Microbiology of Infectious Diseases

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Questions and Answers

What is the primary role of DNA-ase in relation to diseases?

It helps in bacterial replication.

It synthesizes bacterial toxins.

It plays a role in pathogenesis. (correct)

It enhances the immune response.

Which of the following statements about Staphylococci's resistance is true?

Staphylococci can withstand drying and heat effectively. (correct)

Staphylococci are killed by a 3% phenol solution in 5 minutes.

Staphylococci are very sensitive to all aniline dyes.

Staphylococci are highly resistant to all forms of antibiotics.

In which environment are Staphylococci typically found?

Only in hospitals and clinics.

Only on human skin.

On clothing and bed linen in the human environment. (correct)

In the air and on various surfaces.

Which of the following conditions can Staphylococci cause?

Meningitis and osteomyelitis. Signup and view all the answers

What is the effect of 1% chloramine on Staphylococci?

It takes 2 to 5 minutes to kill them. Signup and view all the answers

What type of infections can S.aureus cause from direct contamination of a wound?

Pulmonary infection and endocarditis. Signup and view all the answers

How do Staphylococci contribute to mixed infections?

They are found alongside other bacteria like streptococci. Signup and view all the answers

What is the significance of Staphylococci producing Beta-lactamase?

It contributes to their resistance against penicillin. Signup and view all the answers

What is the primary focus of special microbiology?

The morphology and properties of pathogenic microorganisms Signup and view all the answers

Which method is mentioned for the microscopic examination of microorganisms?

Gram staining method Signup and view all the answers

What aspect of infectious diseases is covered in special microbiology?

The role of distinct species in disease etiology and pathogenesis Signup and view all the answers

In what way does medical microbiology serve as propedeutics?

It provides knowledge foundational for all doctors and medical workers. Signup and view all the answers

What are the two main parts of medical microbiology?

General and special microbiology Signup and view all the answers

What does special microbiology elaborate upon regarding infectious diseases?

Laboratory diagnosis and prophylaxis methods Signup and view all the answers

Who edited the handout on special microbiology for foreign students?

M.S.Hovhannisyan Signup and view all the answers

Which of the following best describes the skills and knowledge provided by special microbiology?

It ensures comprehensive biological knowledge and its practical application in medicine. Signup and view all the answers

What is the primary virulence factor of S. pyogenes?

M protein Signup and view all the answers

Which of the following characteristics is associated with streptococci?

They coagulate milk. Signup and view all the answers

What type of serological classification system is used for streptococci?

Lancefield classification Signup and view all the answers

What is the primary purpose of immunoelectrophoresis?

To separate antigens using electric charge Signup and view all the answers

What is the impact of streptolysin-O during infection?

It induces an antibody response in the host. Signup and view all the answers

How does Radioimmunoassay (RIA) determine the concentration of an unknown antigen?

By comparing against known standards Signup and view all the answers

Which entity demonstrates antigenic cross-reactions with different human tissues?

S. pyogenes structural components Signup and view all the answers

Which of the following statements about the Enzyme-Linked Immunosorbent Assay (ELISA) is true?

It involves linking an enzyme to an antigen or antibody. Signup and view all the answers

What is the role of the S. pyogenes exotoxins?

They inhibit lysosomal membrane function. Signup and view all the answers

What role do precipitin bands play in antigen-antibody reactions?

They are formed when antigens and antibodies are in optimal proportions. Signup and view all the answers

Which method is specifically used to measure IgE antibodies in the serum?

Radioallergosorbent test (RAST) Signup and view all the answers

Which statement is true regarding streptococci's fermentation capabilities?

They ferment maltose with acid formation. Signup and view all the answers

What is an important criterion for the classification of streptococci into serological groups?

Group-specific polysaccharide (C substance) Signup and view all the answers

What happens to the radioactivity measured in RIA when more unlabeled antigen is present?

Radioactivity decreases. Signup and view all the answers

What is measured in an ELISA after the addition of the enzyme substrate?

The color reaction using a spectrophotometer Signup and view all the answers

Which of the following is a disadvantage of using RIA?

It involves the use of radioactive materials. Signup and view all the answers

What is the primary causative agent of bacterial dysentery?

Shigella Signup and view all the answers

Which morphological characteristic distinguishes Shigella from other members of the Enterobacteriaceae family?

Non-motility Signup and view all the answers

On which type of media do Shigella produce colorless colonies due to a lack of lactose fermentation?

MacConkey agar Signup and view all the answers

What is the optimal temperature for the growth of Shigella?

37º C Signup and view all the answers

Which group of Shigella is subdivided into 1-10 serovars?

