Rapid antibiotic disk sensitivities of burn eschar and infected wounds

This study was undertaken to develop a more rapid antibiotic sensitivity test of the pathogens in soft tissue infections and burn wound eschar. The proposed rapid antibiotic sensitivity test was performed directly on the clinical specimen rather than on single strains of bacteria isolated from the tissue. By performing the antibiotic sensitivity tests directly on the tissue sample, the physician obtains the test results within seven hours after receiving the specimen rather than 38 to 52 hours later, the time delay encountered with the conventional technique. The modification used did not alter most of the standards advised by the Food and Drug Administration (3), since there was no inclusive change in medium, agar depth or antibiotic sensitivity disk. The changes in the Kirby-Bauer (1) test necessitated by using the clinical specimen did not alter significantly the interpretation of the antibiotic susceptibility. If clinically significant numbers of bacteria, 10(6)-10(9), were present, variations in the inoculum size did not appreciably change the results of the antibiotic susceptibility tests. If the incubation requirement for the standard Kirby-Bauer (1) antibiotic susceptibility test was reduced to seven hours, it also did not significantly limit the accuracy of the test. As expected, the variable most difficult to standardize was the heterogeneous inoculum containing large numbers, 10(7), of different organisms. A zone of inhibition interpreted as sensitive with one organism was occasionally masked by the presence of the confluent growth of an organism in which the zone of inhibition was considered resistant. However, even in this instance, it is possible that mixed culture sensitivities may provide the most valid information in mixed infections, since they more closely simulate the real clinical situation.