Table 1

Concentration of antibiotic producing no turbidity after azithromycin treatment for S. pneumoniae clinical isolates grown in planktonic culture and as biofilms treated with a twofold serial dilution of azithromycin from 2 mg ml^-1 to 2 μg ml^-1 for 24 hours.

S. pneumoniae isolate

Serotype

Planktonic IC* (μg ml^-1)

Biofilm IC^† (μg ml^-1)

Fold Increase (-)

n

BS 68

9V

< 2

4

> 2

6

BS 69⁺

14

< 2

125

> 64

8

BS 71

3

< 2

4

> 2

6

BS 72⁺

23F

< 2

2000

> 1000

6

BS 73

6A

< 2

4

> 2

6

BS 75⁺

19F

< 2

62

> 32

8

* Highest concentration of azithromycin producing no turbidity after overnight incubation with antibiotic with planktonic cells.

^† Highest concentration producing no turbidity after overnight incubation with antibiotic with biofilm cells.

Turbidity was scored by eye as well as by determining the highest concentration that was within the standard deviation of the optical density measurements of 6–8 replicate untreated controls (no antibiotic).

⁺ Indicates high ranked BFI strain.

Hall-Stoodley et al. BMC Microbiology 2008 8:173   doi:10.1186/1471-2180-8-173