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The enteric bacterium Salmonella enterica serovar Typhimurium is a pathogen that is highly adapted for both intracellular and extracellular survival in a range of oxic and anoxic environments. The cytotoxic radical nitric oxide (NO) is encountered in many of these environments. Protection against NO may involve reductive detoxification in low-oxygen environments, and three enzymes, flavorubredoxin (NorV), flavohaemoglobin (HmpA) and cytochrome c nitrite reductase (NrfA), have been shown to reduce NO in vitro. In this work we determined the role of these three enzymes in NO detoxification by Salmonella by assessing the effects of all eight possible combinations of norV, hmpA and nrfA single, double and triple mutations. The mutant strains were cultured and exposed to NO following either glucose fermentation (when nitrite reductase activity is low), or anaerobic respiration (when nitrite reductase activity is high). Wild-type cultures were more sensitive to the addition of a pulse of NO when grown under fermentative conditions compared with anaerobic respiratory conditions. Analysis of the mutant strains suggested an important additive rote for both NorV and NrfA in both environments, since the norV nrfA mutant could not grow after NO addition. The results also suggested a minor role for HmpA in anaerobic detoxification of NO under the two growth conditions, and a larger role for HmpA in aerobic NO detoxification was confirmed. Activity assays and measurements of NO consumption showed that increased nitrite reductase activity correlates with an elevated capacity for NO reduction by intact cells. Taken together, the results reveal a combined role for NorV and NrfA in NO detoxification under anaerobic conditions, and highlight the influence that growth conditions have on the sensitivity to NO of this pathogenic bacterium.

Pathogen amplification and dissemination into the environment through manure spreading on agriculture land is facilitated by the epidemic spread of 'Salmonella enterica' serovar Newport in dairy cattle. A study was conducted to uncover the survival characteristics of 'Salmonella enterica' serovar Newport in manure and manure-amended soils where the pathogen may be amplified.

Salmonella spp. are environmentally persistent pathogens that have served as one of the important models for understanding how bacteria adapt to stressful conditions. However, it remains poorly understood how they survive extreme conditions encountered outside their hosts. Here we show that the rdar morphotype, a multicellular phenotype characterized by fimbria- and cellulose-mediated colony pattern formation, enhances the resistance of Salmonella to desiccation. When colonies were stored on plastic for several months in the absence of exogenous nutrients, survival of wild-type cells was increased compared to mutants deficient in fimbriae and/or cellulose production. Differences between strains were further highlighted upon exposure to sodium hypochlorite, as cellulose-deficient strains were 1,000-fold more susceptible. Measurements of gene expression using luciferase reporters indicated that production of thin aggregative fimbriae (Tafi) may initiate formation of colony surface patterns characteristic of the rdar morphotype. We hypothesize that Taft play a role in the organization of different components of the extracellular matrix. Conservation of the rdar morphotype among pathogenic S. enterica isolates and the survival advantages that it provides collectively suggest that this phenotype could play a role in the transmission of Salmonella between hosts.

Research has been conducted on salmonella infection in wild-living birds in Norway. The authors summarize the records of Salmonella detection in wild birds and compare the isolates via the use of plasmid profile analysis and phage typing.

Several studies have suggested an association between the use of antimicrobial agents in animal feeds and an increased risk that humans will contract resistant strains of bacteria such as Salmonella species, Escherichia coli, and other enteric isolates. The authors of this study evaluated whether animal feeds might serve as sources of antimicrobial-resistant bacteria, especially bacteria that are pathogenic to humans. From July through August 1998, samples of feed ingredients were collected from a total of 50 feed piles located on 12 dairy farms in western Oregon. From a subset of 10 piles, repeated samples were collected over time until each pile was depleted. Analysis of the samples indicated that 42.0 percent of all 50 piles and 60.0 percent of the piles from which there was repeated sampling were presumptive positive for Salmonella. Sixty-two percent of 50 Enterobacteriaceae isolates showed ampicillin resistance, and 10.0 percent displayed tetracycline resistance. Other bacteria displayed varying degrees of resistance to ampicillin, streptomycin, tetracycline, or a combination of these antimicrobials. The extent of antimicrobial-resistant Enterobacteriaceae in feed ingredients observed in this study raises significant concerns about the potential for human health risks from food-producing animals such as dairy cows., Introduction Members of the Enterobacteriaceae family are becoming a source of increased health concern in food safety and clinical medicine (Brock & Madigan, 1991; Wall et al., 1994). In 1996, [...]

