Micologia, Virologia e Microbiologia Clínica 03/04

Summary

This lesson provides an in-depth overview of **Streptococcus** bacteria, covering key characteristics, differentiation from **Staphylococcus**, and hemolysis reactions. It explains the **Lancefield Classification** (Groups A, B, D) based on surface antigens, along with biochemical tests used for identification. The lecture emphasizes **Streptococcus pyogenes** and its role in infections like **pharyngitis**, **necrotizing fasciitis**, and **rheumatic fever**, highlighting the importance of timely treatment. The content also covers the clinical relevance of **Streptococcus pneumoniae** and **Enterococcus**, preparing students for laboratory identification and understanding pathogenic mechanisms.

Takeaways

• 😀 Streptococci belong to the family Streptococcaceae, characterized by Gram-positive cocci that do not form spores or have mobility structures.
• 😀 The main genus in Streptococcaceae is *Streptococcus*, differentiated from the *Micrococcaceae* family through catalase testing. Streptococcus is catalase-negative.
• 😀 Streptococci are categorized based on hemolytic reactions: Gamma (no hemolysis), Beta (complete hemolysis), and Alpha (partial hemolysis).
• 😀 The Lancefield classification divides *Streptococcus* into groups A, B, and D, based on cell wall polysaccharides, with groups A and B being of most medical interest.
• 😀 *Streptococcus pyogenes* (Group A) is Beta-hemolytic and is primarily responsible for throat infections, skin infections, and severe complications such as necrotizing fasciitis.
• 😀 *Streptococcus pyogenes* can also cause non-suppurative diseases like rheumatic fever and glomerulonephritis, often as a sequel to untreated infections like pharyngitis.
• 😀 The presence of streptococci in the oropharynx is common, and many individuals carry the bacteria without symptoms, making it easy to spread through respiratory droplets.
• 😀 Necrotizing fasciitis, also called 'flesh-eating disease,' is a severe consequence of *Streptococcus pyogenes* infection, causing rapid tissue destruction and requiring surgical intervention.
• 😀 *Streptococcus agalactiae* (Group B) is associated with infections in newborns and pregnant women, often affecting the genital and gastrointestinal tracts.
• 😀 Biochemical tests, such as bile esculin and antibiotic sensitivity, are used to differentiate between *Streptococcus* and other related genera like *Enterococcus*.

Q & A

What is the main difference between the Micrococcaceae and Streptococcaceae families?

The main difference is that Micrococcaceae family members, like *Staphylococcus*, are catalase-positive, while Streptococcaceae, represented by the genus *Streptococcus*, are catalase-negative. This means that when exposed to hydrogen peroxide, Micrococcaceae will produce oxygen bubbles, whereas Streptococcaceae will not.

What does the catalase test reveal about *Streptococcus*?

The catalase test is used to differentiate between *Streptococcus* and other catalase-positive organisms like *Staphylococcus*. *Streptococcus* is catalase-negative, meaning it does not break down hydrogen peroxide into oxygen, unlike catalase-positive bacteria which produce bubbles when exposed to hydrogen peroxide.

What are the three types of hemolysis observed in *Streptococcus* species?

The three types of hemolysis are: Gamma hemolysis (no hemolysis), Beta hemolysis (complete hemolysis, where red blood cells are fully broken down, creating a clear zone around the colony), and Alpha hemolysis (partial hemolysis, creating a greenish or brownish discoloration around the colony).

How are *Streptococcus* species classified using Lancefield grouping?

Lancefield grouping classifies *Streptococcus* based on the specific carbohydrate in the bacterial cell wall. Group A includes *Streptococcus pyogenes* (Beta-hemolytic), Group B includes *Streptococcus agalactiae* (Beta-hemolytic), and Group D includes *Enterococcus* and other species (often Alpha-hemolytic).

What are the key biochemical tests used to identify *Streptococcus* species?

Biochemical tests include sugar fermentation tests, enzyme presence testing, and sensitivity or resistance to various chemical agents like antibiotics. For example, the Bile Esculin test helps differentiate *Streptococcus* from *Enterococcus*.

What does the Bile Esculin test indicate in the identification of *Streptococcus* and *Enterococcus*?

The Bile Esculin test identifies whether the bacterium can hydrolyze esculin in the presence of bile. *Enterococcus* typically tests positive, while *Streptococcus* often tests negative, helping differentiate between the two.

What diseases are most commonly caused by *Streptococcus pyogenes*?

*Streptococcus pyogenes* causes a range of infections, including pharyngitis (sore throat), scarlet fever, impetigo, erysipelas, cellulitis, necrotizing fasciitis (flesh-eating disease), pneumonia, bacteremia, and non-suppurative diseases like rheumatic fever and acute glomerulonephritis.

How is *Streptococcus pyogenes* related to necrotizing fasciitis?

*Streptococcus pyogenes* can cause necrotizing fasciitis, a severe infection where the bacteria destroy soft tissue, including muscles and fat. It typically starts with a minor injury, such as a cut or burn, and can rapidly progress, sometimes requiring amputation to prevent further spread.

What are the main symptoms and risk factors for *Streptococcus pyogenes*-caused pharyngitis?

Pharyngitis caused by *Streptococcus pyogenes* typically presents with a sore throat, fever, and difficulty swallowing. It is highly contagious and spreads through respiratory droplets. Risk factors include close contact settings like schools and daycare centers, particularly among children aged 5-15.

What are the complications of untreated *Streptococcus pyogenes* infections?

Untreated infections caused by *Streptococcus pyogenes* can lead to severe complications such as rheumatic fever, which affects the heart and joints, and acute glomerulonephritis, which affects kidney function. These complications are often a result of the body's immune response to the initial infection.