Topic 35 of 50 in the MU Plovdiv syllabus for Microbiology (Medicine, Years 2 and 3). The free AceMed note covers it in 12 sections, about 456 words (4 min of reading), with 15 flashcards.
In this note
Family Mycobacteriaceae: Mycobacterium tuberculosis and Related Species
GENERAL CHARACTERISTICS
VIRULENCE FACTORS
PATHOGENESIS
STAGES OF TUBERCULOSIS
CLINICAL FEATURES
LABORATORY DIAGNOSIS
TREATMENT
Drug Resistance
PREVENTION
BCG Vaccine
Public Health Measures
GENERAL CHARACTERISTICS
Shape: Straight or slightly curved bacilli, slender rods
Gram stain: Weakly Gram-positive (does not stain reliably); acid-fast bacilli (AFB) due to mycolic acid
Staining methods:
Ziehl–Neelsen (ZN) stain: Bright red rods on a blue background
Auramine–rhodamine fluorescent stain: Yellow-green under UV — more sensitive
Oxygen: Obligate aerobe
Motility, spores, capsule: Non-motile, non-spore-forming, no capsule
Growth rate: Slow-growing, doubling time ~18–24 hrs
Colony characteristics: Buff-colored, rough, dry colonies on Lowenstein–Jensen (LJ) medium
PATHOGENESIS
Inhalation of droplets from an active TB patient → enters alveoli
Phagocytosed by alveolar macrophages → M. tuberculosis survives inside due to sulfolipids
Multiplies within macrophages → triggers pro-inflammatory cytokines (e.g., TNF-α)
Recruitment of immune cells → formation of a granuloma (tubercle) to contain infection
Caseous necrosis develops at center of granuloma → latent or active TB
Reactivation occurs when immune defenses weaken → leads to progressive disease and cavitation
STAGES OF TUBERCULOSIS
1. Primary TB
Occurs on first exposure (usually in childhood)
Infects lower part of upper lobe or upper part of lower lobe
