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Multiple combination antibiotic susceptibility testing of nontypeable Haemophilus influenzae biofilms
Robert Slinger1, Francis Chan, Wendy Ferris
1Department of Pediatrics, Ottawa, Ontario, Canada K1H 8L1. slinger@cheo.on.ca
Abstract:
Haemophilus influenzae is a cause of otitis media with effusion (OME). Animal models demonstrate growth of H. influenzae biofilms in OME, which may explain why OME does not respond well to conventional antibiotic therapy. Using a previously developed in vitro model, we performed H. influenzae susceptibility studies to see if H. influenzae biofilm cultures were more resistant to antibiotics than planktonic (broth) cultures, and to determine which antibiotics were most effective against H. influenzae biofilms. H. influenzae isolates were grown as biofilms on polystyrene pins. Biofilm and planktonic minimum inhibitory concentrations (MICs) were measured for 8 antibiotics, and multiple combination testing was performed with 66 groupings of 1, 2, or 3 antibiotics. We found that biofilm cultures were more resistant to antibiotics than planktonic ones. Antibiotic combinations containing rifampin and ciprofloxacin were most effective against biofilms. Biofilm testing reveals differences in effectiveness among antibiotics not apparent from conventional susceptibility testing, and suggests novel antibiotic regimens that could be studied for treatment of OME.
Insights
Haemophilus influenzae biofilms are more resistant to antibiotics than planktonic cultures. Novel antibiotic combinations, particularly those with rifampin and ciprofloxacin, show promise for treating otitis media with effusion (OME).
Area of Science:
- Microbiology
- Infectious Diseases
- Otolaryngology
Background:
- Haemophilus influenzae is a common cause of otitis media with effusion (OME).
- OME often shows poor response to standard antibiotic treatments.
- In vitro and animal models suggest H. influenzae biofilms contribute to OME's antibiotic resistance.
Purpose of the Study:
- To compare antibiotic susceptibility between H. influenzae biofilm and planktonic cultures.
- To identify antibiotics and combinations effective against H. influenzae biofilms.
- To inform potential new therapeutic strategies for OME.
Main Methods:
- H. influenzae isolates were cultured as biofilms on polystyrene pins.
- Minimum inhibitory concentrations (MICs) were determined for 8 antibiotics against biofilm and planktonic cultures.
- Combination testing was performed using 66 different antibiotic groupings (1-3 drugs).
Main Results:
- H. influenzae biofilm cultures exhibited significantly higher antibiotic resistance compared to planktonic cultures.
- Antibiotic combinations including rifampin and ciprofloxacin demonstrated the greatest efficacy against biofilms.
- Biofilm susceptibility testing revealed differential antibiotic effectiveness not observed in standard testing.
Conclusions:
- Antibiotic resistance in H. influenzae biofilms is a key factor in OME treatment failure.
- Rifampin and ciprofloxacin combinations represent a promising novel therapeutic approach for OME.
- In vitro biofilm susceptibility testing is crucial for guiding effective antibiotic selection for OME.
