Knowledge about streptococcal infection.📜📜📜

Streptococcus has a wide variety of bacteria and is widely distributed. Some streptococci are normal human flora, while others are pathogenic bacteria of humans. 

1. What is streptococcus?

Streptococcus is a gram-positive cocci and the bacteria are purple after Gram staining. According to whether hemolysis occurs on blood agar, Streptococcus bacteria are divided into three categories: α-hemolytic streptococcus, β-hemolytic streptococcus and γ-streptococcus.

Medically important streptococci:

1. α-hemolytic streptococcus: Streptococcus pneumoniae, Streptococcus viridans.
2. β-hemolytic streptococcus: Group A Streptococcus (also call streptococcus pyogenes), group B, group C, group D and group G streptococcus.
3. γ-streptococcus: They are generally not causing disease.

2. Common streptococcus infections:

• Streptococcus pneumoniae: Streptococcus pneumoniae is distributed in the nasopharynx of 5-10% of adults and 20-40% of children. Most of the strains are not pathogenic and only a few strains are pathogenic. It is the main pathogen of bacterial pneumonia. It causes diseases such as acute bacterial otitis media, acute bacterial sinusitis, community-acquired pneumonia and lung abscess.
• Streptococcus viridans: It is mainly distributed in the oropharynx and gastrointestinal tract. It1 is a common pathogen causing dental caries, infective endocarditis and bacteremia.
• Streptococcus pyogenes: It is mainly distributed in the throat and is the most pathogenic bacteria among streptococci. It accounts for about 90% of streptococcal infections. It is the main pathogen of acute bacterial pharyngitis and tonsillitis. It can also cause lymphangitis, acute cellulitis, acute rheumatic fever, and glomerulonephritis.

3. Commonly used antibacterial drugs for streptococcal infections.

• Penicillin is the first choice for streptococcal infections. The antibacterial activity of the first and second generation cephalosporins against Streptococcus pneumoniae is less than penicillin. The drug resistance of streptococcus is caused by genetic mutations. Streptococcus pneumoniae is also less resistant to them. Streptococcus is not sensitive to penicillin. Amoxicillin, ceftriaxone and cefotaxime will have good antibacterial activity. 
• Penicillin-resistant Streptococcus pneumoniae is highly sensitive to vancomycin, linezolid and carbapenems.
• The resistance rate of macrolides and clindamycin is high.
• Aminoglycosides have no antibacterial activity against streptococci, but have synergistic effects with β-lactam antibiotics.

Acute bacterial pharyngitis and tonsillitis:

The common pathogen is group A hemolytic streptococcus. Penicillin is the first choice. Optional amoxicillin. Amoxicillin/clavulanic acid should not be used. This is mainly because hemolytic streptococcus does not produce β-lactamase, and clavulanic acid is useless at all. Since non-suppurative complications (acute rheumatic fever and glomerulonephritis) can occur after infection of group A hemolytic streptococcus, antibacterial treatment is aimed at removing bacteria and the course of treatment takes 10 days.

Acute bacterial otitis media and acute bacterial sinusitis:

The common pathogens are Streptococcus pneumoniae, Moraxella catarrhalis and Haemophilus influenzae. The first choice is amoxicillin or amoxicillin/clavulanic acid. 

Mainly reasons:

• Anti-Gram-positive bacteria activity (group A hemolytic streptococcus, streptococcus pneumoniae): amoxicillin ≈ penicillin.
• Anti-Gram-negative bacteria activity (Moraxella catarrhalis, Haemophilus influenzae): amoxicillin/clavulanic acid> amoxicillin> penicillin.

	Common pathogens	Antibacterial drugs
Acute bacterial pharyngitis and tonsillitis	Group A hemolytic streptococcus	l   Penicillin, amoxicillin. l   Patients who are allergic to penicillin can choose tetracyclines or fluoroquinolones that are sensitive to hemolytic streptococci (such as levofloxacin, moxifloxacin).
Acute cellulitis and lymphangitis.	Group A hemolytic streptococcus	l   Penicillin, amoxicillin. l   Amoxicillin/clavulanic acid, ceftriaxone.
Acute bacterial otitis media.	Streptococcus pneumoniae, Moraxella catarrhalis and Haemophilus influenzae.	l   Amoxicillin. l   If Moraxella catarrhalis and Haemophilus influenzae which producing β-lactamase strains are common in the local area, amoxicillin/clavulanic acid should be used. l   If the patient has no effect after taking the medicine for 3 days, it should be considered as possible penicillin-resistant Streptococcus pneumoniae infection. Ceftriaxone should be used.
Acute bacterial sinusitis.	Streptococcus pneumoniae, Moraxella catarrhalis and Haemophilus influenzae.	l   Amoxicillin/clavulanic acid.
Infective endocarditis	Streptococcus viridans.	l   Penicillin is used in combination with gentamicin. l   Combine ceftriaxone or cefotaxime with gentamicin.
Purulent meningitis (age < 1 month)	Group B hemolytic streptococcus, Escherichia coli, Listeria and Klebsiella pneumoniae.	l   Combine ceftriaxone or cefotaxime with ampicillin. l   Gentamicin is combined with ampicillin.