Mercuric ion-resistance operons of plasmid R100 and transposon Tn501: the beginning of the operon including the regulatory region and the first two structural genes

The mercuric ion-resistance operons of plasmid R100 (originally from Shigella) and transposon Tn501 (originally from a plasmid isolated in Pseudomonas) have been compared by DNA sequence analysis. The sequences for the first 1340 base pairs of Tn501 are given with the best alignment with the comparable 1319 base pairs of R100. The homology between the two sequences starts at base 58 after the end of the insertion sequence IS-1 of R100. The sequences include the transcriptional regulatory region, and the homology is particularly strong in regions just upstream from potential transcriptional initiation sites. The trans-acting regulatory gene merR consists of 180 base pairs in both cases and codes for a highly basic polypeptide of 60 amino acids, which is also rich in serine. The Tn501 and R100 merR genes differ in 25 of the 180 base positions, and the resulting polypeptides differ in seven amino acids. The regulatory region before the major transcription initiation site contains potential -35 and -10 sequences and dyad symmetrical sequences, which may be the merR binding sites for transcriptional regulation. The first structural gene, merT, encodes a highly hydrophobic polypeptide of 116 amino acids. The R100 and Tn501 merT genes differ in 17% of their positions, leading to 14 (12%) amino acid changes. This region had previously been shown to encode a protein governing membrane transport of mercuric ions. The second structural gene, merC, would give a 91 amino acid polypeptide with a hydrophobic amino-terminal segment. The Tn501 and R100 merC genes differ at 37 base positions, leading to 10 amino acid changes.

[Effect of plasmids for multiple antibiotic resistance on the change in Salmonella typhimurium phagovar]

The data on the influence of acquired plasmid resistance to antibiotics on S. typhimurium phagovar. Plasmid R was transferred from S. typhimurium strain, isolated from the focus of hospital salmonellosis and resistant to the lytic action of phages, to Escherichia coli K12 and then to antibiotic-sensitive S. typhimurium strains of different phagovars, isolated from patients with alimentary toxicoinfections. The influence of plasmid R on the phagovar of recipient strains, most pronounced in strains of phagovar I, was revealed. The transconjugates of this phagovar considerably changed sensitivity to phages and in some cases acquired resistance to the lytic action of typing phages, thus becoming identical in this feature to the donor of the plasmid.

Plasmid-mediated antibiotic resistance and colicinogeny among Salmonellae in Rio de Janeiro, Brazil

A set of 25 multiple drug-resistant strains selected from Salmonellae isolated from sewage in Rio de Janeiro contained S. typhimurium (60%) and S. agona (20%) as the most frequent serotypes. There was resistance to ampicillin (Ap), 92%; chloramphenicol (Cm), 76%; gentamicin (Gm), 84%; kanamycin (Km), 84%; streptomycin (Sm), 96%; tetracycline (Tc), 76%; trimethoprim-sulfamethoxazole (SuTp), 84% and nalidixic acid (Na), 52%. The most frequent resistance patterns observed were Ap Cm Gm Km Sm Tc SuTp Na and Ap Cm Gm Km Sm Tc SuTp. Two strains, bearing the streptomycin, tetracycline double-resistance pattern were colicinogenic, producing type Ib colicin. The col+ character was cotransferable with the double-resistance; all these markers were associated with the presence of a single 60 Mdal plasmid.

[Analysis of the etiological structure and dynamics of antibiotic resistance in the causative agents of suppurative inflammatory diseases in the patients at a large general hospital]

The structure of the causative agents isolated from patients with pyoinflammatory infections in 1980-1983 was analysed. It was shown that the surgical and urological infections were mainly caused by gram-negative bacteria. The other pyoinflammatory infections were mainly due to gram-positive cocci. A relatively high frequency of the strains of gram-negative bacteria, especially among Pseudomonas spp. and Enterobacter spp., resistant to aminoglycoside antibiotics, such as gentamicin, sisomycin and tobramycin with preserved sensitivity to amikacin and netilmicin in the majority of the strains was shown. Among the beta-lactam antibiotics cephotaxim and cephalotin were most active against gram-negative bacteria and staphylococci, respectively. The majority of the antibiotic resistant strains of gram-negative bacteria had analogous structures and levels of resistance to 7-12 antibiotics which might indicate the occurrence of 1-2 resistance plasmids among the clinical strains.

