Dissemination of a CMY-16 producing clone of P. mirabilis in long-term care and rehabilitation facilities of northern Italy

Abstract number: 1733_177

Nucleo E., Migliavacca R., Spalla M., Terulla C., Debiaggi M., Balzaretti M., Migliavacca A., Navarra A., Pagani L.

Background: The use of cephamycins and b-lactam-inhibitor combinations to counter the threat of extended-spectrum b-lactamases (ESBLs) mediated resistance determined a shift toward non-ESBL phenotypes in species without inducible chromosomal AmpCs. The CMY-LAT-type enzymes are a group of molecular acquired class C b-lactamases (CBLs) that exhibit a broader spectrum of resistance than classical ESBLs.

Methods: 204 non-repetitive P. mirabilis isolates intermediate/resistant to cefotaxime, collected from May 2003 to March 2006 from inpatients in three Long Term Care and Rehabilitation facilities of Northern Italy (ASP S. Margherita, IRCCS S. Maugeri and ASP P. Redaelli), were included in the study. The isolates were recovered from urinary tract.

The production of an ESBL activity was screened by the CLSI diffusion test; IEF of crude bacterial lysates was performed to detect the pIs of b-lactamase bands. The nature of the resistance genes and the clonal relationships between the strains, were studied by molecular techniques such as amplification, sequencing and PFGE (SfiI).

Results: 18/204 (8.8%) strains showed an AmpC phenotype. Analytical IEF revealed the presence of 2 b-lactamase bands, of pI 5.4 and >8.4 respectively, in all the isolates. The pI 5.4 band was unable to hydrolyze extended-spectrum cephalosporins (CTX, CAZ, FEP), monobactams (ATM) and cefoxitin (FOX) and was likely contributed by a TEM-type enzyme. The alkaline pI band was active against both FOX, CTX and CAZ, suggesting the presence of an acquired CBL. PCR and sequencing revealed the occurrence of the CMY-16 enzyme, a variant of the CMY/LAT lineage. All the 18 CMY-16 producers were clonally related. The incidence of CMY genes within the three hospitals was: 10/64 (15.6%) at ASP S. Margherita; 2/15 (13.3%) at IRCCS S. Maugeri; 6/125 (4.8%) at ASP Redaelli respectively.

Conclusion: Resistance of P. mirabilis to expanded-spectrum cephalosporins is an increasing problem in several settings. Acquired AmpC-type b-lactamases are overall less common than class A ESBLs, but emergence of these enzymes in P. mirabilis has been reported in some areas. This report focus on the increasing diffusion of an AmpC-type variant in P. mirabilis; the clinical strains investigated in this work were all clonally related, and shared a common structure of genetic environment of CMY-16 determinant, suggesting a worrisome vertical spread of diffusion.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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