Megumi Kono

R Plasmids in Corynebacterium xerosis Strains

Plasmids coding for resistance to chloramphenicol, erythromycin, kanamycin, streptomycin, and tetracycline have been found in strains of Corynebacterium xerosis isolated from patients with otitis media. Images

Enzymatic Inactivation of a New Aminoglycoside Antibiotic, Sisomicin, by Resistant Strains of Pseudomonas aeruginosa

The antibacterial activity of sisomicin (SS), a new aminoglycoside antibiotic active toward clinical isolates of Pseudomonas aeruginosa, was determined and compared with that of the gentamicin C complex. Both drugs were effective against these strains and showed almost the same antibacterial activity. A few strains were found to be resistant to SS. The antibiotic was inactivated by a cell-free extract from the SS-resistant strains due to acetylation of the drug. Comparative studies of the inactivation of the drugs which lack a 6′-amino group in the amino sugar linked to 2-deoxystreptamine strongly suggested that SS inactivation was due to acetylation of the 6′-amino group of the 4′,5′-didehydropurpurosamine moiety.

Complete nucleotide sequence of pTZ12, a chloramphenicol-resistance plasmid of Bacillus subtilis

The complete nucleotide sequence of pTZ12, a chloramphenicol-resistance (CmR) plasmid (2517 bp) derived from Corynebacterium xerosis plasmid pTZ10, has been determined after propagation in Bacillus subtilis. The nucleotide sequence of pTZ12 suggests that a recombination event may have occurred naturally within the open reading frames for the Rep protein of pT181 (or a pT181-like plasmid) and pC221 (or a pC221-like plasmid).

Mechanism of resistance to some cephalosporins in Staphylococcus aureus.

The mechanism of resistance to some cephalosporins in Staphylococcus aureus strains was investigated with high-pressure liquid chromatography and nuclear magnetic resonance spectrometry. Drug inactivation by penicillinase was found to be the main mechanism of resistance to cefazolin, cephaloridine, and cephalothin in S. aureus.

Microbial degradation of cephalothin by cephalothin-susceptible Escherichia coli.

Cephalothin (CET)-susceptible Escherichia coli, which can degrade CET after prolonged incubation in broth containing a concentration of the drug greater than the minimum inhibitory concentration, was found in a clinical specimen. The substrate specificity of the partially purified enzyme to cephalosporin analogs strongly indicated the occurrence of CET-specific degradation. Nuclear magnetic resonance analysis of the degradation reaction demonstrated the appearance of two new signals attributed to deacetyl CET. This suggests the possibility of the presence of acylesterase.

Prevalence of R factors in Pseudonomas aeruginosa.

There are many reports of R factors in Pseudomonas aeruginosa (Roe, Jones & Lowbury, 1971 ; Witchitz & Chabbert, 1971 ; Bryan, Van den Elzen & Tseng, 1972; Grinsted et al. 1972; Olsen & Shipley, 1973; Iyobe et al. 1974; Van Rensburg & de Kock, 1974) but there has been little work on the prevalence of R factors in clinical isolates of P. aeruginosa (see Holloway & Richmond, 1973). We have surveyed the drug resistances of 89 distinct strains of P. aeruginosa isolated from patients suffering from urinary tract infections and have found that 10 (I 1.2 %) of the isolates transfer one or more of their resistance determinants to drug-sensitive recipients.

Relationship Between Chloramphenicol Acetyltransferase Activity and the Number of Resistance Genes

Various mutants of an Escherichia coli K-12 strain were prepared, in which a chloramphenicol (CM) resistance gene (cml) derived from an R factor, R100-1, was integrated into the chromosome. The CM acetyltransferase (CATase) activity of these strains and the strain carrying R100-1 were determined during exponential growth with the following results. (i) The CATase activity varied, depending upon the site of integration of the cml gene on the chromosome. Activity was found to be higher when the cml gene was integrated nearer the replication origin of the chromosome, the total enzyme activity found was the sum of activities coded by each gene separately. (iii) When the cml gene was in a cytoplasmic state on an R factor, R100-1, the expressed enzyme activity was four-to eightfold higher than that in the chromosomal state, suggesting the existence of about four to eight copies of R factor per chromosome. The CATase activity returned to the level of that expressed by R100-1 when the chromosomal cml gene was detached and picked up by an R factor.

Association of a Penicillin Resistance Gene with a Tetracycline Resistance Plasmid (PTP–2) in Staphylococcus aureus

On transduction with a lysogenic strain of Straphylococcus aureus isolated from a clinical specimen and having tetracycline (TC)-penicillin (PC)-chloramphenicol (CP)-resistant plasmids, the three-drug-resistant strain was frequently obtained. By repeatedly transducing from this strain, a strain (TP-2) having stable resistance to TC and PC could be obtained. In transformation with the deoxyribonucleic acid (DNA) of TP-2 as donor, all of the transformants obtained by selecting with either TC or PC were both TC and PC resistant. According to electron microscopy study of the covalently closed circular DNA of TP-2, the plasmid DNA size was 1.37 ± 0.03 μm (2.84 × 106 daltons). The plasmid (PTP-2) is presumed to be a new plasmid in which the PC resistance gene was integrated into the TC-resistant plasmid. Images

Nuclear magnetic resonance spectrometric assay of beta-lactamase.

Beta-Lactam antibiotics and the crude enzyme were mixed in deuterium oxide and placed in a nuclear magnetic resonance tube. The change of the nuclear magnetic resonance spectrum during the enzymatic reaction was then analyzed to determine beta-lactamase activity. By using beta-lactam antibiotics such as penicillins, cephalosporins, and cephamycins as substrates, a comparison of the beta-lactamase activities was made between the nuclear magnetic resonance spectrometric assay and the iodometric assay. There was a close correlation between these two methods.

High degree of homology of the deduced protein structures of the tetracycline-resistance determinants between Bacillus subtilis plasmid pNS1981 and Staphylococcus aureus plasmid pTP5

The amino acid sequences of the tetracycline-resistance (Tcr) determinants of Bacillus subtilis plasmid pNS1981 and Staphylococcus aureus plasmid pTP5 have been deduced from their nucleotide sequences and compared. The deduced Tcr proteins (TETs) of pNS1981 (458 amino acids) and pTP5 (459 amino acids) show a considerable homology (60% identical). If homologous amino acid replacement is taken into account, the homology becomes 80%. Both TET proteins are highly hydrophobic, as expected for a membrane-binding protein, and their polarities are calculated at 32–33%. The putative secondary structures of both TET proteins have been also shown to be significantly homologous, being abundant in β-sheets. The predicted positions of β-sheets show a nice coincidence between both TET proteins. α-Helix has a tendency to be formed at nonhomologous regions of the primary structures between both TET proteins. However, the predicted positions of α-helices coincide in a frequency greater than 50%. α-Helix and random coil moderately occur at the hydrophilic regions in both TET proteins.