Changing patterns of hospital infections: implications for therapy. Changing mechanisms of bacterial resistance

During the past decade there has been a marked increase in resistance of bacteria to antimicrobial agents. Microorganisms have developed the ability to make altered receptors for antimicrobial agents, have prevented agents from reaching their receptors within the bacterial cell, now have enzymes to destroy antibiotics, and have resistant metabolic pathways. Altered penicillin receptors, penicillin-binding proteins, have been found in Streptococcus pneumoniae, Streptococcus faecalis, Staphylococcus aureus, Neisseria gonorrhoeae, Clostridium, and Pseudomonas aeruginosa. Resistance based on decreased entry of drugs has been found for penicillins, cephalosporins, aminoglycosides, and tetracyclines in the Enterobacteriaceae and Pseudomonas aeruginosa. Beta-lactamase resistance has increased significantly being encountered in Neisseria, Haemophilus, Enterobacteriaceae, and Pseudomonas species. Chromosomal inducible beta-lactamases, which function as cephalosporinases, have been a particular problem in Enterobacter and Citrobacter species, and organisms resistant to the third-generation cephalosporins have been isolated from patients. It is clear that beta-lactamases and changes in cell wall permeability will play an extremely important role in the future of the new penicillins and cephalosporins.

Deletions in Klebsiella pneumoniae R plasmids induced by growth in the presence of acridine orange at high temperature

The generation in vivo of plasmids deleted at specific sites in strains of Klebsiella pneumoniae containing R plasmids, by treatment with high concentrations of acridine orange (1.2 mg/ml) at 42 degrees C are reported. These deletions seem to be site specific because loss of specific restriction fragments after digestion with restriction enzymes was demonstrated.

[Conjugative R-plasmid resistance of Salmonella]

A total of 4801 Salmonella strains of 67 serovars isolated from various sources in 1968-1982 were studied for their sensitivity to 12 drugs. The Salmonella strains of groups A, B, C, D and E amounted to 0.8, 84.6, 6.4, 5.8 and 2.0 per cent, respectively. The Salmonella strains of the other groups amounted to 0.4 per cent. During the 5-year periods, the number of the antibiotic resistant Salmonella strains increased from 57.7 to 93.4 per cent. The conjugative drug resistance was detected in 16 out of the 67 serovars. The Salmonella strains usually resistant to 4-10 drugs were the donors of this conjugative drug resistance. The strains of S. typhimurium responsible for the hospital infections were characterized by the highest levels of the antibiotic polyresistance and the greatest variety of the conjugative R plasmids. The structure of the multiple and conjugative drug resistance of the organisms causing salmonellosis was more frequently defined by the conjugative plasmids of the antibiotic resistance of the S. typhimurium serovar. The Salmonella R plasmids determined various levels of the antibiotic resistance. The highest resistance levels were observed to benzylpenicillin, chloramphenicol and erythromycin and the lowest resistance levels to tetracycline.

[Resistance to antibiotics of Vibrio cholerae and its possible prognostic significance]

Control of antibiotic resistance of Vibrio cholerae in various areas of the world revealed the characteristic features of the situation and tendencies of antibiotic resistance development in this microbial group. It was shown that though the main part of the El Tor vibrio of the 7th cholera pandemia period was highly sensitive to antibiotics, separate strains with stable plasmid antibiotic resistance were isolated. By the end of the 70s the spread of resistant cholera germs was registered. The antibiotic resistance was due to R factor of the incompatibility group C widely spread among microorganisms of the other groups.

Transferable antibiotic resistance in Escherichia coli isolated from urinary-tract infections: hospital v. community patients

In order to study the prevalence of plasmid-mediated antibiotic resistance in E. coli causing urinary-tract infections (UTI) specimens of urine were obtained, from a total of 125 hospital and community patients, and examined bacteriologically and analysed. Thirty-nine (80%) of forty-nine, and thirty-three (65%) of fifty-one hospital and community patients respectively were infected by multiple resistant E. coli. Of these multiple-resistant strains more than three-quarters carried transferable R-plasmids. Antibiotic resistance was transferred en bloc or singly to known sensitive recipient mainly by conjugation by a technique that ensured cell-to-cell contact. Resistance markers in both the donor and the transcipient strains were eliminated by treatment with aminoacridine dyes and ethidium bromide. The result emphasises the need for bacteriological diagnosis of UTI and sensitivity testing prior to antibiotic therapy.

