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Medical Lab Technologist, AIIMS, New Delhi (2026)

30/03/2026

🦠 Mycobacterium tuberculosis

📌 Type / Classification
• Kingdom: Bacteria
• Shape: Rod-shaped (bacillus)
• Staining: Acid-fast bacilli (AFB) due to mycolic acid in cell wall
• Oxygen requirement: Obligate aerobe
• Growth: Slow-growing (takes 2–6 weeks on culture)
• Motility: Non-motile
• Spore formation: Non-spore forming

⚙️ Morphology
• Slender, slightly curved rods
• Arranged singly or in small groups
• Cell wall rich in lipids (mycolic acid) → gives resistance to drying, disinfectants
• Shows “beaded appearance” on staining

⚡ Pathogenesis (How it causes disease)
1. Entry into body
• Spread via airborne droplets (cough/sneeze of infected person)
2. Primary infection
• Bacteria reach alveoli of lungs
• Engulfed by macrophages but survive inside them
3. Multiplication
• Multiply within macrophages → spread to nearby lymph nodes
4. Immune response
• Body forms granuloma (tubercle) to contain infection
• Structure includes:
• Macrophages
• Giant cells (Langhans giant cells)
• Lymphocytes
5. Caseation necrosis
• Center becomes cheese-like (caseous necrosis)
6. Outcomes
• Latent TB: Bacteria dormant
• Active TB: Reactivation when immunity is low

🧪 Laboratory Diagnosis

1. Specimen
• Sputum (most common)
• Gastric lavage (children)
• Bronchoalveolar lavage

2. Microscopy
• Ziehl-Neelsen stain
• Shows red acid-fast bacilli against blue background
• Fluorescent staining (Auramine-rhodamine) → more sensitive

3. Culture
• Gold standard
• Media:
• Lowenstein-Jensen (LJ) medium
• Colonies:
• Rough, buff-colored (“rough, tough, buff”)
• Takes 2–6 weeks

4. Molecular methods
• CBNAAT (GeneXpert)
• Detects TB DNA
• Also detects rifampicin resistance

5. Tuberculin Skin Test (Mantoux test)
• Detects delayed hypersensitivity reaction
• Indicates exposure, not active disease

6. Chest X-ray
• Shows:
• Cavities
• Infiltrates (especially upper lobes)

30/03/2026

Gram negative bacteria

29/03/2026

Virus Envelope

The virus envelope is an outer covering present in some viruses, derived mainly from the host cell membrane.

Structure:
• Composed of a lipid bilayer
• Contains viral glycoproteins (spikes/peplomers) embedded in it
• May include matrix proteins beneath the envelope for structural support

Functions:
• Helps in attachment to host cells (via spikes)
• Facilitates entry of the virus by membrane fusion
• Plays a role in immune evasion

Examples of enveloped viruses:
• HIV infection virus
• Influenza virus
• COVID-19 virus

Important note:
Enveloped viruses are usually more sensitive to heat, drying, and detergents compared to non-enveloped viruses.

⸻

Virus Symmetry

Virus symmetry refers to the arrangement of capsid proteins (capsomeres) around the nucleic acid.

Types of Symmetry:
1. Icosahedral Symmetry (Cubical)
• Capsid forms a 20-sided structure
• Appears spherical
• Efficient and strong structure
• Examples:
• Polio virus
• Adenovirus infection

⸻

2. Helical Symmetry
• Capsid proteins arranged in a spiral (helix) around nucleic acid
• Forms rod-shaped or filamentous viruses
• Examples:
• Rabies virus
• To***co mosaic disease

⸻

3. Complex Symmetry
• Structure is neither purely helical nor icosahedral
• More complicated architecture
• Examples:
• Smallpox virus
• Bacteriophages (head-tail structure)

28/03/2026

🦠 What are Viruses?

Viruses are extremely small, infectious agents that can only replicate inside living host cells. They are not considered fully living because they lack cellular structure and cannot carry out metabolism on their own.

