噬菌体对鸡肉表面耐药沙门氏菌的抑制作用

目的 探究裂解性噬菌体对鸡肉表面耐药沙门氏菌的抑制效果.方法 以实验室前期筛选得到的沙门氏菌噬菌体D1-2和Pu20为研究材料,采用单独使用和1:1混合的方式对生鸡胸肉表面多重耐药沙门氏菌的抑制效果进行研究.结果 与单一噬菌体相比,噬菌体混合制剂对生鸡胸肉表面多重耐药沙门氏菌抑菌效果更显著.在4℃时,采用感染复数(mu...     

Whey protein improves survival and release characteristics of bacteriophage Felix O1 encapsulated in alginate microspheres

Bacterial contamination is a major cause of food poisoning in humans worldwide. Phage therapy is a potential alternative to antibiotics in food animal production. Gastric acidity has been shown to compromise the viability of phage in vitro, hence, may affect the effectiveness of the phage treatment. Microencapsulation of bacteriophage in alginate microspheres protected phage against gastric acids; however, the release rate of phage was too slow when applied in chicks. The current study investigated the in vitro protection and release characteristics of alginate–whey protein microspheres (AWM) containing phage Felix O1 prepared by an extrusion method. Free phage was completely inactivated within minutes in simulated gastric fluid (SGF) at pH 2.0 and pH 2.5, while phage encapsulated in AWM mostly retained their viability after 2.0 h incubation. Encapsulated phage was completely released from the AWM in simulated intestinal fluid (SIF) within 3 h. Moreover, addition of maltodextrin to the encapsulation formula improved phage stability during air drying and storage. Our results show that addition of whey to alginate microsphere improved phage protection against acidic conditions and accelerated the release rate in SIF. AWM could be more suitable for oral phage therapy in chickens.     

Modeling the effect of temperature on growth of Salmonella in chicken

Growth data of Salmonella in chicken were collected at several isothermal conditions (10, 15, 20, 25, 28, 32, 35, 37, 42, and 45 degrees C) and were then fitted into primary models, namely the logistic model, modified Gompertz model and Baranyi model. Measures of goodness-of-fit such as mean square error, pseudo-R(2), -2 log likelihood, Akaike's information, and Sawa's Bayesian information criteria were used for comparison for these primary models. Based on these criteria, modified Gompertz model described growth data the best, followed by the Baranyi model, and then the logistic model. The maximum growth rates obtained from each primary model were then modeled as a function of temperature using the modified Ratkowsky model. Pseudo-R(2) values for this secondary model describing growth rate obtained from Baranyi, modified Gompertz, and logistic models were 0.999, 0.980, and 0.990, respectively. Mean square error values for corresponding models were 0.0002, 0.0008, and 0.0009, respectively. Both measures clearly show that the Baranyi model performed better than the modified Gompertz model or the logistic model.     

Development and validation of a stochastic model for predicting the growth of Salmonella typhimurium DT104 from a low initial density on chicken frankfurters with native microflora

The presence of native microflora is associated with increased variation of Salmonella growth among batches and portions of chicken meat and as a function of temperature. However, variation of Salmonella growth can be modeled using a 95% prediction interval (PI). Because there are no reports of predictive models for growth of Salmonella on ready-to-eat poultry meat products with native microflora and because Salmonella is usually present at low levels on poultry meat, the current study was conducted to develop and validate a stochastic model for predicting the growth of Salmonella from a low initial density on chicken frankfurters with native microflora. One-gram portions of chicken frankfurters were inoculated with 0.5 log CFU of a single strain (ATCC 700408) of Salmonella Typhimurium DT104. Changes in pathogen numbers over time, N(t), were fit to a two-phase linear primary model to determine lag time (lambda), growth rate (mu), and the 95% PI, which characterized the variation of pathogen growth. Secondary quadratic polynomial models for natural log transformations of lambda, mu, and PI as a function of temperature (10 to 40 degrees C) were obtained by nonlinear regression. The primary and secondary models were combined in a computer spreadsheet to create a tertiary model that predicted the growth curve and PI. The pathogen did not grow on chicken frankfurters incubated at 10 to 12 degrees C, but mu ranged from 0.003 log CFU/g/h at 14 degrees C to 0.176 log CFU/ g/h at 30 degrees C to 0.1 log CFU/g/h at 40 degrees C. Variation of N(t) increased as a function of time (i.e., PI was lower during lag phase than during growth phase) and temperature (i.e., PI was higher at 18 to 40 degrees C than at 10 to 14 degrees C). For dependent data (n = 338), 90.5% of observed N(t) values were in the PI predicted by the tertiary model, whereas for independent data (n = 86), 89.5% of observed N(t) values were in the PI predicted by the tertiary model. Based on this performance evaluation, the tertiary model was considered acceptable and valid for stochastic predictions of Salmonella Typhimurium DT104 growth from a low initial density on chicken frankfurters with native microflora.     

