Unusual Clinical Presentation of Mycobacterium fortuitum Infection in an Immunocompetent Woman

Abstract

The Mycobacterium fortuitum group of rapidly growing nontuberculous mycobacteria is an uncommon cause of renal infection, particularly in otherwise healthy hosts. We describe a case of nephritis due to M. fortuitum in an immunocompetent woman with a clinical and radiological diagnosis of renal tuberculosis.

CASE REPORT

A 32-year-old woman was admitted to the hospital because of mild fever and severe pain in the right lumbar region of 3 days' duration. Her history was negative for similar episodes or infections with mycobacteria and other opportunistic microorganisms. Physical examination revealed a temperature of 37.8°C and colic pain in the right flank radiating to the back and the urogenital tract. Laboratory findings demonstrated a hemoglobin level of 13.0 g/dl, a platelet count of 230 × 10⁹/liter, and a white cell count of 10.8 × 10⁹/liter (neutrophils, 7.4 × 10⁹/liter; monocytes, 0.6 × 10⁹/liter; lymphocytes, 3.3 × 10⁹/liter; eosinophils, 0.1 × 10⁹/liter; basophils, 0.1 × 10⁹/liter); the erythrocyte sedimentation rate was 24 mm/h, and C-reactive protein was at 295 mg/dl. Hematuria, proteinuria, and leukocyturia were not detected by urine analysis. Serology for human immunodeficiency virus and syphilis was negative, and the patient was not otherwise immunocompromised. An ultrasound scan performed on the second day showed a discrete dilation of the right pelvic calyceal system without significant pathoanatomical renal changes.

The patient was discharged on the third day with a diagnosis of ureteral colic and lithiasis. However, she continued to suffer from lumbar pain and mild temperature and 2 months later was again admitted for urological evaluation. Intravenous urography showed moderate bilateral dilation of the midproximal ureter, a discrete deformity of the left upper-pole calyx with ill-defined margins, and a small, irregular collection of extracalyceal contrast material. Slight distention of the right pelvis was also noted. No functional abnormalities of the kidneys were documented. Infection with Mycobacterium tuberculosis was suspected on a clinical and radiological basis.

After 3 consecutive days of collection of urine samples for microbiological examination, antituberculosis treatment (with 300 mg oral isoniazid once a day and 600 mg oral rifampin once a day) was started, pending identification and sensitivity test results. Urine samples were decontaminated with equal volumes of N-acetyl-l-cysteine and 3% sodium hydroxide, neutralized with phosphate-buffered saline, centrifuged, and processed for microscopy, culture, and PCR analysis. Smears were stained by the Gram and conventional basic fuchsin (Ziehl-Neelsen) methods, and the resuspended specimens were inoculated into International Union tuberculosis medium (IUTM). PCR analysis using primers specific for M. tuberculosis and the Mycobacterium avium complex was also carried out. All tests performed on the first three urine samples gave negative results. However, acid-fast bacteria from two different urine specimens collected during antituberculosis therapy showed Ziehl-Neelsen staining. Bacteria also gave rise on day 4 to the rapid growth of small, buff-colored colonies on IUTM. Isolates were subcultured on blood agar, chocolate agar, MacConkey agar, brain heart infusion agar, and mannitol-salt agar, all incubated at 35°C in air, and on Sabouraud agar, incubated at 25°C and 35°C (all purchased from Difco Laboratories, Detroit, MI). Mycobacterium fortuitum was isolated and identified in cultures and in biochemical tests (Table 1). Specific diagnostic properties included rapid growth on MacConkey agar, nitrate positivity, urease positivity, catalase positivity at 68°C, NaCl tolerance positivity in Lowenstein-Jensen medium, tellurite positivity, 3-day arylsulfatase test positivity, and pyrazinamidase positivity. The identity of the isolate was confirmed by the API ZYM system (bioMérieux, Marcy l'Etoile, France) (profile, 63130165).

TABLE 1.

Culture and biochemical characteristics of M. fortuitum isolated from urine

Characteristic or test	Result
Growth on:
IUTM	+
Blood agar	+
Chocolate agar	−
MacConkey agara	+
Sabouraud agar (25°C)	−
Sabouraud agar (35°C)	−
Brain heart infusion agar	+
Mannitol-salt agar	−
Growth at:
24°C	−
31°C	+
45°C	+
Growth on 5% sodium chloride (Lowenstein-Jensen)	+
Niacin	−
Nitrate reduction	+
Urease	+
Tween 80 hydrolysis	−
Catalase (pH 7, 68°C)	+
Semiquantitative catalase	>45 mm
Tellurite reduction	+
Arylsulfatase	+
Pyrazinamidase	+
Pigment production	−
API ZYM profile	63130165

^aNon-lactose-fermenting colonies.

