Antimicrobial Susceptibility Patterns Of Haemophilus Influenzae Isolated From Lower Respiratory Tract Infections

Research Article
Shaima'a R. Al-Salihy
H. influenza, Lower respiratory tract infection, Antimicrobial resistance

Objective: Determination of antimicrobial susceptibility patterns of H. influenzae isolated from lower respiratory tract infections to commonly used antimicrobials. Materials and methods: 142 sputum samples were collected from patients with lower respiratory tract infection from June/2013 to April/2014. Specimens were cultured on chocolate agar supplemented with multivitex under 10% CO2 . Isolation and identification of H. influenzae were based on standard bacteriological and biochemical criteria. Serotyping with specific antisera (Bio-RAD laboratories-Japan) was carried out by slide agglutination method. Antibiotic sensitivity test to 12 antimicrobials was determined by disc diffusion method. Furthermore, the minimum inhibitory concentration (MIC) of these antibiotics was assessed by agar dilution method. Results: Throughout the study period 40 isolates of H. Influenzae were obtained. 29(72.5%) were recovered from males (mean age 46 ±18 years), and 11 from females (mean age 41.1 ±13.3 years). All isolates were sensitive to cefotaxime, pipracillin and amikacin. The sensitivity rate to rifampicin was 77.5%, amoxacillin 67.5%, gentamycin 62.5%, vancomycin 60%, chloramphenicol 72.5%, tetracycline 57.5% and for ciprofloxacin 70%. The resistance rate to ampicillin was 72.5%. None of the isolates were sensitive to cloxacillin. The median MIC for cefotaxime, pipracillin and amikacin was 0.5 mg/ml for both type b and nontype b isolates. The median MIC for cloxacillin, gentamycin and rifampicin was >1024, 0.5 and 0.5 mg/ml respectively for both serotypes. Otherwise, the difference in the mean MIC between type b and nontype b was insignificant except for chloramphenicol (P= 0.03) and rifampicin (P=0.02). However, a part from cefotaxime, pipracillin, amikacin and cloxacillin, 30% of isolates that were resistant by disc method became sensitive when retested by agar dilution method. The disc diffusion method showed that 97.5% of isolates were resistant to more than one antimicrobial, while agar dilution method revealed that 87.5% of the isolates were resistant to more than three antimicrobials. The sensitivity of H. influenzae to different antimicrobials neither affected by patient’s age and sex nor by serotype. Conclusion: H. influenzae recovered from lower respiratory tract infections were variably resistant to antimicrobials. Continuous surveillance of antimicrobial susceptibility at the local and national level remains important, in order to guide appropriate empirical antimicrobial therapy.