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Resumen Introducción: Los alimentos de origen animal frecuentemente están implicados en brotes de salmonelosis. Objetivo: Evaluar la frecuencia de Salmonella enterica en carnes molidas de pollo, res y cerdo (un total de 2.592 muestras) obtenidas de mercados sobre ruedas y supermercados de la Delegación Iztapalapa en la Ciudad de México, determinar la susceptibilidad antimicrobiana y efectuar ensayos de adherencia en las cepas aisladas. Métodos: El aislamiento de S. enterica se hizo de acuerdo a la BAM-FDA, la susceptibilidad antimicrobiana de acuerdo con CLSI y el ensayo de adherencia en células HEp-2 conforme a Baffone y cols., 2001. Resultados: Salmonella enterica fue aislada en 511 del total de muestras analizadas (19,7%), de las cuales 244 (47,7%), 152 (29,7%) y 115 (22,5%) correspondieron a carne molida de pollo, res y cerdo, respectivamente. La mayor frecuencia de resistencia de S. enterica a antimicrobianos fue a ampicilina y cloranfenicol en pollo, perfloxacina y ampicilina en res y carbenicilina, ampicilina, cloranfenicol, cefotaxima y perfloxacina en cerdo. Noventa por ciento de las cepas mostraron un patrón de adherencia agregativo. Conclusión: La frecuencia de S. enterica en productos cárnicos es alta, por lo que es importante la adecuada cocción de la carne para disminuir el riesgo de una salmonelosis.

Yersinia enterocolitica has been isolated from a batch of pork-derived products, from healthy and diseased animals, and from different types of milk and dairy products, among others. We studied the prevalence and diversity of Y. enterocolitica isolated from raw cow's milk collected from stables in Mexico City. Of the 1,300 samples analyzed, Y. enterocolitica was isolated in 454, with an average of 25% positive samples for each stable. Of the total isolated bacteria of the Yersinia genus, 44.25% were Y. enterocolitica, 18.28% were Y. kristensenii, 13.65% were Y. intermedia, 14.85% were Y. frederiksenii, and 9.14% were Y. aldovae. Among the different strains of Y. enterocolitica, biotype 1A was present in 70%, biotype 2 in 13.2%, biotype 3 in 8.54%, and biotype 4 in 8.15% of samples. Serotypes O:5, O:3, O:2, and O:9 were found in all biotypes identified. There were no statistically significant differences in the isolation of this bacterium with respect to the stables where they were found, although there was significant difference regarding the time of year. The data obtained in this work show the need to protect public health in Mexico against infections transmitted by raw cow's milk.

Food of animal origin is often involved in salmonellosis outbreaks.To evaluate the frequency of Salmonella enterica in chicken, beef and pork ground meat (a total of 2,592 samples) obtained from travelling markets and supermarkets at the Iztapalapa area of Mexico City, in order to determine the antimicrobial susceptibility and adherence capacity of isolated strains.Isolation of S. enterica was carried out according to the BAM-FDA, the microbial susceptibility according with CLSI and adherence assay on HEp-2 cell line according with Baffone et al., 2001.S. enterica was isolated from 511 of all the analyzed samples (19.7%), from which 244 (47.7%), 152 (29.7%) and 115 (22.5%) corresponded to chicken, beef and pork ground meat, respectively. The highest frequency of resistance of S. enterica to antimicrobials was to ampicillin and chloramphenicol in chicken, perfloxacin and ampicillin in beef and carbenicillin, ampicillin, chloramphenicol, cefotaxime and perfloxacin in pork. Ninety percent of the strains showed an aggregative adherence pattern on HEp-2 cells.The frequency of S. enterica on meat products is high, which is the reason why a proper cooking of these ground meats is important in order to reduce the risk of acquiring salmonellosis.

