Villar H E, Jugo M B, Fernández-Lausi A, Farinati A E
Cátedra de Infectología y Microbiología Clínica, Universidad Católica Argentina, Buenos Aires, Argentina.
Enferm Infecc Microbiol Clin. 1996 May;14(5):308-10.
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.
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.
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).
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.
评估氨苄西林 - 舒巴坦和阿莫西林 - 克拉维酸对耐氨苄西林和阿莫西林的大肠杆菌分离株的体外活性，以及10/10微克氨苄西林 - 舒巴坦纸片和20/10微克阿莫西林 - 克拉维酸纸片区分敏感（S）和耐药（R）分离株的效果。
我们通过肉汤稀释法和纸片扩散试验，对100株连续的耐氨苄西林和阿莫西林的大肠杆菌临床分离株进行了针对氨苄西林 - 舒巴坦和阿莫西林 - 克拉维酸的体外敏感性评估。
对于阿莫西林 - 克拉维酸，64%的分离株敏感，34%中度敏感，2%耐药。相比之下，氨苄西林 - 舒巴坦的体外活性较差，13%的分离株敏感，24%中度敏感，63%耐药。当依据NCCLS的实际标准（R≤11mm且S≥15mm）时，使用10/10微克氨苄西林 - 舒巴坦纸片，我们发现有13%的极重大错误和44%的微小错误。当把抑菌圈直径≤15mm视为R，≥20mm视为S时，结果最佳；然而，错误率也很高（25%微小错误）。对于20/10微克阿莫西林 - 克拉维酸纸片，按照推荐的折点（R≤13mm且S≥18mm），我们发现有31%的微小错误。
我们认为，在评估耐氨基青霉素的大肠杆菌分离株时，纸片扩散试验不适用于这些组合。我们建议不要将一种组合的敏感性或耐药性结果外推至另一种组合，因为它们具有不同的体外活性。
