Recommended minimal standards for description of new staphylococcal species. Subcommittee on the taxonomy of staphylococci and streptococci of the International Committee on Systematic Bacteriology.

In accordance with Recommendation 30b of the International Code of Nomenclature of Bacteria, minimal standards are proposed for the genus Staphylococcus and the description of newly recognized species in this genus. Assignment of a strain to the genus Staphylococcus requires that it is a Gram-positive coccus that forms clusters, produces catalase, has an appropriate cell wall structure (including peptidoglycan type and teichoic acid presence) and G + C content of DNA in a range of 30-40 mol%. The recommended minimal standards for describing a new Staphylococcus species are based on the results of phenotypic and genomic studies of at least five independently isolated strains. They include colony morphology and the results of the following conventional tests: pigment production, growth requirements, fermentative and oxidative activity on carbohydrates, novobiocin susceptibility, enzymic activities (nitrate reductase, alkaline phosphatase, arginine dihydrolase, ornithine decarboxylase, urease, cytochrome oxidase, staphylocoagulase in rabbit plasma, heat-stable nuclease, amidases, oxidases, clumping factor, and haemolytic activity on sheep or bovine blood agar). DNA-DNA hybridization experiments may distinguish species when the difference between the binding in the homologous reaction and the binding in the heterologous reaction expressed as a percentage is less than 70%. In addition, rRNA signature sequence criteria, ribotyping characterization of the nomenclature type strain and other strains of the species, and reference strains of other species is recommended to describe the strains of the new species with sets of genetic attributes and reveal possible grouping errors. This proposal has been endorsed by the members of the Subcommittee on the taxonomy of staphylococci and streptococci of the international Committee on Systematic Bacteriology.

Methicillin-resistant Staphylococcus aureus outbreak in a veterinary teaching hospital: potential human-to-animal transmission.

During a 13-month period, 11 equine patients visiting a veterinary teaching hospital for various diagnostic and surgical procedures developed postprocedural infections from which methicillin (oxacillin)-resistant Staphylococcus aureus (MRSA) strains were isolated. The S. aureus isolates were identified by conventional methods that included Gram staining, tests for colonial morphology, tests for clumping factor, and tests for coagulase and urease activities and were also tested with the API STAPH IDENT system. Antimicrobial susceptibility tests were performed by the disk diffusion method. The biochemical profile and antibiogram of each isolate suggested that the isolates may have come from a common source. Because MRSA strains are very uncommon animal isolates but are rather common human isolates, a nasal swab specimen for culture was collected voluntarily from five persons associated with equine surgery and recovery in an attempt to identify a possible source of the organisms. MRSA strains were isolated from three of the five people, with one person found to be colonized with two biotypes of MRSA. The MRSA isolates from the people appeared to be identical to the isolates from horses. Further study of the isolates included SmaI and EagI macrorestriction analysis by pulsed-field gel electrophoresis conducted in two different laboratories. The results indicated that both the equine and human isolates were members of a very closely related group which appear to have originated from a common source. On the basis of the pattern associated with the infection, it is speculated that the members of the Veterinary Teaching Hospital staff were the primary source of the infection, although the specific mode of transmission is unclear.

Staphylococcus hominis subsp. novobiosepticus subsp. nov., a novel trehalose- and N-acetyl-D-glucosamine-negative, novobiocin- and multiple-antibiotic-resistant subspecies isolated from human blood cultures.

