title: Prevalence and mechanisms of β-lactam resistance in Haemophilus haemolyticus.
abstract: OBJECTIVE
  To compare the phenotypic and genotypic β-lactam resistance profiles of non-typeable Haemophilus influenzae (NTHi) and the closely phylogenetically related Haemophilus haemolyticus.
  
  
  METHODS
  XV-dependent Haemophilus species isolated as normal flora from nasopharyngeal and throat swabs (n = 312) were screened by PCR for markers to determine NTHi and H. haemolyticus identity. All NTHi and H. haemolyticus isolates were subsequently tested for susceptibilities to ampicillin and amoxicillin/clavulanate, and characterized with respect to the presence of blaTEM, blaROB and ftsI gene mutations.
  
  
  RESULTS
  Of the 312 isolates, 236 (75%) were identified as NTHi, 61 (20%) as H. haemolyticus and 15 (5%) as equivocal. PCR for resistance genes showed 15.7% (37/236) of NTHi and 13.1% (8/61) of H. haemolyticus isolates were blaTEM positive and none was positive for blaROB. The blaTEM genes of both species were encoded on similar replicons and associated with the same promoter types. Altered penicillin-binding protein 3 due to the N526K substitution accounted for 31% of both NTHi (73/236) and H. haemolyticus (19/61) isolates, respectively. The presence of N526K in both NTHi and H. haemolyticus was associated with slightly raised ampicillin MICs compared with the H. influenzae Rd and H. haemolyticus ATCC 33390 control strains. In addition, some NTHi gBLNAR-associated substitutions were seen in H. haemolyticus with and without N526K, and appear to represent part of the baseline genotype of that species.
  
  
  CONCLUSIONS
  The phenotypic and genotypic β-lactam resistance in NTHi and H. haemolyticus is very similar, such that H. haemolyticus may represent a reservoir for β-lactam resistance determinants for NTHi.
authors: School of Human Life Sciences, University of Tasmania, Launceston, Tasmania, Australia. elizabeth.witherden@utas.edu.au
authors: Elizabeth A
authors: EA
authors: Witherden
authors: Stephen G
authors: SG
authors: Tristram
mesh_terms: D000293:Adolescent; D000328:Adult; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002675:Child, Preschool; D004269:DNA, Bacterial / Q000235:genetics; D005260:Female; D006190:Haemophilus / Q000187:drug effects* / Q000235:genetics; D006192:Haemophilus Infections / Q000453:epidemiology* / Q000382:microbiology; D006801:Humans; D007223:Infant; D008297:Male; D008826:Microbial Sensitivity Tests; D016133:Polymerase Chain Reaction; D015995:Prevalence; D055815:Young Adult; D018440:beta-Lactam Resistance; D047090:beta-Lactams / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D047090:beta-Lactams