Streptococcus: Medical Importance for Laboratory Technicians PDF

Streptococcus by Heba Rashed Introduction to Streptococcus Bacterial Genus Clinical Significance Research Importance Streptococcus is a genus of Gram- Many Streptococcus species are Streptococcus is a well-studied positive, spherical bacteria that im...

Streptococcus by Heba Rashed Introduction to Streptococcus Bacterial Genus Clinical Significance Research Importance Streptococcus is a genus of Gram- Many Streptococcus species are Streptococcus is a well-studied positive, spherical bacteria that important human pathogens, genus, providing insights into often appear in chains. causing a wide range of infections. bacterial pathogenesis and immunity. Intended Learning Outcomes (ILOs) On completion of this lecture, the student will be able to: 1. To describe the main species of clinical importance 2. To know the morphology and culture characters of streptococcus species 3. List the virulence factors of streptococci 4. To know the laboratory diagnosis of streptococcal infection  Main species of clinical importance Group A Streptococcus (Streptococcus pyogenes Group B Streptococcus (Streptococcus agalactiae Streptococcus pneumoniae Viridans Group Streptococci Group A Streptococcus (Streptococcus pyogenes) : Clinical Importance: This species is responsible for a wide range of infections, including: - Pharyngitis (strep throat) - Scarlet fever - Impetigo - Erysipelas - Cellulitis - Necrotizing fasciitis - Rheumatic fever - Post-streptococcal glomerulonephritis Flash Card Streptococcus pyogenes (Group A strep): o Hemolysis: Beta-hemolysis (clear zone) o Colony appearance: Small, translucent, white colonies. o Catalase: Negative o Bacitracin: Sensitive Group B Streptococcus (Streptococcus agalactiae) : Clinical Importance: Commonly found in the gastrointestinal and genital tracts, this species can cause: - Neonatal sepsis - Neonatal pneumonia - Meningitis - Infections in immunocompromised adults - Urinary tract infections (UTIs) Flash Card Streptococcus agalactiae (Group B strep): o Hemolysis: Beta-hemolysis (narrow clear zone) o Colony appearance: Larger than S. pyogenes, grayish white colonies. o CAMP test: Positive Streptococcus pneumoniae: Clinical Importance: A major cause of: - Pneumonia - Meningitis - Otitis media (middle ear infections) - Sinusitis - Bacteremia Streptococcus pneumoniae: Hemolysis: Alpha-hemolysis (greenish zone) Colony appearance: Mucoid or flattened colonies due to capsule production. Optochin: Sensitive Bile solubility: Positive Viridans Group Streptococci: Includes species such as Streptococcus mutans, S. mitis, S. sanguinis and others. Clinical Importance: I. Commonly associated with dental caries (tooth decay) II. Can cause subacute bacterial endocarditis (especially in individuals with damaged heart valves) Viridans Streptococci: Hemolysis: Alpha or gamma hemolysis Colony appearance: Small, rough, or smooth, non-capsulated colonies. Optochin: Resistant Bile solubility: Negative Streptococcus Taxonomy and Classification Taxonomic Diversity Cell Morphology Lancefield Grouping The genus Streptococcus Streptococci are spherical or ovoid Streptococci are further classified encompasses a diverse group of bacteria that typically arrange in into Lancefield groups based on the Gram-positive bacteria, including chains, a key distinguishing feature presence of specific carbohydrate both commensal and pathogenic of the genus. antigens on the cell surface. species. Cell Structure and Morphology Streptococcus bacteria are Gram-positive cocci, typically arranged in pairs or chains. They have a thick , rigid cell wall composed of peptidoglycan and teichoic acid. The cell surface also features pili and other surface proteins important for adherence and virulence. Streptococcal cells range in size from 0.5-1.0 μm in diameter and lack flagella, instead relying on Brownian motion for movement. The internal structure includes a cytoplasmic membrane, cytoplasm, and genetic material in the form of a single, circular chromosome Growth Requirements Nutrient-Rich Media Oxygen Needs Streptococcus species require Most Streptococcus are nutrient-rich media like blood facultative anaerobes, able to agar or Todd-Hewitt broth for grow in both aerobic and optimal growth and cultivation anaerobic conditions, although in the laboratory. some are strictly aerobic or anaerobic. Temperature Preferences pH Range Streptococcus thrive at 35- Streptococcus prefer a neutral 37°C, the typical human body to slightly acidic pH range of temperature, making them 6.5-7.5, although some species well-adapted to infect and can tolerate a wider pH colonize human hosts. variation. Classification: According to oxygen requirement for growth, streptococci are classified into : 1-Obligate (strict) anaerobes. ( pepto-streptococcus ) 2-Aerobic and facultative anaerobic streptococci Pepto-streptococci are part of normal flora of mouth and upper respiratory tract Aerobic and facultative anaerobes are classified according to hemolysis on blood agar : Beta-haemolytic streptococci that produce complete lysis of red blood cells due to production of streptolysin S Alpha-haemolytic streptococci that cause incomplete lysis of red blood cell with formation of green pigments Nonhaemolytic streptococci  Serological Grouping of Streptococcus 1 Lancefield Grouping 2 Group-Specific Antigens Streptococcus species are classified These group-specific antigens are used into groups based on the antigenic to serologically identify and properties of their cell wall differentiate between the major carbohydrates, known as Streptococcus species of medical Lancefield groups. importance. 