Emerging foodborne diseases

Distribution of genetic marker concentrations for fecal indicator bacteria in sewage and animal feces

Very little is known about the density and distribution of fecal indicator bacteria (FIB) genetic markers measured by quantitative real-time PCR (qPCR) in fecal pollution sources. Before qPCR-based FIB technologies can be applied to waste management and public health risk applications, it is vital to characterize the concentrations of these genetic markers in pollution sources (i.e., untreated wastewater and animal feces). We report the distribution of rRNA genetic markers for several general FIB groups, including Clostridium spp., Escherichia coli, enterococci, and Bacteroidales, as determined by qPCR on reference collections consisting of 54 primary influent sewage samples collected from treatment facilities across the United States and fecal samples representing 20 different animal species. Based on raw sewage sample collection data, individual FIB genetic markers exhibited a remarkable similarity in concentration estimates from locations across the United States ranging from Hawaii to Florida. However, there was no significant correlation between genetic markers for most FIB combinations (P > 0.05). In addition, large differences (up to 5 log(10) copies) in the abundance of FIB genetic markers were observed between animal species, emphasizing the importance of indicator microorganism selection and animal source contribution for future FIB applications.

In vitro anti-listerial activities of crude n-hexane and aqueous extracts of Garcinia kola (heckel) seeds

We assessed the anti-Listerial activities of crude n-hexane and aqueous extracts of Garcinia kola seeds against a panel of 42 Listeria isolates previously isolated from wastewater effluents in the Eastern Cape Province of South Africa and belonging to Listeria monocytogenes, Listeria grayi and Listeria ivanovii species. The n-hexane fraction was active against 45% of the test bacteria with zones of inhibition ranging between 8-17 mm, while the aqueous fraction was active against 29% with zones of inhibition ranging between 8-11 mm. The minimum inhibitory concentrations (MIC) were within the ranges of 0.079-0.625 mg/mL for the n-hexane extract and 10 to >10 mg/mL for the aqueous extract. The rate of kill experiment carried out for the n-hexane extract only, revealed complete elimination of the initial bacterial population for L. grayi (LAL 15) at 3× and 4× MIC after 90 and 60 min; L. monocytogenes (LAL 8) at 3× and 4× MIC after 60 and 15 min; L. ivanovii (LEL 18) at 3× and 4× MIC after 120 and 15 min; L. ivanovii (LEL 30) at 2, 3 and 4× MIC values after 105, 90 and 15 min exposure time respectively. The rate of kill activities were time- and concentration-dependant and the extract proved to be bactericidal as it achieved a more than 3log(10) decrease in viable cell counts after 2 h exposure time for all of the four test organisms at 3× and 4× MIC values. The results therefore show the potential presence of anti-Listerial compounds in Garcinia kola seeds that can be exploited in effective anti-Listerial chemotherapy.

Comparison of real-time PCR, reverse transcriptase real-time PCR, loop-mediated isothermal amplification, and the FDA conventional microbiological method for the detection of Salmonella spp. in produce

Contamination of foods, especially produce, with Salmonella spp. is a major concern for public health. Several methods are available for the detection of Salmonella in produce, but their relative efficiency for detecting Salmonella in commonly consumed vegetables, often associated with outbreaks of food poisoning, needs to be confirmed. In this study, the effectiveness of three molecular methods for detection of Salmonella in six produce matrices was evaluated and compared to the FDA microbiological detection method. Samples of cilantro (coriander leaves), lettuce, parsley, spinach, tomato, and jalapeno pepper were inoculated with Salmonella serovars at two different levels (10(5) and <10(1) CFU/25 g of produce). The inoculated produce was assayed by the FDA Salmonella culture method (Bacteriological Analytical Manual) and by three molecular methods: quantitative real-time PCR (qPCR), quantitative reverse transcriptase real-time PCR (RT-qPCR), and loop-mediated isothermal amplification (LAMP). Comparable results were obtained by these four methods, which all detected as little as 2 CFU of Salmonella cells/25 g of produce. All control samples (not inoculated) were negative by the four methods. RT-qPCR detects only live Salmonella cells, obviating the danger of false-positive results from nonviable cells. False negatives (inhibition of either qPCR or RT-qPCR) were avoided by the use of either a DNA or an RNA amplification internal control (IAC). Compared to the conventional culture method, the qPCR, RT-qPCR, and LAMP assays allowed faster and equally accurate detection of Salmonella spp. in six high-risk produce commodities.

