M. R. Torres-Vitela

Salmonella and Shigella in Freshly Squeezed Orange Juice, Fresh Oranges, and Wiping Cloths Collected from Public Markets and Street Booths in Guadalajara, Mexico: Incidence and Comparison of Analytical Routes

A survey of the presence of Salmonella and Shigella in freshly squeezed orange juice and related samples was conducted in Guadalajara, Mexico. One hundred samples of freshly squeezed orange juice were collected from 49 street booths and 51 small food service establishments. In addition, 75 fresh orange samples, each consisting of five orange units, and 75 wiping cloths were collected from the same establishments from which juice had been collected. Salmonella was isolated from 14, 20, and 23% of samples of orange juice, orange surfaces, and wiping cloths collected from street vendors, while Shigella was isolated from 6, 17, and 5% of these samples. In general, the frequency of isolation of these pathogens in samples from juice serving establishments at public markets was significantly lower than that found among street vendors (P < 0.05). Salmonella enterica serotypes Agona, Typhimurium, and Anatum were found in orange juice, fresh oranges, and wiping cloth samples, while serotype Mexico was found on fresh oranges and in wiping cloths and serotypes Muenchen and Panama were found only in wiping cloth samples. Regarding Shigella species, Shigella sonnei was found in all three types of sample tested; Shigella dysenteriae was found in juice and orange samples, Shigella boydii in orange and wiping cloth samples, and Shigella flexneri on oranges only. Thirty-one percent and 39% of the juice samples showed aerobic plate counts of > or = 5.0 log CFU/ml and Escherichia coli counts of > 3.0 log CFU/ml, respectively. These high counts may indicate poor sanitation and potential exposure to fecal contamination either in the raw materials or during the orange-crushing and juice-serving process. These data may be useful for a further risk assessment of Salmonella or Shigella in unpasteurized, freshly squeezed juice.

Incidence of Salmonella, Listeria monocytogenes, Escherichia coli O157:H7, and Staphylococcal enterotoxin in two types of Mexican fresh cheeses.

Handcrafted fresh cheeses are popular among consumers in Mexico. However, unsafe raw materials and inadequate food safety practices during cheese manufacture and preservation make them a potential public health risk. The incidence of Salmonella, Listeria, Escherichia coli O157:H7, and staphylococcal enterotoxin was analyzed in two types of fresh cheese (panela and adobera) commonly marketed in Mexico. A total of 200 samples, 100 panela and 100 adobera, were acquired from 100 wholesale milk product distributors who supply small retailers in the Guadalajara metropolitan area, Jalisco State, Mexico. Pathogens were identified using culture and immunoassay (miniVidas) methods. The presence of staphylococcal enterotoxin was determined by an immunoassay method. Of the 200 analyzed samples, 92 were positive for at least one of the pathogens. The incidence in the panela samples was 56%: 34% Salmonella, 16% E. coli O157:H7, and 6% L. monocytogenes. In the adobera samples, incidence was 36%: 20% Salmonella, 4% E. coli O157:H7, and 12% L. monocytogenes. Staphylococcal enterotoxin was not detected in any of the 200 samples. Choice of technique had no effect on detection of pathogen incidence, although the immunoassay method identified more Salmonella serotypes than the culture method. Handcrafted panela and adobera fresh cheeses in Mexico frequently contain pathogenic bacteria and therefore pose a public health risk.

Microbiological safety of domestic refrigerators and the dishcloths used to clean them in Guadalajara, Jalisco, Mexico.

Household refrigerators are a potential pathogen contamination source for foods. An evaluation of the microbiological safety of 200 refrigerators in Guadalajara, Jalisco, Mexico, was made by visual inspection, ATP-bioluminescence levels, indicator microorganisms including Escherichia coli and Staphylococcus aureus, and the presence of Listeria monocytogenes and Salmonella. Additionally, interviews of the owners of the refrigerators were carried out to determine relationships between food storage practices, demographic aspects, and microbiological status. Dishcloths used to clean refrigerators were also analyzed. Operational conditions (cleanliness, fullness, organization, frequency of cleaning, and temperature) were evaluated by trained observers. Results showed deficient cleanliness in 55% of refrigerators, 22% were completely full, 43% very disorganized, 28% were usually cleaned only once in 3 to 6 months, and 53% had internal temperatures >7.1°C. ATP-bioluminescence levels were >300 relative light units on 67 and 74% of shelves and drawers, respectively, indicating that surfaces were dirty according to the luminometer manufacturer. Psychrotrophic aerobic bacteria counts on shelves, drawers, and dishcloths were 6.3, 5.2, and 6.3 log CFU/cm(2); for coliform bacteria, 5.2, 3.9, and 4.7 CFU/cm(2); for E. coli, 3.7, 3.5, and 4.8 CFU/cm(2); and for Staphylococcus aureus, 2.1, 2.5, and 2.3 CFU/cm(2), respectively. L. monocytogenes and Salmonella were isolated from 59.5, 20.5, and 17% and 32.5, 8.0 and 12.5% of shelves, drawers, and dishcloths, respectively. Four Salmonella serotypes and nine serogroups (partially serotyped isolates) were identified. The most prevalent were Salmonella Anatum (39.5%), Salmonella group E1 (19.7%), and Salmonella group E1 monophasic (12.5%). Operational conditions and microbiological status were clearly deficient in sampled refrigerators, highlighting the consequent risk of foodborne disease among users. Educational programs are needed to improve the domestic food safety in Mexico.

