A Case of Wound Infection with Providencia rettgeri and Coincident Gout in a Patient from Guam

Abstract

Providencia rettgeri (P. rettgeri) is a ubiquitous organism that is infrequently associated with human disease. Here we report the isolation of this organism from a polymicrobial wound infection resulting from ruptured tophi on a 54-year-old male patient from Guam. We describe the identification and confirmation of this organism, and propose metabolic synergy as a possible mechanism of pathogenesis. To our knowledge, this is the first published report of a wound infection colonized by P. rettgeri from Guam, and the first report to speculate upon the role of bacterial synergy in P. rettgeri pathogenesis.

Providencia rettgeri (P. rettgeri) is a motile, gram-negative rod shaped organism and a member of the Enterobacteriaceae family.¹ It is capable of growth on MacConkey agar, capable of catalyzing the dissociation of urea into ammonia and carbon dioxide, capable of deaminating phenylalanine, and capable of producing gas from glucose fermentation. However, most strains are incapable of fermenting lactose, a defining feature of the genus Providencia.² The first members of this genus were isolated by Leo F. Rettger of the Sheffield Laboratory at Yale University. These isolations were undertaken as part of an epidemiological investigation into a 1904 fowl cholera epidemic.³ However, the organisms were not characterized until about 1918 when Phillip Hadley performed a cursory evaluation of the genus and proposed the name Bacterium rettgeri to refer to an unusual urease producing strain. In 1943, Rustigian and Stuart recommended that Bacterium rettgeri be assigned to the genus Proteus based on biochemical characteristics.³ However, a series of DNA-DNA hybridization studies by Brenner and others in 1978 demonstrated a clear relationship between certain members of the genus Proteus and certain members of the genus Providencia. This recognition resulted in the reassignment of Proteus rettgeri to the genus Providencia.³

The first report of a human infection with P. rettgeri was published in 1951. This report, by Goldfarb and De Bakey, described a case of P. rettgeri-associated empyema.⁴ Antibiotic resistant strains of this organism were reported as early as 1971. These reports were initiated by Traub, Craddock, and others who reported an outbreak of a lactose fermenting, highly antibiotic resistant strain of P. rettgeri among surgical ward patients.⁵ A second large outbreak of P. rettgeri (urinary tract infection) was reported by Edwards, and others, in 1974.⁶ Furthermore, this organism had been implicated in the etiology of gastrointestinal illness in 1986, traveler's diarrhea in 2004, and ocular infection in 2006.^7–9 It is of interest to note that P. rettgeri has been identified as the causative agent of “purple bag syndrome,” an unusual and striking condition in which purple-tinted urine is produced as a result of bacterial enzymatic activity.¹⁰ A 2014 report on the isolation of P. rettgeri from a cluster of surgical infections in Nepal illustrates the presence and significance of this organism in the Asia-Pacific region.¹¹ With regard to antimicrobial susceptibility, P. rettgeri is typically resistant to gentamicin and tobramycin but susceptible to amikacin. There have been reports of extended spectrum beta lactamase (ESBL) producing P. rettgeri in Eastern Europe and New Delhi, and metallo-beta lactamase (NDM-1) producing P. rettgeri isolates in South America and Asia.^11–15

We describe a case of an ampicillin-resistant P. rettgeri wound infection coincident with tophaceous gout in a polymicrobial wound on a patient from Guam. This is the first published report of this organism in association with gouty tophi. This report may represent a sentinel case that indicates the presence of an antibiotic-resistant, human-colonizing strain of P. rettgeri circulating in the Marianas and it may represent the first indication of this organism participating in a synergistic relationship with other bacterial species colonizing a wound site.

Case Report

A 54-year-old man from Guam with no significant travel history, no indication of insect bites, or immunosuppression, and a medical history significant for hypertension, chronic kidney disease, and tophaceous gout was referred to our facility due to the presence of multiple wounds resulting from ruptured tophi, and worsening symptoms. Upon presentation, the wounds were found on the left shin. A punch biopsy was performed and samples were sent to the laboratory for histological analysis and bacterial culture. Histology was negative for neoplasm and bacterial isolate analyses utilizing the Vitek 2 (bioMerieux, Hazelwood MO) phenotypic identification system revealed the presence of 2+ Staphylococcus aureus (S. aureus), 2+ Pseudomonas aeruginosa (P. aeruginosa), and 2+ P. rettgeri.¹⁶ Due to the fact that P. rettgeri is an unusual cause of wound infection, the identity of this isolate was confirmed by matrix-assisted desorption/ionization time of flight mass spectrometry using the Vitek MS (mass spectrometry) system.¹⁷

Sensitivity studies revealed that the isolate was resistant to ampicillin, ampicillin/sulbactam, cefazolin, gentamicin, and trimethoprim/sulfamethoxazole. It was found to be susceptible to ceftriaxone, cefepime, ciprofloxacin, and piperacillin/tazobactam. The patient was initially treated with clindaymycin (300mg QID × 10 days) and ciprofloxacin (500mg BID × 10 days) to cover both gram negative and gram positive pathogens as the Pseudomonas isolate was susceptible to ciprofloxacin and the Staphylococcus isolate was susceptible to clindamycin. Local wound care was initiated with topical polymem silver foam. This treatment was continued daily. At 10 days post-presentation, creatinine levels were elevated to 2.09 mg/dl and potassium levels were elevated to 5.7 mEq/L. The patient also complained of diarrhea. He was therefore advised to stop both ciprofloxacin and clindamycin therapy. Topical treatments with polymem silver foam were continued. At this time, his wounds were greatly improved and without signs of active infection. At a two week follow-up, the initial wounds were in a state of resolution and repeat cultures were positive only for an antibiotic sensitive strain of Pseudomonas aeruginosa and Corynebacterium species (most likely representing a skin contaminant). These results suggest that the abbreviated antibiotic therapy in combination with the topical application of polymem silver foam was effective in eliminating both Providencia and Staphylococcus infections and that it was sufficient to initiate the process of wound resolution.