Honey is a product used as a natural sweetener and in several regions of Mexico and other countries it is also used as a therapeutic agent. Microbiological contamination of honey can occur during its extraction and handling. Due to the use and consumption of honey we highlighted here the importance of the assessment of its microbiological quality. One thousand nine hundred twenty samples obtained from 8 honey-producing states from Mexico were analyzed. From these samples, 40.5% (777/1920) did not comply with the NMX-036-NORMEX-2006 specification. Forty five percent (777/1920) of the samples did not comply with the mesophilic aerobic microorganism specification, neither did 17% (327/1920) of the samples with the specification for molds and 18.1% (348/1920) with the specification for yeasts. With regard to coliform bacteria, the samples contained less than 3 NMP/g. Two percent of the samples contained lactic acid bacteria (LAB), Clostridium perfringens was observed in amounts of more than 100CFU/g. None of the samples from the different states contained more than 100CFU/g of Staphylococcus aureus; Salmonella spp. was absent in all samples. It is important to avoid contamination sources and implement good hygienic practices in order to maintain and improve the quality of Mexican honeys since a large percentage of them are intended for export. If these honeys are intended for therapeutic use, it is necessary to ensure that they comply with all quality parameters and to apply specific treatments that guarantee the removal of any pathogen that may represent a risk to the patients's health.

No reports on the incidence of Clostridium perfringens in popularly-consumed food from Mexico City have been published; neither are there any reports that have analyzed food consumed in popular markets and less established restaurants. Therefore, this study is aimed at providing data to evaluate the relevance of C. perfringens as an etiologic agent of food-borne diseases. Of the 650 analyzed samples, 106 (16.3%) were positive for C. perfringens; 6.4% (16/250) isolates were from barbacoa, 19% (38/200) from head, and 13% (52/200) from gut tacos. The presence of C. perfringens in these popular-consumed foods demonstrates its relevance as an etiologic agent of food-borne diseases, and confirms the great sanitary risk involved in their consumption. These results may serve as a basis for the Mexican sanitary authorities to control the microbiological quality of street-made foods.

The present study is an overview of the role of vegetables as a transmission vehicle of Salmonella in Mexico. One hundred samples of each of 17 different vegetables were analyzed during a period of 18 months. Salmonella was isolated from 98 samples. Salmonella enterica serovar Typhimurium was isolated from the highest percentage of samples with typeable Salmonella isolates (23.9%), followed by S. enterica subsp. arizonae and Salmonella Choleraesuis each from 16.9%, Salmonella Gallinarum from 11.1%, Salmonella Anatum and S. enterica subsp. houtenae each from 9.7%, Salmonella Agona and Salmonella Edinburg each from 4.22%, Salmonella Enteritidis and S. enterica subsp. salamae each from 2.81%, and Salmonella Bongor, Salmonella Pullorum, Salmonella Typhi, and Salmonella C1 flagellar b each from 1.4%. Of the isolated bacteria, 27.6% were nontypeable strains. Salmonella was isolated from 12% of parsley samples, 11% of cilantro samples, 9% of broccoli samples, 9% of cauliflower samples, 9% of "papaloquelite" (Porophyllum ruderale) samples, 9% of purslane (Portulaca oleracea) samples, 7% of long lettuce samples, 7% of spinach samples, 7% of watercress samples, 6% of Chinese parsley samples, 4% of beet samples, 3% of celery samples, 3% of Romaine lettuce samples, 1% of cabbage samples, and 1% of potato samples. The presence of Salmonella Typhi in parsley is noteworthy. No Salmonella isolates were obtained from zucchini and onion. These results indicate that raw or minimally processed vegetables can be contaminated with Salmonella, leading to direct infection of consumers or cross-contamination of other foodstuffs. These contaminated vegetables can represent a severe health risk for the Mexican consumer.

