Susceptibility of Salmonella strains to the antibacterial activity of human serum (HS). Log-phase cultures of the bacteria (1 × 105 CFU/ml) were incubated in 50% human serum (HS), in 50% heat inactivated serum (56°C for 30 min, HS-IN, control 1) or PBS (control 2) for 45 min. Serial dilutions were performed to calculate colony forming units (CFU/ml). The average number of colonies was estimated from three plates. The CFU/ml at time 0 was taken as 100%. Sensitivity to HS differs significantly if p values are less than 0.05 (*).