Biomedical subjects
Publications and source records attributed to T A Kurzynski.
The in vitro susceptibility of 20 isolates of Clostridium difficile to cefotaxime, moxalactam, and cefoperazone was determined by a standard agar dilution method. The median minimal inhibitory concentrations were 64, 32, and 32 mug/ml for cefotaxime, moxalactam, and cefoperazone, respectively.
In the first study, selective sulfamethoxazole-trimethoprim blood agar (SXT-BA) and conventional blood agar (BA) plates incubated under CO2 and anaerobically were compared for their ability to recover group A streptococci from throat cultures. Recovery rates were: SXT-BA (anaerobic), 100%; SXT-BA (CO2), 98%; BA (anaerobic), 89.2%; and BA (CO2), 76.5%. Primary plate bacitracin test results could be read on significantly more of the SXT-BA plates. Readability rates were: SXT-BA (anaerobic), 97%; SXT-BA (CO2), 96%; BA (anaerobic), 70.6%; and BA (CO2), 32.4%. A second study compared with the SXT-BA method versus a BA-double-disk (BA-DD) method which utilizes conventional media with addition of a bacitracin differentiation and a sulfamethoxazole-trimethoprim susceptibility disk placed adjacent to one another in the heavy area of inoculation. Isolation rates were: SXT-BA, 100% and BA-DD, 88%. Readability rates for direct bacitracin tests were: SXT-BA, 92% and BA-DD, 76.2%. In our hands, the SXT-BA method was superior for yielding highest isolation rates and for yielding highest readability rates of direct bacitracin test results.
We compared the selective blood agar medium of Gunn et al. (J. Clin. Microbiol. 5:650-655, 1977) which contains sulfamethoxazole plus trimethoprim (SXT-BA) to the conventional blood agar surface plate (SBA) and a modified blood agar pour plate plus broth method for the recovery of group A streptococci from throat swabs. The influence of CO(2) and ambient air incubation of the SXT-BA and SBA plates was also evaluated. A total of 696 throat swabs from symptomatic children were cultured simultaneously by the five methods and observed after overnight incubation; 204 positive cultures were detected overall. Recovery rates of each individual method were: SXT-BA (CO(2)), 90.7%; SXT-BA (air), 87.7%; pour plate plus broth, 83.3%; SBA (CO(2)), 79.4%; and SBA (air) 77%. Approximately one-half of the false-negative cultures in the SXT-BA (CO(2)) and SXT-BA (air) methods had colony counts of >/=10 to 100 colonies per plate. In contrast, for the SBA (CO(2)), SBA (air), and pour plate plus broth methods, approximately 70% of the false-negative cultures had colony counts of >/=10 to 100/plate. False-positive cultures obtained by the SXT-BA (CO(2)) and SXT-BA (air) methods were 11 and 12.7%, respectively-one-half as high as the rates obtained by the remaining methods. Beta-hemolytic streptococci, groups C, F, and G, are inhibited on the SXT-BA plates and were the primary cause of the higher false-positive rates on SBA and pour plate plus broth methods. An additional 3% positive cultures were obtained by incubating SXT-BA (CO(2)) plates up to 48 h before discarding as negative. We recommend either the SXT-BA (CO(2)) or the SXT-BA (air) method with up to 48 h of incubation for routine use in throat cultures.
Carbenicillin has been advocated for treatment of infections caused by Bacteroides fragilis and other anaerobic bacteria. Wide-scale use of the drug in this setting could result in a substantial increase in carbenicillin-resistant Pseudomonas aeruginosa, an effect that would have serious implications. Thirty-four strains of B. fragilis, one-half from bacteremic infections, were tested in vitro, and penicillin G was found to be twice as active as carbenicillin on an equal weight basis; 94% of the strains were inhibited by 32 microgram of penicillin/ml, a level easily achieved therapeutically. Penicillin killed B. fragilis organisms as rapidly as carbenicillin. In two subjects given equivalent doses (100 mg/kg intravenously) of carbenicillin and aqueous penicillin G, the bactericidal activity of serum against B. fragilis after administration of each drug was the same. Controlled clinical trials of treatment of anaerobic bacterial infections with penicillin G in high dosage, carbenicillin (or closely related ticarcillin), clindamycin, and chloramphenicol should be undertaken. Carbenicillin (and ticarcillin) for the present would seem better reserved for P. aeruginosa infections.
The anaerobic broth disk (AnBD) method of Wilkins and Thiel and a new modification, designated the thioglycolate broth disk method, were compared with an agar dilution technique. The thioglycolate broth disk method was incubated aerobically (AeTBD) or anaerobically (AnTBD). One hundred anaerobic bacteria representing 15 species were tested with clindamycin, chloramphenicol, erythromycin, penicillin, and tetracycline. Agreement of results by the two methods with minimal inhibitory concentration determinations were: AnBD, 95.2%; AnTBD, 91.5%; AeTBD, 94.5%. With clindamycin, chloramphenicol, and penicillin, the agreement of the AeTBD and agar dilution results was 100%, 100%, and 95%, respectively. Using the AeTBD method, only 1.1% of all tests gave false susceptible readings, whereas 4.4% gave false resistant readings. All susceptibility testing errors occurred with tetracycline, erythromycin, and, to a lesser extent, penicillin. For each method, the changes in designation of bacteria as being susceptible or resistant to an antibiotic between trials primarily involved strains with minimal inhibitory concentrations which were +/- one dilution of the respective breakpoint value. The same situation was true for most bacteria that yielded false resistant readings within each trial. False resistant readings with tetracycline were determined to be unrelated to excess cation content of test media. These results reaffirm the reliability of the AnBD method and indicate that the AeTBD modification is equally reliable. The greater convenience and lower cost of the AeTBD method should make possible more widespread performance of susceptibility testing for anaerobic bacteria in hospital laboratories.
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