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P. aeruginosa with hypermutable phenotype in cystic fibrosis patients

Abstract number: P2100

Manno G., Melioli G., Mentasti M., Cirilli N., Manso E., D'Aprile A., Gioffrè F., Scuteri D., Morelli P.

Background: Hypermutable phenotype (HPM) strains are those that have an increased (up to 1,000-fold) spontaneous mutation rate due to defects in genes involved in DNA repair or error avoidance systems. The presence, in cystic fibrosis (CF) patients, of a high proportion of HPM (or mutator) P. aeruginosa (PA) strains, was documented (Oliver et al. 2000). The acquisition of a stable mutator phenotype may confer a selective advantage for PA in the pulmonary environment in CF, because both high mutation rates and increased promiscuous recombination allow faster adaptation. Aim. Determine occurrence and antibiotic resistance PA HMPs in Italian CF pts.

Methods: 154 non-mucoid, 100 mucoid and 18 SCV non-multiresistant PA from 170 pts from 4 Italian CF Centres were studied. HMP was determined as previously described (Macia et al. 2004) by disk-diffusion and Etest for 10 antibiotic; results were read after 24 h at 35°C; plates were re-incubated for further 12 h and HMPs were defined as strains showing a sub-population grown after 36 h and resistant to 3 o more antibiotics. A preliminary comparison between the reference mutation frequencies measurement test (Oliver et al. 2000) was performed on 10 PA strains and PA01, to assess the laboratory agreement with the disk-diffusion test for hypermutability. The genetic relationship of all PA was determined by BOX-PCR.

Results: Our results showed that Macia's test and the reference mutation frequencies measurement test overlap in assessing HMP strains. 32% of pts was colonised with HMPs, mean age 28 yrs; pts without HMPs showed a mean age of 17 yrs. HMPs distribution was 17% in non-mucoid, 28% in mucoid and 39% in SCV strains. No correlation with HMP occurrence and shared genotypes was found. The % of antibiotic resistance in HMPs was AK 33, TO 12, CL9, FEP 51, CAZ 41, MEM 26, P/T42, T/C 47, CIP 35 and LEV 39.

Conclusion: The occurrence of 32% found, confirm previous rates reported from CF pts in other country (Oliver et al. 2000). The high occurrence found of in mucoid (28%) and SCV (39%) strains, typical in long term chronic colonisation, stress the possible role of CF lung environment in inducing the expression of HMPs. In these strains the emerging resistance to TO and particularly to CL is worrisome for antimicrobial treatment implications.

This study was supported by the Italian Cystic Fibrosis Foundation Grant FFC#8/2005

Session Details

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