The antibiotic resistance of Pseudomonas aeruginosa presents a serious problem in medicine as this pathogenic germ is responsible for many diseases of which certain nosocomial infections. The 22 strains of P. aeruginosa were the target of our study as they have a multi-resistance against β-lactamines and aminosids; on the other hand, they are all sensitive to the ciprofloxacine. They all produce the β-lactamases. 15 strains are in favor of hyperproduction of céphalosporinases and all present a penicillinase phenotype. The cleaning out performed on P.aeruginosa is negative. The transfer by conjugation of the plasmid carrying gene of resistance to the ticarcilline and pipéracilline is positive for 12 of the22 studied strains. The experiments of conjugation made it possible to confirm that this resistance could have the plasmidic DNA as a support.