Effect of desiccation on tolerance of salmonella enterica to multiple stresses

Reducing the available water in food is a long-established method for controlling bacterial growth in the food industry. Nevertheless, food-borne outbreaks of salmonellosis due to consumption of dry foods have been continuously reported. Previous studies showed that dried Salmonella cells acquire high tolerance to heat and ethanol. In order to examine if dehydration also induces tolerance to other stressors, dried Salmonella enterica serotype Typhimurium cells were exposed to multiple stresses, and their viability was assessed. Indeed, desiccated S. Typhimurium acquired higher tolerance to multiple stressors than nondesiccated cells. The dried cells were significantly more resistant to most stressors, including ethanol (10 to 30%, 5 min), sodium hypochlorite (10 to 100 ppm, 10 min), didecyl dimethyl ammonium chloride (0.05 to 0.25%, 5 min), hydrogen peroxide (0.5 to 2.0%, 30 min), NaCl (0.1 to 1 M, 2 h), bile salts (1 to 10%, 2 h), dry heat (100°C, 1 h), and UV irradiation (125 μW/cm(2), 25 min). In contrast, exposure of Salmonella to acetic and citric acids reduced the survival of the dried cells (1.5 log) compared to that of nondesiccated cells (0.5 log). Three other S. enterica serotypes, S. Enteritidis, S. Newport, and S. Infantis, had similar stress responses as S. Typhimurium, while S. Hadar was much more susceptible and gained tolerance to only a few stressors. Our findings indicate that dehydration induces cross-tolerance to multiple stresses in S. enterica, demonstrating the limitations of current chemical and physical treatments utilized by the food industry to inactivate food-borne pathogens.

Isolation of Salmonella spp. from lettuce and evaluation of its susceptibility to novel bacteriocins of Bacillus thuringiensis and antibiotics

In this study, 13% of fresh lettuce (Lactuca sativa) samples collected from markets and supermarkets in two cities of Mexico were contaminated with Salmonella spp. From those samples, amplicons of ∼300 base pairs (bp) were amplified, corresponding to the expected size of the invasion (invA) and internal transcribed spacer regions of the 16S and 23S rRNA genes of Salmonella spp. Additionally, Salmonella strains were isolated and harbored plasmids ranging from ∼9 to 16 kbp. From these strains, 91% were resistant to ampicillin and nitrofurantoin, whereas 55% were resistant to cephalothin and chloramphenicol. No resistance was detected to amikacin, carbenicillin, cefotaxime, gentamicin, netilmicin, norfloxacin, and sulfamethoxazole-trimethoprim. When Salmonella isolates were tested against novel bacteriocins (morricin 269, kurstacin 287, kenyacin 404, entomocin 420, and tolworthcin 524) produced by five Mexican strains of Bacillus thuringiensis, 50% were susceptible to these antimicrobial peptides. This is the first report showing that Salmonella strains isolated from lettuce are susceptible to bacteriocins produced by the most important bioinsecticide worldwide, suggesting the potential use of these antibacterial peptides as therapeutic agents or food preservatives to reduce or destroy populations of Salmonella spp.