Key features:
• Made of genetic material (DNA or RNA) + protein coat (capsid)
• Some have an outer envelope
• Obligate intracellular parasites (need host cells)
• Cause diseases in humans, animals, and plants

⸻

📚 Classification of Medically Important Viruses

Viruses are mainly classified based on:
• Type of nucleic acid (DNA or RNA)
• Structure (enveloped or non-enveloped)
• Shape (icosahedral, helical, complex)

🧬 1. DNA Viruses

🔹 Double-stranded DNA (dsDNA) viruses

Family Examples Diseases
Adenoviridae Adenovirus Respiratory infections, conjunctivitis
Herpesviridae HSV, VZV, CMV, EBV Herpes, chickenpox, mononucleosis
Poxviridae Variola virus Smallpox
Papillomaviridae HPV Warts, cervical cancer
Hepadnaviridae HBV Hepatitis B

🔹 Single-stranded DNA (ssDNA) viruses

Family Example Disease
Parvoviridae Parvovirus B19 Fifth disease (erythema infectiosum)

🧬 2. RNA Viruses

🔹 Positive-sense RNA viruses (+ssRNA)

Family Examples Diseases
Picornaviridae Poliovirus, Rhinovirus Polio, common cold
Flaviviridae Dengue, Hepatitis C virus Dengue fever, Hepatitis C
Togaviridae Rubella virus German measles
Coronaviridae SARS-CoV-2 COVID-19

🔹 Negative-sense RNA viruses (-ssRNA)

Family Examples Diseases
Orthomyxoviridae Influenza virus Flu
Paramyxoviridae Measles, Mumps Measles, mumps
Rhabdoviridae Rabies virus Rabies
Filoviridae Ebola virus Hemorrhagic fever

🔹 Double-stranded RNA (dsRNA)

Family Example Disease
Reoviridae Rotavirus Severe diarrhea (children)

🔹 Retroviruses (Special RNA viruses)

Family Example Disease
Retroviridae HIV AIDS

👉 These viruses use reverse transcriptase to convert RNA → DNA.

🧩 Quick Easy Classification Trick

👉 DNA viruses → “HHAPPPPy”
• H – Herpes
• H – Hepadna
• A – Adeno
• P – Pox
• P – Papilloma
• P – Parvo (only ssDNA)
• y – remember exception

👉 RNA viruses → Most are RNA except above

25/03/2026

Needle Stick Injury (NSI)

A needle stick injury is a type of accidental injury caused by a needle (or other sharp medical instrument) that punctures the skin, potentially exposing a person to blood-borne pathogens.

⸻

🦠 Causes of Needle Stick Injury

Common situations where NSI occurs:
1. Recapping needles after use
2. Improper disposal of needles in regular waste instead of sharps containers
3. Handling patients suddenly moving during injections
4. Overfilled sharps containers leading to accidental pricks
5. Lack of training or awareness among healthcare workers
6. Rushing or fatigue during procedures
7. Passing sharp instruments improperly between staff

⸻

⚠️ Risks Associated

NSI can transmit serious infections such as:
• Hepatitis B (HBV)
• Hepatitis C (HCV)
• HIV/AIDS

⸻

🛡️ Prevention of Needle Stick Injury

1. Safe Handling Practices
• Never recap needles
• Do not bend or break needles
• Use one-hand technique if recapping is unavoidable

2. Proper Disposal
• Dispose immediately in puncture-proof sharps containers
• Do not overfill containers

3. Use of Safety Devices
• Use auto-disable syringes or safety-engineered needles

4. Personal Protective Measures
• Wear gloves and protective gear
• Follow standard precautions

5. Training & Awareness
• Regular training programs for healthcare workers
• Follow hospital infection control guidelines

6. Vaccination
• Take vaccination against Hepatitis B

⸻

🚑 Immediate Action After Injury
1. Wash the area with soap and water (do not squeeze)
2. Report immediately to supervisor
3. Seek medical evaluation for post-exposure prophylaxis (PEP)
4. Get tested and follow up

24/03/2026

Nosocomial infection (Hospital-acquired infection, HAI) is an infection that a patient develops after being admitted to a hospital or healthcare facility, which was not present or incubating at the time of admission.
Usually, it appears ≥48 hours after hospitalization.

