Antibacterial effect of roselle extracts (Hibiscus sabadariffa), sodium hypochlorite and acetic acid against multidrug-resistant Salmonella strains isolated from tomatoes.

UNLABELLED: Antibiotic-resistant Salmonella strains were isolated from saladette and red round type tomatoes, and an analysis done of the antibacterial activity of roselle calyx extracts against any of the identified strains. One hundred saladette tomato samples and 100 red round tomato samples were collected from public markets. Each sample consisted of four whole tomatoes. Salmonella was isolated from the samples by conventional culture procedure. Susceptibility to 16 antibiotics was tested for the isolated Salmonella strains by standard test. The antibacterial effect of four roselle calyx extracts (water, methanol, acetone and ethyl acetate), sodium hypochlorite and acetic acid against antibiotic-resistant Salmonella isolates was evaluated on contaminated tomatoes. Twenty-four Salmonella strains were isolated from 12% of each tomato type. Identified Salmonella serotypes were Typhimurium and Typhi. All isolated strains exhibited resistance to at least three antibiotics and some to as many as 12. Over contaminated tomatoes, the roselle calyx extracts produced a greater reduction (2-2·6 log) in antibiotic-resistant Salmonella strain concentration than sodium hypochlorite and acetic acid. SIGNIFICANCE AND IMPACT OF THE STUDY: The presence of multidrug-resistant Salmonella in vegetables is a significant public health concern. Multidrug-resistant Salmonella strains were isolated from raw tomatoes purchased in public markets in Mexico and challenged with roselle Hibiscus sabdariffa calyx extracts, sodium hypochlorite and acetic acid. On tomatoes, the extracts caused a greater reduction in the concentration of antibiotic-resistant Salmonella strains than sodium hypochlorite and acetic acid. Roselle calyx extracts are a potentially useful addition to disinfection procedures of raw tomatoes in the field, processing plants, restaurants and homes.

Behaviour of four diarrheagenic Escherichia coli pathotypes on carrots and in unpasteurized carrot juice.

UNLABELLED: The behaviours of Shiga toxin-producing Escherichia coli (STEC), enteroinvasive E. coli (EIEC), enteropathogenic E. coli (EPEC) and enterotoxigenic E. coli (ETEC) strains on raw carrots at 3 ± 1 and 30 ± 1°C, and in unpasteurized carrot juice at 3 ± 1, 12 ± 1, 20 ± 1, 30 ± 1°C and 37 ± 1°C were determined. Raw carrots were purchased in a local market. Fresh juice was obtained from raw carrots in the laboratory. On whole carrots stored at 30 ± 1 or 3 ± 1°C, no growth was observed for any of the diarrheagenic E. coli pathotype (DEPs) strains studied. After 15 days at 30 ± 1°C, the tested DEPs had decreased from an initial inoculum level of approximately 6 log colony-forming units (CFU) to approximately 3·5 log CFU on whole carrots, while at 3 ± 1°C, they decreased from approximately 2·4 log to 1·6 log CFU. All these DEPs grew in fresh carrot juice at 12 ± 1, 20 ± 1, 30 ± 1 and 37 ± 1°C, reaching counts of approximately 4·2 log, 5·8 log, 6·7 log and 7·5 log CFU ml(-1) , respectively, after 24 h. At 3 ± 1°C, the DEP growth was inhibited at least during 7 days. Thus, storage of carrot juice at unrefrigerated temperatures can result in DEP growth to levels likely to represent a risk to consumers. SIGNIFICANCE AND IMPACT OF THE STUDY: The information presented shows the potential of Shiga toxin-producing Escherichia coli, enteroinvasive E. coli, enteropathogenic E. coli and enterotoxigenic E. coli strains for survival on carrots and growth in carrot juice at warmer temperatures. The information can help food processors in plants and restaurants understand the importance of the implementation of hazard analysis and critical control point (HACCP) strategies for preventing potential diarrheagenic E. coli pathotypes (DEPs) contamination and growth in carrot juice. This is the first report regarding the behaviour these DEPs on carrots and in carrot juice.

Frequency of indicator bacteria, Salmonella and diarrhoeagenic Escherichia coli pathotypes on ready-to-eat cooked vegetable salads from Mexican restaurants.

UNLABELLED: The presence of coliform bacteria, faecal coliforms, Escherichia coli, diarrhoeagenic E. coli pathotypes (DEP) and Salmonella were determined in ready-to-eat cooked vegetable salads (RECS) from restaurants in Pachuca city, Mexico. The RECS were purchased from three types of restaurants: national chain restaurants (A), local restaurants (B) and small restaurants (C). Two restaurants for each A and B, and three for C, were included. Forty RECS samples were purchased at each A and B restaurant and 20 at each C restaurant. Of the overall total of 220 analysed samples, 100, 98·2, 72·3, 4·1 and 4·1% had coliform bacteria, faecal coliforms, E. coli, DEP and Salmonella, respectively. Identified DEP included enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC) and Shiga toxin-producing E. coli (STEC). The EPEC, ETEC and STEC were isolated each from 1·4% of samples. No E. coli O157:H7 were detected in any STEC-positive samples. The analysis of Kruskal-Wallis anova and median test of microbiological data showed that the microbiological quality of RECS did not differ between the different restaurants (P > 0·05). SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report regarding microbiological quality and Salmonella, enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC) and Shiga toxin-producing E. coli (STEC) isolation from ready-to-eat cooked vegetable salads from Mexican restaurants. Ready-to-eat cooked vegetable salads could be an important factor contributing to the endemicity of EPEC, ETEC and STEC, and Salmonella caused gastroenteritis in Mexico.

Presence of indicator bacteria, diarrhoeagenic Escherichia coli pathotypes and Salmonella in fresh carrot juice from Mexican restaurants.

UNLABELLED: Coliform bacteria (CB), faecal coliforms (FC), Escherichia coli, diarrhoeagenic E. coli pathotypes (DEP) and Salmonella frequencies were determined for fresh carrot juice from restaurants in Pachuca city, Mexico. Two hundred and eighty carrot juice samples were purchased in three types of restaurants: (A), national chain restaurants; (B), local restaurants; and (C), very small restaurants. Two restaurants for each A and B, and three for C, were included. Forty juice samples were purchased at each restaurant. All tested juice samples had poor microbiological quality. Of these samples, 100, 96·8, 54·3, 8·9 and 8·6% had CB, FC, E. coli, DEP and Salmonella, respectively. CB were present in all juice samples regardless of source, with limits ranging from 3·6 × 10² to 8·5 × 107 CFU ml⁻¹, and the limits for FC and E. coli were <3 to 1100 MPN ml⁻¹ and <3 to 460 MPN, respectively. DEP and Salmonella were isolated from samples from all the restaurants at levels of 5% or above: DEP, 5% (A1, B2, 10% (A2, B1, C1, C2) and 12·5% (C3); Salmonella, 5% (A1, A2, B2), 7·5% (C2), 10% (C1, 12·5% (B1) and 15% (C3). SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report of microbiological quality and Salmonella, enteroinvasive E. coli (EIEC), enterotoxigenic E. coli (ETEC) and Shiga toxin-producing E. coli (STEC) isolation from fresh carrot juice in Mexico. Fresh carrot juice from restaurants could be an important factor contributing to the endemicity of EIEC-, ETEC- and STEC- and Salmonella-caused gastroenteritis in Mexico.