Tokumitsu Tanaka

Streptomycin and Spectinomycin Resistance Mediated by Plasmids

Resistance to tetracycline (Tc), chloramphenicol (Cm), streptomycin (Sm), and sulfanilamide (Sa) was surveyed in clinical isolates of Escherichia coli and Shigella strains. Among the Sm Sa-resistant strains, the frequency of nonconjugative r (Sm Sa) plasmids was much higher than that of conjugative R plasmids encoding double resistance. The biochemical mechanism of Sm resistance mediated by the conjugative plasmids R(Tc Cm Sm Sa) and R(Cm Sm Sa) and about half the numbers of conjugative R(Tc Sm Sa) and R(Sm Sa) plasmids tested were found to be due to adenylylation of the drug. The remaining conjugative R(Tc Sm Sa) and R(Sm Sa) plasmids and all nonconjugative (Sm Sa) plasmids tested inactivated Sm by phosphorylation.

Drug Resistance and Distribution of R Factors in Salmonella Strains

Drug resistance and the distribution of R factors in Salmonella strains were surveyed using 1,980 strains isolated in Japan from 1955 to 1973. Resistances were mostly restricted to sulfanilamide (SA), tetracycline (TC), and streptomycin (SM), and combinations thereof. The demonstrated frequency of strains resistant to chloramphenicol (CM) was very low as compared with that in Escherichia coli and Shigella strains. In relation to resistance to TC, CM, SM and SA, the frequency of isolation of single resistance was the highest, followed by triple, double, and quadruple resistance in that order. Low frequency of isolation of quadruple resistance was due to the low frequency of CM resistance in Salmonella strains and differed from the E. coli or Shigella group. R factors with single TC resistance was most common, followed by those with TC,SM,SA; SM,SA; TC,CM,SM,SA; and single (SM and SA) resistance, in that order. Kanamycin and ampicillin resistance was unusual and mostly transmissible.

Mutation of R Factors Capable of Specifying Hypersynthesis of Penicillinase

When strains harboring R factor and showing ampicillin (APC) resistance were inoculated on plates containing various concentrations of APC, mutants carrying various levels of APC resistance occurred at high frequencies. Increases in the level of APC resistance were due to a quantitative increase in the formation of penicillinase. By conjugation experiments and transduction analysis, the mutation was found to affect the gene (amp) governing APC resistance on the R factor. The R-factor mutants carrying high and stable APC resistance were conjugally transferred at the same frequency as their parent R factors, and the level of their resistance to drugs other than APC was not distinct from that conferred by their parents. Such R-factor mutants could easily be obtained from wild-type R factors carrying low APC resistance. The hypersynthesis of penicillinase by such R-factor mutants was considered to be due to the replication of the amp gene on the R factor at hyper-rates and the integration of multiple copies of the amp gene (amp-hyper) in the R-factor genome.

Different Patterns of Drug Resistance and R Plasmids between Indole-Positive and-Negative Strains of Klebsiella pneumoniae

Infections caused by gram-negative bacteria have significantly increased in recent years. One of the gram-negative bacteria, Klebsiella pneumoniae, is a major cause of disease. K. pneumoniae strains do not usually produce indole, although some strains are indole positive. According to Bergeys Manual (8th ed.) (1) and in many clinical laboratories, indole-positive strains are classified as K. pneumoniae. However, indole-positive strains are different from indole-negative strains in their pathogenicity, such as severe diarrhea (4), and antibiotic susceptibity (3). This paper presents a comparative study of drug resistance and R plasmids in K. pneumoniae in indole-positive and -negative strains. The 94 clinical isolates of K. pneumoniae used in this study were derived from various parts of Japan. Seventy-six isolates (81%) were indole-negative and 18

Conjugal transferability of multiple resistance in Shigella strains

Shigella strains isolated in Japan between 1971 and 1979 were surveyed for drug resistance and distribution of R plasmids. Of 2,510 strains, 89.3% were resistant to either one or various combinations of four drugs, tetracycline, chloramphenicol, streptomycin, and sulfanilamide. About 66% of the Shigella isolates were quadruply resistant. The frequency of isolation of R plasmids from quadruply resistant Shigella strains was the highest when compared with other strains resistant to various combinations of the four drugs. The conjugal transferability of 204 quadruply resistant strains isolated between 1977 and 1979 was tested by various mixed‐culture methods. Among the total strains examined, 70.6% carried transferable resistance when tested by the conventional broth culture method, 90.2% transferred their resistance when, in addition the replica‐plating methcd was used and 97.5% could transfer their resistance when the membrane filter method was also used. Although the remaining five strains could not transfer their resistance by any of the mixed culture methods, the drug resistance of four of the five strains was mobilized by the concomitant presence of F‐tet or T‐kan plasmid.

Rifampicin Resistant Strains of Bacteria from Tuberculosis Patients Treated with the Drug

According to the wide use of chemotherapeutic agents, drug resistant strains of bacteria appeared in many countries and have become one of the most important problems in practical medicine (6) . Chemotherapeutic agents that are used for the treatment of patients, cause appearance of resistant strains and select the resistant strains in parallel with the use of drug. Then, the practical use of chemotherapeutic agents and control of their use have become one of the urgent problems in practical medicine. Rifampicin has a wide antibacterial spectrum and is characteristic as antituberculosis drug. According to the fact that rifampicin (RFP) is used only for the treatment of tuberculosis patients in sanatoria for a long term, we investigated appearance of RFP-resistant strains of bacteria and their selection in RFP-treated patients. Tuberculosis patients at 5 sanatoria were randomly selected and they were all daily treated with oral administration of 400 mg of rifampicin (RFP) . Heart infusion agar (HIA, Eiken Chemical Co., Tokyo) was used for the isolation of Escherichia coli strains from the faeces. HIA-Lac agar consisted of 1,000 ml of HIA, 15 g of lactose and 40 ml of 0.2% bromthymol blue. EMB-Lac agar consisted of 1,000 ml of EMB agar (Difco) and 15 g of lactose. HIA-salt medium was used for isolation of Staphylococcus aureus from sputa and consisted of 1,000 ml of HIA and 75 g of sodium chloride. Peptone water was used for liquid culture and consisted of 1,000 ml of distilled water, 5 g of NaCl and 10 g of peptone. E. coli strains were isolated from the faeces. A small volume of saline solution was added to faeces. The mixed material was streaked on HIA-Lac plates and incubated at 37 C. After 20 hr of incubation, 100-150 lactose-fermenting colonies were randomly picked and streaked on EMB-Lac agar plates. The biological and biochemical properties of these colonies were examined and E. coli strains were used for further studies. S. aureus strains were isolated from the sputa. Sputum was suspended in a small volume of saline solution and the mixed material was streaked on HIA-salt plates. The biological and biochemical properties of these colonies were examined and S. aureus strains were used for further studies. The MIC (minimum inhibitory concentration) of RFP was examined using 100 E. coli and 100 S. aureus strains. They were all of clinical origin and the stock