A new subspecies, Staphylococcus hominis subsp. novobiosepticus, isolated from human blood cultures, a wound, a breast abscess and a catheter tip, is described on the basis of a study of 26 strains isolated between 1989 and 1996. DNA-DNA reassociation reactions, conducted under stringent conditions, and macrorestriction pattern analysis demonstrated that these strains are closely related to previously characterized S. hominis strains isolated from human skin and clinical specimens, but are significantly divergent. S. hominis subsp. novobiosepticus can be distinguished from S. hominis (now named S. hominis subsp. hominis) by its combined characteristics of novobiocin resistance and failure to produce acid aerobically from D-trehalose and N-acetyl-D-glucosamine. Furthermore, all 26 strains of the new subspecies are resistant to nalidixic acid, penicillin G, oxacillin, kanamycin and streptomycin, and were either resistant or had intermediate resistance to methicillin and gentamicin. Most strains were also resistant to erythromycin, clindamycin, chloramphenicol, trimethoprim/sulfamethoxazole and ciprofloxacin. Based on a comparison of the sequences of a 1001 bp mecA amplification product from reference methicillin-resistant staphylococci, the mecA gene present in S. hominis subsp. novobiosepticus was identified as homologue A, commonly found in S. aureus and many coagulase-negative staphylococcal species. The type strain of S. hominis subsp. novobiosepticus is ATCC 700236T. Descriptions of S. hominis subsp. novobiosepticus subsp. nov and S. hominis subsp. hominis are given and the description of S. hominis is emended.

Delimiting the genus Staphylococcus through description of Macrococcus caseolyticus gen. nov., comb. nov. and Macrococcus equipercicus sp. nov., and Macrococcus bovicus sp. no. and Macrococcus carouselicus sp. nov.

Four species of the newly proposed genus Macrococcus, namely macrococcus caseolyticus gen. nov., comb. nov. (formerly Staphylococcus caseolyticus Schleifer, Kilpper-Bälz, Fischer, Faller and Endl 1982, 19VP), Macrococcus equipercicus sp. nov., Macrococcus bovicus sp. nov. Macrococcus carouselicus sp. nov., are described on the basis of a phylogenetic analysis comparing 16S rRNA sequences, DNA-DNA liquid hybridization, DNA base composition, normalized ribotype patterns, macrorestriction pattern analysis and estimation of genome size using PFGE, cell wall composition, phenotypic characteristics and plasmid profiles. Compared with their closet relatives, members of the genus Staphylococcus, these organisms demonstrated significantly lower 16S rRNA sequence similarities (93.4-95.3%), higher DNA G+C content (38-45 mol%), absence of cell wall teichoic acids (with the possible exception of M. caseolyticus), unique ribotype pattern types and macrorestriction patterns, smaller genome size (approx. 1500-1800 kb) and generally larger Gram-stained cell size (1.1-2.5% microns in diameter). Macrococci can be distinguished from most species of staphylococci (except Staphylococcus sciuri, Staphylococcus vitulus and Staphylococcus lentus) by thier oxidase activity. The four Macrococcus species can be distinguished from one another on the basis of DNA-DNA hybridization, ribotype pattern types, macrorestriction patterns and their phenotypic properties, including colony morphology, cell morphology, haemolysins, Staphy Latex agglutination, acid production from a variety of carbohydrates, acetoin production, nitrate reduction, aesculin hydrolysis, and DNase and urease activities. The type species is M. equipercicus. The type strains of M. equipercicus, M. caseolyticus, M. bovicus and M. carouselicus are ATTCC 51831T (= DD 9350T) ATCC 13548T (= TDD 4508T) (Schleifer et al. 1982, ATCC 51825T (= DD 4516T) and ATCC 51828T (= DD 9348), respectively.

Identification of Staphylococcus species and subspecies by the chaperonin 60 gene identification method and reverse checkerboard hybridization.

