However, by the end of the time period studied (2004–2005), ST213 was the predominant genotype in all four states (Figure 3). Figure 3 Distribution

of the percentage of Typhimurium STs according to the time period and geographic 3-MA supplier location. We found a strong association between STs and antimicrobial resistance. ST213 isolates presented higher percentages of resistance (> 50%) than ST19 isolates, the only exception was ciprofloxacin for which all the isolates were susceptible (Table 3). All the isolates resistant to ceftriaxone belonged to ST213, while all the isolates from STs 19, 302 and 429 were ceftriaxone susceptible. The group of isolates resistant to ceftriaxone (n = 36) was associated with very high percentages (> 95%) of resistance to ampicillin, chloramphenicol, sulfisoxazole, streptomycin and tetracycline, here after referred to as the pentaresistant

phenotype. Table 3 Percentage of antimicrobial resistant strains for the two main Typhimurium STs.   Antimicrobial resistance   AMPa CHL SSS STR TET GM KM NAL SXT CIPb CRO ST19 61 51 75 80 75 7 10 10 22 0 0 ST213(cmy-2)c 68 (97) 90 (94) 98 (97) 97 (97) 97 (100) 59 (55) 37 (33) 72 (61) 82 (92) 0 53 (100) a AMP:ampicillin, CHL: chloramphenicol, SSS: sulfisoxazole, STR: streptomycin, TET: tetracycline, GM: gentamicin, KM: kanamycin, NAL: nalidixic acid, SXT: timethoprim-sulfametoxazole, find more CIP: ciprofloxacin, CRO: ceftriaxone. b All the strain were sensitive to CIP according with CLSI [78], including twelve strains with low-level resistance [see Additional file2]. c The

number in parenthesis is the percentage corresponding to ST213 strains positive for cmy-2. The resistance patterns varied across geographic locations. Yucatán was the state with the higher level of multidrug resistance, with an average of seven resistances per isolate; while Sonora presented the lowest levels of resistance with an average of four. Michoacán and San Luis presented intermediate values, both with an average of six. Furthermore, the ST213 ceftriaxone Ketotifen resistant isolates PI3K Inhibitor Library displayed a differential geographic pattern, ranging from 97% of the ST213 isolates in Yucatán to 0% in Sonora, with intermediate levels in Michoacán and San Luis Potosí (Figure 3). Distribution and associations of pCMY-2 Isolates resistant to ceftriaxone were subjected to PCR analysis to detect the presence of the bla CMY-2 gene (Figure 1C). All 36 isolates resistant to ceftriaxone were positive, whereas the 12 sensitive isolates tested were negative [see Additional file2]. Sequencing (564 bp) of cmy-2 for 16 isolates revealed that all carried an identical allele, suggesting a common origin. The BLAST searches showed that this allele was identical to most of the 100 hits targeting the Enterobacteriaceae (Escherichia, Salmonella, Klebsiella, Proteus and Citrobacter). To determine the location of the cmy-2 gene, plasmid profiles for 25 isolates were hybridized with the corresponding radioactive probe.