BACTE LEC: STREP

What are streptococci?

Catalase-negative, Gram-positive cocci that commonly appear in pairs or chains.

What families within the order Lactobacillales are especially discussed?

Streptococcaceae and Enterococcaceae.

What organism belongs to Streptococcaceae?

Streptococcus.

What organism belongs to Enterococcaceae?

Enterococcus.

What other related groups are included?

Aerococcaceae, Lactobacillaceae, Carnobacteriaceae, and Leuconostocaceae.

What is the typical Gram reaction of streptococci?

Gram-positive.

What is the typical shape of streptococci?

Cocci.

What is the typical size of streptococci?

~0.5–1.2 μm.

What is the catalase reaction of streptococci?

Negative.

What is the typical arrangement of streptococci?

Pairs/chains; some irregular clusters.

What is the oxygen requirement of the majority of streptococci?

Facultative anaerobes.

What types of hemolysis can streptococci show on blood agar?

α, β, or γ depending on organism.

What is the first important laboratory clue for Streptococcus/related organisms?

Gram-positive cocci + catalase negative.

What arrangement suggests Streptococcus/Enterococcus?

Chains/pairs.

What organisms should be considered when Gram-positive cocci appear in clusters?

Organisms such as Staphylococcus, but some catalase-negative organisms can also appear cluster-like.

What does catalase negative indicate in Gram-positive cocci?

Streptococcus/Enterococcus/related catalase-negative GPC.

What are the three types of hemolysis examined on sheep blood agar?

β-hemolysis, α-hemolysis, and γ/no hemolysis.

When is Lancefield grouping primarily useful?

Primarily for β-hemolytic streptococci.

What targeted biochemical tests are listed for Streptococcus/Enterococcus identification?

PYR, CAMP, hippurate hydrolysis, bile esculin, optochin, bile solubility, VP, and salt tolerance.

What methods can be used for confirmation when necessary?

Serologic grouping, PCR, MALDI-TOF MS, and additional biochemical testing.

What does identification of streptococci rely on?

Cell-wall structure, hemolysis, antibody reactions, Lancefield classification, and biochemical characteristics.

What is α-hemolysis?

Partial hemolysis of red blood cells.

What appearance does α-hemolysis produce on agar?

A greenish discoloration around the colony.

What does α-hemolysis represent?

Altered/partial RBC destruction.

What are classic examples of α-hemolytic streptococci?

S. pneumoniae and Viridans streptococci.

What is β-hemolysis?

Complete hemolysis.

What appearance does β-hemolysis produce?

A clear zone surrounding the colony.

What are classic examples of β-hemolytic streptococci?

S. pyogenes, S. agalactiae, some group C/G streptococci, and some S. anginosus group organisms.

What types of β-hemolytic streptococci are included in the source?

Large-colony pyogenic strains and some small-colony strains.

What is γ-hemolysis?

No visible hemolysis.

What does γ-hemolysis NOT mean?

It does not mean "weak hemolysis."

What does γ-hemolysis mean?

There is no hemolysis.

What is Lancefield grouping?

Classification of certain streptococci according to carbohydrate antigens in their cell walls.

What does Lancefield classification identify?

Cell-wall carbohydrate antigens.

How can serologic grouping identify a Lancefield group?

Using specific antibodies/latex agglutination.

Which organism is important for Lancefield Group A?

S. pyogenes.

Which organism is important for Lancefield Group B?

S. agalactiae.

Which organisms are associated with Lancefield Group C?

S. dysgalactiae subsp. equisimilis and others.

Which organisms are associated with Lancefield Group G?

S. dysgalactiae subsp. equisimilis and others.

Which organisms are associated with Lancefield Group D?

Enterococci and S. bovis group.

Is S. pneumoniae classified by Lancefield grouping?

No.

What does S. pneumoniae possess that may cause confusion with Lancefield grouping?

A C polysaccharide.

How is the C polysaccharide of S. pneumoniae related to Lancefield grouping?

It is unrelated to Lancefield grouping.

What is the Lancefield group of S. pyogenes?

Group A.

What type of hemolysis does S. pyogenes produce?

β.

What is the catalase reaction of S. pyogenes?

Negative.