Inhibition of nalidixic acid-resistant salmonella on marinated chicken skin

Marination is widely used to enhance flavor and increase consumer acceptability of meat and poultry products. The impact of such marination on the safety and shelf life of poultry meat was evaluated in this study. A series of experiments were conducted to determine the efficacy of teriyaki and lemon pepper marinades against multiple strains of nalidixic acid (NAL)-resistant Salmonella. NAL-resistant Salmonella serovar (Typhimurium, Heidelberg, and Senftenberg) cultures were inoculated onto chicken skin at 0.6 to 3.14 log CFU/g in a 12-well titer plate. Inoculated chicken skin was exposed to teriyaki or lemon pepper marinades for up to 32 h and stored at 4 or 25°C to determine the prevalence of Salmonella. To determine Salmonella survival, a three-strain cocktail of Salmonella was inoculated at low (ca. 4 log CFU/g) and high (8 log CFU/g) levels onto chicken skin that was then marinated with either teriyaki or lemon pepper marinade for up to 32 h and stored at 4 or 25°C. Prevalence of Salmonella was significantly reduced (P ≤ 0.05) by teriyaki marinade at all levels of contamination regardless of storage temperature. Lemon pepper marinade reduced Salmonella prevalence (P ≤ 0.05) at low levels of contamination (10¹ and 10² CFU/g), whereas no significant effect (P > 0.05) was observed at higher levels of contamination. Marination of chicken skin with teriyaki marinade greatly reduced Salmonella prevalence and survival (P ≤ 0.05) regardless of the storage temperature, indicating the antimicrobial potential of this marinade for poultry and meat products.

A waterborne Campylobacter jejuni outbreak on a Greek island

A case-control and a case-crossover study were performed to investigate a Campylobacter jejuni outbreak in Crete in 2009. Most cases originated from rural areas, served by a different water-supply system from that of the adjacent town. Thirty-seven cases and 79 controls were interviewed; cases were interviewed for two different time periods for the case-crossover study. Stool cultures, PFGE and MLST subtyping were run in human samples. Univariately, consumption of tap water was associated with C. jejuni infection. Stratified analysis revealed that water-supply system was an effect modifier of this association. In the multivariable analysis, the rural areas' water supplier and drinking tap water were risk factors. No risk factors were revealed in the case-crossover study. No Campylobacter were isolated in the tested water samples. There is strong epidemiological evidence that tap water was the vehicle of the outbreak.

Improving Foodborne Illness Prevention Among Transplant Recipients

The U.S. Department of Agriculture developed a food safety brochure to educate transplant recipients and their caregivers about the risk of contracting foodborne illnesses and safe food-handling prevention practices. Qualitative research was conducted with transplant recipients and caregivers to collect information on participants’ food safety concerns, knowledge, and practices; changes in food safety knowledge and practices after receiving the food safety brochure; preferred communication channels and dissemination strategies for delivering the brochure; and evaluation of the brochure. Many participants received food safety information from a health care provider, but the content and format varied by institution. Most participants are not following recommended practices to cook and chill food safely, and many participants consume high-risk foods associated with foodborne illnesses. After reading the brochure, many participants made or plan to make at least one food safety recommendation. The research findings were used to refine the brochure before nationwide distribution.

Prevalence and antimicrobial resistance of Campylobacter jejuni and Campylobacter coli isolated from cattle between 2002 and 2006 in France

Feces from 2,255 cattle (calves, young beef cattle, and culled cows) were collected at slaughter from nine departments across France. Campylobacter was recovered from 16.5% of the 2,255 samples (C. jejuni from 12.8% and C. coli from 3.7%), predominantly from calves. Antimicrobial resistance to six antibiotics of medical and/or veterinary interest was tested with the E-test. Resistance to tetracycline was found in most isolates (52.8% of C. jejuni isolates and 88.1% of C. coli isolates) in contrast to low but consistent resistance to ampicillin and erythromycin. Only two C. coli isolates were resistant to gentamicin. Multiple resistance was frequently detected in C. jejuni and C. coli isolates, and 0.8% (3 of 372) of the isolates were resistant to five of the six antimicrobials. An upward trend in the resistance to quinolones and fluoroquinolones in C. jejuni from calves was found; resistance to nalidixic acid reached 70.4% in 2006 and fluoroquinolone resistance increased from 29.7 to 70.4% during 2002 through 2006. All data were analyzed in parallel using clinical breakpoints or epidemiological cutoff values, and the results overlapped largely, except those for gentamicin. This 5-year survey (2002 through 2006) gives the first overview of the prevalence and antimicrobial resistance of C. jejuni and C. coli in cattle in France and documents to what extent cattle may contribute to the environmental reservoir of Campylobacter in France in the context of recurrent reports on links between human campylobacterioses and livestock. The results underline a notable increase in the resistance to fluoroquinolones in C. jejuni from cattle that may be of significant importance for public health.

