Restriction fragment mapping of nontypable haemophilus influenzae: a new tool to study this middle ear pathogen

Isolates of nontypable haemophilus influenzae (NTHI) recovered from paired nasopharyngeal (NP) and middle ear (ME) fluid cultures performed simultaneously on seven children with otitis media with effusion (OME) were studied by analysis of the restriction fragment patterns produced from total genomic DNA. This method provides a sensitive measure of the genetic similarities between strains. In the seven pairs examined, the NP and ME strains were indistinguishable from one another, whereas each pair was distinct from the other, except for two siblings in whom all four strains were identical. This information provides evidence that the pathogenesis of OME caused by NTHI involves spread of the bacteria from NP to the ME. Analysis of paired NP and ME isolates from three children with recurrent OME caused by NTHI indicated that the second episode was caused by the reinfection with a different strain rather than persistence and reemergence of the first strain. Finally, DNA analysis of strains from two siblings with concurrent OME suggested that person-to-person transmission of NTHI can occur among children. These findings suggest that at any one time the NTHI population in the NP is relatively homogenous, at least at the time of acute upper respiratory disease. Our observation that the strains present at the second episode of otitis media were different than the strains present in the first episode is consistent with strain replacement in the NP. Restriction fragment mapping analysis of genomic DNA of NTHI could provide a powerful tool for investigating the rate of turnover of the NTHI population in the NP.