Risk associated with diagnostic-therapeutic invasive procedures in intensive care units

Patients admitted to intensive care units are extremely susceptible to infection due to hospital acquired pathogens. One of the most important reasons for the occurrence of infection is attributable to the fact that these patients are exposed to several prosthetic devices for diagnostic or therapeutic procedures. From this point of view the problem of prostheses-associated infection is presently of major concern in hospital acquired infection since the number of artificial polymers implanted in the human body is rapidly increasing in many medical fields. Several types of plastic and metal prostheses are utilized for medical purposes and they greatly differ in tissue compatibility. Only recently some information has been obtained about their susceptibility to bacterial adhesion and colonization. The thermodynamic approach considers hydrophobicity, or surface free energy, as the major factor in facilitating bacterial attachment, but probably this approach is inherently too simplistic and does not consider important factors such as conditioning films bathing the surface of the polymer. Moreover, in this model bacteria are considered as individual cells, but the available body of evidence indicates that cells form aggregates embedded in a matrix sticking to the surface. This sessile mode of growth, as opposed to that of free living cells (planktonic) has profound effect on growth, shape, metabolism of attached bacteria influencing sensitivity to antibiotic, disinfectants and to cellular and humoral host defenses. Adherent bacteria cannot be easily ingested by polymorphonuclear neutrophils (PMNs) which are rendered ineffective by aspecific activation upon contact with several polymers. All these factors contribute to make these infections chronic and cryptic by posing difficult diagnostic and therapeutical problems.