Staphylococcus Vs Streptococcus, a comprehensive analysis

Staphylococcus Vs. Streptococcus.
A Comprehensive Analysis. Comparison and Contrast.

Author:
Dr.B.Fidanoski, DMD

I. Mutual Characteristics: Both genera are Gram positive and have the similar spherical cell shape, therefore there are called cocci (in Greek coccus means granule).

II. Visual differentiation between Staphylococci and Streptococci by cellular arrangement:

When performing laboratory analysis, after Gram staining, first thing we should do is put a piece of a colony under microscope and observe cellular arrangement of the bacteria. Both staphylococci and streptococci have round, spherical cell shape, but the arrangement of cells is different due to a different binary fission. Streptococci form a chain of round cells, because their division occurs in one linear direction, whereas staphylococci divide in various directions forming grape-like clusters.

III. Biochemical differentiation between Staphylococci and Streptococci with CATALASE test:

The main criterion for differentiation between Staphylococcus and Streptococcus genera is the catalase test. Staphylococci are catalase positive whereas Streptococci are Catalase negative. Catalase is an enzyme used by bacteria to induce the reaction of reduction of hydrogen peroxide into water and oxygen.

III-A. Biochemical differentiation among Staphylococci:

There are at least three Staphylococci species of clinical importance:
1. Staphylococcus aureus is the most pathogenic for humans
2. Staphylococcus epidermidis, which is part of the normal flora and is of low pathogenicity, and
3. Staphylococcus saprophyticus which can cause urinary tract infections, especially in sexually active young women.

1.Differentiation between Staphylococcus aureus and other Staphylococci:
- COAGULASE test which is positive for Staphylococcus aureus (generally accepted criterion for the identification) and negative for all other Staphylococci. Coagulase is an enzyme used by S.aureus to induce coagulation and convert soluble fibrinogen into fibrin which will protect bacteria from the immune system. It is also a clumping factor for bacteria’s coalescence. All other staphylococcus species can be collectively referred to as coagulase-negative staphylococci.
- STAPHYLOSLIDE test that will determine if bacteria has two types of proteins: Fibrinogen receptor and Protein A. With this test S. aureus will cause notable agglutination. Agglutination will not be seen if the isolate is S. epidermidis or S. saprophyticus.
- Presence of HEMOLYSIS. While others don’t have any, Staphylococcus aureus has Beta hemolysis. 2.Differentiation between Staphylococcus epidermis and Staphylococcus saprophyticus can be made with reaction to NOVOBIOCIN (antibiotic produced by the actinomycete Streptomyces nivens and used to treat infections by gram-positive bacteria). S. saprophyticus is resistant to novobiocin (at a concentration of 5 mg), and this is used to differentiate the organism from S. epidermidis which is susceptible to novobiocin.

	Staphylococcus aureus	*Staphylococcus epidermidis*	Staphylococcus saprophyticus
Catalase test	+	+	+
Coagulase test	+	-	-
Staphyloslide test	+	-	-
Colour differences in colonies	Gold – yellow	White	White to yellow
Hemolysis test	Beta	None	None
Reaction to Novobiocin	Sensitive	Sensitive	Resistant

III-B. Biochemical differentiation among Streptococci:
The various streptococci have genus-species Latin names. However, traditionally, clinical laboratories report them by their type of hemolysis and Lancefield serological group. The first step in correctly identifying a Streptococcus in the clinical laboratory is an accurate determination of the type of hemolysis the organism produces. Streptococci may be classified into two main divisions on the basis of their hemolytic action on blood agar:
I. Beta hemolytic—complete hemolysis of erythrocytes
These are arranged into 18 groups A-U known as Lancefield groups. Groups are determined by PRECIPITIN test, serologic test to measure a specific reaction between antigen (C carbohydrate, located in the cell wall) and antibody which results in a visible precipitate.
Group A Streptococci (Streptococcus pyogenes) is among the most important human pathogens. Their important diagnostic criterion is susceptibility to Bacitracin (polypeptide antibiotic obtained from a strain of the bacterium Bacillus subtilis and used as a topical treatment for certain bacterial infections, especially those caused by cocci). Many strains have a hyaluronic acid capsule that is antiphagocytic. Group B Streptococci (Streptococcus agalactiae) are bacitracin resistant.
Group D include Enterococci (Streptococcus faecalis) and Non-enterococci (Streptococcus bovis). Enterococci grow in 6.5% NaCl and are not killed by penicillin G (the most commonly used penicillin compound, used primarily in the form of its stable salts, also called benzylpenicillin). Non-enterococci are inhibited by 6.5% NaCl and killed by Penicillin G.
II. Non-Beta Hemolytic (Alpha hemolytic—partial or green hemolysis of erythrocytes or Gamma hemolytic—no hemolysis.). Differentiation among this group can be made with OPTOCHIN test. Members of this group are:
Streptococcus pneumoniae: Inhibited by Optochin (ethyl hydrocupreine).
Viridans group of Streptococci (Streptococcus mitis, Streptococcus sanguis and Streptococcus mutans): not inhibited by optochin and not bile-soluble, in contrast to S.pneumoniae. Streptococcus mutans synthesizes polysaccharides (dextrans) that are found in dental plaque and lead to dental caries

