Survival of Campylobacter jejuni and Salmonella enterica Typhimurium in vacuum-packed, moisture-enhanced pork

The abilities of Campylobacter jejuni and Salmonella enterica Typhimurium to survive in vacuum-packaged, moisture-enhanced pork stored at 4 or 10°C were examined. Pork loins were surface inoculated with either C. jejuni or Salmonella Typhimurium and then moisture enhanced to a target of 10 or 20%. The enhanced pork loins were sliced 1 cm thick and vacuum packaged. A pork loin without moisture enhancement was sliced and vacuum packaged as a control. Samples were collected, plated, and the numbers of surviving organisms were determined periodically during storage at 4 and 10°C. The numbers of C. jejuni or Salmonella Typhimurium in samples with different moisture enhancement levels were similar (P > 0.05). No significant differences (P > 0.05) in C. jejuni counts were observed between samples at 10°C and those at 4°C. In contrast, the numbers of Salmonella Typhimurium in samples at 10°C had significantly (P < 0.05) increased (0.41 log CFU/g) from those at the refrigerated temperature of 4°C. Vacuum storage at 4 and 10°C for 28 days did not result in dramatic reductions in the mean numbers of C. jejuni and Salmonella Typhimurium. Our findings indicate that vacuum packaging under chilled conditions will not add substantially to safety for moisture-enhanced pork. Strict hygienic practices or the implementation of decontamination technologies is recommended.     

Influence of prior growth conditions, pressure treatment parameters, and recovery conditions on the inactivation and recovery of Listeria monocytogenes, Escherichia coli, and Salmonella Typhimurium in turkey meat

The relatively high prevalence of Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella enterica serovar Typhimurium in various food products is of great concern to the food industry. The objective of this study was to determine the pressure-inactivation of the pathogens in a representative food model as affected by prior growth temperature, physiological age of the culture, pressure level and treatment temperature. The effect of post-treatment conditions (incubation temperature and gas atmosphere) on the bacterial recovery was also determined. The pathogens being studied were inoculated into sterile turkey breast meat to a final level of ca. 3 logCFU/g and then grown to two stages, the early stage (representative of exponential phase) and late stage (representative of stationary phase), at 15, 25, 35, and 40 °C. Turkey meat samples were pressure-treated at 400 and 600 MPa for 2 min at initial sample temperatures of 4, 20 and 40 °C. Following treatment, bacterial counts in the samples were determined aerobically or anaerobically at incubation temperatures of 15, 25, 35, and 40 °C. Pressure inactivation of the bacterial pathogens increased as a function of the pressure levels and treatment temperatures. Generally speaking, early stage cells were more resistant than late stage cells (P<0.05). The incubation gas atmosphere did not affect bacterial recovery. Bacteria grown at 15-35 °C underwent higher population reductions than those grown at 40 °C. With regard to recovery temperatures, low temperatures promoted greater recovery of injured early and late stage cells than higher temperatures (P<0.05). This study indicates the importance of environmental conditions to which bacteria are exposed prior to pressure treatment and recovery conditions of the bacteria after pressure treatment when considering the adequacy of pressure treatments to enhance the microbiological safety of foods.     

Reduction of Salmonella Typhimurium and Listeria monocytogenes on produce by trisodium phosphate

The application of trisodium phosphate (TSP) on produce against food-borne bacteria has not been extensively evaluated. This research studied the effect of 20 and 50 mg/ml TSP in reducing Salmonella Typhimurium (ST) and Listeria monocytogenes (Lm) on model produce (lettuce and peppers). Washed and air-dried Iceberg lettuce (3 × 3 cm²) and Jalapeno peppers (25–30 g) were spiked with S. Typhimurium or L. monocytogenes (～7 log₁₀ CFU/ml). Samples were treated with 20 or 50 mg/ml TSP, 200 mg/L sodium hypochlorite (for comparison with traditional washes) or water (control rinse) for 15 or 30 s. Treatments were immediately neutralized with trypticase soy broth (TSB) containing 30 mg/ml beef extract, serially diluted, plated on Xylose Lysine Tergitol 4 (XLT4) agar for ST and Tryptic Soy Agar (TSA) for Lm and incubated at 37 °C for 24–48 h. Results showed that 20 mg/ml TSP and 200 mg/L sodium hypochlorite caused 5–6 log₁₀ CFU/ml reduction in ST on both lettuce and peppers after 15 s and 30 s, while 50 mg/ml TSP reduced ST to undetectable levels on both produce at both contact times. For overnight Lm cultures, a mere reduction of 0.21 and 0.28 log₁₀ CFU/ml was obtained using 20 and 50 mg/ml TSP after even 5 min, while 200 mg/L sodium hypochlorite decreased Lm by ～1 log₁₀ CFU/ml after 30 s and 1 min on lettuce, and decreased pure culture Lm to undetectable levels after 3 min. Thus, 50 mg/ml TSP appears effective against ST with negligible effects against Lm, whose mode of action needs to be understood.     

