No abstract

f Quorum sensing (QS) in Pseudomonas aeruginosa regulates the production of many virulence factors and plays an important role in the pathogenesis of P. aeruginosa infection. N-acyl homoserine lactones (AHL) are major QS signal molecules. Recently, a novel AHL-lactonase enzyme, AiiM, has been identified. The aim of this study was to evaluate the effect of AiiM on the virulence of P. aeruginosa in a mouse model of acute pneumonia. We developed a P. aeruginosa PAO1 strain harboring an AiiM-expressing plasmid. The production of several virulence factors by the AiiM-expressing strain was examined. Mice were intratracheally infected with an AiiM-expressing PAO1 strain. Lung histopathology, bacterial burden, and bronchoalveolar lavage (BAL) fluid were assessed at 24 h postinfection. AiiM expression in PAO1 reduced production of AHL-mediated virulence factors and attenuated cytotoxicity against human lung epithelial cells. In a mouse model of acute pneumonia, AiiM expression reduced lung injury and greatly improved the survival rates. The levels of proinflammatory cytokines and myeloperoxidase activity in BAL fluid were significantly lower in mice infected with AiiM-expressing PAO1. Thus, AiiM can strongly attenuate P. aeruginosa virulence in a mammalian model and is a potential candidate for use as a therapeutic agent against P. aeruginosa infection. Pseudomonas aeruginosa is a Gram-negative pathogen responsible for opportunistic and health care-associated infections, such as pneumonia and urinary tract-, surgical site-, and catheterrelated bloodstream infections (1). Often, these infections are difficult to treat because of biofilm formation and intrinsic resistance to many antibiotics. In addition, P. aeruginosa easily develops resistance to many currently used antibiotics; therefore, the development of novel treatment strategies is imperative.Recently, the quorum-sensing (QS) system has attracted attention as a new therapeutic target (2). P. aeruginosa has two wellcharacterized QS systems (the LasR-LasI and RhlR-RhlI systems) which mainly utilize two N-acyl homoserine lactone (AHL) molecules, namely, N-3-oxododecanoyl-L-homoserine lactone (3-oxo-C12-HSL) and N-butyryl-L-homoserine lactone (C4-HSL) (3). These systems regulate the production of various virulence factors, including pyocyanin, elastase, and rhamnolipid, which play important roles in promoting the infection (4). In addition, 3-oxo-C12-HSL itself has immunomodulatory activity, stimulates cytokine production, and induces neutrophil or macrophage apoptosis (5, 6).Previous studies showed that AHL-negative mutant P. aeruginosa had considerably lower virulence than the wild-type strain (7,8). Thus, AHL inhibitor could be a therapeutic agent for infections by Gram-negative bacteria.The first AHL-inactivating enzyme, AHL-lactonase AiiA, was isolated from Bacillus species (9). Recently, Wang et al. have found a novel AHL-lactonase, termed AiiM, from Microbacterium testaceum, which resides on the leaf surface of potato (10,11). AiiM is a member of the ␣/␤ hydrola...

c; Global COE Program, Nagasaki University, Nagasaki, Japan d Acinetobacter baumannii is one of the main pathogens that cause ventilator-associated pneumonia (VAP) and is associated with a high rate of mortality. Little is known about the efficacy of macrolides against A. baumannii. In order to confirm the efficacy of azithromycin (AZM) against VAP caused by multidrug-resistant A. baumannii (MDRAB), we used a mouse model that mimics VAP by placement of a plastic tube in the bronchus. AZM (10 and 100 mg/kg of body weight) was administered subcutaneously every 24 h beginning at 3 h after inoculation. Phosphate-buffered saline was administered as the control. Survival was evaluated over 7 days. At 48 h postinfection, mice were sacrificed and the numbers of viable bacteria in lungs and bronchoalveolar lavage fluid were compared. Histopathological analysis of lung specimens was also performed. The treatment groups displayed significantly longer survival than the control group (P < 0.05). AZM did not have an antimicrobial effect. Histopathological examination of lung specimens indicated that the progression of lung inflammation was prevented in the AZM-treated groups. Furthermore, total cell and neutrophil counts, as well as cytokine levels, in bronchoalveolar lavage fluid were significantly decreased (P < 0.05) in the AZM-treated groups. AZM may have a role for the treatment of VAP with MDRAB because of its anti-inflammatory effects.

5We conducted a retrospective observational study on patients with MRSA bacteremia who 6 were hospitalized between 2008 and 2011. We used univariate and multivariate analysis to 7 evaluate the predictors associated with 30-day mortality. The 7-day and 30-day mortality 8 rates were 12.0% and 25.3%, respectively. According to multivariate analysis, the 9 independent predictors that associated with 30-day mortality were leukopenia, low serum