Microbiology - Bacteria, Gram-Positives

Front 1

Describe the 5 steps of a gram stain:

Back 1

For any stain you must first smear the substance to be stained onto a slide and then heat it to fix the bacteria on the slide

Gram stain:

1) Pour on crystal violet stain, wait 60s

2) Wash off with water and flood with iodine solution, wait 60 s

3) Wash off with water and "decolorize" with 95% alcohol

4) Counter-stain with safranin (red), wait 30s

5) Wash off with water

Front 2

What colour do Gram-positive bacteria stain?

Back 2

Blue (crystal violet)

Front 3

What colour do Gram-negative bacteria stain?

Back 3

Red (safranin)

Front 4

What's another name for transpeptidase?

Back 4

Penicillin-binding protein

Front 5

Which kind of bacteria has teichoic acid in its cell wall?

Why is this polysaccharide important?

Back 5

Gram positive bacteria have teichoic acid in their peptidoglycan layer (cell wall).

Teichoic acid is important in that it acts as an antigenic determinant and is thus important for serologic identification of many gram-positive species

Front 6

Gram-positive bacteria have which important polysaccharide in their cell wall?

Back 6

Teichoic acid, which acts as an antigenic determinant

Front 7

"Cell wall" means what?

Back 7

In bacteria, "cell wall" refers to the peptidoglycan layer just outside the lipid membrane in both gram-positive and gram-negative bacteria.

Front 8

Describe the cell wall of gram-positive bacteria:

Back 8

The cell wall of gram-positive bacteria consists of a single layer: the peptidoglycan layer. The peptidoglycan layer in gram-positive bacteria is very thick, with extensive cross-linking of the amino-acid side chains.

The peptidoglycan layer of gram-positives contains the antigenic determinant teichoic acid.

Front 9

Describe the cell wall of gram-negative bacteria:

Back 9

From inside to outside:

1) Cytoplasmic membrane (lipid bilayer)

2) Periplasmic space (gel containing proteins and enzymes)

3) Thin peptidoglycan layer (contains murein lipoprotein, does not contain teichoic acid)

4) Outer membrane (phospholipid bilayer containing lipopolysaccharide, LPS)

Front 10

Describe the differences between the peptidoglycan layer of gram-positive and gram-negative bacteria:

Back 10

The peptidoglycan layer of gram-positives is thick, with extensive cross-linking between the amino-acid side chains. It contains teichoic acid.

The peptidoglycan layer of gram-negatives is thin and does not contain teichoic acid but rather murein lipoprotein.

Front 11

In gram-negative bacteria, which layer lies just outside the lipid bilayer?

Back 11

The periplasmic space (followed by a thin, peptidoglycan layer)

Front 12

Name the molecule that attaches the peptidoglycan layer to the outer membrane of a gram-negative bacteria:

Back 12

Murein lipoprotein

Front 13

Describe the outer membrane of gram-negative bacteria:

Back 13

This outer membrane is a phospholipid bilayer similar to the cytoplasmic membrane (hydrophilic heads on the outside, hydrophobic tails on the inside).

The outermost part of this layer contains LPS

Front 14

Describe the components and structure of lipopolysaccharide (LPS):

Back 14

3 components:

Outer - O-specific side chain, or O-antigen

Core - lipoprotein core

Inner - lipid A, a potent endotoxin

Front 15

Which important molecule is contained in the outer membrane of gram-negative bacteria?

Back 15

Lipopolysaccharide (LPS)

Protein A, a component of LPS, is also known as endotoxin. It is released when these cells are lysed, causing disease.

Front 16

What is murein?

Back 16

Murein is another name for peptidoglycan.

Front 17

What is peptidoglycan?

Describe the structure of peptidoglycan.

Back 17

Peptidoglycan is a polymer of disaccharide sub-units. Each disaccharide unit contains an amino acid side chain, which are cross-linked together to form the polymer.

Front 18

Which enzyme is responsible for the cross-linking together of the amino acid side chains of the disaccharide units of peptidoglycan?

Back 18

Transpeptidase (penicillin-binding protein)

Front 19

Why do gram-positive bacteria stain blue while gram-negative bacteria stain red?

Back 19

Fundamentally this is due to structural differences in their cell walls.

It's the peptidoglycan layer of both cells that absorbs dye.

Gram-positives, with their thick peptidoglycan layers, absorb the crystal violet well. It does not wash off when the sample is washed with iodine and the bacteria stain blue accordingly.

