title: Serotypes, antimicrobial susceptibility, and beta-lactam resistance mechanisms of clinical Haemophilus influenzae isolates from Bulgaria in a pre-vaccination period.
abstract: OBJECTIVE
  To determine the serotypes, antimicrobial susceptibility, and beta-lactam resistance mechanisms of Haemophilus influenzae strains isolated from invasive and respiratory tract infections (RTIs) prior to the introduction of Haemophilus influenzae type b (Hib) vaccination in Bulgaria.
  
  
  METHODS
  A total of 259 isolates were serotyped by polymerase chain reaction. Susceptibility to antibiotics and beta-lactamase production were determined, and DNA sequencing of the ftsI gene was performed for ampicillin non-susceptible strains.
  
  
  RESULTS
  The invasive H. influenzae infections in children were mainly due to serotype b (94.5% in meningitis and 88.9% in other invasive cases). Non-typeable strains (97.4%) were the most frequently found H. influenzae strains in RTIs both in children and adults. Non-susceptibility to ampicillin occurred in 22% of all strains. Ceftriaxone and levofloxacin were the most active agents tested. Ampicillin resistance occurred in 34.4% of invasive strains, and beta-lactamase production was the only mechanism found. Among respiratory tract isolates, ampicillin non-susceptible strains (18%) were classified into the following groups: beta-lactamase-positive, ampicillin-resistant (BLPAR) strains (7.2%); beta-lactamase-negative, ampicillin-non-susceptible (BLNAR) strains (8.2%); and beta- lactamase-positive, amoxicillin-clavulanate-resistant (BLPACR) strains (2.6%). Among 21 BLNAR and BLPACR strains there were 9 different patterns of multiple-amino acid substitutions in penicillin-binding protein 3. Of these, most isolates (81.0%) belonged to group II, defined by the Asn526Lys substitution.
  
  
  CONCLUSIONS
  Beta-lactamase production was more common among invasive strains than in respiratory isolates. BLNAR and BLPACR H. influenzae were found only among respiratory tract isolates.
authors.affiliation: Department of Medical Microbiology, Faculty of Medicine, Medical University of Sofia, Sofia, Bulgaria. lenasetchanova@hotmail.com
authors.forename: Lena Petrova
authors.initials: LP
authors.lastname: Setchanova
authors.forename: Tomislav
authors.initials: T
authors.lastname: Kostyanev
authors.forename: Rumyana
authors.initials: R
authors.lastname: Markovska
authors.forename: George
authors.initials: G
authors.lastname: Miloshev
authors.forename: Ivan Gergov
authors.initials: IG
authors.lastname: Mitov
mesh_terms: D000293:Adolescent; D000328:Adult; D019943:Amino Acid Substitution; D000668:Ampicillin Resistance; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002031:Bulgaria / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D005798:Genes, Bacterial; D006192:Haemophilus Infections / Q000453:epidemiology / Q000382:microbiology*; D018073:Haemophilus Vaccines / Q000008:administration & dosage; D006193:Haemophilus influenzae / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D006801:Humans; D008826:Microbial Sensitivity Tests; D016133:Polymerase Chain Reaction; D015995:Prevalence; D017422:Sequence Analysis, DNA; D012703:Serotyping
chemical_list: D000900:Anti-Bacterial Agents; D018073:Haemophilus Vaccines