Halicin Is Effective Against Staphylococcus aureus Biofilms In Vitro

Abstract

BackgroundBiofilms protect bacteria from the host immune system and many antibiotics, making the treatment of orthopaedic infections difficult. Halicin, a recently discovered antibiotic, has potent activity against nonorthopaedic infections in mice and the planktonic, free-living forms of many bacterial species, including Staphylococcus aureus, a common cause of orthopaedic infections. Importantly, halicin did not induce resistance in vitro and was effective against drug-resistant bacteria and proliferating and quiescent bacteria. Quiescence is an important cause of antibiotic tolerance in biofilms. However, whether halicin acts on biofilms has not been tested.Questions/purposes(1) Does halicin reduce the viability of S. aureus in less mature and more mature biofilms as it does in planktonic cultures? (2) How do the relative effects of halicin on S. aureus biofilms and planktonic cultures compare with those of conventional antibiotics (tobramycin, cefazolin, vancomycin, or rifampicin) that are commonly used in clinical orthopaedic infections?MethodsTo measure minimal biofilm eradication concentrations (MBECs) with less mature 3-day and more mature 7-day biofilms, we used 96-well peg plates that provided high throughput and excellent reproducibility. After S. aureus-Xen36 biofilm formation, planktonic bacteria were removed from the cultures, and the biofilms were exposed to various concentrations of halicin, tobramycin, cefazolin, vancomycin, or rifampicin for 20 hours. Biofilm viability was determined by measuring resazurin reduction or by counting colony-forming units after sonication. To determine effects of halicin and the conventional antibiotics on biofilm viability, we defined MBEC75 as the lowest concentration that decreased viability by 75% or more. To determine effects on bacterial viability in planktonic cultures, minimum inhibitory concentrations (MICs) were determined with the broth dilution method. Each result was measured in four to 10 independent experiments.ResultsWe found no differences between halicin’s effectiveness against planktonic S. aureus and 3-day biofilms (MIC and MBEC75 for 3-day biofilms was 25 μM [interquartile range 25 to 25 and 25 to 25, respectively]; p > 0.99). Halicin was eightfold less effective against more mature 7-day biofilms (MBEC75 = 200 μM [100 to 200]; p < 0.001). Similarly, tobramycin was equally effective against planktonic culture and 3-day biofilms (MIC and MBEC75 for 3-day biofilms was 20 μM [20 to 20 and 10 to 20, respectively]; p > 0.99). Tobramycin’s MBEC75 against more mature 7-day biofilms was 320 μM (320 to 480), which is 16-fold greater than its planktonic MIC (p = 0.03). In contrast, the MBEC75 for cefazolin, vancomycin, and rifampicin against more mature 7-day biofilms were more than 1000-fold (> 1000; p < 0.001), 500-fold (500 to 875; p < 0.001), and 3125-fold (3125 to 5469; p = 0.004) greater than their planktonic MICs, respectively, consistent with those antibiotics’ relative inactivity against biofilms.ConclusionHalicin was as effective against ...

Research

“…Investigators from Indianapolis (Indiana, USA) therefore sought to test the effectiveness of halicin against biofilms in vitro. 1…”

“…Investigators from Indianapolis (Indiana, USA) therefore sought to test the effectiveness of halicin against biofilms in vitro. 1 Biofilms were exposed to various concentrations of halicin, tobramycin, cefazolin, vancomycin, or rifampicin for 20 hours, with biofilm viability determined by measuring resazurin reduction or by counting colony-forming units after sonication. The investigators found no differences between halicin’s effectiveness against planktonic S. aureus and three-day biofilms, although the drug was eight-fold less effective against seven-day biofilms.…”

CORR Insights®: Halicin Is Effective Against Staphylococcus aureus Biofilms In Vitro

“…The authors of this study [5] tested a new antimicrobial agent, halicin, on the biofilms of the S. aureus strain Xen36 and compared its efficacy with the efficacy of other commonly used antibiotics such as tobramycin, cefazolin, vancomycin, and rifampicin. The model used planktonic cells and 3-day- and 7-day-old biofilms.…”

Safety and efficacy evaluation of halicin as an effective drug for inhibiting intestinal infections

“…Halicin has garnered substantial attention in recent years because of its potential therapeutic applications. As a potential broad-spectrum antibacterial agent, halicin showed remarkable efficacy against both Gram-positive and Gram-negative bacteria ( Stokes et al, 2020 ; Booq et al, 2021 ; Higashihira et al, 2022 ). Halicin has a lower likelihood of inducing bacterial resistance than traditional antibiotics.…”