170 Perspecfives in Microbiology 



mals and fowl have increased our total meat resources 

 almost overnight, and to a significant degree. 



These striking successes and the facility with which the 

 antibiotics can be, and often are, prescribed for the treat- 

 ment of undiagnosed febrile illness have led to the wide- 

 spread misapprehension that the problem of infectious 

 disease has been or soon will be solved. The truth falls 

 somewhat short of this optimistic appraisal. The problem 

 of infectious disease has been met only in part, and indeed 

 only in small part. A number of common and serious bac- 

 terial infections are not amenable to treatment with any 

 of the antibiotics yet discovered; antibiotic-resistant staphy- 

 lococci present a special and as yet unsolved problem; the 

 chemotherapy of many protozoal and helminthic infections, 

 world-wide in scope and affecting large segments of the 

 population, is highly unsatisfactory; and although the 

 rickettsial infections and a number of diseases caused by the 

 larger viruses respond satisfactorily to treatment with some 

 of the antibiotics, the smaller viruses are not similarly sus- 

 ceptible. 



Cell PermeabilJfy, a Possible Limiting Factor 



It has been suggested that the small viruses are resistant 

 to therapy because, as intracellular organisms, they cannot 

 be reached by the drugs. But recent studies in our labora- 

 tory with radioactive penicillin and streptomycin indicate 

 that at least these two antibiotics do penetrate into some 

 types of mammalian cell in concentrations consistent with 

 a simple diffusion equilibrium. Permeability, as such, may 

 therefore not be the important consideration which limits 

 their therapeutic action within the cell. Conceivably, the 

 larger viruses and the rickettsiae have a more complex 

 structure and more complex metabolic pathways, which 

 offer numerous points of attack for the selective cytotoxic 

 action of, for example, chloramphenicol or a tetracycline. 



