["Tet-gene pick up" by a F-plasmid in Proteus mirabilis]

[Bioassay for the detection of hydroxamate-iron-chelators (Aerobactin)]

Different Salmonella strains were tested for aerobactin production in a hydroxamate-bioassay with the aerobactin indicator strain E. coli LG 1522. The majority of hospital strains of Salmonella typhimurium produce hydroxamate siderophore. On the other hand S. typhimurium strains belonging to phage type n. c. 1/72/n. c., biochemical type b from human and animal sources, were unable to produce this siderophore. Serotypes other than S. typhimurium for example the multiresistent S. wien hospital strains, which were isolated in western europe and in the GDR, can excreate hydroxamate siderophore. Plasmids pIE 528 and pIE 5 234 isolated from Salmonella hospital strains produce hydroxamate siderophore in the enterobactin negative Salmonella typhimurium-strain enb-7. Thus, the hydroxamate bioassay may be a useful supplementary test for epidemiological strain characterization.

Plasmid-borne streptothricin resistance in gram-negative bacteria

Plasmids, which code for a new type of drug resistance due to the acetylation of streptothricin and belonging to various incompatibility groups (I1, I2, W3, FII, S, X, and N) were identified in gram-negative bacteria. The gene for the acetyltransferase is closely linked to a gene for the streptomycin/spectinomycin adenylyltransferase AAD-3" on a novel type of a transposon, designated Tn1825. This is related to Tn7.

Characterization of conjugative plasmids belonging to a new incompatibility group (IncZ)

More than 30 conjugative R plasmids between 60 and 70 Md in size were identified in wild type strains of Enterobacteriaceae isolated in German Democratic Republic, Bulgaria, Mongolia, Poland, Ethiopia, Iraque, and Soviet Union. They have been characterized by means of several genetic and molecular techniques as members of a new incompatibility group, termed IncZ. The properties of these plasmids including digestion pattern after EcoRI treatment demonstrate a phylogenetic relatedness.

[Distribution of transferable trimethoprim and gentamicin resistance plasmids in Enterobacteriaceae]

Following the employment of trimethoprim/sulfonamid and gentamicin in the general clinical praxis transferable plasmids with respective resistance function were identified at first in enteric bacteria from sewage before they could be detected in patient strains. Whereas the trimethoprim resistance plasmids represent different incompatibility groups (C, FII, I5, K, M, N, S, U) the gentamicin resistance plasmids are very similar IncM members of 62 MD in size. Therefore a clonal distribution of a particular gentamicin resistance plasmid has to be taken into consideration.

Translocation of the tetracycline resistance determinant from R100-1 to the Escherichia coli K-12 chromosome

Pairs of normally incompatible derivatives of R100-1 (one ChlS TetR, the other ChilR TetS) were forced to coexist in a recA host by selection for ChlR TetR cells. After many generations stable derivatives were isolated. The analysis of none independent stabilization experiments showed that in each case TetR was translocated from the plasmid to the chromosome of the host. No evidence for the joint integration of other plasmid genes (those controlling transfer, antibiotic resistance, incompatibility, or origin of transfer replication) was obtained. One of the chromosomal TetR determinants was mapped close to metE.