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Immuno/Micro/Viro > Test 3-1 > Flashcards

Test 3-1 Flashcards

1
Q

Medical microbiology

A

is the study of the dynamic interaction between microbes and the human host. This interaction (or symbiosis) involves commensalism, mutualism and parasitism.

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2
Q

Normal flora

A

(microbiota) tend to be commensal or mutual symbionts adapted to the special conditions found in various body locations. Normal flora tend to avoid injuring the host, and are often beneficial to the host.

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3
Q

Pathogen:

A

any microorganism that has the capability to cause disease.

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4
Q

Virulence:

A

The ability of a microorganism to cause disease.

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5
Q

Virulence factor:

A

factors (e.g. toxins) produced by organisms that enable it to infect, cause disease, and/or kill the host.

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6
Q

Virus:

A

Smallest infectious particle (0.03- 0.3 µm). Viruses are obligate intracellular pathogens; they require a host cell for replication.

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7
Q

Bacterium:

A

Simple, unicellular, prokaryotes with no nuclear membrane, mitochondria, Golgi bodies or endoplasmic reticulum that reproduce by asexual division. 0.1- 10 µm.

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8
Q

Fungus:

A

More complex cellular structure, eukaryotic organism with well-defined nucleus, mitochondria, Golgi bodies and endoplasmic reticulum. Fungi exist as unicellular yeast or in filamentous forms (mold). Fungi replicate sexually and asexually. 4- 10 µm.

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9
Q

Parasite:

A

The most complex microbes. Eukaryotes that exist as single cellular (Leishmania) or multicellular (Shistosome). Wide range in size: tiny protozoa (4 µm) to multicellular worms (many meters long).

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10
Q

Eukaryotes characteristics

A

-Major groups: Algae, fungi, protozoa, plants animals -Size:≥4 µm -Cell wall: Absent or composed of chitin -Cell membrane: Contains sterols -Nucleus: Classic nuclear membrane -Chromosomes (DNA arrangement):Multiple strands of DNA with histones; diploid genome -Mitochondria: present -Golgi bodies: present -Endoplasmic reticulum: present -Reproduction: Sexual and asexual -Ribosomes: 80S (60S + 40S) -Respiration: Via mitochondria

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11
Q

Characteristics -Prokaryotes:

A

-Major groups bacteria -Size 0.1-10 µm -Cell wall Usually present, complex structure containing lipids, proteins and peptidoglycan -Cell membrane No sterols -Nucleus No nuclear membrane -Chromosomes (DNA arrangement) Single, circular DNA, lacks histones, haploid genome -Mitochondria absent -Golgi bodies absent -Endoplasmic reticulum absent -Reproduction Asexual (binary fission) -Ribosomes 70S (50S +30S) -Respiration Via cell membrane

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12
Q

Brightfield (light) microscopy-

A

the specimen is visualized by transillumination, with light passing up through the condenser to the specimen. The image is then magnified by the lenses. Three different objective lenses are commonly used (low power- 10X, high-dry- 40X, and oil immersion- 100X). You can visualize most bacteria, but not viruses, by light microscopy.

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13
Q

Darkfield microscopy-

A

The same objective and ocular lenses used in brightfield microscopes are used in darkfield microscopes. A special condenser is used that prevents transmitted light from directly illuminating the specimen. Only scattered light reaches the specimen and passes into the lens systems, which causes the specimen to be brightly illuminated against a black background. Resolving power is improved over brightfield and this allows you to visualize extremely thin bacteria (spirochetes).

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14
Q

Phase-contrast microscopy-

A

Enables the internal details of microbes to be examined. Parallel beams of light are passed through objects of different densities.

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15
Q

Fluorescent microscopy-

A

typically involves staining microorganisms with fluorescent dyes and examining with a specially designed fluorescent microscope. Organisms and specimens stained with fluorochromes appear brightly illuminated against a dark background.

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16
Q

Electron microscopy-

A

magnetic coils rather than lenses are used to direct a beam of electrons from a tungsten filament through a specimen and onto a screen. Because a much shorter wavelength of light is used, magnification and resolution are improved dramatically. Individual viral particles can be seen with electron microscopy.

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17
Q

Detection of bacterial antigens-

A

Bacterial antigens can be detected in patient specimens (blood, sputum, urine etc.) Antigens can take multiple forms such as toxins, membrane proteins, membrane carbohydrates etc. Identification is often done by immunoassay such as ELISA (enzyme-linked immunosorbent assay).

