Microbiology: Growth, Structure, Control, and Antimicrobials

Comprehensive vocabulary flashcards covering microbial control (physical and chemical), growth phases, bacterial structures and taxonomy, and antimicrobial pharmacology.

Sterilization

The treatment of an object or material to ensure the complete destruction of all living microbes, spores, and viruses.

Microbicidals

Agents that kill microbes; also commonly referred to as germicidals.

Commercial Sterilization

The process of eliminating all pathogens in a product, particularly within the food supply.

Sanitization

The practice of reducing pathogen numbers or discouraging their growth on an object without achieving full sterilization.

Thermal Death Point (TDP)

The minimum temperature required to kill a specific microbial species within a designated time period.

Thermal Death Time

The time required to kill a given microbial species at a specific temperature.

Autoclave

A sterilization apparatus using pressurized steam, typically operated at $15\,psi$ at $121^\circ\text{C}$ for 15–30 minutes to destroy bacteria and endospores.

Holding Pasteurization (LTLT)

A pasteurization method where milk is heated to $63^\circ\text{C}$ ($145^\circ\text{F}$) and held for $30\,min$.

Flash Pasteurization (HTST)

High-Temperature Short-Time pasteurization where milk is heated to $72^\circ\text{C}$ ($161^\circ\text{F}$) for $15\,sec$.

Ultra-High-Temperature (UHT) Sterilization

A process heating milk to $135\text{--}150^\circ\text{C}$ ($275\text{--}302^\circ\text{F}$) for $1\text{--}4\,sec$ to produce a nearly sterile, shelf-stable product.

HEPA Filter

High-Efficiency Particulate Air filter designed to trap microorganisms and sterilize air.

Lyophilization

Also called freeze drying; a process where food is frozen with liquid nitrogen and subjected to a vacuum pump to draw off water.

Antiseptics

Chemical agents used to destroy or inhibit pathogens on living body tissue.

Disinfectants

Chemical agents used on inanimate surfaces to reduce or eliminate pathogenic microbes.

Degerming

The mechanical removal of microorganisms from an object's or skin's surface.

Phenol Coefficient (PC)

A numeric score indicating the relative disinfecting efficacy of a chemical agent compared to phenol under identical laboratory conditions.

Disk Diffusion Method

An assay evaluating the effectiveness of chemical agents or antibiotics against bacteria by measuring zones of inhibition around chemical-soaked paper disks.

Quaternary Ammonium Compounds (Quats)

Cationic detergents that react with cell membranes to destroy certain bacteria and viruses.

Binary Fission

An asexual reproduction process in prokaryotes where a cell doubles in mass, replicates its DNA, forms a transverse septum, and splits into two identical daughter cells.

Generation Time

The doubling time interval required between successive binary fissions in a microbial population.

Lag Phase

The initial period in a bacterial growth curve where cells adapt to their environment without actively dividing.

Log (Exponential Growth) Phase

The period of exponential population growth in a bacterial culture during which human disease symptoms usually manifest.

Stationary Phase

The growth phase where cell reproductive rates equalize with cell death rates due to nutrient limits.

Decline Phase

The exponential death phase of a bacterial population caused by waste accumulation and scarcity of resources.

Bacterial Growth Curve

A graph depicting the 4 distinct phases of a bacterial population over time: lag, log, stationary, and decline phases.

Endospores

Highly resistant, dormant survival structures produced by species of Bacillus and Clostridium in response to nutrient limitation.

Dipicolinic Acid

A organic acid complexed with Calcium ($Ca^{2+}$) in the endospore core that stabilizes DNA and proteins and helps dehydrate the spore.

Endospore Structure

A multilayered spore consisting of an exosporium, spore coat, cortex, core wall, and a core containing condensed DNA, ribosomes, and dipicolinic acid.

Psychrophiles

Prokaryotes that grow optimally at cold temperatures below $15^\circ\text{C}$.

Mesophiles

Microorganisms that thrive at moderate temperatures between $10^\circ\text{C}$ and $45^\circ\text{C}$, including human body pathogens.

Thermophiles

Prokaryotes that multiply best at high temperatures around $60^\circ\text{C}$.

Hyperthermophiles

Extreme Archaea that grow optimally at temperatures above $80^\circ\text{C}$.

Obligate Aerobes

Organisms that strictly require oxygen for growth and survival.

Obligate Anaerobes

Organisms that are killed or inhibited by the presence of oxygen.

Facultative Prokaryotes

Microbes that can grow either in the presence of oxygen or in its absence.

Acidophiles

Acid-tolerant prokaryotes that grow optimally below $\text{pH } 6$.

Halophiles

Salt-tolerant or salt-requiring prokaryotic organisms.

Complex Medium

A culture medium containing chemically unidentified nutrients, such as peptone or beef extract.

Synthetic Medium

A growth medium in which the exact chemical formula and amount of every constituent is known.

Selective Medium

A growth medium formulated with components that inhibit specific microbes while permitting others to grow.

Differential Medium

A culture medium designed with specific chemical indicators to visually distinguish species based on biochemical features.

Proteobacteria

The largest and most diverse bacterial phylum, including E. coli and many human pathogens.

Firmicutes

A phylum comprising major Gram-positive bacterial genera such as Bacillus, Clostridium, Staphylococcus, and Streptococcus.

Actinobacteria

A Gram-positive bacterial phylum that includes Streptomyces, the producer of the antibiotic streptomycin.