3 Common Groupings 4 Diagnostic Significance The most clinically relevant Serological grouping is an Streptococcus groups are A, B, C, important initial step in the D, F, and G, each associated with identification and differentiation distinct disease patterns. of Streptococcus isolates in the clinical microbiology laboratory. Streptococcus pyogenes (β-haemolytic streptococci Group A) Strept.pyogenes (Group A beta haemolytic)is a Gram-positive cocci,nonmotile,nonspore,they are arranged in chains Culture characters Strept.Pyogenes does not grow on ordinary media (nutrient agar)but requires enriched medium(blood agar),it produces β-haemolysis. Catalase negative. Streptococcus Infections: Clinical Manifestations Skin and Soft Tissue Respiratory Tract Invasive Infections Post-Infectious Infections Infections Sequelae Streptococcus can lead Streptococcus can cause Streptococcal pharyngitis to life-threatening Streptococcal infections a range of skin and soft (strep throat) is a invasive infections like can trigger autoimmune tissue infections, common presentation, bacteremia, meningitis, conditions like rheumatic including impetigo, causing a sore throat, endocarditis, and toxic fever and cellulitis, necrotizing fever, and swollen lymph shock syndrome. These glomerulonephritis. fasciitis, and erysipelas. nodes. More severe present with high fever, These occur weeks after These present with infections like organ dysfunction, and the initial infection and redness, swelling, and pneumonia and rapid progression. can cause long-term pain at the site of empyema can also occur. complications. infection. Clinical Manifestations of S. pyogenes 1 Throat Infections 2 Skin Infections S. pyogenes is a leading It can cause skin infections cause of strep throat, like impetigo, cellulitis, and resulting in severe sore necrotizing fasciitis, leading throat, fever, and swollen to painful, red, and swollen lymph nodes. skin lesions. 3 Rheumatic Fever 4 Toxic Shock Syndrome Untreated strep throat can S. pyogenes can also lead to an autoimmune produce toxins that lead to a reaction causing rheumatic life-threatening condition fever, damaging the heart, called toxic shock syndrome, joints, and central nervous causing high fever, rash, system. and organ failure. Diagnosis of S. pyogenes Infections Clinical Presentation Evaluate the patient's symptoms, such as sore throat, fever, and skin lesions to identify potential S. pyogenes infections. Throat Culture Perform a throat swab and culture the sample to detect the presence of S. pyogenes bacteria. Rapid Antigen Test Use a rapid antigen detection test to quickly identify the presence of S. pyogenes Group A Streptococcus. Molecular Diagnostics Employ nucleic acid amplification tests, such as PCR, to accurately detect and identify S. pyogenes genetic material. Streptococcus agalactiae (Group B Streptococcus) Streptococcus agalactiae, also known as Group B Streptococcus (GBS), is a leading cause of invasive infections in newborns and pregnant women. It can cause life-threatening conditions like sepsis, meningitis, and pneumonia in neonates. GBS is a common colonizer of the human gastrointestinal and genitourinary tracts, and transmission typically occurs during childbirth from a colonized mother to her infant. Specimen: CSF and sputum Direct Gram stained film showing gram positive cocci arranged in chains among pus cells Culture on Blood agar: β- (complete) hemolysis = clear zone. The colonies identified by Gram stained film shows Gram positive cocci arranged in chains and biochemical tests Biochemical identification 1. Catalase negative 2. Bacitracin sensitivity : resistant to bacitracin. 3. CAMP test : positive CAMP test It is used to differentiate between Streptococcus agalactiae and other beta haemolytic streptococci Procedure: Strept. agalactia produce CAMP factor that synergistically act with beta lysin of Staph aureus and enhance the lysis of red blood cells while S. pyogenes not produce CAMP factor Clinical Manifestations of S. agalactiae Neonatal Infections Maternal Infections Adult Infections S. agalactiae can cause life- Pregnant women can develop In adults, S. agalactiae can threatening infections in urinary tract infections or cause skin and soft tissue newborns, including sepsis, colonization of the birth canal infections, bacteremia, pneumonia, and meningitis. with S. agalactiae, risking endocarditis, and pneumonia, transmission to the infant. especially in the elderly or immunocompromised. Diagnosis of S. agalactiae Infections Culture Antigen Detection S. agalactiae can be identified through Rapid antigen tests can identify S. agalactiae bacterial culture from clinical specimens such surface proteins, providing a fast diagnosis as urine, blood, or cerebrospinal fluid. without the need for culture. 