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18
Q

Detection of specific bacterial nucleic acids-

A

In large teaching hospitals and reference laboratories, many biochemical tests have been replaced recently with sequencing bacterial specific genes (16S rRNA gene) or proteomics. PCR (polymerase chain reaction) is used frequently to amplify and detect specific bacterial nucleic acid.

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19
Q

Culture-

A

Culture media can be divided into four general categories: (1) enriched nonselective media, (2) selective media, (3) differential media and (4) specialized media.

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20
Q

Nonselective media

A

1) Blood agar: Recovery of bacteria and fungi 2) Sabouraud dextrose agar: Recover of fungi

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21
Q

selective,differential media

A

1) MacConkey agar: Selective for Gram-negative bacteria; differential for lactose fermenting species. Bacteria that ferment lactose produce acid which causes a red color 2) Mannitol salt agar: selective for staphylococci, differential for S. aureus Staphylococci can grow in high salt and S. aureus can ferment mannitol, producing yellow-colored colonies on this agar 3) Lowenstein-Jensen and Middlebrook Selective for mycobacteria

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22
Q

specialized agar

A

1) Cystine-tellurite agar: Corynebacterium diphtheriae (black colonies) 2) Regan Lowe agar: Bordetella pertussis

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23
Q

Detection of antibody responses to bacteria (serology) -

A

the humoral immune response provides a history of a patient’s infections. The antibody type and titer, and the identity of the antigenic targets provide serologic data about an infection. Serologic testing is used to identify viruses and other agents that are difficult to isolate and grow in the lab (such as intracellular bacteria). Specific IgM antibody, found during the first 2 to 3 weeks of a primary infection, is a good indicator of a recent primary infection.

24
Q

Taxonomy- classification types

A
  1. Visible features: shape (rod, cocci, spirochete), presence of spores, Gram reaction—– a) coccus/cocci (circular) b) diplococcus (double circle) c) bacillus/bacilli ( rectangular) d) coccobaccilus/coccobacilli (oval) e) spirochete (swirly rods)
  2. Nutrition: growth media, oxygen utilization, optimal temperature
  3. End products: production of specific enzymes (e.g. urease), toxins (e.g. streptolysin O), metabolites
  4. Surface molecules: LPS, capsule, flagella, Lancefield antigens etc.
  5. More recent nucleic acid analysis is altering some of the current classification.
25
Q

The cell wall relationship to capsule

A

cell wall is internal to the capsule

26
Q

gram + characteristics

A

Outer membrane: -
Peptidoglycan layer: Thicker
Lipopolysaccharide: -
Teichoic acid: Often present
Sporulation: Some strains
Capsule: Sometimes present
Lysozyme: sensitive
Antibacterial activity of penicillin: More sensitive
Exotoxin production: Some strains

27
Q

gram - characteristics

A

Outer membrane: +
Peptidoglycan layer: Thinner
Lipopolysaccharide +
Teichoic acid -
Sporulation -
Capsule Sometimes present
Lysozyme Resistant
Antibacterial activity of penicillin More resistant
Exotoxin production Some strains

28
Q

legionella staining

A

is weak

29
Q

leptospira gram staining

A

not good bc theyre too thin to be visualized

30
Q

mycoplasma gram staining

A

do not have cell walls so they dont stain

31
Q

Mycobacteria gram staining

A

have a peptidoglycan layer which is intertwined with covalently attached to an arabinogalactan polmer and surrounded by a waxlike lipid coat of mycolic acid, cord factor, wax D, and sulfolipids. These bacteria are described as staining acid-fast. In the acid fast stain, bacteria are stained red with carbol fuchsin, acid alcohol is used to destain and methylene blue is used to counterstain. Mycobacteria and other acid-fast bacteria (nocardia) are resistant to destaining with acid alcohol and remain red.

32
Q

Peptidoglycan

A

is a high-molecular-weight cross-linked polymer consisting of glycan chains cross-linked by peptide chains. Peptidoglycan forms the rigid structure of the bacterial cell wall. It provides protection from physical/mechanical, osmotic, chemical and biological stresses. Importantly, peptidoglycan is ESSENTIAL for bacterial survival and UNIQUE to prokaryotes (bacteria) making it a very important target for antibacterial drugs. We will focus on the synthesis of peptidoglycan in the next lecture.

