Pseudomonas mendocina Urinary Tract Infection: A Case Report and Literature Review

Pseudomonas mendocina is a Gram-negative bacillus from the family Pseudomonadaceae. The first P. mendocina-related infection was reported in 1992. Although a rare cause of infections, P. mendocina has been known to cause severe infections that require intensive treatment. We present the first documented case of urinary tract infection caused by P. mendocina. An 83-year-old male with a past medical history of diabetes, hypertension, coronary artery disease, and prostate cancer with bone metastases, currently being treated with abiraterone and prednisone, presented with subjective fever, fatigue, altered mental status, dysuria, and hematuria of one-week duration. He was found to have a complicated urinary tract infection with an incidental asymptomatic COVID-19 infection on admission. The patient was empirically treated with ceftriaxone and switched to cefepime for broader coverage on day two of hospitalization. Urine culture reported the presence of P. mendocina with resistance only to fluoroquinolones. Ceftriaxone was reinstated. The patient was successfully treated with a seven-day course of ceftriaxone (days 1-3, days 6-7) and cefepime (days 4-5) but continued to remain inpatient for a later symptomatic COVID-19 pneumonia with discharge on day 15. The majority of P. mendocina infections present as skin and soft tissue infections, infective endocarditis, meningitis, and bacteremia. Ours is the first documented case of urinary tract infection caused by P. mendocina, particularly in an immunocompromised COVID-19 patient, and the second to report P. mendocina with resistance to fluoroquinolones. This report contributes to the growing literature regarding P. mendocina-related infections.

A systematic review of current literature reveals endocarditis, meningitis, and bacteremia to be the most common presentations of P. mendocina infections [18]. In the United States, there have been four documented cases of P. mendocina-related infections, which include three reports of bacteremia and one report of infective endocarditis [13][14][15][16]. In this case report, we present the first documented case of urinary tract infection caused by P. mendocina.
Suprapubic or costovertebral tenderness was not elicited on the abdominal exam. A genitourinary exam revealed no masses, blood, or discharge at the penile meatus. There was no edema, erythema, lesions, or warmth noted in the penis or scrotum.
Laboratory evaluation revealed pancytopenia with a WBC count of 2530/μL, absolute neutrophil count of 1200/μL, hemoglobin of 11.1 g/dL, and a platelet count of 106/μL ( Table 1). A urinalysis demonstrated RBC 16/hpf, WBC 13/hpf, protein 100 mg/dL, urobilinogen 4 mg/dL, with small amounts of blood, negative nitrite, trace leukocyte esterase, and few bacteria ( Table 2). A standard pre-admission COVID-19 screening test was positive. Chest X-rays showed mild right basilar hazy reticulation and minimal left basilar opacification ( Figure 1). The patient was admitted with a complicated urinary tract infection and a concurrent asymptomatic incidental COVID-19 infection. Therapy was initiated with ceftriaxone.

FIGURE 1: Chest X-ray of our patient on admission
The patient remained febrile during the first three days of admission with a maximum temperature of 38.5°C (101.4 °F). Absolute neutrophil count and WBC increased to 4300/μL and 5060/μL, respectively, on day 2 of admission ( Table 1). Preliminary urine culture reported >100,000 CFU/mL of Gram-negative rods. Multiple blood cultures were negative for the presence of bacteria. Due to the persistence of fever, the antibiotic coverage was broadened to cefepime while awaiting final speciation.
A urine culture report from our hospital microbiology department demonstrated the presence of P. mendocina with resistance to ciprofloxacin and levofloxacin. The provided antibiotic susceptibilities of the P. mendocina isolate from our patient are summarized in Table 3. MICs were not available to us retrospectively. Following the report, cefepime was discontinued and ceftriaxone was reinstated. By day 7 of admission, the patient no longer endorsed hematuria or dysuria. Absolute neutrophil count and WBC were 3800/μL and 4680/μL on day seven of admission ( Table 1). The patient received a total of seven days of ceftriaxone (days 1-3, days 6-7) and cefepime (days 4-5). The patient was intermittently febrile, likely due to underlying malignancy and COVID-19 infection. A repeat urinalysis obtained due to the persistence of fevers showed no bacteria, with negative nitrite, negative leukocyte esterase, and moderate blood ( Table 2). Complete resolution of urinary symptoms post-antibiotic therapy suggested that these symptoms were due to his urinary tract infection and less likely his prostate cancer. The hospital course was complicated by hypoxic respiratory failure due to COVID-19 infection, requiring prolonged hospitalization. The patient was successfully discharged after a 15-day hospital stay.

