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Journal of Clinical Microbiology, June 2006, p. 2311-2313, Vol. 44, No. 6
0095-1137/06/$08.00+0     doi:10.1128/JCM.02125-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

CASE REPORT

First Report of Septicemia Caused by an Obligately Anaerobic Staphylococcus aureus Infection in a Human

Sandra L. Peake,¹ John Victor Peter,¹ Louisa Chan,¹ Rolf P. Wise,³ Andrew R. Butcher,² and David I. Grove^2*

Department of Intensive Care, The Queen Elizabeth Hospital, Woodville, South Australia 5011, Australia,¹ Department of Clinical Microbiology and Infectious Diseases, Institute of Medical and Veterinary Science, The Queen Elizabeth Hospital, Woodville, South Australia 5011, Australia,² Infectious Diseases Laboratories, Institute of Medical and Veterinary Science, Adelaide, South Australia 5000, Australia³

Received 10 October 2005/ Returned for modification 26 October 2005/ Accepted 22 March 2006

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In this case report, we describe the first instance of septicemia caused by an obligately anaerobic Staphylococcus aureus in a human. A 45-year-old man presented with septicemia, septic arthritis, and multiple pulmonary abscesses, which were caused by an obligately anaerobic S. aureus. The clinical and microbiological features that led to the diagnosis are discussed. Genotyping cannot at present reliably separate S. aureus subsp. aureus from S. aureus subsp. anaerobius, but phenotypic characteristics suggest that the present isolate is a previously undescribed strain of anaerobic Staphylococcus aureus.

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A 45-year-old farmhand with no significant past medical history presented with left hip pain that had been increasing over 1 week. There had been no trauma to the hip. Clinical examination in the emergency department revealed a fully conscious man who was febrile (39°C), tachycardic (140 heartbeats/minute), and tachypneic (40 breaths/minute). He had bibasal crackles in both lungs and epigastric tenderness. The left upper thigh was swollen, warm, and tender, with induration over the medial aspect, and marked pain was induced by movement of the left hip. There was evidence of phlebitis of the superficial veins of the left leg and small left inguinal nodes. Abnormal values on admission to the hospital are summarized in Table 1. Of note were neutropenia, thrombocytopenia, abnormal liver function with evidence of coagulopathy, and raised creatinine kinase levels. A chest radiograph showed bibasal patchy alveolar infiltrates. He was treated with flucloxacillin and ciprofloxacin, with a presumptive diagnosis of septic arthritis/psoas abscess and bronchopneumonia/acute lung injury. Over the next 12 h, the patient's clinical state worsened, with increasing shortness of breath, hypoxemia, and features of a prerenal azotemia, necessitating transfer to the intensive care unit. An increase in the swelling over the left leg was noted, and a computed tomography scan indicated an effusion. An urgent left hip arthrotomy and washout was performed. Pus was drained from the hip capsule. Cultures of blood, pus, and tissue from the left hip grew an obligately anaerobic Staphylococcus aureus sensitive to flucloxacillin and vancomycin. However, because the patient developed a generalized macular-papular rash in response to flucloxacillin, vancomycin was substituted. In view of the severity of the illness, gentamicin and rifampin were added for synergy. Additional complications were septic shock, respiratory failure due to extensive bilateral lung cavitation, and thrombosis of the long saphenous vein. Clinical improvement was gradual, with discharge from the intensive care unit after 4 weeks and from the hospital after a further 4 weeks of rehabilitation. The search for an underlying predisposing condition, such as human immunodeficiency virus infection, was negative.

