Isolation of Viridans Streptococci as the causative agent of pneumonia in bronchoalveolar lavage samples of patients with pneumonia

Pneumonia is one of the most important causes of death worldwide and its accurate diagnosis is extremely important. Typically, Viridans Streptococci are not the cause of pneumonia, but in patients with an underlying illness, they can be problematic. Also, due to contamination with the microbial flora of the upper respiratory tract, they may be isolates from a pure culture, which makes it difficult for the physicians and laboratory staff to diagnose. The aim of this study was to evaluate the incidence of Streptococci Viridans as a cause of pneumonia in patients with underlying disease.
This cross-sectional retrospective (2011-2014) study was carried out using a medical records of patients admitted to the infectious disease ward of city hospitals in Tehran, Iran. The patients, including people with pneumonia that were confirmed by X-ray and also had an underlying disease. The BAL samples were obtained from these patients and were cultured. The antibiotic susceptibility test was done for Streptococcus viridans isolates.
The results reveal that out of 168 pneumonia patients, VS have been isolated from BAL samples of 54 cases (32 %). In 31 cases (57%) VS were the only isolated pathogen. In none of the samples, the pneumococcus was not isolated. According to results of antibiotic susceptibility test, the highest rate of resistance was seen for cotrimoxazole, and the lowest rate was seen for vancomycin and ceftazidime.
Regarding the high frequency reported of Streptococcus viridans as a cause of pneumonia in the period of study and the lack of isolation of other organisms, such as pneumococcus, it is possible that the BAL sample be contaminated with the normal flora of the respiratory system. Although the BAL is very valuable sample for the diagnosis of pneumonia causative agent, but based on the culture of this sample alone, it can not report Streptococcus viridans as a cause of pneumonia.