Discussion
Pseudomonas aeruginosa has been known to cause severe nosocomial and opportunistic infections in immunocompetent and immunocompromised adults [19]. P. mendocina, however, is a rare cause of human infections and is less frequently reported in the literature.
P. mendocina can infect both immunocompromised and immunocompetent hosts. Most of the reported P. mendocina-related infections occurred in immunocompetent adults with several comorbidities, as shown in Table 4. A few cases were reported in immunocompromised adults. Gani et al. reported bacteremia in a patient with resistant HIV/AIDS [16]. Huang et al. reported meningitis in a patient with a history of diabetes mellitus type 2 and buccal cancer [3]. Gupta et al. previously reported a wound infection in a patient with diabetes mellitus type 2 and a prolonged history of asthma and intermittent corticosteroid use [7]. Our patient had a 10-year history of prostate cancer with bone metastases and was receiving treatment with abiraterone 1000 mg daily with an injection every three months and prednisone 5 mg daily. His immune system might be compromised due to his prostate cancer and treatment. It can be argued that P. mendocina caused an opportunistic urinary tract infection in our immunocompromised patient.
Recent literature has documented the increase in opportunistic infections in patients with concomitant COVID-19 infections [20]. In particular, fungal infections remain the most common opportunistic infections amongst immunocompromised adults with COVID-19 [21,22]. Studies have also reported the association of COVID-19 with bacterial infections [23]. These infections are classified as nosocomial infections and are associated with increased morbidity and mortality among COVID-19 patients. In these patients, Staphylococcus aureus and Haemophilus influenzae are the most common bacterial infections [24]. Mycoplasma pneumoniae, Pseudomonas aeruginosa, and Legionella pneumophila are other important bacterial pathogens that were detected among COVID-19 patients [22]. However, to date, no report has shown infection of P. mendocina in those with COVID-19 infections. We suspect that the combination of active COVID-19 infection and our patient's cancer status and treatment increases the risk for P. mendocina infection.
Multiple sources of P. mendocina were proposed but never confirmed in previous case reports. In the firstever report of P. mendocina, Aragone et al. proposed that P. mendocina caused infective endocarditis by entering through thorn pricks and handling of damp earth as the patient was a florist with previous aortic valve placement and a permanent pacemaker [2]. Johansen et al. suspected that bacteria was introduced during one of the three cardiac operations, resulting in infective endocarditis [8]. Gupta et al. proposed that P. mendocina was present in soil and water, which gained entry into a leg wound when the patient fell while working on his farm [7]. In the case reported by Nseir et al., since the patient owned "a new pet cockatiel that he fed and watered directly from his mouth," the shared drinking water might be the source of P. mendocina [11]. In our patient, the source of P. mendocina was not identified.
Our case report adds to the current literature regarding P. mendocina infections. Although further research is required to identify the underlying pathogenicity and mechanism of P. mendocina infections, our report contributes to the growing body of publications that can help guide clinical management and treatment of P. mendocina infections in the future.

Conclusions
P. mendocina is a gram-negative bacillus that rarely causes infections in humans. When it does, P. mendocina has been known to cause skin and soft tissue infections, infective endocarditis, meningitis, and bacteremia. Our case is the first to report a urinary tract infection caused by P. mendocina and the second with fluoroquinolone resistance. In particular, this is also the first report on P. mendocina infection in an immunocompromised patient with COVID-19. Our report is the fifth documented case of P. mendocinarelated infections in the United States, contributing to the growing literature regarding P. mendocina-related infections.

Additional Information Disclosures
Human subjects: Consent was obtained or waived by all participants in this study. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.