Efficacy of Vancomycin against Biofilms of Neonatal Staphylococcus epidermidis Bloodstream Isolates
Methods: BF’s of 7 neonatal S. epidermidis isolates were produced using 96-well microtiter plates. Following appropriate dilutions from overnight cultures grown in TSB medium, 0.2ml of 10^6 bacteria/mL were used to inoculate microtiter wells. After a 24h-incubation at 37oC, the plates were washed with phosphate-buffered saline solution and stained with 1% safranin solution. BF formation was evaluated spectrophotometrically by optical density (OD) measurement at 595nm. The BF producer strain 35983 RP12 was used as control. BF-producing isolates were then incubated with no antibiotic or with VAN at two-fold dilutions of 0.007-256mg/L for an additional 24h, and bacterial damage (BD) was assessed by XTT reduction assay. BF MIC were determined as >50% BD compared to controls. All isolates were studied 4 times with 5 experimental replicates per condition. Differences were compared by ANOVA with Bonferroni post-test.
Results: Two of seven S. epidermidisisolates were strong BF producers (OD>0.270; SP), whereas the remaining five produced BF of intermediate strength (0.14<OD<0.270; IP). Median VAN BF MIC for IP isolates was 32mg/L, the same as that of the control strain (p=ns). Maximum BD for those isolates was 65.6% at 64mg/L. VAN did not reach a BF MIC for SP isolates, as the maximum BD produced was 45% at 128mg/L. Of note, VAN efficacy at higher concentrations tended to decrease (45%-41.1% for SP and 64-60% for IP at 128-256mg/L).
Conclusion: Despite the variable BF production among neonatal S. epidermidis isolates, high MICs were observed for VAN against mature BF of S. epidermidis. Even at very high concentrations, VAN was not totally effective against BF, suggesting difficulty in eradication of S. epidermidisBF.
Funded by NeoVanc European Commission program.
V. Ramos Martin, None
W. Hope, None
E. Roilides, None