Patient description: The patient is a 60-year-old woman admitted to the stroke department with a recent history of a second course of intravenous antibiotics for aspiration pneumonia. She is febrile and complained of abdominal pain and diarrhea (bowel movements eight times in 3 hours, large volumes of greenish, liquid stool each time). The patient's abdomen is generally tender and distend with hyperactive bowel sounds. She is febrile (38.4°C), tachycardic (113/min) and hypotensive (80/40 mmHg). The stool samples must were positive for Clostridium difficile toxin.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Healthcare-associated Pneumonia (HCAP) Hospital Acquired Pneumonia (HAP) Ventilator Associated Pneumonia (VAP) Subjects 18 years or older at the time of signing informed consent Subjects who have provided written informed consent or their informed consent has been provided by a legally authorized representative Subjects who meet the clinical diagnosis for hospital-acquired bacterial pneumonia (HABP), ventilator-associated bacterial pneumonia (VABP), or healthcare-associated bacterial pneumonia (HCABP) All subjects must fulfill at least 1 of the following clinical at screening: 1. New onset or worsening of pulmonary symptoms or signs, such as cough, dyspnea, tachypnea (eg, respiratory rate > 25 breaths/minute), expectorated sputum production, or requirement for mechanical ventilation 2. Hypoxemia (eg, a partial pressure of oxygen [PaO2] < 60 mm Hg while the subject is breathing room air, as determined by arterial blood gas [ABG], or worsening of the ratio of the PaO2 to the fraction of inspired oxygen [PaO2/FiO2]) 3. Need for acute changes in the ventilator support system to enhance oxygenation, as determined by worsening oxygenation (ABG or PaO2/FiO2) or needed changes in the amount of positive end-expiratory pressure 4. New onset of or increase in (quantity or characteristics) suctioned respiratory secretions, demonstrating evidence of inflammation and absence of contamination All subjects must have at least 1 of the following signs: 1. Documented fever (ie, core body temperature [tympanic, rectal, esophageal] ≥ 38°C [100.4°F], oral temperature ≥ 37.5°C, or axillary temperature ≥ 37°C) 2. Hypothermia (ie, core body temperature [tympanic, rectal, esophageal] ≤ 35°C [95.0°F], oral temperature ≤ 35.5°C and axillary temperature ≤ 36°C) 3. Leukocytosis with a total peripheral white blood cell (WBC) count ≥ 10,000 cells/mm³ 4. Leukopenia with total peripheral WBC count ≤ 4500 cells/mm³ 5. Greater than 15% immature neutrophils (bands) noted on peripheral blood smear All subjects must have a chest radiograph during screening showing the presence of new or progressive infiltrate(s) suggestive of bacterial pneumonia. A computed tomography (CT) scan in the same time window showing the same findings could also be acceptable All subjects must have a suspected Gram-negative infection involving the lower respiratory tract  Subjects who have known or suspected community-acquired bacterial pneumonia (CABP), atypical pneumonia, viral pneumonia, or chemical pneumonia (including aspiration of gastric contents, inhalation injury) Other exclusions based on the prescribing information of meropenem or linezolid, prior antibiotic usage, age, and pregnancy