Modeling the growth of Listeria monocytogenes based on a time to detect model in culture media and frankfurters

In the current study, temperature dependent growth of Listeria monocytogenes strain H7776, with an initial inoculum level of approximately 0.1 CFU/mL or g, was modeled based on "time to detect" (TTD) using the Arrhenius equation. The activation energies (E(a)) obtained from specific growth rate and lag phase duration in tryptic soy broth (TSB) and frankfurters were compared. At 4 degrees C, the TTD for L. monocytogenes was 217 h in TSB and 48 h in portions of frankfurters. The TTD decreased as temperature increased from 4 to 36 degrees C in both culture media and frankfurters, and this relationship was modeled using the Arrhenius equation. Based on this model, the E(a) values for the TTD in TSB and frankfurters averaged 22.7 and 18.7 kcal/mol, respectively, and were not significantly different (p<0.05). Linear regression was performed on the exponential part of the growth curve to evaluate specific growth rate constants at each temperature using the Monod model. The E(a) values were also calculated based on the specific growth rate and the lag phase of L. monocytogenes in TSB and frankfurters incubated in the same range of temperatures. The average E(a) values for the specific growth rates and the lag phase durations in TSB cultures were 19 and 21 kcal/mol, respectively. In frankfurters, the average E(a) values were slightly greater for both specific growth rate and lag phase duration (29 and 35 kcal/mol, respectively), but these values were not significantly different from the E(a) calculated for the TTD in each medium. These results indicate that the TTD concept can be used to develop and validate safety-based shelf life models.     

Effects of static magnetic fields on growth and membrane lipid composition of Salmonella typhimurium wild-type and dam mutant strains

This study was carried out to explore the adaptive mechanisms of S. typhimurium particularly, the implication of the Dam methyltransferase in the remodelling of membrane lipid composition to overcome magnetic field stress. With this aim, we focused our analyses on the increase in viable numbers and membrane lipid modifications of S. typhimurium wild-type and dam mutant cells exposed for 10h to static magnetic fields (SMF; 200 mT). For the wild-type strain, exposure to SMF induced a significant decrease (p<0.05) of CFU at 6h, followed by an increase between 8 and 10h. Growth of the dam mutant was significantly affected (p<0.05) after 6h and no recovery was observed until 10h, highlighting a different behavior of SMF stressed wild-type and dam mutant strains. SMF significantly affected the phospholipid proportions in the two strains. The most affected were those of the acidic phospholipids, cardiolipins (CL). In the dam strain the phospholipid response to SMF followed a globally similar trend as in the wild-type with however lower effects, leading mainly to an unusual accumulation of CL. This would in part explain the different behavior of the wild-type and the dam strain. Results showed a significant increase of membrane cyclic fatty acids Cyc17 and Cyc19 in the wild-type strain but only the Cyc17 in the dam strain and a meaningful increase of the total unsaturated fatty acids (UFAs) to total saturated fatty acids (SFAs) ratios of the exposed cells compared to controls from 3 to 9h (p<0.05) for both strains. The net increase of the total UFAs to total SFAs ratios seemed to result mainly from the increase of (C18:1) proportion (p<0.05) and to a lower extent from that of (C16:1) (p<0.05). These modifications of cyclic and unsaturated fatty acid proportions constitute an adaptive response to SMF stress in S. typhimurium wild-type and dam mutants to maintain an optimum level of membrane fluidity under SMF.     