Cyanobacteria

Photosynthetic prokaryotes that produce oxygen using chlorophyll, key to early atmospheric oxygenation.

Chlamydiae

A phylum of extremely small, obligate intracellular pathogenic bacteria.

Euryarchaeota

A phylum of Archaea containing methanogens, extreme halophiles, and thermoacidophiles.

Crenarchaeota

A phylum of Archaea that inhabit hot, acidic environments like hot springs and volcanic vents.

Bacterial Shapes

The primary morphological forms of bacteria: spheres (cocci), rods (bacilli), and spirals (vibrios, spirilla, spirochetes).

Prokaryotic Cell Structure

An overview of bacterial cellular organization including cytoplasm, nucleoid, ribosomes, inclusions, plasmids, cell membrane, cell wall, glycocalyx, pili, and flagella.

Pili (Fimbriae)

Thin protein fibers made of pilin and adhesins that extend from the bacterial surface to facilitate attachment to tissues and surfaces.

Conjugation Pili

Specialized protein tubes (sex pili) that bridge two bacterial cells to allow transfer of genetic material such as plasmids.

Flagella

Long, helical appendages composed of flagellin protein, a hook, and a rotating basal body that provide cell motility.

Endoflagella

Axial filaments in spirochetes situated between the peptidoglycan layer and outer membrane that rotate to exert torsional movement.

Glycocalyx

An outer polysaccharide layer external to the cell wall that functions as a virulence factor, preventing phagocytosis and dehydration.

Capsule

A thick, bound polysaccharide layer of glycocalyx that tightly coats the bacterial cell wall.

Peptidoglycan

The main carbohydrate-protein structural component of bacterial cell walls, consisting of alternating NAG and NAM units cross-linked by tetrapeptides.

Teichoic Acid

An essential acidic polymer found in the thick peptidoglycan layer of Gram-positive cell walls; absent in Gram-negative bacteria.

Endotoxin (Lipid A)

The toxic lipid component of lipopolysaccharide (LPS) present in the outer membrane of Gram-negative bacteria.

Plasmids

Small, extrachromosomal circular DNA molecules carrying nonessential genes that can code for antibiotic resistance or virulence factors.

Metachromatic Granules

Polyphosphate inclusion bodies located in the cytoplasm of bacteria like Corynebacterium diphtheriae that store inorganic phosphate.

Selective Toxicity

The property of an antimicrobial agent to harm or kill a target pathogen without causing significant toxicity to the host.

Chemotherapeutic Index

The ratio evaluating drug safety, defined as $\text{Chemotherapeutic Index} = \frac{\text{Toxic dose}}{\text{Therapeutic dose}}$.

Broad-Spectrum Antibiotics

Drugs effective against a wide range of microbial groups, including both Gram-positive and Gram-negative species.

Narrow-Spectrum Antibiotics

Antimicrobials that target only a limited, specific group of pathogenic bacteria.

Major Antibacterial Targets

The six primary cellular targets for antibacterial drugs: cell wall synthesis, cell membrane function, ribosome/translation, nucleic acid synthesis, DNA precursor synthesis, and RNA transcription.

Sulfonamides

Synthetic antimetabolite drugs that competitively inhibit bacterial folic acid synthesis by structural analogy to para-aminobenzoic acid (PABA).

Beta-Lactam Antibiotics

A large class of cell wall synthesis inhibitors containing a beta-lactam ring, including penicillins, cephalosporins, carbapenems, and monobactams.

Beta-Lactamase

A bacterial enzyme that inactivates beta-lactam antibiotics by hydrolyzing and opening the beta-lactam ring.

Vancomycin

A glycopeptide antibiotic of last resort targeting Gram-positive cell wall synthesis, commonly used to treat MRSA.

Bacitracin

A polypeptide antibiotic produced by Bacillus subtilis that blocks cell wall precursor transport by inhibiting bactoprenol dephosphorylation; toxic internally.

Polymyxin B

A polypeptide antibiotic produced by Bacillus polymyxa that damages Gram-negative cell membranes; restricted to topical applications due to kidney toxicity.

Ribosomal Target Antibiotics

Antibacterial agents that selectively inhibit protein synthesis by binding to either the bacterial 30S subunit (aminoglycosides, tetracyclines) or 50S subunit (chloramphenicol, macrolides, lincosamides).

Aminoglycosides

Antibiotics such as streptomycin and gentamicin that attach to the 30S ribosomal subunit, causing mRNA misreading.

Tetracyclines

Broad-spectrum antibiotics targeting the 30S subunit to block tRNA attachment; side effects include tooth discoloration and bone growth stunting.

Macrolides

Antibiotics like erythromycin and azithromycin that bind to the 50S subunit to inhibit polypeptide elongation.

Chloramphenicol

A broad-spectrum antibiotic inhibiting peptide bond formation on the 50S subunit; can induce aplastic anemia and Gray syndrome.

Quinolones

Synthetic drugs like ciprofloxacin that inhibit bacterial DNA replication by blocking topoisomerase/gyrase activity.

Rifampin

An antibacterial drug that inhibits transcription by binding to bacterial RNA polymerase; key in treating tuberculosis.

Minimum Inhibitory Concentration (MIC)

The lowest concentration of an antimicrobial agent that prevents visible growth of a bacterium in vitro.

Superinfection

An opportunistic secondary infection occurring when antibiotic therapy destroys normal microbiota, enabling resistant pathogens to proliferate.