Antibiotic susceptibility and genotypic characterization of Haemophilus influenzas strains isolated from nasopharyngeal specimens from children in day-care centers in eastern France

Objective To determine the overall carriage rate for Haemophilus influenzae in young children in day-care centers, the frequency of resistance to vari ous classes of antibiotic, and the clonal relationship between isolates of the various resistant phenotypes. Methods Nasopharyngeal (NP) specimens were obtained and cultured on chocola te agar with bacitracin. Antibiotic susceptibility testing and serotyping w ere performed for all isolates. The genetic polymorphism of ampicillin-susc eptible and beta -lactamase-producing isolates was studied by pulsed-field gel electrophoresis using SmaI. Results Of the 596 NP secretion cultures, 152 (25.5%) were positive for H. influenzae. Sixty-four (42.1%) isolates produced beta -lactamase and two (1 .3%) were ampicillin resistant but did not produce beta -lactamase. We were unable to serotype 150 isolates; one isolate belonged to capsular serotype e and one to serotype f. Forty-six major DNA patterns were identified amon g 76 randomized isolates. beta -lactamase producing isolates more frequentl y showed EP than ampicillin-susceptible isolates P < 10(-4). The frequency of isolates with EP was significantly lower in day-care centers attended by less than 20 children than in those attended by more than 20 children (P = 0.020). Conclusions Resistance due to <beta>-lactamase production has disseminated in some day-care centers, mostly by person-to-person spread but also via th e possible conjugal transfer of large plasmids between strains. The size of day-care centers may affect the risk of transmission.