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.

Individuals belonging to five families, 12 genera, and 19 different species of bats from dengue endemic areas in the Gulf and Pacific coasts of Mexico were examined by ELISA, RT-PCR, and for the presence of dengue virus (DV) NS1 protein. Nine individuals from four species were seropositive by ELISA: three insectivorous, Myotis nigricans (four positives/12 examined), Pteronotus parnellii (3/19), and Natalus stramineus (1/4), and one frugivorous Artibeus jamaicensis (1/35) (12.86% seroprevalence in positive species). DV serotype 2 was detected by RT-PCR in four samples from three species (all from the Gulf coast - rainy season): two frugivorous, A. jamaicensis (2/9), and Carollia brevicauda (1/2), and one insectivorous, M. nigricans (1/11). The latter was simultaneously positive for NS1 protein. DV RT-PCR positive animals were all antibody seronegative. M. nigricans showed positive individuals for all three tests. This is the first evidence suggesting the presence of DV in bats from Mexico.

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.Human listeriosis is a public health problem of low incidence but high mortality, requiring prompt diagnosis and adequate antibiotic therapy (1). Over the last 2 decades a high number of food-borne listeriosis outbreaks have occurred, some with high mortality rates (2,13,19). Antibiotic resistance and inefficient empirical treatment of Listeria infections could be responsible for this increased mortality (4). Since the first multiresistant Listeria monocytogenes strain was observed in France (14), different antibiotic resistance patterns in environmental, food, and clinical sources have been reported (7,12,20). Information on the presence of Listeria monocytogenes in Mexico is scarce, and the frequency of listeriosis is unknown. The purpose of this study was to determine the presence of Listeria spp. in fish, oysters, and saline waters in an area where fish are caught for local and regional consumption and to determine the sensitivities of the L. monocytogenes isolates to different antimicrobial agents.A total of 66 oyster, 66 fish, and 144 estuarine water samples were collected over a 12-month period (June 2001 to May 2002) from 12 sites of the Pueblo Viejo lagoon, Veracruz, Mexico (Fig. 1). Fish and oyster samples were transported on dry ice in separate thermal containers, and estuarine water samples were collected in sterile plastic bottles (Nalgene) and transported to the laboratory on ice. Oyster and fish samples were processed as previously described (9). Seawater samples were filtered through a 14-cm-diameter and 0.45-m-pore membrane (Millipore). Twenty-five milliliters of seawater or 25 g oyster or fish samples was added to 225 ml enrichment broth (EB; Merck) and incubated at 30°C for 24 to 48 h. The filter used for the water samples was washed with 100 ml peptone solution (0.1%), added to 225 ml EB, and incubated at 4°C for 7 days. Afterwards, a 0.1-ml sample was streaked in Oxford agar (Oxoid) and incubated at 30°C for 24 to 48 h. L. monocytogenes isolates were identified and serotyped as previously described (8). Antibiotic sensitivity was assessed using the Kirby-Bauer disk diffusion assay. The test and control strains were seeded in Mueller-Hinton agar supplemented with 0.5% defibrinated sheep blood and 0.1% esculin (17). Commercially available disks (Bio-Rad) with the following antibiotics were used: ampicillin, cephalothin, cefotaxime, ceftazidime, cefuroxime, dicloxacillin, erythromycin, gentamicin, pefloxacin, penicillin, tetracycline, and trimethoprim-sulfamethoxazole. MICs at which 50% of the isolates were inhibited (MIC 50 s) and MIC 90 s were calculated by following the CLSI (formerly NCCLS) guidelines (11). L. monocytogenes ATCC 19114, Escherichia co...

The thermostable direct hemolysin (TDH) and TDH-related hemolysin (TRH) are the main virulence factors of Vibrio parahaemolyticus. We isolated V. parahaemolyticus from seawater, fish, and oysters obtained from the Pueblo Viejo Lagoon in Veracruz, determined the serogroups, phenotypically and genotypically characterized TDH and TRH, and investigated the presence of the toxR gene. A total of 46 V. parahaemolyticus strains were isolated, and all of them amplified the 368-bp toxR gene fragment. The trh gene was not identified in any of the strains; 4 of the 46 strains were Kanagawa phenomenon (KP) positive and amplified the 251-bp tdh gene fragment. The most frequent serogroup was serogroup O3. This is the first report of the presence of KP-positive tdh-positive environmental V. parahaemolyticus strains in Mexico.Vibrio parahaemolyticus is a halophilic gram-negative bacterium that is widely distributed in coastal waters worldwide and is associated with gastroenteritis, wound infections, and septicemia (5). V. parahaemolyticus infections are frequently reported in coastal areas, apparently because of the high consumption of sea products and direct contact with estuarine waters (19).Epidemiological studies have revealed an association between the Kanagawa phenomenon (KP) and gastroenteritis (23,25). KP is a type of beta-hemolysis induced by the thermostable direct hemolysin (TDH) in Wagatsuma agar. Most (90%) of the strains isolated from clinical cases show this type of hemolysis, while only 1 to 2% of the strains of environmental origin are KP positive (20).Several cases of gastroenteritis caused by hemolytic but KPnegative TDH-negative V. parahaemolyticus strains were reported in the 1980s (11), which led to identification of a new hemolysin known as TDH-related hemolysin (TRH) (12,13,30). TDH and TRH are encoded by the tdh and trh genes, respectively; these two genes both have 567-bp open reading frames, and they show 68.6% sequence similarity. These hemolysins are considered the main virulence factors of this microorganism (20).In the present study we determined the prevalence of V. parahaemolyticus in seawater, oyster, and fish samples collected from the Pueblo Viejo Lagoon in Veracruz, an important estuary on the coastline of the Gulf of Mexico. The strains isolated were serotyped and screened for hemolytic activity and for the presence of the toxR, tdh, and trh genes. MATERIALS AND METHODSA total of 266 seawater, oyster, and fish samples were collected from 12 different sites in the Pueblo Viejo Lagoon (Fig. 1) The fish and oysters were transported in individually labeled and sealed plastic bags to avoid contamination. Seawater samples were collected in labeled plastic jars. The samples were placed in sealed containers with dry ice and transported frozen to the laboratory for analysis. The time between sample collection and analysis was approximately 24 h.V. parahaemolyticus strain isolation and identification. V. parahaemolyticus was isolated and identified as described in the Bacteriological Analytical Manua...