ROSAMICIN - INVITRO ACTIVITY COMPARISON WITH ERYTHROMYCIN AND OTHER ANTIBIOTICS AGAINST CLINICAL ISOLATES FROM THE GENITOURINARY TRACT AND NEISSERIA-MENINGITIDIS

Rosamicin in vitro activity was compared with that of erythromycin and other antimicrobics against clinical urinary tract isolates, genital pathogens and Neisseria meningitidis. Although the susceptibility or resistance to the two macrolides almost perfectly paralleled each other, the activity of rosamicin was greater than that of erythromycin against most species tested, including the Enterobacteriaceae, non-fermentative Gram-negative bacilli, N. gonorrhoeae, N. meningitidis and Haemophilus vaginalis. No differences were seen between the two against Staphylococcus aureus, and erythromycin was superior against Streptococcus pyogenes. Significant increased activity of both drugs was observed against Gram-negative bacilli upon alkalinization of the media. The differences between bacteriostatic and bactericidal levels of rosamicin were greater against Gram-negative bacilli than Gram-positive cocci. The effect of inoculum size on increasing the minimal inhibitory concentrations (MIC) of rosamicin was significant above inocula of 105 bacteria/ml, but not below this level. Dilution-zone size regression analyses showed good correlation with rosamicin, yielding suggested susceptibility break-points of 1 μg/ml and 24 mm zone of inhibition with 15-μg discs. The erythromycin regression analysis data in this study suggest that the NCCLS zone size criteria may be too low. The exquisite susceptibility of genital pathogens to rosamicin plus the pharmacologic concentration of rosamicin in prostate, urethra and vaginal secretions renders this drug worthy of further investigation for possible use in genital tract infections. © 1979, JAPAN ANTIBIOTICS RESEARCH ASSOCIATION. All rights reserved.