Research indicates that the bacterial species Escherichia coli and Salmonella enterica do not track minute changes within their thermal environments. Large-scale variations in body temperatures, including those as broad as ectothermic and endothermic, result in modest thermal property changes.

Researchers used conventional serotyping and the ribosomal spacer-heteroduplex polymorphism method to identify more than 40 different Salmonella serotypes in the Tech River watershed on the south coast of France. Some serotypes were only found after storms and could represent contamination from farms.

A method, called the agar underlay method, for culture and recovery of sublethally heat-injured bacteria has been developed. The method has advantages vs other injury recovery methods. Unlike agar overlay methods, the underlay method allows the typical selective-medium colony morphology to develop for food-borne pathogens that are heat-injured, for instance Escherichia coli O157:H7 and Salmonellla typhimurium. Colonies can be more easily picked for further characterization.

A comparative study between the performance of commercial PCR-based Salmonella enterica detection methods and the culture-based methods in spiked and naturally contaminated samples of feed mill scrapings (FMS), palm kernel meal (PKM), pelleted feed (PF), rape seed meal (RSM), soybean meal (SM), and wheat grain (WG) is presented. A statistical model that describes the detection probability when different levels (CFU) of Salmonella contamination are present in feed materials is also presented.

The levels of two key pathogens, Salmonella and Campylobacter, are assessed along with the indicator organism Escherichia coli in aerosols within and outside poultry sheds. The studies have shown that the public health risk from these organisms in poultry environments via the aerosol pathway is very minimal.

Sulfonamide-resistant Escherichia coli and Salmonella isolates from pigs and chickens in Ontario and Quebec are screened for sul1, sul2 and sul3 by PCR. Each sul gene is distributed differently across populations, with a significant difference between distribution in commensal Escherichia coli and Salmonella isolates and sul3 restricted mainly to porcine Escherichia coli isolates.

The plasmid component of the genome of Salmonella Kentucky CVM29188, a multidrug-resistant strain that is isolated from a chicken meat sample with resistance to streptomycin, tetracycline, ampicillin and ceftiofur, is described. A combination of in silico and in vivo approaches, including comparative plasmid transfer, and PCR-based plasmid screenings, is used for providing insights into the genetic basis for multidrug resistance phenotypes of the isolate that provide new clues about virulence evolution and host adaptation in the Salmonella serovar.

Several groups of beetles and their larvae are artificially contaminated with a mixture of Salmonella enterica serovar Paratyphi B variant Java and three C. jejuni strains and are kept for different time intervals before they are fed to individually housed chicks. The results revealed that Salmonella and Campylobacter might be transmitted via beetles or their larvae to flocks in successive rearing cycles and need an intensive control program to eliminate insects from broiler houses.

A small focused library of brominated furanones is synthesized to test their activity against Salmonella enterica serovar typhimurium biofilm formation. The results demonstrated the potential use of brominated furanones in the prevention of biofilm formation by Salmonella serovar typhimurium.

The aerobic plate counts (APC) and the prevalences and loads of Salmonella and Escherichia coli 0157:H7 is measured to examine the hide and carcass hygiene of cull cattle at slaughter in four geographically distant regions of the United States. The pathogen prevalence on hides and carcasses is not affected by the season, however postintervention carcass contamination is significantly reduced due to the use of one or more intervention processes employed at each of the four processing plants examined.

The correlation between autoinducer-2 (AI-2) activity and biofilm formation by Salmonella and Escherichia coli O157:H7 on food contact surfaces is evaluated. The studies have shown that biofilm formation is similar between AI-2-positive and -negative strains and hence the AI-2 -based quorum sensing activity has not affected biofilm formation on food contact surfaces under monoculture conditions.

A study was conducted to determine the prevalence of protozoa on spinach and lettuce and to examine their interactions with Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes. The presence of protozoa found on leafy vegetables and their sequestration of enteric bacteria in vesicles revealed that protozoa might play critical role in the ecology of human pathogens on produce for food safety and public health.

The summary of heat-resistance data in meat and poultry of various strains of Salmonella, Listeria monocytogenes, Escherichia coli O157:H7 and Listeria innocua M1 is discussed. The age of the culture, growth conditions and pH are some of the factors that influence heat resistance in the organisms.

Research has been conducted on lytic bacteriophages. The authors report that these bacteriophages experimentally contaminated with Campylobacter and Salmonella have been applied to chicken skin, and that after the application the bacteriophages have shown the increase in titer, and have reduced the pathogen numbers.

Research has been conducted on Salmonella enterica infection source. The authors report that abattoir holding pens can serve as infection source, and identify a potential control point for Salmonella contamination in the preharvest pork production chain.