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      Prosthetic Valve Endocarditis due to Kytococcus schroeteri

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          Abstract

          To the Editor: Bacteria belonging to the former genus Micrococcus, the so-called micrococci, are usually regarded as contaminants from skin and mucous membranes. Nevertheless, micrococci have been reported as emerging pathogens in immunocompromised patients and have been described in severe infections ( 1 – 4 ). We describe what is, to our knowledge, the first case of prosthetic valve endocarditis caused by the newly described micrococcal species, Kytococcus schroeteri. Accurate identification of this species is of particular importance as kytococci—in contrast to other micrococcal species—are frequently resistant to penicillin and oxacillin ( 5 ). A 34-year-old woman was admitted to the hospital with acute, severe aortic regurgitation, attributable to a dissection of both the ascending and descending aorta, which extended into the supraaortic and iliac arteries. Immediate surgical intervention was performed by implantation of an aortic arch (St. Jude Medical Inc., St. Paul, MN) conduit and reimplantation of the supraaortic arteries. Ten weeks later, the patient was admitted to the hospital because of fever of 39°C. Laboratory studies showed a leukocyte count of 15.3 x 109/L with 87% neutrophils and elevated C-reactive protein (180 mg/L). Transesophageal echocardiography and computed tomography suggested an abscess next to the prosthesis and showed vegetations on the prosthetic valve, which suggested endocarditis. Blood cultures yielded gram-positive cocci on four separate occasions during an 11-day period. Treatment, performed according to the antimicrobial susceptibilities of the isolates, consisted of vancomycin, gentamicin, and rifampin for 21 days. Within 1 week, the fever resolved and the leukocyte count returned to normal. Four days after antimicrobial therapy was initiated, right-sided hemiparesis and aphasia, thought to be due to an embolic cerebral stroke, developed. After those events, the aortic arch prosthesis was replaced without further complications. Blood culture specimens were injected into BACTEC Plus culture vials for aerobic and anaerobic cultures and processed in BACTEC 9240 blood culture system (Becton Dickinson, Cockeysville, MD). Growth was detected in four different aerobic blood cultures after incubation of 3 to 5 days. Aerobic subcultures on Columbia agar supplemented with 5% sheep blood showed tiny, muddy-yellow colonies without hemolysis after 24 h of incubation. After 48 h, the size of colonies increased, a feature typical of K. sedentarius, which is known to grow slightly more slowly than other members of the former Micrococcus genus. No or very weak reactions were found after 24 h incubation when the ID32 STAPH ATB gallery (bioMérieux Vitek, Hazelwood, MO) was used. After 48 h, the reactions with this gallery resembled those of M. luteus or M. lylae. The probability of identification was indicated as 99.0% (M. luteus, T index of 0.77) for the profile 000003000 and 51.8% (M. lylae, T index of 0.98) and 47.2% (M. luteus, T index of 0.93), respectively, for the profile 000001000. When the ID-GPC card (VITEK 2, bioMérieux Vitek) was used, a poor selectivity was observed (M. luteus, T index 0.95; Kocuria rosea, T index 0.84). All isolates were resistant to oxacillin, penicillin, fosfomycin, ampicillin, and erythromycin and susceptible to vancomycin, teicoplanin, gentamicin, netilmicin, chloramphenicol, imipenem, rifampin, tetracycline, amoxicillin/clavulanate, and ciprofloxacin, as determined by disk diffusion method performed on Mueller-Hinton agar. When arbitrarily primed-polymerase chain reaction with prolonged ramp times ( 6 ) was used, isolates were shown to be clonal, representing one strain (DSM 13884T). Since colony formations, resistance pattern, and growth rate of this strain did not correspond with the species identification, as obtained by automated systems, further phenotypic and molecular studies were conducted, confirming the micrococcal nature of this unknown strain and justifying the classification as a distinct species, Kytococcus schroeteri sp. nov ( 7 ). In addition to the Micrococcus genus, bacteria belonging to the former genus Micrococcus were recently divided into the genera Kocuria, Nesterenkonia, Kytococcus, and Dermacoccus, followed by rearrangement into two families (Micrococcaceae, Dermatophilaceae) of the suborder Micrococcineae (5). The traditional identification of the micrococci is based on their susceptibility to lysozyme and bacitracin and their resistance to lysostaphin and nitrofurantoin, in contrast to staphylococci, which display the opposite pattern. In automated identification systems, micrococci are included only in a limited manner. A prospective study showed an overall accuracy of results of 61.0% concerning Micrococcus species when the STAPH-IDENT strip (bioMérieux) was compared with conventional identification methods ( 8 ). Micrococcal species are ubiquitous inhabitants of the human skin and mucous membranes and are usually disregarded as contaminants in clinical specimens. Yet, various severe infections such as arthritis, central nervous system infection, pneumonia, peritonitis, hepatic abscess, endocarditis, and nosocomial blood stream infections have been documented ( 1 , 3 , 4 , 9 ). Since early reports of endocarditis caused by gram-positive cocci that appear in tetrads and packets often did not reliably differentiate between micrococci and phenotypically similar microorganisms, such as coagulase-negative staphylococci, the frequency of micrococcal endocarditis is difficult to ascertain and might be underestimated. However, several cases of endocarditis attributable to M. lylae, M. luteus, K. sedentarius, and unspecified micrococci have been reported ( 1 ). Regarding micrococci, data on antimicrobial susceptibilities are rare, and often the species affiliation remains unclear. In contrast to most micrococcal isolates, K. sedentarius isolates, as well as those reported here, are resistant to penicillin G and oxacillin. In the patient we describe, therapy was performed with vancomycin, gentamicin, and rifampin, resulting in bacteriologic eradication and clinical cure. However, a generally accepted therapeutic regime for severe infections with kytococcal species has not yet been defined. Concerning micrococci other than kytococci, a combination of rifampin with ampicillin has been effective ( 3 ). Successful treatment has also been achieved with vancomycin, clindamycin, penicillin, gentamicin, or a combination of these agents. Overall, rifampin shows the highest activity against all micrococcal species ( 10 ). This report is the first case of K. schroeteri causing endocarditis on an artificial heart valve. The repeated recovery of this species from blood cultures strongly suggests a pathogenic role. We conclude that isolation of micrococci from blood specimens cannot always be disregarded as etiologically irrelevant. Results performed by automated identification systems should be interpreted with caution if micrococci are involved.

