IN VITRO BIOLOGICAL ACTIVITY OF CEPHALOTHIN

Abstract

Cephalothin is a "broad-spectrum" antibiotic active in low concentrations against Diplococcus pneumoniae, Streptococcus pyogenes and Staphylococcus aureus Shigella, Salmonella and Proteus mirabilis were the most sensitive of the gram-negative organisms. Escherichia coli and Aerobacter aerogenes were suppressed to a lesser degree, whereas Pseudomonas aeruginosa and Herellea were highly resistant. Penicillin-sensitive and -resistant strains of S. aureus were equally susceptible to cephalothin. Exposure to increasing concentrations of the drug very frequently led to the development of resistance in gram-negative organisms; this was observed less often with S. aureus. Cephalothin stimulated the production of penicillinase by staphylococci which remained sensitive to the cephalosporanic-acid derivatives despite repeated subculture in increasing concentrations of the agent. Cephalothin was not inhibited by penicillinase. This antibiotic was more toxic to cultures of human amnion and mouse embryo cells than benzyl penicillin-G but was less injurious than oxytetracycline, chlortetracycline and demethylchlortetracycline; tetracycline produced about the same degree of cellular damage as cephalothin.