Pelvic Abscess Due to Ochrobactrum anthropi in an Immunocompetent Host: Case Report and Review of the Literature

Abstract

Ochrobactrum anthropi infection is rare in humans and is generally associated with immunocompromised hosts with indwelling foreign bodies. We report a case of pelvic abscess with O. anthropi after a routine appendectomy in an immunocompetent patient and review the literature on O. anthropi infection in patients with normal immune function.

CASE REPORT

A 49-year-old man with no past medical illnesses presented with increasing right lower abdominal pain of 3-day duration. One day prior to admission, he had nausea but denied any vomiting or diarrhea. On physical examination, the patient had a temperature of 38°C, heart rate of 121 beats per minute, and blood pressure of 105/60 mm Hg. Abdominal exam revealed distention, bilateral lower quadrant tenderness to palpation with evidence of guarding, and absent bowel sounds. Laboratory findings were significant for an elevated white blood cell count of 23,500/mm³ with a differential of 77% polymorphonuclear leukocytes (3% bands), 11% lymphocytes, 9% monocytes, 2% eosinophils, and 1% basophils. The clinical diagnosis of acute appendicitis was made.

A computed tomography (CT) scan of the abdomen and pelvis confirmed findings of acute appendicitis without any evidence of free air, free fluid, or colonic obstruction. The patient underwent a laparoscopic appendectomy, which demonstrated an indurated, purulent appendix with perforation. Postoperatively, he was treated with intravenous levofloxacin (500 mg daily) and metronidazole (500 mg every 6 hours). On the second postoperative day, the patient became febrile to 39°C, and a repeat CT scan of the abdomen and pelvis showed an encapsulated fluid collection in the deep pelvis anterior to the rectum. The antibiotic regimen was changed to imipenem (500 mg every 8 hours) and vancomycin (1 g daily).

The next day, the patient underwent a CT-guided, transgluteal drainage of the abscess. Laboratory analysis of the pelvic fluid showed 1,700 red blood cells/mm³, 93,200 white blood cells/mm³ with a differential of 100% polymorphonuclear leukocytes and the presence intracellular bacteria noted. Microscopy showed gram-positive bacilli that were later identified by culture as Clostridium difficile and Clostridium bolteae, a member of the Clostridium clostridioforme group (9). The identification of C. bolteae was confirmed by PCR and sequencing of the 16S ribosomal RNA genes. The C. difficile isolate was positive for toxins A and B. The patient experienced diarrhea, but a stool specimen for C. difficile toxins A and B tested negative. The antibiotic therapy was changed to intravenous metronidazole (500 mg every 8 hours). The patient did well initially and remained afebrile, but experienced worsening abdominal distention.

By postoperative day 8, his white blood cell count had increased to 16,000/mm³. A CT scan of the abdomen and pelvis showed a high-grade small bowel obstruction in the lower right quadrant involving the distal jejunum and proximal ileum, as well as a small fluid collection in the anterior perirectal space. The patient underwent reoperative exploration with lysis of dense adhesions of the right lower quadrant. Pelvic washings were obtained for aerobic and anaerobic culture, and intravenous levofloxacin (500 mg daily) was added to the antibiotic regimen.

On hospital day 14, the pelvic cultures yielded a gram-negative, highly motile, oxidase-positive bacillus subsequently identified as Ochrobactrum anthropi by API 20 NE (bio-Merieux Inc., St. Louis, MO). The identification was confirmed by PCR and sequencing of the 16S rRNA genes. Susceptibility testing was performed using the PASCO broth microdilution panel (BBL, Difco, Sparks, MD), except for imipenem, which was tested by the Kirby-Bauer disk diffusion method using commercially available antibiotic disks. The isolate was susceptible to levofloxacin (MIC ≤ 0.5 μg/ml), gentamicin (MIC = 4 μg/ml), imipenem (26-mm zone), and trimethoprim-sulfamethoxazole (TMP-SMX; MIC < 1/19 μg/ml) but was resistant to cefepime (MIC > 16 μg/ml) and tobramycin (MIC > 8 μg/ml). There was also sparse growth of coagulase-negative Staphylococcus and Lactobacillus spp. from the enrichment broth. The patient slowly recovered and was discharged on postoperative day 23 with no further complications. Antibiotic therapy with oral levofloxacin and metronidazole was continued for 5 days. The patient remained well after a 2-month follow-up.

Discussion.

O. anthropi is a gram-negative, aerobic bacillus previously classified as CDC group Vd. O. anthropi is motile by means of its peritrichous flagella and is characterized by its production of urease and oxidase, as well as its inability to ferment lactose. It can readily be distinguished from Pseudomonas spp. due to its lack of production of fluorescent pigments. Its name comes from the Greek word “ochros,” meaning pale, due to the pale yellow colonies formed in cultures. Additional microbiological analysis of O. anthropi is reviewed in greater detail elsewhere (7, 12).

O. anthropi infrequently causes human infection, usually associated with immunocompromised hosts and indwelling catheters. We report a case of pelvic abscess with O. anthropi after a routine appendectomy in an immunocompetent patient. We also review the literature on O. anthropi infection in patients with normal immune function and its unusual antimicrobial susceptibility pattern.