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          Most cited references 11

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          Taxonomic dissection of the genus Micrococcus: Kocuria gen. nov., Nesterenkonia gen. nov., Kytococcus gen. nov., Dermacoccus gen. nov., and Micrococcus Cohn 1872 gen. emend.

          The results of a phylogenetic and chemotaxonomic analysis of the genus Micrococcus indicated that it is significantly heterogeneous. Except for Micrococcus lylae, no species groups phylogenetically with the type species of the genus, Micrococcus luteus. The other members of the genus form three separate phylogenetic lines which on the basis of chemotaxonomic properties can be assigned to four genera. These genera are the genus Kocuria gen. nov. for Micrococcus roseus, Micrococcus varians, and Micrococcus kristinae, described as Kocuria rosea comb. nov., Kocuria varians comb. nov., and Kocuria kristinae comb. nov., respectively; the genus Nesterenkonia gen. nov. for Micrococcus halobius, described as Nesterenkonia halobia comb. nov.; the genus Nesterenkonia gen. nov. for Micrococcus halobius, described as Nesterenkonia halobia comb. nov.; the genus Dermacoccus gen. nov. for Micrococcus nishinomiyaensis, described as Dermacoccus nishinomiyaensis comb. nov.; and the genus Kytocossus gen. nov. for Micrococcus sedentarius, described as Kytococcus sedentarius comb. nov. M. luteus and M. lylae, which are closely related phylogenetically but differ in some chemotaxonomic properties, are the only species that remain in the genus Micrococcus Cohn 1872. An emended description of the genus Micrococcus is given [corrected].
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            Kytococcus schroeteri sp. nov., a novel Gram-positive actinobacterium isolated from a human clinical source.

            A strain of a gram-positive, coccoid, yellow-pigmented bacterium was isolated from human blood. The bacterium was aerobic, non-encapsulated and non-motile. Phenotypically, the bacterium closely resembled Kytococcus sedentarius, but could be distinguished from this species by physiological tests and chemotaxonomic investigations. The peptidoglycan type is L-Lys-Glu2, variation A4alpha. The predominant menaquinones are MK-8 and MK-7. The major cellular fatty acids are iso-C17:1, iso-C17:0, iso-C15:0 and anteiso-C17:0. The strain contains catalase and does not produce acid from carbohydrates. The ability to hydrolyse Tween 80 and the lack of alpha-glucosidase activity are the most characteristic features. The results of comparative 16S rDNA analysis revealed that the strain represents a novel species within the genus Kytococcus, for which the name Kytococcus schroeteri sp. nov. is proposed. The type strain is strain Muenster 2000T (= DSM 13884T = CCM 4918T).
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              Micrococcus folliculitis in HIV-1 disease.

              Organisms with little pathogenic potential in immunocompetent hosts may produce disease in HIV-1 + patients. We describe three HIV-1 + patients in late disease who presented with pruritic papules with central ulceration over the face and arms. In all the patients the eruptions had been present for months, and the patients did not develop sepsis. Biopsy specimens in all the patients showed large Gram-positive cocci, forming tetrads. Colony morphology, catalase positivity and coagulase negativity, and resistance to nitrofurantoin were used to separate micrococci from staphylococci. Micrococcus species are usually considered normal inhabitants of the skin; however, in patients with HIV-1 disease, Micrococcus species can produce localized cutaneous infections.
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                Author and article information

                Journal
                Emerg Infect Dis
                EID
                Emerging Infectious Diseases
                Centers for Disease Control and Prevention
                1080-6040
                1080-6059
                November 2003
                : 9
                : 11
                : 1493-1495
                Affiliations
                [* ]University Hospital of Münster, Münster, Germany
                []University Hospital of the Saarland, Homburg/Saar, Germany
                []Mathias-Spital, Rheine, Germany
                [§ ]German Collection of Microorganisms and Cell Cultures, Braunschweig, Germany
                Author notes
                Address for correspondence: Karsten Becker, University of Münster, Institute of Medical Microbiology, Domagkstr. 10, 48149 Münster, Germany; fax: (49) 251 83-55350; email: kbecker@ 123456uni-muenster.de
                Article
                02-0683
                10.3201/eid0911.020683
                3035532
                14725260
                Categories
                Letters to the Editor

                Infectious disease & Microbiology

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