Nisin penetratesStaphylococcus aureusbiofilms but shows differences in killing effects against sessile and planktonic cells

Abstract

17Biofilms may restrict antimicrobial penetration and contribute to the recalcitrance of 18 bacterial infections. In this work, we investigated the penetration of nisin into S. aureus 19 biofilms and compared the susceptibility of S. aureus planktonic and sessile cells to this 20 lantibiotic. Biofilms were grown under continuous flow in CDC reactors and calcein 21 fluorescence was used to monitor the effect of nisin on the cytoplasmic membrane of S. 22 aureus cells. Confocal scanning laser microscopy (CLSM) showed that calcein was lost 23 within approximately 20 min in CDC biofilms, demonstrating that nisin penetrated to the 24 bottom of the biofilm and caused membrane permeabilization. Viability analysis using PI 25 staining showed that nisin was bactericidal against S. aureus sessile cells. Time-kill 26 assays were performed against S. aureus in the following conditions: homogenized 27 exponential planktonic (HEP), homogenized stationary planktonic (HSP), homogenized 28 CDC biofilm (HB) and intact CDC biofilm (IB). The mean viability reduction of HEP and 29 HSP were 6.71 and 1.64 log CFU.ml -1 , respectively, confirming that stationary S. aureus 30 cells were much less susceptible than exponential cells. The HB and IB treatments 31 showed mean viability reductions of 1.25 and 0.50 log CFU.ml -1 , respectively. Nisin 32 activity against S. aureus was not limited by its ability to penetrate the bacterial biofilm, 33 but the killing efficacy of the antimicrobial peptide was reduced by the physiological 34 status of the biofilm-grown cells. 35 36 37 38 3 Importance 39Biofilms represent a major problem to control microorganisms in industrial environments 40 and medical devices. We developed a direct real-time microscopic visualization 41 technique to demonstrate experimentally that the antimicrobial peptide nisin is able to 42 penetrate S. aureus biofilms. Our results confirmed that nisin caused membrane 43 permeabilization of sessile bacteria and revealed qualitative agreement between 44 viability loss and membrane integrity loss. This approach could improve the evaluation 45 of antibacterial susceptibility breakpoints when testing the efficacy of standard and 46 novel antimicrobials. 47 48

Inhibition of bacterial adherence to vascular catheters by the antimicrobial peptide AP7121

“…De hecho, la adhesión de tres bacterias médicamente relevantes (S. aureus, S. epidermidis y E. faecalis) se inhibió significativamente tubos de succión tratados con nisina (Bower et al, 1998). Godoy-Santos et al (2018) demostraron que la nisina producía permeabilización de la membrana de bacterias sésiles y mostró concordancia entre la pérdida de viabilidad y la pérdida de integridad de la membrana.…”

Burkholderia cepacia Complex Bacteria: a Feared Contamination Risk in Water-Based Pharmaceutical Products

“…However, some compounds, including antibiotics, still can penetrate through biofilms, depending on the nature of both the compound and the biofilm (98, 100). The antimicrobial peptide nisin was able to penetrate through the biofilm structure, causing bacterial death, even though the viability loss was more pronounced in the case of planktonic cells than in biofilm-grown bacterial populations (101). Within the biofilm, the development of a microenvironment characterized by lower nutrient/oxygen availability and reduced bacterial growth is likely to occur together with the production of enzymes that can be involved in the degradation/neutralization of chemicals (27).…”