When gram-negatives are first stained, however, the crystal blue is trapped in the outer membrane. This membrane is dissolved away, with the colour along with it, when the alcohol is added. The safranin that is later added thus reaches the peptidoglycan layer and the bacteria stain red.

Front 20

Name the 7 gram-positive bacteria that cause disease in humans (excluding mycobacteria):

Back 20

Gram-positive cocci:

Enterococcus
Streptococcus
Staphylococcus

Gram-positive bacilli:

Bacillus
Clostridium
Corynebacterium
Listeria

Front 21

Name 4 genera of gram-positive bacilli that cause disease in humans:

Back 21

Spore forming:
-Bacillus
-Clostridium

Non spore-forming:
-Corynebacterium
-Listeria

Front 22

Name 3 genera of Gram-positive cocci that cause disease in humans:

Back 22

Enterococci
Streptococci
Staphylococci

Front 23

Name the 4 principal bacterial shapes:

Back 23

1) Cocci (spherical)
2) Bacilli (rods)
3) Spiral shaped
4) Pleomorphic (lacking a distinct shape)

Front 24

Name three classes of disease-causing bacteria that are not visualized well with gram stain:

Back 24

Mycobacteria (weakly gram-positive)
-don't stain well, do better with acid-fast stain

Spirochetes (weakly gram-negative)
-too small for light microscope, require dark-field microscope

Mycoplasma
-no cell wall, don't stain

Front 25

Name the only spiral-shaped class of bacteria:

Back 25

The spirochetes are the only spiral shaped bacteria. They are gram-negative bacteria and include treponema, leptospira, and borrelia.

Front 26

Name a gram-negative coccus:

(Hint: there's only one)

Back 26

Neisseria

Front 27

Name three spirochetes:

Back 27

Treponema (syphilis)
Borrelia (Lyme disease)
Leptospira (leptospirosis)

Front 28

Are spirochetes gram-positive or gram-negative?

Back 28

Spirochetes are gram-negative.

Front 29

How is the genus Mycobacterium classified by Gram-stain and shape?

Back 29

Technically these are gram-positive bacilli. These bacteria stain better with the acid-fast staining technique, however.

Front 30

What is an obligate aerobe?

Name 1 obligate aerobic bacteria.

Back 30

Bacteria that require oxygen to make energy (make use of glycolysis, Krebs, and electron transport chain just like us).

Example: Bacillus cereus

Front 31

What are facultative anaerobes?

Back 31

Facultative anaerobes are aerobic bacteria that can, when they have to, grow in the absence of oxygen by fermentation.

Front 32

How do microaerophilic bacteria make energy?

Can they tolerate oxygenated environments?

Back 32

They use fermentation and have no electron transport system.

They can tolerate low amounts of oxygen because they possess superoxide dismutase

Front 33

When classifying bacteria by their ability to handle oxygen, what 4 major groups are there?

Back 33

1) Obligate aerobes
2) Facultative anaerobes
3) Microaerophilic bacteria
4) Obligate anaerobes

Front 34

What is the Group A streptococcus bacterium?

Back 34

Streptococcus pyogenes

Front 35

Which antigen is used to distinguish the many species of streptococci?

Back 35

Lancefield antigens (C carbohydrate)

Front 36

What does the "group A" in group A beta hemolytic streptococci refer to?

Back 36

Lancefield antigen group A

Front 37

What's the difference between alpha and beta hemolytic streptococci?

Back 37

Alpha-hemolytic streptococci only partially lyse RBCs on a blood agar plate, beta-hemolytics completely lyse the RBCs

Front 38

Name 2 important members of the Anginosus species group, also known as the Streptococcus milleri group

Back 38

Streptococcus anginosus

Streptococcus intermedius

Streptococcus constellatus

Front 39

Name 2 bugs of the genus Enterococcus that cause disease in humans:

Back 39

Enterococcus faecium

Enterococcus faecalis

Front 40

What does VRE stand for?

Back 40

Vancomycin resistant enterococci

Front 41

Broadly speaking, name the categories of streptococci as well as the important pathogenic streptococci that don't fit into those categories.

Back 41

Lancefield group A:
-Strep. pyogenes (beta-hemolytic)

Lancefield group B:
-Strep. agalactiae (beta-hemolytic)

Lancefield group D:
-Enterococci (E. faecalis, E. faecium)
-Non-enterocci (S. bovis, S. equinus)


Other:

Viridans group streptococci:
-includes Mitis group, Salivarious group, Mutans group, and Angiosus group

Strep. pneumoniae (no Lancefield antigen, alpha-hemolytic)

Front 42

Name the two subtypes of Lancefield group D streptococci:

Back 42

1) Enterococci (E. faecalis, E. faecium)

2) Non-enterococci (S. bovis, S. equinus)

Note that this is the historical classification. Enterococci are now considered their own genus.

