The incidence of antibiotic resistance in gram-negative bacilli in a general hospital.

Five antibiotics-penicillin, streptomycin, aureomycin, chloromycetin, and terramycin-are now readily available for the treatment of diseases due to bacterial infection, and for the treatment of wounds infected either primarily or by hospital cross-infection. There is considerable overlapping in the selective activity of these antibiotics in that they are effective against Gram-positive bacteria in varying degree. The last four are also variably effective against the Gram-negative bacteria. There is, in addition, absolute selective activity in regard to some micro-organisms. Streptomycin alone is therapeutically effective against Myco. tuberculosis; chloromycetin has a special selective action against the Rickettsiae; aureomycin and terramycin have a special selective action against the larger viruses. It is, therefore, important in every case to attempt to obtain a pure culture of the infecting organism, and to evaluate its sensitivity to the various antibiotics. The widespread use of antibiotics has also produced the problem of antibiotic resistant organisms, a problem which is as important, in relation to the Gramnegative bacilli, as it is to the Gram-positive cocci, and it was felt that an analysis of the results of routine sensitivity tests over 12 months might yield significant information. Bact. coli, P. vulgaris, Ps. pyocyanea, H. influenzae, and Bact. friedldnderi were studied with regard to their sensitivity to streptomycin, aureomycin, chloromycetin, and terramycin. The period under review is the 12 months from January 1, 1950, to December 31, 1950. From January 1, 1950, to June 30, 1950, streptomycin only was available. From July 1, 1950, onwards aureomycin, chloromycetin, and terramycin were gradually added to the battery of antibiotics, until, in the final period, October 1, 1950, to December 31, 1950, all four antibiotics were used in the sensitivity tests. The blood-agar plate medicated disc method of sensitivity testing has been used throughout. The method is simple and gives all the information that is required for control of antibiotic therapy. The antibiotics used in the tests were prepared in the following strengths.