In vitro antibacterial activity of doripenem against clinical isolates from French teaching hospitals: proposition of zone diameter breakpoints

MIC score, a new tool to compare bacterial susceptibility to antibiotics application to the comparison of susceptibility to different penems of clinical strains of Pseudomonas aeruginosa

This study aimed to compare the susceptibility to carbapenems (imipenem, meropenem and doripenem) of clinical strains of Pseudomonas aeruginosa. It also studied whether susceptibility to imipenem or meropenem could predict, reliably, susceptibility to doripenem. Pseudomonal strains were collected from respiratory specimens, half of them from cystic fibrosis patients. MICs were determined according to European Committee on Antimicrobial Susceptibility Testing recommendations. Carbapenems were compared according to the susceptible, intermediate or resistant categories. A new approach also allowed comparing these carbapenems in a 'MIC score' taking into account the differences in breakpoints between drugs. One hundred thirty-nine strains were studied. They were found to be statistically more susceptible to meropenem than to the two other drugs. However, this difference was small: less than one dilution between the agents. This study also highlighted a significant correlation between susceptibility to penems taken in pairs. However, susceptibility to imipenem or meropenem did not reliably predict susceptibility to doripenem. Despite potential differences in resistance mechanisms, the Pseudomonas aeruginosa strains showed close susceptibility to three carbapenems. This was true for both cystic fibrosis patients and others. However, there were variations between strains. That justifies MICs to be determined for each of the three penems. This might be useful in case of elevated MICs and/or for potentially difficult-to-treat infections such as pneumonia in patients with cystic fibrosis patients.

Comparison of in Vitro Activity of Doripenem versus Old Carbapenems against Pseudomonas Aeruginosa Clinical Isolates from both CF and Burn Patients

PURPOSE

The antimicrobial activity of doripenem in comparison of imipenem, meropenem and ertapenem among Pseudomonas aeruginosa isolated from burn and Cystic Fibrosis (CF) patients were determined.

METHODS

Metallo-β-lactamase (MBL) genes in imipenem non susceptible P. aeruginosa isolates were detected using PCR method. The in vitro susceptibilities of doripenem, imipenem, meropenem and ertapenem were determined by Etests. MIC50 and MIC90 for corresponding antibiotics were determined individually in burn and CF isolates.

RESULTS

Among isolates which were resistant to imipenem, 16 isolates were positive for the bla IMP gene. All isolates had no bla VIM gene. All MBL producing isolates were excluded. MIC50/MIC90 of doripenem in CF and burn isolates were 0.75/>32 and >32/>32 mg/L respectively. The corresponding values for imipenem in CF and burn isolates were 2/>32 and >32/>32 mg/L, respectively.

CONCLUSION

The susceptibility rate of doripenem is higher than that of imipenem and meropenem among P.aeruginosa isolated from CF patients, whereas, there is no difference between the efficiency of doripenem and old carbapenems in non MBL producing P.aeruginosa isolates in burn patients.

Structure and function of OprD protein in Pseudomonas aeruginosa: from antibiotic resistance to novel therapies

Pseudomonas aeruginosa (P. aeruginosa) is a common pathogen isolated from patients with nosocomial infections. Due to its intrinsic and acquired antimicrobial resistance, limited classes of antibiotics can be used for the treatment of infection with P. aeruginosa. Of these, the carbapenems are very important; however, the occurrence of carbapenem-resistant strains is gradually increasing over time. Deficiency of the outer membrane protein OprD confers P. aeruginosa a basal level of resistance to carbapenems, especially to imipenem. Functional studies have revealed that loops 2 and 3 in the OprD protein contain the entrance and/or binding sites for imipenem. Therefore, any mutation in loop 2 and/or loop 3 that causes conformational changes could result in carbapenem resistance. OprD is also a common channel for some amino acids and peptides, and competition with carbapenems through the channel may also occur. Furthermore, OprD is a highly regulated protein at transcriptional and post-transcriptional levels by some metals, small bioactive molecules, amino acids, and efflux pump regulators. Because of its hypermutability and highly regulated properties, OprD is thought to be the most prevalent mechanism for carbapenem resistance in P. aeruginosa. Developing new strategies to combat infection with carbapenem-resistant P. aeruginosa lacking OprD is an ongoing challenge.