Isolation of carbapenemase-producing Pseudomonas otitidis from a patient with chronic otitis media

Abstract number: P1854

Lee K., Kim C.K., Yong D., Yum J.H., Chung M.H., Chong Y., Thaller M.C., Rossolini G.M.

Objectives: To report otitis media due to metallo-b-lactamase (MBL)-producing isolate of Pseudomonas otitidis.

Methods: A 53-year-old man visited a Korean Eye and ENT hospital in April 2005. The patient had chronic otitis media since childhood. At the time of the visit, otalgia was absent but purulent discharge from perforated tympanic membrane was present. Prulent material was cultured and susceptibility was determined by tests of CLSI disk diffusion, broth microdilution and E-test. 16S rRNA gene sequencing was used to identify the species.

Results: A culture of the purulent material yielded two isolates, identified as Pseudomonas aeruginosa (PAE) by conventional tests, of which one was resistant to imipenem (IPM) and meropenem (MICs, >32 ug/ml) but susceptible to aztreonam, ceftazidime, cefepime, cefpiramide, cefoperazone-sulbactam, piperacillin, pipracillin-tazobactam, ciprofloxacin and trimethoprim-sulphamethoxazole (SXT). The IPM-resistant isolate was positive for MBL activity by the IPM-disk Hodge, and an IPM-EDTA plus SMA double disk synergy test. IPM-hydrolysing activity was detectable in a crude cell extract, independently of carbapenem exposure. However, PCR was negative for IMP-1, VIM-2 and SIM-1 genes, which were the only MBL genes reported in Korea at that time. Tests performed to investigate possible misidentification showed that the isolate was an oxidase-positive glucose nonfermenter, but pyocyanin and fluorescein production were negative. Many of the biochemical tests were inconsistent for PAE or Stenotrophomonas maltophilia. ID32 GN failed to identify the isolate. 16S rRNA gene sequencing identified it as P. otitidis, a new species causing otic infections, first isolated in the U.S.A. and reported in 2006. The patient was successfully treated with SXT and topical ofloxacin.

Conclusion: To our best knowledge, this is the first report of a P. otitidis infection outside the U.S.A. This observation underscore the possibility that some PAE isolates from otic infections could actually be P. otitidis. The mechanism of carbapenem resistance of this isolate, possibly due to production of a narrow-spectrum MBL, is under investigation. The clinical significance of the peculiar susceptibility pattern needs further study.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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