Enteric bacterial pathogen detection in southern sea otters (Enhydra lutris nereis) is associated with coastal urbanization and freshwater runoff

Although protected for nearly a century, California's sea otters have been slow to recover, in part due to exposure to fecally-associated protozoal pathogens like Toxoplasma gondii and Sarcocystis neurona. However, potential impacts from exposure to fecal bacteria have not been systematically explored. Using selective media, we examined feces from live and dead sea otters from California for specific enteric bacterial pathogens (Campylobacter, Salmonella, Clostridium perfringens, C. difficile and Escherichia coli O157:H7), and pathogens endemic to the marine environment (Vibrio cholerae, V. parahaemolyticus and Plesiomonas shigelloides). We evaluated statistical associations between detection of these pathogens in otter feces and demographic or environmental risk factors for otter exposure, and found that dead otters were more likely to test positive for C. perfringens, Campylobacter and V. parahaemolyticus than were live otters. Otters from more urbanized coastlines and areas with high freshwater runoff (near outflows of rivers or streams) were more likely to test positive for one or more of these bacterial pathogens. Other risk factors for bacterial detection in otters included male gender and fecal samples collected during the rainy season when surface runoff is maximal. Similar risk factors were reported in prior studies of pathogen exposure for California otters and their invertebrate prey, suggesting that land-sea transfer and/or facilitation of pathogen survival in degraded coastal marine habitat may be impacting sea otter recovery. Because otters and humans share many of the same foods, our findings may also have implications for human health.

AI-2 does not function as a quorum sensing molecule in Campylobacter jejuni during exponential growth in vitro

BACKGROUND

Campylobacter jejuni contains a homologue of the luxS gene shown to be responsible for the production of the signalling molecule autoinducer-2 (AI-2) in Vibrio harveyi and Vibrio cholerae. The aim of this study was to determine whether AI-2 acted as a diffusible quorum sensing signal controlling C. jejuni gene expression when it is produced at high levels during mid exponential growth phase.

RESULTS

AI-2 activity was produced by the parental strain NCTC 11168 when grown in rich Mueller-Hinton broth (MHB) as expected, but interestingly was not present in defined Modified Eagles Medium (MEM-alpha). Consistent with previous studies, the luxS mutant showed comparable growth rates to the parental strain and exhibited decreased motility halos in both MEM-alpha and MHB. Microarray analysis of genes differentially expressed in wild type and luxS mutant strains showed that many effects on mRNA transcript abundance were dependent on the growth medium and linked to metabolic functions including methionine metabolism. Addition of exogenously produced AI-2 to the wild type and the luxS mutant, growing exponentially in either MHB or MEM-alpha did not induce any transcriptional changes as analysed by microarray.

CONCLUSION

Taken together these results led us to conclude that there is no evidence for the role of AI-2 in cell-to-cell communication in C. jejuni strain NCTC 11168 under the growth conditions used, and that the effects of the luxS mutation on the transcriptome are related to the consequential loss of function in the activated methyl cycle.

Prevalence of Salmonella in vegetables from Mexico

The present study is an overview of the role of vegetables as a transmission vehicle of Salmonella in Mexico. One hundred samples of each of 17 different vegetables were analyzed during a period of 18 months. Salmonella was isolated from 98 samples. Salmonella enterica serovar Typhimurium was isolated from the highest percentage of samples with typeable Salmonella isolates (23.9%), followed by S. enterica subsp. arizonae and Salmonella Choleraesuis each from 16.9%, Salmonella Gallinarum from 11.1%, Salmonella Anatum and S. enterica subsp. houtenae each from 9.7%, Salmonella Agona and Salmonella Edinburg each from 4.22%, Salmonella Enteritidis and S. enterica subsp. salamae each from 2.81%, and Salmonella Bongor, Salmonella Pullorum, Salmonella Typhi, and Salmonella C1 flagellar b each from 1.4%. Of the isolated bacteria, 27.6% were nontypeable strains. Salmonella was isolated from 12% of parsley samples, 11% of cilantro samples, 9% of broccoli samples, 9% of cauliflower samples, 9% of "papaloquelite" (Porophyllum ruderale) samples, 9% of purslane (Portulaca oleracea) samples, 7% of long lettuce samples, 7% of spinach samples, 7% of watercress samples, 6% of Chinese parsley samples, 4% of beet samples, 3% of celery samples, 3% of Romaine lettuce samples, 1% of cabbage samples, and 1% of potato samples. The presence of Salmonella Typhi in parsley is noteworthy. No Salmonella isolates were obtained from zucchini and onion. These results indicate that raw or minimally processed vegetables can be contaminated with Salmonella, leading to direct infection of consumers or cross-contamination of other foodstuffs. These contaminated vegetables can represent a severe health risk for the Mexican consumer.

