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Staphylococcus lugdunensis: case report and discussion

2014; Wiley; Volume: 55; Issue: 4 Linguagem: Inglês

10.1111/ajd.12209

1440-0960

Stephen Donoghue, Dunja Ana Vekic, Michael C. Wehrhahn, Margot Whitfeld,

Mycobacterium research and diagnosis

Staphylococcus lugdunensis has been reported as a highly virulent coagulase-negative staphylococcus (CoNS) species implicated in endocarditis and joint infections. Recent studies have confirmed that S. lugdunensis is a significant pathogen in causing skin and soft tissue infections, with a clinical incidence that is likely to be underreported. A 59-year-old HIV-positive man presented with an erythematous lesion measuring 2 × 3 cm on his lower back with a central punctum, (Fig. 1). The surrounding skin was tender to palpation with mild erythema and induration. There was no associated fever or any history of recent injury, procedure or trauma. His CD4 count was > 800 and the HIV viral load was undetectable, with a nadir CD4 count of 380 in 1996. Clinical image of 2 × 3-cm erythematous nodular lesion with a central punctum and superficial pustule on patient's lower back. The lesion was drained and the seropurulent fluid sent for culture and microscopy, with S. aureus as the suspected pathogen documented on the pathology request form. Results showed leucocytes 3+, with no bacteria visualised on microscopy. Culture sensitivities demonstrated a pure growth of a CoNS, with subsequent laboratory-initiated speciation performed in the light of pure growth enabling the identification of S. lugdunensis. Antibiotic susceptibilities demonstrated the organism to be susceptible to all antibiotics tested, including penicillin. Following drainage and commencement of oral flucloxacillin the lesion reduced in size, with complete resolution observed within 4 weeks. Multiple similar lesions were excised over a 7-year period, prior to and following the patient's presentation; however histopathology confirmed these to be epidermoid cysts and cultures were not performed. S. lugdunensis has been largely unreported in the dermatology literature,1, 2 although infections are well documented in infectious disease, microbiology and cardiology journals.3 In laboratory-based retrospective analyses the skin has been consistently demonstrated to be the most common site of clinically significant S. lugdunensis infection (Table 1). Therefore, it is important for dermatologists to appreciate the pathogenic role of this potentially virulent organism, which has previously been regarded as a commensal bacterium. 84.6% of isolates clinically significant 55% of these were from skin wounds, abscesses and cellulitis 73% of infections were below the waist Of those above the waist, 71% were abscesses 75% of isolates clinically significant Abscesses 35% Wound infections 30% Cellulitis 15% Skin abscesses (36%) Wound infections (25%) Paronychia (13%) Freney first isolated S. lugdunensis from human clinical specimens in Lyons, France in 1988.3 The characteristic laboratory features of S. lugdunensis are in keeping with other staphylococci: the gram stain is positive with cocci seen in clusters and it is easily isolated from routine media. Depending on the media used, there may be beta haemolysis seen and a characteristic odour may also alert the laboratory scientist to the possibility of this organism. The colony morphology may be variable in a pure culture and resemble mixed coagulase negative staphylococci or mixed skin flora. Furthermore, while belonging to the coagulase-negative staphylococci family, a variable proportion of strains are positive for clumping factor (bound coagulase) and are sometimes detected on slide-based tests used for the detection of coagulase. This may lead to the misidentification of S. lugdunensis as S. aureus. It is therefore likely that the clinical incidence of S. lugdunensis has been largely underreported, with few laboratories routinely performing speciation of coagulase-negative staphylococci. More widespread use of matrix assisted laser desorption ionisation and time of flight mass spectrometry (MALDI-TOF MS) technology will make organism speciation simpler. MALDI-TOF MS involves laser pulsation with the resultant generation of ions that are read by a mass spectrometer, and with the subsequent spectra referenced to a database for microbial identification. This takes only a matter of minutes, is highly accurate and has revolutionized microbiology laboratories worldwide.10 This technology is increasingly available in Australia and is now utilised in most tertiary hospital and private laboratory settings. Both a skin commensal and a pathogen responsible for nosocomial and community acquired infections, S. lugdunensis can behave like S. aureus and may proceed along a similar aggressive course.11 It is reported to represent 5 to 6% of coagulase-negative staphylococci isolated from skin lesions, with S. lugdunensis more likely than S. epidermidis or other CoNS to be clinically significant when isolated from superficial infections.1 The commensal role of S. lugdunensis was examined in Sweden in 2009 when multiple body sites of 75 healthy individuals were swabbed, including the nose, axillae, perineum, groin, breast and toes. Significantly more of the 525 skin swabs obtained yielded S. lugdunensis (50/75) than S. aureus (16/75). The groin, axilla and lower extremities were the most frequent sites of S. lugdunensis colonisation, with S. aureus rarely found at these sites. This study demonstrates that, although they are both integral skin flora, S. lugdunensis and S. aureus differ in their site and frequency of colonisation.12 The clinical relevance of