The first identified case of O. anthropi was reported in 1980 in a debilitated patient with a pancreatic abscess (2). Since then, Ochrobactrum has been isolated from other human clinical sources such as blood, urine, wounds, feces, and oral and vaginal secretions, leading to its specific epithet anthropi (12). The natural habitat and distribution of O. anthropi have been a subject of debate, as it is found in a wide variety of environmental and clinical sources, including soil, water, indwelling catheters, retained foreign bodies, and contaminated pharmaceuticals (16). It has been suggested that, because of its biological characteristics and spectrum of disease, O. anthropi occupies a microbial niche similar to that of Pseudomonas species (3, 6).

A Medline search of the term Ochrobactrum anthropi from 1989 to 2005 yielded 122 citations, representing 41 published reports of clinical cases of O. anthropi infection. A review of this literature indicates that this opportunistic pathogen is often associated with nosocomial infection in debilitated patients, most commonly catheter-associated bacteremia. This may be due to its ability to adhere to various synthetic materials such as silicone tubing (1).

Conversely, infection by O. anthropi in healthy individuals is markedly less common. Our literature review yielded 15 cases of O. anthropi infections reported in immunocompetent hosts (Table 1). These include three cases due to trauma, such as foot puncture wounds, and confirm the presence of O. anthropi in the environment and its ability to cause infection (3, 6, 17). O. anthropi was also isolated in three reported cases of endophthalmitis, two of which were associated with cataract extraction (4, 11, 13). Two cases of osteomyelitis caused by O. anthropi were reported in patients with no predisposing factors (14, 20). Other cases were associated with foreign bodies, such as prosthetic valves, sepsis associated with an infected venous catheter, and contaminated pharmaceuticals (8, 10, 15, 16, 18, 19). In all reported cases, the patients survived and the infection was cured without any known long-term sequelae.

TABLE 1.

Case reports of Ochrobactrum anthropi infection in immunocompetent hosts

Reference or source	Yr	Age (yr)/sex	Diagnosis	Contributing factor	Treatmenta
3	1987	14/M	Osteochondritis	Foot trauma	CLI/RIF
5	1993	74/F	Necrotizing fasciitis	Unknown	IPM
4	1996	66/M	Endophthalmitis	Cataract surgery	CIP
6	1996	29/M	Cellulitis	Foot trauma	RAD
10	1997	45/M	Sepsis	Venous catheter	None
8	1997	40/F	Chest wall abscess	Foreign body	VAN/RIF/CIP/SXT
13	1999	64/M	Endophthalmitis	Vitrectomy	IPM/MIN/CIP
14	1999	2/M	Osteomyelitis	Unknown	CLI/RIF
16	2000	39/F	Endocarditis	Contaminated pharmaceuticals	VAN/GEN/OFX
11	2001	61/M	Endophthalmitis	Cataract extraction	VAN/GEN/CAZ/CLI
20	2002	62/F	Osteomyelitis	Unknown	CRO/CIP
15	2003	30/F	Sepsis	Contaminated pharmaceuticals	OFX/GEN
17	2003	30/F	Sepsis	Trauma	Unknown
19	2004	65/F	Endocarditis	Prosthetic valve	MEM/GEN
18	2005	64/F	Endocarditis	Prosthetic valve	Unknown
PRb	2005	49/M	Pelvic abscess	Abdominal surgery	LVX/metronidazole

^aCAZ, ceftazidime; CIP, ciprofloxacin; CLI, clindamycin; CRO, ceftriaxone; GEN, gentamicin; IPM, imipenem; LVX, levofloxacin; MEM, meropenem; MIN, minocycline; OFX, ofloxacin; RAD, cephradine; RIF, rifampin; SXT, trimethoprim-sulfamethoxazole; VAN, vancomycin.

^bPR, present report.

These cases indicate that O. anthropi is able to affect patients with normal immune system function but who usually have recognized risk factors. Our case is unique as it is from an intra-abdominal source in an immunocompetent patient without foreign-body or contaminated-solution exposure and thereby expands the spectrum of O. anthropi infection in humans. It is possible that there have been other similar cases but that cases are underestimated, as routine laboratories may not go on to identify this infrequent and relatively metabolically inert isolate.

The therapeutic approach to O. anthropi infection is a rising challenge due to its resistance to antibiotics, such as various beta-lactams, commonly employed in empirical treatment of gram-negative infections. In a review of in vitro antibiotic susceptibilities from case reports, Cieslak et al. found that O. anthropi isolates were uniformly resistant to ampicillin-clavulanate, piperacillin-tazobactam, cefotaxime, ceftriaxone, and aztreonam (7). Generally, the organism was susceptible to gentamicin, fluoroquinolones (ciprofloxacin, levofloxacin), carbapenems (imipenem), and TMP-SMX. Our isolate showed this typical pattern of antibiotic susceptibility as well.

Currently, the optimal choice among available therapies is undetermined. Some reports have noted that removal of infected catheters or surgical debridement or both were sufficient to resolve the infection (6, 10). A variety of antibiotic regimens have also been attempted. Historically, the greatest efficacy was obtained by treatment with intravenous TMP-SMX (8). However, recent evidence supports the use of fluoroquinolones, which were shown to be effective in our patient (15, 16, 20).

In summary, O. anthropi is an infrequently encountered, aerobic, gram-negative bacillus that is generally associated with infected indwelling catheters and prosthetic material in debilitated hosts. To our knowledge, this case is the first report of a pelvic abscess due to O. anthropi in a previously healthy individual and thereby expands the already wide spectrum of disease caused by infection with this organism. Our case highlights the ability of O. anthropi to cause disease in patients with normal immune system function and illustrates the challenges of proper therapeutic antimicrobial selection.