medlab

Naming Convention

Bacteria are named by genus (capitalized) and species (lowercase), e.g., Streptococcus pyogenes.

Cell Wall

Determines shape; site for many antibiotics; classifies into Gram-positive (purple) and Gram-negative (pink).

Cell Membrane

Thin, lipid-protein layer inside the cell wall; regulates material exchange.

Chromosome

Circular double-stranded DNA; contains genetic information.

Nucleoid

Area in cytoplasm housing the chromosome.

Cytoplasm

Liquid matrix (mostly water) with nutrients and wastes.

Plasmid

Extra, smaller DNA; can transfer between cells.

Pili

Hair-like structures for attachment and plasmid exchange (sex pili facilitate conjugation).

Ribosomes

Site of protein synthesis (bacterial ribosomes are 70S; humans are 80S).

Flagella

Responsible for motility

Endospores

Resistant forms of bacteria under unfavorable conditions

Liquid (Broth)

Growth in suspension.

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Solid

Solidified with agar (1.5%); used in petri dishes.

Semi-Solid

Contains less agar (0.7%).

Enrichment Media

Enhanced growth of specific organisms.

Blood Agar Plate (BAP)

Shows hemolysis patterns (alpha, beta, gamma).

Selective Media

Inhibits certain organisms; promotes others.

CNA

Enhances Gram-positive species.

Differential Media

Distinguish organisms based on characteristics.

Mannitol Salt Agar (MSA)

Differentiates Staphylococcus species.

MacConkey Agar (MAC)

Identifies lactose fermenters and non-fermenters.

Aerobic

Requires O₂

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Anaerobic

Cannot tolerate O₂

Microaerophilic

Requires low O₂ levels

Facultative

Can grow with or without O₂.

Acidophiles

Prefer pH < 5.0

Neutrophiles

Prefer pH 6.0-8.0

Alkaliphiles

Prefer pH > 9.0.

Psychrophiles

0°C to 20°C

Mesophiles

20°C to 45°C (most pathogens)

Thermophiles

> 45°C

Osmotic Pressure

Importance in food preservation; most bacteria inhibited in >1% salt. Exception: Halophiles require high salt.

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Sterilization

Eliminates all microbes.

Disinfection

Reduces microbial load, not complete kill.

Antiseptics

Reduce microbial growth on living tissues.

Bactericidal

kills bacteria

Bacteriostatic

inhibits bacterial growth

Streak Plating

Technique for isolating colonies from mixed cultures.

Gram Staining Reagents

Crystal Violet (purple), Iodine (fixes dye), Alcohol (decolorizer), Safranin (counterstain).

Gram Staining Results

Positive (purple) or Negative (pink) based on cell wall structure.

Streptococcus pyogenes

strep throat, scarlet fever

Streptococcus pneumoniae

pneumonia

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Staphylococcus aureus

Boils, carbuncles, pneumonia, and septicemia

Escherichia coli

urinary tract infection

Pseudomonas aeruginosa

Respiratory and urogenital infections

Neisseria gonorrhea

gonorrhea

Normal Flora

Beneficial bacteria that prevent pathogenic colonization.

Pathogen Acquisition

Aerosols, contact, ingestion, and vectors.

Catalase Test

Distinguishes staphylococci from streptococci.

Coagulase Test

Positive in "Staphylococcus aureus"

Oxidase Test

Differentiates "Pseudomonas" from "Enterobacteriaceae".

Monotrichous flagella

single flagellum

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Lophotrichous Flagella

tuft of flagella at one end of the cell

Peritrichous flagella

flagella all over the cell

Amphitrichous flagella

flagella at both ends

Atrichous flagella

no flagella