Rare Urinary Tract Infection by Rodentibacter pneumotropicus (formerly, Pasteurella pneumotropica) in an Immunocompetent Patient

Introduction

The description of the bacterium protagonist in the present case, Rodentibacter pneumotropicus, has changed over time. Originally, it was classified by Jawetz in 1950 as Pasteurella pneumotropica [1]. It is a gram-negative bacillus originally described as belonging to the [Pasteurella] genus (the brackets indicate an earlier misclassification; however, this is the name that was used in the cited literature), which was commonly found in the respiratory tract of various mammals, including rodents and laboratory animals [2]. Despite its tropism for infecting these organisms, it is also capable of infecting humans [3].

In the past, differentiation of [P. pneumotropica] from other Pasteurella species relied on observing positive cultures for urease activity, maltose use, and reactions with mannitol; these characteristics helped to differentiate this bacterium from others within the Pasteurella genus [4]. In humans, it is reported to occur as an opportunistic infection, most frequently in immunocompromised individuals, particularly those in close contact with animals, such as laboratory animal caretakers or pet owners. Reported infections in humans from R. pneumotropicus [P. pneumotropica] range from local skin infections to more severe cases, including abscess, septic arthritis, respiratory infections, and bone involvement. However, infections caused by R. pneumotropicus [P. pneumotropica] are rare in humans [5].

Approximately 70% of human infections attributed to bacteria from the Pasteurella genus are caused by P. multocida, with an estimated annual incidence of approximately 0.19 per 100 000 individuals. The identification of isolates from other species, such as R. pneumotropicus [P. pneumotropica], is considerably less common [6].

The capacity of R. pneumotropicus [P. pneumotropica] to colonize the respiratory tract of rodents and, occasionally, to infect humans, highlights the importance of understanding its biology and clinical significance. The pathophysiology of R. pneumotropicus [P. pneumotropica] infection includes the ability to adhere to host cells, evade the body’s immune response by inhibiting complement system activation, and secrete toxins that cause local damage and facilitate infection spread [7].

Treatment with routine antibiotics resolves the infection, but it has to be based on bacterial susceptibility. Previous studies have demonstrated that strains of R. pneumotropicus [P. pneumotropica] isolated from blood cultures are sensitive to aminopenicillins or their combination with beta-lactamase inhibitors, second- and third-generation cephalosporins, macrolides, fluoroquinolones, aminoglycosides, and fosfomycin [8].

The analysis of published cases of infections caused by Pasteurella species across diverse clinical contexts underscores the importance of identifying and managing these infections, particularly in immunocompromised individuals. Infections frequently result from animal bites or scratches, and empirical antibiotic treatment followed by adjustments on the basis of antimicrobial sensitivity is effective in treating Pasteurella bacteremia.

In recent years, the bacterium originally described by Jawetz and classified as Pasteurella pneumotropica was reclassified as R. pneumotropicus because of advances in molecular phylogenetics. Earlier classifications relied on phenotypic characteristics, which led to confusion due to the organism’s variability. DNA–DNA hybridization studies and 16S rRNA gene sequencing demonstrated that R. pneumotropicus [P. pneumotropica] was genetically distinct from Pasteurella multocida, the type species of the genus Pasteurella. Further whole-genome analyses showed that the R. pneumotropicus [P. pneumotropica] complex formed a monophyletic group distinct from other Pasteurellaceae, leading to the establishment of Rodentibacter as a separate genus. This taxonomic update has improved the accuracy of bacterial identification and clarified their epidemiology and clinical implications [9].

According to this update, R. pneumotropicus is now described as a gram-negative facultative anaerobic bacterium that colonizes the mucous membranes of rodents, particularly laboratory mice and rats. As an opportunistic pathogen, it primarily causes localized infections under immunosuppressive conditions or when host defenses are compromised. The species is non-hemolytic, oxidase- and catalase-positive, and does not require X-factor for growth. It can be distinguished from other Rodentibacter species by its ability to ferment certain carbohydrates and its genetic profile, closely aligning with other members of the newly established genus Rodentibacter [10].

