Bacterial Metabolism and Genetics

Entner-Doudoroff Pathway

• Converts glucose-6-phosphate to pyruvate
• Generates one NADPH per glucose molecule
• Consumes one ATP
• Aerobic process

Anaerobic Utilization of Pyruvic Acid (Fermentation)

• Alcohol fermentation: produces ethanol as the main end product
• Homolactic fermentation: produces lactic acid as the end product
• Heterolactic fermentation: Produces a mix of end products including lactic acid, carbon dioxide, alcohols, formic acid, and acetic acid

Bacterial Genetics

• Bacterial genome:
• Bacterial chromosome: Single, closed, circular piece of double-stranded DNA
• Plasmids: Small circular pieces of extrachromosomal, double-stranded DNA
  • Plasmids often carry genes associated with antibiotic resistance, toxins, and virulence factors
  • Located in the cytoplasm of the cell and are self-replicating
  • Can be degraded or integrated into existing bacterial genetic material
  • If compatible, can replicate in the cytoplasm

Specimen Collection and Processing

• Processing should occur immediately to prevent temperature decrease, which can cause pH to drop and bacterial death
• Specimen Collection Procedures:
• Stool:
  • Collect and process immediately
  • Should be used to identify intestinal parasites (Ascaris lumbricoides, Trichuris trichiura)
  • Used to identify intestinal protozoa (Giardia lamblia, Entamoeba histolytica)
• Throat swab:
  • Used to diagnose strep throat (pharyngitis) caused by bacteria Streptococcus pyogenes
• Wound specimen:
  • Should be aspirated rather than swabbed
  • Must record the type of wound and its anatomical location
  • Should be investigated for bacteria that can cause wound infection

Selective Media for Bacterial Growth

• MacConkey Agar:
  • Selective and differential for gram-negative bacteria
  • Bile salts and crystal violet inhibit the growth of most gram-positive bacteria
  • Lactose is the sole carbohydrate source
  • Neutral red acts as a pH indicator
• Bismuth Sulfite Agar:
  • Selective medium for the isolation of Salmonella spp. from stool specimens
  • Bismuth sulfite and brilliant green inhibit the growth of most gram-positive organisms and many lactose-fermenting gram-negative rods normally found in stool
• Esculin agar:
  • Oxgall (bile salts) is a selective ingredient that inhibit the growth of gram-positive organisms
  • Esculin is the differential component; its hydrolysis produces iron salts that darken the medium
• Phenylalanine Deaminase Agar:
  • Detects an organism's ability to deaminate phenylalanine
  • Positive reaction can differentiate Proteus, Providencia, and Morganella spp.
  • A dark green slant is observed upon addition of ferric chloride
• Salmonella-Shigella Agar:
  • Selects for Salmonella and some strains of Shigella from stool specimens
  • Contains bile salts, sodium citrate, and brilliant green to inhibit gram-positive bacteria and several lactose-fermenting gram-negative rods

Stapylococcal Coagulase

• Bound Coagulase:
  • Also known as "clumping factor"
  • Agglutinates human, rabbit, or pig plasma
  • Directly converts fibrinogen to fibrin
• Free Coagulase:
  • Known as "tube coagulase"
  • Causes a clot to form when bacterial cells are incubated with plasma

Streptococcal Infections

• Streptococcal pharyngitis:
  • S. pyogenes most common pathogen (Strep throat)
• Pyodermal infections:
  • Impetigo, Erysipelas, cellulitis, Scarlet fever
• Necrotizing fasciitis:
  • Flesh eating disease
• Streptococcal Toxic Shock syndrome (STSS)
• Post-Streptococcal sequelae:
  • Rheumatic fever, acute glomerulonephritis

Streptococcal Laboratory Identification

• On SBA:
  • Small, transparent, smooth beta-hemolytic
• Key tests:
  • Bacitracin susceptibility: S. pyogenes (sensitive, S) vs other beta-hemolytic (resistant, R)
  • PYR hydrolysis: Positive

Viridans Streptococci

• Means "green"
• Characterized by alpha-hemolysis
• Commonly found in the mouth and oropharynx

Viridans Streptococci Clinical Infections

• Most common cause of subacute bacterial endocarditis
• Associated with gingivitis and dental caries

Viridans Streptococci Laboratory Identification

• PYR: Negative
• LAP: Positive
• 6.5% NaCl: Negative (Group D)
• Bile esculin: Positive

Explore the fundamental processes of bacterial metabolism, including the Entner-Doudoroff pathway and various fermentation methods. Additionally, delve into the structure and function of bacterial genomes, including plasmids and their roles in antibiotic resistance. Test your knowledge on these essential microbiology topics.