Short communicationOprD mutations and inactivation in imipenem-resistant Pseudomonas aeruginosa isolates from China

- OprD loss due to different types of mutations was the main imipenem resistance mechanism in P. aeruginosa.
- For isolates without OprD loss, reduced transcriptional expression of oprD was found.
- No mutational OprD loss or reduced expression of oprD was found in imipenem-susceptible isolates.
- Only one isolate produced MBLs (IMP9), lower than other reports in China.
- AmpC might play a role in reducing susceptibility to imipenem in isolates without OprD loss.

To investigate the mechanisms involved in imipenem resistance of Pseudomonas aeruginosa in southern China, 61 imipenem-resistant P. aeruginosa clinical isolates were collected from 4 hospitals between October 2011 and June 2012. All isolates were resistant to imipenem, whereas 21.3% were susceptible or intermediate to meropenem. Variable degrees of resistance to other β-lactam and non-β-lactam antimicrobials were observed. PFGE revealed high-level of clonal diversity. Among the 61 isolates, 50 isolates had OprD loss by disrupted oprD mutations, including 43 with frameshift mutations of oprD and 7 with a premature stop codon by single point mutation. Six isolates were oprD-negative by PCR, suggestive of a major disruption of oprD genes. Five isolates had intact oprD but had reduced expression of oprD genes. In addition, only one isolate with disrupted oprD mutation by a premature stop codon was confirmed to be a metallo-β-lactamase producer (IMP-9). Our results show that the loss of OprD, as well as reduced expression of oprD and MBL production, were the predominant mechanisms of imipenem resistance in P. aeruginosa in southern China.