Loss of penicillinase plasmids of Staphylococcus aureus after treatment with L-ascorbic acid

When 2 clinical strains of plasmid-mediated penicillin-resistant Staphylococcus aureus were treated with 1 mM sodium ascorbate for 6 h, 12-35% colony-forming units (CFU) irreversibly lost their ability to produce beta-lactamase. Agarose gel electrophoresis showed the disappearance of the plasmid bands from the lysates of colonies in which susceptibility to penicillin was induced by ascorbate treatment. Since ascorbic acid is a compound that is completely non-toxic, the possibility of its therapeutic use in the treatment of multiresistant bacterial diseases is proposed.

Alteration of bacterial DNA structure, gene expression, and plasmid encoded antibiotic resistance following exposure to enoxacin

Enoxacin inhibits growth of Escherichia coli K12 strains primarily by binding to the GyrA subunit of DNA gyrase (topoisomerase II); strains with gyrA, but not gyrB, mutations are less susceptible to the bactericidal effects of this agent. In sensitive strains, enoxacin completely inhibits DNA synthesis within 5 min and produces drug-gyrase-DNA complexes at numerous sites throughout the E. coli chromosome, as shown by the formation of linear DNA molecules after detergent treatment. Enoxacin, even at subminimal inhibitory concentrations, induces the bacterial SOS system, even in partially resistant gyrA strains. This drug also inhibits the induced expression of the lacZ encoded beta-galactosidase, regardless of whether this gene is located on the chromosome, a low copy number F' plasmid or high copy number Col E1 related plasmids. This inhibition of gene expression at subminimal inhibitory concentrations is likely to be a factor, in addition to gyrase inhibition, in the elimination of Col E1 plasmids and to the reduction in R plasmid conjugal transfer. Enoxacin enhances the bactericidal effects of kanamycin in both in-vitro and in-vivo models, suggesting that this quinolone may be effective in the treatment of infections due to strains resistant to antibacterials as a consequence of plasmid encoded resistance determinants.

Elimination of antibiotic-resistant plasmids by quinolone antibiotics

Of 7 plasmids we tested, the plasmid pORF2 was eliminated in vitro with the most efficiency by treatment with subinhibitory concentrations of novobiocin, coumermycin and 10 quinolones. It showed a cure rate of 43% by enoxacin; 12% by novobiocin, pefloxacin, ciprofloxacin and CI-934; 7% by coumermycin and ofloxacin; 9% by amifloxacin; and 4% by AM-833. On the other hand, pSC194, pBR322 and pMH612 were poorly cured in vitro by quinolones, except pSC194 which was cured 33% by enoxacin. R1, pP1603, and pUB110 were unaffected by the treatment. Mice were challenged intraperitoneally with a 2XLD50 of Escherichia coli carrying the ORF2 plasmid and were treated per os with 1 X or 1/2 X ED50 of either enoxacin or CI-934. The frequency of loss of ampicillin resistance determined 3 h after treatment shows curing effects of 92% for CI-934, 89% for enoxacin and 20% for untreated control.

Effect of subinhibitory concentrations of ampicillin on the R plasmid transfer in Escherichia coli

The effects of subinhibitory concentrations (sub-MICs) of ampicillin on R plasmid transfer in Escherichia coli were studied. Each donor strain culture was separated into two parts; one was mixed with a recipient strain culture for mating, the other was treated with the sub-MIC of ampicillin and then mixed with the recipient strain culture. In both cases the R plasmid transfer frequency was determined at 30, 60, 90 and 120 min of mating. Results showed that there exists a general decrease in the transfer frequencies under sub-MIC treatment (two plasmids did not transfer at all). The proportion of aggregates and the number of cells that compose them were not affected by the sub-MIC of ampicillin. Our study supports the idea that the changes induced in E. coli by sub-MICs of ampicillin did not affect the function of the surface structures responsible for aggregation but did affect the proteins implicated in DNA transfer, situated on the cell surface.

[The role of R plasmids in the resistance of bacteria in air]

The study of Escherichia coli J 53, used as a model, has revealed that some R plasmids isolated from Serratia marcescens and Klebsiella pneumoniae, found to be the cause of the outbreak of hospital infection, ensure, besides multiple drug resistance, also their viability in the air.

[Fecal coliforms in sewage waters. I. Resistance to antibiotics, heavy metals and colicinogeny]

Qualitative bacteriological analysis was carried out in two sewage treatment plants in the city of Rio de Janeiro during the period 1984-1985. Specific points of the plants were selected for the collection of affluent and effluent samples. The study involved the isolation and the identification of 540 cultures of Escherichia coli that were analyzed for their resistance to eight antibiotics (sulfadiazine, streptomycin, tetracycline, chloramphenicol, kanamycin, ampicillin, nalidixic acid and gentamycin), and three heavy metals (copper sulphate, mercuric chloride and zinc sulphate) as well as colicinogeny. About 95% of the isolated cultures from the effluents had genetic markers while the samples originated from the affluents showed 70%.