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TABLE 1. Abnormal values on admission of the patient to the hospital

The blood samples collected from the patient were inoculated into aerobic (BD Bactec Plus Aerobic/F) and anaerobic (BD Bactec Lytic/10 Anaerobic/F) bottles and incubated in a Bactec 9000 series blood culture system (Becton Dickinson Company, Sparks, Maryland). The following day, pus and tissue specimens from the left hip joint were received and incubated on both blood agar (Columbia agar base with 5% defibrinated horse blood) and chocolate agar (Oxoid Australia, Thebarton, South Australia, Australia) under aerobic, microaerophilic, and anaerobic conditions. Staphylococci were recovered within 24 h from the anaerobic blood culture bottle, but there was no growth in the aerobic bottle after 6 days of incubation. The same organism was recovered from both pus and tissue specimens inoculated on both media but only when cultured under anaerobic conditions in an anaerobic incubator (Forma Scientific Anaerobic System model 1024; Forma Scientific, Marietta, Ohio). An initial presumptive identification as Staphylococcus aureus subsp. anaerobius was made using the criteria described by Bannerman (1), in particular, gram-positive cocci in clumps, strict anaerobic growth, and positive tube coagulase and DNase tests. The organism was resistant to metronidazole and penicillin but susceptible to cefoxitin (and hence flucloxacillin) and vancomycin on Kirby-Bauer disk susceptibility testing by the CLSI (formerly NCCLS) method (9).

Further biochemical testing to confirm the subspecies identification included conventional biochemical tests and commercial identification systems (API 20A and API rapid ID32A) Vitek as well as the anaerobic identification [ANI] card (bioMérieux, Durham, North Carolina). The organism was not identified to the species level with the Vitek ANI card (profile 1600014710) or the API rapid 32A system (profile 3002500000), as neither test system contains anaerobic staphylococci in its database. The API 20A system, which does provide data for anaerobic staphylococci, gave a nondiagnostic profile (65104066). Conventional biochemical test results along with results from the commercial kit systems were compared with those published by Bannerman (1) for S. aureus subsp. aureus and S. aureus subsp. anaerobius as well as Staphylococcus saccharolyticus, the only other described anaerobic Staphylococcus species (Table 2). S. saccharolyticus was excluded, as it does not produce coagulase and is negative for sucrose and maltose fermentation. S. aureus subsp. aureus and S. aureus subsp. anaerobius could not be differentiated. The biochemical phenotype of this organism therefore represents a previously undescribed strain of an obligately anaerobic S. aureus that is weakly catalase positive, positive for clumping factor, tube coagulase positive, and positive for DNase, nitrate, urease, mannose, trehalose, and N-acetylglucosamine (Table 2).

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TABLE 2. Comparison of growth characteristics and biochemical reactions for the Staphylococcus isolate from the patient and two S. aureus subspecies and S. saccharolyticus

The isolate was further characterized by performing partial sequencing of both the 16S rRNA gene and the RNA polymerase B gene (rpoB). The rpoB gene has been reported to offer greater discrimination between Staphylococcus species than the 16S rRNA gene (5). Briefly, DNA was extracted from growth of the isolate on the agar plate using PrepMan Ultra reagent according to the manufacturer's instructions (Applied Biosystems, Foster City, California). Portions of the 16S rRNA gene were amplified using universal primers under conditions that had been developed in-house (unpublished), and the resultant amplicons were sequenced on an Applied Biosystems 3700 capillary sequencer. The 958-base-pair sequence (GenBank accession no. AY859409) exactly matched the sequences of several strains of S. aureus subsp. aureus as well as a strain of S. aureus subsp. anaerobius in the GenBank database (National Center for Biotechnology Information, National Library of Medicine, Bethesda, Maryland). Sequencing of this part of the gene identified the isolate to the species level as S. aureus but was unable to distinguish between subspecies. Likewise, a portion of the rpoB gene was amplified (8) and sequenced as described above. The 815-base-pair sequence (GenBank accession no. DQ 418781) exactly matched the sequence of one strain of S. aureus subsp. aureus in the GenBank database and closely matched several other strains with up to three base mismatches. There is currently only one sequence for S. aureus subsp. anaerobius in the database for which there was a single base mismatch (strain CIP 103780; GenBank accession no. AF325894). The same single base mismatch was determined for another culture collection strain of S. aureus subsp. anaerobius (DSM 20714; A. Mellmann, personal communication). In the absence of extensive sequence data, sequencing of the rpoB gene was also unable to determine an identity for this isolate beyond the species level.