	Lancefield group	Hemolysis	Diagnostic features
*S. pyogenes*	A	Beta	Bacitracin sensitive
*S. agalactiae*	B	Beta	Bacitracin resistant Hippurate hydrolyzed
*S. faecalis (Enterococcus)*	D	Alpha or Beta or none	Growth in 6.5% NaCl
*S. bovis*	D	Alpha or none	No Growth in 6.5% NaCl
*S. pneumoniae*	Not applicable	Alpha	Bile soluble Inhibited by optochin
Viridans group	Not applicable	Alpha	Not bile soluble Not inhibited by optochin

Significance of Catalase test in Microbiology

All aerobes and facultative anaerobe microorganisms use oxygen for growth and metabolism. The superoxide anion is a product of oxygen reduction and is capable of participating in destructive reactions potentially lethal to the cell. Moreover, products of secondary reactions may amplify toxicity.
For example, one hypothesis holds that the superoxide anion reacts with hydrogen peroxide in the cell:
O₂ + H₂O₂ ' OH+ OH^.+ O₂
This reaction, known as the Haber-Weiss reaction, generates a free hydroxyl radical (OH^.), which is the most potent biologic oxidant known. It can attack virtually any organic substance in the cell. Aerobe and facultative anaerobe microorganisms contain a high concentration of an enzyme called superoxide dismutase. This enzyme converts the superoxide anion into ground-state oxygen and hydrogen peroxide, thus freeing the cell of destructive superoxide anions:
2O₂ + 2H^{+ Superoxide Dismutase} O₂ + H₂ O₂
The hydrogen peroxide generated in this reaction is an oxidizing agent, but it does not damage the cell as much as the superoxide anion and tends to diffuse out of the cell. Many organisms possess catalase or peroxidase or both to eliminate the H₂O₂. Catalase is enzyme that decomposes hydrogen peroxide (H₂O₂) to water and ground-state oxygen
H₂O₂ + H₂O₂^Catalase 2H₂O + O₂Catalase test is particularly useful in differentiating staphylococci genus and family of micrococcacae (genera: Arthrobacter and Micrococcus) , which are catalase-positive, from streptococci and enterococci, which are catalase-negative.
How to perform the test? - Dip a capillary tube into 3%H₂O_2. .Touch a colony .Observe the tube for bubble indicating a positive reaction. Result: Bubles: positive, no bubbles: negative reaction.

Special Features - catalase is found in most aerobic and facultative anaerobic bacteria. The main exception is Streptococci, which have catalase negative test. Catalase is not found in anaerobes.
Precautions in interpretation: It is important not to contaminate the bacterial colony under test with blood agar. Red blood cells contain catalase and their presence will give a false positive result. Old cultures may loose their catalase activity, possible resulting in a false negative result.

Microorganism	Catalase test
Staphylococci	Positive (exception: Staphylococcus aureus, subspecies anaerobius is catalase negative)
Streptococci	Negative
Actinomyces israelii	Negative
Fusobacterium	Negative
Prevotella melaninogenica	Negative
Family of Enterobacteriaceae	Positive
- Escherichia colli	Rare types from moderate to mostly non-reactive
- Salmonella	Moderate positive reaction
- Shigella	Mostly non-reactive
Clostridium	Negative

As stated in Catalase Test as an Aid to the Identification of Enterobacteriaceae research paper published in 1972, family of enterobacteriaceae have differentiation of catalase positive reaction, from vigorous ( Serratia, Proteus and Providencia), moderate ( Salmonella, some rare types of Escherichia, Enterobacter and Klebsiela) to non-reactive (most types of Escherichia and Shigella).

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Bibliography:

Levinston W., Jawetz E.; Microbiology and Immunology, 4-th edition 1996

University of Kentucky: http://www.mc.uky.edu/oaa/curriculum/iid98/manual/00lab2.htm

University of Texas, Houston Medical School: http://medic.med.uth.tmc.edu/path/tests.htm

TAYLOR W.I. and ACHANZAR D.; Catalase Test as an Aid to the Identification of
Enterobacteriaceae- 1972 American Society for Microbiology

The University of Newcastle, Australia: http://whitewolf.newcastle.edu.au/techinfo/proc_bacto_biochem.html

Microbionet: http://www.microbionet.com.au

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author: Dr. Boban Fidanoski, DT, DMD