Background and Aims Haemophilus influenzae (Hi) is a human pathogen responsible for various infections in both children and adults.
We describe in this study the susceptibility patterns and β-lactam resistance mechanisms of 62 ampicillin-resistant H.i strains isolated from children at the children’s hospital of Tunis during 2009 and 2010.
Materials and Methods All strains were identified and serotyped using conventional methods. Antimicrobial susceptibility was determined by E-test. The antibiotics tested were amoxicillin, amoxicillin-clavulanate, cefixim, cefuroxim, cefotaxim, cefpodoxim and imipenem. The β-lactamase production was performed using the nitrocefin test. We determined the resistance genes (bla TEM-1, bla ROB-1 and ftsI) by PCR.
Results Isolates were identified as non capsulated and were classified into 3 groups according to their β-lactam resistance mechanisms: β-lactamase positive ampicillin-resistant (BLPAR: 50%); β-lactamase negative ampicillin-resistant (BLNAR: 40.32%) and β-lactamase positive amoxicillin-clavulanate-resistant (BLPACR: 9.68%). All strains showed high amoxicillin, amoxicillin-clavulanate, cefuroxim and imipenem MICs. Among these, the less active one was imipenem with MIC50 >32mg/l in all strains. The highest MICs of cefuroxim were in BLPACR strains (2–4mg/l). MICs ranges of this antibiotic were 0.5–6 mg/l in BLNAR and 0.125–4 mg/l in BLPAR. Cefotaxim, cefixim and cefpodoxim were the most active agents tested against our strains.
Conclusion This study indicates that many β-lactams are ineffective among some Hi strains. So, it’s important to have an appropriate usage of antibiotics to stop these phenomena. We must make other investigations to know if these strains belonged to the same clone or if it’s a question of an outbreak in our hospital.