S. lugdunensis was first described when it was implicated as a causative organism in endocarditis.13 Since this time more than 80 further case reports of S. lugdunensis endocarditis have been reported, primarily involving native left-sided valves.11 A review of S. lugdunensis endocarditis estimated its mortality to be 50%, with mortality rates higher with S. lugdunensis than other CoNS.14 S. lugdunensis has also been implicated in urinary tract, prosthetic joint, central nervous system and surgical wound infections as well as peritonitis and osteomyelitis (see Table 1).5 The previously unrecognised role of S. lugdunensis as a primary skin pathogen was clearly demonstrated in a 1991 study, in which 155 S. lugdunensis specimens were isolated over a 5-year period. Of the specimens collected, 84.6% were found to be clinically significant, with 55% of these infections originating from skin wounds, abscesses or cellulitis.4 This study examined that pattern of infection and emphasised that although S. lugdunensis is a causative organism in endocarditis, peritonitis and infected hip prostheses, it occurs in greatest frequency in skin and soft tissue infection. More recently, 20 cases of skin and tissue infections due to S. lugdunensis were reported in 2010.6 The frequency of skin infections due to S. lugdunensis was calculated to be 0.42%, with infection found to be secondary to trauma, surgery or skin disease in 15 of the 20 patients (75%). Of the 20 cases, abscesses (seven cases), surgical wound infections (six cases) and cellulitis (three cases) were the most common clinical presentations. Twelve infections were community acquired (60%) and S. lugdunensis was the only pathogen isolated from 15 of the 20 specimens (75%). All patients were cured after therapy with antibiotics, either associated with or not associated with surgical drainage. The duration of antibiotic treatment ranged from 5 to 21 days, with all isolates susceptible to most of the antibiotics tested.6 Although this study demonstrated that S. lugdunensis is penicillin sensitive, a 3-year retrospective study demonstrated that 80% of isolates (> 50% from skin) were penicillin resistant (80%).8 This potential variability in the antibiotic resistance profile of S. lugdunensis is far greater than historical estimates and demonstrates the need for testing antibiotic sensitivities when coagulase-negative staphylococci are encountered. S. lugdunensis was further recognised as a pathogenic organism in epidermoid cysts when, in 2008, the culture results of 152 patients with epidermoid cysts over a 7-year period were reported. The cysts were classified as inflamed (115) and uninflamed (37), based on their clinical appearance. S. lugdunensis was isolated from 18 of the inflamed cysts and was the most common organism identified. It was not cultured from the uninflamed cysts.2 This is of relevance to our case, in which the lesion in question was observed to have a central punctum. In 2010 a Danish study reported an optimal identification method for S. lugdunensis. The recognition of a characteristic bleach-like odour on Columbia sheep blood agar combined with colony pleomorphism and prominent beta-haemolysis after 2 days of incubation led to an 11-fold increase in the detection of S. lugdunensis. By these methods, 491 S. lugdunensis infections were found over a 4-year period, corresponding to an incidence of 53 per 100 000/year, an increase from five infections/100 000 inhabitants in preceding years. Of these cases, 75% were found in general practice, with skin abscesses (36%), wound infections (25%) and paronychia (13%) being the most common manifestations. It was postulated that the preferred niche for S. lugdunensis might be in areas that contain apocrine sweat glands, specifically the anogenital region, axillae, mammary areolae, eyelids and auditory canals.7 Unlike S. aureus and more recently coagulase-negative S. epidermidis,15 S. lugdunensis is yet to be implicated as a triggering or complicating factor in atopic dermatitis. The increasing recognition of S. lugdunensis as a skin pathogen highlights the need for dermatologists to request that inflamed cysts, surgical wounds, abscesses and paronychia be cultured with the possibility of S lugdunensis considered. This possibility should be highlighted to the laboratory and documented on the pathology request form, so that pure or near pure growths of coagulase-negative staphylococci are not disregarded and dismissed as ‘no pathogenic organisms found’. The increased use of newer techniques for speciating bacteria will mean that relevant growth of such organisms and their antibiotic sensitivities will be obtained.10 Although S. lugdunensis is said to behave like S. aureus, its preferred sites of colonisation and subsequent sites of infection differ dramatically. Similarly, a variable antibiotic resistance profile due to the production of beta lactamase and penicillin resistance has been shown,9 with traditional antibiotics often being ineffective in treating infection with S. lugdunensis. This further highlights the need for the careful consideration of this organism in the appropriate clinical setting, allowing for its subsequent identification, speciation and targeted treatment. As awareness by both clinicians and laboratories increases about the pathogenic potential of S. lugdunensis, with modern technology allowing easy and rapid speciation, it is expected that a greater number of isolates of S. lugdunensis will be reported. Its well-documented skin pathogenicity and variable antibiotic profile make it an important organism not to be disregarded by dermatologists worldwide. Douglass Hanly Moir for funding online access to this letter.