Beta-lactam resistance mechanisms in clinical isolates of Proteus spp. in Portugal: plasmid-mediated inhibitor resistant TEM and extended-spectrum b-lactamases

Abstract number: 1733_63

Manageiro V., Mendonça N., Louro D., Ferreira E., Caniça on behalf of the Antimicrobial Resistance Surveillance Program in Portugal M.

Objectives: The aim of this study was to evaluate b-lactamase mechanisms responsible for b-lactam resistance in clinical strains of Proteus spp. isolated from hospitals covering several regions of Portugal. The clonal diversity of amoxicillin-resistant (AML-R) isolates of P. mirabilis was also analysed.

Methods: During a 6 months period (January to June 1999), 460 consecutive nonduplicate clinical strains of Proteus spp. (429 P. mirabilis, 29 P. vulgaris and 2 P. penneri) were isolated from patients in 16 Portuguese Hospitals and Public Health Institutions. Antibiotic susceptibility tests were performed according to NCCLS and French Society of Microbiology guidelines. ESBL Etest confirmed ESBL production. Isoelectric points of b-lactamases were estimated by isoelectrofocusing. Beta-lactamase resistant genes were searched by PCR-multiplex method and blaTEM genes were identified by nucleotide sequencing, using specific primers. The genetic relatedness among P. mirabilis TEM-producers (n = 42) was investigated by pulsed-field gel electrophoresis (PFGE).

Results: AML resistance was observed in 35% of isolates (135 P. mirabilis, 27 P. vulgaris and 1 P. penneri). AML-R P. mirabilis strains were divided in 4 groups: non-TEM producer strains (11%), and penicillinase (86%), IRT-type (2%) and ESBL (1%) producer strains. The coding region of blaTEM genes identified in P. mirabilis revealed that 76% were parental genes (blaTEM-1A, blaTEM-1B, blaTEM-1C, blaTEM-1F or blaTEM-1G), 1% was blaESBL gene (blaTEM-10B), 3% blaIRT-19 genes (blaTEM-74F) and 18% were non-ESBL blaTEM genes. A new gene, named blaTEM-156A, was detected in 3% of P. mirabilis strains. Five different promoter regions were identified among blaTEM genes. Thirty-two PFGE profile types were identified: 26 included clones genetically unrelated and the remaining 6 included clones related/closely related or undistinguishable (with >80% and 100% similarity, respectively).

Conclusion: TEM-1 was the main b-lactamase produced by Proteus spp. associated with the weak promoter P3 in the respective coding gene. TEM-10 enzyme was responsible for the ESBL phenotype and TEM-74 (IRT-19) for the IRT phenotype in P. mirabilis. Antimicrobial resistance to cefuroxime and narrow-spectrum cephalosporins in P. vulgaris and P. penneri were associated with the hyperproduction of cefuroximases. This study emphasizes the need to carefully prescribe b-lactams in infections due to P. mirabilis.