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New etiopathogenic concepts of ventilator-associated pneumonia
1Pulmonary & Critical Care Division, Winthrop University Hospital, Mineola, NY 11501, USA.
Abstract:
Ventilator-associated pneumonia develops as a consequence of impaired host defenses and exposure to large numbers of potential pathogens. Both of these processes interact and allow colonization of the airways with enteric gram-negative bacteria to occur through the molecular mechanism of bacterial adherence. Bacterial adherence is a cell-cell interaction mediated by the following variables: (1) host receptors, (2) bacterial adhesins, and (3) the proper microenvironment on the respiratory mucosa. For gram-negative bacteria, an important adhesin may be the pili that project from the cell surface, and important epithelial receptors for adhesins may be glycoproteins contained in respiratory mucus. The proper microenvironment for adherence to take place is a mixture of exposed cell receptors, prolonged bacterial-epithelial cell contact, impaired airway defenses, presence of proteases, and an optimal pH. In some way, all of the risk factors discussed impact either directly or indirectly with this basic molecular process. Once adherence is accomplished, potential pathogens may begin to colonize the respiratory tract. Once colonization occurs, bacteria may proliferate on the respiratory mucosa. At this point, the general status of host defenses determines whether colonization progresses to overt parenchymal lung infection.
Insights
Ventilator-associated pneumonia (VAP) arises from weakened defenses and pathogen exposure, leading to bacterial adherence in airways. Understanding this molecular process is key to preventing VAP progression.
Area of Science:
- Microbiology
- Infectious Diseases
- Pulmonary Medicine
Background:
- Ventilator-associated pneumonia (VAP) is a significant nosocomial infection.
- It results from a complex interplay between host defenses and microbial factors.
- Gram-negative bacteria are common causative agents in VAP.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying bacterial adherence in the respiratory tract.
- To identify key factors contributing to the colonization of airways by gram-negative bacteria.
- To understand how risk factors for VAP influence bacterial adherence.
Main Methods:
- The study focuses on the molecular mechanisms of bacterial adherence.
- It examines host receptors, bacterial adhesins (e.g., pili), and the respiratory mucosal microenvironment.
- Analysis includes factors like exposed cell receptors, contact time, host defenses, proteases, and pH.
Main Results:
- Bacterial adherence is a critical step in the pathogenesis of VAP.
- Pili on gram-negative bacteria act as adhesins, binding to glycoprotein receptors in respiratory mucus.
- An optimal microenvironment, including exposed receptors and impaired defenses, facilitates adherence.
Conclusions:
- Bacterial adherence is a fundamental molecular process enabling airway colonization in VAP.
- All VAP risk factors ultimately impact this adherence mechanism.
- The progression from colonization to infection depends on the host's immune status.