Change in attachment of Salmonella Typhimurium, Yersinia enterocolitica, and Listeria monocytogenes to pork skin and muscle after hot water and lactic acid decontamination

The attachment of Salmonella enterica subsp. enterica serovar Typhimurium, Yersinia enterocolitica, and Listeria monocytogenes to pig skin and muscle tissue decontaminated with 80 °C water or 55 °C, 1% lactic acid for 5 and 15 s was investigated. Attachment properties differed between skin and muscle surfaces. A significantly higher number of firmly attached bacteria was found on the decontaminated skin surface compared to the non-treated skin surface, both on hot water (P < 0.0001) and on lactic acid treated skin (P < 0.001). At the muscle surfaces, no such difference in attachment were shown between hot water treated surfaces and non-treated surfaces. In contrast, for lactic acid decontamination, significantly fewer bacteria attached to the treated muscle surfaces (P < 0.0001). The study did not show significant differences in surface attachment, between Salmonella, Yersinia and Listeria, which indicate that surface and environmental factors may influence attachment more than bacterial properties. A more profound location of attached bacteria at muscle compared to skin was indicated. Confocal laser scanning microscopy studies showed that bacteria located in deep tissue structures of non-decontaminated and decontaminated skin and muscle surfaces. In the latter, bacteria tended to “hide” between the muscle fibres and may be entrapped at those sites. The finding of changed attachment properties at skin after decontamination may play a role in cross- and recontamination, during subsequent meat processing.     

Comparison of sampling procedures for recovery of Listeria monocytogenes from stainless steel food contact surfaces

A number of techniques exist for microbiological sampling of food processing environments in food industries. In the present study the efficacies of nine sampling procedures for the recovery of Listeria monocytogenes from food contact surfaces, including a new sampling device consisting of a miniroller, were evaluated and compared. A stainless steel table was inoculated with L. monocytogenes strain 935 (serovar 4b, human origin) and L. monocytogenes strain 437/07 (serovar 1/2b, food origin), at 10(5) CFU/100 cm(2). L. monocytogenes strain 935 was best recovered with the minirollers (recovery of up to 6.27%), while poor recoveries (<0.30%) were obtained with the towel (one-ply composite tissue), alginate swab, metallic swab, and Petrifilm methods. In the case of L. monocytogenes strain 437/07 the replicate organism detection and counting (RODAC) ALOA contact plates yielded the best recoveries (4.15%), followed by the minirollers (up to 1.52%). Overall, recovery percentages with the minirollers were higher with stomacher homogenization than with Vibromatic agitation. The recovery percentages obtained for the Listeria strain of human origin were higher than those obtained with the food strain for all sampling procedures except Petrifilm and RODAC ALOA. With the miniroller device coated with wool fiber, the recovery of L. monocytogenes can be improved from 2 to 17 times over recoveries obtained with the sponge and cotton swab. This is the first report of a miniroller device for microbiological sampling in the available literature. The novel sampling procedure is convenient to apply on surfaces, is cost-effective, and results in better recovery of L. monocytogenes than do the conventional methods.     

Antibacterial activities of phenolic benzaldehydes and benzoic acids against Campylobacter jejuni, Escherichia coli, Listeria monocytogenes, and Salmonella enterica

