resulted in levels of 1 to 3 log10 CFU/g in the final mayonnaise. Cells of S. enterica serovar Enteritidis had increased stability in the mayonnaise when they were subjected to low pH in two stages, first to pH 5.8 and afterward to pH 4.5 before addition to the mayonnaise. The pH of the mayonnaise was between 4.2 to 4.5 and remained stable over the storage period. Low-level S. enterica serovar Enteritidis remained stable in artificially contaminated mayonnaise for 4 weeks at 4 degrees C.

Food safety education: what should we be teaching to consumers?

Food safety education is most effective when messages are targeted toward changing behaviors most likely to result in foodborne illness. The five major control factors for pathogens are personal hygiene, adequate cooking, avoiding cross-contamination, keeping food at safe temperatures, and avoiding foods from unsafe sources. Pathogens associated with poor personal hygiene have the highest incidence and costs. Inadequate cooking and cross-contamination have lower incidence. Keeping food at safe temperatures and unsafe food sources have the lowest incidence, although costs per case are sometimes very high. We recommend that consumer food safety educators primarily focus on hand washing, adequate cooking, and avoiding cross-contamination. Secondary messages should focus on keeping food at safe temperatures and avoiding food from an unsafe source. Evaluation tools are needed to evaluate self-reported behavior changes. The evaluation questions must focus on salient behaviors that are most likely to result in foodborne illnesses and must withstand rigorous standards of reliability and validity.

Analytical chromatography for recovery of small amounts of staphylococcal enterotoxins from food

Sample preparation is an important element in the detection of toxins in food samples. In this work, a simple analytical sample preparation method for recovery of small amount of staphylococcal enterotoxin B (SEB) and staphylococcal enterotoxin A (SEA) in food samples was developed. Cation exchanger carboxymethylcellulose (CM) was used for small-scale batch chromatography isolation of SEB from infant formula and from mushrooms spiked with SEB. The resulting materials were analyzed for SEB by Western immunoblotting. Nearly all of the extraneous substances in the sample were removed by this procedure with no significant loss of the toxin. Using this method, even small amounts of SE (0.75 ng/g) can be recovered and immunologically analyzed by Western blotting or by ELISA with a very low background. Because this method is effective, rapid, simple and inexpensive, it has the potential to be a general method for the preparation of samples used for analysis of SEs.

Perceived etiology of foodborne illness among public health personnel

Few data exist about perceptions regarding the etiology of foodborne illness. Among public health staff throughout Tennessee, the three pathogens most commonly believed to cause foodborne illness in the United States actually account for only 12% of disease. Fewer than 3% of respondents correctly identified the leading cause of foodborne illness.

PCR detection of Salmonella enterica serotype Montevideo in and on raw tomatoes using primers derived from hilA

Salmonellae have been some of the most frequently reported etiological agents in fresh-produce-associated outbreaks of human infections in recent years. PCR assays using four innovative pairs of primers derived from hilA and sirA, positive regulators of Salmonella invasive genes, were developed to identify Salmonella enterica serotype Montevideo on and in tomatoes. Based on examination of 83 Salmonella strains and 22 non-Salmonella strains, we concluded that a pair of hilA primers detects Salmonella specifically. The detection limits of the PCR assay were 10(1) and 10(0) CFU/ml after enrichment at 37 degrees C for 6 and 9 h, respectively. When the assay was validated by detecting S. enterica serotype Montevideo in and on artificially inoculated tomatoes, 10(2) and 10(1) CFU/g were detected, respectively, after enrichment for 6 h at 37 degrees C. Our results suggest that the hilA-based PCR assay is sensitive and specific, and can be used for rapid detection of Salmonellae in or on fresh produce.

