Online Microbiology Notes

Agglutination – definition, reactions and applications

February 25, 2020October 16, 2017 by Sagar Aryal

Agglutination- Introduction and Applications

Agglutination definition Agglutination is an antigen-antibody reaction in which a particulate antigen combines with its antibody in the presence of electrolytes at a specified temperature and pH resulting in the formation of visible clumping of particles. It occurs optimally when antigens and antibodies react in equivalent proportions. This reaction is analogous to the precipitation reaction in that antibodies act as …

Laboratory Diagnosis, Treatment and Prevention of Bacillus cereus

January 4, 2020October 16, 2017 by Sagar Aryal

Laboratory Diagnosis of Bacillus cereus SPECIMENS: Faeces, vomitus, remaning food (if any), eye specimen (corneal swab) DIRECT DETECTION METHODS Microscopically the organisms appear as large gram positive rods in singles, pairs, or serpentine with square ends after Gram staining. Endospores formation are seen as unstained oval or round region within centre of cell. Spores are oval (ellipsoidal) and not swelling the …

Clinical manifestation and Pathogenicity of Bacillus cereus

January 2, 2020October 15, 2017 by Sagar Aryal

Clinical manifestation of Bacillus cereus A. Food poisoning Two forms of food poisoning: vomiting disease (emetic form) and diarrheal disease (diarrheal form). Emetic form The emetic form of disease results from the consumption of contaminated rice. Most bacteria are killed during the initial cooking of the rice, but the heat-resistant spores survive. If the cooked rice is not refrigerated, the …

Types of Precipitation Reactions

February 26, 2020October 15, 2017 by Sagar Aryal

Precipitation reactions can be broad of three types: Precipitation in solution. Precipitation in agar. Precipitation in agar with an electric field. Precipitation in solution Ring test and flocculation test are examples of precipitation in solution. It is also called simple precipitation. Ring test: In this test, a clear solution of the test antigen is layered slowly over the clear solution …

Virulence factors and Clinical manifestation of Staphylococcus aureus

June 28, 2020October 14, 2017 by Sagar Aryal

Virulence factors of Staphylococcus aureus A. Cell wall components Polysaccharide Capsule: inhibits phagocytosis Peptidoglycan: activates complement, IL-1, chemotactic to PMNs Teichoic acid: species specific, mediate binding to fibronectin Protein A: It binds to the Fc region of IgG and complement ,exerting an anti-opsonin effect. Fibronectin binding protein(FnBP): promote binding to ,mucosal cells and tissue matrices. Clumping factor: FnBP enhances clumping …

Precipitation Reaction – definition and applications

February 26, 2020October 14, 2017 by Sagar Aryal

Precipitation definition It is a type of antigen-antibody reaction, in which the antigen occurs in a soluble form. When a soluble antigen reacts with its specific antibody, at an optimum temperature and PH in the presence of electrolyte antigen-antibody complex forms insoluble precipitate. This reaction is called a precipitation reaction. A lattice is formed between the antigens and antibodies; in …

Cultural and Biochemical characteristics of Staphylococcus aureus

June 28, 2020October 13, 2017 by Sagar Aryal

Cultural characteristics of Staphylococcus aureus Staphylococci grow readily on most bacteriologic media under aerobic or microaerophilic conditions. Colonies on solid media are round, smooth, raised, and glistening. S. aureus usually forms gray to deep golden yellow colonies. Mannitol Salt Agar: circular, 2–3 mm in diameter, with a smooth, shiny surface; colonies appear opaque and are often pigmented, golden yellow. Tryptic Soy …

Introduction to Antigen-Antibody Reactions

October 9, 2020October 13, 2017 by Sagar Aryal

Introduction to Antigen-Antibody Reactions The interactions between antigens and antibodies are known as antigen–antibody reactions. The reactions are highly specific, and an antigen reacts only with antibodies produced by itself or with closely related antigens. Antibodies recognize molecular shapes (epitopes) on antigens. Generally, the better the fit of the epitope (in terms of geometry and chemical character) to the antibody …

Laboratory diagnosis of Streptococcus pyogenes

January 1, 2020October 12, 2017 by Sagar Aryal

Laboratory diagnosis of Streptococcus pyogenes 1. Specimens Throat swab Pus Cerebrospinal fluid Blood Serum for antibody determinant 2. Smear Gram staining Purple color cocci in chain arrangement Not to be confused with Viridans Streptococci from throat swab sample since both have same appreance 3. Culture Culture on blood agar Addition of bacitracin in inoculum: S pyogenes are sensitive to bacitracin …

Properties and Function of different classes of Antibodies

January 6, 2020October 12, 2017 by Sagar Aryal

Properties and Function of different classes of Antibodies Antibodies are glycoproteins produced in membrane-bound or secreted form by B lymphocytes in response to exposure to foreign structures known as antigens. The human immunoglobulins are a family of proteins that confer humoral immunity and perform vital roles in promoting cellular immunity. There are five classes of antibodies or immunoglobulins termed immunoglobulin …