Research

Background: Biofilm formation among staphylococci is common; however the optimal conditions for in vitro biofilm formation of Staphylococcus epidermidis (SE) and Staphylococcus aureus (SA) are unknown. Cation adjustment is not always mentioned in published work, since media may come cation adjusted from the manufacturer. We evaluated the effects of cation adjustment of tryptic soy broth (TSB) using CaCl2 and MgSO4.
 
Methods: Control SE strains included biofilm positive (BF+) ATCC 35984 and isogenic biofilm negative (BF-) mutant M7 and 3 control SA strains were tested. Biofilm was evaluated by a modified version of the Christensen method (Christensen GD et al 1985). TSB was supplemented with 1% glucose and 2% NaCl (sTSB). Elemental calcium at 25 or 50mg/L and/or magnesium at 12.5mg/L were tested. Glucose and NaCl supplementation were tested separately (results not shown). An inoculum of 107 CFU/mL was added to 96 well plates in 8 replicates with incubation at 37°C for 24h. Then, plates were rinsed 3 times with normal saline and stained with 2% crystal violet for 15 min. Excess stain was removed with deionized water. Adherent stain was solubilized with 95% ethanol. Optical density (OD) was read at 570nm on a spectrophotometer, with media controls subtracted from results. Average OD was compared by t test.
Related People: Kerry L. LaPlante
1 University of Rhode Island, College of Pharmacy, Kingston, RI
2 Providence Veterans Affairs Medical Center, Providence, RI
3 Rhode Island College, Providence ,RI
4 Warren Alpert Medical School of Brown University, Providence, RI