A previous study (S. H. Goh et al., J. Clin. Microbiol. 34:818-823, 1996) demonstrated that a 600-bp region of the chaperonin 60 (Cpn60) genes from various bacterial isolates could be amplified by PCR with a pair of degenerate primers and that the products could be used as species-specific probes for Staphylococcus aureus, S. epidermidis, S. haemolyticus, S. lugdunensis, S. saprophyticus, and S. schleiferi. To further validate the utility of bacterial Cpn60 genes as universal targets for bacterial identification (ID), reverse checkerboard chemiluminescent hybridization experiments were performed with DNA probes from 34 different Staphylococcus species and subspecies. With the exception of probes from the Cpn60 genes of S. intermedius and S. delphini, which cross hybridized, all were species specific. Two subspecies of both S. capitis and S. cohnii were differentiated from one another, while DNAs from the two S. schleiferi subspecies cross hybridized. When 40 known Staphylococcus isolates were tested in a blind experiment by the Cpn60 gene method, 36 strains, representing six species and one subspecies (S. sciuri, S. caseolyticus, S. hominis, S. warneri, S. hyicus, S. haemolyticus, and S. capitis subsp. ureolyticus), were correctly identified. DNA from the four remaining isolates, known to be S. hyicus bovine strains, failed to hybridize to DNA from the S. hyicus target strain or any other Staphylococcus species. However, DNAs from these S. hyicus isolates did cross hybridize with each other. New DNA sequence data and evidence from previous studies suggest some genetic divergence between the two groups of S. hyicus isolates. Our results demonstrate that this Cpn60 gene-based ID method has the potential to be a basic method for bacterial ID. Studies are in progress to further validate the utility of this Cpn60 gene system for ID of Staphylococcus and other genera, including those of slow-growing microorganisms.

Pulsed-field gel electrophoresis of Staphylococcus hyicus and Staphylococcus chromogenes genomic DNA and its taxonomic, epidemiologic and ecologic applications in veterinary medicine.

One hundred and thirty-eight strains of Staphylococcus hyicus and 21 strains of S. chromogenes isolated from animals were analyzed by pulsed-field gel electrophoresis (PFGE) after restriction endonuclease Smal digestion of chromosomal DNA. Eighty-eight strains of S. hyicus from pigs with or without exudative epidermitis (EE) generated 16 to 26 fragments in the size range of < 1 to 485 kb, and yielded 39 different patterns. With regard to the strains from pigs with EE, PFGE patterns differed according to the country of origin. Outbreaks of EE occurring on four separate pig farms in Japan involved S. hyicus with different PFGE patterns. The PFGE patterns shown by S. hyicus strains from 4 kinds of animals were compared. Strains from pigs differed from those isolated from chickens (n = 45; 18 to 24 fragments of < 1 to 425 kb), cows (n = 3; 17 to 19 fragments of < 1 to 475 kb), and goats (n = 2; 16 or 17 fragments of < 1 to 1,125 kb). Also, each of the chicken, cow and goat strains had a host-specific fragment. The results suggest that PFGE analysis might be a useful marker for distinguishing ecovars within S. hyicus. In contrast, strains of S. chromogenes from pigs and cows generated 17 to 24 fragments ranging from < 1 to 545 kb. The PFGE patterns of S. chromogenes strains were more highly conserved than those of S. hyicus. S. chromogenes strains could be distinguished from S. hyicus strains by fragments within the range of 305 to 545 kb. The results indicate that PFGE analysis could be used to distinguish between S. hyicus and S. chromogenes. We conclude that PFGE analysis is a useful tool not only for species or strain identification but also for epidemiologic or ecologic studies of S. hyicus and S. chromogenes.

Ribotype delineation and description of Staphylococcus sciuri subspecies and their potential as reservoirs of methicillin resistance and staphylolytic enzyme genes.

Three subspecies of Staphylococcus sciuri, S. sciuri subsp. sciuri Kloos, Schleifer, and Smith 1976, 23AL emend. Kloos et al. 1997 [corrected], S. sciuri subsp. carnaticus subsp. nov., and S. sciuri subsp. rodentium subsp. nov., are described on the basis of their ribotype patterns, DNA-DNA liquid hybridization data, and phenotypic characteristics. Normalized ribotyping subdivided the S. sciuri patterns into three blocks of patterns, each corresponding to a subspecies. Each subspecies formed a separate, well-defined DNA similarity group when DNA-DNA hybridizations were conducted under stringent (70 degrees C) reassociation conditions. S. sciuri subsp. sciuri could be distinguished from the other subspecies on the basis of its ability to produce acid from D-cellobiose, alkaline phosphatase activity, and inability to produce either clumping factor or protein A. S. sciuri subsp. carnaticus could be distinguished by its ability to produce acid aerobically from D-xylose and maltose, inability to produce acid from D-melezitose, and smaller colony size on P agar. S. sciuri subsp. rodentium could be distinguished by its positive reaction in the latex agglutination test for clumping factor and/or protein A and generally higher frequencies and levels of oxacillin and methicillin resistance. All 40 strains of S. sciuri tested (including representatives of all three subspecies) hybridized with the mecA gene probe. All strains of S. sciuri subsp. sciuri, 79% of the strains of S. sciuri subsp. carnaticus and 89% of the strains of S. sciuri subsp. rodentium exhibited extracellular, staphylolytic enzyme activity. This activity was associated with an enzyme(s) that immunoblotted with a lysostaphin-specific monoclonal antibody; however, only three strains hybridized with a lysostaphin (end) gene probe. The type strain of S. sciuri subsp. carnaticus is DD 791 (= ATCC 700058), and the type strain of S. sciuri subsp. rodentium is DD 4761 (= ATCC 700061).

