Role of β−lactamase in the susceptibility of clinical isolates to β−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) Keywords: Antibiotic Susceptibility, MIC, β−lactam antibiotic, β−lactamase inhibitor