This study evaluates that P. aeruginosa, A. baumannii, K. pneumonia and Staph aureus which are obtained from patients' tracheal aspiration culture who treated with mechanical ventilation will be compared with Lactobacillus (LAB) members and nisin bactriocin in the laboratory. The aim is to investigate the probiotics' antimicrobial properties and effects on these bacteria's growth rate.

Ventilator associated pneumonia (VAP) is one of the most commonly seen hospital-acquired infections that occurs in patients who receive mechanical ventilation. VAP usually occurs 48-72 hours after mechanical ventilation and is related increased incidence of multidrug-resistant infections, increased antibiotic use, extended mechanical ventilation time, increased patient stay in the intensive care unit (ICU), and increased patient stay in the hospital. One recent intervention is the probiotic therapy which is a nonantibiotic strategy for maintenance of the host's aerodigestive microbial balance and VAP prevention.Common causative pathogens of VAP include Gram negative bacteria such as Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter species, and Gram-positive bacteria such as Staphylococcus aureus. In this study, these Gram negative pathogens obtained from mechanical ventilated patients' tracheal aspiration culture and reference bacteria strains will be compared with Lactobacillus (LAB) members and nisin in the laboratory. Probiotics' antimicrobial properties and effects on these bacteria's (obtained from patients and reference strains) growth rate will be investigated.

Inclusion Criteria:

• Patients who mechanically ventilated at least 48 hours in the intensive care unit

Exclusion Criteria:

• Patients who mechanically ventilated less than 48 hours

Patients who mechanically ventilated at least 48 hours will be included. Patients' tracheal aspirate cultures will be used for study. Pseudomonas aeruginosa, Acinetobacter baumanii, Staphylococcus aureus and Klebsiella pneumoniae will be isolated from tracheal aspiration cultures.Antimicrobial effects of Lactobacillus members will be investigated on the bacteria's growth rate in the laboratory.