Abstract
Antimicrobial activities of sulbactam (SBT) with ampicillin (ABPC) or with cefoperazone (CPZ), in other words, the effects of SBT, an β-lactamase inhibitor, against β-lactamase producing strains of clinical isolates, were studied using microdilution broth method.
1. β-Lactamase producing strains such as Staphylococcus aureus, Branhamella catarrhalis, Haemophilus influenzae, Escherichia coli and Klebsiella pneumoniae decompose benzylpenicillin (PCG) which is one of substrates of the acidimetry disc method and show a strong reaction, while they do not decompose cefazolin (CEZ), another substrate, showing no or weak reaction. Thus, it is suspected that β-lactamases produced by these organisms are mainlypenicillinase (PCase).
MIC-distributions of ABPC and CPZ against these clinical isolates which seemed to produce PCase shifted to lower MIC ranges with MIC's reduced to 1/4 or below when 0.025 to 0.39 μg/ml of SBT was added.
2. It appears that β-lactamase produced by Proteus vulgaris may be oxyiminocephalosporinase (CXase), because P. vulgaris showed strong reaction on CEZ, but moderate reaction on PCG In the acidimetry disc method.
MIC-distribution of ABPC and CPZ against P. vulgaris shifted to a lower range with MIC's of 1/4 or below when 0.20 to 0.39 μg/ml of SBT was added.
3. All the test strains of Pseudomonas aeruginosa showed strong reaction on CEZ but only 56% of the test strains showed reaction on PCG. It appears that the β-lactamases which showed strong reaction on CEZ is cephalosporinase and is encoded in chromosome, while those β-lactamase that showed strong reaction on PCG is encoded in a plasmid which was acquired secondarily by P. aeruginosa.
MIC-distribution of CPZ against P. aeruginosa shifted to a lower range with MIC values of 1/2 or below with the addition of SBT at 1.56 μg/ml.
4. It appears that the synergy of SBT with ABPC or with CPZ against the PCase or CXase producing strains may occur in the presence of SBT at a concentration far less than that reported previously.