Front 43

What is pneumococcus?

Back 43

Another name for Strep. pneumoniae

Front 44

Describe the Quellung reaction:

Back 44

When pneumococci on a lide smeare are mixed with a small amount of anti-serum and methylene blue, the capsule will appear to swell, allowing for rapid identification of the organism.

Front 45

Name 2 important lab tests to identify pneumococcus:

Back 45

Quellung reaction

Optochin sensitivity

Front 46

Name the bacterial species sensitive to Optochin:

Back 46

Strep. pneumoniae

Front 47

What is the function of the enzyme catalase?

Back 47

Catalase breaks down hydrogen peroxide (H202).

Front 48

Name an important enzyme that staphylococci possess that streptococci do not:

Back 48

Catalase

Front 49

How do staphylococci appear on Gram stain?

Back 49

Violet, grape-like clusters

Front 50

Which species of staphylococci is coagulase positive?

Back 50

Staph. aureus

Front 51

Name the three pathogenic species of staphylococci:

Back 51

1) Staph. aureus
2) Staph. saprophyticus
3) Staph. epidermidis

Front 52

Name the two coagulase-negative pathogenic staphylococci:

Back 52

Staph. saprophyticus
Staph. epidermidis

Front 53

What is the etymology of saprophyticus?

Back 53

From Greek for "putrid plant." A saprophyte, in biology, is an organism that attains energy from dead and decaying plants.

Front 54

What is an exotoxin?

Back 54

Exotoxins are substances excreted by microorganisms that cause disease.

Front 55

What is an enterotoxin?

Back 55

Enterotoxins are exotoxins that act on the GI tract. They cause symptoms of food poisoning and diarrhea.

Front 56

What is the difference between endotoxin and exotoxin?

Back 56

Endotoxin is lipid A, a component of the lipopolysaccharide (LPS) found in the outer membrane of Gram-negative bacteria.

It is not excreted from cells, like exotoxins, but rather a normal part of the outer membrane that sheds off during lysis, causing symptoms.

Front 57

Why might treating a patient who has a gram-negative infection with antibiotics actually worsen their symptoms?

Back 57

Gram-negative bacteria contain lipopolysaccharide (LPS) in their outer membranes. Protein A, a component of LPS, is a toxin known as endotoxin. This toxin is released when the bacterial cell lyses and can cause disease.

Front 58

What does MRSA stand for?

What is HA-MRSA?

CA-MRSA?

Back 58

Methicillin Resistant Staphylococcus aureus

OR

Multi-drug resistant Staph. aureus

HA-MRSA is hospital acquired MRSA

CA-MRSA is community acquired MRSA

Front 59

Which enzyme does Staph aureus possess that renders it immune to some penicillins?

Back 59

Penicillinase (a specific type of beta-lactamase)

Front 60

What does VRSA stand for?

Back 60

Vancomycin resistant Staph. aureus

Front 61

What are the two broad categories of gram-positive bacilli and the members of these categories?

Back 61

1) Spore-forming rods
-Bacillus
-Clostridium

2) Non spore-forming rods
-Corynebacterium
-Listeria

Front 62

What is an endospore?

Back 62

Endospores are not true spores in that they are not strictly reproductive structures but stripped-down, dormant versions of the bacteria themselves that bacteria reduce themselves to in nutrient-deficient environments.

Spores can reactivate later, when environmental conditions improve. They can even revive hundreds and some say up to millions of years later.

Front 63

Are bacteria of the genus Bacillus aerobic or anaerobic?

Back 63

Aerobic

Front 64

Are bacteria of the genus Clostridium aerobic or anaerobic?

Back 64

Anaerobic

Front 65

Name the two pathogenic species of the genus Bacillus

Back 65

Bacillus anthracis (anthrax)

Bacillus cereus (gastroenteritis)

Front 66

How is the genus Bacillus classified by Gram-stain and shape?

Back 66

Gram-positive rods (spore-forming)

Front 67

How is the genus Clostridium classified by Gram-stain and shape?

Back 67

Gram-positive bacilli (spore-forming)

Front 68

How is the genus Staphylococcus classified by Gram-stain and shape?

Back 68

Gram-positive cocci

Front 69

How is the genus Streptococcus classified by Gram-stain and shape?