1 2 3 PCR Assays Molecular methods like PCR can rapidly detect the presence of S. agalactiae genetic material in patient samples.  Streptococcus pneumoniae (Pneumococcus) Streptococcus pneumoniae, also known as pneumococcus, is a Gram-positive bacterium that is a leading cause of pneumonia, meningitis, and other severe infections. It is a common colonizer of the upper respiratory tract, particularly in young children. Pneumococcus can cause a range of clinical presentations, from mild upper respiratory tract infections to life-threatening invasive disease. Morphology: It is normal inhabitants of the upper respiratory tract of humans. Gram-positive, ovoid arranged in pairs (diplococci), lancet shaped. They are capsulated. Capsules may appear as unstained halos around the organism. Cultural characters: Streptococcus pneumoniae, grows on blood agar, producing alpha haemolysis or greenish discolouration which cannot differentiates S. pneumoniae from commensal Strept. viridans on blood agar Virulence factors: The capsule is the most important virulence factor Pneumococci is the most common type of bacterial pneumonia, accounting for most cases of community-acquired pneumonia (CAP)  Laboratory identification of Strept. pneumoniae Direct gram stained film showing gram positive diplococci capsulated among pus cells. Capsules appear as unstained halos around the organism. Culture on Blood agar: alpha hemolysis The colonies identified by Gram stained lm shows Gram positive diplococci capsulated Biochemical identification 1. Catalase negative Pneumococci in sputum , Capsules appear as unstained halos around 2. Quellung test is positive the organism. 3. Tests for differentiation from Strept. viridans Capsule swelling test ( Quellung reaction) This test is used for identification and typing of pneumococci Method: The test is done by mixing of sputum specimen or suspension of pneumococcal culture with specific antiserum on a microscopic slide and examined by oil immersion lens. If antiserum is specific for the pneumococci, the antibodies precipitated on capsule margin and become visible or swollen  Streptococcus Viridans Group While usually not highly virulent, the Overview The Streptococcus viridans group is a Clinical Significance viridans streptococci can cause collection of Gram-positive bacteria opportunistic infections, particularly in that are normal inhabitants of the immunocompromised individuals. They human oral cavity, upper respiratory are a common cause of subacute tract, and gastrointestinal tract. They bacterial endocarditis and may also are generally considered less cause oral and systemic infections. pathogenic than other Streptococcus species. Sample Collection and Transport for Streptococcus 1 Proper Specimen Collection Collect samples from appropriate sites, such as throat, skin lesions, or blood, using sterile technique to avoid contamination. 2 Transport in Appropriate Media Place the specimen in transport media, such as Stuart's or Amies medium, to maintain viability during transit to the lab. 3 Timely Delivery to Laboratory Ensure the sample reaches the lab as soon as possible, typically within 2 hours, to allow for prompt processing and analysis. Infections: Diagnosis Sample Collection 1 Appropriate specimen types based on infection site Preliminary Tests 2 Gram staining, catalase, and other rapid ID Culture Identification 3 Selective/differential media, biochemical tests Serological Assays 4 Antibody detection for acute vs. convalescent Accurate diagnosis of Streptococcus infections relies on a combination of clinical history, sample collection, laboratory tests, and interpretation. This typically involves Gram staining, culture identification, and serological assays to detect antibodies. Prompt and reliable diagnosis is key to guiding appropriate treatment. Susceptibility Testing Sample Preparation 1 Obtain pure Streptococcus isolate, prepare standardized inoculum Disk Diffusion 2 Apply standardized inoculum, place antibiotic disks, incubate Interpretation 3 Measure zone of inhibition, compare to breakpoints Reporting 4 Report susceptible, intermediate, or resistant for each antibiotic Accurate antibiotic susceptibility testing is critical for guiding appropriate antimicrobial therapy for Streptococcus infections. The disk diffusion method is a common technique used in clinical microbiology labs to determine resistance patterns and inform treatment decisions. Conclusion: The Importance of Streptococcus Diagnostics Accurate and timely diagnosis of Streptococcus infections is crucial for effective patient management and public health surveillance. Proper laboratory identification allows clinicians to initiate appropriate antimicrobial therapy, track emerging resistance patterns, and monitor disease outbreaks.