Evidence for broken minocycline by NMR and HPLC techniques: a new additional resistance mechanism mediated by tetB determinant.

As demonstrated by microbiological assays, a decrease in the active minocycline level occurs in spent media from each Escherichia coli K12 recipient containing one of 10 different plasmids bearing tetB determinants. No such decrease was detected when tetA, C, D or E determinants were tested under the same conditions. Likewise, no decrease in tetracycline or doxycycline levels was detected when 20 plasmids bearing tetA to E determinants were tested. Studies carried out by nuclear magnetic resonance and high pressure liquid chromatography proved that minocycline is broken by a mechanism mediated by the tetB determinant. This new mechanism can be considered as additional to the active efflux of minocycline.

[Occurrence of R plasmids belonging to incompatibility group incC in Aeromonas hydrophila strains isolated from sewage water (author's transl)]. / Présence de plasmides de résistance appartenant au groupe d'incompatibilité C chez Aeromonas hydrophila isole d'eaux résiduaires.

The susceptibility to antimicrobial agents of 321 strains of Aeromonas hydrophila was studied: 319 strains were found to be resistant to one or several antibiotics. Transfer of resistance markers was obtained from 24 strains. Five plasmids from these strains were classified into incompatibility group incC. Epidemiological consequences of R plasmid diffusion in water bacteria are discussed.

[R plasmids incompatibility groups in epidemic Salmonella (author's transl)]. / Groupes d'incompatibilité des plasmides r chez les souches de Salmonella épidémiques.

The susceptibility to antimicrobial agents of 410 strains belonging to six serotypes of epidemic Salmonella (S. wien, S. saint-paul, S. panama, S. heidelberg, S. isangi and S. brandenburg) was studied. Resistance to one or more antibiotics was shown for 228 of these strains. Study of resistance transfer was investigated for 25 multiresistant strains of different epidemic origin. Resistance was coded for by conjugative R plasmids except in the case of S. brandenburg. From 20 strains of Salmonella, 39 plasmids were transferred to E. coli K12. Twenty-nine of these plasmids were classified into 7 incompatibility groups: IncFI, FII, I1, I2, N, C, M. These same groups were also found for 84 R plasmids from different enterobacteria. The "epidemic character" of these Salmonella serotypes does not seem to be associated with carriage of any particular R plasmid.

[Trimethoprim resistance plasmids: transferability and incompatibility groups (author's transl)]. / Plasmides de résistance au triméthoprime: transférabilité et groupes d'incompatibilité

Over a three year period, 119 strains of enterobacteria isolated from patients have been found resistant to trimethoprim (TMP) and sulfonamides (Su); 11 strains were resistant to TMP only. MIC of TMP were between 32 and 2048 microng/ml. Three groups of strains are described: (1) thymineless variants (2 strains); (2) TMP resistance non-transferable into Escherichia coli K12 (95 strains); (3) TMP resistance transferable into E. coli K12 (33 strains). TMP marker and Su marker have been transferred independantly from 13 strains; they were cotransferred from 20 strains. The incompatibility group of 31 plasmids has been determined: 10 belong to the fi+ type, group FII; 21 belong to the fi--type, group 6, group 7, group 10, group N and group I1. Epidemiological implications of such a wide range of incompatibility groups among a small number of plasmids specifying TMP resistance are discussed.

[Independence of plasmids harboured in the "Escherichia coli" of patients in hospital without antibiotics (author's transl)]. / Indépendance des plasmides hébergés par les Escherichia coli de malades hospitalisés sans antibiothérapie

A study has been carried out of the faeces of nine patients in the same surgical ward. Viable counts and detection of drug resistance were effected by a replica plating method. Bacteria harbouring the drug resistance pattern (ST) were found in seven faeces. Among them, five R plasmids (ST) were transferred to Escherichia coli K12 and have been differentiated by incompatibility studies. As they didn't belong to the same incompatibility group it was concluded that they were not the same incompatibility group it was concluded that they were not the same plasmid acquired in the hospital. One of these R plasmids (ST) was unclassifiable into a known incompatibility group. So, a new incompatibility group, group 12, is proposed.

[Instability of group FII plasmids in "Salmonella panama" (author's transl)]. / Instabilité des plasmides de type FII chez Salmonella panama

Almost all Salmonella panama isolated in France only harbour R plasmids of incompatibility groups I1 (K Col Ib) and N (T). Reference R plasmids belonging to 11 incompatibility groups have been introduced into S. panama. All are stable after 50 generations except those of group FII. FII instability cannot be explained either by the presence of a group FII cryptic plasmid or by restriction enzymes in S. panama.

[Genetic map and structure in "Escherichia coli" K12 of a resistance plasmid isolated from "Salmonella ordonez" (author's transl)]. / Carte génétique et strucutre chez Escherichia coli K12 d'un plasmide de résistance isolé de Salmonella ordonez

A resistance plasmid called R IP173 has been transferred into E. coli K12 from a multiresistant strain of S. ordonez isolated during an epidemic in Dakar. This plasmid mediates for colicine Ib production and resistance to ampicillin, streptomycin, spectinomycin, kanamycin, chloramphenicol, tetracycline and sulfonamides. It is transducible "en bloc" by the phage P1-kc between strains of E. coli K12. Compatibility studies have shown that R IP173 belongs to the fi- class, I1 group. It is transferred "en bloc" in conjugation experiments between E. coli K12 strains. But during transfers from S. ordonez into E. coli, incomplete variants are obtained, lacking different markers. A deletion map was obtained after analysis of 19 different variants, and it is suggested that the loss of markers results from the loss of genetic material during transfer. In this particular case, the deletions observed in transduction or conjugation experiments lead to identical genetic maps.

Incompatibility groups and the classification of fi - resistance factors.

Incompatibility between R factors has been reported by several authors, and four incompatibility groups have already been described by Datta and Hedges among Rfi(-) factors. The stability of 12 plasmids in pairs was studied after 116 crosses, and five new groups were found, designated 5, 6, 7, 8, and 9. Each plasmid studied belongs to one single group. Incompatibility between plasmids in pairs is a clear-cut phenomenon, is easy to observe, and can provide a reliable method for recognizing and classifying resistance factors, and for tracing their spread among bacterial species.