Microbiology Chapter on Micrococcus and Streptococcus

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Questions and Answers

Which characteristic is NOT true about Kocuria spp. based on the provided content?

They are catalase positive.

They do not cause hemolysis.

They are classified under the genus Micrococcus. (correct)

They can appear yellow when cultured.

What is the result of the Furazolidone test for Micrococcus?

Resistant (correct)

Variable response

Inconclusive

Sensitive

Which species listed is NOT a notable species of Streptococcus?

S.pyogenes

S. pneumoniae

S. aureus (correct)

S. agalactiae

What type of infections can Kocuria spp. cause in immune-compromised individuals?

Acute endocarditis (C) Signup and view all the answers

What is the characteristic morphology of Streptococcus bacteria?

Gram (+ve) cocci in chains (B) Signup and view all the answers

Which of the following antibiotics is NOT typically used to treat Micrococcus infections?

Amoxicillin (C) Signup and view all the answers

Which media enhances the growth of Streptococcus species?

Blood or serum and glucose (D) Signup and view all the answers

Which of the following statements about Kocuria spp. is TRUE?

They are classified as facultative anaerobes. (C) Signup and view all the answers

What characterizes beta-hemolytic streptococci?

Complete lysis of red cells surrounding the colony. (A) Signup and view all the answers

Which classification system categorizes streptococci based on carbohydrate antigens in the cell wall?

Lancefield classification (D) Signup and view all the answers

Which of the following is an example of an alpha-hemolytic streptococcus?

Streptococcus pneumoniae (B) Signup and view all the answers

What type of hemolytic reaction is associated with gamma-hemolytic streptococci?

No lysis of red cells. (C) Signup and view all the answers

Which group is identified as Group A in Lancefield classification?

Streptococcus pyogenes (A) Signup and view all the answers

What does Brown's classification depend on?

Degree of blood hemolysis. (B) Signup and view all the answers

Which organism is found in the untippable group of Lancefield classification?

Streptococcus pneumoniae (C) Signup and view all the answers

In Sherman's classification, which physiological characteristic is NOT considered?

Presence of lactose (B) Signup and view all the answers

What is the general shape and arrangement of Micrococcus species?

Cocci in tetrads (D) Signup and view all the answers

Which of the following is a characteristic of Micrococcus species?

Non-capsulated (B) Signup and view all the answers

Identify a notable species of Micrococcus.

M. luteus (B) Signup and view all the answers

Which classification system is used to organize Streptococcus species?

Lancefield's classification (A) Signup and view all the answers

What kind of media supports the growth of Micrococcus species?

Nutrient agar (D) Signup and view all the answers

Which characteristic is NOT true about Micrococcus species?

They can ferment glucose. (A) Signup and view all the answers

What is the pathogenic risk of Micrococcus in certain populations?

Commensal but can be opportunistic in immunocompromised (C) Signup and view all the answers

Which biochemical test is important for diagnosing Streptococcus species?

PYR test (A) Signup and view all the answers

What is one of the diseases caused by S.pyogenes that is classified as a post-streptococcal condition?

Rheumatic fever (C) Signup and view all the answers

Which enzyme produced by S.pyogenes facilitates the spread of bacteria through tissues by breaking down connective tissue?

Hyaluronidase (A) Signup and view all the answers

Which of the following is a major virulence factor of S.pyogenes that aids in adherence to host tissues?

M Protein (C) Signup and view all the answers

What type of testing is initially performed to differentiate S.pyogenes from S.agalactiae?

Antibiotic sensitivity (D) Signup and view all the answers

What is the role of exotoxins produced by S.pyogenes?

To cause toxic shock syndrome (D) Signup and view all the answers

How does the hyaluronic acid capsule of S.pyogenes contribute to its pathogenicity?

By resisting phagocytosis (B) Signup and view all the answers

Which type of specimen is NOT suitable for diagnosing S.pyogenes infections?

Saliva sample (D) Signup and view all the answers

What is a common symptom associated with scarlet fever caused by S.pyogenes?

Rash (A) Signup and view all the answers

What is a primary characteristic of Enterococcus faecalis?

It generally appears in pairs or short chains. (D) Signup and view all the answers

Which of the following diseases is commonly associated with Enterococcus faecalis?

Urinary tract infections (D) Signup and view all the answers

Which characteristic differentiates Enterococcus faecalis from non-enterococcal streptococci?

Growth in 6.5% NaCl (C) Signup and view all the answers

What type of hemolysis is Enterococcus faecalis typically classified under?

Alpha-hemolytic or non-hemolytic (D) Signup and view all the answers

Why is Lancefield Grouping not reliable for identifying Enterococcus faecalis?

It produces no recognizable antigens. (C) Signup and view all the answers

Which of the following is NOT a biochemical test commonly performed for Enterococcus faecalis?

Optochin sensitivity (A) Signup and view all the answers

What notable feature is characteristic of Viridans group streptococci?

