Pseudomonas aeruginosa RsmA Plays an Important Role during Murine Infection by Influencing Colonization, Virulence, Persistence, and Pulmonary Inflammation

Abstract

The ability of Pseudomonas aeruginosa to cause a broad range of infections in humans is due, at least in part, to its adaptability and its capacity to regulate the expression of key virulence genes in response to specific environmental conditions. Multiple two-component response regulators have been shown to facilitate rapid responses to these environmental conditions, including the coordinated expression of specific virulence determinants. RsmA is a posttranscriptional regulatory protein which controls the expression of a number of virulence-related genes with relevance for acute and chronic infections. Many membrane-bound sensors, including RetS, LadS, and GacS, are responsible for the reciprocal regulation of genes associated with acute infection and chronic persistence. In P. aeruginosa this is due to sensors influencing the expression of the regulatory RNA RsmZ, with subsequent effects on the level of free RsmA. While interactions between an rsmA mutant and human airway epithelial cells have been examined in vitro, the role of RsmA during infection in vivo has not been determined yet. Here the function of RsmA in both acute and chronic models of infection was examined. The results demonstrate that RsmA is involved in initial colonization and dissemination in a mouse model of acute pneumonia. Furthermore, while loss of RsmA results in reduced colonization during the initial stages of acute infection, the data show that mutation of rsmA ultimately favors chronic persistence and results in increased inflammation in the lungs of infected mice.Pseudomomas aeruginosa is a metabolically versatile gramnegative bacterium that is capable of causing opportunistic infections in plants, animals, and humans. In humans, P. aeruginosa infections occur in the gastrointestinal tract and respiratory system and in patients with ocular infections, burn wounds, and cystic fibrosis (CF). The characteristics of acute and chronic infections caused by P. aeruginosa are quite distinct and are associated with selected expression of a certain subset of virulence factors. The pathogenesis of acute infections, such as ventilator-associated pneumonia, is thought to require the expression of a functional type III secretion system (T3SS), along with other toxins and proteases (37). These infections typically result in systemic infections and ultimately mortality. On the other hand, individuals with CF are usually colonized with P. aeruginosa early in life (1), and while P. aeruginosa can reach densities of 10 9 CFU/ml of sputum (33), P. aeruginosa infections in the lungs of CF patients are minimally invasive and rarely progress to septicemia. Rather, it is the inflammation and deterioration of pulmonary function resulting from chronic P. aeruginosa infection that is the main cause of mortality in CF patients. Therefore, investigating the mechanism(s) by which P. aeruginosa colonizes and becomes firmly established is critical for understanding the nature of life-long infections in CF patients.The substantial proportion of the P. aeruginosa g...

Regulation of Bacterial Virulence by Csr (Rsm) Systems

“…5) (113, 125). In a mouse model of acute P. aeruginosa infection, rsmA mutation significantly reduced colonization during the initial stages of infection, but the loss of rsmA ultimately favored persistent infection (112). RsmA also represses the expression of the acyl homoserine lactone (AHL)-producing quorum-sensing systems las and rhl in P. aeruginosa; however, quorum-sensing signals have complex and seemingly conflicting roles in the regulation of acute and chronic virulence phenotypes (126).…”

“…In P. fluorescens, this includes genes involved in the production and secretion of the antimicrobial factors alkaline metalloprotease A, hydrogen cyanide, and 2,4-diacetylphloroglucinol (59,118,119). In P. aeruginosa, RsmA studies have focused on genes involved in T3SS, T6SS, motility, quorum sensing, and biofilm formation (80,85,112,120,121). Pseudomonas syringae strains cause many important diseases of higher plants and will be discussed below along with the other plant pathogens.…”

“…P. aeruginosa is the most prevalent human pathogen of this group and a major cause of morbidity and mortality in immunocompromised, burned, or wounded patients, as well as debilitating and difficult-to-treat chronic lung infections of cystic fibrosis (CF) patients (112)(113)(114). Although P. fluorescens is a biocontrol agent that protects plants against fungal pathogens, it is included here because it has served as an important model for studies of Pseudomonas Csr/Rsm systems (115)(116)(117).…”

The Multiple Signaling Systems Regulating Virulence in Pseudomonas aeruginosa

“…Binding of RsmZ and RsmY to the small RNAbinding protein RsmA (PA0905) activates the production of genes involved in biofilm formation and represses multiple genes involved in acute virulence and motility. As a consequence, in a mouse model of acute pneumonia, a mutation in RsmA reduced colonization during the initial infection stages but ultimately favored chronic infection (140).…”

Inactivation of the hmgA gene of Pseudomonas aeruginosa leads to pyomelanin hyperproduction, stress resistance and increased persistence in chronic lung infection

“…The murine model of chronic lung infection using P. aeruginosa-laden agarose beads was established by following previously described protocols (Macia et al, 2006;Mulcahy et al, 2008). Briefly, for the preparation of the agarose beads, P. aeruginosa strains were grown to late-exponential phase, washed and mixed at a 1 : 10 ratio with 2 % agarose in PBS (pH 7.4).…”