Community acquired pneumonia due to gram negative bacilli and its antibiotic sensitivity pattern in a tertiary care centre

Ashish Jitendranath, Sudin Koshy


Background: Gram negative bacteria along with Pseudomonas constitute a significant cause of morbidity and mortality due to pneumonia. As a result it is essential to have appropriate empirical antimicrobial treatment strategies based on the sensitivity pattern of a particular region. In cases with high likelihood of gram negative pneumonia it is essential to start appropriate empirical antibiotics as early as possible to reduce the morbidity and mortality. This study is done to know the antibiotic pattern of gram negative organisms isolated from the institute so that the study can constitute an empirical antibiotic regimen.

Methods: A retrospective study was done from January to March 2016. Patients admitted in the medicine and pulmonology department of the hospital who were diagnosed to have pneumonia symptoms. Patients with symptoms, signs and radiological features of pneumonia and sputum cultures with gram negative organisms were included in the study. Gram staining of all samples were taken and bartlet grading was done. All the sputum samples were cultured on blood agar, chocolate agar and macconkey agar. The colonies were then identified using biochemical tests. Antibiotic sensitivity was done following CLSI 2015 guidelines. We also tested for Amp C, ESBL and MBL using standard testing protocol.

Results: During the study period in 120 cases of pneumonia, there was growth of pathogenic organism. Among the GNB isolated Klebsiella spp was the most common organism isolated at 33.9% followed by Pseudomonas aeruginosa and Escherichia coli at 22.1%. Out of the 53 gram negative samples isolated 4 (7%) were Amp C positive, 10 (18.8%) were ESBL positive and there was one single case of MBL. The antibiotic sensitivity showed that all the isolates were sensitive to colisitin (100%), while Klebsiella spp, Pseudomonas spp, and Escherichia coli were 100% sensitive to imipenem and meropenem. Resistance pattern of all the isolates showed that the isolates exhibited high resistance to amoxycillin-clavulunate, cefuroxime and cotrimoxazole. While resistance against ceftazidime and cefipime was >40%. On the other hand, isolates showed a low level of resistance against piperacillin tazobactam and cefoperazone-sulbactam. Extremely low level of resistance was observed against imipenem and meropenem, while colistin showed no resistance among the isolates obtained in this study.

Conclusions: The study showed that gram-negative bacteria and P. aeruginosa form a relevant part of the microbial pattern of CAP in patients who require hospitalization, particularly those with severe CAP. Initiating antibiotics with gram negative coverage should be considered in this subgroup of patients since initiating the correct antibiotic plays a critical role in the outcome of pneumonia.



Community acquired pneumonia, Gram negative bacilli, Pseudomonas, Colistin

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