Bacillus cereus can cause diarrhea and emetic syndromes after ingestion of food contaminated with it. This ability is due to the production of enterotoxins by this microorganism, these being the hemolysin BL complex, which is involved in the diarrheal syndrome, and cereulide, which is responsible for the emetic syndrome. The detection of genes associated with the production of these toxins can predict the virulence of strains isolated from contaminated food. In this paper, we analyzed 100 samples of vegetables, 25 of each kind (broccoli, coriander, carrot, and lettuce) obtained from different markets in Mexico City and its metropolitan area. B. cereus was isolated in 32, 44, 84, and 68% of the samples of broccoli, carrot, lettuce, and coriander, respectively. The hblA gene (encoding one of the three subunits of hemolysin BL) was amplified in 100% of the B. cereus isolates, and the ces gene (encoding the cereulide) could not be amplified from any of them. This is the first report of B. cereus isolation from the vegetables analyzed in this work and, also, the first report in Mexico of the isolation from vegetables of strains with potential virulence. The results should serve as evidence of the potential risk of consuming these foods without proper treatment.

We analyzed the presence of Listeria spp. in oyster, fish, and seawater samples and tested isolates for antibiotic sensitivity. Listeria monocytogenes was found in 4.5% of fish samples and 8.3% of seawater samples and was not recovered from oysters. Multiresistant environmental strains were found, representing a potential threat to human health.

Aims This work aims to demonstrate the presence of several genes and factors associated with virulence in strains isolated from the environment at Pueblo Viejo Lagoon, State of Veracruz, Mexico. Methods and Results In this study, we investigated the production of V. vulnificus virulence factors, as cytolysin (haemolysin), RTX toxin, metalloprotease, siderophores, capsular polysaccharide, adhesion structures (like type IV pili), and polar and lateral flagella, involved in swimming and swarming (or, at least, the presence of genes encoding some of them) in 40 strains of V. vulnificus isolated from water and food. The results indicate that strains of environmental origin possess potential virulence characteristics. Conclusions Caution should be exercised when consuming raw shellfish (especially by those more susceptible risk groups). Significance and Impact of the Study This is the first work focused on the evaluation of V. vulnificus virulence factors in Mexico.

The presence of Vibrio vulnificus was analyzed in oyster and estuarine water samples from Mexico by PCR amplification of the vvhA gene and some putative virulence factors were tested. Samples were collected from 12 different sampling points over a one-year period; 31% samples were positive for V. vulnificus and all isolates were identified as biotype 1. All strains were cytotoxic and proteolytic, 98% showed adherence to epithelial cells, 91.4% were DNase-positive, 77.6% were mucinase-positive, 97.8% were lecithinase-positive and 79.8% were lipase positive. Regarding colony morphology, 51% strains were opaque, 20% were translucid, 28% were both opaque and translucid, and 80.8% showed a capsule. This is the first report on the isolation of V. vulnificus strains from environmental samples in Mexico, which may pose a health risk for local fisherman and seafood consumers.

A total of 160 meat product samples were collected from commercial outlets in Mexico City to investigate the presence of different species of Yersinia by the 4 degrees C enrichment method after 1, 3, 5, and 7 days of incubation using alkaline treatment and isolating in cefsulodin-Irgasan-novobiocin and MacConkey agars with Tween 80. Overall, Yersinia spp. were isolated from 27% of the samples analyzed, whereas 40% of the raw and only 13% of the precooked samples were contaminated. Although 2,970 colonies showed Yersinia characteristics, only 706 (24%) actually corresponded to this genus: 49% were Yersinia enterocolitica, 25% Yersinia kristensenii, 15% Yersinia intermedia, 9% Yersinia frederiksenii, and 2% Yersinia aldovae; 10% corresponded to biotype 2, 2% to biotype 3, and 4% to biotype 4. The presence of Yersinia in raw and cooked meat products represents a health risk for consumers in Mexico, where further clinical studies are needed to assess the epidemiological importance of this pathogen.

The presence of Campylobacter spp. was investigated in 100 samples of roasted chicken tacos sold in well-established commercial outlets and semisettled street stands in Mexico City. From 600 colonies displaying Campylobacter morphology only 123 isolates were positive. From these isolates, 51 (41%) were identified as C. jejuni, 23 (19%) as C. coli, and 49 (40%) as other species of this genus. All of the 27 positive samples came from one location where handling practices allowed cross-contamination of the cooked product. The results indicate that these ready-to-consume products are contaminated with these bacteria, representing a potential risk for consumers, especially in establishments lacking adequate sanitary measures to prevent cross-contamination.