Brief Report

Effect of antimicrobial peptides on planktonic growth, biofilm formation and biofilm-derived bacterial viability of Streptococcus pneumoniae

Michael T. Boswell, Riana Cockeran
Southern African Journal of Infectious Diseases | Vol 36, No 1 | a226 | DOI: https://doi.org/10.4102/sajid.v36i1.226 | © 2021 Michael T. Boswell, Riana Cockeran | This work is licensed under CC Attribution 4.0
Submitted: 21 June 2020 | Published: 25 January 2021

About the author(s)

Michael T. Boswell, Department of Internal Medicine, Division of Infectious Diseases, Faculty of Medicine, Steve Biko Academic Hospital, Pretoria, South Africa; and Department of Immunology, Faculty of Health Sciences, University of Pretoria, Pretoria, South Africa
Riana Cockeran, Department of Immunology, Faculty of Health Sciences, University of Pretoria, Pretoria, South Africa; and Department of Immunology, Tshwane Academic Division, National Health Laboratory Services, Pretoria, South Africa


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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.

Keywords

antimicrobial peptides; Streptococcus pneumoniae; LL37; biofilm; cathelicidins; bacterial growth.

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