Risk of Salmonellosis associated with consumption of chocolate in Mexico

To assess the potential risk of salmonellosis associated with consumption of chocolate, the prevalence of Salmonella spp. was investigated in retail wrapped and nonwrapped solid chocolate in Guadalajara, Mexico. Previously, the efficiency of preenrichment and enrichment methods to isolate low numbers of Salmonella in chocolate was compared. Though not completely efficient, a preenrichment in nonfat milk without brilliant green, followed by enrichment in tetrathionate and selenite cystine broths gave better results than the other methods studied. Regarding the survey of retail chocolate, Salmonella was isolated from 2 (4.5%) of 44 samples of wrapped chocolate and from none of 56 samples of nonwrapped chocolate. The serovars identified were Salmonella agona and Salmonella derby . There were no significant differences between coliform counts or total bacterial counts obtained from wrapped and nonwrapped chocolate. The presence of Salmonella in chocolate is of concern due to the several low-infective-dose Salmonella outbreaks that have been linked to chocolate. On the other hand, a technique capable of detecting low numbers of Salmonella in chocolate is still needed.

The Role of Foods in Salmonella Infections

Carlos Alberto Gomez-Aldapa1, Ma. del Refugio Torres-Vitela2, Angelica Villarruel-Lopez2 and Javier Castro-Rosas1* 1Center of Chemical Research, Institute of Basic Sciences and Engineering Autonomous University of Hidalgo State, City of Knowledge Carretera Pachuca-Tulancingo, Mineral de la Reforma, Hidalgo 2Laboratory of Food Safety, University Center of Exact Sciences and Engineering University of Guadalajara, Marcelino Garcia Barragan, Guadalajara, Jalisco Mexico

Incidence of Vibrio cholerae in Fresh Fish and Ceviche in Guadalajara, Mexico

The incidence of Vibrio cholerae O1 and non-Ol was determined in fresh fish and ceviche, a marinated raw fish dish ready for consumption. Fresh red snapper ( Lutjanus purpureous ) and mackerel ( Scomberomorus sierra ) were obtained from distribution centers, and ceviche from street vendors and small open restaurants in Guadalajara, Mexico. In addition to V. cholerae , the fish samples were tested for aerobic plate count (APC), total volatile nitrogen (TVN), trimethylamine (TMA), and the ceviche for APC, coliforms, and pH. V. cholerae O1 and non-O1 was isolated from 10% and 26% ofthe fish respectively. The mean data for the fish samples were in the region of: APC, 106 CFU/g of fish; more than 25 mg of TVN per 100 g of fish, but less than 5 mg of nitrogen as TMA per 100 g. Eleven percent of the ceviche obtained from street vendors and 6% obtained from restaurants were positive for V. cholerae O1. The mean APC and coliform counts were 6.6 and 4.8 log CFU/g of fish respectively, and the pH of the ceviche ranged from 3.0 to 4.5. All the strains of V. cholerae O1 isolated during this study were identified as biotype El Tor, serotypes Inaba and Ogawa. For both fresh fish and ceviche, the frequency of isolation of V. cholerae was highest during the summer months.

Survival of vibrio cholerae O1 in ceviche and its reduction by heat pretreatment of raw ingredients

The survival of Vibrio cholerae O1 serotypes Inaba and Ogawa was determined in ceviche prepared from inoculated ground fish. Ground mackerel purchased from a seafood distribution center was inoculated with V. cholerae and stored at 8 or 20 degrees C. Counts of V. cholerae decreased in 2.6 to 2.7 log10 CFU/g during 96 h of storage at 8 degrees C or 2.5 to 2.6 log10 CFU/g during 24 h at 20 degrees C. Survival studies indicated that serotype Inaba decreased its number following a linear or retarded trend, whereas serotype Ogawa followed an accelerated death trend. No effect of the initial level of inoculum was observed. Odor scores of ceviche indicated that this food became marginally acceptable within as little as 48 h of storage at 8 degrees C or 3 h at 20 degrees C and were related to total volatile nitrogen values but not to aerobic plate counts, pH, or coliform counts. A heat pretreatment that consisted of stirring 100 g of inoculated ground fish into 40 ml of boiling water produced an 8-log reduction of V. cholerae within 3 min without affecting the color, odor, or flavor of ceviche prepared with such pretreated fish. According to this study, V. cholerae present in contaminated ceviche will likely survive longer than the shelf life of this food. Preheating the ground raw fish used for preparing ceviche for 3 min should effectively eliminate V. cholerae O1, providing science-based conditions for implementing a critical control point if a hazard analysis critical control point plan were to be developed for preparation of ceviche.

