Cross Resistance to Antibiotics: Effect of Exposures of Bacteria to Carbomycin or Erythromycin in Vitro

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Abstract
The antibacterial spectrum of carbomycin parallels very closely that of erythromycin. Both of these new antibiotics are highly active against Gram-positive and Gram-negative cocci, moderately active against strains of Hemophilus and are essentially inactive against coliform and enteric bacilli. Against susceptible bacterial strains, erythromycin is usually from 4-16 times more active than carbomycin wt. Repeated subcultures of staphylococci and of certain strains of streptococci in the presence of increasing concns. of either of these antibiotics result in fairly rapid and marked increases in resistance not only to the antibiotic to which it was exposed but to the other agent as well.