A Study on the Mechanism of Action of Penicillin as Shown by Its Effect on Bacterial Morphology

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Abstract
The alterations in the microscopic appearance of staphylococci when broth cultures are exposed to effective concs. of penicillin consist in enlargement of the bacteria within 3 hrs. This is then followed by lysis which is nearly complete in 10 hrs. Streptococci under similar conditions show occasional giant forms but little microscopic evidence of lysis. Pneumococci evidently become lysed without exhibiting marked morphologic changes. The capsules of the pneumococci were found to remain intact for sometime after the bacteria themselves failed to stain, at which time subcultures were sterile. This seemed to indicate that the pneumococcus capsule was readily penetrated by penicillin without offering the organism any protection against it. Similar findings were obtained in various human infections with pneumococci, as well as in exptl. infections in mice. The capsule stain employed was an india ink prepn. counterstained with safranine.