Genomic DNA fingerprinting, using pulsed-field gel electrophoresis, of Staphylococcus intermedius isolated from dogs.

OBJECTIVES: To investigate the degree of polymorphism in the pulsed-field gel electrophoresis (PFGE) patterns of Staphylococcus intermedius and to assess the value of this typing method for discriminating strains. SAMPLE POPULATION: 52 S intermedius isolates from diseased and healthy dogs. PROCEDURE: Chromosomal DNA of S intermedius was digested with restriction endonuclease Sma I, and the fragments were separated by PFGE in a 1% agarose gel. RESULTS: Sma I cut the chromosomal DNA into 15 to 23 fragments ranging from about < 1 to 679 kb, and most of the detectable fragments were < 155 kb. Nine fragments, 115, 48, 33, 26, 16, 13, 10, 4, and < 1 kb, were shared by all or almost all (> 71%) of the strains examined. Of the 52 strains, each had a different pattern. S intermedius had a high degree of restriction fragment length polymorphism. The PFGE patterns obtained for S intermedius were stable and reproducible when the strains were tested in the different experiments. CONCLUSIONS: Genomic DNA fingerprinting by PFGE is an effective technique for discriminating S intermedius strains. The PFGE method appears to be a useful molecular marker for epidemiologic or ecologic studies of S intermedius.

Comparison of the SmaI-digested chromosomes of Staphylococcus epidermidis and the closely related species Staphylococcus capitis and Staphylococcus caprae.

Pulsed-field gel electrophoresis was used to examine the chromosomal polymorphisms existing within and between four closely related members of the Staphylococcus epidermidis species group, S. epidermidis, Staphylococcus caprae, Staphylococcus capitis subsp. capitis, and S. capitis subsp. ureolyticus. SmaI was chosen as the restriction endonuclease for this study because it generated only a few well-separated chromosomal fragments. Each of the species and subspecies showed distinct SmaI digest patterns. The strains examined in this study were collected over a 20-year period from various geographical locations. The results indicate that DNA fragment patterns are unique to each species and subspecies and represent a reasonably stable component in the chromosome structure. S. caprae and S. capitis demonstrated considerable conservation in chromosome structure as indicated by the large numbers of conserved SmaI digest fragments. The polymorphisms found within each species appear to be linked to the species' character variability. The genome size of each Staphylococcus strain was extrapolated from the SmaI digest fragment pattern obtained by pulsed-field gel electrophoresis. The average genome size for S. epidermidis is 2,364 +/- 119 kb; for S. caprae strains from humans it is 2,600 +/- 157 kb and for S. caprae strains from goats it is 2,493 +/- 15 kb; for S. capitis subsp. capitis it is 2,456 +/- 71 kb; and for S. capitis subsp. ureolyticus it is 2,276 +/- 90 kb.

Identification of the Staphylococcus sciuri species group with EcoRI fragments containing rRNA sequences and description of Staphylococcus vitulus sp. nov.