We evaluated the bactericidal activities of 35 benzaldehydes, 34 benzoic acids, and 1 benzoic acid methyl ester against Campylobacter jejuni, Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica when these compounds were substituted on the benzene ring with 0, 1, 2, or 3 hydroxy (OH) and/or methoxy (OCH3) groups in a pH 7.0 buffer. Dose-response plots were used to determine the percentage of the sample that induced a 50% decrease in CFU after 60 min (BA50). Of the 70 compounds tested, 24 were found to be active against all four pathogens, and additional 4, 10, and 12 were found to be active against three, two, and one of the pathogens, respectively. C. jejuni was approximately 100 times as sensitive as the other three pathogens. The 10 compounds that were most active against the four pathogens (with average BA50 values ranging from 0.026 to 0.166) and are candidates for studies of activity in foods or for disinfections were 2,4,6-trihydroxybenzaldehyde, 2,5-dihydroxybenzaldehyde, 2,3,4-trihydroxybenzaldehyde, 2-hydroxy-5-methoxybenzaldehyde, 2,3-dihydroxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 4-hydroxy-2,6-dimethoxybenzaldehyde, 2,5-dihydroxybenzaldehyde, 2,4-dihydroxybenzaldehyde. and 2-hydroxybenzaldehyde. Comparison of the chemical structures of the test compounds and their activities revealed that (i) the aldehyde (CHO) group was more active than the carboxyl (COOH) group whether or not OH groups were present; (ii) compounds were most active with trisubstituted OH > disubstituted OH > monosubstituted OH; (iii) for disubstituted derivatives, 2-OH enhanced activities were exhibited by benzaldehyde but not by benzoic acid; (iv) compounds were more active with OH than with OCH3, irrespective of the position of substitution on the benzene ring; (v) compounds with mixed OH and OCH3 groups exhibited variable results, i.e., in some cases OCH3 groups enhanced activity and in other cases they did not; (vi) methoxybenzoic acids were largely inactive; and (vii) gallic acid was 20 times as active against S. enterica at pH 7.0 as it was at pH 3.7, suggesting that the ionization of its OH groups may enhance bactericidal activity.     

Inhibition of Salmonella Typhimurium and Listeria monocytogenes in mung bean sprouts by chemical treatment

This study was undertaken to compare the efficacies of chlorous acid (268 ppm), sodium hypochlorite (200 ppm), and lactic acid (2%) in eliminating total mesophilic microorganisms, Salmonella Typhimurium, and Listeria monocytogenes on commercial mung bean sprouts immediately after treatment and during posttreatment refrigerated storage. Treatment with sodium hypochlorite for 10 min did not reduce the total aerobic count. However, treatment with lactic acid and chlorous acid for 10 min initially reduced the total aerobic count by 0.6 and 0.8 log CFU/g, respectively, and maintained the same level or a lower level of the total aerobic count during the storage time. Treatment with chlorous acid reduced Salmonella Typhimurium from 5.0 log to undetectable levels (<0.48 log CFU/g), and the pathogen remained undetectable over a 9-day storage period. Treatment with lactic acid resulted in an initial 3-log reduction and further reduced the number of Salmonella Typhimurium cells to undetectable levels after 3 days. For L. monocytogenes, treatment with chlorous acid resulted in an initial 5-log reduction, and treatment with lactic acid resulted in a 2-log reduction at the beginning and undetectable levels after 9 days. When chemically injured cells were investigated by the selective overlay method, no statistical difference was observed (P < 0.05) between the number of injured cells recovered following treatment with chlorous acid and the number of bacteria counted on selective media, whereas sodium hypochlorite generated more injured cells than the other treatments did. These data suggest that treatment with chlorous acid may be useful in reducing total mesophilic microorganisms, Salmonella Typhimurium, and L. monocytogenes in commercial mung bean sprouts.     

Campylobacter, Salmonella, Listeria monocytogenes, verotoxigenic Escherichia coli, and Escherichia coli prevalence, enumeration, and subtypes on retail chicken breasts with and without skin

