Analysis ofHaemophilus influenzaeserotype f isolated from three Japanese children with invasiveH. influenzaeinfection. Issue 4 (April 2015) - Hoshino, Tadashi
Abstract : N/A: In Japan, publicly subsidized Haemophilus influenzae serotype b vaccines became available in 2011; consequently, the incidence of invasive H. influenzae infection in paediatric patients of less than 5 years of age decreased dramatically. In 2013, the first case of H. influenzae serotype f (Hif) meningitis in a Japanese infant was reported, and another case of Hif meningitis in a Japanese infant was observed in 2013. We experienced a fatal paediatric case of Hif bacteraemia in 2004; therefore, we conducted an analysis of the three Hif strains isolated from these three Japanese children with invasive Hif infections. All three strains were β‐lactamase‐non‐producing, ampicillin‐sensitive strains, with MICs of 1 µg ml −1 or less. However, one of the three strains showed slightly elevated MICs for ampicillin (1 µg ml −1 ), cefotaxime (0.25 µg ml −1 ) and meropenem (0.13 µg ml −1 ). A molecular analysis by multilocus sequence typing identified all three strains as sequence type (ST) 124, which is a predominant invasive Hif strain in many countries. Sma I‐digested PFGE showed variable DNA fragmentation patterns among the strains, suggesting that some highly virulent strains have originated from a single ST124 clone and caused invasive Hif infections in Japan. Additional studies are needed to determine the factors that have led to the clonal expansion of virulent ST124 strains.