ABSTRACT
Haemophilus influenzae can cause invasive and severe infections in both adults and children such as otitis media, sinusitis, pneumonia, meningitis and bacteremia. The emerging antibiotic resistance in recent years against ampicillin and several other antibiotics among strains of H. influenzae gives cause for serious concern. Here, we investigate ß-lactamase (BL) activity in clinical isolates of H. influenzae, profile their resistance to antibiotics, and characterize the clonal relationship of the isolates. Antibiotic susceptibilities of 92 clinical isolates of H. influenzae (March 2011-May 2012) were determined using the disk diffusion method according to the Clinical & Laboratory Standards Institute (CLSI), and BL activity was detected using the nitrocefin disk method. The Rep-PCR method was used to characterize clonality of the isolates. All strains were found to be susceptible to levofloxacin and cefotaxime. Four isolates out of 92 (4.3%) were found resistant to ampicillin, one isolate (1.1%) was resistant to amoxicillin/clavulanic acid, 21 isolates (22.8%) were resistant to trimethoprim-sulfamethoxazole (SXT), and three isolates (3.3%) showed BL activity. One strain was BL-negative but resistant to ampicillin. The three isolates with BL activity and four isolates with resistance to ampicillin did not have a clonal relationship. Three distinct clones [clone A (with subclones A1 and A2), clone B, and clone C] were identified among the SXT-resistant strains. Most of the H. influenzae isolates in this study were susceptible to the antibiotics while SXT resistance was relatively more prevalent, which suggests that significant obstacles in the therapeutic use of antibiotics against H. influenzae strains are not expected in our region.
Subject(s)
Anti-Bacterial Agents/pharmacology , Disk Diffusion Antimicrobial Tests , Haemophilus influenzae/isolation & purification , Adult , Blood/microbiology , Bronchoalveolar Lavage Fluid/microbiology , Cerebrospinal Fluid/microbiology , Child , Disk Diffusion Antimicrobial Tests/methods , Drug Resistance, Microbial/drug effects , Drug Resistance, Microbial/genetics , Ear/microbiology , Genotype , Genotyping Techniques/methods , Haemophilus influenzae/genetics , Humans , Infant , Microbial Sensitivity Tests/methods , Sputum/microbiology , beta-Lactamases/geneticsABSTRACT
AIM: The in vitro activity of colistin in combination with sulbactam, netilmicin, and vancomycin against colistin-resistant A. baumannii strains was investigated. Furthermore, the clonal relationship of the strains was analyzed. METHODS: Clonal relationship was investigated using rep-PCR. To screen for synergysm, the fractional inhibitory concentration index (FICI) was calculated using checkerboard assay. The killing kinetics of the combination of colistin with vancomycin was assessed using time-kill assay. RESULTS: Three different clones were found among 10 clinical isolates of colistin-resistant A. baumannii strains. Thereof, 8 strains were susceptible to netilmicin. Synergistic interaction was detected in 1 strain with the combination of colistin-netilmicin, in 5 strains with colistin-sulbactam, and in 9 strains with colistin-vancomycin. None of combinations had antagonistic activity. Colistin-vancomycin combination resulted in rapid bactericidal activity. CONCLUSION: These results show a distinct in vitro synergism between colistin and vancomycin, which might be useful to treat infection with multiple-resistant strains, prevent emergence of resistant strains, and to lower doses for both antibiotics to be used.