3种方法鉴定鸡肉粉中沙门氏菌的比对研究

目的采用3种方法对鸡肉粉中沙门氏菌进行检测。方法3份样品的前处理依据组织方提供的《作业指导书》进行,每瓶样品直接加入4.5 mL灭菌去离子水复溶,作为初始样本,后续实验依据GB4789.4-2016《食品安全国家标准食品微生物学检验沙门氏菌检验》操作。鉴定分离出疑似菌后,加入了实时荧光定量PCR法、基质辅助激光解吸电离飞行时间质谱法2种方法作为辅助检测,并用全自动微生物鉴定系统进行生化鉴定,再结合生化鉴定与血清学实验综合评判检测结果。结果使用3种鉴定方法在JS015、JS110、JS140样本中均检出沙门氏菌。结论本研究采用的实时荧光定量PCR法、基质辅助激光解吸电离飞行时间质谱法2种方法均能快速准确鉴定出沙门菌,特别是基质辅助激光解吸电离飞行时间质谱法和血清学分型配合使用,对沙门菌的快速鉴定有重要意义。     

The effect of temperature on the growth and persistence of Salmonella in fermented liquid pig feed

Two studies were conducted to investigate the effect of temperature on the fate of Salmonella enterica subsp. enterica serovar typhimurium DT104:30 in fermented liquid pig feed. These were (1) by co-inoculation of feed with S. typhimurium DT104:30 and Pediococcus pentosaceus, as the fermenting organism, and (2) by fermenting feed for 48, 72 or 96 h prior to inoculation with S. typhimurium DT104:30. In co-inoculated feed incubated at 20 degrees C, S. typhimurium DT104:30 persisted for at least 72 h. In contrast, in feed incubated at 30 degrees C, no S. typhimurium DT104:30 were detectable 48 h after inoculation. In prefermented feed, S. typhimurium DT104:30 died four to five times faster in feed maintained at 30 degrees C (D(value) 34-45 min) compared with feed maintained at 20 degrees C (D(value) 137-250 min). This was not entirely due to differences in lactic acid concentration as feed fermented for 72 or 96 h at 20 degrees C and feed fermented for 48 h at 30 degrees C contained similar concentrations of lactic acid (160-170 mM). Low numbers of S. typhimurium DT104:30 were still detectable in fermented feed 24 h after inoculation at 20 degrees C. In contrast, none were detectable 6-7 h after inoculation at 30 degrees C. The results of these studies indicate that it would be advisable for pig producers to control the temperature of liquid feed tanks to reduce the risk of Salmonella contamination.     

Response surface models for effects of temperature and previous growth sodium chloride on growth kinetics of Salmonella typhimurium on cooked chicken breast

Response surface models were developed and validated for effects of temperature (10 to 40 degrees C) and previous growth NaCl (0.5 to 4.5%) on lag time (lambda) and specific growth rate (mu) of Salmonella Typhimurium on cooked chicken breast. Growth curves for model development (n = 55) and model validation (n = 16) were fit to a two-phase linear growth model to obtain lambda and mu of Salmonella Typhimurium on cooked chicken breast. Response surface models for natural logarithm transformations of lambda and mu as a function of temperature and previous growth NaCl were obtained by regression analysis. Both lambda and mu of Salmonella Typhimurium were affected (P < 0.0001) by temperature but not by previous growth NaCl. Models were validated against data not used in their development. Mean absolute relative error of predictions (model accuracy) was 26.6% for lambda and 15.4% for mu. Median relative error of predictions (model bias) was 0.9% for lambda and 5.2% for mu. Results indicated that the models developed provided reliable predictions of lambda and mu of Salmonella Typhimurium on cooked chicken breast within the matrix of conditions modeled. In addition, results indicated that previous growth NaCl (0.5 to 4.5%) was not a major factor affecting subsequent growth kinetics of Salmonella Typhimurium on cooked chicken breast. Thus, inclusion of previous growth NaCl in predictive models may not significantly improve our ability to predict growth of Salmonella spp. on food subjected to temperature abuse.     

Survival and growth of alkali-stressed Listeria monocytogenes on beef frankfurters and thermotolerance in frankfurter exudates

