Tablet Diffusion Research Articles

Determination of susceptibility of anaerobic bacteria to beta-lactam antibiotics by a tablet diffusion test.

A standardized tablet diffusion test and a reference agar dilution test was evaluated for susceptibility testing of anaerobic bacteria to beta-lactam antibiotics. 74 freshly isolated anaerobic bacteria and three control strains (Cl. perfringens ATCC 13124 B. fragilis ATCC 25285, B. thetaiotaomicron ATCC 29741) were tested. The in vitro activities of 7 beta-lactam antibiotics were compared with metronidazole and clindamycin. Most active were metronidazole and clindamycin. Cefoxitin had the best activity of the beta-lactam antibiotics, whereas piperacillin and carbenicillin had good activities. High resistance rates were found for penicillin, ampicillin, cefuroxime and cefotaxime. MIC on control strains fell well within range set by the National Committee for Clinical Laboratory Standards (NCCLS). Correlation between MIC and inhibition zone diameters was generally good. Tablet diffusion can be used to divide anaerobic bacteria into three susceptibility categories. In addition all bacterial strains were tested for production of beta-lactamase by a nitrocefin tube test. Beta-lactamase production by the nitrocefin test indicated reduced sensitivity to beta-lactam antibiotics.

Antimicrobial susceptibility of Flavobacterium meningosepticum strains identified by DNA-DNA hybridization.

Antimicrobial susceptibilities of 52 strains of Flavobacterium meningosepticum were determined by an agar plate dilution technique and by a tablet diffusion method. No useful susceptibility differences between the two main DNA relatedness groups within F. meningosepticum were found. All strains produced beta-lactamase and were resistant to most beta-lactam antibiotics. Ciprofloxacin, rifampicin and clindamycin appear to be the most promising for treating infections caused by F. meningosepticum.

Polymyxin susceptibility in staphylococci differentiating coagulase-positive and coagulase-negative strains.

47 staphylococcal reference strains representing 13 species were tested for polymyxin sensitivity using tablet and disc diffusion methods. Corresponding MIC and IC50 values were determined with a plate dilution assay. Coagulase-positive strains were found to be more resistant towards polymyxin, and could thereby be separated from coagulase-negative strains. Furthermore, 100 recently isolated staphylococci from clinical specimens were tested, and again the coagulase-positive strains could be identified by their smaller tablet inhibition zones. We conclude that the polymyxin test is an aid in the fast differentiation of staphylococci in laboratories performing primary sensitivity tests.