In vitro interference of tigecycline at subinhibitory concentrations on biofilm development by Enterococcus faecalis.
OBJECTIVE
Since biofilm formation is the hallmark of Enterococcus faecalis isolates, the aim of this study was to quantify biofilm formation in the presence of subinhibitory concentrations of tigecycline.


METHODS
Interference of tigecycline on biofilm formation was spectrophotometrically quantified using 20 biofilm-producing E. faecalis isolates with tigecycline MICs of 0.12 (8 strains) or 0.25 mg/L (12 strains). Biofilm production was measured in antibiotic-free tryptic soy broth supplemented with 1% glucose and compared with biofilm production in the same medium with tigecycline at subinhibitory concentrations (0.25× or 0.5× MIC, similar to trough concentrations in serum or concentrations in the colon after a standard dose) by reading the optical density at 450 nm (OD(450)) after staining with Crystal Violet.


RESULTS
In the presence of subinhibitory tigecycline concentrations, pooled OD(450) values for the 20 strains [median (IQR)] were significantly lower than those for controls: 0.468 (0.379-0.516) for antibiotic-free controls versus 0.295 (0.200-0.395) for 0.25× MIC tigecycline (P < 0.001) and 0.287 (0.245-0.479) for 0.5× MIC tigecycline (P < 0.001), with significant differences between pooled OD(450) values obtained with each concentration of tigecycline (P = 0.022). In 17 out of 20 (85%) strains the OD(450) obtained with 0.25× MIC tigecycline was significantly (P < 0.05) lower than the basal OD(450), while this occurred in 12 out of 20 (60%) strains with 0.5× MIC.


CONCLUSIONS
In vitro tigecycline subinhibitory concentrations were able to interfere with biofilm formation by E. faecalis.
Microbiology Department, Hospital Central de la Defensa Gómez-Ulla, Madrid, Spain.
Juan Ramón
JR
Maestre
Lorenzo
L
Aguilar
María
M
Mateo
María-José
MJ
Giménez
María-Luisa
ML
Méndez
Luis
L
Alou
Juan-José
JJ
Granizo
José
J
Prieto
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development*; D003470:Culture Media / Q000737:chemistry; D013293:Enterococcus faecalis / Q000187:drug effects* / Q000502:physiology*; D005840:Gentian Violet / Q000378:metabolism; D006801:Humans; D008826:Microbial Sensitivity Tests; D008911:Minocycline / Q000031:analogs & derivatives* / Q000494:pharmacology; D013053:Spectrophotometry; D013194:Staining and Labeling / Q000379:methods; D000078304:Tigecycline
D000900:Anti-Bacterial Agents; D003470:Culture Media; D000078304:Tigecycline; D008911:Minocycline; D005840:Gentian Violet