This study examined the prevalence, counts, and subtypes of Campylobacter, Salmonella, Listeria monocytogenes, verotoxigenic Escherichia coli (VTEC), and E. coli on raw retail chicken breast with the skin on versus the skin off. From January to December 2007, 187 raw skin-on chicken breasts and 131 skin-off chicken breasts were collected from randomly selected retail grocery stores in the Region of Waterloo, Ontario, Canada. Campylobacter isolates were recovered from a higher proportion of the skin-off chicken breasts, 55 (42%) of 131, than of the skin-on chicken breasts tested, 55 (29%) of 187 (P = 0.023). There was no difference in the proportion of Salmonella isolates recovered from the two meat types (P = 0.715): 40 (31%) of 131 skin-off chicken breasts versus 61 (33%) of 187 skin-on chicken breasts. L. monocytogenes isolates were recovered from a statistically lower proportion of the skin-off chicken breasts, 15 (15%) of 99, than of the skin-on chicken breasts, 64 (34%) of 187 (P = 0.001). There was no difference in the proportion of E. coli isolates recovered from the skin-off chicken breasts, 33 (33%) of 99, than from the skin-on chicken breasts, 77 (41%) of 187 (P = 0.204). VTEC was detected on a single skin-off chicken breast. Campylobacter jejuni was the most frequent species isolated on both types of chicken meat: skin-on, 48 (87%) of 55, and skin-off, 51 (94%) of 54. Salmonella serotypes Kentucky and Heidelberg and L. monocytogenes serotype 1/2a were the most frequently detected serotypes from both skin-off and skin-on chicken breasts. Although there appeared to be a trend toward higher enumeration values of these pathogens and E. coli on the skin-on chicken, the differences did not exceed 1 log. This study suggested that skin-off chicken breast may represent a higher risk of consumer exposure to Campylobacter, a similar risk for Salmonella, VTEC, and E. coli, and a lower risk for L. monocytogenes than skin-on chicken breast.     

Contamination of chicken carcasses in Gauteng, South Africa, by Salmonella, Listeria monocytogenes and Campylobacter

The presence of the foodborne pathogens, Salmonella spp., Listeria monocytogenes and Campylobacter spp., on 99 fresh and frozen chicken carcasses sourced from various retailers in Gauteng, South Africa, was investigated. Using culture methods, 60.6% of the carcasses were found to be contaminated with one or more pathogens, with 19.2%, 19.2% and 32.3% of the carcasses being found to harbour Salmonella, L. monocytogenes and Campylobacter, respectively. The extent of contamination with one or more pathogens was not significantly different (p>0.1) between fresh or frozen samples or between samples from butcheries, supermarkets or street vendors. Significantly more (p<0.1) fresh carcasses from butcheries than from other outlets were contaminated with Salmonella, while more fresh carcasses from supermarkets were contaminated with Campylobacter. The proportion of carcasses with L. monocytogenes from all sources were similar. Polymerase chain reaction (PCR) results indicate an even higher extent of pathogen contamination, but the PCR techniques need to be further refined before they can be used routinely.     

Stability of electrolyzed oxidizing water and its efficacy against cell suspensions of Salmonella typhimurium and Listeria monocytogenes

Electrolyzed oxidizing (EO) water has proved to be effective against foodborne pathogens attached to cutting boards and poultry surfaces and against spoilage organisms on vegetables; however, its levels of effectiveness against Listeria monocytogenes and Salmonella Typhimurium in cell suspensions have not been compared with those of other treatments. In this study, the oxidation reduction potentials (ORPs), chlorine concentrations, and pHs of acidic and basic EO water were monitored for 3 days at 4 and 25 degrees C after generation. There were no differences between the pHs or ORPs of acidic and basic EO waters stored at 4 or 25 degrees C. However, the free chlorine concentration in acidic EO water stored at 4 degrees C increased after 24 h. In contrast, the free chlorine concentration in acidic EO water stored at 25 degrees C decreased after one day. Cell suspensions of Salmonella Typhimurium and L. monocytogenes were treated with distilled water, chlorinated water (20 ppm), acidified chlorinated water (20 ppm, 4.5 pH), acidic EO water (EOA), basic EO water (EOB), or acidic EO water that was "aged" at 4 degrees C for 24 h (AEOA) for up to 15 min at either 4 or 25 degrees C. The largest reductions observed were those following treatments carried out at 25 degrees C. EOA and AEOA treatments at both temperatures significantly reduced Salmonella Typhimurium populations by > 8 log10 CFU/ml. EOA and AEOA treatments effectively reduced L. monocytogenes populations by > 8 log10 CFU/ml at 25degrees C. These results demonstrate the stability of EO water under different conditions and that EO water effectively reduced Salmonella Typhimurium and L. monocytogenes populations in cell suspensions.     

