The goal of this clinical study is to demonstrate that the application of pharmacodynamic dosing principles to the antibiotic treatment of hospitalized subjects with culture-documented pneumonia (including HABP, VABP and HCAP) requiring mechanical ventilation can inhibit the emergence of antibiotic-resistant organisms during treatment and therefore may improve the rate of a satisfactory clinical response. Antibiotic resistance is defined as an increase in meropenem or aminoglycoside MIC by two tube dilutions (fourfold) from baseline. In animal models of infection, the pharmacodynamic driver for bactericidal effect by β lactam antibiotics such as meropenem is the proportion of the dosing interval during which plasma drug levels are maintained above the MIC of the causative pathogen. The hypothesis of this study is that prolongation of time above MIC by increasing total meropenem dose and the duration of infusion will counter-select for the emergence of antimicrobial resistance during the treatment of hospitalized subjects with pneumonia (i.e. HABP, VABP and HCAP) caused by P.aeruginosa, Acinetobacter species (spp), or other pathogens with intermediate susceptibility to meropenem, and that the addition of parenteral aminoglycosides (amikacin, tobramycin or gentamicin) and nebulized aminoglycoside (tobramycin) given along optimal pharmacodynamic principles will further reduce the likelihood of resistance emergence, particularly among the non-fermenting Gram-negative bacilli, such as Pseudomonas aeruginosa and Acinetobacter spp. The observed incidence of resistance emergence to meropenem will be compared across therapeutic regimens.