Klebsiella and Enterobacter strains derived from hospital infections. II. Occurrence and characterization of R-, Lac- and Col- plasmids and their clinical-epidemiological significance.

A total of 269 hospital Klebsiella strains and 103 hospital Enterobacter strains showed 34 and 10 different antibiotic resistance patterns, respectively. Among multiple resistant Klebsiella and Enterobacter strains the Ap Sm Cm Tc resistance pattern was the most frequent (K. aerogenes). Antibiotic resistant strains carried R-plasmids in 27.5%. The presence of R-plasmids was demonstrable in 2.9% of single antibiotic resistant, in 12.8% of double antibiotic resistant, and in 71.4% of multiple antibiotic resistant Klebsiella strains. R-plasmid carriage was most frequent in strains of the species K. pneumoniae and K. atlantae. Transfer frequency of R-plasmids of multiple resistant strains was generally higher into Escherichia coli K12 recipient (10-1 to 10-2) than into K. pneumoniae recipient (10-3 to 10-5). Regarding the individual resistance determinants, transfer frequency of Km-Nm resistance was the highest (65.1%). The lac-plasmid was demonstrable in 18 out of the 77 R-plasmid carrying Klebsiella strains. R- and Lac-plasmids of single and multiple resistant Klebsiella strains could be transferred into E. coli and Klebsiella recipients in mice in vivo. As many as 67% showed fi- and 33% showed fi+ character among the demonstrated 112 R-plasmids. Regarding their incompatibility, the studied five plasmids belonged to groups FI, FII and I alpha. Altogether 14 different groups could be distinguished among R-plasmids on the basis of their phage restriction capability on phage lambda and coliphages T, and another group of R-plasmids showing no restriction at all. Fi+ character was demonstrated in 54.5% of R-plasmids showing phage restriction capability and in 10.9% of R-plasmids showing no phage restriction. Nearly twice as many R-plasmids carrier strains were found among non-typable ones as among those typable by phages. Three R-plasmids showed phage-modification among 51 R-plasmids restrictive for phages. In addition to the phage-type of Klebsiella strains, R-plasmids can also be used as an epidemiologic marker.