What is the PYR reaction of S. pyogenes?

Positive.

What is the major virulence factor of S. pyogenes discussed in the source?

M protein.

What diseases are associated with S. pyogenes?

Pharyngitis, scarlet fever, impetigo, erysipelas, necrotizing fasciitis, rheumatic fever, and glomerulonephritis.

How does the source characterize S. pyogenes?

One of the most aggressive pathogens encountered in clinical microbiology.

What are the two important hemolysins of S. pyogenes?

Streptolysin O and Streptolysin S.

What are the characteristics of Streptolysin O?

Oxygen-sensitive and immunogenic.

What cells can Streptolysin O lyse?

RBCs, leukocytes, and platelets.

Under what conditions is Streptolysin O responsible for hemolysis?

Appropriate oxygen-limited conditions.

Why is Streptolysin O clinically important?

The host produces antistreptolysin O (ASO) antibodies.

What are the characteristics of Streptolysin S?

Oxygen-stable and nonimmunogenic.

What cells can Streptolysin S lyse?

RBCs, leukocytes, and platelets.

What does Streptolysin S contribute to?

The β-hemolytic appearance on blood agar.

Why does S. pyogenes show β-hemolysis?

Its hemolysins damage cells, producing the visible hemolytic reaction.

What is M protein?

A surface protein extending through the bacterial cell wall.

What is notable about the amino-terminal region of M protein?

It is highly variable.

How many M protein serotypes are described in the source?

100 serotypes.

What does M protein contribute to?

Immune evasion.

What does M protein interact with?

Factor H, fibrinogen, and complement pathways.

How do M protein interactions affect complement-mediated clearance?

They interfere with effective complement-mediated clearance.

What diseases are associated with M protein?

Rheumatic fever and acute glomerulonephritis.

What can antibodies against M protein cross-react with?

Human heart tissue.

What sequence connects S. pyogenes infection to rheumatic fever?

S. pyogenes infection → immune response → rheumatic fever.

What mechanism involving M protein contributes to rheumatic fever?

Antibodies against M protein cross-react with heart tissue.

What enzyme does S. pyogenes produce that affects C5a?

C5a peptidase.

What does C5a normally do?

C5a is a chemotactic factor.

What cells does C5a help attract?

Neutrophils and monocytes.

What does C5a peptidase do?

It inactivates C5a.

What is the result of C5a destruction?

Less chemotactic attraction and reduced immune-cell recruitment.

How does C5a peptidase help S. pyogenes?

It helps the organism evade host defense.

What are streptococcal pyrogenic exotoxins important for?

Scarlet fever and streptococcal toxic shock syndrome.

How can streptococcal pyrogenic exotoxins act?

As superantigens.

What do superantigens cause?

Excessive immune activation.

Which inflammatory mediators are released during excessive immune activation?

IL-1, IL-2, IL-6, TNF, interferons, and other cytokines.

What can excessive inflammatory response lead to?

Shock and organ failure.

What is the most common bacterial cause of acute pharyngitis according to the source?

S. pyogenes.

What localized throat disease is caused by S. pyogenes?

Pharyngitis.

What skin infections are caused by S. pyogenes?

Impetigo and erysipelas.

What invasive disease is caused by S. pyogenes?

Necrotizing fasciitis.

What is necrotizing fasciitis popularly associated with?

"Flesh-eating bacteria."

What does necrotizing fasciitis involve?

Destruction of deeper tissues and can be life-threatening.

What toxin-mediated disease is associated with streptococcal pharyngitis plus a characteristic rash?

Scarlet fever.

What can streptococcal toxic shock syndrome involve?

Multisystem disease, renal failure, respiratory failure, rash, and diarrhea.

What is the sequence for rheumatic fever after S. pyogenes respiratory infection?

S. pyogenes respiratory infection → M-protein-directed immune response → cross-reaction with heart tissue → rheumatic fever.

What are associated findings of rheumatic fever?

Fever, endocardial/cardiac inflammation, subcutaneous nodules, and polyarthritis.

What is the sequence for acute glomerulonephritis after S. pyogenes infection?

S. pyogenes infection → antigen-antibody complexes → deposition in glomeruli → inflammation/damage → acute glomerulonephritis.