Abstract:
Streptococcus pneumoniae is a leading cause of pneumonia mortality globally. Pneumococcal
disease is often associated with prolonged colonisation of hosts and this process is facilitated by
biofilm formation that is largely resistant to conventional antibiotics. We investigated the effects
of antimicrobial peptides (AMPs) lysozyme, lactoferrin, LL37 and a combination of all three on
planktonic growth, biofilm formation and biofilm-derived bacterial viability by S. pneumoniae,
serotype 23F. Planktonic growth and biofilm-derived bacterial viability were determined using
standard colony-forming techniques, while biofilm formation was measured using a crystal
violet based spectrophotometric method. Relative to controls, lysozyme significantly reduced
biofilm formation (0.08 OD vs. 0.10 OD at 570 nm, p = 0.01), while LL37 and the AMP combination
increased biofilm formation (0.14 OD vs. 0.10 OD at 570 nm, p = 0.01). The combination of AMPs
significantly decreased planktonic growth (1.10 × 108
colony-forming units per millilitres [CFU/
mL] vs. 2.13 × 108 CFU/mL, p = 0.02). Biofilm-derived bacterial viability was greatly reduced by
exposure to a combination of AMPs (1.05 × 105
CFU/mL vs. 1.12 × 106
CFU/mL, p = 3.60 × 10−8).
Streptococcus pneumoniae displays marked resistance to the individual AMPs. A combination of
lysozyme, lactoferrin and LL37 effectively inhibited planktonic growth and biofilm-derived
bacterial viability; however, persister cell growth was still evident after exposure.
