| Pseudomonas aeruginosa is a gram negative bacterium,water and soil habitats.It is also an important opportunistic pathogen that causes life-threatening infections in burned patients,individuals with compromised immune system,and cystic fibrosis(CF)patients.In natural and clinical setting,biofilms(surface-associated communities of microorganism)enhance survival,enabling organisms to adapt to changing conditions collectively instead of as single cells.Many factors affect biofilm formation,such as extracellular polysaccharides and proteins,bacterial motility,quorum-sensing,and virulence factors,etc..Therefore,study of these factors of P.aeruginosa strains from different origins is helpful to better understand the bacterial adaptation and may lead to therapeutic methods dealing with P.aeruginosa infections and biofilms..In this study,we determined the Psl polysaccharide production and MIC(Minimal Inhibitory Concentration)of 27 P.aeruginosa strains isolated from different sources,to define whether the production of Psl affects the MIC.We found that antibiotic treatment is the main reason for bacteria to gain drug-resistance,and Psl polysaccharide production does not directly affect the MIC value of planktonic bacteria.P.aeruginosa most likely utilize different strategies to show resistance to antibiotics while they produce little or higher amount of Psl polysaccaride.The motilities of all 27 P.aeruginosa strains were also examined.Three modes of motilities were tested,including swimming,swarming and twitching.Our results showed that most strains isolated from human body lost motilities,especially CF origin strains.This may be due to the long term adaption of bacteria to the CF environment.Strains isolated from liquid environment have better motilities,especially those from fresh water.In summary,our results indicate that motilities are very important for bacterial survival in natural environments.The quorum sensing(QS)signal molecular and virulence factors(pyocyanin and elastase)secreted from the 27 strains were detected.We found that all strains from natural environments had the ability to produce the two kinds of QS signals(C4-AHL and C12-HSL).However CF origin strains often lost one or two kinds of QS signals,Among the strains from the other human source,all can produced C12-HSL,a few lost the ability to synthesis of C4-HSL.Strains lacking production of C4-HSL did not synthesis of elastase,yet no directly correlation was found between pyocyanin production and QS.Our results suggested QS was important for bacterial survival in natural environments and bacteria might have multiple strategies to control the production of the virulence factors to balance the needs between better growth and adaption to different threatens.The attachment is the first step of the biofilm development.This study tested the attachment of the 27 strains using rapid biofilm assay.Result showed that the attachment of the strains from natural environment were generally stronger than those from human body.Most CF isolates showed poor attachment.Consistent with previously reports,Strains produce higher amount of Psl polysaccharide(at wild type level or above)had better attachment.However,a few strains with little Psl can have attachment at wild type level.This suggested many factors were involved in the attachment besides Psl polysaccharide,In summary,our data showed that CF isolated P.aeruginosa strains were tend to reduce any bacterial surface structures and extracellular material including flagella and Type IV Pili that promoted motilities,Psl polysaccharide,QS signal moleculars,and secreted virulence factors.In contrast,most these strain showed strong antibiotic resistance.This may be a result of the selection of human immune system and long term adaption to the stress in CF environment. |
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