Bakteriologie 1 + 2

MVZ Labor Ravensburg

  • Labor Dr. Gärtner, Dr. Vera Forsbach-Birk

  • Specialization in Microbiology and Bacteriology.

Bacteria of Interest

  • Important pathogens discussed:

    • Listeria monocytogenes

    • Methicillin-resistant Staphylococcus aureus (MRSA)

Overview of Bacterial Classification

  • Many bacteria are acknowledged, some are well-known, but most are not (e.g., Pseudomonas aeruginosa, Paraburkholderia phymatum).

Systematic Approach

  • A phylogenetic tree based on sequence comparisons of 16S rRNA genes is essential for classification.

Medical Relevance

  • Focus on medically relevant pathogens:

    • Gram-positive: Staphylococcus aureus

    • Gram-negative: Escherichia coli

Staphylococcus aureus

  • Also referred to as the "Jack of all trades" due to its significant role in various infections.

Clinical Manifestations

  • Local skin infections: can involve the skin, mucous membranes, and connective tissue.

  • Types include:

    • Abscess formation: yellow, creamy pus

    • Furuncles and carbuncles (infections of hair follicles).

    • Phlegmon (inflammation spreading through tissues).

    • Invades through:

      • Endogenous pathways: via lymphatic or hematogenous spread from a primary infection (e.g., abscess).

      • Exogenous pathways: post-trauma or surgical intervention.

    • Potential to cause serious conditions such as Osteomyelitis, Pneumonia, and Endocarditis.

Toxin-related Infections

  • Staphylococcal Scalded Skin Syndrome (SSSS): blistering due to toxin release.

  • Toxic Shock Syndrome: triggers a severe systemic inflammatory response, results from Toxic shock syndrome toxin-1, produced by a minority (1%) of S. aureus strains.

  • Foodborne illness from heat-stable enterotoxins leads to short incubation symptoms like nausea, vomiting, and diarrhea.

Virulence Factors of Staphylococcus aureus

Protein A

  • Binds to Fc regions of antibodies, preventing opsonization and phagocytosis.

Coagulase

  • Converts fibrinogen to fibrin, aiding in creating a protective barrier around bacteria. Diagnostic detection involves mixing rabbit plasma, leading to coagulation.

Clumping Factor

  • Another fibrin-precipitating enzyme facilitating bacterial agglutination during detection.

Hemolysins

  • Impact red blood cells; classified into:

    • Alpha-hemolysis: partial lysis resulting in green discoloration.

    • Beta-hemolysis: complete lysis with a clear zone around colonies.

    • Gamma-hemolysis: no lyis of red blood cells.

Laboratory Detection

Microscopic Examination

  • Gram-positive cocci in clusters (resembling grapes).

Culture Characteristics

  • Growth pattern and staining characteristics help differentiate.

  • Oxidase positive, Catalase positive.

Identification Techniques

  • Differentiate based on metabolic products generated on culture media.

API System

  • Utilizes a series of biochemical tests for identification of bacterial species.

  • Capable of identifying over 700 species; less than 1000 biochemical tests applied within 18-24 hours of incubation.

MALDI-TOF MS

  • Proficient in identifying microorganisms quickly by mass spectrometry, differentiating protein signatures to assign species.

Coagulase-negative staphylococci

  • Usually non-pathogenic skin flora like Staphylococcus epidermidis, occasionally pathogenic with device-related infections.

  • Staphylococcus saprophyticus: common in uncomplicated urinary tract infections.

Streptococci Classification

  • Gram-positive cocci arranged in chains.

  • Significant groups based on Lancefield classification:

    • Group A: S. pyogenes (causes sore throat, skin infections).

    • Group B: S. agalactiae (potentially harmful to neonates).

    • Viridans group: often associated with dental infections and endocarditis.

Streptococcus pneumoniae (Pneumococcus)

  • Encapsulated, gram-positive diplococci directly causing pneumonia and meningitis.

  • Cultured in specialized media; sensitive to optochin.

Shigella

  • Distinguished species: S. dysenteriae (produces Shiga toxin).

  • Infectious doses are very low, leading to outbreaks especially in developing countries.

Campylobacter and Helicobacter infections

  • Campylobacter jejuni known for gastroenteritis, can cause reactive arthritis.

  • Helicobacter pylori associated with gastric ulcers and malignancy, presents unique diagnostic challenges.

Prevention and Diagnosis

  • Awareness of normal flora, characteristics of clinical pathogens, and recommended vaccinations are key to controlling infections. Vaccinations:

    • Essential for prevention of significant infections.

    • Laboratory confirmations are crucial for management and reporting infectious diseases.