Characteristics of Microorganisms (Weeks 2-4)

Q: What does bacterial morphology refer to?

A: Cell shape and arrangement determined by the cell wall.

Q: What is a rod-shaped bacterium called?

A: Bacillus (plural: bacilli).

Q: What is a spherical or round bacterium called?

A: Coccus (plural: cocci).

Q: What is a curved rod-shaped bacterium called?

A: Vibrio (plural: vibrios).

Q: What is a rigid wave-shaped bacterium called?

A: Spirillum (plural: spirilla).

Q: What is a flexible wave-shaped bacterium called?

A: Spirochete (plural: spirochetes).

Q: What is a pair of cocci called?

A: Diplococcus.

Q: What is a chain of cocci called?

A: Streptococcus.

Q: What is a grape-like cluster of cocci called?

A: Staphylococcus.

Q: What are the three major staining techniques used to visualize bacteria?

A: Simple stain, Gram stain, and Acid-fast stain.

Q: What does a simple stain do?

A: Stains all bacteria the same color.

Q: What is the most common dye used in a simple stain?

A: Crystal violet.

Q: What does a Gram stain differentiate?

A: The type of cell wall.

Q: What color do Gram-positive bacteria appear after a Gram stain?

A: Purple.

Q: What colour do Gram-negative bacteria appear after a Gram stain?

A: Red.

Q: What is iodine used for in a Gram stain?

A: It acts as a mordant, causing crystal violet to stick to the bacteria.

Q: What is safranin used for in a Gram stain?

A: It is a red stain that colors Gram-negative bacteria.

Q: What is the difference between Gram-positive and Gram-negative bacteria in terms of cell wall thickness?

A: Gram-positive bacteria have a thick cell wall, while Gram-negative bacteria have a thin cell wall.

Q: What is the acid-fast stain used for?

A: Identifying mycobacteria, such as those causing tuberculosis.

Q: How is the acid-fast stain different from the Gram stain?

A: The red stain is used first, and acid/alcohol is used to wash the first stain.

Q: What color do mycobacteria appear after an acid-fast stain?

A: Red, indicating a waxy cell wall.

Q: What is the role of ribosomes in bacteria?

A: They make proteins, and some antibiotics attack them.

Q: What is the glycocalyx composed of?

A: A sticky layer of polysaccharides and small proteins.

Q: What are the roles of the glycocalyx?

A: Protection, adhesion, and water balance.

Q: Which types of bacteria commonly have a glycocalyx?

A: Many rod-shaped and spherical bacteria, not spiral.

Q: Give an example of a bacterium with a glycocalyx and its associated disease.

A: Haemophilus influenzae, which causes meningitis.

Q: What is a thick and tightly bound glycocalyx called?

A: A capsule.

Q: What is a thin and flowing glycocalyx called?

A: A slime layer.

Q: Give an example of a bacterium with a slime layer and its associated infections.

A: Pseudomonas aeruginosa, which causes urinary and lung infections.

Q: What is a biofilm?

A: Colonies of glycocalyx-covered bacteria that form a film.

Q: What is the bacterial cell wall responsible for?

A: Cell shape and protection against osmotic pressure changes.

Q: What are the main components of a Gram-positive bacterial cell wall?

A: Peptidoglycan (protein and carbohydrate) and teichoic acid.

Q: What is teichoic acid and its role in Gram-positive bacteria?

A: A component made of phosphate and alcohol with a high negative charge, acting as an antigen.

Q: What are the main components of a Gram-negative bacterial cell wall?

A: Lipopolysaccharide (LPS), endotoxin, and a periplasmic region.

Q: What makes Gram-negative bacteria more difficult to kill?

A: Their multiple layers, including an outer membrane and a thin peptidoglycan layer.

Q: What are the key differences between Gram-positive and Gram-negative bacteria?

A: Thicker peptidoglycan, no outer membrane, and teichoic acid in Gram-positive; thinner peptidoglycan, outer membrane, and LPS in Gram-negative.

Q: What are the cytoplasmic contents of bacteria?

A: Ribosomes, inclusion bodies, a single chromosome, and plasmids.

Q: What are plasmids, and what is their significance?

A: Small circular pieces of bacterial DNA that can carry genes for antibiotic resistance, acting as 'emergency' genetic material.

Q: What are bacterial endospores, and when are they formed?

A: Dormant and resistant stages of specific bacterial cells formed when moisture or nutrient supply is low.

Q: What are some diseases caused by spore-forming bacteria?

A: Anthrax, tetanus, gas gangrene, botulism, and C. difficile.

Q: What are the two main types of bacterial appendages?

A: Flagella and pili.

Q: What is the function of flagella in bacteria?

A: The function of flagella in bacteria is to allow bacteria to move (motility).

Q: What are flagella made of?

A: Flagella are made of rigid protein subunits called flagellin.

Q: How do bacteria move by ‘chemotaxis’?

A: Bacteria move by ‘chemotaxis’ by moving towards favorable conditions and away from unfavorable conditions.

Q: How do bacteria behave in unfavorable vs. favorable conditions?

A: In unfavorable conditions, bacteria have long tumbles and short runs; in favorable conditions, they have short tumbles and long runs.

Q: What happens when bacteria move clockwise versus counterclockwise?

A: When bacteria move clockwise, they tumble; when they move counterclockwise, they run.

Q: What are pili and what are they made of?

A: Pili are short, hair-like appendages made of a protein called pilin.

Q: What functions do pili perform in bacteria?

A: Pili help bacteria attach to other bacteria and surfaces, and transfer genetic material to another bacterial cell.

Q: What is the function of 'fimbriae'?

A: Fimbriae are sticky pili that help bacteria attach to surfaces or other cells.

