Beta-Lactamases in Salmonella Isolates from Argentina.

DI CONZA J; POWER P; RADICE M; MOLLERACH M; GUTKIND G

L’Aquilla, Italia.

Congreso; International Congress on ß-lactamases.; 1999

Plasmid borne extended-spectrum beta-lactamases (ESBLs) contribute to the high levels of resistance to third generation cephaloeporins within non-typhoid Salmonella spp isolated in our country (up to 30% in some hospitals). Twenty five salmonella isolates from pediatric patients at "Hospital de niños R. Gutierrez", Santa Fe, Argentina, were divided in three groups according to their susceptibility patterns. The first group included those strains completely susceptible to beta-lactams antibiotics. The second seven strains resistant to penicilins and cephalotin. The third group was composed by six strains resistant to cefotaxime (CTX) (MICs = 64 mg/ml). Group two and three were all Salmonella Infantis. Crude extracts from second group revealed the presence of one enzyme with an apparent pI of 5.4 using ampicillin iodommetric overlay (100 mg/ml) after analytical isoelectrofocusing. Highly resistant isolates (group 3) also displayed the presence of an ESBL with an apparent pI 8,2, active on ceftriaxone (1000 mg/l). PCR amplification and colony blot hybridization confirmed the presence of TEM-1 in both the second and third groups. CTX-M-derived beta-lactamases were also present in the third group, being responsible for the third-generation cephalosporin resistance in these isolates. Resistance to beta-lactams and aminoglycosides could be transferred by conjugation to Escherichia coli CAG12177. A single plasmid (55 kb) was identified in resistant salmonella isolates and in transconjugants. In E. coli DH10B, transformed with plasmids isolated from the second group, different nolecular weight plasmids could be alternatively recovered from different clones: a high molecular plasmid 55 kb) in good agreement with that observed in the donors, a plasmid about 5 kb, or another of 2.5 kb. The smaller plasmids conferred resistance to ampicillin and cephalotin but not to aminoglycosides. In all cases the presence of TEM-1 was confirmed by colony blot hybridization. Using plasmids obtained from the third group, up to date, only resistance to penicillins and first generation cephalosporins was transferred detecting an unique plasmid approximately 5 kb. Presence of TEM-1 was confirmed by colony blot hybridization