It is important to highlight that distinguishing R. pneumotropicus from other bacteria was a challenge under the new taxonomic classification. However, it can be differentiated from closely related species such as Rodentibacter heylii, Rodentibacter ratti, and Muribacter muris using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) mass spectrometry, which is based on the unique mass spectra profiles of these bacteria. Using MALDI-TOF mass spectrometry, R. pneumotropicus exhibited characteristic mass spectral peaks at 3653, 6524, and 7307 m/z, which help differentiate it from the above-mentioned closely related species [11].

As previously explained, the medical literature scarcely documents incidents in humans. There have only been a few cases reported between 1984 and 2023 under the previous classification of [Pasteurella pneumotropica], and none in humans under the new classification of R. pneumotropicus. Reported cases under the old classification are summarized in Table 1.

The present article presents a case of an immunocompetent patient with a complicated urinary tract infection caused by R. pneumotropicus, which had been classified as [P. pneumotropica] in the clinical laboratory report.

Case Report

INITIAL PRESENTATION:

A 37-year-old male patient came to our emergency room in Mexico, with gastrointestinal symptoms, including diarrhea with more than 15 liquid evacuations in 48 hours. The diarrhea was described as brown without blood or mucus, and there was no fever or vomiting. At the beginning, the patient denied contact with animals, except for his dog, but later reported exposure to rodents at his workplace due to an infestation. Differential diagnoses at this stage included infectious gastroenteritis, inflammatory bowel disease, and functional gastrointestinal disorders. The patient was initially treated with probiotics; however, there was no clinical improvement.

PROGRESSION AND DIAGNOSTIC WORKUP:

As symptoms persisted, the patient was referred to the urology department and a colonoscopy was performed, revealing mild chronic colitis with nodular lymphoid hyperplasia. Over time, the patient experienced significant weight loss of 16 kg and developed intense right lumbar colic pain radiating to the right flank with nausea. A non-contrast abdominal CT scan revealed an obstructive stone in the proximal ureter, and urine examination showed hematuria (10 erythrocytes per field). The remainder of the laboratory tests were normal. A prostate ultrasound revealed a 52 g mass, leading to further evaluation and eventual ureteroscopy with laser lithotripsy and placement of a double J catheter.

THERAPEUTIC DECISIONS:

Postoperatively, the patient developed acute urinary retention, which did not respond to medical management, requiring urinary catheter placement on 2 occasions, with persistence of lower urinary symptoms despite management with 0.4 mg of tamsulosin every 12 hours. His fever persisted even though the first urine culture from the general urine examination yielded a negative result. He received in-hospital management with 1g of meropenem and 1g of paracetamol (acetaminophen) every 8 hours. This treatment regimen was also insufficient, as the patient continued to experience persistent fever and leukocytosis for 48 hours. A second urine culture specific for the genus Pasteurella was performed, and for this test, the laboratory identified and reported the presence of R. pneumotropicus [P. pneumotropica]. An antibiogram was done, which showed sensitivity to quinolones. The patient then underwent bipolar transurethral resection of the prostate with the removal of the double J catheter. Gram per gram tissue culture of the prostatic parenchyma revealed the presence of Staphylococcus epidermidis, which was also sensitive to fluoroquinolones. The patient was prescribed 500 mg of ciprofloxacin every 12 hours for 30 days based on the histopathological findings of prostatic hyperplasia with chronic prostatitis.

FINAL OUTCOME AND FOLLOW-UP:

After 48 hours of being afebrile, the patient was discharged without complications. During follow-up, he remained asymptomatic, with complete resolution of urinary and gastrointestinal symptoms.

