Phenotypic and molecular characterization of beta-lactam resistance and capsular typing of colonizing Haemophilus influenzae strains isolated from neutropenic patients in Tunisia.

OBJECTIVE

The aim of this study was to determine the overall percentage of beta-lactams susceptibility, beta-lactamase production, penicillin binding protein (PBP) modification and serotypes of colonizing Haemophilus influenzae strains.

DESIGN

A total of 50 isolates of colonized H. influenzae, isolated from neutropenic patients. The prevalence of beta-lactams resistance and beta-lactamase production were recorded for each strains using E-test strips and chromogenic cephalosporin test, then were determined their resistance genes (bla(TEM) and bla(ROB)) by PCR as well as their capsular types by standard slide agglutination serotyping (SAST) and capsular genes amplification.

RESULTS

Thirty-two percent of the 50 strains were amoxicillin resistant, among these, 20% were resistant by beta-lactamase production, and they produced all type TEM beta-lactamase. Four percent of the isolates had PBP modification and three strains (6%) associated the two resistance mechanisms. Slide agglutination serotyping showed that 95.8% of the strains were unencapsulated, and 4.1% were of serogroup b. The result was confirmed by PCR capsular typing.

CONCLUSION

By the light of these results, our findings suggest that it becomes important to follow the evolution of the resistance background of our strains, and that the majority of colonizing H. influenzae strains isolated in our center are unencapsulated.