Microbiology: Bacteria and Pathogens Flashcards

Question 1

Define Gram Stain.

Accepted Answer

A differential staining technique that sorts most bacteria into two groups by how their cell wall holds the crystal violet dye after an alcohol wash, guiding early identification.

Question 2

What is Gram-Positive?

Accepted Answer

A bacterium whose thick peptidoglycan layer traps the crystal violet–iodine complex during decolorization, so the cell appears purple under the microscope after Gram staining.

Question 3

What is Gram-Negative?

Accepted Answer

A bacterium with a thin peptidoglycan layer sandwiched under an outer membrane, so alcohol strips the crystal violet and the safranin counterstain leaves it pink or red.

Question 4

What is Peptidoglycan?

Accepted Answer

The mesh-like polymer of sugar chains cross-linked by short peptides that forms the bacterial cell wall, giving the cell its shape and resistance to bursting under osmotic pressure.

Question 5

Define Lipopolysaccharide (LPS).

Accepted Answer

The large molecule making up the outer membrane of gram-negative bacteria, whose toxic lipid A portion is the endotoxin that triggers fever and shock when the cell dies.

Question 6

What is Coccus?

Accepted Answer

A bacterium with a spherical or roughly round shape, named for the arrangement it forms after division, such as pairs, chains, or grape-like clusters.

Question 7

Define Bacillus (Rod).

Accepted Answer

A bacterium with an elongated rod or cylinder shape, in contrast to spherical cocci, and one of the basic morphologies reported on a Gram stain.

Question 8

What is Spirochete?

Accepted Answer

A slender, spiral or corkscrew-shaped bacterium that moves by internal axial filaments running along its length, producing a distinctive twisting motility hard to see on a standard Gram stain.

Question 9

What is Endospore?

Accepted Answer

A dormant, tough survival structure that certain gram-positive bacteria form inside themselves, resisting heat, drying, and disinfectants until conditions improve and the cell resumes growing.

Question 10

What is Capsule?

Accepted Answer

A sticky outer layer, usually of polysaccharide, surrounding some bacteria that resists being engulfed by immune cells, making it a major virulence factor rather than a structural essential.

Question 11

What is Flagellum?

Accepted Answer

A long, whip-like protein appendage that rotates to propel a bacterium through liquid, giving it directed motility toward nutrients or away from harm.

Question 12

Define Pilus (Fimbria).

Accepted Answer

A short hair-like surface projection that lets a bacterium stick to host cells or surfaces; a specialized longer sex pilus instead pulls two cells together for gene transfer.

Question 13

Define Obligate Aerobe.

Accepted Answer

A bacterium that requires oxygen to grow because it depends on aerobic respiration and cannot generate enough energy without it.

Question 14

Define Obligate Anaerobe.

Accepted Answer

A bacterium that grows only without oxygen, because oxygen produces toxic byproducts it lacks the enzymes to neutralize, so exposure to air kills it.

Question 15

Define Facultative Anaerobe.

Accepted Answer

A bacterium that uses oxygen for respiration when it is present but can switch to fermentation and grow without it, thriving across a wide range of conditions.

Question 16

What is Catalase?

Accepted Answer

A bacterial enzyme that breaks hydrogen peroxide into water and oxygen; the bubbling test using it separates the staphylococci, which are positive, from the streptococci, which are negative.

Question 17

What is Coagulase?

Accepted Answer

An enzyme that clots blood plasma; the test for it identifies Staphylococcus aureus, which is positive, and separates it from the coagulase-negative staphylococci like S. epidermidis.

Question 18

Define Acid-Fast Stain.

Accepted Answer

A staining method for bacteria whose waxy mycolic-acid cell wall resists ordinary dyes; these organisms hold the red carbol fuchsin even after an acid-alcohol wash.

Question 19

What is Exotoxin?

Accepted Answer

A toxic protein actively secreted by living bacteria, often highly potent and targeted at a specific tissue, and frequently the direct cause of a disease's symptoms.

Question 20

What is Endotoxin?

Accepted Answer

The lipid A part of gram-negative lipopolysaccharide, a toxin released when the cell wall breaks apart, provoking fever, inflammation, and in large amounts life-threatening shock.

Question 21

Define Virulence Factor.

Accepted Answer

Any bacterial trait or molecule, such as a capsule, toxin, or adhesin, that helps an organism colonize a host, evade defenses, or cause damage and thereby produce disease.

Question 22

What is Pathogen?

Accepted Answer

A microorganism capable of causing disease in a host, distinguished from the harmless or beneficial microbes that make up most of the microbial world.

Question 23

Define Normal Flora (Microbiota).

Accepted Answer

The community of microorganisms that routinely live on and inside a healthy body without causing harm, often competing with pathogens and aiding functions like digestion.

Question 24

Define Opportunistic Pathogen.

Accepted Answer

A microbe that is usually harmless but causes disease when it reaches an unusual site or when a host's defenses are weakened by illness, injury, or immune suppression.

Question 25

What is Zoonosis?

Accepted Answer

An infectious disease that spreads from animals to humans, whether by direct contact, bites, contaminated food, or an insect vector carrying the organism between species.

Question 26

Define Nosocomial Infection.

Accepted Answer

An infection acquired in a healthcare setting during treatment for another condition, also called a hospital-acquired infection, often involving drug-resistant organisms and devices like catheters.

Question 27

Define Staphylococcus Aureus.

Accepted Answer

A gram-positive coccus growing in grape-like clusters that is catalase-positive and coagulase-positive, causing skin abscesses, food poisoning, and more serious bloodstream and heart-valve infections.

Question 28

Define Streptococcus Pyogenes.

Accepted Answer

A gram-positive coccus arranged in chains, the Group A beta-hemolytic streptococcus, responsible for strep throat, impetigo, scarlet fever, and post-infectious rheumatic fever.

Question 29

Define Streptococcus Pneumoniae.

Accepted Answer

A gram-positive, lancet-shaped diplococcus with a protective polysaccharide capsule, the most common cause of community-acquired pneumonia and a frequent cause of meningitis and ear infections.

Question 30

Define Escherichia Coli.

Accepted Answer

A gram-negative rod and facultative anaerobe that is a normal gut resident, yet the leading cause of urinary tract infections and, in certain strains, foodborne illness.

Question 31

Define Mycobacterium Tuberculosis.

Accepted Answer

A slow-growing, acid-fast bacterium with a waxy mycolic-acid wall that causes tuberculosis, spreading through inhaled droplets and typically attacking the lungs.

Question 32

Define Clostridioides Difficile.

Accepted Answer

A gram-positive, spore-forming, obligate anaerobe that overgrows the colon after antibiotics wipe out normal flora, producing toxins that cause severe diarrhea and pseudomembranous colitis.

Question 33

Define Helicobacter Pylori.

Accepted Answer

A curved, helical gram-negative bacterium that colonizes the stomach lining and produces urease to neutralize acid, and is the main cause of peptic ulcers and chronic gastritis.

Question 34

What is MRSA?

Accepted Answer

Methicillin-resistant Staphylococcus aureus, a strain carrying the mecA gene that makes it resistant to methicillin and most beta-lactam antibiotics, complicating treatment of its infections.