Discussion. At initial isolation, this infection was thought to be due to S. aureus subsp. anaerobius, a low-virulence organism that is the etiological agent of abscess disease, a specific lymphadenitis of sheep and goats (3, 4). This led to detailed questioning of the patient's relatives, who reported that he had worked on a strawberry farm for the 2 months prior to the illness. His job was to harvest the strawberries and prepare the soil with sheep manure. He later revealed that on many occasions he worked in the fields without wearing gloves and often sustained injuries from thorns, which probably provided the portal of entry.

From microbiological and clinical perspectives, there were a few unusual characteristics to his illness. First, the isolate grew only under strict anaerobic conditions, in contrast to S. aureus subsp. aureus, which grows under both aerobic and anaerobic conditions, and S. aureus subsp. anaerobius, which may grow under microaerophilic conditions (1). Second, catalase activity, a feature of S. aureus subsp. aureus but not of S. aureus subsp. anaerobius, was only weakly exhibited by this organism (11). Though catalase activity has been proposed to play a role in the virulence of S. aureus subsp. aureus (11), severe human infections by catalase-negative S. aureus have been reported in the literature (2, 6, 10). There was no obvious underlying illness that predisposed him to such a dramatic multisystemic infection. S. aureus subsp. anaerobius has been shown to produce extracellular toxins and enzymes like S. aureus subsp. aureus (11). It is possible that the organism isolated from the patient shares with S. aureus subsp. anaerobius and S. aureus subsp. aureus the ability to produce toxins that may have contributed to the observed manifestations in this individual. On further analysis, our isolate was positive for the Panton-Valentine leukocidin gene when tested by the method of Lina et al. (7). This, along with possibly other unidentified virulence factors, may have played a part in this patient's illness, particularly the extensive bilateral pulmonary cavitation, as this toxin has been associated with severe hemorrhagic staphylococcal pneumonia in young adults (7).

This organism had phenotypic features that did not match exactly those of either S. aureus subsp. aureus, S. aureus subsp. anaerobius, or S. saccharolyticus. Genetic testing could not differentiate between either of the two subspecies of S. aureus. Unfortunately, only a limited number of 16S rRNA and rpoB gene sequences are available to assess both the identity and divergence between subspecies of S. aureus. These gene targets will be of only limited usefulness within this species until they are sequenced for more strains.

S. aureus subsp. anaerobius had never been reported previously as infecting humans. The features mentioned above suggest that the present obligately anaerobic isolate of S. aureus is a mutant or variant strain of S. aureus subsp. anaerobius or an undescribed subspecies of S. aureus.

 
Panton-Valentine leukocidin gene testing was kindly performed by Mark Woolley, Flinders Medical Centre, Bedford Park, South Australia, Australia. Sequence data for S. aureus subsp. anaerobius rpoB gene and helpful comments were kindly provided by Alexander Mellmann (University Hospital, Münster, Germany).

There was no financial support for this article, and none of the authors had any conflicts of interest.

 
* Corresponding author. Mailing address: Department of Clinical Microbiology and Infectious Diseases, Institute of Medical and Veterinary Science, The Queen Elizabeth Hospital, Woodville, South Australia 5011, Australia. Phone: 61 8 8222 6728. Fax: 61 8 8222 6425. E-mail: david.grove{at}imvs.sa.gov.au.

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Journal of Clinical Microbiology, June 2006, p. 2311-2313, Vol. 44, No. 6
0095-1137/06/$08.00+0     doi:10.1128/JCM.02125-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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This Article Abstract Full Text (PDF) 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 HighWire Citing Articles via Google Scholar Google Scholar Articles by Peake, S. L. Articles by Grove, D. I. Search for Related Content PubMed PubMed Citation Articles by Peake, S. L. Articles by Grove, D. I.