Loss of the skin barrier facilitates the colonization of underlying tissues with various bacteria, where they form biofilms that protect them from antibiotics and host responses. Such wounds then become chronically infected. Topical antimicrobials are a major component of chronic wound therapy, yet currently available topical antimicrobials vary in their effectiveness on biofilm-forming pathogens. In this study, we evaluated the efficacy of Next Science wound gel technology (NxtSc), a novel topical agent designed to kill planktonic bacteria, penetrate biofilms, and kill the bacteria within. In vitro quantitative analysis, using strains isolated from wounds, showed that NxtSc inhibited biofilm development by Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae by inhibiting bacterial growth. The gel formulation NxtSc-G5, when applied to biofilms preformed by these pathogens, reduced the numbers of bacteria present by 7 to 8 log10 CFU/disc or CFU/g. In vivo, NxtSc-G5 prevented biofilm formation for 72 h when applied at the time of wounding and infection and eliminated biofilm infection when applied 24 h after wounding and infection. Storage of NxtSc-G5 at room temperature for 9 months did not diminish its efficacy. These results establish that NxtSc is efficacious in vitro and in vivo in preventing infection and biofilm development by different wound pathogens when applied immediately and in eliminating biofilm infection already established by these pathogens. This novel antimicrobial agent, which is nontoxic and has a usefully long shelf life, shows promise as an effective agent for the prevention and treatment of biofilm-related infections.
In Pseudomonas aeruginosa, type IV pili (TFP)-dependent twitching motility is required for development of surface-attached biofilm (SABF), yet excessive twitching motility is detrimental once SABF is established. In this study, we show that mucin significantly enhanced twitching motility and decreased SABF formation in strain PAO1 and other P. aeruginosa strains in a concentration-dependent manner. Mucin also disrupted partially established SABF. Our analyses revealed that mucin increased the amount of surface pilin and enhanced transcription of the pilin structural gene pilA. Mucin failed to enhance twitching motility in P. aeruginosa mutants defective in genes within the pilin biogenesis operons pilGHI/pilJK-chpA-E. Furthermore, mucin did not enhance twitching motility nor reduce biofilm development by chelating iron. We also examined the role of the virulence factor regulator Vfr in the effect of mucin. In the presence or absence of mucin, PAO?vfr produced a significantly reduced SABF. However, mucin partially complemented the twitching motility defect of PAO?vfr. These results suggest that mucin interferes with SABF formation at specific concentrations by enhancing TFP synthesis and twitching motility, that this effect, which is iron-independent, requires functional Vfr, and only part of the Vfr-dependent effect of mucin on SABF development occurs through twitching motility.
Diabetes affects 25.8 million people in the United States, or 8.3% of the population, and these numbers are even higher in developing countries. Diabetic patients are more susceptible to the development of chronic wounds with debilitating bacterial infections than nondiabetics. Previously, we compared the ability of the opportunistic pathogen Pseudomonas aeruginosa to cause biofilm-associated infections in chronic wounds of diabetic and nondiabetic mice (C. Watters, K. DeLeon, U. Trivedi, J. A. Griswold, M. Lyte, K. J. Hampel, M. J. Wargo, and K. P. Rumbaugh, Med. Microbiol. Immunol. 202:131-141, 2013). Unexpectedly, we observed that insulin-treated diabetic mice had significantly more biofilm in their wounds, which correlated with higher antibiotic tolerance. Here, we investigated whether insulin treatment modulates the diabetic immune system to favor P. aeruginosa biofilm formation. Utilizing a murine chronic wound model, we found that DNA protected P. aeruginosa in the wounds of insulin-treated diabetic mice from antibiotic treatment. We also observed increased numbers of neutrophils, reduced numbers of macrophages, and increased cell death in the wounds of diabetic mice on insulin therapy. Taken together, these data suggest that high levels of lysed neutrophils in the wounds of diabetic mice on insulin, combined with fewer macrophages to remove the cellular debris, contribute to increased DNA levels, which enhance P. aeruginosa biofilms.
The Pseudomonas aeruginosa fimbrial structures encoded by the cup gene clusters (cupB and cupC) contribute to its attachment to abiotic surfaces and biofilm formation. The P. aeruginosa pvcABCD gene cluster encodes enzymes that synthesize a novel isonitrile functionalized cumarin, paerucumarin. Paerucumarin has already been characterized chemically, but this is the first report elucidating its role in bacterial biology. We examined the relationship between the pvc operon and the cup gene clusters in the P. aeruginosa strain MPAO1. Mutations within the pvc genes compromised biofilm development and significantly reduced the expression of cupB1-6 and cupC1-3, as well as different genes of the cupB/cupC two-component regulatory systems, roc1/roc2. Adjacent to pvc is the transcriptional regulator ptxR. A ptxR mutation in MPAO1 significantly reduced the expression of the pvc genes, the cupB/cupC genes, and the roc1/roc2 genes. Overexpression of the intact chromosomally-encoded pvc operon by a ptxR plasmid significantly enhanced cupB2, cupC2, rocS1, and rocS2 expression and biofilm development. Exogenously added paerucumarin significantly increased the expression of cupB2, cupC2, rocS1 and rocS2 in the pvcA mutant. Our results suggest that pvc influences P. aeruginosa biofilm development through the cup gene clusters in a pathway that involves paerucumarin, PtxR, and different cup regulators.
The accumulation of thick stagnant mucus provides a suitable environment for the growth of Pseudomonas aeruginosa and Staphylococcus aureus within the lung alveoli of cystic fibrosis (CF) patients. These infections cause significant lung damage, leading to respiratory failure and death. In an artificial mucin containing medium ASM+, P. aeruginosa forms structures that resemble typical biofilms but are not attached to any surface. We refer to these structures as biofilm like structures (BLS). Using ASM+ in a static microtiter plate culture system, we examined the roles of mucin, extracellular DNA, environmental oxygen (EO2), and quorum sensing (QS) in the development of biofilm-like structures (BLS) by P. aeruginosa; and the effect of EO2 and P. aeruginosa on S. aureus BLS.
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