Cells of Listeria monocytogenes exposed at 4 degrees C to 1% solutions of two alkaline cleaners or alkali-adapted in tryptose phosphate broth (pH 10.0) at 37 degrees C for 45 min, followed by 4 degrees C for 48 h, were inoculated onto beef frankfurters containing high fat (16 g) and high sodium (550 mg) or low fat (8 g) and low sodium (250 mg) per 57-g serving. Frankfurters were surface inoculated (2.0 log10 CFU/g), vacuum packaged, stored at -20, 4, or 12 degrees C, and analyzed for populations of L. monocytogenes at 2-day to 2-week intervals. Populations did not change significantly on frankfurters stored at -20 degrees C for up to 12 weeks. After storage at 4 degrees C for 6 weeks (I week before the end of shelf life), populations of control cells and cells exposed to alkaline cleaners were ca. 6.0 log10 CFU/g of low fat, low sodium (LFLS) frankfurters and ca. 3.5 log10 CFU/g of high fat, high sodium (HFHS) frankfurters. Growth of alkali-adapted cells on both types of frankfurters was retarded at 4 degrees C. Growth of L. monocytogenes on frankfurters stored at 12 degrees C was more rapid than at 4 degrees C, but a delay in growth of alkali-adapted cells on HFHS and LFLS frankfurters was evident during the first 9 and 6 days, respectively. Alkali-adapted cells had a significantly (P < or = 0.05) lower logistic D59 degrees C-value (decimal reduction time) than alkaline cleaner-exposed cells, but the D59 degrees C-value was not different from that of control cells. Cells exposed to a nonbutyl alkaline cleaner, and then heated in LFLS frankfurter exudates, had a significantly lower D62 degrees C-value than cells that had been exposed to some of the other treatments. Growth characteristics of L. monocytogenes inoculated onto the surface of frankfurters may be altered by previous exposure to alkaline environments. Differences in growth characteristics of L. monocytogenes on HFHS versus LFLS beef frankfurters stored at refrigeration temperatures indicate that composition influences the behavior of both alkaline-stressed and control cells.     

Biocontrol of Salmonella Typhimurium in RTE foods with the virulent bacteriophage FO1-E2

Antimicrobial agents can be incorporated into edible films to provide microbiological stability, since films can be used as carriers of a variety of additives to extend product shelf life and reduce the risk of microbial growth on food surfaces. Addition of antimicrobial agents to edible films offers advantages such as the use of small antimicrobial concentrations and low diffusion rates. The aim of this study was to evaluate inhibition by vapor contact of Aspergillus niger and Penicillium digitatum by selected concentrations of Mexican oregano (Lippia berlandieri Schauer), cinnamon (Cinnamomum verum) or lemongrass (Cymbopogon citratus) essential oils (EOs) added to amaranth, chitosan, or starch edible films. Essential oils were characterized by gas chromatography-mass spectrometry (GC/MS) analysis. Amaranth, chitosan and starch edible films were formulated with essential oil concentrations of 0.00, 0.25, 0.50, 0.75, 1.00, 2.00, or 4.00%. Antifungal activity was evaluated by determining the mold radial growth on agar media inoculated with A. niger and P. digitatum after exposure to vapors arising from essential oils added to amaranth, chitosan or starch films using the inverted lid technique. The modified Gompertz model adequately described mold growth curves (mean coefficient of determination 0.991 ± 0.05). Chitosan films exhibited better antifungal effectiveness (inhibition of A. niger with 0.25% of Mexican oregano and cinnamon EO; inhibition of P. digitatum with 0.50% EOs) than amaranth films (2.00 and 4.00% of cinnamon and Mexican oregano EO were needed to inhibit the studied molds, respectively). For chitosan and amaranth films a significant increase (p<0.05) of lag phase was observed among film concentrations while a significant decrease (p<0.05) of maximum specific growth was determined. Chitosan edible films incorporating Mexican oregano or cinnamon essential oil could improve the quality of foods by the action of the volatile compounds on surface growth of molds.     

Development and validation of primary, secondary, and tertiary models for growth of Salmonella Typhimurium on sterile chicken

Models are used in the food industry to predict pathogen growth and to help assess food safety. However, criteria are needed to determine whether models provide acceptable predictions. In the current study, primary, secondary, and tertiary models for growth of Salmonella Typhimurium (10(4.8) CFU/g) on sterile chicken were developed and validated. Kinetic data obtained at 10 to 40 degrees C were fit to a primary model to determine initial density (N0), lag time (lambda), maximum specific growth rate (micromax), and maximum population density (Nmax). Secondary models for N0, lambda, micromax, and Nmax as a function of temperature were developed and combined with the primary model to create a tertiary model that predicted pathogen density (N) at times and temperatures used and not used in model development. Performance of models was evaluated using the acceptable prediction zone method in which experimental error associated with growth parameter determinations was used to set criteria for acceptable model performance. Models were evaluated against dependent and independent (validation) data. Models with 70% prediction or relative errors (RE) in an acceptable prediction zone from -0.3 to 0.15 for micromax, -0.6 to 0.3 for lambda, and -0.8 to 0.4 for N, N0, and Nmax were classified as acceptable. All secondary models had acceptable goodness of fit and were validated against independent (interpolation) data. Percent RE in the acceptable prediction zone for the tertiary model was 90.7 for dependent data and 97.5 for independent (interpolation) data. Although the tertiary model was validated for interpolation, an unacceptable %RE of 2.5 was obtained for independent (extrapolation) data obtained with a lower N0 (10(0.8) CFU/g). The tertiary model provided overly fail-dangerous predictions of N from a lower N0. Because Salmonella concentrations on chicken are closer to 10(0.8) than 10(4.8) CFU/g, the tertiary model should not be used to help assess chicken safety.     

