Role of lactamase in the susceptibility of clinical isolates to lactam antibiotics

Combination of lactam antibiotic with lactamase inhibitor has been proven to overcome resistance caused by lactamase production. An evaluation to the MIC of some lactam antibiotics to b-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 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. -lactamase production was identified using Cefinase disk. Sixtyfour percent of isolates were capable of producing lactamase. All E.coli and K.pneumoniae tested were lactamase producer, none of Proteus sp, Pseudomonas sp, and S.epidermidis tested produced lactamase. In lactamase producing group, Sulbactam was able to reduce resistance to CFP from 25% to 5%. About 20% of 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 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 -lactamase. -lactamase inhibitor could reduce resistance of -lactamase producing organism to -lactam antibiotic from 25 to 5 percent. (Med J Indones 2004; 13: 140-5)