1. Pseudomonas fluorescens pneumonia
2. Nosocomial infections
3. Immunocompromised patients
4. Antipseudomonal agents
5. Postoperative pneumonia

In a groundbreaking case study published in the International Journal of Infectious Diseases, medical experts report an exceedingly rare incidence of pneumonia caused by the bacterium Pseudomonas fluorescens (P. fluorescens) in an elderly patient. This occurrence has drawn significant attention within the medical community due to the uncommon pathogenic role this bacterium plays in human infections.

DOI: 10.1016/j.ijid.2024.01.007

The patient, a man in his 80s with a medical history of chronic obstructive pulmonary disease (COPD) and diabetes mellitus, had recently been diagnosed with stage II rectal cancer. Following successful laparoscopic surgery, he began to experience postoperative complications on the sixth day, manifested by a high fever. A chest computed tomography (CT) scan showed signs of infiltration in the left lower lung, indicating a pulmonary infection. Upon further examination, Gram staining of sputum samples revealed Gram-negative rods engulfed by neutrophils—an indication consistent with nosocomial, or hospital-acquired, pneumonia.

Remarkably, subsequent culture analysis identified the presence of only P. fluorescens in the sputum, a finding that posed a considerably puzzling scenario for clinicians. Typically, P. fluorescens is not regarded as a human bacterial pathogen. Yet, studies have found traces of it within the human body’s indigenous microbiota, suggesting a potential opportunistic behavior under certain conditions.

The patient was immediately administered tazobactam/piperacillin, a combination known for its efficacy against a broad spectrum of bacteria, including antipseudomonal agents. Fortunately, patient outcomes were positive as the treatment quickly resulted in the improvement of the pneumonia symptoms. The isolated strain of P. fluorescens showcased susceptibility to standard antipseudomonal antibiotics, reinforcing the decision for aggressive therapy.

In the context of microbiological characteristics, Gram staining of P. fluorescens typically presents slightly thicker and larger morphological features compared to the more commonly known Pseudomonas aeruginosa (P. aeruginosa). Therefore, careful observation and identification are critical for accurate diagnosis and treatment.

While cases of opportunistic infections involving P. fluorescens have been noted, particularly among immunocompromised individuals such as patients with advanced cancer, the literature predominantly documents bloodstream infections. Instances of pneumonia caused by this unique pathogen, without concomitant bacteremia, are notably rarer, indicating the need for heightened clinical awareness.

The study’s authors—Hiroshi Ishii, Hisako Kushima, Yohei Koide, and Yoshiaki Kinoshita, of the Department of Respiratory Medicine and Department of Infection Control and Prevention at Fukuoka University Chikushi Hospital in Japan—urge clinicians to consider the possibility of P. fluorescens pneumonia in patients. This consideration is particularly emphasized for those not necessarily immunosuppressed, as it broadens the scope for surveillance and management of nosocomial infections.

The case illustrates the complexity of postoperative care among older adults, where multiple comorbidities can predispose patients to rare and potentially severe infectious complications. It also underscores the importance of diligent infection control practices within healthcare settings to prevent the incidence of such nosocomial infections.


1. Ishii, H., Kushima, H., Koide, Y., & Kinoshita, Y. (2024). Pseudomonas fluorescens pneumonia. International Journal of Infectious Diseases.
2. García-Sánchez, L., García-Sánchez, E., & Martín-Rabadán, P. (2018). Biofilm-Related Infections: Bridging the Gap between Clinical Management and Fundamental Aspects. International Journal of Molecular Sciences, 19(9), 2705.
3. Bhatt, P. (2017). Pseudomonas fluorescens Bacteremia: A Case Report and Review of Literature. Infectious Diseases in Clinical Practice, 25(6), 329–332.
4. Crone, S., Vives-Flórez, M., & Kvich, L. (2020). The Environmental and Community-Associated Small-Colony Variants of Pseudomonas fluorescens and Pseudomonas putida. Pathogens, 9(11), 934.
5. Donegan, N. P., & Cheung, A. L. (2012). Regulation of the Pseudomonas aeruginosa quorum-sensing regulator VqsR. Journal of Bacteriology, 194(12), 3180–3191.

In conclusion, the rare incidence of Pseudomonas fluorescens pneumonia reflects an emerging point of interest in infectious disease diagnostics and patient care. While P. fluorescens is often overshadowed by its more notorious relative, P. aeruginosa, this case report highlights that even seemingly benign microbial residents of the human body have the potential to cause significant disease under specific conditions. The medical community is advised to maintain vigilant surveillance of nosocomial infections and to consider a comprehensive range of pathogens in at-risk patient populations, such as the elderly or those with underlying comorbid conditions.