STUDIES ON THE DETECTION AND RESISTANCE TRANSFER OF TRANSFERABLE AND NON-TRANSFERABLE PLASMIDS IN CLINICALLY-ISOLATED STRAINS OF SERRATIA MARCESCENS

Abstract

The majority of reports hitherto concerning the drug-resistance factor in Serratia marcescens deal only with the detection of transferable plasmids through conjugal transfer, and practically no reports have appeared that have investigated down at the DNA level, whereby DNA is extracted and non-transferable plasmids are detected after transformation. Consequently, as part of our study into drug resistance, the resistance type of 99 clinically-isolated strains of Serratia marcescens was investigated. Further, transferable and non-transferable plasmids were examined in resistant strains, and the plasmid DNA was confirmed using agarose gel electrophoresis. In particular, amongst the various drugresistance plasmids, the PC-resistance was investigated by examining the type of β-lactamase produced from substrate specificity.
As a result, resistance to TC, CER and ABPC were not considered to be the intrinsic resistance of Serratia marcescens, especially in the case of ABPC whereby resistance plasmids occurred at a high frequency.
Transferable plasmids are divided into three groups according to the test facility and the period of isolation: group A (control group; isolated during March, 1979 to February, 1980), group B₁ (former group; isolated during June, 1980 to July, 1980), and group B₂ (latter group; isolated during August, 1980 to December, 1980). The ABPC and KM resistance type plasmids were most frequently observed in the A and B₁ groups, whilst, in group B₂ SM, SA, ABPC and KM, resistance type plasmids occurred at a high frequency. These were considered to be epidemic plasmids that changed rapidly in a short period of time.
Moreover, the results suggest that non-transferable plasmids assume transferability, and that not only transferable but also non-transferable plasmids are clinically important.