Haemophilus influenzae biofilms: hypothesis or fact?

Many publications state that nontypeable Haemophilus influenzae (NTHi) produces biofilms. Here, we review many of the publications that have led to acceptance by some that NTHi expresses a biofilm-specific phenotype as a distinct part of its life cycle. Biofilm formation was originally invoked to explain the failure to culture NTHi from middle-ear effusions, recalcitrance to antibiotics and its pathogenic behaviour. We argue that the current evidence for NTHi biofilm formation in vitro and in vivo is inconclusive. We consider that NTHi biofilm is hypothesis not fact, and although it might yet prove to be correct, there has been little or no consideration of alternative interpretations for the in vitro and in vivo observations. Uncritical acceptance of a distinctive NTHi biofilm phenotype has the potential to mislead and could confuse and compromise research efforts aimed at improving management and prevention of NTHi diseases of the human respiratory tract.