Detection of Listeria monocytogenes in pigs and pork

In this study, we surveyed hogs (n = 300) as well as pork products (ground pork and raw chitterlings) for Listeria monocytogenes. Pig specimens collected before (tonsil swabs) and after slaughter (tonsils, lymph nodes, carcass swabs, and rectal contents) were examined for L. monocytogenes by enrichment with conventional enrichment broths followed by subculturing to selective agar. A multiplex polymerase chain reaction assay targeting the highly conserved 16S rRNA gene of the Listeria species as well as the hlyA gene unique to L. monocytogenes was used to screen aliquots of the enrichment (method I) as well as to confirm presumptive Listeria colonies from Columbia agar with 0.05% glucose supplemented with polymyxin B-acriflavine-lithium chloride-ceftazidime-aesculin-mannitol (PALCAM; method II). Subculturing to PALCAM agar was the more sensitive of the two methods on the basis of the overall detection of Listeria. For hog tissues, method I detected L. monocytogenes (0.87% positive) and no other Listeria spp. in all samples (n = 1,849). In contrast, method II detected significantly more (P < 0.05) L. monocytogenes (2.38%) and Listeria spp. (0.38%) in these tissues. For small intestines (n = 300 raw chitterlings), L. monocytogenes was identified in 8.3% of enrichments with University of Vermont modified Listeria enrichment broth; plating to PALCAM slightly improved recovery (9%). Overall, ground pork samples (n = 340) harbored L. monocytogenes (45% positive) and other Listeria species (1.5% positive), as determined by method I. Subculturing to PALCAM significantly (P < 0.05) improved the detection of L. monocytogenes (50.2%) but not that of other Listeria species (1.7%). L. monocytogenes isolates (n = 243) were assigned to serotype 1 (53.5%), serotype 4 (25%), and serotypes other than 1 and 4 (21.4%).     

Nonaplex real-time PCR detection of Listeria monocytogenes, Campylobacter, Salmonella and enteropathogene E. coli after universal enrichment in food samples

A universal cultivation media for Listeria monocytogenes, Salmonella and enteropathogenic Escherichia coli in conjunction with a highly efficient nonaplex PCR for the determination of L. monocytogenes, Campylobacter, Salmonella and enteropathogenic E. coli was developed and compared to classical microbiological assays. The achieved detection limit was at 2 colony-forming units per g for all analytes. The method allows screening of food samples within 24 h and is partly automatable. A ring trial showed that it can be easily established in other laboratories showing its robustness. The presented method yields results similar to the classical ISO methods based on cultivation.     

Incidence of Salmonella, Campylobacter jejuni, Campylobacter coli, and Listeria monocytogenes in poultry carcasses and different types of poultry products for sale on the Belgian retail market.

From January 1997 to May 1998, 772 samples of poultry carcasses and poultry products for sale on the retail market in Belgium were analyzed for the presence of Salmonella spp., Salmonella Enteritidis, Campylobacter jejuni, C. coli, and Listeria monocytogenes per 100 cm2 or 25 g. Poultry samples were contaminated with Salmonella (36.5%), C. jejuni and C. coli (28.5%), and L. monocytogenes (38.2%). In about 12.3% of the poultry samples, the L. monocytogenes contamination level exceeded 1 CFU per g or cm2. Significant differences in pathogen contamination rates of poultry products were noticed between the poultry products originating from Belgian, French, and U.K. abattoirs. Poultry products derived from broiler chickens running free in pine woods until slaughtering age (12 to 13 weeks) had a significantly (P < 0.05) lower contamination rate of Salmonella than poultry products from enclosed broilers slaughtered at the age of 6 to 8 weeks. A significantly (P < 0.05) lower pathogen contamination rate was noted for Salmonella, C. jejuni, and C. coli for poultry cuts without skin compared to poultry cuts with skin on. An increase in pathogen contamination rate was noticed during cutting and further processing. To diminish C. jejuni, C. coli, Salmonella, and L. monocytogenes contamination rates, hygienic rules of slaughter and meat processing must be rigorously observed. At the moment, zero tolerance for these pathogens is not feasible, and there is a need to establish criteria allowing these pathogens to be present at reasonable levels in the examined poultry samples.     

