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Antibiotic Resistance & Bacterial Pneumonia

Clinician's Brief (Capsule)

December 2014

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Bacterial pneumonia is a relatively common acquired inflammatory lung disease, caused by bacterial colonization of the lower airways and lung parenchyma. Tracheal washes are a useful sampling technique for bacterial culture and sensitivity; however, antimicrobials are often empirically chosen and started prior to completion of test results. This study sought to determine the proportion of airway bacterial isolates resistant to empirically selected and recently administered antimicrobials and assess the impact of resistance on length of hospital stay and morbidity or mortality.

A retrospective study examined 111 cases of canine bacterial pneumonia in which tracheal wash samples were submitted for aerobic bacterial culture. Each case was assigned to 1 of 3 groups: community-acquired pneumonia, aspiration pneumonia, or other causes. Overall, 26.1% of the dogs had at least 1 bacterial isolate resistant to the empirically selected antimicrobials. Despite lacking statistical significance, there was a trend toward longer hospital stays in dogs with bacterial isolates that showed resistance to empirical choices. A higher incidence (57.4% of dogs with available susceptibility data) was found of in vitro bacterial resistance to antimicrobials that had been administered in the 4 weeks before pneumonia diagnosis. Results suggested avoiding use of any recently administered antimicrobials while selecting empiric antimicrobial therapy and awaiting susceptibility results.


This study highlighted two important concepts. This first is the decision to perform sampling for aerobic culture and sensitivity testing. This study supported that empiric antibiotic therapy is often ineffective based on culture and sensitivity data and provides strong evidence for collecting samples after diagnosis. The second concept is that recent antibiotic therapy may change bacteria flora, potentially leading to an increased rate of antimicrobial resistance. The take-home is to strongly consider performing an aerobic culture in any dog with pneumonia before starting empiric therapy and consider it mandatory for dogs that have received antimicrobials in the preceding 4 weeks.—Elizabeth A. Rozanski, DVM, DACVIM, DACVECC


In vitro bacterial isolate susceptibility to empirically selected antimicrobials in 111 dogs with bacterial pneumonia. Proulx A, Hume DZ, Drobatz KJ, Reineke El. JVECC 24:194-200, 2014.

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