Isolation of multidrug-resistant Haemophilus influenzae harbouring multiple exogenous genes from a patient diagnosed with acute sinusitis.

In paediatric patients, β-lactams and macrolides are widely used to treat acute otitis media and sinusitis, which are often caused by either Streptococcus pneumoniae or Haemophilus influenzae. However, resistant isolates have emerged and are becoming more prevalent. H. influenzae generally acquires antimicrobial resistance by mutation or by expression of β-lactamase. In this study, we isolated H. influenzae from a paediatric patient diagnosed with acute sinusitis. This strain harboured multiple exogenous resistance genes: bla, mef(A) and tet(M). DNA sequencing suggested that both mef(A) and tet(M) had been transferred from S. pneumoniae or another Streptococcus. This typical outpatient had not been exposed to excessive levels of antibiotics and had no underlying diseases, strongly suggesting that this type of resistant isolate could become more prevalent.