Reduction of Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes with electrolyzed oxidizing water on inoculated hass avocados (Persea americana var. Hass).

This study was intended to evaluate the bactericidal effect of electrolyzed oxidizing water (EOW) and chlorinated water on populations of Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes inoculated on avocados (Persea americana var. Hass). In the first experiment, inoculated avocados were treated with a water wash applied by spraying tap water containing 1 mg/liter free chlorine for 15 s (WW); WW treatment and then spraying sodium hypochlorite in water containing 75 mg/liter free chlorine for 15 s (Cl75); WW treatment and then spraying alkaline EOW for 30 s (AkEW) and then spraying acid EOW (AcEW) for 15 s; and spraying AkEW and then AcEW. In another experiment, the inoculated avocados were treated by spraying AkEW and then AcEW for 15, 30, 60, or 90 s. All three pathogen populations were lowered between 3.6 and 3.8 log cycles after WW treatment. The application of Cl75 did not produce any further reduction in counts, whereas AkEW and then AcEW treatment resulted in significantly lower bacterial counts for L. monocytogenes and E. coli O157:H7 but not for Salmonella. Treatments with AkEW and then AcEW produced a significant decrease in L. monocytogenes, Salmonella, and E. coli O157:H7 populations, with estimated log reductions of 3.9 to 5.2, 5.1 to 5.9, and 4.2 to 4.9 log CFU/cm², respectively. Spraying AcEW for more than 15 s did not produce any further decrease in counts of Salmonella or E. coli O157:H7, whereas L. monocytogenes counts were significantly lower after spraying AcEW for 60 s. Applying AkEW and then AcEW for 15 or 30 s seems to be an effective alternative to reduce bacterial pathogens on avocado surfaces.

Adhesion and colonization of Vibrio cholerae O1 on shrimp and crab carapaces.

The potential of Vibrio cholerae O1 to attach to and colonize the carapaces of shrimp and crabs was evaluated. One million cells of V. cholerae O1 were spread within a circle on the external surfaces of separated carapaces and stored at 22 +/- 0.2 degrees C in a moist environment to permit adherence. Attached vibrios were counted directly by an immunofluorescence technique and by the pour plate technique after detachment of the cells. To study the colonization process, rifampicin-resistant strains of V. cholerae O1 were used. V. cholerae O1 strains, including those resistant to rifampicin, were able to attach to shrimp and crab carapaces. Dorsal crab carapaces showed higher levels of attachment than ventral carapaces. Colonization of V. cholerae O1 on these carapaces was also demonstrated. Both attachment and colonization on the shrimp exoskeleton were optimal at a salinity of 1.0 to 1.5%, a pH of 6.0 to 7.0, and a temperature of 37 degrees C. Less than 2% attachment at 3 degrees C contrasted with >20% attachment at 37 degrees C. Even at 3% NaCl, some attachment was observed. Although attachment percentages may appear low (2 to 20%), they represent significant numbers, about 3.7 to 5.6 log10 CFU per carapace. A rugose V. cholerae O1 strain attached to and colonized the shrimp carapace in a fashion very similar to that of the smooth strain from which it was derived. The ability of V. cholerae O1 to attach to and colonize exoskeletons of edible crustaceans provides a potential means of survival in aquatic environments. Concentrations of vibrios that may be reached on a single crab or shrimp carapace are clearly of concern with regard to public health.

Quantitative survival of native Salmonella serovars during storage of frozen raw pork.

The quantitative survival of material contaminants of Salmonella serovars was studied in raw pork during frozen storage. Raw pork samples were obtained from public markets in Guadalajara, Mexico, and tested for Salmonella. Three positive samples were selected for survival studies in three different trials. Populations of Salmonella were determined by the most probable number (MPN) method, with isolation on bismuth sulfite agar plates. One typical colony was selected from each plate and subjected to serovar identification. Approximately 20 colonies were serotyped for each portion of frozen pork at each sampling time during storage. During frozen storage, numbers of Salmonella were reduced from 7-11 to 1.6 MPN g(-1) over a period of 22 weeks in Trial 1, from 1500 9000 to 2.5 MPN g(-1) over 42 weeks in Trial 2, and from 2000-20,000 to 20 MPN g(-1) over 78 weeks in Trial 3. The number of different Salmonella serovars identified was 10, 14 and 29 for Trials 1, 2 and 3, respectively. In Trial 3, S. agona, S. newbrunswick, S. drypool and S. anatum predominated over the other 25 serovars identified. S. agona was not only the most prevalent, but also the most abundant. At 15 weeks of storage, estimated MPNs of this serovar were 700 g(-1) of pork. Most serovars were detected sporadically; nine were isolated only once, and nine only twice. Serovars such as S. derby and S. newlands appeared only at the first sampling time, while others such as S. schwarzengrund, S. dublin and S. newport appeared only at the last sampling time. Most serovars identified in this study are commonly isolated from human clinical sources and from raw or processed foods in Mexico.

[Poisoning by enterotoxin from Staphylococcus aureus associated with mocha pastry. Microbiology and epidemiology]. / Intoxicación por enterotoxina de Staphylococcus aureus asociado al consumo de pastel de moka. Microbiología y epidemiología.

