Search

Susceptibility of 150 Corynebacterium isolates (91 strains of C.pseudodiphtheriticum and 59 strains of the ANF group corynebacteria) to 21 antibacterial drugs was determined by the method of serial dilutions in a solid medium. It was shown that the MIC of the drugs for the diphtheroids was within the ranges of < 0.015 to > 32.0 micrograms/ml. 66 per cent of the Corynebacterium strains circulating in St. Petersburg was resistant at least to 1 antibacterial drug. The Corynebacterium isolates with moderate resistance to erythromycin and lincomycin (57.3 per cent) and resistant to trimethoprime (16.7 per cent) were the most frequent. 8.0 per cent of the diphtheroids was resistant at least to 4 antibacterial drugs. No significant difference in the susceptibility of the ANF group corynebacteria and C.pseudodiphtheriticum to the drugs was observed. Gentamicin, rifampicin, tetracycline and doxycycline showed high activity against the corynebacteria at present circulating in St. Petersburg. When antibacterial therapy of the infection due to corynebacteria fails it is necessary to estimate antibioticograms of Corynebacterium pure cultures.

The transducing ability of 17 Pseudomonas pseudomallei bacteriophages has been studied. Five of them were found to be capable of transducing the transposon Tn7 markers TpR, SmR into the strain Pseudomonas mallei C-5. The transduced bacterial recipients became lysogenic and acquired resistance to trimethoprim and streptomycin. Transduction of transposon Tn7 has been confirmed by DNA-DNA hybridization.

In vitro activity of 13 antibiotics and drug preparations as well as some of their combinations was studied with respect to Brucella melitensis. It was shown that the strains of B. melitensis were sensitive to sisomicin, amikacin, gentamicin, cefotaxime, rifaprim +, nitroxoline and trimethoprim. Variations in the doxycycline sensitivity depending on the strain were observed. The strains of B. melitensis were resistant to cephalexin, phosphomycin, chinoxydine, dioxydine and oxolinic acid. Combinations of sisomicin and trimethoprim at a ratio of 1:10 and sisomicin and nitroxoline at a ratio of 1:2 had a summation effect.

Strains of all Y. pestis varieties except for those isolated from voles are highly sensitive to trimethoprim when grown on cultivation media, even when thymidine is added to the medium. The ability to grow on thymidine-containing rich media after trimethoprim addition is a property differentiating Y. pestis variety isolated from voles from the other varieties. These data were confirmed by testing 360 Y. pestis strains obtained from collections of several antiplague institutes and stations of the USSR.

We demonstrate the possibility of using the T4 phage frd gene as an insertion inactivation marker within pBR322, in plasmids with changing copy number and expression of foreign genes under control. The structural part of the frd genes contains unique recognition sites for EcoRI and SalI endonucleases. Transformants with recombinant plasmids carrying the frd gene grow on media with up to 500 mkg/ml trimethoprim, whatever the gene dosage.

It was shown that 9 strains of P. mallei were sensitive to sulfanilamides and their combinations with trimethoprim: sulfamonomethoxine + trimethoprim (2.5:1), sulfamethoxazole + trimethoprim (5:1) and sulfazin + trimethoprim (2.5:1 and 5:1). In regard to multiple lowering of the minimum bactericidal concentration of both drugs the combinations of sulfazin with trimethoprim (5:1 or 2.5:1) and sulfamethoxazole with trimethoprim (5:1) or biseptol proved to be the most active. The activity of the sulfamonomethoxine combination with trimethoprim (sulfate) was lower.

The effect of exogenic addition of purines and pyrimidines on trimethoprim sensitivity was studied in 134 vaccinal and virulent strains of the plague causative agent isolated at various periods in 12 natural plague foci. 74 strains proved to be sensitive to low concentrations of trimethoprim in the cultivation media irrespective of the presence or absence of thymine or thymidine in them. In this respect the strains differed from many other bacterial species which in the presence of thymidine or thymine were resistant to high concentrations of trimethoprim. 60 natural arginine deficient strains of the plague causative agent from Transcaucasia and Mongolia showed high levels of resistance to trimethoprim on media with thymine or thymidine. The possible mechanism of the plague microbe sensitivity to trimethoprim in the presence of thymine or thymidine is discussed with an account of the literature and original data.

One hundred and eighty-six clinical strains of Enterobacteriaceae isolated in the Krasnodar region and Krasnodar in 1982 from patients with acute intestinal diseases were studied. 137 strains of Shigella were investigated in detail. It was shown that S. flexneri, S. sonnei, S. boydii and S. dysenteriae accounted for 77, 15, 5 and 2 per cent, respectively. 78.1 per cent of the wild Shigella strains were resistant to antibiotics and in 43.9 per cent of the strains this property was controlled by conjugative R plasmids. 11 variants of the antibiotic resistance spectra were revealed. However, strains of SmTcApCm, SmTc and SmTcAp phenotypes were the most frequent. Among the resistant strains 80.3 per cent were resistant to tetracycline, 75.7 per cent to streptomycin, 50.4 per cent to ampicillin, 31.7 per cent to chloramphenicol, 1.8 per cent to trimethoprim, and 0.9 per cent to kanamycin. The investigation showed that the strains isolated in one region usually had similar phenotypes of antibiotic resistance. The frequency of the plasmid transfer varied from 10(-1) to 10(-7). However, the majority of the plasmids were transferred at a frequency of 10(-4)-10(-5). Only one of the investigated plasmids had a capacity for transmitting fd phage sensitivity to the host cells. 33 plasmids belong to the fi+ type and the others belong to the fi- type. The majority of the plasmids have molecular weights of 46 to 50 mD.