Invasiveness in chickens, stress resistance and RpoS status of wild-type Salmonella enterica subsp. enterica serovar typhimurium definitive type 104 and serovar enteritidis phage type 4 strains

The heat and acid resistance and the ability to survive airdrying on commonly used kitchen surfaces were assessed for clinical and environmental strains of Salmonella enterica subsp. enterica serovar Typhimurium, definitive type (DT) 104. Three out of thirty-eight strains of DT 104 were found to be more sensitive in stationary phase to the stresses examined than the other strains. This compares to a previous study by the authors which showed that seven out of forty serovar Enteritidis phage type (PT) 4 strains were more sensitive. RpoS activity was examined indirectly in selected strains of DT 104 and PT 4. In those with normal stress resistance a 100-fold induction of an RpoS-dependent spvR/A:'::luxCDABE fusion was observed upon entry into stationary phase. The sensitive strains examined showed either no induction or a reduced level of spvR/A:'::luxCDABE expression. The rpoS gene was sequenced from these strains and three were found to harbour mutations including one deletion, one base-pair substitution resulting in a nonsense codon, and one insertion causing a frameshift resulting in an early stop codon. Strains with negligible or reduced spvR/A:'::luxCDABE expression had low stress resistance. All strains of DT 104 could be recovered from liver and spleen tissues of infected hens 14 d post-infection, but one with no induction of spvR/A:'::luxCDABE expression was significantly less likely to be recovered from chicken reproductive tissues, liver or spleen than the majority of other strains, including one with reduced spvR/A:'::luxCDABE expression. This work has demonstrated that clinical and environmental strains of DT 104 and PT 4 not infrequently harbour mutations in the rpoS allele. It is possible that the rpoS mutations may have occurred during the initial isolation of the strains. The ability of a strain to cause infection, however, also depends on factors such as host susceptibility and dose.

Effect of delayed placement on the incidence of Campylobacter jejuni in broiler chickens

An experiment was conducted with broiler chickens to evaluate the effect of delayed placement on reused litter and the isolation of Campylobacter jejuni. The experiment also assessed the presence of C. jejuni in the crop following feed withdrawal periods in cages vs floor environments. Trial 1 utilized 320 female broiler chicks obtained from a commercial hatchery. The chicks were randomly placed into the following experimental groups that were replicated four times with 20 chicks per pen: 1) 0-h, 2) 24-h, 3) 48-h, and 4) 72-h delayed placement. Fecal samples were collected via the cloaca at 7, 14, 21, and 28 d of age; enriched in Bolton broth; and plated onto BBL agar. Campylobacter jejuni was isolated at 1 wk of age in the 48- and 72-h experimental groups but did not differ significantly from the others. Sampling results at 14 d of age showed that 63, 68, 73, and 80% of chicks were positive for the 0-, 24-, 48-, and 72-h treatments, respectively. At 28 d of age, 100% of all chicks sampled tested positive. In Trial 2, 60 market age broilers were evaluated for the presence of C. jejuni in the crop by subjecting them to 0-, 4-, 8-, 12-, and 16-h feed withdrawal times on litter or in wire cages. Crops were collected aseptically from the broilers, stomached, enriched in Bolton broth, and then plated on BBL agar. There were no significant (P < 0.05) differences between cage and floor withdrawal times for the presence of C. jejuni in the crop samples of broilers; however, there were significant differences in the length of withdrawal on the presence of C. jejuni. Collectively, these results suggested that the isolation of C. jejuni occurred earlier in broilers that were subjected to delayed placement on reused litter and that extended feed withdrawal times in cages or on litter may increase the possibility that the crop of broilers may contain a higher isolation rate of C. jejuni.

Evaluation of the Alexon-trend ProSpecT Campylobacter microplate assay

We evaluated stool specimens known to contain or be free of Campylobacter by traditional culture, using the ProSpecT Campylobacter microplate assay (Alexon-Trend, Ramsey, Minn.). This rapid enzyme immunoassay for the detection of Campylobacter-specific antigens demonstrated 96% sensitivity and 99% specificity and is an acceptable alternative method of Campylobacter detection.