Strains of a new species, Staphylococcus vitulus, were isolated from food and a variety of mammals. This species was recognized on the basis of the results of an analysis of genomic EcoRI fragments containing portions of the rRNA operons. The patterns of hybridized fragments obtained from strains belonging to the new taxon were sorted into a distinguishable cluster and were distinct from the Staphylococcus lentus and Staphylococcus sciuri patterns. The results of DNA-DNA hybridization reactions demonstrated that strains in this cluster were more closely related to S. lentus and S. sciuri than to other Staphylococcus species and yet were significantly different. While these strains had some of the phenotypic characteristics of the S. sciuri species group, the newly recognized taxon could be distinguished by its very small colonies on P agar, absence of alkaline phosphatase activity, and lack of acid production from L-arabinose, maltose, N-acetylglucosamine, D-mannose, and raffinose. The type strain of the new species is strain DD 756 (= ATCC 51145).

Update on clinical significance of coagulase-negative staphylococci.

The clinical significance of coagulase-negative Staphylococcus species (CNS) continues to increase as strategies in medical practice lead to more invasive procedures. Hospitalized patients that are immunocompromised and/or suffering from chronic diseases are the most vulnerable to infection. Since CNS are widespread on the human body and are capable of producing very large populations, distinguishing the etiologic agent(s) from contaminating flora is a serious challenge. For this reason, culture identification should proceed to the species and strain levels. A much stronger case can be made for the identification of a CNS etiologic agent if the same strain is repeatedly isolated from a series of specimens as opposed to the isolation of different strains of one or more species. Strain identity initially can be based on colony morphology, and then one or more molecular approaches can be used to gain information on the genotype. Many of the CNS species are commonly resistant to antibiotics that are being indicated for staphylococcal infections, with the exception of vancomycin. The widespread use of antibiotics in hospitals has provided a reservoir of antibiotic-resistant genes. The main focus on mechanisms of pathogenesis has been with foreign body infections and the role of specific adhesins and slime produced by Staphylococcus epidermidis. Slime can reduce the immune response and opsonophagocytosis, thereby interfering with host defense mechanisms. As we become more aware of the various strategies used by CNS, we will be in a better position to compromise their defense mechanisms and improve treatment.

Species distribution of coagulase-negative staphylococcal isolates at a community hospital and implications for selection of staphylococcal identification procedures.

A total of 499 coagulase-negative staphylococci (CoNS) were isolated from a variety of clinical specimens at a community hospital. Ten different species and many strains of CoNS were identified. Staphylococcus epidermidis was the most common isolate. The species distribution suggests that S. saprophyticus and, to a lesser extent, S. haemolyticus may be important in urinary tract infections. S. lugdunensis may be a significant isolate from wound infections. Frequently, mixed cultures were found with either multiple species or multiple strains of the same species of CoNS. These mixed cultures could not be detected by colony morphology upon initial overnight incubation of the cultures but could be distinguished following colony development for several days. In addition, sequential positive cultures from an individual patient often yielded different species or different strains of the same species which again could not be detected upon initial observations of colony morphology. Procedures for the identification of the CoNS need to be improved, and microbiology laboratories should consider the use of more definitive identification procedures for the CoNS.

Evaluation of the Vitek Systems Gram-Positive Identification card for species identification of coagulase-negative staphylococci.

Vitek Systems' Gram-Positive Identification test (GPI) card was evaluated for the ability to identify 12 coagulase-negative Staphylococcus species and subspecies. The bionumber generated from the GPI card was examined for its potential use in epidemiological studies. Results indicated that the GPI card had a high degree of correlation with the conventional methods of identification. The species identified with the greatest accuracy were Staphylococcus epidermidis (92%), S. haemolyticus (95%), S. capitis subsp. capitis (88%), and S. saprophyticus (100%). S. hominis (63%) was identified with the least accuracy. The bionumber was found to have limited epidemiological value because of the frequent occurrence of a few major bionumbers.

Susceptibility of Staphylococcus species and subspecies to fleroxacin.