Discussion

ANTIMICROBIAL RESISTANCE:

The selection of appropriate treatment for infections caused by R. pneumotropicus depends on antimicrobial susceptibility testing. Although in this case the bacterium was sensitive to fluoroquinolones, antimicrobial resistance is a growing concern. Some strains of R. pneumotropicus [P. pneumotropica] have been reported to exhibit acquired resistance mechanisms, particularly against beta-lactams and macrolides. For example, in a case of septicemia in a patient with a prosthetic mitral valve, R. pneumotropicus [P. pneumotropica] was identified and confirmed by 16S rRNA sequencing, showing sensitivity to quinolones but intermediate resistance to penicillins [19]. This emphasizes the importance of performing antibiograms to personalize antimicrobial therapy and prevent the emergence of resistance.

PATHOGENICITY MECHANISMS:

The pathogenicity mechanisms of R. pneumotropicus include adhesion to host cells, immune system evasion by inhibiting complement activation, and toxin secretion that causes tissue damage and promotes infection spread. These strategies have been primarily studied in respiratory infections, so their relevance in urinary infections is an area requiring further research. An example of this is a documented case of respiratory tract colonization in a patient with alpha-1 antitrypsin deficiency, in which the bacterium persisted despite initial therapy, suggesting immune evasion mechanisms.

:

The hospital where the diagnosis was made reported the case as [Pasteurella pneumotropica], reflecting a lack of update in the nomenclature used in its microbiological database. Although scientific literature has already established the new classification of this bacterium, many clinical laboratories and hospitals continue to use the old name, which can cause confusion in the diagnosis and clinical management of these infections. In this article, although American Medical Association style dictates that we use the current name, R. pneumotropicus, we decided to include the name [Pasteurella pneumotropica] to refer to this clinical case of R. pneumotropicus infection, as this was how it was identified at Hospital Angeles Puebla.

This case not only represents an extremely rare urinary infection caused by R. pneumotropicus but also highlights the need for constant updates in clinical microbiology to improve the diagnosis and treatment of unusual infections. Additionally, it raises questions about the pathogenicity of this bacterium in the urinary tract and its potential impact on immunocompetent patients, justifying the need for further studies in this field.

Conclusions

This case report describes a rare urinary tract infection caused by R. pneumotropicus (previously categorized as [Pasteurella pneumotropica]), a bacterium that was not previously documented in the literature as a causative agent of urinary tract infections. The patient, an immunocompetent individual, responded favorably to treatment guided by an antibiogram, underscoring the importance of precise microbiological identification and tailored antibiotic therapy. The rarity of this manifestation highlights the need for clinicians to consider uncommon pathogens in the differential diagnosis of urinary tract infections, particularly when standard treatments fail to resolve symptoms. It also underscores the importance of constant updating by the entire medical team, to achieve a clinical practice that is up to date with new scientific contributions.

The identification of this bacterium in this context raises important questions about its virulence mechanisms and transmission pathways, as they remain poorly understood. As this microorganism is traditionally associated with rodent populations and occasionally with immunocompromised hosts, its ability to infect immunocompetent individuals suggests a broader pathogenic potential than the one previously recognized. This case underscores the importance of investigating the ecological niches, reservoirs, and transmission dynamics of R. pneumotropicus, as well as its potential to colonize and infect humans in body systems that are not normally targeted by this species.

Future research should focus on elucidating the virulence factors that enable R. pneumotropicus to cause infections in diverse host environments, including the urinary tract. Additionally, studies exploring its antibiotic resistance patterns, genomic variability, and potential zoonotic transmission routes are warranted. Such investigations could provide valuable insights into the epidemiology of this bacterium and inform strategies for prevention, early detection, and treatment of infections caused by rare or emerging pathogens.

This case not only expands the known spectrum of infections caused by R. pneumotropicus but also highlights the broader significance of considering rare and atypical microorganisms in medical practice. As the boundaries of microbial pathogenesis continue to evolve, ongoing research and clinical vigilance will be essential to address the challenges posed by emerging and uncommon infectious agents, emphasizing the precise categorization of pathogens and the judicious use of antibiotics, particularly in light of the growing threat of antimicrobial resistance. Such measures are vital to ensuring effective treatment strategies and mitigating the impact of these evolving pathogens on public health.