Pseudomonas aeruginosa is an opportunistic pathogen capable of group behaviors including swarming motility and biofilm formation. Swarming motility plays an important role in the bacterium's spread to new environments, attachment to surfaces, and biofilm formation. Bacterial biofilm is associated with many persistent infections and increased resistance to antibiotics. In this study, we tested the effect of a 2-alkyl-4(1H)-quinolone (AHQ) signal, the Pseudomonas quinolone signal (PQS) on P. aeruginosa swarming and biofilm formation. Our results show that PQS repressed the swarming motility of P. aeruginosa PAO1. Such repression was independent of its cognate receptor PqsR and was not related to changes in the flagellae, type IV pili or the production of the surface-wetting agent rhamnolipid surfactant. While PQS did not affect twitching motility in PAO1, a pqsR deletion abolished twitching motility, indicating that pqsR is required for twitching motility. Our results also indicate that the enhancement of biofilm formation by PQS is at least partially dependent on the GacAS-Rsm regulatory pathway but does not involve the las or rhl QS systems.

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...

Streptococcus pneumoniae is a major cause of invasive infection in young infants and older adults. There are currently 90 capsular serotypes identified and 23 serotypes (