Twenty-four Staphylococcus species or subspecies were examined for their susceptibilities to the fluoroquinolone fleroxacin (Ro 23-6240) by disk diffusion (5-micrograms disk) and by agar dilution for the determination of MICs. Resistant strains were further tested for their susceptibilities to oxacillin and the fluoroquinolone ciprofloxacin. Reference strains of the novobiocin-resistant species (Staphylococcus saprophyticus, Staphylococcus cohnii, Staphylococcus xylosus, Staphylococcus arlettae, and Staphylococcus gallinarum) had an intrinsic intermediate susceptibility (MIC, 4 micrograms/ml) to fleroxacin. Fleroxacin resistance was not observed in the reference strains of the novobiocin-susceptible species (MIC, 0.5 to 2.0 micrograms/ml). Clinical isolates of coagulase-negative species were generally less susceptible to fleroxacin than were reference strains. Seven percent of the Staphylococcus epidermidis clinical strains were resistant (MIC, greater than or equal to 8 micrograms/ml) to fleroxacin. Of these strains, 77% were resistant to oxacillin and 50% were resistant to ciprofloxacin. Thirty-four percent of the Staphylococcus haemolyticus clinical strains were resistant to fleroxacin, and 9% had intermediate susceptibility. Of the resistant strains, 95% were resistant to oxacillin and 77% were resistant to ciprofloxacin, while 23% had intermediate susceptibility to ciprofloxacin. Fleroxacin is an effective antimicrobial agent against most staphylococci.

Susceptibility of Staphylococcus species and subspecies to teicoplanin.

Twenty-four Staphylococcus species and their subspecies were examined for their susceptibilities to teicoplanin by disk diffusion (30-micrograms disk) and agar dilution for the determination of MICs. Moderately susceptible and resistant clinical strains were further tested for their susceptibilities to oxacillin and vancomycin. Teicoplanin resistance was not observed in the reference strains of the various Staphylococcus species isolated from healthy volunteers or animals. However, the novobiocin-resistant species Staphylococcus saprophyticus, Staphylococcus cohnii, Staphylococcus xylosus, Staphylococcus arlettae, Staphylococcus kloosii, and Staphylococcus gallinarum were less susceptible to teicoplanin (MIC, 2 to 8 micrograms/ml) than most of the novobiocin-susceptible species were (MIC, 0.5 to 4 micrograms/ml). Clinical isolates of coagulase-negative species were generally less susceptible to teicoplanin than were reference strains. Seven percent of the Staphylococcus epidermidis clinical strains were moderately susceptible (MIC, 16 micrograms/ml) to teicoplanin. Of these strains, 70% were oxacillin resistant. For Staphylococcus haemolyticus strains, 11% were resistant (MIC, greater than 16 micrograms/ml) and 21% were moderately susceptible to teicoplanin. Of these strains, 95% were oxacillin resistant, No strains of S. epidermidis or S. haemolyticus were intermediate or resistant to vancomycin. Teicoplanin appears to be less active in vitro against oxacillin-resistant S. haemolyticus. However, teicoplanin is an effective antimicrobial agent against many Staphylococcus species.

Staphylococcus cohnii subspecies: Staphylococcus cohnii subsp. cohnii subsp. nov. and Staphylococcus cohnii subsp. urealyticum subsp. nov.

Two major subspecies of Staphylococcus cohnii, namely S. cohnii subsp. cohnii, from humans, and S. cohnii subsp. urealyticum, from humans and other primates, are described on the basis of a study of 14 to 25 strains and 18 to 33 strains, respectively. DNA-DNA hybridization studies conducted in our laboratory in 1983 (W. E. Kloos and J. F. Wolfshohl, Curr. Microbiol. 8:115-121, 1983) demonstrated that strains representing the different subspecies were significantly divergent. S. cohnii subsp. urealyticum can be distinguished from S. cohnii subsp. cohnii on the basis of its greater colony size; pigmentation; positive urease, beta-glucuronidase, and beta-galactosidase activities; delayed alkaline phosphatase activity; ability to produce acid aerobically from alpha-lactose; and fatty acid profile. The type strain of S. cohnii subsp. cohnii is ATCC 29974, the designated type strain of S. cohnii Schleifer and Kloos 1975b, 55. The type strain of S. cohnii subsp. urealyticum is ATCC 49330.

Identification of Staphylococcus species and subspecies with the MicroScan Pos ID and Rapid Pos ID panel systems.