Discussion

Wound infections with P. rettgeri are rarely reported in the literature. To date, there has been no confirmed association between P. rettgeri and topheaceous gout. A PubMed search using the Boolean search terms “wound” and “Providencia rettgeri” yielded only seven results.¹⁸ Three of those were in reference to the flora recovered from snakes and snake bites, one was in reference to horse wounds, two were a study of the attraction of certain insects to volatile compounds released from wound infections, and one was a study on catheter-associated urinary tract infections.^19–25 In contrast, a search using the Boolean search terms “wound” AND “Staphylococcus” yielded 7,375 results, the majority of which were directly related to skin and soft tissue infection.²⁶

The fact that P. rettgeri is not often associated with wound infection is rather surprising given that this is an organism with an almost ubiquitous presence in the environment. It has been isolated from such diverse locations as fresh water sources, run-off wastewater, and explosive-contaminated soil.^27,28 In addition, this organism has been found living as either a commensal or a pathogen in several invertebrate and vertebrate species including the fruit fly (Drosophila melanogaster), the Black Cobra (Naja naja karachiensis), the snake Bothrops jararaca, and several species of waterfowl, horses, and alligators.^{19–22,30–32} Interestingly, screwworm flies (Calliphoridae) appear to be attracted to organic compounds generated by fresh cultures of P. rettgeri indicating that mechanical vector transmission may be possible.^23,24

In the present case, it is unclear where the organism was acquired. However, it is significant that the patient had a history of tophaceous gout and presented in the clinic with multiple ruptured tophi. Superinfection of gouty tophi is a well-known complication of the condition and it is one of the most common reasons for surgical intervention.³³ It is possible that P. rettgeri was inoculated into ruptured tophi during water or soil exposure. It is also possible that prior colonization with Pseudomonas and Staphylococcus set the stage for P. rettgeri superinfection by triggering local attenuation of the immune response and by initiating the formation of a protective biofilm. However, given that the pathophysiology of gout involves the accumulation of uric acid crystals at the site of tophi formation, the fact that P. aeruginosa produces urate oxidase, which initiates the hydrolysis of uric acid to urea and the fact that P. rettgeri is capable of the hydrolysis of urea to ammonia and carbon dioxide, it is tempting to speculate that the colonization of a site with multiple tophi was the result of a urea-based chemotactic response initiated by the degradation of uric acid by P. aeruginosa.^34–36 Indeed, certain strains of Helicobacter pylori have shown both a urease dependent and a urease independent chemotactic response to urea.^36–38

If the local decomposition of uric acid to urea initiated by P. aeruginosa was sufficient to drive secondary colonization by P. rettgeri, the decomposition of urea to ammonia by this organism may have been partially responsible for the tissue damage at the wound site. Indeed, scenarios in which pathogenesis is augmented by metabolic synergy has been described for several oral pathogens and such a scenario would explain the initiation of wound resolution following the antibiotic-mediated elimination of P. rettgeri.^39,40 However, further studies will be required to determine whether P. aeruginosa and P. rettgeri synergize in vivo, whether this activity increases pathogenesis and whether this activity is accelerated in cases of gout.

The contribution of P. rettgeri to the pathology of wound infection has yet to be determined. It is often difficult to differentiate between those organisms that merely colonize a wound site and those organisms that are truly pathogenic.⁴¹ No definitive virulence factors have been described for P. rettgeri. Nonetheless, there is mounting evidence to suggest that, under certain conditions, urease can act as a general virulence factor.⁴² The reported toxicity of bacteria-produced ammonia to epithelial cells supports the notion of wound-site pathology catalyzed by bacterial urea and uric acid degradation.^42,43 This hypothesis is especially attractive with respect to the present case, given the role of uric acid in the pathology of gout, the ability of P. aeruginosa to decompose uric acid, and the ability of P. rettgeri to convert the resulting end products to ammonia. A 2001 report by Murray and Comearu describes a case of hyperammonemia resulting from a P. rettgeri infection.⁴³⁴ This case was so severe that the patient suffered a coma that only resolved with the elimination of P. rettgeri by antibiotic therapy.³⁶ This report clearly demonstrates that the urease activity of P. rettgeri is significant, and that it is capable of altering clinical outcomes.

Conclusion

Although P. rettgeri is rarely reported as the sole cause of wound infection, the isolation of this organism from a wound site should not be summarily dismissed. P. rettgeri maintains two traits that may serve to aggravate tissue injury. These are the possession of antimicrobial resistance mechanisms and the ability to produce ammonia from urea. Either of these traits can potentially influence the ecology of the wound site and alter the kinetics of wound healing. In the present case, antibiotic therapy appeared to eliminate both the P. rettgeri infection and the S. aureus infection and elimination of these two organisms appeared to correlate with the initiation of wound resolution. Despite the fact that P. rettgeri is a known producer of ammonia, it is impossible to determine the extent to which this organism contributed to overall wound pathology. A greater understanding of the pathophysiology of P. rettgeri (including the role of metabolic synergy as a mechanism of virulence) will be required to develop the means to reliably discriminate between cases of colonization versus cases of infection, to identify and eliminate bacterial synergy, and to facilitate the development of proper treatment guidelines.

The views expressed in this manuscript are those of the authors and do not reflect the official policy or position of the Department of the Army, Department of Defense, or the US government.

Conflict of Interest

None of the authors identify a conflict of interest.