Effect of Serum Proteins on Planktonic Growth and Biofilm Formation of Helicobacter pylori in vitro

The growth of the gastric bacteria Helicobacter pylori can occur both planktonic and by developing biofilm (BF). Fetal calf serum (FCS) is used for in vitro growth of H. pylori in the liquid medium but is also considered in protocols for BF formation. However, evidence suggests that high percentages of FCS may impair H. pylori BF formation. The study focused on assessing the effect of protein saturation of FCS on H. pylori BF formation in vitro. A clinical isolate of H. pylori characterized genotypically by PCR as vacA s2/m2, cagA+ was used. Bacterial growth and BF formation were measured spectrophotometrically in Brain-Heart-Infusion (BHI) and Brucella-Broth (BB), alone or in combination with β-Cyclodextrin (β- CD) and FCS. The effect of different percentages of FCS (0, 2.5, 5.0, and 7.5%) and bovine serum albumin (BSA) at equivalent protein concentrations on BF formation was evaluated. The results indicated that the best planktonic growth occurred in BB, with a 4-fold increase compared to BHI when β-CD/FCS was used and that this growth was also dependent on the concentration of FCS or BSA used. BB medium was also the most suitable for BF generation; however, increasing FCS or BSA concentrations proportionally inhibited its formation. It is concluded that in vitro serum protein saturation generates a steric effect that inhibits BF structuring, using a cagA+ H. pylori strain with a lower virulence version of the vacA gene (s2/m2), estab¬lishing that the absence of serum improves BF formation but decreases planktonic growth.