The accuracies of the MicroScan Pos ID and Rapid Pos ID panel systems (Baxter Diagnostic Inc., MicroScan Division, West Sacramento, Calif.) were compared with each other and with the accuracies of conventional methods for the identification of 25 Staphylococcus species and 4 subspecies. Conventional methods included those used in the original descriptions of species and subspecies and DNA-DNA hybridization. The Pos ID panel uses a battery of 18 tests, and the Rapid Pos ID panel uses a battery of 42 tests for the identification of Staphylococcus species. The Pos ID panel has modified conventional and chromogenic tests that can be read after 15 to 48 h of incubation; the Rapid Pos ID panel has tests that use fluorogenic substrates or fluorometric indicators, and test results can be read after 2 h of incubation in the autoSCAN-W/A. Results indicated that both MicroScan systems had a high degree of congruence (greater than or equal to 90%) with conventional methods for the species S. capitis, S. aureus, S. auricularis, S. saprophyticus, S. cohnii, S. arlettae, S. carnosus, S. lentus, and S. sciuri and, in particular, the subspecies S. capitis subsp. capitis and S. cohnii subsp. cohnii. The Rapid Pos ID panel system also had greater than or equal to 90% congruence with conventional methods for S. epidermidis, S. caprae, S. warneri subsp. 2, S. xylosus, S. kloosii, and S. caseolyticus. For both MicroScan systems, congruence with conventional methods was 80 to 90% for S. haemolyticus subsp. 1, S. equorum, S. intermedius, and S. hyicus; and in addition, with the Rapid Pos ID panel system congruence was 80 to 89% for S. capitis subsp. ureolyticus, S. warneri subsp. 1, S. hominis, S. cohnii subsp. urealyticum, and S. simulans. The MicroScan systems identified a lower percentage (50 to 75%) of strains of S. lugdunensis, S. gallinarum, S. schleiferi, and S. chromogenes, although the addition of specific tests to the systems might increase the accuracy of identification significantly.

Selection of colony, plasmid, and virulence variants of Staphylococcus epidermidis NRC853 during growth in continuous cultures exposed to erythromycin.

A continuous-culture system was developed to study changes in the structure of Staphylococcus epidermidis populations exposed to subminimum inhibitory concentrations of erythromycin. Continuous-culture experiments were carried out in a dextrose-free, tryptic soy broth medium supplemented with lactic acid and sodium lactate (MTSB-D). The multiresistant (penicillin-, tetracycline-, and erythromycin-resistant) S. epidermidis strain NRC853 was subjected to a series of experiments: (i) growth individually in continuous culture in the absence and presence of erythromycin and (ii) growth in mixed culture with the erythromycin-susceptible S. epidermidis strain NRC852 in the absence and presence of erythromycin. Strain NRC853 produced colony morphology variants during continuous culture in the presence of 0.05 and 0.1 microgram of erythromycin per ml. Variants (A, B, and C) were different from their wild-type parent on the basis of colony size, sector pattern, and/or the ability to transmit light. A variants rapidly lost a 2.7-MDa tetracycline resistance plasmid. B and C variants formed an ermC plasmid multimer series from unit size to a 16-mer and exhibited an approximately twofold increase in erythromycin MIC over that of the wild-type parent. They slowly lost the tetracycline resistance plasmid. The small-colony B variant demonstrated an increased virulence in the neonatal mouse weight gain test and an increase in fibronectin binding compared with the wild-type parent. The presence of a competing strain drastically increased the frequency of all variants.

Staphylococcus capitis subsp. ureolyticus subsp. nov. from human skin.

A new subspecies, Staphylococcus capitis subsp. ureolyticus, was isolated from human skin and is described on the basis of studies of 15 to 26 strains. DNA-DNA reassociation reactions demonstrated that these strains were closely related to Staphylococcus capitis but were significantly divergent. The strains of S. capitis subsp. ureolyticus can be distinguished from S. capitis by their positive urease activity, their ability to produce acid from maltose under aerobic conditions, their fatty acid profile, and their colony morphology. The type strain of the new subspecies is strain ATCC 49326.