Laboratory Diagnosis of Bacterial Infections

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Questions and Answers

What is the first step in the Gram stain procedure?

Primary stain with Crystal violet

Decolorization with Alcohol

Application of Mordant called Iodine

Fix the smear on the glass slide (correct)

Which type of microscope is specifically used for the detection of Treponema pallidum?

Dark Field Microscope (correct)

Ordinary Light Microscope

Fluorescence Microscope

Electron Microscope

What is the primary stain used in the Ziehl-Neelsen stain method?

Carbol fuchsin (correct)

Safranin

Sulphuric acid

Methylene blue

For a urinary tract infection, which specimen is considered adequate for diagnosis?

Mid-stream urine Signup and view all the answers

Which type of bacterial cell wall structure contributes to the red appearance of Gram negative bacteria after staining?

Thin peptidoglycan layer Signup and view all the answers

What is the appearance of Gram positive bacteria after staining?

Purple Signup and view all the answers

What type of bacteria appears red when stained using the Ziehl-Neelsen method?

Mycobacterium tuberculosis Signup and view all the answers

Which technique is used to determine the motility of bacterial samples?

Wet Mount Preparation Signup and view all the answers

What component is used for decolorization in the Ziehl-Neelsen stain procedure?

Sulphuric acid with alcohol Signup and view all the answers

What is an indirect method to detect bacterial infection?

Serology Signup and view all the answers

Which of the following is not a type of culture media classification based on its ingredients?

Differential media Signup and view all the answers

Which media type is exemplified by the use of blood, useful for supporting fastidious bacterial growth?

Enriched media Signup and view all the answers

Which stain is specifically used for identifying acid-fast bacteria?

Ziehl-Neelsen Stain Signup and view all the answers

What should be done if there is a delay in transporting the specimen to the laboratory?

Use transport media Signup and view all the answers

What color do Gram positive bacteria appear after using the Gram staining technique?

Purple Signup and view all the answers

Which of the following specimens is suitable for diagnosing respiratory tract infections?

Throat swab Signup and view all the answers

What is the purpose of transport media in bacterial culture?

To maintain organism viability during transport Signup and view all the answers

Which of the following describes the use of PCR in bacterial identification?

Direct detection of genetic material Signup and view all the answers

Which of the following is a common symptom associated with Mycobacterium tuberculosis infection?

Night sweats Signup and view all the answers

Which medium would support all organisms present in a specimen but not be selective for any particular type?

Nutrient broth Signup and view all the answers

Study Notes

Lecture 9: Laboratory Diagnosis of Bacterial Infections (I)

The lecture covers laboratory diagnosis of bacterial infections, focusing on specimen collection, bacterial identification, and result interpretation.

Specimen Collection & Transport

Samples must be collected before antimicrobial therapy begins.
Samples should be representative of the infection's source (e.g., CSF for meningitis, sputum for respiratory tract infections).
Samples should be collected in an appropriate sterile container.
Adequate sample volume is essential.
Complete request forms containing pertinent information (date, sample type, department, etc.) must be included.
Samples should be transported rapidly to the lab. Transport media should be used if delay is anticipated.

Bacterial Identification

Direct Detection: Methods for directly identifying the causative bacteria, their antigens, or genetic material.
- Microscopic examination (using various types of microscopes like ordinary light, dark field, fluorescence, and electron).
- Culture and antibiotic sensitivity testing to identify specific bacteria and their susceptibility to different antibiotics.
- Antigen detection to identify specific bacterial antigens.
- Molecular tests (like PCR) to detect bacterial genetic material.
Indirect Detection: Detects antibodies produced in response to a bacterial infection, not the bacteria itself.
- Serology, which detects specific antibodies against the bacteria in blood.

Microscopic Examination

Types of microscopes:
- Ordinary light microscope, dark field microscope, fluorescence microscope, and electron microscope.
- Dark field microscopes are used to detect Treponema pallidum (syphilis).
- Fluorescence microscopes use UV light to detect Mycobacteria, certain intracellular organisms (e.g., Chlamydia), and viruses.
- Electron microscopes are used to visualize viruses.
Unstained (Wet Mount) Preparations: used to observe bacterial motility (e.g., Vibrio cholerae, Salmonella, E. coli, Proteus).
Stained Preparations: used to determine bacteria's staining reaction, shape, and arrangement.
- Gram stain: classifies bacteria into Gram-positive (purple) and Gram-negative (red) based on cell wall structure.
- Ziehl-Neelsen stain (Acid-Fast Stain): detects bacteria like Mycobacterium spp. (e.g., those causing tuberculosis) which retain the stain during decolorization due to their waxy cell walls.

Gram Stain Steps

Fix the specimen on a glass slide (heating or alcohol).
Apply crystal violet (primary stain).
Apply iodine (mordant).
Decolorize with alcohol (95% ethanol).
Apply safranin (counter stain).
Examine stained smear using oil immersion lens (100x magnification).

Bacterial Culture

Clinical samples are inoculated onto various culture media under specific temperature and atmospheric conditions.
Media are classified by consistency: liquid (broth) and solid/semi-solid (agar plates).
Media are also classified by ingredients and usage:
- Transport media maintain viability during transport. Examples include Stuart, Amies, and Carry & Blair media.
- Culture media support bacterial growth. Examples include simple (nutrient agar and nutrient broth), enriched (blood agar, chocolate agar, Loffler's serum agar), and selective (media that inhibit growth of unwanted organisms). -Differential media, such as blood agar, help classify bacteria based on hemolysis (breakdown of red blood cells) β (complete), α (partial), γ (no hemolysis).

Ziehl-Neelsen Stain

Used for identifying Mycobacteria species (like Mycobacterium tuberculosis) with high lipid content in their cell walls.
Primary stain: Carbol fuchsin.
Decolorization: Sulfuric acid with alcohol.
Counterstain: Methylene blue.
Examine under oil immersion.

Case Study

A 45-year-old man with a six-month history of night sweats, fever, and cough producing sputum, and weight loss, likely has Mycobacterium tuberculosis infection.
Ziehl-Neelsen stain is crucial for diagnosis of Mycobacterium tuberculosis.

Important Note: This summary emphasizes concepts for understanding the methodology. Visual components, details about microbes, and specific results from a sample are necessary for a full lab report.

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Description

This quiz focuses on the laboratory diagnosis of bacterial infections, emphasizing specimen collection and bacterial identification techniques. It addresses the importance of sample handling, types of specimens, and methods for direct detection of bacteria. Ideal for students and professionals in microbiology and laboratory medicine.