Effectiveness of Topical Antibiotics on Staphylococcus Aureus Biofilm in Vitro

Background

In vitro biofilm-producing capacity in isolates of Staphylococcus aureus and Pseudomonas aeruginosa collected from the sinus cavities after endoscopic sinus surgery (ESS) are associated with a poor outcome in patients with chronic rhinosinusitis (CRS). However, conventional oral antibiotic therapy is frequently ineffective in eradicating bacteria in the biofilm form. Increasing the concentration of antibiotics may offer a means of countering this resistance. The aim of this study was to determine the in vitro activity of moxifloxacin (MOXI) against S. aureus in biofilm form (recovered from patients with CRS at least 1 year post-ESS).

Method

This study was performed in a research microbiology laboratory, where five isolates of S. aureus with known biofilm-forming capacity were cultured in Tryptic Soy Broth 0.5% glucose in 96-well plates at 37°C for 24 hours. After visual confirmation of biofilm formation, plates were incubated in phosphate-buffered saline (PBS) or with MOXI at concentrations of 0.1×, 1×, 100×, and 1000× minimal inhibitory concentration (MIC) for an additional 24 hours. Biofilm from 3 wells of each concentration were collected and sonicated and the number of viable bacteria was determined by serial dilution and plating.

Results

After incubation, the number of viable bacteria was similar for nontreated and MOXI-treated biofilms at MIC and sub-MIC levels. However, MOXI at 1000X (0.1–0.2 mg/mL) gave a 2 to 2.5 log reduction in number of viable bacteria.

Conclusion

In vitro results show that increased concentrations of antibiotics, easily attainable in topical solutions, are effective in killing bacteria in bacterial biofilms. This suggests a role for topical antibiotic therapies in the treatment of biofilm infections.

Biofilm Formation by Staphylococcus Aureus and Pseudomonas Aeruginosa is Associated with an Unfavorable Evolution after Surgery for Chronic Sinusitis and Nasal Polyposis

OBJECTIVES: To determine whether biofilm-forming capacity of bacteria demonstrated in chronic rhinosinusitis (CRS) has an impact on persistence of the disease following endoscopic sinus surgery (ESS).

METHOD: Thirty-one bacterial strains recovered from 19 patients with CRS at least 1 year post-ESS. Evolution of disease was assessed by questionnaire and endoscopy as favorable or unfavorable. The bacteria were cultured on a 96-well culture plaque and a semi-quantitative method using crystal violet to quantify biofilm production was used.

RESULTS: Twenty-two of 31 samples produced a biofilm thicker or equal to the positive control. Biofilm production was noted in 6/10 Pseudomonas aeruginosa isolates, 8/10 Staphylococcus aureus, and 8/11 coagulase-negative staphylococci. Biofilm formation was associated with a poor evolution for Pseudomonas aeruginosa and Staphylococcus aureus, but not coagulase-negative staphylococcus.

CONCLUSION: There is a correlation between in vitro biofilm-producing capacity by Pseudomonas aeruginosa and Staphylococcus aureus and unfavorable evolution after ESS, suggesting a role for biofilm production in chronic sinusitis.

Use of an in vitro assay for determination of biofilm-forming capacity of bacteria in chronic rhinosinusitis

BACKGROUND

Bacterial biofilms are increasingly implicated in the pathogenesis of chronic disease and have been established in several chronic ear, nose, and throat conditions, including chronic sinusitis (CRS). However, this relies on specialized imaging methods not widely available. We wished to assess the capacity of an easily performed, inexpensive in vitro test to assess biofilm production by bacteria recovered from individuals with CRS with or without nasal polyposis.

METHODS

Bacterial isolates were recovered from patients consulting an academic tertiary rhinology practice. Biofilm formation was determined with an in vitro staining method using crystal violet. Ten isolates of Pseudomonas aeruginosa, Staphylococcus aureus, and 11 of coagulase-negative staphylococcus from patients with CRS having previously undergone endoscopic sinus surgery for >1 year were assessed. Samples were cultured 24 hours at 37 degrees C on 96-well plates in tryptic soy broth 0.5% glucose medium. After staining with crystal violet, optical density at 570 nm was measured to quantify biofilm production. Biofilm-forming capacity was compared with positive and negative controls for each species obtained from commercial sources.

RESULTS

Positive controls all grew biofilms, with a tendency of lesser biofilm formation at higher dilutions. Twenty-two of 31 clinical samples produced a biofilm greater or equal to the positive control. Biofilm was recovered consistently for all three species studied.

CONCLUSION

This in vitro assessment method is capable of detecting biofilm-forming capacity in bacteria recovered from individuals with CRS. This simple assay may be a useful complement to existing techniques for clinical research.