c Dimethyl sulfoxide (DMSO) is commonly used as a solvent to dissolve water-insoluble drugs or other test samples in both in vivo and in vitro experiments. It was observed during our experiment that DMSO at noninhibitory concentrations could significantly inhibit pyocyanin production in the human pathogen Pseudomonas aeruginosa. Pyocyanin is an important pathogenic factor whose production is controlled by a cell density-dependent quorum-sensing (QS) system. Investigation of the effect of DMSO on QS showed that DMSO has significant QS antagonistic activities and concentrations of DMSO in the micromolar range attenuated a battery of QS-controlled virulence factors, including rhamnolipid, elastase, and LasA protease production and biofilm formation. Further study indicated that DMSO inhibition of biofilm formation and pyocyanin production was attained by reducing the level of production of an autoinducer molecule of the rhl QS system, N-butanoyl-L-homoserine lactone (C 4 -HSL). In a mouse model of a burn wound infection with P. aeruginosa, treatment with DMSO significantly decreased mouse mortality compared with that for mice in the control group. The capacity of DMSO to attenuate the pathogenicity of P. aeruginosa points to the potential use of DMSO as an antipathogenic agent for the treatment of P. aeruginosa infection. As a commonly used solvent, however, DMSO's impact on bacterial virulence calls for cautionary attention in its usage in biological, medicinal, and clinical studies. Pseudomonas aeruginosa is a prevalent opportunistic pathogen capable of causing various infections in humans, including pneumonia and urinary tract infections, bloodstream infections, and infections in burn patients (1). The chronic infection caused by P. aeruginosa and the associated pulmonary inflammation are ultimately responsible for the majority of cases of mortality in patients with cystic fibrosis (2). The ability of P. aeruginosa to cause diverse infections is attributed to its myriad virulence factors and biofilm-forming capability, which are controlled by the intercellular quorum-sensing (QS) communication system (3-5).P. aeruginosa has two acyl-homoserine lactone (AHL)-mediated QS systems, known as the las and rhl QS systems. The las and rhl systems consist of the transcriptional activators LasR and RhlR, respectively, and the signal synthases LasI and RhlI, respectively. The major signals in the las and rhl systems are N-(3-oxododecanoyl)-HSL (3-oxo-C 12 -HSL) and N-butanoyl-L-homoserine lactone (C 4 -HSL), respectively (5). P. aeruginosa employs these QS systems to control a wide range of extracellular virulence factors, including pyocyanin, elastase, and rhamnolipid (7-12). The AHL-mediated QS systems also play a crucial role in biofilm formation by P. aeruginosa, a common cause of resistance to antibiotics and the difficulties with the treatment of infections (13). The las system influences the activation of pel and, accordingly, biofilm matrix formation (14), and the rhl system contributes to the maintenance of the bio...

New antimicrobial agents are urgently needed to treat infections caused by drug-resistant pathogens and by pathogens capable of persisting in biofilms. The aim of this study was to identify traditional Chinese herbs that could inhibit biofilm formation of Pseudomonas aeruginosa, an important human pathogen that causes serious and difficult-to-treat infections in humans. A luxCDABE-based reporter system was constructed to monitor the expression of six key biofilm-associated genes in P. aeruginosa. The reporters were used to screen a library of 36 herb extracts for inhibitory properties against these genes. The results obtained indicated that the extract of Herba patriniae displayed significant inhibitory effect on almost all of these biofilm-associated genes. Quantitative analysis showed that H. patriniae extract was able to significantly reduce the biofilm formation and dramatically altered the structure of the mature biofilms of P. aeruginosa. Further studies showed H. patriniae extract decreased exopolysaccharide production by P. aeruginosa and promoted its swarming motility, two features disparately associated with biofilm formation. These results provided a potential mechanism for the use of H. patriniae to treat bacterial infections by traditional Chinese medicines and revealed a promising candidate for exploration of new drugs against P. aeruginosa biofilm-associated infections.

Antipathogenic compounds that target the virulence of pathogenic bacteria rather than their viability offer a promising alternative approach to treat infectious diseases. Using extracts from 30 Chinese herbs that are known for treating symptoms resembling infections, we identified an active compound falcarindiol from Notopterygium incisum Ting ex H. T. Chang that showed potent inhibitory activities against Pseudomonas aeruginosa multiple virulence factors. Falcarindiol significantly repressed virulence-related genes, including the type III secretion system (T3SS); quorum sensing synthase genes lasIR and rhlIR; lasB; motility-related genes fliC and fliG; and phenazine synthesis genes phzA1 and phzA2. P. aeruginosa swarming motility and pyocyanin production were reduced significantly. In a burned mouse model, falcarindiol treatment significantly reduced the mortality in mice infected with P. aeruginosa, indicating that falcarindiol is a promising antipathogenic drug candidate for treating P. aeruginosa infections.