Plasmid-mediated resistance of some Gram-negative bacterial species to brands of cefuroxime and ceftriaxone

Twenty two different strains of Gram-negative bacteria, namely Pseudomonas aeruginosa, Proteus mirabilis, Klebsiella pneumoniae, Escherichia coli andHaemophilus influenzae were tested for susceptibility to 10 different brands of ceftriaxone and cefuroxime. Some of the highly resistant strains were processed for antibiotic resistance curing and extraction of plasmid DNA. Of the 10 brands of ceftriaxone and cefuroxime, 2 brands of ceftriaxone were more effective on the Gram-negative bacteria than the remaining ceftriaxone and cefuroxime brands. The highly resistant strains were resistant not only to these 2 brands but also to tetracycline, amoxicillin, cotrimoxazole, nitrofurantoin, gentamicin, nalidixic acid and ofloxacin, used in antibiogram and as also evident in high minimum inhibitory concentrations recorded for the strains against the brands of ceftriaxone and cefuroxime. Some of the resistant strains were found to lose their resistance to curing following treatment with different concentrations of a mutagen, acridine orange. Of the 8 multiple drug resistant (MDR) strains of the bacteria selected for plasmid DNA, 5 strains and a sensitive strain of H. influenzae had single plasmid DNA copy ranging in size between 24 - 28 kb. The high level multiple drug resistance of the bacterial strains tested was due not only to variation in the brands of ceftriaxone and cefuroxime but more especially to R-plasmid mediation.