Back 69

Gram-positive cocci

Front 70

How is the genus Enterococcus classified by Gram-stain and shape?

Back 70

Gram-positive cocci

Front 71

What is the neurotoxic exotoxin released by C. tetani called?

Back 71

Tetanospasmin

Front 72

Name 4 species of the genus Clostridium that cause disease in humans and the diseases they cause:

Back 72

1) C. botulinum
-Botulism

2) C. tetani
-Tetanus

3) C. perfringens
-Cellulitis, clostridial myonecrosis (gas gangrene), wound infections

4) C. dificile
-Pseudomembranous colitis

Front 73

Name two pathogenic species of the genus Bacillus:

Back 73

B. anthracis (anthrax)
B. cereus (food poisoning)

Front 74

How are chlamydia and rickettsia similar to viruses? What makes them different?

Back 74

Chlamydia and rickettsia are similar to viruses in that they are small obligate intracellular parasites. They use their host's ATP for energy and are thus energy parasites.

They differ from viruses in that they

Front 75

Name two obligate intracellular genera of bacteria:

Back 75

Chlamydia

Rickettsia

Front 76

Bacteria belonging to which genera are the only gram-negative cocci?

Back 76

Neisseria

They hang out in pairs and are, as such, called diplococci.

Front 77

What does NTM stand for?

Back 77

NTM stands for non-tuberculous mycobacteria.

Front 78

What colour do acid-fast bacteria stain?

Back 78

Red

Front 79

What is mycolic acid?

Back 79

Mycolic acid is a very large fatty acid that forms the backbone of mycosides, which are importante virulence factors for M. tuberculosis

Front 80

What are mycosides?

Back 80

Mycosides glycolipids composed of mycolic acid molecules bound to a carbohydrate molecules.

Mycosides such as cord factor, sulfatides, and Wax D are virulence factors for M. tuberculosis.

Front 81

What is cord factor?

Back 81

Cord factor is a mycoside formed by the union of 2 mycolic acid molecules with the disaccharide trehalose.

The presence of cord factor causes M. tuberculosis to appear to grow in cords.

Cord factor is a major virulence factor for M. tuberculosis.

Front 82

What are sulfatides?

How do they addo to M. tuberculosis virulence?

Back 82

Sulfatides are mycosides with sulfate groups attached to the carbohydrate (trehalose).

Sulfatides prevent phagosomes containing bacteria from fusing to the lysosomes that would degrade them, thus accounting for the factultative intracellular nature of early M. tuberculosis infection.

Front 83

What is the name of the large fatty acid found in mycosides?

Back 83

Mycolic acid

Front 84

What is Wax D?

Back 84

...

Front 85

What is the disaccharide in cord factor and sulfatides?

Back 85

Trehalose

Front 86

What's the name of the glycolipid molecule present in M. tuberculosis virulence factors?

Back 86

These molecules, which are fusions of mycolic acid and carbohydrates, are called mycosides.

Mycosides.

Front 87

What's anaerobic about anaerobic bacteria?

Back 87

It's not that there's something unique in the anaerobic environment that these bacteria need to survive, but rather that oxygen kills them so they need an environment without it to survive.

Why does oxygen kill these organisms?

Molecular oxygen is very reactive and can form hydrogen peroxide, superoxide radicals, and a hydroxyl radical. All of these are toxic and are broken down.

Anaerobic bacteria to varying degrees lack the enzymes responsible for breaking these reactive groups down.

Catalase breaks down hydrogen peroxide.

Peroxidase also breaks down hydrogen peroxide.

Superoxide dismutase breaks down the superoxide radical.

Front 88

If anaerobes, by definition, can't handle the presence of oxygen, how do they survive on, in, and around our bodies?

Back 88

Despite our constant immersion in air, anaerobes are able to colonize the many oxygen-deficient or oxygen-free microenvironments of the body. Often these are created by the presence of facultative organisms whose growth reduces oxygen and decreases the local oxidation-reduction potential. Such sites include the sebaceous glands of the skin, the gingival crevices of the gums, the lymphoid tissue of the throat, and the lumina of the intestinal and urogenital tracts.

Front 89

Describe the typical pathogenesis of anaerobic infection.

Back 89

The anaerobic flora normally lives in a harmless commensal relationship with the host. However, when displaced from their niche on the mucosal surface into normally sterile tissues, these organisms may cause life-threatening infections. This can occur as the result of trauma (eg, gunshot, surgery), disease (eg, diverticulosis), or isolated events (eg, aspiration).

In other words, normal flora sites are the origin of most infections.