5333. Bacterial culture. Throat. Streptococcus pyogenes (group A Streptococcus). Antimicrobial resistance profile with MIC (if Streptococcus pyogenes is detected)

Bacteriological examination of throat material for Streptococcus pyogenes (Group A β-hemolytic Streptococcus) is the gold standard for diagnosing acute bacterial tonsillopharyngitis. The test is aimed at identification of the pathogen, determination of its quantity in the biomaterial, and assessment of antimicrobial susceptibility.

If the result is positive, an antibiotic susceptibility test with MIC (minimal inhibitory concentration) is performed to help the physician select effective antibacterial therapy.

Automated identification of microorganisms is performed using MALDI-TOF mass spectrometry on the MALDI Biotyper sirius IVD System analyzer (Bruker, Germany).

Streptococcus pyogenes (Group A β-hemolytic Streptococcus) is one of the most common bacterial pathogens causing acute upper respiratory tract and skin infections. It is transmitted mainly by airborne droplets or contact with contaminated objects, especially in crowded settings such as kindergartens, schools, and hospitals.

According to CDC and IDSA guidelines, this pathogen is the primary cause of purulent tonsillitis in both children and adults and a source of potentially severe complications such as rheumatic fever, post-streptococcal glomerulonephritis, otitis media, sinusitis, and abscesses.

The source of infection is an infected individual or an asymptomatic carrier.

A throat culture allows not only detection of the pathogen but also assessment of colony growth levels, which is essential for differentiating active infection from carrier status. A high S. pyogenes titer in combination with clinical manifestations (sore throat, fever, purulent exudates, regional lymphadenopathy) indicates active infectious inflammation requiring etiotropic treatment. A low titer in the absence of symptoms may indicate transient carriage, which does not always require therapy but has epidemiological significance.

The specimen is collected with a sterile swab from the posterior pharyngeal wall, tonsils, or affected mucosal areas. If the pathogen is detected, an antibiotic susceptibility test with determination of the minimal inhibitory concentration (MIC) is performed to select the most effective antibiotic according to clinical guidelines and international standards (EUCAST and CLSI).

The clinical relevance of the result depends not only on the presence of the pathogen but also on its quantitative level. A high S. pyogenes titer combined with symptoms (sore throat, fever, purulent deposits, regional lymphadenopathy) indicates active infection requiring etiological treatment. A low titer without symptoms may suggest transient carriage, which may not require therapy but is epidemiologically important.

According to IDSA protocols, antibiotic therapy for streptococcal pharyngitis should aim to eradicate the pathogen, reduce symptom duration, prevent complications, and lower transmission risk. Determining MIC helps avoid ineffective treatment, especially in cases of recurrence or resistance to standard antibiotics.

In case of a positive result, the final decision on therapy should be made by a physician, taking into account the clinical condition of the patient, laboratory findings, and the epidemiological context.

• In cases of recurrent tonsillitis or pharyngitis.
• Before prescribing antibiotics to confirm the bacterial etiology of the disease.
• After contact with patients diagnosed with scarlet fever.
• For epidemiological monitoring in childcare or educational institutions.
• Prior to ENT surgical interventions.
• In patients with suspected rheumatic fever or post-streptococcal glomerulonephritis.

• Various types of biological material depending on the test