Group A - S. dysenteriae Signup and view all the answers

Which of the following statements is true regarding glucose fermentation by dysentery bacilli?

They ferment glucose with acid formation. Signup and view all the answers

What is a characteristic biochemical property of Shigella compared to E. coli?

Shigella does not produce hydrogen sulphide. Signup and view all the answers

Which Shigella species is known for fermenting lactose late, after 48-72 hours?

S. sonnei Signup and view all the answers

Study Notes

Special Microbiology

Focuses on pathogenic microorganisms that cause infectious diseases.
Covers morphology, physiology, biological, and antigenic properties of distinct species.
Examines the role of specific microorganisms in different infectious diseases.
Focuses on the etiology, pathogenesis, and laboratory diagnosis of infectious diseases.
Discusses methods of prophylaxis (prevention) and treatment of infectious diseases.

Microbiological Laboratory Diagnostic Methods

Microscopic Examination:
- Smears are prepared from samples.
- Stained with the Gram method.
- Examined under a microscope to identify microorganisms based on morphology and staining properties.
Immunoprecipitation:
- Antigens and antibodies diffuse towards each other, forming visible precipitation bands.
- Indicates specific antigen-antibody interactions.
Immunoelectrophoresis:
- Combines electrophoresis with diffusion of antigens and antibodies.
- Separates antigens with greater precision.
- Useful for identifying normal and abnormal serum proteins.
Radioimmunoassay (RIA):
- Used to quantify antigens or haptens by using radioactively labeled materials.
- Based on competition between labeled and unlabeled antigens for binding to specific antibodies.
- Measures radioactive complexes to determine the concentration of the unlabeled antigen.
Radioallergosorbent Test (RAST):
- A type of RIA used to measure the amount of IgE antibodies reacting with a known allergen.
Enzyme-Linked Immunosorbent Assay (ELISA):
- Widely used for quantifying antigens and antibodies.
- Involves linking enzymes to known antigens or antibodies, which react with patient specimens.
- Enzyme activity, measured by adding a substrate, indicates the presence and amount of the target molecule.

Genus Staphylococcus

Gram-positive, spherical bacteria that can be found in clusters.
Commonly associated with skin infections, but can cause systemic infections as well.
Some species are part of the normal human flora, like S. epidermidis.
S. aureus is a major pathogen, known for its ability to produce toxins.
Staphylococci are resistant to factors like drying, heat, and disinfectants.
They can develop resistance to antibiotics, particularly penicillin due to the production of Beta-lactamase enzyme.

Pathogenesis and Diseases caused by Staphylococcus

Staphylococcal infections occur through skin and mucous membrane entry.
Systemic infections, such as septicemia, can occur when staphylococci overcome lymphatic barriers and enter the bloodstream.
Staphylococci produce various toxins that contribute to pathogenesis.
Common local infections include abscesses, boils (furuncles), carbuncles, osteomyelitis, dermatitis, eczema, peritonitis, and meningitis.
Secondary infections can occur in individuals with compromised immune systems.

Genus Streptococcus

Gram-positive, spherical bacteria that occur in chains.
Some species, like S. pyogenes, are associated with throat infections, skin infections, and rheumatic fever.
Other species are part of the normal human flora, like S. viridans.
Streptococci are catalase-negative (unlike staphylococci).
They are classified into serological groups based on the group-specific polysaccharide (C substance).

Pathogenic Factors of Streptococcus

Adherence: They attach to host cells.
Colonization: They proliferate on the host surface.
Invasion: They penetrate host tissues.
Toxin Production: They produce exotoxins such as:
- Haemolysins:
  - Streptolysin-S: Non-antigenic, oxygen-stable, and responsible for hemolysis around colonies.
  - Streptolysin-O: Antigenic, oxygen-labile, induces the production of anti-streptolysin O (ASO) antibodies.
Enzyme Production: They secrete enzymes that contribute to tissue damage.

Genus Shigella

Gram-negative, non-motile bacilli that are the causative agents of bacterial dysentery.
They are facultative anaerobes and grow well on common culture media.
Lack flagella, but possess microvilli and fimbriae.
Classified into four groups (A, B, C, D) and several serotypes based on their somatic (O) antigens.
Differentiated from other Enterobacteriaceae based on their lack of lactose fermentation.
Ferment glucose, except S. sonnei which ferments it after 48-72 hours.
They do not ferment lactose, liquefy gelatin, or produce hydrogen sulfide.

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Description

This quiz focuses on special microbiology, particularly pathogenic microorganisms responsible for infectious diseases. It covers aspects such as morphology, physiology, and the diagnostic methods used in microbiology laboratories. Test your knowledge on laboratory techniques and the prevention and treatment of infectious diseases.