Metallo-β-Lactamase Production by Pseudomonas otitidis : a Species-Related Trait

Abstract

Susceptibility to several ␤-lactams and ␤-lactamase production was investigated in a collection of 20 strains of Pseudomonas otitidis, a new Pseudomonas species that has been recently recognized in association with otic infections in humans. All strains appeared to be susceptible to piperacillin, cefotaxime, ceftazidime, and aztreonam, while resistance or decreased susceptibility to carbapenems was occasionally observed. All strains were found to express metallo-␤-lactamase (MBL) activity and to carry a new subclass B3 MBL gene, named bla POM , that appeared to be highly conserved in this species. P. otitidis, therefore, is the first example of a pathogenic Pseudomonas species endowed with a resident MBL. The POM-1 protein from P. otitidis type strain MCC10330 exhibits the closest similarity (60 to 64%) to the L1 MBL of Stenotrophomonas maltophilia. Expression in Escherichia coli and Pseudomonas aeruginosa revealed that, similar to L1 and other subclass B3 MBLs, POM-1 confers decreased susceptibility or resistance to carbapenems, penicillins, and cephalosporins but not to aztreonam. Expression of the POM MBL in P. otitidis is apparently constitutive and, in most strains, does not confer a carbapenem-resistant phenotype. However, a strong inoculum size effect was observed for carbapenem MICs, and carbapenem-resistant mutants could be readily selected upon exposure to imipenem, suggesting that carbapenem-based regimens should be considered with caution for P. otitidis infections. Pseudomonas otitidis is a newPseudomonas species that has recently been recognized in association with otic infections in humans, including acute otitis externa, acute otitis media, and chronic suppurative otitis media (2). Genotypically and phenotypically, P. otitidis is closely related to Pseudomonas aeruginosa (2), and this similarity likely accounts for the belated identification of this new pathogenic species within the Pseudomonas genus.The susceptibility of P. otitidis was previously investigated with several antimicrobial agents, including aminoglycosides, fluoroquinolones, macrolides, ␤-lactams, tetracycline, chloramphenicol, and polymyxin B, and overall, the behavior of this species appeared to be similar to that of P. aeruginosa (2). However, of ␤-lactams, only piperacillin was tested, while no information is available on the susceptibility of this species to antipseudomonal cephalosporins, aztreonam, and carbapenems.In this work, we investigated the susceptibility of P. otitidis to several ␤-lactams and the production of ␤-lactamase activity by this species. Results revealed that P. otitidis strains constitutively produce a novel subclass B3 metallo-␤-lactamase (MBL), that was named POM (after P. otitidis metallo-␤-lactamase), which is active on carbapenems and other ␤-lactams. MATERIALS AND METHODSBacterial strains. The P. otitidis strains investigated in this work included 19 strains from the collection previously described by Clark et al. (2) and a clinical isolate from South Korea (isolate YMC-Po/06) cultured from the puru...

POM-1 metallo-β-lactamase–producing Pseudomonas otitidis isolate from a patient with chronic otitis media

“…MICs of piperacillin, cefotaxime, and aztreonam were slightly higher than those tested by Etest (AB bioMérieux, Solna, Sweden) (Thaller et al, 2011). The results of an imipenem-disk Hodge test and a double-disk synergy test using disks of imipenem and EDTA + sodium mercaptoacetic acid were positive, indicating production of a metallo-β-lactamase (MBL) (Lee et al, 2010), but bla IMP-1 -, bla VIM-2 -, or bla SIM-1 -like, present in Korea at that time, was not detectable by polymerase chain reaction.…”

“…The results of an imipenem-disk Hodge test and a double-disk synergy test using disks of imipenem and EDTA + sodium mercaptoacetic acid were positive, indicating production of a metallo-β-lactamase (MBL) (Lee et al, 2010), but bla IMP-1 -, bla VIM-2 -, or bla SIM-1 -like, present in Korea at that time, was not detectable by polymerase chain reaction. An investigation resulted in finding a new MBL, POM-1 (Thaller et al, 2011).…”

“…We suggest that Pseudomonas isolates with no bluegreen pigment and with unusual β-lactam susceptibility should be identified by analyzing the 16S rRNA gene sequence. It was suggested that detection of bla POM-1 could be used for identification of P. otitidis isolates (Thaller et al, 2011).…”

Genetic and Biochemical Characterization of an Acquired Subgroup B3 Metallo-β-Lactamase Gene, bla AIM-1 , and Its Unique Genetic Context in Pseudomonas aeruginosa from Australia

“…These include Stenotrophomonas maltophilia (L1) (42), Janthinobacterium lividum (THIN-B) (23), Chryseobacterium meningosepticum (GOB-1) (1), Legionella gormanii (FEZ-1) (2), Caulobacter crescentus (CAU-1) (10), CAR-1 from Erwinia carotovora (29), POM-1 (32), and the recently reported ISCR1-associated SMB-1 (38). The MBL genes carried by these environmental bacteria encode subgroup B3 MBLs that are not closely related to the mobile B1 members (43).…”

Biochemical Characterization of the POM-1 Metallo-β-Lactamase from Pseudomonas otitidis

“…POM-1 is a subclass B3 MBL recently identified in Pseudomonas otitidis (2), a Pseudomonas species that is found associated with otic infections in humans and can also be found as a free-living aquatic Pseudomonas species in some environments (3)(4)(5). As such, POM-1 represents the first example of a resident MBL found in a pathogenic Pseudomonas species (2).…”