Contribution of quorum sensing to the virulence of Pseudomonas aeruginosa in pressure ulcer infection in rats.
ABSTRACT The impact of quorum sensing (QS) in in vivo models of infection has been widely investigated, but there are no descriptions for ischemic wound infection. To explore the role of QS in Pseudomonas aeruginosa in the establishment of ischemic wound infection, we challenged a pressure ulcer model in rats with the PAO-1, PAO-1 derivatives ΔlasIΔrhlI and ΔlasRΔrhlR strains, which cannot induce the virulence factor under QS control, thus the reduced tissue destruction was expended in these mutant strains. However unexpectedly, on postwounding day 3, the inflammatory responses in the three groups were similarly severe and the numbers of bacteria in tissue samples did not differ among the three strains. Biofilm formation was immature in QS-deficient strains, defined by the absence of dense bacterial aggregates and extracellular polymeric substance, which was confirmed by scanning electron microscopy. The Pseudomonas aeruginosa QS signal, acylated homoserine lactone, was only quantified from wound samples in the PAO-1 group. The swimming and twitching motilities were significantly enhanced in the ΔlasRΔrhlR group compared with the PAO-1 group in vitro. A significantly larger wound area was correlated with the bacterial motility. The inflammation in the early phase of bacterial challenge to wounds with immature biofilm formation in the QS-deficient strains indicated that the role of QS was more crucial for the chronic phase than for the acute phase of infection. The present findings indicate a difference in the importance of QS in ischemic wound infections compared with other infection models.
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ABSTRACT: The recent literature suggests that chronic wound biofilms often consist of multiple bacterial species. However, without appropriate in vivo, polybacterial biofilm models, our understanding of these complex infections remains limited. We evaluate and compare the effect of single- and mixed-species biofilm infections on host wound healing dynamics using a quantitative, in vivo, rabbit ear model. Six-mm dermal punch wounds in New Zealand rabbit ears were inoculated with Staphylococcus aureus strain UAMS-1, Pseudomonas aeruginosa strain PAO1, or both, totaling 10/6 colony-forming units/wound. Bacterial proliferation and maintenance in vivo were done using procedures from our previously published model. Wounds were harvested for histological measurement of wound healing, viable bacterial counts using selective media, or inflammatory cytokine (IL-1β, TNF-α) expression via quantitative reverse-transcription PCR. Biofilm structure was studied using scanning electron microscopy (SEM). For comparison, biofilm deficient mutant UAMS-929 replaced strain UAMS-1 in some mixed-species infections. Bacterial counts verified the presence of both strains UAMS-1 and PAO1 in polybacterial wounds. Over time, strain PAO1 became predominant (p<0.001). SEM showed colocalization of both species within an extracellular matrix at multiple time-points. Compared to each monospecies infection, polybacterial biofilms impaired all wound healing parameters (p<0.01), and increased expression of IL-1β and TNF-α (p<0.05). In contrast, mixed-species infections using biofilm-deficient mutant UAMS-929 instead of wild-type strain UAMS-1 showed less wound impairment (p<0.01) with decreased host cytokine expression (p<0.01), despite a bacterial burden and distribution comparable to that of mixed-wild-type wounds. This study reveals that mixed-species biofilms have a greater impact on wound healing dynamics than their monospecies counterparts. The increased virulence of polybacterial biofilm appears dependent on the combined pathogenicity of each species, verified using a mutant strain. These data suggest that individual bacterial species can interact synergistically within a single biofilm structure.PLoS ONE 01/2012; 7(8):e42897. · 3.53 Impact Factor
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ABSTRACT: Understanding the pathology resulting from and polymicrobial wound infections is of great importance due to their ubiquitous nature, increasing prevalence, growing resistance to antimicrobial agents, and ability to delay healing. Methicillin-resistant USA300 is the leading cause of community-associated bacterial infections resulting in increased morbidity and mortality. We utilized a well-established porcine partial thickness wound healing model to study the synergistic effects of USA300 and on wound healing. Wound re-epithelialization was significantly delayed by mixed-species biofilms through suppression of keratinocyte growth factor 1. showed an inhibitory effect on USA300 growth while both species co-existed in cutaneous wounds . Polymicrobial wound infection in the presence of resulted in induced expression of USA300 virulence factors Panton-Valentine leukocidin and α-hemolysin. These results provide evidence for the interaction of bacterial species within mixed-species biofilms and for the first time, the contribution of virulence factors to the severity of polymicrobial wound infections.PLoS ONE 01/2013; 8(2):e56846. · 3.53 Impact Factor