Abstract
Chronic wound infections are often caused by multi-species biofilms and these biofilm-embedded bacteria exhibit remarkable tolerance to existing antibiotics, which presents huge challenges to control such infections in the wounds. In this investigation, we established a polymicrobial biofilm composed of P. aeruginosa, S. aureus, K. pneumoniae, and A. baumannii. We tested a cocktail therapy comprising 405-nm blue light (BL), carvacrol (Ca), and antibiotics on the multispecies biofilm. Despite the fact that all strains used to form the biofilm were susceptible to ciprofloxacin (CIP) in planktonic cultures, the biofilm was found to withstand ciprofloxacin as well as BL-Ca dual treatment, mainly because K. pneumoniae outgrew and became dominant in the biofilm after each treatment. Strikingly, when ciprofloxacin was combined with BL-Ca, the multispecies biofilms succumbed substantially and were eradicated at an efficacy of 99.9%. Mechanistically, BL-Ca treatment increased membrane permeability and potentiated the anti-biofilm activity of ciprofloxacin, probably by facilitating ciprofloxacin’s entrance of the bacteria, which is particularly significant for K. pneumoniae, a species that is refractory to either ciprofloxacin or BL-Ca dual treatment. The results suggest that bacterial membrane damage can be one of the pivotal strategies to subvert biofilm tolerance and combat the recalcitrant multispecies biofilms.
Highlights
Biofilm is a common bacterial lifestyle in nature
Bacteria could attach to the provided pipette tip and initiated biofilm establishment
Five pathogens that are commonly found in chronic wounds including Gram-negative E. coli, K. pneumoniae, A. baumannii, P. aeruginosa, and Gram-positive S. aureus were mixed and incubated for 48 h in Lubbock Chronic Wound Pathogenic Biofilm (LCWPB)
Summary
Biofilm is a common bacterial lifestyle in nature. These bacterial aggregates have been found in a variety of niches ranging from pond water to catheters, from chronic wounds to airway mucus. Several hypotheses have been proposed to address increased antibiotic tolerance of biofilms over their planktonic counterparts [1,2,3]: i.e., (i) matrix barrier retards penetrations of cationic compounds like aminoglycosides [4];. Biofilm accounts for over 60% of human infections [8], many of which are polymicrobial [9,10,11] Chronic wounds such as diabetic foot ulcers are filled with polymicrobial biofilm, where Staphylococcus, Pseudomonas, Escherichia, Klebsiella, and Acinetobacter have been frequently isolated together [12]. After gentamicin treatment, P. aeruginosa in a wound-like polymicrobial biofilm showed a two-fold higher survival than in the mono-species biofilm [13]. P. aeruginosa can enhance S. aureus tolerance to aminoglycoside antibiotics by inducing small-colony
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