Modeling the inactivation of Salmonella Typhimurium, Listeria monocytogenes, and Salmonella Enteritidis on poultry products exposed to pulsed UV light

Pulsed UV light inactivation of Salmonella Typhimurium on unpackaged and vacuum-packaged chicken breast, Listeria monocytogenes on unpackaged and vacuum-packaged chicken frankfurters, and Salmonella Enteritidis on shell eggs was explained by log-linear and Weibull models using inactivation data from previous studies. This study demonstrated that the survival curves of Salmonella Typhimurium and L. monocytogenes were nonlinear exhibiting concavity. The Weibull model was more successful than the log-linear model in estimating the inactivations for all poultry products evaluated, except for Salmonella Enteritidis on shell eggs, for which the survival curve was sigmoidal rather than concave, and the use of the Weibull model resulted in slightly better fit than the log-linear model. The analyses for the goodness of fit and performance of the Weibull model produced root mean square errors of 0.059 to 0.824, percent root mean square errors of 3.105 to 21.182, determination coefficients of 0.747 to 0.989, slopes of 0.842 to 1.042, bias factor values of 0.505 to 1.309, and accuracy factor values of 1.263 to 6.874. Overall, this study suggests that the survival curves of pathogens on poultry products exposed to pulsed UV light are nonlinear and that the Weibull model may generally be a useful tool to describe the inactivation patterns for pathogenic microorganisms affiliated with poultry products.     

The antimicrobial effect of thiamine dilauryl sulfate in tofu inoculated with Escherichia coli O157:H7, Salmonella Typhimurium,Listeria monocytogenes and Bacillus cereus

Food Science and Biotechnology - Thiamine dilauryl sulfate (TDS) is a food additive that is used as a bactericidal agent. This study examines the antimicrobial effect of TDS on tofu inoculated with...     

Occurrence of Escherichia coli O157:H7, Listeria monocytogenes, Salmonella and Campylobacter spp. on beef carcasses in Northern Ireland

A survey of beef carcasses was conducted in all 10 European community approved abattoirs in Northern Ireland to determine the incidence of Escherichia coli O157:H7. Analyses were based on excised samples of neck meat taken less than 48 h post-kill. Overall, 780 carcasses were sampled and all were negative for E. coli O157:H7. A sub-set of samples was analysed for the presence of Listeria monocytogenes (n=200), Salmonella (n=200) and Campylobacter spp.(n=100). L. monocytogenes was not detected but Listeria innocua was found on five carcasses and Listeria seeligeri on one. Three carcasses carried salmonellas; Salmonella Mbandaka was found on two and Salmonella Thompson on one. Campylobacter spp. were not detected on any carcasses. The results indicate that very few beef carcasses in Northern Ireland appear to carry any of the four pathogens sought, and this may help explain the low incidence of E. coli O157:H7 in the Northern Ireland human population, relative to the rest of the UK.     

Enhanced antimicrobial activity of nisin in combination with allyl isothiocyanate against Listeria monocytogenes,Staphylococcus aureus,Salmonella Typhimurium and Shigella boydii

This study was designed to evaluate the synergistic antimicrobial effect of nisin and allyl isothiocyanate (AITC) against Listeria monocytogenes, Staphylococcus aureus, Salmonella Typhimurium and Shigella boydii. The synergistic interactions between nisin and AITC were observed against all foodborne pathogens, showing the fractional inhibitory concentrations <1. The populations of L. monocytogenes and S. aureus at the combined treatment of nisin and AITC were decreased to below 1 log CFU mL^?1 after 10‐h incubation at 37 °C. The changes in fatty acid profiles of all strains were substantially influenced by nisin alone and the combined treatment of nisin and AITC. A good agreement was observed among cell viability, membrane permeability and depolarisation activity in response to nisin and AITC. The results suggest that nisin and AITC as synergistic inhibitors could be an effective approach to achieve satisfactory antimicrobial activity against a wide range of foodborne pathogens.     

Laboratory-scale preparation of soft cheese artificially contaminated with low levels of Escherichia coli O157, Listeria monocytogenes, and Salmonella enterica serovars Typhimurium, Enteritidis, and Dublin

The production of cheese with incurred low levels of pathogenic microorganisms stressed by the production process was the aim of the study. A standard protocol for the preparation of artificially contaminated soft cheese on a laboratory scale was developed. Milk for cheese preparation was artificially contaminated with pathogenic target microorganisms at low levels, between 1 and 10 CFU/ml. Two strains of Escherichia coli OI157:H7, two strains of Listeria monocytogenes, and three Salmonella spp. (Salmonella enterica serovars Typhimurium, Enteritidis, and Dublin) were investigated. The food pathogens in the cheese were exposed to the entire production process. All three microorganism species survived the cheese production process and were detected in the final product at concentrations between 1 and 50 CFU/g. The cheese produced contains target microorganisms that have been exposed to curd formation, drainage, setting, and ripening. This cheese can be used to validate microbiological methods or to examine the target microorganisms in a natural food environment at low concentrations. It represents an alternative to artificial contamination of cheese by adding target microorganisms to a final cheese product.     

