Microbial quality of oysters sold in Western Trinidad and potential health risk to consumers.
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The prevalence and characteristics of Escherichia coli and Salmonella spp. as well as counts of E. coli in raw oysters, condiments/spices, and raw oyster cocktails sampled from 72 vendors across Western Trinidad were determined. The microbial quality of the water used in the preparation of raw oysters was also investigated. Of 200 samples each of raw oysters, condiments/spices and oyster cocktails tested, 154 (77.0%), 89 (44.5%) and 154 (77.0%) respectively yielded E. coli. The differences were statistically significant (P = < 0.001; chi square = 62.91). The mean E. coli count per g in the ready-to-eat oyster cocktail ranged from 1.5 x 10(3) +/- 2.7 x 10(3) in Couva to 8.7x10(6) +/- 4.9x10(7) in San Fernando. One hundred and forty-six (73.0%) oyster cocktails contaminated with E. coli had counts that exceeded the recommended standard of 16 per g. Of a total of 590 E. coli isolates from various sources tested, 24 (4.1%), 20 (3.4%) and 69 (11.7%) were mucoid, haemolytic and non-sorbitol fermenters respectively. Twelve (2.0%) isolates of E. coli were O157 strains, while 92 (46.0%) of 200 E. coli isolates tested belonged to enteropathogenic serogroups. Ninety (45.0%) and 73 (36.5%) of 200 water samples contained total coliforms and faecal coliforms respectively, with counts that exceeded 2.2 coliforms per 100 ml. Salmonella spp. were isolated from 7 (3.5%), 1 (0.5%) and 2 (1.0%) of 200 samples each, of raw oysters, condiments/spices and oyster cocktails respectively. Oysters pose a health risk to consumers in Trinidad, particularly from colibacillosis and salmonellosis, and the need for increased public awareness of this hazard cannot be over-emphasized. (+info)
Characterization of unexpected growth of Escherichia coli O157:H7 by modeling.
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Modeling of batch kinetics in minimal synthetic medium was used to characterize Escherichia coli O157:H7 growth, which appeared to be different from the exponential growth expected in minimal synthetic medium and observed for E. coli K-12. The turbidimetric kinetics of 14 of the 15 O157:H7 strains tested (93%) were nonexponential, whereas 25 of the 36 other E. coli strains tested (70%) exhibited exponential kinetics. Moreover, the anomaly was almost corrected when the minimal medium was supplemented with methionine. These observations were confirmed with two reference strains by using plate count monitoring. In mixed cultures, E. coli K-12 had a positive effect on E. coli O157:H7 and corrected its growth anomaly. This demonstrated that commensalism occurred, as the growth curve for E. coli K-12 was not affected. The interaction could be explained by an exchange of methionine, as the effect of E. coli K-12 on E. coli O157:H7 appeared to be similar to the effect of methionine. (+info)
Agar underlay method for recovery of sublethally heat-injured bacteria.
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A method of recovering sublethally heat-injured bacteria was developed. The procedure (termed the agar underlay method) uses a nonselective agar underlaid with a selective medium. In a two-chambered petri dish, the Lutri plate (LP), a nonselective agar is inoculated with a population of sublethally heat-injured bacteria. After a 2-h repair incubation period, selective agar is added to the bottom chamber of the LP and incubated. By diffusing through the nonselective top agar, selective agents from the underlay medium impart selectivity to the system. By the agar underlay method, recovery rates of the heat-injured food-borne pathogens Escherichia coli O157:H7 and Salmonella typhimurium were not different (P > 0. 05) from recovery rates determined with nonselective media. Sublethally heat-injured cells (60 degrees C for 1.5 min in buffer or 80 degrees C for 30 s on meat surfaces) grew and produced a typical colony morphology and color reaction when the agar underlay procedure was used with the appropriate respective selective agars. Unlike agar overlay methods for injury repair, the agar underlay procedure allows the typical selective-medium colony morphology to develop and allows colonies to be more easily picked for further characterization. Higher recovery rates of heat-injured fecal enterococci from bovine fecal samples and total coliforms from animal waste lagoons were obtained by the agar underlay method with selective agars than by direct plating on the respective selective media. (+info)
Establishment of the PCR system specific to Salmonella spp. and its application for the inspection of food and fecal samples.
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We established the PCR detection system specific to Salmonella species using Salmonella enterotoxin gene (stn). The detection limit was one bacterial cell per one gram of fecal and minced-meat samples using enrichment procedure by Tripticase soy broth or Salmonella enrichment broth, respectively. We concluded that this PCR system is useful for the practical application in the field of the public hygiene. (+info)
Antimicrobial actions of degraded and native chitosan against spoilage organisms in laboratory media and foods.
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The objective of this study was to determine whether chitosan (poly-beta-1,4-glucosamine) and hydrolysates of chitosan can be used as novel preservatives in foods. Chitosan was hydrolyzed by using oxidative-reductive degradation, crude papaya latex, and lysozyme. Mild hydrolysis of chitosan resulted in improved microbial inactivation in saline and greater inhibition of growth of several spoilage yeasts in laboratory media, but highly degraded products of chitosan exhibited no antimicrobial activity. In pasteurized apple-elderflower juice stored at 7 degrees C, addition of 0.3 g of chitosan per liter eliminated yeasts entirely for the duration of the experiment (13 days), while the total counts and the lactic acid bacterial counts increased at a slower rate than they increased in the control. Addition of 0.3 or 1.0 g of chitosan per kg had no effect on the microbial flora of hummus, a chickpea dip; in the presence of 5.0 g of chitosan per kg, bacterial growth but not yeast growth was substantially reduced compared with growth in control dip stored at 7 degrees C for 6 days. Improved antimicrobial potency of chitosan hydrolysates like that observed in the saline and laboratory medium experiments was not observed in juice and dip experiments. We concluded that native chitosan has potential for use as a preservative in certain types of food but that the increase in antimicrobial activity that occurs following partial hydrolysis is too small to justify the extra processing involved. (+info)
Development of methods to detect "Norwalk-like viruses" (NLVs) and hepatitis A virus in delicatessen foods: application to a food-borne NLV outbreak.