液相色谱-串联质谱法检测鸡肉中金刚烷胺

目的建立鸡肉中金刚烷胺的液相色谱-串联质谱测定方法。方法鸡肉样品中的金刚烷胺用甲醇-1%三氯乙酸(1:1,v/v)提取,经固相萃取柱净化、浓缩后,采用液相色谱-串联质谱法在正离子模式下检测。结果该方法检测限为5.0μg/kg。在1~100μg/kg范围内线性关系良好,相关系数r0.999。在低、中、高三个添加水平下,该方法的平均回收率为89.0%~98.7%,相对标准偏差为0.3%~2.5%(n=5),变异系数为1.9%~5.5%(n=5)。结论本方法灵敏度高、准确性好、适用于鸡肉中金刚烷胺残留的检测。     

GC-MS based metabolomics for rapid simultaneous detection of Escherichia coli O157:H7, Salmonella Typhimurium, Salmonella Muenchen, and Salmonella Hartford in ground beef and chicken

A metabolomic-based method for rapid detection of Escherichia coli O157:H7, Salmonella Hartford, Salmonella Typhimurium, and Salmonella Muenchen in nonselective media was developed. All pathogenic bacteria were grown in tryptic soy broth (TSB) at 37 °C followed by metabolite quantification at 2-h intervals for 24 h. Results were compared with the metabolite profiles similarly obtained with E. coli K12, Pseudomonas aeruginosa, Staphylococcus aureus, Saccharomyces cereviseae, and Aspergillus oryzae grown individually or as a cocktail under the same conditions. Principal component analysis (PCAS) discriminated pathogenic microorganisms grown in TSB. Metabolites responsible of PCAS classification were dextrose, cadaverine, the aminoacids L-histidine, glycine, and L-tyrosine, as well as the volatiles 1-octanol, 1-propanol, 1butanol, 2-ethyl-1-hexanol, and 2,5-dimethyl-pyrazine. Partial least square (PLS) models based on the overall metabolite profile of each bacteria were able to detect the presence of Escherichia coli O157:H7 and Salmonella spp. at levels of approximately 7 ± 2 CFU/25 g of ground beef and chicken within 18 h.     

Rapid detection of Salmonella in chicken washes by immunomagnetic separation and flow cytometry.

Use of flow cytometry to rapidly detect Salmonella in chicken carcass washes was investigated. A direct immunomagnetic separation method was used to prepare samples and was found to be an effective method for separating target cells from debris in chicken carcass washes. When flow cytometry was combined with immunomagnetic separation, the average lowest detectable level of Salmonella detected was 2.3 x 10(4) CFU/ml. Fifty of 100 wash samples from six groups were inoculated with 2 x 10(-1) CFU of Salmonella Typhimurium per milliliter. After 18 h of enrichment at 37 degrees C, all samples were tested for Salmonella using flow cytometry and conventional culture methods. An identification correlation of 96% was found between flow cytometry and xylose-lysine-tergitol agar plating. Quantitative analysis established a significant linear relationship between the enumeration results of flow cytometry and xylose-lysine-tergitol agar plate counts (R2 = 0.796). Time required for flow cytometry, including sample processing and flow cytometric analysis, was less than 1 h.     

