Variable reactions are observed in the 6. Vagococcal strains have rarely been isolated from human infections. The vagococcal strains were split from the Lactococcus genus. These organisms were previously known as motile lactococci. In fact, only the motility characteristic of the vagococci differentiates the vagococci from the lactococci. These bacteria are included in the identification of the enterococcus because of phenotypic similarities.
Like the lactococci the Leuconostoc s were once not thought to cause human infections. However, there are many reports of human infections caused by different Leuconostoc species. Species of the Leuconostoc genus are the only catalase negative gram positive cocci that produce gas from MRS broth.
As stated earlier all strains are intrinsically resistant to vancomycin. No other catalase negative, gram positive cocci has these characteristics. Some strains grow in 6. Like the Leuconostoc s the pediococci are intrinsically resistant to vancomycin. They too were thought to be nonpathogenic for humans but there are several reports indicating that this is changing. The Pediococcus strains appear very similar to the viridans streptococci on blood agar media and can be easily misidentified as viridans streptococci.
All strains of pediococci tested have been resistant to vancomycin and all strains of viridans streptococci have been sensitive to vancomycin.
This new genus of gram positive cocci has just recently been described. The origin of this genus is from a collection of viridans-like streptococci that most closely resembled Streptococcus uberis.
What makes Globicatella distinct from the viridans streptococci is that all the Globicatella strains were PYR positive, LAP negative and grow in broth containing 6. This genus contains only one species. The tetragenococci differ from the pediococci by vancomycin resistance. The pediococci are vancomycin resistant and the tetragenococci are vancomycin sensitive. Other characteristics are similar. These bacteria grow very poorly on blood agar plates and will often take 48 h to grow.
These bacteria may also resemble the viridans streptococci; occasionally the tetrads are not formed and only pairs and short chains are observed in the gram stain. One species was previously identified as a streptococci, G. On blood agar plates some of the strains give an wide-zone alpha hemolytic reaction after extended incubation. Identifying these bacteria is difficult and an extended set of physiologic characteristics may have to be determined before final identification is possible.
These bacteria are characteristically negative in most tests listed in Table 1. Some strains are positive in both the PYR and LAP tests but other strains may fail to give a positive reaction in either. Salt tolerant Gemella -like genera include the Alloiococcus , Dolosigranulum , Facklamia , and Ignavigranum. The Aerococcus sp.
All strains grow in broth containing 6. The strains grow well on blood agar media and form colonies somewhat smaller than the enterococci but larger than the viridans streptococci after overnight incubation. Only one species of this genus is presently known, A. These bacteria have been isolated from the ear fluids of children with otitis. Like the Gemella e this bacterium is difficult to grow. Often 2 to 3 days are necessary for growth to develop on rabbit blood agar plates.
They are differentiated from the Gemella e by the 6. Alloiococci grow in 6. Two species of this genus are presently known. These bacteria have been isolated from wound infections. Like the Alloiococci and Gemella e these bacteria grow very slowly on blood agar media. The physiologic characteristics of helocococci are similar to the aerococci in that they are PYR positive, LAP negative, and grow in broth containing 6.
All isolates have been non-motile. Nutritionally variant streptococci NVS can be identified by demonstrating that the strain requires pyridoxal or grows on an agar plate only when a bacteria that satellites is present.
In addition to this requirement, NVS also give positive PYR tests, which helps to differentiate these strains from viridans streptococci. The most convenient way to begin to identify the streptococci is to determine the hemolysis of the bacteria on blood agar plates. As mentioned earlier the techniques for determining hemolysis is described in detail in; Isolation and Identification of streptococci, Part 1. Collection, transport, and determination of hemolysis, Annex 1. Identification is confirmed by demonstrating the presence of the group A antigen on the streptococcal cells.
All S. Some strains of S. Non-pyogenes strains grow more slowly and form smaller colonies than do S. When this occurs the strain should be tested for voges-proskauer VP reaction. See Table 2 , for correct identification. Like group A streptococci, identification is confirmed by demonstrating that the streptococcal cells contain group B antigen. Since the group B antigen is not identified with any other streptococcal strain the terms Lancefield group B and S. The group C antigen is found with several different species and the S.
Some have suggested that these strains be called S. Group F streptococci: S. Most of these strains have group F antigen, the next most frequently identified strain will have no group antigen, and only rarely will an anginosus strain have group A, C, or G antigen.
Technically some of these strains may be S. The majority of these strains will require additional carbon dioxide in the atmosphere for growth on blood agar plates. Often growth is not apparent until 48 h of incubation. Some of the strains are associated with infections of swine and they have specific group antigens.
This bacterium may be submitted as a group A streptococci because it may react with the group A antibody in the latex slide agglutination assay. It is also PYRase positive but is not sensitive to bacitracin.
Whenever a latex agglutination group A positive bacterium is submitted that is not sensitive to bacitracin the group reaction should be confirmed using the Lancefield extraction procedure. Strains with group R, S, and T antigens are very similar to each other physiologically and the taxonomist have suggested that these strains should be called S. The strains are found commonly in swine and may be transmitted to man. There are several reports of farmers and abattoir workers being infected with group R S.
Identification of these bacteria is difficult without having knowledge that the infecting strain may be related to nonhuman sources. Demonstration of the group R, S, and T antigens with specific antisera is also difficult. It is suggested that if group R streptococci is the suspected agent in an infection the cells may have to be extracted with the formamide extraction technique in order to extract the group antigen.
