A comparison of susceptibility of Pseudomonas aeruginosa clinical isolates to carbapenem antibiotics in our hospital

: We investigated the susceptibility of 400 Pseudomonas aeruginosa (P. aeruginosa) clinical isolates to 3 antipseudomonal carbapenems, namely, doripenem (DRPM), meropenem (MEPM), and imipenem (IPM). The test strains were isolated from the following specimens: respiratory (n = 194), urinary (n = 61), digestive (n = 38), pus (n = 36), skin (n = 21), blood (n = 9), upper respiratory tract and oral cavity (n = 8), and others (n = 33) at Osaka City University Hospital from July to October 2013. Test strains were categorized as susceptible, ≤ 2 μg/mL; intermediate, 4 μg/mL; and resistant, ≥ 8 μg/mL according to Clinical and Laboratory Standards Institute criteria (M100-S22), updated on January 2012. To compare the antimicrobial activities of these 3 carbapenems, the susceptibility rate for each agent was analyzed. Susceptibility to DRPM, MEPM, and IPM was 78.3%, 74.3%, and 64.8%, respectively, whereas resistance was 12.5%, 22.8%, and 28.5%, respectively. The frequency of strains resistant to DRPM was significantly lower than that for MEPM (p < 0.001) and IPM (p < 0.001). To compare the activities of the 3 carbapenems against the P. aeruginosa clinical isolates, we plotted the numbers of strains against each minimum inhibitory concentration (MIC) level. The MICs of DRPM were lower than those of MEPM in 19.8% of strains, and lower than those of IPM in 41.8% of strains, and the MICs of MEPM were lower than those of IPM in 33.0% of strains. Further, we found that 7.7% of the MEPM-resistant strains were susceptible to DRPM, 23.7% of the IPM-resistant strains were susceptible to DRPM, and 9.6% of the IPM-resistant strains were susceptible to MEPM; however, none of the MEPM-resistant strains was susceptible to IPM, and none of the DRPM-resistant strains was susceptible to MEPM or IPM. In conclusion, the in vitro activity of DRPM against the P. aeruginosa clinical isolates was superior to those of MEPM and IPM.