Effect of penicillin on the multiplication of meningopneumonitis organisms (Chlamydia psittaci).

Although formation of infectious particles of meningopneumonitis organism in L cells was completely inhibited by 1 or more units of penicillin per ml, multiplication of reticulate bodies was observed, by light microscopy, in the presence of 200 units of penicillin per ml in stained smears of infected cells. When reticulate bodies were purified from cultures containing penicillin after 18, 30, and 45 hr of incubation, continuously increasing yields were obtained. When penicillin was added to infected cultures 0 to 15 hr after infection, no increase in infectivity was observed at 40 hr, but when antibiotic was added between 20 and 35 hr, partial synthesis of infectious particles was observed at 40 hr. On the other hand, removal of penicillin from an infected culture before 15 hr after infection did not affect the final yields of infectivity when assayed at 40 hr, but elimination of penicillin after 20 hr resulted in a decrease in infectivity. In suspensions of (32)P-labeled purified reticulate bodies grown in cultures containing penicillin and harvested 18 and 40 hr after infection, the (32)P distributions obtained by acid fractionation were similar to those of reticulate bodies from penicillin-free cultures. Cell membranes of reticulate bodies were also prepared from 40-hr cultures with penicillin. The size and shape of purified membranes, as seen by electron microscopy, and their amino acid compositions were similar to membranes prepared from reticulate bodies grown without penicillin, except that very small structures were observed in membranes from cultures containing penicillin. These results indicated that penicillin does not inhibit reproduction of reticulate bodies and formation of their cell membranes, but does inhibit the formation of elementary body cell envelopes.