The formamide extraction technique is described in Annex 2 Part II of Isolation and identification of streptococci. Table 2. Table 3. Differentiation of gram-positive cocci, atypical variants of group A streptococcci.
Non-hemolytic variants of S. The non-beta hemolytic varieties of S. The non-beta hemolytic varieties of these species are also included in the viridans streptococci identification tables. In all likelihood beta-hemolytic varieties of the S.
Table 4. Identification of the Streptococcus anginosus group. Data in table compiled from references 14, , In some instances where only the S. Pneumococcal surveillance cultures, pneumococcal epidemiologic investigation cultures, and non-sterile site isolates sputum are cultures that are examined only for pneumococci.
If the tests for optochin susceptibility and bile solubility are negative then the report can simply be no pneumococci present. Streptococcus pneumoniae : S. They can be identified and differentiated from the viridans streptococcal species by their susceptibility to optochin and bile solubility. On occasion, some strains of viridans streptococci are susceptible to optochin or partially soluble in bile, but rarely will a culture of viridans streptococci be positive in both tests.
Cultures suspected of being pneumococci isolated from systemic sources non-respiratory that are optochin susceptible and bile soluble but fail to serotype should be tested with the GenProbe pneumococcus probe. All pneumococcal cultures should be serotyped by the Quellung reaction, with CDC produced typing antisera, see instructions below and Annex 3. Positive Quellung reactions are considered definitive identification of pneumococci.
Table 5. Identification of nonbeta hemolytic gram-positive cocci in chains. See footnote in Table 2 for positive and negative reactions. Note that the only way to differentiate S. Table 6. Shows key test in the differentiation of the virdidans streptococci. Most species can only be identified to viridans species group. The VP test aids in the identification and differentiation of the viridans streptococcal species and is a key reaction for the S. The urea test is particularly useful in the identification of Streptococcus salivarius.
Identification of major groups of viridans Streptococcus species. Table 7. Identification of Abiotrophia and Granulicatella species 1. No reaction on bile-esculin medium. All strains require pyridoxal for growth and satillite around staphylococcus culture on blood agar plates. The enterococci are gram positive cocci, occur in singles, pairs, and short chains. Cells are sometimes coccobacillary when gram stains are prepared from agar plate growth.
Cells are more oval and in chains when gram stains are prepared from thioglycolate broth. The enterococci are facultatively anaerobic and optimum growth occurs at 35C. Most strains grow at 10C and 45C. Motility is observed with some species.
Most strains produce leucine aminopeptidase LAP. Enterococci do not contain cytochrome enzymes but on occasion the catalase test is positive. A pseudo catalase is sometimes produced and a weak effervescence is observed in the catalase test. Nearly all strains are homofermentive, gas is not produced and lactic acid is the end product of glucose fermentation. Most strains produce a cell-wall associated glycerol teichoic acid antigen that is identified as the streptococcal group D antigen.
Detection of the group D antigen is sometimes difficult and depends upon the extraction procedure and the quality of the antiserum used. Presumptive identification of a catalase negative gram positive cocci as an Enterococcus or Vagococcus can be accomplished by demonstrating that the unknown strain is vancomycin sensitive, PYR and LAP positive, and grows in 6.
Once established that the unknown catalase-negative gram-positive coccus is an Enterococcus the tests listed in Table 8 can be used to identify the species. The species into 5 Groups based on the reactions in acid formation in mannitol, sorbitol, and sorbose broths and hydrolysis of arginine. Group I consists of E. These species form acid in all three of the aforementioned Carbohydrate broths but do not hydrolyze arginine.
Group II consists of E. These species form acid in mannitol broth, hydrolyze arginine, but fail to form acid in sorbose broth and give variable reactions in sorbitol broth. Group III consists of E. These species hydrolyze arginine but do not form acid in mannitol, sorbitol or sorbose broths. Group IV contains E. These species are sorbose negative and not hydrolyze arginine.
Group V consists of E. The pigmentation test aids in the identification of E. These enterococci produce a yellow pigment that can be detected on several different media. The pyruvate utilization test aids in the differentiation of E. This test is also used to help differentiate between E. The tellurite tolerance test aids in the differentiation of E.
Table 8. Phenotypic characteristics used for the identification of Enterococcus species and some physiologically related species of other gram-positive cocci. Lactococcus strains identified to the genus level by the tests listed in Table 1.
Identification of the Lactococcus species is accomplished by performing the tests listed in Table 9. The majority of lactococcal isolates identified from human sources resemble L.
Gram-positive cocci are often isolated from clinical samples. Catalase is an enzyme that converts hydrogen peroxide to water and oxygen gas. The test is easy to perform; bacteria are simply mixed with H 2O 2. If bubbles appear due to the production of oxygen gas the bacteria are catalase positive. If no bubbles appear, the bacteria are catalase negative. Staphylococcus and Micrococcus spp.
If a Gram-positive cocci is catalase positive and presumed to be a staphylococci, the coagulase test is often performed. This test assays for the presence of coagulase, an enzyme that coagulates blood plasma, and can differentiate between Staphylococcus aureus coagulase positive and Staphylococcus epidermidis coagulase negative. If, in contrast, a Gram-positive cocci is catalase negative and thought to be a streptococci, antibiotic susceptibility tests can differentiate between pathogenic streptococci Streptococcus pneumoniae and Streptococcus pyogenes , and the normal floral streptococci e.
Streptococcus mitis. Rachel Watson, M.
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