Detection of live Salmonella sp. cells in produce by a TaqMan-based quantitative reverse transcriptase real-time PCR targeting invA mRNA

Salmonella enterica contamination in foods is a significant concern for public health. When DNA detection methods are used for analysis of foods, one of the major concerns is false-positive results from the detection of dead cells. To circumvent this crucial issue, a TaqMan quantitative real-time RT-PCR (qRT-PCR) assay with an RNA internal control was developed. invA RNA standards were used to determine the detection limit of this assay as well as to determine invA mRNA levels in mid-exponential-, late-exponential-, and stationary-phase cells. This assay has a detection limit of 40 copies of invA mRNA per reaction. The levels of invA mRNA in mid-exponential-, late-exponential-, and stationary-phase S. enterica cells was approximately 1 copy per 3 CFU, 1 copy per CFU, and 4 copies per 10(3) CFU, respectively. Spinach, tomatoes, jalapeno peppers, and serrano peppers were artificially contaminated with four different Salmonella serovars at levels of 10(5) and less than 10 CFU. These foods were analyzed with qRT-PCR and with the FDA's Bacteriological Analytical Manual Salmonella culture method (W. A. Andrews and T. S. Hammack, in G. J. Jackson et al., ed., Bacteriological analytical manual online, http://www.cfsan.fda.gov/ approximately ebam/bam-5.html, 2007). Comparable results were obtained by both methods. Only live Salmonella cells could be detected by this qRT-PCR assay, thus avoiding the dangers of false-positive results from nonviable cells. False negatives (inhibition of the PCR) were also ruled out through the use of an RNA internal control. This assay allows for the fast and accurate detection of viable Salmonella spp. in spinach, tomatoes, and in both jalapeno and serrano peppers.

A comparison of cecal colonization of Salmonella enterica serotype Typhimurium in white leghorn chicks and Salmonella-resistant mice

Background

Salmonellosis is one of the most important bacterial food borne illnesses worldwide. A major source of infection for humans is consumption of chicken or egg products that have been contaminated with Salmonella enterica serotype Typhimurium, however our knowledge regarding colonization and persistence factors in the chicken is small.

Results

We compared intestinal and systemic colonization of 1-week-old White Leghorn chicks and Salmonella-resistant CBA/J mice during infection with Salmonella enterica serotype Typhimurium ATCC14028, one of the most commonly studied isolates. We also studied the distribution of wild type serotype Typhimurium ATCC14028 and an isogenic invA mutant during competitive infection in the cecum of 1-week-old White Leghorn chicks and 8-week-old CBA/J mice. We found that although the systemic levels of serotype Typhimurium in both infected animal models are low, infected mice have significant splenomegaly beginning at 15 days post infection. In the intestinal tract itself, the cecal contents are the major site for recovery of serotype Typhimurium in the cecum of 1-week-old chicks and Salmonella-resistant mice. Additionally we show that only a small minority of Salmonellae are intracellular in the cecal epithelium of both infected animal models, and while SPI-1 is important for successful infection in the murine model, it is important for association with the cecal epithelium of 1-week-old chicks. Finally, we show that in chicks infected with serotype Typhimurium at 1 week of age, the level of fecal shedding of this organism does not reflect the level of cecal colonization as it does in murine models.

Conclusion

In our study, we highlight important differences in systemic and intestinal colonization levels between chick and murine serotype Typhimurium infections, and provide evidence that suggests that the role of SPI-1 may not be the same during colonization of both animal models.

