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 Duncan's 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.

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.

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

El presente estudio se realizó para conocer la incidencia de contaminación por Salmonella del pescado preparado y puesto a la venta en 89 comercios fijos y ambulantes de la ciudad de Guadalajara, Jalisco, México. El pH de las muestras analizadas osciló entre 3,8 y 5,2 (mediana= 4,55), y su temperatura, entre 9 y 29 C. El 16 porciento de las 221 muestras estudiadas (porciones de 20 g) fueron positivas a Salmonella. Los porcentajes de positividad de las muestras vendidas en establecimientos fijos y ambulantes fueron, respectivamente, 12 y 20 porciento. Estos porcentajes fueron más elevados en las épocas templadas y calurosas que en las frías. Para aislar Salmonella, el uso de preenriquecimiento resultó ser menos eficiente que el enriquecimiento directo. En dos de las ocho muestras con pH menor de 4,0 se aislaron Salmonella. Los resultados indican que el consumo de ceviche supone un riesgo para la salud, especialmente en las personas cuya resistencia a los enteropatógenos transmitidos por alimentos es baja, y que, por tanto, debe hacerse hincapié en el escaso valor del jugo de limón como garante de la inocuidad del ceviche

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

El presente estudio se realizó para conocer la incidencia de contaminación por Salmonella del pescado preparado y puesto a la venta en 89 comercios fijos y ambulantes de la ciudad de Guadalajara, Jalisco, México. El pH de las muestras analizadas osciló entre 3,8 y 5,2 (mediana= 4,55), y su temperatura, entre 9 y 29 C. El 16 porciento de las 221 muestras estudiadas (porciones de 20 g) fueron positivas a Salmonella. Los porcentajes de positividad de las muestras vendidas en establecimientos fijos y ambulantes fueron, respectivamente, 12 y 20 porciento. Estos porcentajes fueron más elevados en las épocas templadas y calurosas que en las frías. Para aislar Salmonella, el uso de preenriquecimiento resultó ser menos eficiente que el enriquecimiento directo. En dos de las ocho muestras con pH menor de 4,0 se aislaron Salmonella. Los resultados indican que el consumo de ceviche supone un riesgo para la salud, especialmente en las personas cuya resistencia a los enteropatógenos transmitidos por alimentos es baja, y que, por tanto, debe hacerse hincapié en el escaso valor del jugo de limón como garante de la inocuidad del ceviche

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.