[Susceptibility and R plasmids conjugation tests for 44 strains of gram negative bacilli in a burn unit]

44 strains of 9 species Gram negative bacilli were isolated and identified in a burn unit, among them 25 strains were from patients and 19 from ward environment. All strains were tested for susceptibility to antibiotics and R plasmids. Using both agar dilution and disc diffusion methods to test susceptibility to 12 kinds of antibiotics, namely, Streptomycin Chloramphenicol, Tetracycline, Ampicillin, Kanamycin, Gentamycin, Nalidixic acid, Amikacin Rifampin, Carbenicillin, Cefazolin and Polymyxin, we found that all 44 strains were susceptible to Rifampin and Polymyxin. To the other 10 kinds of antibiotics, the susceptibilities varied. 40 strains of bacteria (91%) were resistant to 3 kinds or more of antibiotics, i.e, multiple resistant bacteria, 2 strains resistant to 2 kinds of antibiotics (4.6%), and 2 strains susceptible to all 12 kinds of antibiotics (4.6%). The multiple resistant strains consisted of 9 strains (22.5%) of R plasmid-harboured bacteria, Pseudomonas aeruginosa 2 strains, Citrobacter 4 strains, Proteins 1 strain, Enterobacter aerogenes 1 strain and Escherichia coli 1 strain. All the R plasmids carried the marks of resistance to chloramphenicol, tetracycline, ampicillin, kanamycin, gentamycin, streptomycin, and carbenicillin, but no one carried marks of resistance to Cefazolin and Amikacin indicating that drug-resistance of the last two antibiotics might not be mediated by R plasmids. Two strains of Citrobacter freundii isolated from 2 patients and showing susceptibility to all antibiotics were induced to be Rifampin-resistance (Rif) strains without changing their original biological characters. They both could receive the R plasmids of the multiple resistance strains one from patient and the other from ward environment.(ABSTRACT TRUNCATED AT 250 WORDS)