Bactericidal activities of plant essential oils and some of their isolated constituents against Campylobacter jejuni,Escherichia coli,Listeria monocytogenes,and Salmonella enterica

An improved method of sample preparation was used in a microplate assay to evaluate the bactericidal activity levels of 96 essential oils and 23 oil compounds against Campylobacter jejuni, Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica obtained from food and clinical sources. Bactericidal activity (BA50) was defined as the percentage of the sample in the assay mixture that resulted in a 50% decrease in CFU relative to a buffer control. Twenty-seven oils and 12 compounds were active against all four species of bacteria. The oils that were most active against C. jejuni (with BA50 values ranging from 0.003 to 0.009) were marigold, ginger root, jasmine, patchouli, gardenia, cedarwood, carrot seed, celery seed, mugwort, spikenard, and orange bitter oils; those that were most active against E. coli (with BA50 values ranging from 0.046 to 0.14) were oregano, thyme, cinnamon, palmarosa, bay leaf, clove bud, lemon grass, and allspice oils; those that were most active against L monocytogenes (with BA50 values ranging from 0.057 to 0.092) were gardenia, cedarwood, bay leaf, clove bud, oregano, cinnamon, allspice, thyme, and patchouli oils; and those that were most active against S. enterica (with BA50 values ranging from 0.045 to 0.14) were thyme, oregano, cinnamon, clove bud, allspice, bay leaf, palmarosa, and marjoram oils. The oil compounds that were most active against C. jejuni (with BA50 values ranging from 0.003 to 0.034) were cinnamaldehyde, estragole, carvacrol, benzaldehyde, citral, thymol, eugenol, perillaldehyde, carvone R, and geranyl acetate; those that were most active against E. coli (with BA50 values ranging from 0.057 to 0.28) were carvacrol, cinnamaldehyde, thymol, eugenol, salicylaldehyde, geraniol, isoeugenol, citral, perillaldehyde, and estragole; those that were most active against L monocytogenes (with BA50 values ranging from 0.019 to 0.43) were cinnamaldehyde, eugenol, thymol, carvacrol, citral, geraniol, perillaldehyde, carvone S, estragole, and salicylaldehyde; and those that were most active against S. enterica (with BA50 values ranging from 0.034 to 0.21) were thymol, cinnamaldehyde, carvacrol, eugenol, salicylaldehyde, geraniol, isoeugenol, terpineol, perillaldehyde, and estragole. The possible significance of these results with regard to food microbiology is discussed.     

Antimicrobial effect of herb extracts against Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella typhimurium associated with beef

The effects of plant extracts against pathogenic bacteria in vitro are well known, yet few studies have addressed the effects of these compounds against pathogens associated with muscle foods. A series of experiments was conducted to determine the effectiveness of a commercially available, generally recognized as safe, herb extract dispersed in sodium citrate (Protecta One) or sodium chloride (Protecta Two) against Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes associated with beef. In the first experiment, E. coli O157:H7, Salmonella typhimurium, and L. monocytogenes inoculated onto beef and subjected to surface spray treatments with 2.5% solutions of Protecta One or Protecta Two were not affected by immediate application (day 0) of the herbal extracts. However, after 7 days of storage at 4 degrees C, E. coli O157:H7 was reduced by >1.3 log10 CFU/cm2 by Protecta Two; L. monocytogenes was reduced by 1.8 and 1.9 log10 CFU/cm2 by Protecta One and Protecta Two, respectively; Salmonella typhimurium was not reduced >0.3 log10 CFU/cm2 by either extract by day 7. In the second experiment, 2.5% Protecta Two (wt/vol or wt/wt) added to inoculated lean and adipose beef trim, processed, and packaged as ground beef chubs (80% lean, 20% adipose), did not reduce pathogen populations >0.5 log10 CFU/g up to 14 days at 4 degrees C. In the third experiment, surface spray treatments of beef with 2.5% lactic acid or 2.5% solutions of Protecta One or Protecta Two, vacuum packaged, and stored up to 35 days at 4 degrees C did reduce E. coli O157:H7, L. monocytogenes, and Salmonella Typhimurium slightly. These studies suggest that the use of herb extracts may afford some reductions of pathogens on beef surfaces; however, the antimicrobial activity may be diminished in ground beef by adipose components.