🔬 Common Causes

Nosocomial infections occur due to a combination of microorganisms, host factors, and hospital environment:

1. 🦠 Infectious Agents
• Bacteria: E. coli, Klebsiella, Pseudomonas, Staphylococcus aureus
• Viruses: Influenza, Hepatitis B/C
• Fungi: Candida

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2. 🏥 Hospital-related Factors
• Poor sterilization of instruments
• Contaminated surfaces, beds, equipment
• Overcrowding in wards
• Improper waste disposal

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3. 👨‍⚕️ Healthcare Practices
• Poor hand hygiene by staff
• Invasive procedures (catheters, IV lines, ventilators)
• Prolonged hospital stay
• Overuse or misuse of antibiotics → resistance

4. 🧑‍⚕️ Patient-related Factors
• Weak immune system
• Old age or infants
• Chronic diseases (diabetes, cancer)
• Surgical wounds or burns

⚠️ Common Types of Nosocomial Infections
• UTI (Urinary tract infection) – from catheter use
• Surgical site infections (SSI)
• Pneumonia – especially ventilator-associated
• Bloodstream infections (sepsis)

🛡️ Prevention

1. 🧼 Infection Control Practices
• Strict hand hygiene (hand washing/alcohol rub)
• Use of PPE (gloves, masks, gowns)
• Isolation of infected patients

2. 🧽 Sterilization & Disinfection
• Proper cleaning of instruments
• Regular disinfection of hospital surfaces
• Use of sterile techniques in procedures

3. 💉 Safe Medical Practices
• Avoid unnecessary catheterization
• Proper care of IV lines and ventilators
• Rational use of antibiotics (antibiotic stewardship)

4. 🏥 Hospital Management
• Adequate ventilation
• Waste management systems
• Training of healthcare workers

5. 🧑 Patient Awareness
• Maintain personal hygiene
• Follow doctor instructions
• Report symptoms early

20/03/2026

🦠 Klebsiella: Morphology, Pathogenesis & Lab Diagnosis

🔬 1. Morphology
• Gram-negative bacilli (rod-shaped)
• Short, plump rods with rounded ends
• Non-motile (no flagella)
• Capsulated → thick polysaccharide capsule (important virulence factor)
• Non-spore forming
• Arranged singly, in pairs or short chains

👉 Capsule gives colonies a mucoid (sticky, glistening) appearance.

⸻

⚠️ 2. Pathogenesis

Klebsiella pneumoniae is an opportunistic pathogen, commonly causing infections in hospitalized or immunocompromised patients.

🔑 Virulence Factors
• Capsule (K antigen)
→ Prevents phagocytosis
• Endotoxin (LPS)
→ Causes fever, inflammation, shock
• Fimbriae (adhesins)
→ Helps bacteria attach to host tissues
• Siderophores
→ Help in iron acquisition

⸻

🧬 Mechanism of Disease
1. Colonizes respiratory or gastrointestinal tract
2. Enters lungs/urinary tract
3. Capsule prevents immune clearance
4. Causes tissue destruction & inflammation

⸻

🏥 Clinical Diseases
• Pneumonia
→ “Currant jelly sputum” (blood-tinged sputum)
• Urinary tract infection (UTI)
• Septicemia
• Liver abscess (especially in diabetics)
• Wound infections

⸻

🧪 3. Laboratory Diagnosis

🧫 Specimens
• Sputum (pneumonia)
• Urine (UTI)
• Blood (septicemia)
• Pus (wound infections)

⸻

🔍 Microscopy
• Gram stain: Gram-negative bacilli
• Capsule seen as clear halo (negative staining)

⸻

🧬 Culture
• Grows on:
• MacConkey agar → Lactose fermenting colonies (pink)
• Blood agar → large, mucoid colonies

👉 Colonies are large, slimy, and sticky due to capsule

⸻

🧪 Biochemical Tests
• Lactose fermenter
• Indole: negative (K. pneumoniae)
• Urease: positive
• Citrate: positive
• Non-motile

⸻

🧫 String Test (Important)
• Colony forms a string >5 mm when stretched → indicates hypervirulent strain

⸻

🧬 Advanced Tests
• PCR (for virulence genes)
• Antibiotic sensitivity testing (important due to MDR strains like ESBL, KPC)

18/03/2026

🧬 DNA Double Helix – Explanation

This diagram shows the structure of DNA (Deoxyribonucleic Acid), which carries genetic information.

