Microbiology for the MCAT

Bacteria

• Prokaryotic, cell wall (peptidoglycan)
• Gram+: Thick peptidoglycan (purple); Gram−: Thin + outer membrane (pink)
• Shapes: cocci (spheres), bacilli (rods), spirilla (spirals)
• Binary fission (asexual, rapid)

Viruses

• Obligate intracellular parasites; DNA or RNA genome
• Lytic: Replicate immediately, lyse cell
• Lysogenic: Integrate into host genome
• Retroviruses (HIV): RNA → DNA via reverse transcriptase

Microbial Genetics

• Transformation: Uptake of free DNA
• Transduction: DNA transfer via bacteriophage
• Conjugation: Direct transfer via pilus (F-plasmid)
• Plasmids often carry antibiotic resistance genes

Antimicrobials

• Target cell wall (penicillin), protein synthesis (tetracycline), DNA (fluoroquinolones)
• Resistance: mutation or horizontal gene transfer