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Journal of Clinical Microbiology, November 2007, p. 3844-3846, Vol. 45, No. 11
0095-1137/07/$08.00+0     doi:10.1128/JCM.00761-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

CASE REPORTS

Capnocytophaga cynodegmi Peritonitis in a Peritoneal Dialysis Patient

Departments of Clinical Microbiology,¹ Nephrology, Copenhagen University Hospital Herlev,² Department of Bacteriology, Mycology and Parasitology, Statens Serum Institut, Copenhagen, Denmark³

Received 10 April 2007/ Returned for modification 5 June 2007/ Accepted 12 September 2007

	ABSTRACT

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The first reported case of peritonitis caused by Capnocytophaga cynodegmi is presented. The patient was treated with peritoneal dialysis and had contact with a cat. C. cynodegmi is part of the normal oral flora of dogs and cats but is very rarely isolated in clinical specimens from humans.

	CASE REPORT

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A 67-year-old male with end-stage renal failure due to hypertensive nephrosclerosis was treated with automated peritoneal dialysis (HomeChoice PRO; Baxter Healthcare, IL) for 2 years, before he was admitted with sudden onset of fever and abdominal pain. The dialysate was cloudy. He had recently been extensively examined for episodic diarrhea without a definite diagnosis being reached. His C-reactive protein level was 223 mg/liter, and his white cell count was 9.5 x 10⁹/liter in blood. The Combur-test (Roche Diagnostics, Mannheim, Germany) gave a positive result for granulocytes in the dialysis fluid. Continuous ambulatory peritoneal dialysis and intraperitoneal administration of gentamicin and vancomycin was started. Culturing of the dialysate taken on admission for the presence of bacteria gave a negative result. No eosinophilic granulocytes were seen upon microscopy of the dialysate. Examination for Mycobacterium tuberculosis by PCR was negative. Due to the negative culture results and the lack of clinical effect of the antibiotic treatment, intestinal ischemia was suspected. Nine days after debut of symptoms, the peritoneal dialysis catheter was removed, and treatment with hemodialysis was instituted. Systemic antibiotic treatment with cefuroxime, gentamicin, and metronidazole was initiated when thin, filamentous, gram-negative rods with tapered ends were isolated from two of the four blood culture bottles (BACTEC; Becton Dickinson, MD) in which the peritoneal fluid had been inoculated 5 days after admission and from one out of four blood culture bottles inoculated 7 days after admission. The bottles had been incubated from 3 to 6 days before growth was observed.

After initiation of systemic antibiotic therapy, the patient recovered rapidly. One month later, he had a new peritoneal catheter inserted, and he resumed automated peritoneal dialysis as he had previously undergone. Except for frequent visits by the neighbor's cat, which he occasionally fed, he had no close contact with cats or dogs.

Subculture of the bacteria was performed on 5% horse blood agar (Oxoid, Basingstoke, United Kingdom) in an atmosphere enriched with 5% CO₂.

Colonies were convex and smooth, and a metallic sheen was observed. The organism showed gliding motility and symbiotic growth with a Staphylococcus aureus streak. It was positive for production of oxidase, catalase, beta-galactosidase (o-nitrophenyl-ß-D-galactopyranoside), and arginine decarboxylase. The bacterial organism fermented glucose, lactose, sucrose, inulin, and raffinose. It did not ferment mannitol, melibiose, and glycogen. Indole was not produced, and nitrate and nitrite were not reduced.

The strain was characterized by partial 16S rRNA gene sequencing. For this procedure, DNA was released by heating the isolated bacteria at 95°C for 5 minutes. PCR amplification of parts of the 16S rRNA gene was performed by using primers BSF8 and BSR534 (526 bp; short sequence) as previously described (4) and by using primers BSF8 and BSR1407 (1,399 bp; long sequence). The data obtained were compared to deposited sequences in the NCBI database (The National Center for Biotechnology, Bethesda, MD) using the BLAST search engine. The short sequence resulted in a best taxon match with C. cynodegmi (GeneID [gi] 49065935; GenBank [gb] accession no. AY643076.1) with the number of identical bases/total number of bases and percent identical bases of 442/449 and 98, respectively; the scorebits were 835. The next best taxon match was Capnocytophaga canimorsus (gi 49065937; gb accession no. AY643078.1); the difference in scorebits between the best and next best taxon match was 8. The long sequence also resulted in a best taxon match with C. cynodegmi (gi 49065935; gb accession no. AY643076.1) with the number of identical bases/total number of bases and percent identical bases of 885/895 and 98, respectively, and the scorebits were 1,570. The next best taxon match was C. canimorsus (gi 49065934; gb accession no. AY643075.1). The difference in scorebits between the best and next best taxon match was 6. Based on the phenotypical and molecular results, the isolate was identified as C. cynodegmi.

Antimicrobial susceptibility testing of the strain was performed using disc diffusion tests (antimicrobial susceptibility test discs; Oxoid), and MICs were determined by using Etest (AB Biodisk, Solna, Sweden) on 5% horse blood agar (Oxoid) and chocolate agar (Oxoid). The plates were streaked with S. aureus from the discs to the center of the plates and on one site of the Etest strip at a distance of 1 cm for the bacteria to grow. They were incubated for 4 days at 36.5°C in a humidified incubator in an atmosphere containing 5% CO_2. The antimicrobial susceptibility test results are shown in Table 1.