Antibacterial Activities of Hibiscus sabdariffa Extracts and Chemical Sanitizers Directly on Green Leaves Contaminated with Foodborne Pathogens

Leafy greens have been associated with foodborne disease outbreaks in different countries. To decrease microbial contamination of leafy greens, chemical agents are commonly used; however, a number of studies have shown these agents to have limited antimicrobial effect against pathogenic bacteria on vegetables. The objective of this study was to compare the antibacterial effect of Hibiscus sabdariffa calyx extracts (water, methanol, acetone, and ethyl acetate), sodium hypochlorite, acetic acid, and colloidal silver against foodborne bacteria on leafy greens. Thirteen foodborne bacteria were used in the study: Listeria monocytogenes, Shigella flexneri, Salmonella serotypes Typhimurium Typhi, and Montevideo, Staphylococcus aureus, Escherichia coli O157:H7, five E. coli pathotypes (Shiga toxin-producing, enteropathogenic, enterotoxigenic, enteroinvasive, and enteroaggregative), and Vibrio cholerae O1. Each foodborne bacterium was separately inoculated on romaine lettuce, spinach, and coriander leaves. Separately, contaminated leafy greens were immersed in four hibiscus extracts and in sanitizers for 5 min. Next, green leaves were washed with sterile tap water. Separately, each green leaf was placed in a bag that contained 0.1% sterile peptone water and was rubbed for 2 min. Counts were done by plate count using appropriate dilutions (in sterile peptone water) of the bacterial suspensions spread on Trypticase soy agar plates and incubated at 35 ± 2°C for 48 h. Statistically significant differences ( P < 0.05) were calculated with an analysis of variance and Duncans test. All 13 foodborne bacteria attached to leafy greens. Roselle calyx extracts caused a significantly greater reduction ( P < 0.05) in concentration of all foodborne bacteria on contaminated romaine lettuce, spinach, and coriander than did the sodium hypochlorite, colloidal silver, and acetic acid. Dry roselle calyx extracts may potentially be a useful addition to disinfection procedures for romaine lettuce, spinach, and coriander.

Comparison of the antimicrobial activities of roselle calyx extracts and chemical sanitizers directly onto contaminated cucumbers

Cucumbers are associated with foodborne disease caused by Salmonella. Fruits and vegetables in restaurants and homes in Mexico are disinfected using sodium hypochlorite and colloidal silver solutio...

Behavior and Inactivation of Enterotoxin-Positive Clostridium perfringens in Pork Picadillo and Tamales Filled with Pork Picadillo under Different Cooking, Storage, and Reheating Conditions

This study analyzed the behavior of Clostridium perfringens in individual ingredients and tamales containing different pathogen concentrations upon exposure to different temperatures and methods of cooking, storage, and reheating. In ground pork, C. perfringens cells were inactivated when exposed to 95°C for 30 min. Three lots of picadillo inoculated with 0, 3, and 5 log CFU/g C. perfringens cells, respectively, were exposed to different storage temperatures. At 20°C, cell counts increased 1 log in all lots, whereas at 8°C, counts decreased by 2 log. Four lots of tamales prepared with picadillo inoculated with 0, 2, 3, and 7 log CFU/g prior to the final cooking step exhibited no surviving cells (91°C for 90, 45, or 35 min). Four lots of tamales were inoculated after cooking with concentrations of 0, 0.6, 4, and 6 log CFU/g of the pathogen and then stored at different temperatures. In these preparations, after 24 h at 20°C, the count increased by 1.4, 1.7, and 1.8 log in the tamales inoculated with 0.6, 4, and 6 log inoculum, respectively. When they were stored at 8°C for 24 h, enumerations decreased to <1, 2.5, and 1.9 log in the tamales inoculated with 0.6, 4, and 6 log of C. perfringens cells, respectively. However, when the lots were exposed to 20°C and then 8°C, 0.8, 1.8, and 2.4 log changes were observed for the tamales inoculated with 0.6, 4, and 6 log, respectively. Microwaving, steaming, and frying to reheat tamales inoculated with 6 log CFU/g C. perfringens cells showed that the pathogen was inactivated after 2 min of exposure in the microwave and after 5 min of exposure to steam. In contrast, no inactivation was observed after 5 min of frying. The tamales inoculated with spores (7 log most probable number [MPN]/g) showed a decrease of 2 log after steaming or frying, and no survival was observed after microwaving. Tamales inoculated with spores (7 log MPN/g) after cooking were susceptible to microwaves, but 2.4 and 255 MPN/g remained after frying and steaming, respectively.