Evaluation of three different molecular markers for the detection of Staphylococcus aureus by polymerase chain reaction

The aim of this study was to target three genes of Staphylococcus aureus-fmhA (coding for a factor of unknown function), catalase and femA (coding for a factor essential for methicillin resistance) to establish and validate a PCR assay for the detection of this pathogen. Two pairs of primers were designed for fmhA and one pair each for catalase and femA genes. The PCR assays were standardized and found to give specific amplicons under similar reaction parameters. Target specificity of the primers was confirmed by DNA sequencing of the amplicons. While the initial inclusivity and exclusivity test reactions were in agreement in case of three of the primer pairs, one pair based on fmhA gene produced a non-specific product with a template DNA used in exclusivity test reactions. Forty-five strains of S. aureus were subjected to these PCR assays for their evaluation. Three among the four pairs of primers, one against each gene detected all the 45 strains precisely whereas one of the PCR assays using primers targeting the fmhA gene did not generate the specific amplicon with several of the strains. Seven unidentified strains of Gram-positive cocci subjected to these PCR assays produced negative results for each culture. Six of the strains were identified as Staphylococcus haemolyticus and one strain as Staphylococcus arlettae by 16S ribosomal gene analyses. All the three assay systems showed a detection limit of 100 cells per 20mul reaction assay. For validation of these assay systems, 80 coded samples of 11% skimmed milk spiked with different pathogens were received from NICED (National Institute of Cholera and Enteric Diseases), Kolkata and subjected to these PCR assays. All the three assays could detect S. aureus correctly in two of the samples. Amongst 150 raw milk samples, 36 (24%) were found positive for S. aureus. We conclude that fmhA, catalase and femA genes are conserved in S. aureus and, therefore, could be used as specific targets for its detection and identification by PCR. The protocols developed herein could be used for rapid and specific detection of this pathogen in food, clinical and environmental samples, especially milk.

Inactivation of Shigella boydii 18 IDPH and Listeria monocytogenes Scott A with power ultrasound at different acoustic energy densities and temperatures

The effect of acoustic energy density (AED) on inactivation of Shigella boydii 18 IDPH and Listeria monocytogenes Scott A in a cell suspension was studied at sublethal temperatures and at AEDs of 0.49, 0.85, and 1.43 W/mL. The effect of temperature on ultrasonic inactivation of L. monocytogenes Scott A at 35, 50, and 65 degrees C was examined at an AED of 1.43 W/mL. Increasing AED increased the rate of inactivation for both S. boydii and L. monocytogenes. The destruction of S. boydii and L. monocytogenes followed 1st order kinetics in a 20-min treatment, except for S. boydii inactivation at 1.43 W/mL where a tailing effect was observed after 15 min. At sublethal temperatures, the D-values of S. boydii were 8.8, 4.3, and 2.5 min for AEDs of 0.49, 0.85, and 1.43 W/mL, whereas those for L. monocytogenes at the 3 AED levels were 31.5, 13.5, and 7.3 min, respectively. Ultrasonic treatment of L. monocytogenes at 35 and 50 degrees C enhanced inactivation. However, at 65 degrees C, application of ultrasound did not result in additional inactivation compared to thermal treatment alone at the same temperature. With the experimental conditions and the ultrasound system used in this study, an upper temperature limit for thermosonication was evident above which no added killing due to ultrasound was observed.

Salmonella challenges: prevalence in swine and poultry and potential pathogenicity of such isolates

