PHYSICO-CHEMICAL ASPECTS OF THE ADHESION AND ... - EPFL

SUMMARY
Nosocornial (hospital acquired) pneumonia is a major medical complication in intubated
and mechanically ventilated patients. The bacterium Pseudomonns aerugir~osa is one of the
most prevalent nosocomial pathogen, responsible for 30 % of nosocomial infections, of which
47 % are ventilator-associated pneumonia (VAP). Prolonged intubation with an endotracheal
device is a major risk factor for VAP, where colonization of the upper respiratory tract by
P. neruginosa occurs in 90 % of patients, with a mortality reaching 40 % despite aggressive
antibiotic therapy. Therefore, a new strategy to prevent or at least to delay the occurrence of
VAP due to P. neruginosa is desirable. Successful bacterial colonization of the upper
respiratory tract involves the formation of biofilms on the surface of the intubation devices.
As it is generally accepted that biofilm formation is initiated by the crucial event of adhesion
of bacteria to a solid support. we investigated in this dissertation whether bacterial adhesion
could be reduced by surface modification of the polymer commonly used in endotracheal
devices, medical grade poly(viny1 chloride ) (PVC).
Initial bacterial adhesion can be considered for the most part in terms of colloidal
interaction forces goveined by physicochemical properties of the bacteria, the substratum
surface and the surrounding environment, as described in the extended DLVO theory.
Deviations from theory-based predictions arise from the fact that bacteria are not smooth
colloidal particles, but possess surface structural features like pili, flagella and
lipopolysaccharides (LPS), that may favour the subsequent molecular and irreversible
attachment of bacteria to a solid surface. Attempts to prevent the attachment of pathogens to
the endotracheal tubes first require a better insight of the biomaterial and bacteriai properties
involved in this process. The surface characteristics of a biomaterial can affect the affinity of
the bacteria for the polymer. In order to change the substrate accordingly, some
physicochemical properties of the bacteria must be known. We tested a wide range of P.
neruginosa strains, including the wildtype PAOI. specific mutants and clinical isolates from
tracheal secretions or the blood of patients presenting a VAP. It was demonstrated that the
surface of most P. aeruginosa strains was hydrophobic and negatively charged. Their overall
adhesion efficiency to untreated PVC pieces varied widely, which could be partly explained
by structural peculiarities of the surfaces of the strains. Generally, hydrophobic bacteria
adhere more than hydrophilic bacteria, and preferentially on hydrophobic supports.