In the previous papers, mikamycin was reported to be apparently a single antibiotic, and the biological activities were studied with a crude material^1–3). However improvements of the cultural conditions and further chemical studies revealed that mikamycin is composed of a few biologically active substances. A couple of them were isolated and purified by means of repeated chromatography, continuous extraction with ether, and recrystalization. The main component was designated mikamycin A and the second one mikamycin B¹⁴⁾ These two antibiotics, produced by a single organism, were observed to exhibit a marked synergistic actions both in vitro and in vivo. Mikamycin is closely related to, if not identical with, PA 114^4,5), streptogramin^6,7), staphylomycin^8–11) or E 129^12,13). In the present publication some of biological studies of these two constituents of mikamycin will be reported, with particular reference to the synergism between them.

A number of antibiotics have been reported to have the antiamebic effect. Among them are anisomycin, chlortetracycline, oxytetracycline, erythromycin, cycloheximide, and prodigiosin, most of which have been tested in the treatment of amebiasis and proved to be more or less effective. Several other antibiotics such as fumagillin, trichomycin, eurocidin and candimycin which are effective for eumycetes or malignant tumors have been also found to have antiamebic activities.

Most of the antibiotics cited above, however, have the antibacterial effects. The growth of Entamoeba histolytica in culture media is much influenced by the associated bacterial flora. It has been demonstrated by many investigators that some kinds of bacteria well support the growth of amebae while others do not. The ameba cannot grow in culture media without the accompanying growth of some symbiotic bacterial species. Therefore, it is very difficult to test in vitro the antiamebic effect of some antibiotics which have the bacteriostatic activities. They may stop the bacterial growth and only secondarily inhibit the growth of amebae.

In the present study, the antibiotics which do not have antibacterial effect were selected for screening test. All of the culture filtrates of streptomycetes tested were prepared in the Laboratory of Antibiotics in our Institute under the direction of Dr. Hata and were sent to our Parasitology Laboratory. By the screening tests of the culture filtrates of more than 300 strains of streptomycetes, a number of filtrates were found to have the amebicidal activities in vitro. Extract from one of these effective filtrates, which was named Protomycin was studied extensively on its amebicidal effects in vitro and in vivo. Results of the experimental works on this substance are described in this report.

The cross-resistance is one of the most important problems in the chemotherapy of infectious diseases and some important suggestions for chemotherapy have been given by cross-resistance studies. A new antibiotic kanamycin sound by Umezawa, et al ., will be usually utilized for tuberculous patients who have been already treated by several courses of chemotherapy with other drugs, especially with two or three drugs of streptomycin, isoniazid and PAS, and, in some cases, also of viomycin, cycloserine, and 4-acetylaminobenzaldehyde-thiosemicarbazone. Subsequently, the problem of cross-resistance and of selection of chemotherapeutic drugs that may be used in combination with kanamycin must be very important for such patients.

Cross-resistance studies have been usually made by utilizing not any constant size of inoculum and their meanings have not been accurately interpreted. According to our opinions, however, it appears that cross-resistance may occur from two origins; the one is a decreased susceptibility to a drug of “individual mutants” resistant to an another drug and the other is an increased mutation rate to a drug resistance in a “mutant population” resistant to an another drug. Kanamycin susceptibility of various drug-resistant mutants have been studied in the foregoing paper¹⁾ and, following the study, mutation frequency to kanamycin resistance in various drug-resistant strains will be studied in the present paper.

For the chemotherapy of tuberculosis with kanamycin, it appears most important to delay the emergence of kanamycin resistance in Mycobacterium tuberculosis and, for the purpose, it appears at present to be most useful to utilize kanamycin with other known antituberculous drugs in view of our knowledges concerning with this problem. It is the purpose of the present paper to concern with the problem what a kind of combination of antituberculous drugs with kanamycin is most effective for delaying the emergence of kanamycin resistance in M. tuberculosis.

Cross resistance appears to be one of the most interesting problems in the points of bacterial genetics as well as of the chemotherapy of tuberculosis. The authors have once concerned with the problem of cross resistance with reference to kanamycin resistance in Mycobacterium tuberculosis and reported that viomycin-resistant mutants of the organism are less sensitive to kanamycin and mutation frequency to kanamycin resistance in viomycin-resistant mutants is higher than that in sensitive nonmutants as well as mutants resistant to various antituberculous drugs^1),2). Following the previous studies, the present paper will concern with the remaining problem of cross resistance, that is, sensitivity of kanamycin-resistant mutants to other antituberculous drugs and mutation frequencies to other antituberculous drugs in kanamycin-resistant mutants of M. tuberculosis.

Clinical trials of kanamycin for treatment of pulmonary tuberculosis were first made by Donomae, et al.¹⁾ In order to evaluate the effectiveness of this new drug, these authors examined the effect on 79 fresh cases who had not received any chemotherapy and on 31 old cases who had received chemotherapy using streptomycin, PAS and INH. According to these authors, combination of kanamycin and PAS is equally effective as that of streptomycin and PAS.

Number of cases resistant to most powerful chemotherapeutic agents, streptomycin and INH, are increasing and they are often also resistant to PAS. The present authors often encounter the cases who show formation of new lesions, or spreading or deterioration of old lesions inspite of continuation of chemotherapy using these drugs. In these cases, tubercle bacilli isolated from the sputa are usually resistant to all these drugs. As reported by Yanagisawa, et al.²⁾, tubercle bacilli resistant to streptomycin are sensitive to kanamycin and there is no cross resistance relation between kanamycin and other drugs effective to tuberculosis. Kanamycin is one of most effective drugs to tuberculosis, and, therefore, at present it is most worthy for treatment of the cases who do not respond to other powerful drugs such as streptomycin and INH and who show exacerbation or spreading or deterioration of old lesions. To evaluate effectiveness of kanamycin on such cases is the purpose of the present study. Such 10 cases were selected and have been treated by kanamycin for a year. This paper describes results of observations on these cases during the treatment.