Role of [beta]-lactamase in the susceptibility of clinical isolates to [beta]-lactam antibiotics

Combination of β-lactam antibiotic with β-lactamase inhibitor has been proven to overcome resistance caused by β-lactamase production. An evaluation to the MIC of some β-lactam antibiotics to β-lactamase producing isolates will be reported. A. anitratus, E. coli, K. pneumoniae, Proteus sp, Pseudomonas sp, S. aureus, S. epidermidis, S. pneumoniae, S. viridans, and β-hemolytic Streptococcus, were challenged to Ampicillin/Sulbactam (AMS), Amoxicillin/Clavulanic acid (AMC), Cefoperazone (CFP), Cefoperazone/Sulbactam (CSL), Ceftriaxone (CRO), dan Cefotaxime (CTX) using ETest techniques. β-lactamase production was identified using Cefinase disk. Sixtyfour percent of isolates were capable of producing β-lactamase. All E. coli and K. pneumoniae tested were β-lactamase producer, none of Proteus sp, Pseudomonas sp, and S. epidermidis tested produced β-lactamase. In β-lactamase producing group, Sulbactam was able to reduce resistance to CFP from 25% to 5%. About 20% of β-lactamase producing isolates which were resistant to CFP, were susceptible to CSL. Susceptibility of S.viridans to AMS, AMC, CFP, and CSL was higher than 80%, but less than 50% to CRO and CTX. S. pneumoniae was less susceptible to tested antibiotics, 50 to 60% susceptibility was shown to AMC, CFP, and CSL. S.aureus was 60 to 70% susceptible, while β-haemolytic Streptococcus showed good response to the tested antibiotics. Only 30% or less of K. pneumoniae and E. coli was susceptible to AMS and AMC. A. anitratus showed good susceptibility only to AMS (78%) and CSL (89%). Sixtyfour percent of isolate studied produced β-lactamase. β-lactamase inhibitor could reduce resistance of β-lactamase producing organism to β-lactam antibiotic from 25 to 5 percent. (Med J Indones 2004; 13: 140-5)