A brief description of a foodborne outbreak due to S. aureus enterotoxin associated with the consumption of mocha cake in the city of Guadalajara is presented. The cake was prepared in a bakery and affected nearly 100 persons. S. aureus was isolated from the nose and skin of one of the pastry cooks. A S. aureus strain isolated from the cake involved in the outbreak was not only unable to grow in the mocha cream, but it actually decreased in numbers by 2 log after 72 h of storage at 30 degrees C. The pH of mocha cream ranged from 6.2 to 6.6, and water activity from 0.833 to 0.859, with a media of 0.841. In preparing mocha cake at the shop, one half of the dough used to be sprayed with a sucrose solution in water (20% w/v); mocha cream was spread on the other half of the dough before overlapping the two halves. When mocha cake was prepared in this manner, and stored at 30 degrees C, S. aureus increased in number by more than 4 log after 48 h. S. aureus did not grow in the cake stored at 4-7 degrees C. Contributory factors in this outbreak were an increase of water activity in the interphase of the mocha and the cake dough, storage of the cake in an unrefrigerated area, and an unusually high ambient temperature (28-32 degrees C) at that time.

[Contamination of fish ceviche by Salmonella in Guadalajara++, Jalisco, Mexico]. / Contaminación del ceviche de pescado por Salmonella en Guadalajara, Jalisco, México.

This study was done to find out the incidence of Salmonella contamination of fish prepared and sold in 89 fixed and mobile food-vending establishments in the city of Guadalajara, Jalisco, Mexico. The pH of the samples analyzed varied between 3.8 and 5.2 (median = 4.55), and their temperature ranged from 9 to 29 degree C. Of the 221 samples studied (20 g each), 16% were positive for Salmonella. The proportions positive in fixed and mobile establishments were, respectively, 12% and 20%. The positive percentages were higher during mild and hot periods than during cold weather. The preenrichment technique proved less efficient for isolating Salmonella than direct enrichment. Salmonella was isolated from two of eight samples with pH below 4.0. The results indicate that eating ceviche may pose a health risk, especially for persons whose resistance to food-transmitted enteropathogens is low. Therefore, it should be emphasized that lime juice does not guarantee the safety of ceviche.

[Incidence of Vibrio parahaemolyticus in raw fish, oysters, and shrimp]. / Incidencia de Vibrio parahaemolyticus en pescado, ostión y camarón crudos.

The incidence of Vibrio parahaemolyticus in fresh seafood sold in Guadalajara, was studied by two procedures. These two procedures were compared to choose a reliable technique when outbreaks of V. parahaemolyticus illness occur. For one year, 57 samples of fresh oysters, fish and shrimp were analyzed for mesophilic aerobic bacteria (MAB) content, V. parahaemolyticus and pH. Total volatile nitrogen (TVN) was also determined in samples of fish and shrimp. MAB were counted by the pour plate method, and TVN was determined by modified Conway's micro diffusion technique. V. parahaemolyticus was investigated in 20-g samples by enrichment in lauryl dextrose salt broth (LDSB), isolating on plates of thiosulfate citrate bile sucrose agar (TCBS) and bile salts No. 3 agar (BS No. 3), and by direct isolation on TCBS and BS No.3 agar plates. Vibrio was characterized by tests described in standard methods, based upon the halophilism of the organism. Global percent of Vibrio parahaemolyticus positive samples was 45.6%, being 71.4% in fish, 44.0% in oysters, and 27.6% in shrimp. The use of two techniques enhanced the ability to recover the vibrio. There was a greater number of positives during the warm months (p = 0.0038). Means of TVN and pH in both positive and negative samples were not significantly different. Means of MAB counts were similar either in positive or negative samples.

Survival and Growth of Salmonella and Shigella on Sliced Fresh Fruit.

The ability of five strains of enteropathogenic bacteria ( Shigella sonnei , S. flexneri , S. dysenteriae , Salmonella derby , and S. typhi ) to survive and grow on sliced jicama, papaya, and watermelon was investigated. Fruit portions were obtained aseptically and inoculated on the surface with washed suspensions of each microorganism. The test organisms survived, and in most cases increased in numbers when inoculated fruits were stored at room temperature (25-27°C) for up to 6 h. Suspensions of papaya and watermelon in sterile distilled water supported growth of S. sonnei and S. typhi , respectively. Application of lemon juice to the surface of jicama and papaya reduced the count of S. typhi somewhat, but growth resumed after several hours. Practical recommendations are presented to control risks of contamination and subsequent growth of enteric pathogens on fruits and fruit salads during preparation and sale.

Antagonismo de cepas de Streptococcus Lactobacillus y Leuconostoc procedentes de quesos frescos no pasteurizados contra algunas bacterias enteropatogenas. / Antagonism of Streptococcus, Lactobacillus and Leuconostoc strains isolated from fresh raw cheeses against some enteropathogenic bacteria

Diez cepas de cada uno de los generos Streptococcus, Lactobacillus y Leuconostoc, fueron aisladas de quesos frescos no pasteurizados del comercio, y determinada su capacidad para antagonizar 13 cepas de Staphylococcus aureus, 13 de Salmonella (3 serotipos) y 13 de Shigella (dysenteriae, flexneri, sonnei y boydii). El efecto antagonico se determino con base a la capacidad para inhibir el desarrollo del patogeno sobre placa de agar APT inoculada con la bacteria lactica. Los primeros se probaron a dos niveles: aproxidadamente 4 veces mayor y 30 veces menor que la del lactico en las zonas de contacto. Todas las cepas se mostraron muy activas excepto 4 de Lactobacillus, con nulo efecto hacia las 33 de patogenos, y 2 de Leuconostoc que resultaron ineficientes contra las 13 de Shigella. El Streptococcus presento la mayor y mas consistente capacidad antagonista incluidos los inoculos altos del patogeno. Entre estos, las cepas de Shigella (con la salvedad anotada) exhibieron la mayor susceptibilidad. La manifiesta capacidad antagonista de las bacterias lacticas que forman parte de la flora natural de la leche cruda, contribuye a explicar el limitado papel de los quesos frescos no pasteurizados en la incidencia directa de gastroenteritis en la poblacion