Ventilator-associated pneumonia (VAP) refers to a lower respiratory tract nosocomial infection acquired >48h after being intubated in Intensive Care Units. Pathogenesis of VAP is mechanical and associated with microaspiration and leakage of oropharyngeal secretions around the endotracheal tube. A novel approach to VAP will attempt to explore how the abrupt ecological order of acute infection (high bacterial biomass, low community diversity) emerges from the dynamic homeostasis of a pre-existing ecosystem in which lung microbiota and local immunity interaction play their essential role.

Therefore, the investigators aim to explore if oral and lung microbiota modifications with local immunity changes, contribute in the pathogenesis of VAP in patients intubated for non-pulmonary reasons. Early changes in the host microbiota with the innate immunity system impairs tissue homeostasis and may represent a new distinct condition and a potential tool for early diagnosis and prevention of VAP.

Several factors are involved in the pathogenesis of VAP: the presence of endotracheal tube, the creation of bacterial biofilms around the device, host characteristics (comorbidities, surgery, antibiotic exposure) and, finally, immunological factors (including modulation of cytokine expression). In this study, patients mechanically ventilated for non-pulmonary reasons, will be followed up to 15 days of ventilation, estubation or death (whichever comes first). For microbiota analysis, all patients who develop VAP in the first 15 days of MV will be selected and matched (1:1; by center, gender, age (+/- 10 years), reason for intubation, duration of intubation), with a patient who do not developed VAP during MV. The optimal matching algorithm will be used to identify the control group that minimizes the total intra-pair dissimilarity.

The investigators plan to enroll about 700 MV patients for non-pulmonary conditions in order to describe VAP and non-VAP patients' characteristics identify. The investigators estimate that at least 70 patients will develop VAP in the first 15 days of MV. Microbiota and immunological analysis will be longitudinally performed on tracheal aspirate samples and oro-pharyngeal swab. The investigators will performe microbiota analyses on tracheal aspirate and oropharyngeal swab according to the following time schedule:

• VAP patient, 3 times: intubation (T0), the 24h before VAP development (T pre-VAP) and at VAP development (T-VAP).
• non-VAP patient, 2 times: intubation (T0) and a second sample, selected at the time point (day), corresponding to T-VAP of his/her matched VAP-patient (T no-VAP).

The investigators will perform immunological analysis on tracheal aspirate for all patients at intubation and at T-VAP or T no-VAP time.

Inclusion Criteria:

• Older than 18 years
• Patients ventilated for reasons other than pulmonary failure with an expected need for MV longer than 48 hours

Exclusion Criteria:

• Admission in ICU with a pneumonia
• Clinical Pulmonary Infectious Score (CPIS) > 6
• Antibiotic therapy > 3 days prior to the start of MV

All adult patients mechanicaly ventilated for non pulmonary conditions