Effect of storage temperature and time on the behavior of Salmonella, Listeria monocytogenes, and background microbiota on whole fresh avocados (Persea americana var Hass).

Avocados are popular fruits; however, contamination of whole fresh avocados and avocado products with foodborne pathogens has raised concern about their safety. Recalls and import alerts of avocado products due to contamination with Listeria monocytogenes cause important economic losses. The behavior of Salmonella, L. monocytogenes, and background microbiota on whole fresh avocados at 5 and 25 °C as affected by temperature and time of storage was investigated. Whole fresh avocados were inoculated by immersion in suspensions containing six rifampicin-resistant strains of Salmonella or L. monocytogenes, and stored at 5 °C for 48 d, or at 25 °C for 11 d. At selected sampling times, avocados were removed from storage and pathogens enumerated. The log counts of both pathogens at each temperature were fitted to the Weibull distribution nonlinear model to estimate kinetic parameters including the time for the first 1-log reduction (δ), the shape of the curve (ρ), and the time for two (2-D) and three (3-D) log reductions. Salmonella and L. monocytogenes initial populations (approx. 7 log CFU/avocado) decreased during storage at 5 and 25 °C; L. monocytogenes mean counts were higher than those observed for Salmonella (P < 0.05). L. monocytogenes showed a lower rate of decline at 5 °C when compared to Salmonella. In general, the ability of both pathogens to survive on the surface of avocados stored at room temperature was similar. Salmonella and L. monocytogenes counts decline over time on the epicarp of whole avocados; however, if the initial number of cells is large enough, the pathogens could be present for large periods of time. Simultaneously, psychrotrophic microorganisms (PM), aerobic plate count (APC), coliforms (C) and yeasts/molds (Y/M) were enumerated from non-inoculated avocados stored at 5 and 25 °C. Initial mean counts for PM, APC, C and Y/M ranged from 6.1 to 6.6 log CFU/avocado and showed no change (P > 0.05) during storage at both temperatures. Good agricultural and handling practices from farm to fork are crucial to prevent or minimize contamination of whole avocados; otherwise, if large numbers of pathogens contaminate the fruit, they could survive and be transferred to the pulp, or to other ready to eat foods, representing a risk for consumers.

Microbiological Quality and Incidence of Salmonella on Cherry Tomatoes at Retail in Querétaro, México.

Multiple outbreaks related to Salmonella in tomatoes require an evaluation of the risk associated with cherry tomatoes due to the increase in its production, consumption, and marketing in Mexico's central region. The purpose of this study was to determine the microbial quality of cherry tomatoes obtained from two retail sale points (supermarkets and local markets). Cherry tomato samples (333) were collected from four supermarkets and from four local markets, and the contents of aerobic plate count, molds and yeasts, total coliforms, and Escherichia coli were quantified; the presence of Salmonella was simultaneously determined. The median values of the microbial populations were obtained, and the data were analyzed per the sampling site by using the Wilcoxon and Kruskal-Wallis tests. The median of aerobic plate count content in tomatoes obtained from supermarkets ranged between 2.2 and 4.4 log CFU/g, and in markets from 2.9 to 4.8 log CFU/g. For molds and yeasts, the tomatoes from supermarkets (2.0 to 4.1 log CFU/g) and markets (1.5 to 4.5 log CFU/g) showed similar contents. Regardless of the sampling site, the values of total coliforms were very low, ranging from 1.0 to 1.8 log CFU/g. E. coli was detected in 5.4 and 20.1% of samples from supermarkets and markets, respectively; in both sites, the content was low (0.3 to 5.8 most probable number per g). The incidence of Salmonella was 14.1% in supermarkets and 7.8% in local markets. The results obtained from this investigation highlight the elevated risk for consumer health associated with the ingestion of cherry tomatoes.

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.