Curing of plasmid pE194 with novobiocin and coumermycin A1 in Bacillus subtilis and Staphylococcus aureus

Plasmid pE194 determining macrolide-lincosamid-streptogramin B resistance could be eliminated with novobiocin and coumermycin A1 in Bacillus subtilis and Staphylococcus aureus. In both organisms the curing effect depended on the temperature. In the case of Staphylococcus aureus it increased very much at high temperatures, while in the case of Bacillus subtilis only a moderate increase could be observed. The curing activity of coumermycin was substantially weaker than that of novobiocin in both bacteria. This difference decreased at higher temperatures only in Staphylococcus aureus. In Bacillus subtilis the curing with novobiocin could be antagonized with coumermycin in accordance with the growth experiments reported previously.

[Comparative antibiotic sensitivity of NAG vibrios]

Six hundred and forty eight NAG vibrio strains isolated at various periods from patients and carriers and from environmental objects such as surface of water reservoirs and sewage were studied with respect to their sensitivity to 14 antibiotics with the method of serial dilutions in solid media. Irrespective of the isolation place, object and time, the NAG vibrios were highly resistant to penicillins and polymyxin M. At the same time they were highly sensitive to gentamicin (MIC 1-2 micrograms/ml), levomycetin (MIC 0.5-1 micrograms/ml) and tetracyclines (MIC 0.25-1 micrograms/ml). Study of the recipient capacity of NAG vibrios with respect to R plasmids showed that they could be recipients of exogenic R plasmids of various incompatibility groups.

[Plasmid characteristics of Salmonella strains of various origins]

Salmonella antibiotic-resistant strains, isolated from patients with hospital infections and from various environmental objects, showed lower virulence than antibiotic-sensitive strains in experiments on mice infected by intraperitoneal and enteral routes. Salmonella strains, sensitive to antimicrobial preparations, contained 1-2 plasmids, while those with multiple drug resistance contained 3-10 plasmids varying in their molecular weight. All these strains, with the exception of one laboratory strain, carried a plasmid with a molecular weight of about 60 Md. A decrease in the virulence of Salmonella strains, carrying R-plasmid, with respect to mice, their natural host, in experimental infection by the above-mentioned routes was probably unrelated to the loss of this plasmid. 80% of Salmonella strains with multiple resistance to antibiotics yielded positive results in the keratoconjunctival and conjunctival tests as compared with 42% of sensitive strains. These data suggest that Salmonella strains, carrying R-plasmid, retained pronounced capacity for local colonization.

[Sensitivity to chlorine-containing disinfectants of Salmonella typhi strains with transmissible drug resistance]

Sensitivity of 201 S. typhi strains to antibiotics and chlorine containing disinfectants was studied. The strains were isolated in the regions of the Left Bank Ukraine. Among the typhoid cultures the proportion of R+ strains was on the whole equal to 29.3 per cent. Chloramine resistant strains amounted to 21.8 per cent. Among chloramine resistant strains the number of the cultures carrying R plasmids was 3 times higher than that of the strains sensitive to disinfectant. Simultaneous transfer of the R plasmid and chloramine resistance to the recipient strain suggested that resistance of the S. typhi strains to chloramine was of plasmid nature.

Trimethoprim resistance in commensal bacteria isolated from farm animals

Trimethoprim resistance was examined in faecal bacteria obtained from chickens, sheep, cattle and pigs. The incidence of trimethoprim resistance in porcine strains was 17% (157/922) and, whereas 15.8% (146/922) of these bacteria were highly resistant, only 4% (37/922) of the isolates possessed trimethoprim resistance plasmids. Highly resistant porcine strains were obtained from 44% of the pig farms (41/93) but transferable trimethoprim resistance was found in isolates from 11% (10/93) of the farms. There was an association between the carriage of trimethoprim resistance plasmids and certain farms. Most of the resistance plasmids were not identical with those found in human clinical bacteria but one porcine plasmid was the same as the most ubiquitous trimethoprim resistance plasmid in Edinburgh.

Pyrimethamine-sulfadoxine still effective against Plasmodium falciparum in Jayapura, Irian Jaya: RI-type resistance in 2 of 18 patients

The sensitivity of Plasmodium falciparum infections to pyrimethamine-sulfadoxine was studied in 18 Indonesian patients in Jayapura, Irian Jaya. In 16 of the 18 patients parasitaemia was cleared by day 6 and the patients remained without parasitaemia through day 28. Two of the 18 patients had late recrudescences consistent with RI-type resistance; one each on days 14 and 21. Pyrimethamine-sulfadoxine is still an effective antimalarial for most patients with falciparum malaria in Jayapura.