They are optochin resistant. (D) Signup and view all the answers

Which species within the Viridans group is known for causing dental caries?

Streptococcus mutans (B) Signup and view all the answers

Study Notes

Micrococcus

Gram-positive cocci arranged in tetrads (groups of four)
Non-motile, non-capsulated, and non-sporulated
Found in the upper respiratory tract and skin, often as commensals or opportunistic pathogens in immunocompromised individuals
Notable species include Micrococcus varians, Micrococcus luteus (Milk Micrococci), and Micrococcus roseus (Dust of the air)
Strictly aerobic, growing at 37°C
Grows on ordinary media (Nutrient agar) and Blood agar (Gamma hemolysis)
Produces rose or pink colonies on mannitol salt agar, except for M. luteus which produces yellow colonies
Previously classified into the genus Micrococcus, but now reclassified into Kocuria species based on phylogenetic and chemotaxonomic analysis

Streptococcus

Gram-positive cocci arranged in chains
Non-motile and non-sporulated
May or may not be capsulated
Facultative anaerobic, growing poorly on ordinary media but better in the presence of blood, serum, and glucose
Notable species include Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus pneumoniae, and Enterococcus faecalis

Classification of Streptococcus

Brown's classification: based on hemolytic reactions on blood agar
- Beta-hemolytic (β): complete lysis of red blood cells, clear zone around colonies; most pathogenic
- Alpha-hemolytic (α): partial hemolysis, greenish discoloration around colonies; mild pathogenic
- Gamma-hemolytic (γ): non-hemolytic; saprophytic
Lancefield classification: based on carbohydrate antigens in the cell wall; groups A-H, K-V, and untippable groups
- Group A: S. pyogenes - pharyngitis, skin infections
- Group B: S. agalactiae - neonatal infections
- Group D: Enterococcus faecalis (previously Streptococcus faecalis) - nosocomial infections, endocarditis
- Untippable group: S. pneumoniae - pneumonia in humans
Sherman's classification: based on hemolytic reaction, Lancefield group, and specific physiological characteristics including fermentation and tolerance tests

Streptococcus pyogenes

Causes pharyngitis (strep throat), scarlet fever (complication of strep throat), skin infections (impetigo, necrotizing fasciitis, cellulitis)
Associated with post-streptococcal diseases like rheumatic fever and rheumatic kidney, which are autoimmune reactions triggered by similarities between heart muscle antigens and Streptococcus antigens
Virulence factors include:
- M protein: evades phagocytosis by immune cells, helps adherence to host tissues
- Hyaluronic acid capsule: resists phagocytosis by immune cells
- Protein F: adherence to host cells
- Lipoteichoic acid: found in gram-positive cell walls
- Hyaluronidase: breaks down connective tissue, facilitates bacterial spread
- Streptokinase: dissolves blood clots, facilitating bacterial spread
- DNase: breaks down DNA
- C5a peptidase: inactivates complement system for immune evasion
- Hemolysins (Streptolysin O and S): lyse red and white blood cells, causing tissue damage and infection spread
- Exotoxins (e.g., SpeA, SpeB): cause toxic shock syndrome and scarlet fever

Diagnostic Tests for Streptococcus pyogenes

Samples: blood, throat swabs, or other infected sites
Gram stain: Gram-positive cocci in chains
Blood culture: Streptococcus pyogenes is Beta-hemolytic
Antibiotic sensitivity: Bacitracin-sensitive
PYR test: positive
Rapid antigen detection: latex agglutination tests from throat swabs
Serological tests: detect antibodies against Streptococcus pyogenes including Lancefield grouping

Enterococcus faecalis (Group D Streptococcus)

Often arranged in pairs or short chains
Commensal bacterium found in the human large intestine
Can tolerate high salt concentrations (6.5% NaCl) and bile presence
Usually non-hemolytic or alpha-hemolytic
Naturally resistant to many antibiotics
Major cause of nosocomial infections, particularly in patients with indwelling medical devices
Causes urinary tract infections (UTIs)
Diagnostic tests:
- Samples: blood, urine, CSF, wound swabs, catheter tips
- Biochemical tests: PYR test positive, growth in 6.5% NaCl
Lancefield grouping is not reliable for identifying E. faecalis because it lacks typical group-specific carbohydrates.

Viridans Group Streptococci (VGS)

Heterogeneous group of organisms; can be commensals or pathogens
Alpha-hemolytic or non-hemolytic
Optochin-resistant
Not soluble in bile salts
Notable species: Streptococcus mutans (dental caries), Streptococcus salivarius
Causes endocarditis and bacteremia

Streptococcus pneumoniae (Diplococcus pneumoniae)

Untippable group in Lancefield classification - lacks Lancefield antigens
Differentiated from VGS through specific tests and characteristics.

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Description

Explore the fascinating characteristics of Micrococcus and Streptococcus, including their morphology, growth conditions, and clinical significance. This quiz covers the classification, notable species, and the environments where these bacteria thrive. Perfect for microbiology students looking to test their knowledge on these important genera.