Antimicrobial susceptibility was tested by inoculation into Middlebrook 7H11 agar supplemented with 10% oleic acid-albumin-dextrose-catalase (Table 2). As susceptibility tests revealed resistance to the antituberculosis drugs being administered, the treatment was changed to ofloxacin (400 mg twice a day). After 3 days of ofloxacin treatment, the temperature normalized and the lumbar pain disappeared. Therapy was continued for 14 days. Repeated urine samples and urine cultures were negative for acid-fast bacteria, and the treatment was discontinued. The patient remained afebrile and asymptomatic during follow-up.

TABLE 2.

Antimicrobial susceptibility testing for isolated M. fortuitum

Antibiotic	MIC (mg/liter)	Resulta
Isoniazid	0.2	R
Isoniazid	1.0	R
Cycloserine	30.0	R
Capreomycin	10.0	R
Rifampin	1.0	R
Ethambutol	7.5	S
Para-aminosalicylic acid	8.0	R
Ethionamide	10.0	S
Kanamycin	6.0	R
Pyrazinamide	25.0	R
Streptomycin	2.0	R
Ciprofloxacin	5.0	S
Ofloxacin	5.0	S
Clarithromycin	15.0	R
Imipenem	10.0	S
Amikacin	30.0	S
Rifabutin	1.0	R
Rifabutin	2.0	R
Gentamicin	10.0	S
Netilmicin	30.0	S
Pefloxacin	5.0	S

^aR, resistant; S, sensitive.

M. fortuitum is a member of the rapidly growing Reunion Group IV nontuberculous mycobacteria (NTM). It is a ubiquitous organism frequently acquired from environmental sources, such as water, soil, and dust, and from nosocomial sources (4, 11, 16). It is a gram-positive bacillus, frequently confused with contaminant species such as corynebacteria. M. fortuitum is increasingly recognized as an opportunistic pathogen causing disseminated infection, mainly in patients with impaired cellular immunity or receiving glucocorticoid therapy. Rarely, infections can occur in otherwise healthy hosts. Clinical presentation includes mainly cutaneous and soft tissue infections; localized posttraumatic wound infections; surgical wound infections, especially following augmentation mammaplasty; and keratitis, lymphadenitis, arthritis, osteomyelitis, rarely meningitis, endocarditis, and hepatitis, mostly in AIDS patients or other immunocompromised patients (1, 6, 10, 12, 13, 14, 15, 16, 17). Previously rare, cases of peritonitis in dialysis patients, catheter-associated sepsis, pulmonary infection, and pleural effusion, including empyema, are now on the increase (2, 6, 7). M. fortuitum has also been associated with disseminated lesions in dialysis patients (18). It has been detected in urine from otherwise healthy hosts with neither significant pathoanatomical nor functional renal disorders (9). Urinary M. fortuitum infection in subjects suspected of having a specific disease of the genitourinary tract has been described only rarely, and then almost exclusively in immunocompromised patients or patients being treated with glucocorticoids (3, 5, 8).

Three main comments are in order. This is one of the few documented cases of renal infection due to M. fortuitum in an apparently healthy subject with a diagnosis of urolithiasis. This is the first case of M. fortuitum isolation in our laboratory. Prolonged urinary tract elimination of M. fortuitum has been described in the past, mainly from AIDS and hemodialysis patients (3, 8, 18), but primary localization in renal tissue causing a colic-like syndrome in an immunocompetent patient is a rare, possibly unique case. Secondly, the similar clinical and radiological presentations of atypical mycobacteriosis and renal tuberculosis suggest the need for specific microbiological and drug susceptibility investigations to avoid the administration of unsuccessful and potentially harmful treatments, given that most rapidly growing NTM are resistant to traditional antituberculosis agents (11). In this respect, although cases of NTM infection have increased recently because of the dissemination of human immunodeficiency virus infection and the extensive use of chemotherapy and immunosuppressive treatments, isolation and identification of NTM from otherwise healthy hosts are becoming more common (11, 15, 16). Finally, this report highlights the role and potential of traditional culture methods in the identification of atypical microorganisms. A number of commercially available automated assays have recently been developed, and newer genetic methods, such as molecular probes, PCR-based restriction fragment length polymorphism analysis, and 16S rRNA gene sequence analysis, have been recommended for more-accurate detection and characterization of tuberculous mycobacteria and NTM. Nevertheless, conventional biochemical and culture methods, together with acid-fast smear microscopy, still retain all of their potential in the diagnostic work-up of and therapeutic approach to these increasingly common infections.