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.

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...

No abstract

Abstract:We report herein the microwave assisted synthesis, without solvents and catalysts, of 6-substituted quinoxalines and 7-substituted pyrido [2,3b]pyrazines. The compounds were obtained in good yields and short reaction times using the mentioned procedure and two new structures are reported. A complete 1 H-and 13 C-NMR assignment was performed using 1D and 2D-NMR. Additionally, an in vitro screening was performed on Gram-positive and Gram-negative bacteria using amoxicillin as positive reference. Compounds bearing a pyridyl group tended to have higher antibacterial activity, but the best activity against Bacillus subtilis and Proteus mirabilis was observed with quinoxaline derivatives.

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.

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.

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.