[Effect of prophages on transfer frequency of conjugative plasmid G 873].

Transfer of the conjugative plasmid G873 on filters and mixed cultivation of the donor and recipient cells in liquid media is described. In the both systems the use of the lysogenic recipient cells (phages of serogroups B and F) in the crossings increased mor than 100-fold the frequency of plasmid transfer. The conjugative transfer of the plasmid in the mixed cultivation system was proved.

[Differentiation of methicillin-resistant strains of Staphylococcus aureus by prophage specificity].

By inducing with mitomycin C the following phages were isolated from all the tested 32 methicillin resistant strains of S. aureus: the serogroup B phage was isolated from 2 strains, the serogroup B and F phages were isolated from 5 strains and the serogroup F phage was isolated from 25 strains. The phages were divided into 5 groups by the antiphage immunity.

Instability of in vitro resistance to imipenem in Pseudomonas aeruginosa.

In 3 from 19 clinical isolates of Pseudomonas aeruginosa imipenem-resistant subpopulations could be detected in vitro. In comparison to their wild strains these imipenem-resistant cells were lacking an outer-membrane-protein of 50 kD. In the subpopulation derived from Pseudomonas aeruginosa 76 resistance to imipenem was found to be instable.

Biochemical aspects of the resistance to nourseothricin (streptothricin) of Escherichia coli strains.

In most cases Escherichia coli strains phenotypically resistant against nourseothricin (streptothricin) harbour a plasmid which codes for an acetyltransferase. This enzyme transfers an acetyl group from acetyl-coenzyme A to an amino group of the beta-lysine (peptide) chain of the antibiotic, thus inactivating it. Additionally, the penetrability for nourseothricin of the cell wall is drastically reduced in a high percentage of the resistant strains.

Resistance of Escherichia coli to nourseothricin (streptothricin): reduced penetrability of the cell wall as an additional, possibly unspecific mechanism.

The resistance of E. coli strains to the antibiotic nourseothricin is known to be caused by an acetyltransferase acetylating the beta-lysine chain of the antibiotic. In addition, most of the resistant strains exhibit reduced penetrability of the outer membrane, presumably caused by a reduced amount of available negative charges.