Transductional analysis of imipenem-ceftazidime-and azactam resistant Pseudomonas aeruginosa strains from nosocomial infections.

Six strains of P. aeruginosa, resistant to IMI, CTZ and/or AZA, or to two of these drugs even to all three antibiotics, have been analysed by transduction by standard transducing phages F116 and G101, propagated on these strains, as well by a wildtype phage isolated from one of P. aeruginosa strains resistant to CTZ and AZA. Analysis of occurrence of resistance determinants in individual sets of transductants allows us to conclude that all three antibiotic-resistance determinants are separable by transduction and, thus, the resistance to any of these three antibiotics is genetically governed by independent determinants. None strain, resistant to these antibiotics, could hydrolyse any of these drugs, with an exception of slow hydrolysis of IMI, observed also by other investigators [8]. In contrast, strains hydrolysed classical, first-generation cephalosporins as well as Cefoxitin, and transferability of these two determinants could be proved by transfers, to Enterobacteriaceae (P. aeruginosa are naturally resistant to these two antibiotics). Thus, resistance to IMI, CTZ and/or AZA, is not co-transferred, with determinants of resistance to more classical cephalosporins.

Transduction of amikacin, gentamicin and tobramycin resistance in Pseudomonas aeruginosa with phage F 116 and AP 19, a new wildtype phage.

Amikacin-, tobramycin-, gentamicin- as well as carbenicillin-resistance has been found to be transducible, in various combinations of spectra both with the phage F 116 propagated on an Amikacin-resistant wild-type strain of Pseudomonas aeruginosa (No. BE 11) and with the phage AP 19 isolated from a different Amikacin-resistant strain (No. 578). Both strains were found to transfer Amikacin-resistance genes presumably by conjugation thus possessing an R plasmid coding for multiple antibiotic resistance. Evidence is presented that classical as well as wild-type phages may acquire and transmit antibiotic resistance genes among pseudomonads. This is particularly significant in view of the importance to preserve Amikacin as an effective reserve antibiotic for treatment of poly-resistant infections including those caused by P. aeruginosa.