In this study, pneumonia panel tests were performed in combination with culture tests and Gram staining, and the selection of antimicrobial agent(s) was investigated, especially when resistant organisms were detected. The administration of antibiotics might be appropriately determined for each patient based on the collation of the results of Gram staining and the patient’s condition.

The pneumonia panel is a highly sensitive test, whose results are reportedly supported by quantitative PCR testing and sequencing analysis in 871 of 875 samples that were panel positive and culture negative (manufacturer’s instructions). Moreover, not only is the test capable of quickly identifying the causative organism, but can also simultaneously detect drug resistance genes, making it extremely useful in the treatment of acute pneumonia. However, specimen quality is extremely important since it determines the overall quality of the test, and each facility should develop its own rejection rules (manufacturer’s instructions). As shown by the results of this study, the best indication for the pneumonia panel is patients with pneumonia under intubation because good quality sputum can be obtained from these patients. However, it is difficult to make poor sputum quality an absolute contraindication for the panel test. This is because it is difficult to obtain good quality sputum from non-intubated patients, and the quality of sputum in patients with aspiration pneumonia is inherently poor.

In this study, Gram staining was performed concomitantly with the pneumonia panel. The quality of the sputum was evaluated, and the results of each test could be confirmed for better selection of the antimicrobial agent(s). Three specific patterns are possible. First, when Gram staining of a good quality sputum specimen is indicative of the presence of an inflammatory causative organism, the pneumonia panel can confirm whether the organism is potentially drug resistant, which will aid in the selection of the antimicrobial agent. Second, when a drug resistance gene is detected in the pneumonia panel, a decision is made whether or not to cover the resistant organisms on the basis of the sputum quality, bacterial species, and phagocytosis by leukocytes determined by Gram staining (for example Fig. 4) and the general condition of the patient. Third, if resistant bacteria are detected when the quality of sputum is poor in a patient, we should consider whether a patient have aspiration pneumonia or not. Thus, antibiotic escalation may be selected depending on the patient’s condition. In summary, the pneumonia panel is a highly sensitive test, and not all species detected in the panel are targets for treatment. Confirmation of the species, number of bacteria, and phagocytosis by leukocytes by Gram staining can better define the treatment target, and it is particularly useful in detecting resistant bacteria in the pneumonia panel. Thus, the combined use of the panel and Gram staining is expected to lead to better selection of antimicrobial agents.

Gram staining showing presence of GPC and phagocytosis by leukocytes

Although several studies have investigated pneumonia panels over the past few years [1, 2, 7, 12, 14], no study has examined them in conjunction with Gram staining. Combination with Gram staining may lead to better selection of antimicrobial agents, and we expect to our study to form the foundation of further research in the future.

There are several limitations to this study. First, the sample size was small and the study was conducted at a single institution, making generalization of the findings difficult. Second, we were unable to examine whether aspiration pneumonia was related to the quality of sputum. It is important to enroll a large sample population and conduct a detailed multicenter study in the future.