Salmonellosis is the second leading cause of bacterial foodborne illness in the United States, and the great majority of these infections are associated with the consumption of products such as meat, poultry, eggs, milk, seafood, and fresh produce contaminated with Salmonella. The per capita consumption of meat and poultry in United States has increased significantly over the past century. This increase is especially evident with poultry products, where there has been a nearly 6-fold increase in chicken consumption and 17-fold increase in turkey consumption since 1909. The per capita consumption of pork has also increased over this time from 18.7 to 21.7 kg/yr. With this increase in meat and poultry consumption, the dynamics of animal production and consumer exposure have changed leading to new challenges in limiting salmonellosis. To meet the demands of consumers, more intensive agricultural practices have been adopted, which has likely changed the population characteristics of Salmonella present among poultry flocks and swine populations. In Salmonella isolated from swine in the United States, S. Typhimurium has replaced S. Choleraesuis as the predominant serovar in recent years. Among isolates from turkeys collected in 2004, serovars S. Senftenberg and S. Hadar were most common overall; however, S. Heidelberg was most common from clinical diagnostic sources, potentially indicating increased virulence. Salmonella Heidelberg was also the most commonly detected serovar among chicken isolates from clinically ill birds and Salmonella surveillance samples. Overall among the 10 serovars most commonly associated with human infections, 6 are also found in the top serovars of swine and poultry. These include S. Typhimurium, S. Enteritidis, S. Heidelberg, S. Montevideo, S. Saintpaul, and S. I 4,[5],12:i:-.

Impact of feed supplementation with antimicrobial agents on growth performance of broiler chickens, Clostridium perfringens and enterococcus counts, and antibiotic resistance phenotypes and distribution of antimicrobial resistance determinants in Escherichia coli isolates

The effects of feed supplementation with the approved antimicrobial agents bambermycin, penicillin, salinomycin, and bacitracin or a combination of salinomycin plus bacitracin were evaluated for the incidence and distribution of antibiotic resistance in 197 commensal Escherichia coli isolates from broiler chickens over 35 days. All isolates showed some degree of multiple antibiotic resistance. Resistance to tetracycline (68.5%), amoxicillin (61.4%), ceftiofur (51.3%), spectinomycin (47.2%), and sulfonamides (42%) was most frequent. The levels of resistance to streptomycin, chloramphenicol, and gentamicin were 33.5, 35.5, and 25.3%, respectively. The overall resistance levels decreased from day 7 to day 35 (P < 0.001). Comparing treatments, the levels of resistance to ceftiofur, spectinomycin, and gentamicin (except for resistance to bacitracin treatment) were significantly higher in isolates from chickens receiving feed supplemented with salinomycin than from the other feeds (P < 0.001). Using a DNA microarray analysis capable of detecting commonly found antimicrobial resistance genes, we characterized 104 tetracycline-resistant E. coli isolates from 7- to 28-day-old chickens fed different growth promoters. Results showed a decrease in the incidence of isolates harboring tet(B), bla(TEM), sulI, and aadA and class 1 integron from days 7 to 35 (P < 0.01). Of the 84 tetracycline-ceftiofur-resistant E. coli isolates, 76 (90.5%) were positive for bla(CMY-2). The proportions of isolates positive for sulI, aadA, and integron class 1 were significantly higher in salinomycin-treated chickens than in the control or other treatment groups (P < 0.05). These data demonstrate that multiantibiotic-resistant E. coli isolates can be found in broiler chickens regardless of the antimicrobial growth promoters used. However, the phenotype and the distribution of resistance determinants in E. coli can be modulated by feed supplementation with some of the antimicrobial agents used in broiler chicken production.

Prevalence of multidrug resistant Salmonella in Coriander, mint, carrot, and radish in Bareilly and Kanpur, northern India

We examined 974 samples (304 coriander, 212 mint, 258 carrot, and 200 radish) collected from vegetable vendors in two cities, Bareilly (n = 832) and Kanpur (n = 142), in northern India during the early summer season in 2004. Salmonella was isolated from 35 samples (9 coriander, 5 mint, 10 radish, and 11 carrot) while Escherichia coli was detected in 181 samples (67 coriander, 44 mint, 36 carrot, and 34 radish). None of the E. coli belonged to the O:157 serogroup. Five Salmonella isolates from samples collected at Kanpur (3 coriander and 2 mint) belonged to 4 different serovars of S. enterica ssp. enterica-S. Mons, S. Rottenest, S. Saintpaul, and S. Weltevreden. Thirty Salmonella isolates from samples collected at Bareilly (11 carrot, 10 radish, 6 coriander, and 3 mint) belonged to 7 serovars-S. Anatum, S. Bsilla, S. Newport, S. Saintpaul, S. Teko, S. Virchow, and S. Weltevreden. The majority (82.9%) of Salmonella isolates were multidrug resistant. One quarter of the isolates were resistant to >or=10 antibiotics. Based on antibiotic resistance patterns, 35 isolates could be classified into 23 resistotypes. None of the 35 isolates was resistant to streptomycin and ceftriaxone, while >80% were resistant to sulfamethoxazole, nalidixic acid, and kanamycin. Resistance to imipenem (>20%) and amikacin (>30%) was also common. The correlation between presence of Salmonella and E. coli on raw vegetables was not significant (p = 0.13).

