Pseudomonas otitidis Bacteremia in a Patient with Cancer during the Palliative-care Phase.

Introduction

Pseudomonas otitidis was first described in 2006 as a causative agent of otic infections ( 1 ). This organism is a member of the genus Pseudomonas which is frequently isolated from ear infections ( 2 - 4 ) and is characterized by the production of chromosomal metallo-beta-lactamase (MBL), named P. otitidis metallo-β-lactamase (POM-1) ( 5 ). Infections other than ear infections are rare, but necrotizing fasciitis and panperitonitis have been reported ( 6 ). To date, only two cases of bacteremia caused by P. otitidis have been reported in immunocompromised patients ( 7 , 8 ). We herein report a case report of bacteremia in an immunocompromised patient during the palliative-care phase.

Case Report

A 79-year-old Japanese man with postoperative recurrence of advanced appendiceal cancer and chronic kidney disease was admitted to our hospital for palliative care. The patient's condition stabilized after hospitalization. On day 5, the patient developed a fever with chills, and ampicillin/sulbactam was initiated (3 g every 12 h) for a presumed upper respiratory infection. On day 7, two sets of blood cultures revealed the presence of Pseudomonas spp. An infectious disease consultation was also performed.

A physical examination revealed the following: blood pressure, 115/68 mmHg; pulse rate, 81 beats/min; temperature, 37.4°C; respiratory rate, 20 breaths/min; and oxygen saturation, 98% on room air. Physical examination results, including otitis media and other foci, were unremarkable. Initial laboratory tests revealed a white blood cell count of 8,800/μL with 87% neutrophils, a hemoglobin level of 11.5 mg/dL, and a platelet count of 234,000/μL. A serum chemistry evaluation revealed the following results: blood urea nitrogen, 81 mg/dL; creatinine, 4.5 mg/dL; sodium, 135 mEq/L; potassium, 4.4 mEq/L; chloride, 105 mEq/L; albumin, 3.1 g/dL; total protein, 5.4 g/dL; aspartate aminotransferase, 43 IU/L; alanine aminotransferase, 18 IU/L; lactate dehydrogenase, 257 IU/L; alkaline phosphatase, 233 U/L; total bilirubin, 0.5 mg/dL; glucose, 108 mg/dL; C-reactive protein, 24.6 mg/dL. The urinalysis results were normal, and chest radiography revealed no pneumonia.

Piperacillin/tazobactam treatment was started (2.25 g every 8 h) after 2 sets of blood cultures were obtained. Precise identification was difficult using a MicroScan WalkAway 40 Plus system (Siemens Healthcare Diagnostics, Tokyo, Japan). A strain was isolated based on whole-cell matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS; MALDI-TOF Biotyper; Beckman Coulter, Tokyo, Japan), and P. otitidis was identified with a score of 2.12. A blood culture on admission revealed P. otitidis . The P. otitidis strain exhibited susceptibility to piperacillin, piperacillin/tazobactam, ceftazidime, cefepime, gentamicin, amikacin, and levofloxacin but was resistant to meropenem ( Table ). The patient was successfully treated with a two-week course of piperacillin/tazobactam. Unfortunately, however, he died on day 36 from Candida glabrata fungemia ( Figure ).

Discussion

We successfully treated P. otitidis bacteremia in a patient with appendiceal cancer during the palliative-care phase. Pseudomonas otitidis is mostly associated with ear infections, such as otitis externa and otitis media ( 2 - 4 ). In addition, severe infections, such as necrotizing fasciitis and diffuse peritonitis, have been reported ( 6 ). Two cases of bacteremia have been reported previously. Caixinha et al. reported the first case of bacteremia caused by P. otitidis in a 59-year-old patient with a history of moderate chronic obstructive pulmonary disease, bronchiectasis, and recurrent pneumonia ( 7 ). Mori et al. reported that a 70-year-old Japanese man with multiple myeloma developed cellulitis and bacteremia during chemotherapy, and P. otitidis was identified using MALDI-TOF MS ( 8 ). Similarly, the present report describes the case of an immunocompromised patient who developed bacteremia while receiving palliative care for cancer. This disease has raised concerns owing to its potential to cause infections in immunocompromised patients, as in the present case ( 6 ). In our case, there were no evident signs of otitis media or respiratory or urinary tract infections and no indications of hepatobiliary or peripheral catheter-related infections. As a result, no definitive infectious focus was identified, leading us to conclude that the source of infection was unknown. At the time of admission, there were no signs of infection, which was considered to have developed after hospitalization. Whether the infection is community-acquired or healthcare-associated thus remains unclear; however, a gastrointestinal source of bacterial translocation is a possible consideration. It is important to recognize that P. otitidis can cause bacteremia in immunocompromised patients.

P. otitidis is homologous to Pseudomonas aeruginosa among Pseudomonas spp. in the 16S rRNA gene analysis and is similar to P. aeruginosa in terms of its biochemical properties and colony shape ( 1 ). It is difficult to distinguish P. otitidis from P. aeruginosa using phenotypes alone; therefore, molecular biological techniques such as 16S rRNA gene analyses are used to facilitate differentiation. P. otitidis is characterized by MBL production via the possession of a chromosomal MBL gene. It was the first species in the genus Pseudomonas to possess a chromosomal MBL-producing gene ( 5 , 9 ). POM-1 is most similar to the PAM family produced by related Pseudomonas spp. Among other genera, it is most similar to the L1-family of Stenotrophomonas ( 5 , 9 ). POM-1 has high substrate resolution for carbapenems and penicillins ( 5 , 9 ). Drug susceptibility testing of clinical isolates often shows intermediate to high resistance to carbapenems but susceptibility to piperacillin and cephalosporins ( 3 , 5 ). In previous cases, the use of advanced diagnostic methods, such as MALDI-TOF MS and gene sequencing, has enabled accurate identification ( 7 , 8 ). Thus, if a suspected Pseudomonas pathogen is susceptible to penicillin or cephalosporin antibiotics but resistant to carbapenems, P. otitidis should be considered and confirmed using MALDI-TOF MS. Regarding piperacillin/tazobactam treatment, piperacillin hydrolysis by POM-1, a metallo-β-lactamase produced by P. otitidis , raises concerns about its appropriateness ( 5 , 9 ). Cephalosporin-based therapy may thus have been a better choice in the present case. There have been several reported cases in which improvement was observed with the use of quinolone antibiotics, and if the susceptibility results show sensitivity, treatment with quinolones could be considered. However, the further accumulation of cases is required ( 3 , 6 ). Although Pseudomonas otitidis lacks AmpC β-lactamase, resistance mechanisms such as efflux pumps may contribute to increased minimum inhibitory concentrations ( 5 ). While piperacillin/tazobactam was effective, cephalosporins may be more reliable when POM-1 is present ( 5 , 9 ).

In conclusion, we report a case of bacteremia caused by P. otitidis that was diagnosed using MALDI-TOF MS and successfully controlled using antipseudomonal antibiotic therapy in a patient with advanced appendiceal cancer during the palliative-care period. Clinicians and microbiologists should be aware that P. otitidis can cause bacteremia, particularly in immunocompromised patients.

This report was in accordance with the principles of the Declaration of Helsinki. The patient's family provided consent for the publication of the case report.

The authors state that they have no Conflict of Interest (COI).

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