⸻

🔹 1. Double Helix Structure
• DNA consists of two twisted strands forming a double helix (spiral shape)
• Looks like a twisted ladder

⸻

🔹 2. Sugar-Phosphate Backbone
• The outer part of each strand is made of:
• Deoxyribose sugar
• Phosphate group
• These alternate to form the backbone
👉 Provides strength and support

⸻

🔹 3. Nitrogenous Base Pairs
• The “rungs” of the ladder are base pairs

✔ Complementary pairing:
• Adenine (A) ↔ Thymine (T)
• Cytosine (C) ↔ Guanine (G)

👉 This pairing is specific and constant

⸻

🔹 4. Hydrogen Bonds
• Bases are held together by hydrogen bonds
• A–T → 2 bonds
• C–G → 3 bonds
👉 Helps maintain structure but allows easy separation during replication

⸻

🔹 5. Antiparallel Strands
• The two strands run in opposite directions:
• One strand: 5′ → 3′
• Other strand: 3′ → 5′

👉 Called antiparallel arrangement

⸻

🔹 6. Major & Minor Grooves
• Twisting creates:
• Major groove
• Minor groove

👉 Important for protein binding (e.g., enzymes, transcription factors)

⸻

🔹 7. One Complete Turn
• One full twist of helix contains:
• ~10 base pairs
• Length ≈ 3.4 nm (nanometers)

⸻

📝 Quick Summary

👉 DNA = Double helix + Complementary bases + Antiparallel strands

⸻

🎯 Exam Tip
• Remember:
“A = T, C ≡ G” (C-G has stronger bonding)

18/03/2026

🧪 Classification of Fats (Lipids)

Lipids are classified based on chemical composition and function.

⸻

1️⃣ Based on Chemical Composition

🔹 A. Simple Lipids

👉 Esters of fatty acids with alcohol
• Fats (Triglycerides) → Glycerol + 3 fatty acids
• Waxes → Fatty acid + long-chain alcohol

⸻

🔹 B. Compound (Complex) Lipids

👉 Lipids + additional groups
• Phospholipids → Contain phosphate (e.g., lecithin)
• Glycolipids → Contain carbohydrate
• Lipoproteins → Lipid + protein

⸻

🔹 C. Derived Lipids

👉 Products formed after hydrolysis
• Fatty acids
• Glycerol
• Steroids (cholesterol)

⸻

2️⃣ Based on Saturation

🔹 A. Saturated Fats
• No double bonds
• Solid at room temperature
• Example: Butter, animal fat

⸻

🔹 B. Unsaturated Fats

➤ Monounsaturated (MUFA)
• One double bond
• Example: Olive oil

➤ Polyunsaturated (PUFA)
• Multiple double bonds
• Example: Fish oil

⸻

3️⃣ Based on Function

🔹 A. Storage Lipids
• Triglycerides
• Energy reserve

⸻

🔹 B. Structural Lipids
• Phospholipids
• Cell membrane component

⸻

🔹 C. Regulatory Lipids
• Steroid hormones
• Prostaglandins

18/03/2026

🧬 Classification of Amino Acids

Amino acids can be classified in multiple ways:

⸻

1️⃣ Based on Side Chain (R Group)

🔹 A. Non-polar (Hydrophobic)
• Glycine
• Alanine
• Valine
• Leucine
• Isoleucine
• Methionine
• Proline

⸻

🔹 B. Polar (Uncharged)
• Serine
• Threonine
• Asparagine
• Glutamine
• Tyrosine
• Cysteine

⸻

🔹 C. Acidic (Negatively charged)
• Aspartic acid
• Glutamic acid

⸻

🔹 D. Basic (Positively charged)
• Lysine
• Arginine
• Histidine

⸻

2️⃣ Based on Nutritional Requirement

🔹 A. Essential Amino Acids

(Cannot be synthesized in body)

👉 Mnemonic: PVT TIM HALL
• Phenylalanine
• Valine
• Threonine
• Tryptophan
• Isoleucine
• Methionine
• Histidine
• Arginine
• Leucine
• Lysine

⸻

🔹 B. Non-Essential Amino Acids

(Synthesized in body)
• Alanine
• Aspartate
• Glutamate
• Serine
• Glycine
• Proline
• Asparagine
• Glutamine

⸻

3️⃣ Based on Metabolism

🔹 A. Glucogenic

→ Converted into glucose
• Most amino acids

⸻

🔹 B. Ketogenic

→ Form ketone bodies
• Leucine
• Lysine

⸻

🔹 C. Both Glucogenic & Ketogenic
• Isoleucine
• Phenylalanine
• Tyrosine
• Tryptophan
• Threonine

⸻

4️⃣ Based on Structure

🔹 A. Aliphatic
• Glycine, Alanine, Valine

🔹 B. Aromatic
• Phenylalanine
• Tyrosine
• Tryptophan

🔹 C. Sulfur-containing
• Cysteine
• Methionine

18/03/2026

🧪 Classification of Carbohydrates

Carbohydrates are classified mainly based on number of sugar units and functional groups.