In humans, infections with C. canimorsus and C. cynodegmi often follow a bite by a dog or cat or other contact with these animals. C. cynodegmi has been regarded as less pathogenic than C. canimorsus. Both C. canimorsus and C. cynodegmi can be phagocytized and multiply intracellularly in mouse macrophage cells, but only C. canimorsus causes a cytotoxic effect, probably due to a toxin produced by this species (5). It is well-known that C. canimorsus may cause fulminant septicemia, disseminated intravascular coagulation, meningitis, and endocarditis, often in splenectomized patients (7, 11), while C. cynodegmi seems to cause more localized infections. The reported cases of C. cynodegmi infections in humans include five cases of localized wound infections, most resulting from dog bites or cat scratches (1); localized cellulitis following a bite by her cat in a patient with diabetes and rheumatoid arthritis treated with prednisolone and a tumor necrosis factor alpha blocking agent (9); cellulitis with pus discharge from puncture wounds and regional lymphadenopathy, pneumonitis, and bacteremia in a diabetic patient who had been bitten by a dog (12); and fatal fulminant sepsis with disseminated intravascular coagulation and meningitis in a patient with diabetes who had been previously splenectomized and bitten by a dog (8). In the latter case, C. cynodegmi was differentiated from C. canimorsus by a nitrate reduction reaction only, leaving doubt concerning a correct species identification. Furthermore, isolation of C. cynodegmi from a corneal ulcer and endophthalmitis caused by C. cynodegmi after corneal transplantation have been reported (1, 10). In the present case, a patient treated with peritoneal dialysis contracted peritonitis caused by C. cynodegmi. Peritonitis caused by C. canimorsus following puncture of the peritoneal dialysis tubing by a cat has been reported (3). The present patient may have been infected by contamination of the dialysis catheter by secretions from the cat with which he had contact.

The scarcity of reports concerning C. cynodegmi infections may be due to low pathogenicity, but it also may be due to difficulties in culturing and identifying the bacteria. The fastidiousness of C. cynodegmi may explain the negative cultures from our patient on admission. Capnocytophaga bacteria are slowly growing, thin, gram-negative rods with tapered ends that show gliding motility and require CO₂ for growth. C. cynodegmi and C. canimorsus are differentiated from other members of the genus by being catalase and oxidase positive. C. cynodegmi is differentiated from C. canimorsus by being sucrose, raffinose, melibiose, and inulin positive and may reduce nitrate to nitrite (14); our isolate of C. cynodegmi, however, showed negative results for fermentation of melibiose. 16S rRNA gene sequencing verified the identification of the bacteria as C. cynodegmi. Susceptibility testing of Capnocytophaga may be difficult due to the fastidious nature and slow growth of the bacteria. There is no standardized method for susceptibility testing of Capnocytophaga. C. canimorsus has been reported to be sensitive to penicillin, ampicillin, piperacillin, ofloxacin, cefuroxime, cefotaxime, imipenem, erythromycin, and clindamycin (2, 13). Sarma and Mohanty (12) reported that their isolate of C. cynodegmi was sensitive to penicillin, amoxicillin, ofloxacin, cefuroxime, cefotaxime, ceftazidime, ceftriaxone, erythromycin, clindamycin, and vancomycin. By using a nonstandardized method, our isolate of C. cynodegmi seemed to be sensitive to penicillin, ampicillin, piperacillin-tazobactam, cefuroxime, cefotaxime, meropenem, tetracycline, and rifampin and resistant to erythromycin and gentamicin (Table 1). Incubation in an atmosphere with CO₂ which is necessary for C. cynodegmi to grow may decrease the pH of the medium. This may possibly result in smaller zone sizes and elevated MIC results for erythromycin and gentamicin (13). In this case, no clinical effect of gentamicin was observed.

The patient did not belong to any of the six risk groups for zoonotic infections defined by the Centers for Disease Control and Prevention (www.cdc.gov/healthypets), but the general recommendations of hand washing after contact with pets should also be an important preventive measure in patients treated with peritoneal dialysis.

Nucleotide sequence accession number. The long 16S rRNA gene sequence has been deposited in GenBank database under accession number bankit1012538 EU122391.

	FOOTNOTES

 
* Corresponding author. Mailing address: Department of Clinical Microbiology, Copenhagen University Hospital Herlev, Herlev Ringvej, DK-2730 Herlev, Copenhagen, Denmark. Phone: 45 44884715. Fax: 45 44883772. E-mail: chaper{at}heh.regionh.dk

Published ahead of print on 19 September 2007.

	REFERENCES

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This Article Abstract Full Text (PDF) Other Versions of this Article: JCM.00761-07v1 45/11/3844    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Pers, C. Articles by Bangsborg, J. Search for Related Content PubMed PubMed Citation Articles by Pers, C. Articles by Bangsborg, J.