Development and validation of a tertiary simulation model for predicting the potential growth of Salmonella typhimurium on cooked chicken

The growth of Salmonella typhimurium (ATCC 14028) on the surface of autoclaved ground chicken breast and thigh burgers incubated at constant temperatures from 8 to 48 degrees C in 2 degrees C increments was investigated and modeled. Growth curves at each temperature were fit to a two-phase linear primary model to determine lag time (lambda) and specific growth rate (mu). Growth of S. typhimurium on breast and thigh meat was not different. Consequently, secondary models that predicted lag time and specific growth rate as a function of temperature were developed with the combined data for breast and thigh meat. Five secondary models for lag time and three secondary models for specific growth rate were compared. A new version of the hyperbola model and a cardinal temperature model were selected as the best secondary models for lag time and specific growth rate, respectively. The secondary models were combined in a computer spreadsheet to create a tertiary simulation model that predicted the potential growth (log10) increase) of S. typhimurium on cooked chicken as a function of time and temperature. Probability distributions and simulation were used in the tertiary model to model the secondary model parameters and the times and temperatures of abuse. The outputs of the tertiary model were validated (prediction bias of -4% for lambda and 1% for mu and prediction accuracy of 10% for lambda and 8% for mu) and integrated with a previously developed risk assessment model for Salmonella.     

Quantification of the contamination of chicken and chicken products in the netherlands with Salmonella and Campylobacter

The research described in this contribution provides quantitative data on contamination levels with Salmonella and Campylobacter in chicken and chicken products in The Netherlands at retail level using the most probable number method and direct counting. Most samples contained <10 Salmonella per carcass, both in fresh (89%) and frozen (68%) products, contamination levels with Campylobacter varied from <10 (18%) to more than 5,500 (18%) per fresh carcass. Most frozen samples (57%) contained < 10 Campylobacter per carcass.     

Reduction of Escherichia coli O157:H7 and Salmonella enterica serovar Enteritidis in chicken manure by larvae of the black soldier fly

Green fluorescent protein-labeled Escherichia coli O157:H7 and Salmonella enterica serovar Enteritidis were inoculated at 10(7) CFU/g into cow, hog, or chicken manure. Ten- or 11-day-old soldier fly larvae (Hermetia illucens L.) (7 to 10 g) were added to the manure and held at 23, 27, or 32 degrees C for 3 to 6 days. Soldier fly larvae accelerated inactivation of E. coli O157:H7 in chicken manure but had no effect in cow manure and enhanced survival in hog manure. The initial pH values of the hog and chicken manure were 6.0 to 6.2 and 7.4 to 8.2, respectively, and it is surmised that these conditions affected the stability of the larval antimicrobial system. Reductions of E. coli O157:H7 populations in chicken manure by larvae were affected by storage temperature, with greater reductions in samples held for 3 days at 27 or 32 degrees C than at 23 degrees C. Pathogen inactivation in chicken manure by larvae was not affected by the indigenous microflora of chicken manure, because Salmonella Enteritidis populations in larvae-treated samples were approximately 2.5 log lower than control samples without larvae when either autoclaved or nonautoclaved chicken manure was used as the contaminated medium during 3 days of storage. Extending the storage time to 6 days, larvae again accelerated the reduction in Salmonella Enteritidis populations in chicken manure during the first 4 days of storage; however, larvae became contaminated with the pathogen. After 2 days of feeding on contaminated manure, Salmonella Enteritidis populations in larvae averaged 3.3 log CFU/g. Populations decreased to 1.9 log CFU/g after 6 days of exposure to contaminated chicken manure; however, the absence of feeding activity by the maggots in later stages of storage may be responsible for the continued presence of Salmonella Enteritidis in larvae. Transfer of contaminated larvae to fresh chicken manure restored feeding activity but led to cross-contamination of the fresh manure.     

Prevalence of Salmonella on retail broiler chicken meat carcasses in Colombia

A cross-sectional study was performed to estimate the prevalence of Salmonella on retail market chicken carcasses in Colombia. A total of 1,003 broiler chicken carcasses from 23 departments (one city per department) were collected via a stratified sampling method. Carcass rinses were tested for the presence of Salmonella by conventional culture methods. Salmonella strains were isolated from 27 % of the carcasses sampled. Logistic regression analysis was used to determine potential risk factors for Salmonella contamination associated with the chicken production system (conventional versus free-range), storage condition (chilled versus frozen), retail store type (supermarket, independent, and wet market), poultry company (integrated company versus nonintegrated company), and socioeconomic stratum. Chickens from a nonintegrated poultry company were associated with a significantly (P < 0.05) greater risk of Salmonella contamination (odds ratio, 2.0) than were chickens from an integrated company. Chilled chickens had a significantly (P < 0.05) higher risk of Salmonella contamination (odds ratio, 4.3) than did frozen chicken carcasses.