⸻

1️⃣ Based on Number of Sugar Units

🔹 A. Monosaccharides (Simple sugars)
• Cannot be hydrolyzed further
• General formula: (CH₂O)n

Examples:
• Glucose
• Fructose
• Galactose

Further classification:
• By carbon number:
• Trioses (3C)
• Tetroses (4C)
• Pentoses (5C) → Ribose
• Hexoses (6C) → Glucose
• By functional group:
• Aldoses (–CHO) → Glucose
• Ketoses (C=O) → Fructose

⸻

🔹 B. Oligosaccharides (2–10 units)

➤ Disaccharides (2 monosaccharides)
• Sucrose (Glucose + Fructose)
• Lactose (Glucose + Galactose)
• Maltose (Glucose + Glucose)

➤ Trisaccharides (3 units)
• Raffinose

⸻

🔹 C. Polysaccharides (>10 units)

➤ Homopolysaccharides (same monomer)
• Starch
• Glycogen
• Cellulose

➤ Heteropolysaccharides (different monomers)
• Hyaluronic acid
• Heparin

⸻

2️⃣ Based on Reducing Property

🔹 Reducing Sugars
• Have free aldehyde/ketone group
• Examples: Glucose, Lactose

🔹 Non-reducing Sugars
• No free functional group
• Example: Sucrose

⸻

3️⃣ Based on Function

🔹 Storage Carbohydrates
• Starch (plants)
• Glycogen (animals)

🔹 Structural Carbohydrates
• Cellulose
• Chitin

18/03/2026

🦠 Pathogenesis of Streptococcus (esp. S. pyogenes)

🔬 1. Entry & Colonization
• Enters through respiratory tract / skin
• Adheres to epithelial cells using:
• M protein (major virulence factor)
• Lipoteichoic acid

⸻

⚔️ 2. Virulence Factors

🛡️ Antiphagocytic Factors
• M protein → prevents phagocytosis
• Capsule (hyaluronic acid) → mimics host tissue

⸻

💥 Enzymes (Spread of infection)
• Streptokinase → dissolves clots
• Hyaluronidase → spreads through tissues
• DNase → liquefies pus

⸻

☠️ Toxins
• Streptolysin O (SLO) → hemolysis (oxygen labile)
• Streptolysin S (SLS) → hemolysis (oxygen stable)
• Pyrogenic exotoxins (Spe) → cause:
• Scarlet fever rash
• Toxic shock–like syndrome

⸻

🧬 3. Immune-Mediated Complications
• Rheumatic fever
• Due to molecular mimicry (M protein cross-reacts with heart tissue)
• Acute glomerulonephritis
• Immune complex deposition in kidneys

⸻

🧪 Laboratory Diagnosis of Streptococcus

🧫 1. Specimen Collection
• Throat swab (pharyngitis)
• Pus (skin infections)
• Blood (sepsis)

⸻

🔍 2. Microscopy
• Gram stain:
👉 Gram-positive cocci in chains

⸻

🧬 3. Culture
• Grown on blood agar
• Shows:
• β-hemolysis (clear zone around colonies)

⸻

🧪 4. Biochemical Tests

✅ Catalase Test
• Negative (distinguishes from Staphylococcus)

✅ Bacitracin Sensitivity
• S. pyogenes → Sensitive (Group A)

⸻

🧫 5. Serological Tests
• A*O (Antistreptolysin O) titer
👉 Indicates recent infection
• Anti-DNase B test

⸻

⚡ 6. Rapid Antigen Detection Test (RADT)
• Detects Group A antigen from throat swab
• Quick diagnosis in pharyngitis

Medical Lab Technologist

30/03/2026

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