Hospital-acquired pneumonia (HAP) is defined as an infection of the pulmonary parenchyma in patients who acquire the condition at least 48 hours after admission to the hospital or within 14 days after discharge from the hospital. Ventilator-Associated Pneumonia (VAP) represents a significant sub-set of HAP occurring in Intensive Care Units (ICUs) and is defined as pneumonia that occurs more than 48 to 72 hours after tracheal intubation and is thought to affect 10% to 20% of patients receiving mechanical ventilation for more than 48 hours. In critically ill patients, the susceptibility of the bacteria isolated in VAP depends on the duration of stay in the ICU and on MV as well as the previous use of antibiotics. VAP has been classified into early and late onset. Early-onset VAP occurs within less than 96 hours of ICU admission and is generally due to antimicrobial-sensitive bacteria.Late-onset VAP occurs after 96 hours of ICU admission and may be caused by an MDR pathogen. Resistance genes may be transferred to bacterial species capable of causing kinds of infections other than the original one. Successful genes may then be further selected and transferred to new hosts and in that process ,being amplified and established as important resistance genes, especially if the selection pressure of antibiotics continues. As an example, resistance to sulfonamides has been found throughout the world encoded by only two resistance genes. Antibiotic resistance genes carried in bacterial chromosomes and genetic elements have been suggested as potential emerging environmental pollutants