β-Lactamase Activities and Resistance to Antibiotics of Haemophilus influenzae, H. parainfluenzae and H. aphrophilus Strains Identified in Throat Cultures from Children

Haemophilus bacteria are normally present in the upper respiratory tract of healthy individuals. However, these bacteria could be opportunistic pathogens especially in children. The present study was conducted to determine beta-lactamase activity of Haemophilus from the throat cultures of children with upper respiratory tract infections. 154 Haemophilus strains were isolated from throat swabs of 208 children whom had upper respiratory tract infections. Among the 154 Haemophilus strains isolated, 117 H. influenzae (76%), 35 H. parainfluenzae (22.7%), and two H. aphrophilus (13%) were identified by API NH. beta-Lactamase activity was positive in 42 isolates of 117 H. influenzae isolates, while it was negative in 75 isolates. beta-Lactamase activity was positive in 20 H. parainfluenzae isolates, and negative in 15. All the H. aphrophilus isolates were beta-lactamase negative. It is known that beta-lactamase positive Haemophilus bacteria are resistant to some antibiotics. Therefore, the antibiotic resistance of Haemophilus was further investigated in relation to beta-lactamase activity. The in vitro antibacterial susceptibilities of Haemophilus strains for ampicillin, sulbactam-ampicillin, trimethoprim-sulfamethoxazole, gentamicin, chloramphenicol and ciprofloxacin were tested by disk diffusion method on chocolate agar. In 42 beta-lactamase-positive H. influenzae isolates, 32 isolates were resistant against ampicillin. In 20 beta-lactamase-positive H. parainfluenzae isolates, 16 were resistant against ampicillin. The two beta-lactamase negative H. aphrophilus were sensitive to ampicillin. Biotypes and serotypes were also investigated. Biotypes of H. influenzae strains were as follows: 40 strains biotype II, 25 strains biotype I, 14 strains biotype III, and 38 strains biotypes VII, VIII, V, and IV. Biotypes of 35 H. parainfluenzae strains were: 6 strains biotype III, 5 strains biotype I, 5 strains biotype IV. Biotypes of remaining 19 isolates were II, VIII, VI and VII. The serotypes of H. influenzae strains were determined by specific antiserums. Serotypes of 117 H. influenzae found were type a, b, c, d, and f.