33
Q

List the steps of a Gram stain

A
  1. Bacteria are heat fixed or otherwise dried onto a slide and stained with Crystal violet
  2. Crystal violet is precipitated with iodine
  3. Unbound and excess stain is removed by washing with an acetone-based decolorizer
  4. A red counter stain, safranin, is added to stain any decolorized cells
34
Q

expected results of gram stain

A
  • For gram-positive bacteria, which turn purple the stain gets trapped in the thick, cross-linked mesh-like peptidoglycan layer.
  • Gram-negative bacteria have a thin peptidoglycan layer that does not retain the crystal violet so the cells are counterstained with safranin and turn red.
35
Q

Lipopolysaccharide (LPS)

A

is found in the outer leaflet of the Gram-negative outer membrane. It consists of three structural sections: Lipid A, core polysaccharide, and O antigen.

36
Q

Lipid A:

A

Essential for bacterial viability. Lipid A is responsible for the endotoxin activity of LPS. It has a phosphorylated glucosamine disaccharide backbone with fatty acids attached to anchor the structure in the outer membrane.

37
Q

Core polysaccharide:

A

Branched polysaccharide of 9 to 12 sugars

38
Q

O antigen:

A

O antigen is attached to the core and extends away from the bacteria. It is a long linear polysaccharide consisting of 50 to 100 repeating saccharide units of 4 to 7 sugars per unit.

39
Q

LPS structure is used to classify bacteria.

A

The basic structure of lipid A is identical for related bacteria and is similar for all gram-negative Enterobacteriaceae. The O antigen distinguishes serotypes (strains) of a bacterial species. For example, the O157:H7 (O antigen: flagellin) serotype identifies the E. coli agent of hemolytic-uremic syndrome.

40
Q

How LPS works

A

LPS binds to CD14 and TLR4 on phagocytes and antigen presenting cells which triggers production of proinflammatory cytokines such as TNF-alpha, IL-1 and IL-6. LPS is also referred to as endotoxin, and endotoxin is sufficient to cause septic shock because of the massive inflammatory response that it triggers.

41
Q

Pili (fimbrae):

A

composed of protein subunits called pilin which form a tube like structure with a hollow core and form hair-like structures on the surface of Gram-negative and Gram-positive bacteria. Common or somatic pili are usually involved in attachment to epithelial cells. Sex pili are involved in exchanged of genetic material (usually a plasmid) from one bacteria to another. A given bacterium will on have a single sex pilus. Sex pili are encoded on an F plasmid and are also referred to as F pili.

42
Q

Flagella (H antigen):

A

rotating helical structures attached to the plasma membrane and involved in locomotion. Flagella can be organized around the plasma membrane in different ways (polar, all around the bacteria, etc.) and this arrangement can be useful in identifying specific organisms.

43
Q

Capsule

A

(slime layer, glycocalyx, K antgen): Many pathogenic bacteria are surrounded by a capsule. The capsule is usually (but not always) made of polysaccharide. It is a very important virulence factor, and one of the main functions of the capsule is thought to be protection from phagocytosis. A biofilm is an organized community of bacterial cells that has a capsule/slime layer surrounding the entire community.

44
Q

biofilm does what?

A

protects the community and essentially walls it off from the immune system and/or from physical/chemical attack.

45
Q

Quellung test use:

A

used to identify bacterial capsules; treating with anti-capsular antibodies results in a visible “swelling” of the capsule.

46
Q

Some gram-positive, but never gram negative, bacteria are

A

are spore formers: vegetative (active state) to dormant state

47
Q

The spore is a

A

dehydrated, multishelled structure that is highly resistant to environmental stressors such as intense heat (boiling), radiation, and attack by most enzymes and chemical agents (antiseptics, disinfectants). They can exist for centuries as viable spores. Spores can be aerosolized. The germination of spores into the vegetative state is stimulated by disruption of the outer coat by mechanical stress, pH, heat or another stressor (such as exposure to acidic pH in the stomach) and requires water and a triggering nutrient.

48
Q

The spore has (structurally)

A

an inner membrane, two peptidoglycan layers and an outer keratin-like protein coat.

49
Q

The endospore contains

A

a complete copy of the chromosome, the bare minimum concentrations of essential proteins and ribosomes, and a high concentration of calcium bound to dipicolinic acid.

50
Q

gram neg bacteria are (compared to gram +)

A

more complex - have an outer membrane and periplasmic space

less peptidoglycan

51
Q

gram + bacteria peptidoglycan compraed to gram -

A

MORE peptidoglycan in gram +

52
Q

peptidoglycan is only found on —>

A

bacteria!!! = drug target – it is essential to bacterial life

53
Q

virulence factors on gram +?

A

teichoic acid and Lipoteichoic acid - important to attachment

54
Q

All gram - bacteria have

A

LPS

55
Q

endospores are only made by

A

GRAM + bacteria

Immuno/Micro/Viro (14 decks)

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