Q: What is the process of conjugation in bacteria?

A: Conjugation is the process by which sex pili transfer DNA from one bacterium to another, specifically plasmids.

Q: How might superbugs have evolved in relation to pili?

A: Superbugs may have evolved due to bacteria sharing genetic information through pili, which allowed them to adapt and develop resistance.

Q: What is binary fission in bacteria?

A: Binary fission is a process where bacteria split apart, resulting in exponential growth (e.g., 2 to 4 to 8, etc.).

Q: How does bacterial reproduction differ from mitosis?

A: Bacterial reproduction through binary fission is a less complex process than mitosis.

Q: How fast do bacteria typically reproduce?

A: Bacteria generally reproduce at a rapid rate, typically between 20 minutes to 30 hours.

Q: What is the generation (doubling) time for bacteria?

A: The generation (doubling) time is the time, in minutes, for a population of bacteria to double.

Q: Describe the stages of the bacterial growth curve.

A: The bacterial growth curve consists of the lag phase (small growth), exponential/logarithmic phase (population explodes), stationary phase (growth stabilizes), and death phase (decline in population).

Q: What happens during the lag phase of bacterial growth?

A: During the lag phase, there is a small number of bacteria growing and not much dying.

Q: What is exponential or logarithmic growth in bacteria?

A: Exponential or logarithmic growth is when the bacterial population increases rapidly, such as from 1 E. coli to 1 billion in 10 hours under ideal conditions.

Q: What temperature range is optimal for pathogen growth?

A: Pathogens grow best between 35℃ to 42℃.

Q: What is the optimal pH range for bacterial growth?

A: Bacteria usually grow best between a pH of 7.0 to 7.5.

Q: At what temperatures do psychrophiles, mesophiles, and thermophiles grow?

A: Psychrophiles grow at 0 - 20℃, mesophiles grow at 20-40℃, and thermophiles grow at 40 - 90℃.

Q: Why does body temperature increase during bacterial infections?

A: Body temperature goes up to slow the growth of bacterial infections.

Q: What are aerobes and anaerobes in bacteria?

A: Aerobes are bacteria that breathe oxygen, while anaerobes are bacteria that do not breathe oxygen.

Q: Why is oxygen both beneficial and harmful to bacteria?

A: Oxygen is an excellent energy-converting molecule but generates toxic oxygen-free radicals. Aerobic bacteria must break down free radicals or die.

Q: What is the difference between obligate aerobes and obligate anaerobes?

A: Obligate aerobes require oxygen for life (e.g., Tuberculosis), while obligate anaerobes cannot grow in oxygen and will die if exposed (e.g., Tetanus).

Q: What are facultative anaerobes/aerobes?

A: Facultative anaerobes/aerobes can live with or without oxygen (e.g., E. coli).

Q: What are microaerophiles?

A: Microaerophiles require a small amount of oxygen, but too much oxygen is toxic to them (e.g., mucus bacteria causing oral/digestive diseases).

Q: What do bacteria need for growth, and what are the different nutritional patterns?

A: Bacteria need water and food. The different nutritional patterns are autotrophs (make their own food), heterotrophs (need food from outside sources), saprobes (eat dead organisms), and parasites (eat live organisms).

Q: What are pathogens, and what do they do?

A: Pathogens are bacteria that cause disease.

Q: How is agar used in bacterial cultivation?

A: Agar, a polysaccharide from marine red algae, provides a semi-solid surface for bacterial growth. Agar powder is added to nutrients, heated to dissolve, and poured to solidify below 36℃.

Q: What is complex media, and what does it include?

A: Complex media includes beef extract, peptone, and sodium chloride. It allows most bacteria to grow well (0.5% sodium chloride).

Q: What is selective media, and give an example?

A: Selective media selects the environment it wants to grow in. Example: high salt agar (7.5% instead of 0.5%), which Staphylococci grow well in.

Q: What is differential media, and give an example?

A: Differential media allows many bacteria to grow but they grow differently in different media. Example: blood agar, differentiates between Staphylococcus aureus/epidermidis and Streptococcus pyogenes.

Q: What is combined selective and differential media, and give an example?

A: Combined selective and differential media includes ingredients for both selecting and differentiating bacteria. Example: Mannitol salt agar with phenol red (pH indicator).

Q: If a wound swab grows bacteria in high salt and the bacteria turn yellow on mannitol salt agar, which bacteria is the patient likely infected with?

A: Staphylococcus aureus. The staphylococccus bacterium grows in high salt and the yellow colour comes from the aureus.

Q: If a wound swab grows bacteria in high salt and the mannitol salt agar remains red, which bacteria is the patient likely infected with?

A: Staphylococcus epidermidis. The staphylococccus bacterium grows in high salt and the red colour comes from the epidermidis.

Q: If a sore throat swab grows bacteria on blood agar and the bacterium turns yellow, which bacteria is the patient likely infected with?

A: Streptococcus pyogenes.

Q: How does turbidity measure bacterial cell number?

A: Turbidity measures bacterial cell number by shining light through a beaker. More cells block more light, and cell count is based on light scatter. It does not indicate if the cells are alive.

Q: What is direct microscope count, and what is its limitation?

A: Direct microscope count involves multiplying the counted cells. It does not indicate if the cells are alive.

Q: What is the standard plate method, and what does it determine?

A: The standard plate method determines CFUs (colony-forming units). It involves drawing a line, counting along the line, and multiplying using equations. It indicates if the cells are alive.

Q: What are the streak plate and pour plate methods?

A: The streak plate method spreads bacteria to isolate colonies, while the pour plate method involves mixing bacteria with liquid agar to isolate colonies.