Identification of chicken-specific fecal microbial sequences using a metagenomic approach

In this study, we applied a genome fragment enrichment (GFE) method to select for genomic regions that differ among different fecal metagenomes. Competitive DNA hybridizations were performed between chicken fecal DNA and pig fecal DNA (CP) and between chicken fecal DNA and an avian DNA composite consisting of turkey, goose, and seagull fecal DNA extracts (CB) to enrich for chicken-specific DNA fragments. A total of 471 non-redundant chicken metagenomic sequences were retrieved and analyzed. All of the clone sequences were similar to prokaryotic genes, of which more than 60% could not be assigned to previously characterized functional roles. In general terms, sequences assigned characterized functional roles were associated with cellular processes (11.7%), metabolism (11.0%) and information storage and processing (13.4%). Approximately 53% of the non-redundant sequences are similar to genes present in intestinal bacteria belonging to Clostridia (20.9%), Bacteroidetes (15.0%), and Bacilli (17.3%). Twenty-five sequences from the CP and CB clone libraries were selected to develop chicken fecal-specific PCR assays. These assays were challenged against fecal DNA extracted from 21 different animal species, including mammals and birds. The results from the host-specificity studies showed that 12 of the assays had a high degree of specificity to chicken feces. In addition, three assays were specific to chicken and turkey while another four assays tested positive to more than two avian species, suggesting a broader distribution of some of the enriched gene fragments among different avian fecal microbial communities. Fecal pollution signals were detected using chicken-specific assays in contaminated water samples, although the PCR assays showed different detection limits. These results indicate the need for multiple assays to detect poultry fecal sources of pollution. The competitive DNA hybridization approach used in this study can rapidly select for numerous chicken fecal metagenomic regions that can be used as potential genetic markers for fecal source tracking.

Ecology of Increasing Diseases: Population Growth and Environmental Degradation

The World Health Organization (WHO) and other organizations report that the prevalence of human diseases during the past decade is rapidly increasing. Population growth and the pollution of water, air, and soil are contributing to the increasing number of human diseases worldwide. Currently an estimated 40% of world deaths are due to environmental degradation. The ecology of increasing diseases has complex factors of environmental degradation, population growth, and the current malnutrition of about 3.7 billion people in the world.

Consumer home refrigeration practices: results of a web-based survey

To reduce bacterial growth and to ensure the quality and safety of food products, the U.S. Department of Agriculture and the U.S. Food and Drug Administration advise consumers to clean their refrigerators regularly, use a refrigerator thermometer, and keep refrigerator temperatures at 40 degrees F (4.4 degrees C) or below. We conducted a nationally representative Web-enabled survey (n = 2,060) to collect data on refrigerator thermometer ownership, home refrigerator temperatures, and the frequency of home refrigerator cleaning. We stratified the sample to provide results for pregnant women, older adults (60 years or older), and the remaining population. About half of all respondents had cleaned their refrigerators at least 1 month before the survey. Only 11% of all respondents had a thermometer in their refrigerator before the survey. Older adults (77.5%) were more likely than the remaining population (70.4%) to have their refrigerators at the recommended temperature (P < 0.01). Older adults who were not married and who lived alone were less likely to have refrigerator thermometers and to have their refrigerators at a recommended temperature (P < 0.05). For all respondents, those who had previously owned a refrigerator thermometer were more likely to have their refrigerators at the recommended temperature than were respondents who did not previously own a thermometer (P < 0.01). Food safety educators can use the survey findings and results of previous research to target educational materials and help consumers, especially those at risk for listeriosis, to safely store refrigerated foods at home.