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"Norwalk-like viruses" (NLVs) and hepatitis A virus (HAV) are the most common causes of virus-mediated food-borne illness. Epidemiological investigations of outbreaks associated with these viruses have been hindered by the lack of available methods for the detection of NLVs and HAV in foodstuffs. Although reverse transcription (RT)-PCR methods have been useful in detecting NLVs and HAV in bivalve mollusks implicated in outbreaks, to date such methods have not been available for other foods. To address this need, we developed a method to detect NLVs and HAV recovered from food samples. The method involves washing of food samples with a guanidinium-phenol-based reagent, extraction with chloroform, and precipitation in isopropanol. Recovered viral RNA is amplified with HAV- or NLV-specific primers in RT-PCRs, using a viral RNA internal standard control to identify potential sample inhibition. By this method, 10 to 100 PCR units (estimated to be equivalent to 10(2) to 10(3) viral genome copies) of HAV and Norwalk virus seeded onto ham, turkey, and roast beef were detected. The method was applied to food samples implicated in an NLV-associated outbreak at a university cafeteria. Sliced deli ham was positive for a genogroup II NLV as determined by using both polymerase- and capsid-specific primers and probes. Sequence analysis of the PCR-amplified capsid region of the genome indicated that the sequence was identical to the sequence from virus detected in the stools of ill students. The developed method is rapid, simple, and efficient. (+info)
Dietary clay in the chemoprevention of aflatoxin-induced disease.
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Aflatoxins are harmful by-products of mold growth and, though invisible to the naked eye, are potentially fatal. The aflatoxin problem is long-standing and inextricable. Concerns about the aflatoxins originate from the strong implications of their involvement in disease and death in humans and animals, yet scientists and clinicians are still seeking ways to effectively deal with these dangerous and elusive chemicals. Safe, practical, and effective strategies for the detoxification of aflatoxin-contaminated food and feed are highly desirable. A simple and effective approach to the chemoprevention of aflatoxicosis has been to diminish or block exposure to aflatoxins via the inclusion of HSCAS clay in the diet. HSCAS clay acts as an aflatoxin enterosorbent that tightly and selectively binds these poisons in the gastrointestinal tract of animals, decreasing their bioavailability and associated toxicities. Further studies to delineate the molecular mechanisms of action have shown that the dicarbonyl system of aflatoxin is essential for tight binding by HSCAS. In these studies, adsorption data was fitted to multiple isotherm equations including the Langmuir, multi-Langmuir, general Freundlich, Langmuir-Freundlich, Toth and various transforms. Information derived included: the Gibbs standard free energy change of adsorption, enthalpy of adsorption, capacity, affinity, and heterogeneity coefficient. Computer modeling was also utilized to provide additional structural information and insight into the mechanism. Evidence suggests that aflatoxins may react at multiple sites on HSCAS particles, especially the interlayer region, but also at edges and basal surfaces. Since clay and zeolitic minerals comprise a broad family of functionally diverse chemicals, there may be significant hidden risks associated with their indiscriminate inclusion in the diet. All aflatoxin binding agents should be rigorously tested, paying particular attention to their effectiveness and safety in aflatoxin-sensitive animals and their potential for interactions with critical nutrients. (+info)
Electron paramagnetic resonance studies of the membrane fluidity of the foodborne pathogenic psychrotroph Listeria monocytogenes.
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Listeria monocytogenes is a foodborne psychrotrophic pathogen that grows at refrigeration temperatures. Previous studies of fatty acid profiles of wild-type and cold-sensitive, branched-chain fatty acid deficient mutants of L. monocytogenes suggest that the fatty acid 12-methyltetradecanoic (anteiso-C(15:0)) plays a critical role in low-temperature growth of L. monocytogenes, presumably by maintaining membrane fluidity. The fluidity of isolated cytoplasmic membranes of wild-type (SLCC53 and 10403S), and a cold-sensitive mutant (cld-1) of L. monocytogenes, grown with and without the supplementation of 2-methylbutyric acid, has been studied using a panel of hydrocarbon-based nitroxides (2N10, 3N10, 4N10, and 5N10) and spectral deconvolution and simulation methods to obtain directly the Lorentzian line widths and hence rotational correlation times (tau(c)) and motional anisotropies of the nitroxides in the fast motional region. tau(c) values over the temperature range of -7 degrees C to 50 degrees C were similar for the membranes of strains SLCC53 and 10403S grown at 10 degrees C and 30 degrees C, and for strain cld-1 grown with 2-methylbutyric acid supplementation (which restores branched-chain fatty acids) at 30 degrees C. However, strain cld-1 exhibited a threefold higher tau(c) when grown without 2-methylbutyric acid supplementation (deficient in branched-chain fatty acids) compared to strains SLCC53, 10403S, and supplemented cld-1. No evidence was seen for a clear lipid phase transition in any sample. We conclude that the fatty acid anteiso-C(15:0) imparts an essential fluidity to the L. monocytogenes membrane that permits growth at refrigeration temperatures. (+info)