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Introduction: A rise in antimicrobial resistance makes it imperative to study the bacterial aetiology and antimicrobial susceptibility profiles of commonly isolated organisms causing lower respiratory tract infections from both the community and the hospital setting. Aim: To study the bacterial aetiology of Lower Respiratory Tract Infections (LRTI) cases from the community and hospital in the present setting and determine the antimicrobial susceptibility profile of the frequently isolated pathogens. Material and Methods: A prospective observational study was conducted over 15 months at a 1531-bedded tertiary care hospital in Delhi, India. All consecutive sputum, Endotracheal (ET) aspirates and Broncho-Alveolar Lavages (BAL) samples submitted for culture and susceptibility testing were included. Infectious Diseases Society of America (IDSA) definitions were used to categorise the Patients as Community Acquired Pneumonia (CAP) or Hospital-Acquired Pneumonia (HAP) cases. Isolates were identified using conventional methods including colony morphology, gram’s staining, motiliy and biochemical reactions and antimicrobial susceptibility was performed as per CLSI guidelines by disk diffusion. Colistin MIC was determined by agar dilution method. E-test strips were used to determine the MICs of penicillin, cefotaxime and ceftriaxone for isolates of Streptococcus pneumoniae. Results: A total of 4748 samples received, 2555 were sputum, 2141 ET aspirates and 52 BAL samples. A total of 792 non-duplicate organisms were isolated of which 316 isolates were from CAP as compared to 476 isolates from HAP. K. pneumoniae (31%), P. aeruginosa (22%), E. coli (16%) and Acinetobacter species (16%) were the most common bacteria isolated from the community. Amongst the cases of HAP, Acinetobacter species (48%), P. aeruginosa (21%), K. pneumoniae (16%), S. aureus (5%) and E. coli (4%) were commonly isolated. Very high rates of resistance to cephalosporins were observed in both CAP and HAP isolates. K. pneumoniae isolates from hospital were also significantly (p-value<0.001) more resistant to carbapenems, aminoglycosides, ciprofloxacins as compared to those from the community. P. aeruginosa CAP strains showed high rates of susceptibility to all first and second line drugs tested (73-100%). In comparison, HAP strains were significantly more resistant to all classes of antimicrobials tested (p-value<0.001). A. baumannii isolates from both community and hospital were highly resistant to all classes of drugs except for colistin. Overall MRSA rate were 60%. CONCLUSION: High prevalence of resistance to most antibiotics amongst Enterobacteriaceae and non-fermenting GNB isolates was observed in HAP cases with only colistin as a last resort drug. Rational use of antibiotics based on local antibiogram is essential to improve treatment outcomes and reduce antimicrobial resistance.