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Abstract According to World Health Organization (WHO), lower respiratory tract infections are the third most common cause of death worldwide. These infections are mainly caused by multidrug-resistant (MDR) bacteria. Between 8% - 28% of patients receiving mechanical ventilation are affected by ventilator associated pneumonia (VAP).The causative microorganisms are extremely resistant rendering the proper choice of antibiotics for treatment difficult. The drugs which disrupt virulence factors of bacteria are more promising as the bacteria cannot develop resistance against them. Quorum sensing inhibitors are used to disrupt intra and inter bacterial communications giving better chance for host defense mechanishms. The aim of current study was to characterize bacteria isolated from VAP patients, to evaluate the effectiveness of some antimicrobial agents, characteraize MDR strains, screen isolates for quorum sensing systems and to evaluate efficacy of different essential oils as quorum sensing inhibitors. Clinical bacterial isolates were recovered from patients having pneumonia associated with mechanical ventilation from intensive care units of Zagazig University Hospital and identified using standard microbiological methods. The specimens were cultured on nutrient agar, blood agar, Mac-Conkey agar and mannitol salt agar and incubated for 24 hours at 37°C. Isolated bacteria were characterized using cultural and biochemical characteristics. A total of 233 bacterial isolates were recovered from 153 endotracheal aspirate samples, compromising 203(87.1%) Gram negative and 30 (12.9%) Gram positive isolates. The major isolates were Klebsiellapneumoniae (36.9%), Escherichia coli (21.03%), Acinetobacter baumannii (14.59%), Pseudomonas aeruginosa (14.16%) and Staphylococcous aureus (12.02%). |