Comparative studies on in vitro activities of kasugamycin and clinically-used aminoglycoside antibiotics

Kasugamycin, a unique aminoglycoside antibiotic, has been used for many years solely for crop protections. In general, aminoglycoside antibiotics possess broad and strong inhibitory activity against both Gram-positive and -negative bacteria, however, kasugamycin merely exhibits limited activity against phytopathogenic microbes such as Pyricularia oryzae and certain strains of pseudomonads. Recently, in human and animal chemotherapy, it has been seriously concerned about the emergence of multiply resistant bacteria by consumption of a large amount of antibiotics not only for therapy but also for growth-promotion of farm animals. It was believed that kasugamycin, the agricultural antibiotic, does not undergo any cross-resistance with other clinically important aminoglycoside antibiotics because of its weak or almost no activity against common pathogenic microbes except for some phytopathogenic fungi and pseudomonads. However, no confirmative study on this fact has been published so far. In this study, we compared activity of kasugamycin with those of twelve clinically used aminoglycoside antibiotics against susceptible standard strains and well-characterized aminoglycoside-resistant strains as well as clinically isolated strains, in order to show the least potential of kasugamycin to create cross-resistant human pathogens against clinically important aminoglycoside antibiotics.