RESUMEN
BACKGROUND: To evaluate the in vitro activity of the ampicillin-sulbactam and amoxicillin-clavulanic acid against Escherichia coli isolations resistant to ampicillin and amoxicillin and the efficacy of the disks of ampicillin sulbactam 10/10 microgram and amoxicillin-clavulanic acid 20/10 micrograms to differentiate the susceptible (S) and resistant (R) isolates. METHODS: We evaluated the in vitro susceptibility of 100 consecutive clinical isolates of ampicillin and amoxicillin resistant E. coli by the broth macrodilution method and disk diffusion test against ampicillin-sulbactam and amoxicillin-clavulanic acid. RESULTS: For amoxicillin-clavulanic acid the 64% of the isolates were susceptible, 34% were moderately susceptible and 2% were resistant. In contrast, the in vitro activity of ampicillin-sulbactam was inferior since 13% of the isolates were susceptible, 24% moderately susceptible and 63% were resistant. By using the disk of ampicillin-sulbactam 10/10 microgram we found a 13% of very major errors and a 44% of minor errors when we consider the actual rules of NCCLS (R < or = 11 mm and S > or = 15 mm). The best results were achieved when we took into account zone size < or = 15 mm as R and > or = 20 mm as S; however, the level of errors was high too (25% minor errors). For the disk of amoxicillin-clavulanic acid 20/10 micrograms we found a 31% of minor errors when using the advised break points (R < or = 13 mm and S > or = 18 mm). CONCLUSIONS: We consider that the disk diffusion tests are not applicable to these combinations when E. coli isolates resistant to aminopenicillin are evaluated. We advise not to extrapolate the results of sensibility or resistance from one combination to the other because it presents a different in vitro activity.
Asunto(s)
Amoxicilina/farmacología , Ampicilina/farmacología , Antibacterianos/farmacología , Ácidos Clavulánicos/farmacología , Escherichia coli/efectos de los fármacos , Sulbactam/farmacología , Ácido Clavulánico , Pruebas de Sensibilidad Microbiana , Valor Predictivo de las Pruebas , Reproducibilidad de los ResultadosRESUMEN
Since resistance to several oral antimicrobials useful for the treatment of pediatric urinary tract infections (UTI) is overwhelming in Argentina, an in vitro investigation was performed testing 400 isolates obtained from urines of children suffering UTI's, 200 collected in 1990 and 200 in 1991. Their susceptibility against oral antimicrobials marketed in Argentina and appropriate for the treatment of UTI was determined by the agar dilution methods. An increase of the resistance to aminopenicillin combined with beta-lactamase inhibitors and to fluoroquinolones was observed comparing the two periods. Cefpodoxime (CPD), cefixime and fluoroquinolones except norfloxacin were the sole oral antimicrobials showing in vitro activity at the 90 per cent level. Unfortunately fluoroquinolones are not yet approved for pediatric use. Consequently we realized an in vitro and in vivo pharmacokinetic study in order to determine CPD activity against E. coli isolated in UTI cases. Five children (6-10 y) showing E. coli UTI infections received 10 mg/kg/d CPD in a single oral daily dose and were treated up to 10 days, 3 had lower UTI and 2 upper UTI. All patients were clinical and bacteriologically cured. Cultures obtained up to 4 weeks after treatment were negative. CPD serum levels at 2 hours after the first dose of treatment showed a median of 2.7 mg/l (2.3-3.4 range). Bactericidal serum titers at the same time against the patients own strain and an E. coli TEM-1 hyperproducer strain (MIC 4,096 mg/l for ampicillin and 0.5 mg/l for CPD) showed a median value of 1/8 against patients strains and 1/2 against the THP strain.(ABSTRACT TRUNCATED AT 250 WORDS)