Effect of bovine lactoferrin against Carnobacterium viridans

Lactoferrin (LF) alone (8 mg/ml) was able to kill 4 log10 CFU/ml of C. viridans at 4, 10 and 30 °C in all purpose tween (APT) or Lauria broth (LB). In the presence of 2.5% NaCl in each broth system, LF activity shifted from a bactericidal to bacteriostatic effect at all tested temperatures. The addition of sodium bicarbonate (SB) up to 0.16 M did not alter the activity of LF in LB broth containing 2.5% NaCl. However, when 5 mg/ml sodium hexametaphosphate (SHMP) was used with 2.5% NaCl, LF regained some of its bactericidal activity at 30 °C in APT but not in LB broth. This reversal did not occur in APT at 4 or 10 °C. Except for the observation with SHMP at 30 °C, neither sodium lactate (SL) nor SHMP enhanced the bactericidal activity of LF in LB or APT broth containing<2.5% NaCl. It was suggested that 2.5% NaCl in LB and APT broths increased media osmolarity and prevented LF access to binding sites on the contracted cell membrane. This is the first report showing a bactericidal effect of unmodified LF at neutral pH and refrigeration temperatures.