Microbiology

Plasmids are extrachromosomal DNA that carry antibiotic resistance genes and can be transferred between bacteria, making them primary vectors for resistance.

Staphylococcus aureus produces coagulase enzyme (plasma coagulation positive), forming clusters and showing variable hemolysis (often alpha or non-hemolytic), distinguishing it from coagulase-negative staphylococci.

Mycolic acids in mycobacterial cell walls create a waxy, hydrophobic barrier that retains acid-fast stains and inhibits antimicrobial penetration.

Attachment proteins (like hemagglutinin in influenza, spike protein in SARS-CoV-2) mediate receptor binding and are immunodominant targets for neutralizing antibodies.

Bacillus cereus produces heat-resistant spores surviving cooking temperatures, causing emetic and diarrheal foodborne illness outbreaks.

Monotrichous bacteria have a single flagellum at one pole, enabling direct, efficient movement. Peritrichous flagella around the cell body create tumbling motion.

Gram-positive bacteria have a thick peptidoglycan layer (20-80 nm) with teichoic acids that retains the crystal violet-iodine complex, resulting in purple coloration.

Staphylococcus aureus is catalase-positive (distinguishes from streptococci) and coagulase-positive (specific identification). Beta-hemolysis results from alpha-toxin production.

Surface glycoproteins (spike proteins in coronaviruses, gp120 in HIV) mediate host cell recognition and attachment. Matrix proteins provide structural support; enzymes have catalytic roles.

Staphylococcus aureus characteristically forms clusters (not chains), produces alpha-hemolysin (alpha-toxin), and is coagulase-positive, distinguishing it from streptococci.