Inhibition of bacterial plasmid replication by stereoselective binding by tricyclic psychopharmacons

Several dibenzazepines, thioxanthene, and phenothiazine stereoisomers were studied for their abilities to inhibit plasmid replication, intracellular transfer of R-plasmid, bacterial ATP-ase, and mouse serum cholinesterase isoenzyme. Partially saturated derivative of desipramine inhibited plasmid replication and transfer, but the fully saturated derivative was inactive. The inhibition of plasmid curing and transfer patterns did not correlate with the inhibition of ATP-ase and cholinesterase. Trans-clopenthixol was more effective in plasmid elimination than the cis-isomer. On the other hand, the cis-isomer inhibited ATP-ase and cholinesterase more than the trans-isomer. The levo- and dextro-methoxytrimeprazine also inhibited plasmid replication and enzyme activity. We believe that the tricyclic configuration of the drugs tested for stereospecific binding to bacterial receptors is more important than its side chain orientation. We believe that there is a similarity between bacterial receptor sites and neural receptor sites. Therefore, this model may be useful in the study of neuropharmacological agents as potential antibacterial agents.

[Role of multiple drug resistance in the biology of pathogenic and opportunistic bacteria]

The significance of cloning of pathogenic and opportunistic multiple drug-resistant bacteria is analysed from the present viewpoints of medicine and veterinary. Distribution of drug-resistant strains in men, animals and environment and occurrence of new type hospital and nosocomial infections are described. The controversial points of the antibiotics role in the formation of multiple drug resistance plasmids, occurrence of hospital resistant strains and the part of R plasmids in changing the biological characteristics of pathogenic and opportunistic bacteria are analysed. It is shown in relation to Salmonella that formation of definite clones of multiple drug resistant bacteria results in significant changing of epidemiology of the diseases caused by these organisms. The data on the identity of the biological and genetic characteristics of the Salmonella strains of some phage vars isolated in hospitals and outside the hospitals, as well as the data on the effect of R plasmids on the Salmonella virulence are presented. The thesis of a higher infective capacity of the strains with multiple drug resistance associated with their increased survival levels and a higher colonization ability is accentuated. The danger of occurrence of new type causative agents on formation of complex plasmids with additional determinants connected with the bacteria pathogenicity is discussed. The tasks of the further investigation of these aspects are formulated and the possible means for the control of this phenomenon are presented.

Tetracycline resistance in Mycoplasma hominis

The composition of the cytoplasmic membrane of a clinical isolate of Mycoplasma hominis that was resistant to tetracycline (minimal inhibitory concentration, 30 micrograms/ml) was compared with that of a susceptible strain (minimal inhibitory concentration, less than 1 microgram/ml). Neither differences in passive permeability of the lipid portion of the membrane to the drug nor modulation of active transport by membrane lipids explained the resistance to tetracycline. Polyacrylamide gel electrophoresis revealed several differences between the membrane protein composition of the two strains. One 25,000-dalton protein was prominent in the membrane of the resistant strain but almost nonexistent in that of the sensitive strain. Therefore, the resistance may have been correlated with differences in protein composition. Preliminary evidence suggested that the resistance trait was plasmid-mediated.

[Effect of conjugative R plasmids on the virulence of antibiotic-sensitive Salmonella strains and their streptomycin-resistant mutants]

The pathogenicity level of antibiotic sensitive and streptomycin resistant strains of S. typhimurium, S. paratyphi B and S. kottbus changed under the effect of identical R plasmids more frequently in contrary directions. The conjugative plasmids of antibiotic resistance widened the ranges of the virulence changes in the Salmonella serovars for albino mice. It was found that 7 out of 8 plasmids studied significantly decreased and increased the virulence of the antibiotic sensitive Salmonella strains. As a rule, R plasmids of various origin decreased the virulence of all the tested streptomycin chromosome resistant causative agents of salmonellosis.

[Localization of Kpnl restriction sites in the r-determinant of plasmid NR1]

Restriction KpnI sites on a molecule of the plasmid NR1 were localized. The position of KpnA (58,0 MD) and KpnB (1,0 MD) fragments on a physical map of the NR1 molecule was shown using endonucleases EcoRI and SaII. Both restriction sites are situated on a r-determinant of the EcoJ fragment of the plasmid NR1.