Escherichia coli O157:H7 is a foodborne pathogenic bacterium that can reside undetected in the gastrointestinal tract of cattle because colonization by this bacterium is asymptomatic. Recent research has indicated that swine can carry and transmit this pathogen as well. The development of more advanced and sensitive detection techniques has improved the limit of detection and increased sensitivity for this important pathogen. This study was undertaken to determine the prevalence of E. coli O157 in cattle and swine in Mexico with the more sensitive detection technique of immunomagnetic bead separation. Samples (n = 60 per farm) were taken from four cattle and four swine farms (n = 240 cattle samples, n = 240 swine samples) located throughout central Mexico in October 2001. The prevalence of E. coli O157 was found to be only 1.25% on cattle farms and 2.1% on swine farms. The prevalence in cattle in this study is lower than that reported in the United States and could be related to the lower reported prevalence of E. coli O157 in humans in Mexico. However, further research is needed to verify prevalence throughout other regions of Mexico, as well as prevalence during other seasons of the year.

Escherichia coli is a common avian pathogen mainly associated with extraintestinal infections such as yolk sac infection (YSI). The aim of this study was to determine the serotypes and the presence of some virulence genes of E. coli strains isolated from different samples in a vertically integrated poultry operation in Mexico. Two hundred sixty-seven E. coli isolates from different samples were serotyped using rabbit serum against the 175 somatic (O) and 56 flagellar (H) antigens of the typing schema. Virulence genes were determined by colony blot hybridization, using DNA probes for st, eae, agg1, agg2, bfp, lt, cdt, slt, and ipaH diarrhea-associated virulence factors. The serogroup of 85% of the strains was determined; O19 (12%), 084 (9%), 08 (6%), and 078 (5%) were the most common. Using the complete antigenic formula (O and H), O19:NM (n = 31) was the serotype most frequently isolated from dead-in-shell embryos and in broilers that had died on the fourth, fifth, sixth, and seventh days after hatch. One hundred ten strains (41.2%) hybridized with one or more of the used probes. Of these, ipaH (72%), eae (30%), and cdt (27%) were the most common. Considering the origin of the respective isolates, 40% of the broiler farm strains were positive for at least one probe. Results show that some avian E. coli strains isolated in Mexico are included in avian pathogenic E. coli serotypes not previously reported, suggesting that they could be specific for this geographic area. The wide distribution of the ipaH gene among nonmotile strains suggests that this invasiveness trait could be important in YSI pathogenesis. On the other hand, some other genes could contribute to E. coli virulence during YSI.

The objective of this study was to determine, in broilers, which modality of disodium fosfomycin (DF) administration and at what dose the best pharmacokinetic (PK) profile could be obtained, taking as reference a 110 field bacterial strains of Escherichia coli minimum inhibitory concentration survey. The DF was administered via drinking water either ad libitum or at a higher concentration having 1 h of water restriction to build up thirst in the birds (loading dose). Dosages tested were 10, 20, 40, and 80 mg/kg per administration, either once or twice daily. Birds included were 24-d-old Cornish broilers randomly assigned to 16 groups of 200 birds per group and 3 replicates per group. The PK of DF was determined after ad libitum administration of either a single- or double-loading dose or after an initial loading dose followed by ad libitum medication. Also, PK after i.v. administration was studied in separate groups. Serial blood samplings were performed in all groups. Serum obtained was analyzed for DF and a possible active metabolite by means of a microbiological agar diffusion assay. The DF showed a short elimination half-life (approximately 2 h after oral loading administration) with a rapid clearance (1.23 to 1.42 mL/kg per h). Apparent volume of distribution-area under the curve values were also low (10 and 80 mg/kg=0.25 L/kg and 0.22 L/kg, respectively). Considering a minimum inhibitory concentration level that inhibited 90% of total strains of 8 µg/mL for E. coli, it is concluded that single-loading administration at 10, 20, 40, and 80 mg/kg complies poorly with sustained serum concentrations over a dosing interval of 24 h. Doses of 10 and 20 mg/kg twice a day also were insufficient to attain therapeutic concentrations. Useful serum concentrations of DF to treat outbreaks of susceptible E. coli require an initial loading dose of 40 mg/kg, followed by an ad libitum medication of 40 mg/kg 8 h later (80 mg/kg per d).

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