study guide 1 exam2

micro 150

What is sterilization?

Complete destruction of all microbial life, including endospores.

What is disinfection?

Destruction of most vegetative cells, but not endospores.

What is antisepsis?

Reduction of microbial count on living tissue such as skin or mucous membranes.

What is sanitization or decontamination?

Reduction of microbial population to safe levels on objects or surfaces.

List microbes from most to least resistant.

Prions → Bacterial endospores → Mycobacteria → Protozoan cysts → Vegetative protozoa → Gram-negative bacteria → Fungi → Gram-positive bacteria → Non-enveloped viruses → Enveloped viruses.

What are the four phases of the bacterial growth curve?

Lag phase, Log (exponential) phase, Stationary phase, and Death phase.

What happens during the lag phase?

Bacteria adjust to the new environment; no rapid division yet.

What happens during the log phase?

Cells divide rapidly and growth increases exponentially.

What happens during the stationary phase?

Growth rate equals death rate; nutrients start depleting.

What happens during the death phase?

Bacteria die due to lack of nutrients and toxin buildup.

What are the main physical methods of microbial control?

Moist heat (autoclave), dry heat, pasteurization, filtration, and radiation.

What are the sterilization conditions for an autoclave?

121°C for 15 minutes under pressure.

What temperature and time are used for pasteurization?

72°C for 15 seconds.

What is the purpose of ultra-high temperature (UHT) pasteurization?

Kills microbes for long shelf life (140°C for 1 second).

What does UV radiation do to DNA?

Causes thymine dimers that lead to mutations and replication errors.

Name the most effective alcohol concentration for killing bacteria.

70% alcohol — it denatures proteins and dissolves lipids.

What does 3% hydrogen peroxide do?

Acts as a mild antiseptic for wounds but not for sterilization.

What is glutaraldehyde used for?

As a high-level disinfectant or sterilant for medical equipment.

Why does bleach kill microbes effectively?

It denatures proteins and destroys cell membranes (10% bleach = sterilizing).

What is chlorhexidine gluconate (Peridex) used for?

As an oral antiseptic in mouthwashes to kill bacteria.

What is the function of silver sulfadiazine?

Used to prevent infection on burn wounds.

How do high salt or high sugar levels preserve food?

They create a hypertonic environment causing plasmolysis (water leaves cells).

What are the main oxygen categories for bacteria?

Obligate aerobe, obligate anaerobe, facultative anaerobe, microaerophile, and aerotolerant anaerobe.

What does an obligate aerobe require?

Oxygen for growth.

What happens to obligate anaerobes in oxygen?

They die because oxygen is toxic to them.

What are facultative anaerobes?

Bacteria that grow with or without oxygen but prefer oxygen.

What is a microaerophile?

Organisms that need only small amounts of oxygen.

What are aerotolerant anaerobes?

Organisms that tolerate oxygen but do not use it for metabolism.

What enzyme converts superoxide radicals to hydrogen peroxide?

Superoxide dismutase (SOD).

What enzyme breaks hydrogen peroxide into water and oxygen?

Catalase.

List temperature classifications for bacteria.

Psychrophile (cold-loving), Psychrotroph (tolerates cold), Mesophile (body temp), Thermophile (hot), and Extreme thermophile (very hot).

What temperature range do psychrophiles prefer?

0°C, can grow below freezing.

What temperature range do psychrotrophs prefer?

10–20°C (refrigerator temperatures).

What temperature range do mesophiles prefer?

25–40°C (body temperature range).

What temperature range do thermophiles prefer?

65–70°C (hot springs).

What temperature range do extreme thermophiles prefer?

Above 100°C (boiling environments).

Describe the effects of hypotonic, isotonic, and hypertonic solutions on plant cells.

Hypotonic → turgid (healthy); Isotonic → flaccid; Hypertonic → plasmolyzed (shriveled).

Describe the effects of hypotonic, isotonic, and hypertonic solutions on animal cells.

Hypotonic → lysis (burst); Isotonic → normal; Hypertonic → shriveled.

What are the five main antibiotic categories?

Cell wall inhibitors, protein synthesis inhibitors, nucleic acid inhibitors, cell membrane disruptors, and folic acid inhibitors.

What do cell wall inhibitors target?

Peptidoglycan synthesis in bacterial cell walls.

Give examples of cell wall inhibitors.

Penicillins, cephalosporins, vancomycin, bacitracin, carbapenems, and monobactams.

What do protein synthesis inhibitors target?

Bacterial ribosomes to stop protein production.

Give examples of protein synthesis inhibitors.

Aminoglycosides, tetracyclines, erythromycin, chloramphenicol, clindamycin.

What do nucleic acid inhibitors target?

Enzymes involved in DNA and RNA synthesis.

Give examples of nucleic acid inhibitors.

Rifampin (RNA) and Quinolones like ciprofloxacin (DNA).

What do cell membrane disruptors do?

Damage bacterial membranes causing leakage and death.

Give examples of cell membrane disruptors.

Polymyxin B and Daptomycin.

What do folic acid inhibitors do?

Block folate synthesis, preventing bacteria from making DNA.

Give examples of folic acid inhibitors.

Sulfonamides and Trimethoprim.

List common antifungal drug endings.

“-azole,” “-fungin,” “-statin” (e.g., fluconazole, caspofungin, nystatin).

What are three mechanisms bacteria use to resist antibiotics?

1. Destroy the drug with enzymes (β-lactamase) 2. Pump the drug out (efflux) 3. Change binding sites so the drug can’t attach.

What are the three methods of horizontal gene transfer in bacteria?

Transformation, Transduction, and Conjugation.

What happens in transformation?

Bacteria take up free DNA from the environment.

What happens in transduction?

A virus (bacteriophage) transfers DNA between bacteria.

What happens in conjugation?

DNA is transferred through direct contact via a pilus.

What does MRSA stand for and what is it resistant to?

Methicillin-resistant Staphylococcus aureus — resistant to methicillin and other penicillins.

What is MDR-TB resistant to?

Isoniazid and rifampin.

What is NDM-1 E. coli resistant to?

β-lactam antibiotics and carbapenems.

What drug resistance is seen in Plasmodium (malaria)?

Resistance to quinine, chloroquine, and artemisinin.

Why does high sugar or salt preserve food?

It creates a hypertonic environment, pulling water out of microbes (plasmolysis).