Effects of the antimutagen cinnamaldehyde on reversion and survival of selected Salmonella tester strains

The antimutagenic activity of trans-cinnamaldehyde (C6H5CH = CHCHO) on chemically induced mutagenesis has been shown in E. coli. Using the Ames Salmonella typhimurium tester strains TA1535 (hisG46 uvrB rfa) and TA100 (TA1535/pKM101), the effects of cinnamaldehyde on spontaneous reversions and reversions induced by 4-nitroquinoline-N-oxide(4NQO) and ethyl methanesulfonate (EMS) have been examined. To observe the effect of cinnamaldehyde in the absence of functional muc genes, a third strain, TA1535/pGW201 (pKM101 muc140: :Tn5) was included in the testing. Modifications of the standard Ames test procedures and direct-plating techniques were employed to study the "antimutagenic" response exerted by cinnamaldehyde. In all strains tested, concentrations of cinnamaldehyde up to 25 micrograms/ml slightly decreased the number of spontaneous reversions and induced reversions were more markedly reduced. The decreases in the numbers of 4NQO-induced revertants were greater than those decreases which occurred for EMS-induced reversions. There was no effect on viability in 1% (v/v) nutrient broth supplemented minimal medium containing 5-25 micrograms/ml of cinnamaldehyde. Cinnamaldehyde did not display any mucAB dependent or independent specificity against the mutagens used. On minimal medium supplemented with histidine and biotin, concentrations of cinnamaldehyde above 10 micrograms/ml were lethal for the strains tested. When the test medium was supplemented with 1-5% (v/v) liquid nutrient broth, viability was not affected at concentrations up to 25 micrograms/ml. For both TA100 and TA1535 the presence of 20 micrograms/ml of cinnamaldehyde in 1% (v/v) liquid nutrient broth-supplemented minimal glucose broth extended the lag phase for 2-4 h with no effect on survival. Depending on the test procedure employed, decreases in numbers of revertants may reflect lethality rather than antimutagenesis. When used to test for antimutagenesis rather than mutagenesis, modifications of the standard Ames test procedure may mimic an antimutagenic response due to a decrease in the total number of revertants seen even though enough cells survive to produce a background lawn.

Bacterial resistance and single-dose therapy of urinary tract infections

In this work, we discuss the effects that the administration of both single and multiple doses of antibiotics are likely to have on antibiotic sensitivity of both the bacteria responsible for the infection and the human normal flora. It is concluded that a single-dose therapy when used under the appropriate conditions has the advantage of having less chances to select resistant strains in the normal bacterial flora.

[Resistance to antibiotics and sulfanilamides of enterobacteria isolated in Ulyanovsk Province]

The data on resistance to 10 antibiotics and sulfanilamides of 178 coprocultures of Enterobacteriaceae isolated from patients in the Ulyanovsk Region are presented. It is indicated that 93.8 per cent of the isolates were resistant to the antibiotics. The majority of the cultures were resistant to ampicillin, tetracycline and streptomycin and sensitive to gentamicin, polymyxin, trimetoprim, rifampicin and nalidixic acid. 43 combinations of the antibiotic resistance types were revealed. 92.7 per cent of the isolates were resistant to the sulfanilamides.

Effect of curing R-plasmids in Salmonella species on their serum sensitivity

Thirteen salmonella strains of clinical isolates were tested for serum sensitivity, antibiotic resistance, colicin production and plasmid existence. Nine serum resistant strains were smooth and harboring plasmids of different sizes. Transfer of R-plasmids by conjugation from three strains to E. coli K12 conferred slight decrease in serum sensitivity. Curing the nine resistant strains with ethidium bromide or acriflavine affected their serum resistance, plasmid content and cell surface. Rough isolate of S. johanesberg became serum sensitive after curing the R-factors. The suggested mechanisms involved in the change in serum sensitivity after curing are discussed.

[Relationship of the pKMR plasmids detected in Shigella circulating in the Krasnodar Territory to incompatibility groups]

Shigella strains showed that in 43.9 per cent of the strains this feature was controlled by conjugative R plasmids. On the whole these were the plasmids allotting the bacterial cell with resistance simultaneously to SmTcCm (37.1 per cent) and SmTc (17.1 per cent). The plasmids with other phenotypes were less frequent: SmApCm, 11.4 per cent, TcApCm, 8.6 per cent; SmTcApCm, 8.6 per cent; Tc, 8.6 per cent; Sm, 2.9 per cent; Cm, 2.9 per cent and TcCm, 2.9 per cent. The incompatibility groups of 19 plasmids were determined: Inc I zeta, 28.6 per cent; Inc zeta I and Inc B, 14.2 per cent; Inc FII, 8.6 per cent and Inc I alpha, 2.9 per cent.

Effect of EDTA-tris on an Escherichia coli isolate containing R plasmids

Solutions of ethylenediaminetetraacetate (EDTA)-tris combined with antibiotics have been shown to be effective in treating selected cases of persistent bacterial infections. Basic techniques in microbial genetics, including mating frequencies, chemical elimination of R plasmids, isolation of plasmid DNA and agarose gel electrophoresis, were used to determine if EDTA-tris has a curing effect on an R plasmid as part of its clinical action. Results of this study indicated that EDTA-tris by itself eliminated an antibiotic resistance marker from a clinical isolate of Escherichia coli and when combined with another chemical curing agent altered the isolate's mating frequency.