Doripenem versus Pseudomonas aeruginosa in vitro: activity against characterized isolates, mutants, and transconjugants and resistance selection potential.
Doripenem is a broad-spectrum parenteral carbapenem under clinical development in Japan and North America. Its activities against (i) Pseudomonas aeruginosa isolates with graded levels of intrinsic efflux-type resistance, (ii) mutants with various combinations of AmpC and OprD expression, (iii) PU21 transconjugants with class A and D beta-lactamases, and (iv) P. aeruginosa isolates with metallo-beta-lactamases were tested by the agar dilution method of the National Committee for Clinical Laboratory Standards. Selection of resistant P. aeruginosa mutants was investigated in single- and multistep procedures. Doripenem MICs for isolates without acquired resistance mostly were 0.12 to 0.5 microg/ml, whereas meropenem MICs were 0.25 to 0.5 microg/ml and imipenem MICs were 1 to 2 microg/ml. The MICs of doripenem, meropenem, ertapenem, and noncarbapenems for isolates with increased efflux-type resistance were elevated, whereas the MICs of imipenem were less affected. The MICs of doripenem were increased by the loss of OprD but not by derepression of AmpC; nevertheless, and as with other carbapenems, the impermeability-determined resistance caused by the loss of OprD corequired AmpC activity and was lost in OprD- mutants also lacking AmpC. The TEM, PSE, PER, and OXA enzymes did not significantly protect P. aeruginosa PU21 against the activity of doripenem, whereas MICs of > or =16 microg/ml were seen for clinical isolates with VIM and IMP metallo-beta-lactamases. Resistant mutants seemed to be harder to select with doripenem than with other carbapenems (or noncarbapenems), and the fold increases in the MICs were smaller for the resistant mutants. Single-step doripenem mutants were mostly resistant only to carbapenems and had lost OprD; multistep mutants had broader resistance, implying the presence of additional mechanisms, putatively including up-regulated efflux. Most mutants selected with aminoglycosides and quinolones had little or no cross-resistance to carbapenems, including doripenem.
Mushtaq
Shazad
S
Antibiotic Resistance Monitoring & Reference Laboratory, Specialist & Reference Microbiology Division, Health Protection Agency Colindale, London NW9 5HT, United Kingdom.
Ge
Yigong
Y
Livermore
David M
DM
D001425:Bacterial Outer Membrane Proteins / Q000235:genetics; D015780:Carbapenems / Q000494:pharmacology*; D003227:Conjugation, Genetic / Q000235:genetics / Q000502:physiology*; D000077726:Doripenem; D024881:Drug Resistance, Bacterial; D004591:Electrophoresis, Polyacrylamide Gel; D005798:Genes, Bacterial / Q000235:genetics; D008826:Microbial Sensitivity Tests; D009154:Mutation / Q000235:genetics / Q000502:physiology*; D011552:Pseudomonas Infections / Q000382:microbiology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics; D001618:beta-Lactamases / Q000096:biosynthesis / Q000235:genetics
D001425:Bacterial Outer Membrane Proteins; D015780:Carbapenems; D000077726:Doripenem; D001618:beta-Lactamases