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Y1B3 (CVS & IBL) 📘 > Microbiology 🦠 > Flashcards

Microbiology 🦠 Flashcards

1
Q

What is the shape and stain of staphylococci?

A

Gram-positive cocci

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2
Q

What is the arrangement of staphylococci?

A

In Clusters

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3
Q

Are staphylococci motile?

A

No

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4
Q

Are staphylococci spore-forming?

A

No

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5
Q

What is the capsule of staphylococci?

A
  • S. aureus forms microcapsule

- Other species may produce slime layer

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6
Q

What are staphylococci classified into?

A

Coagulase positive: S. aureus.

Coagulase-negative: S. epidermidis and S. saprophyticus.

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7
Q

What is the habitat of Steph aureus?

A
  • It is a major pathogen for humans.
  • Present as normal flora on skin & upper respiratory tract (10-40% of normal individuals carry S. aureus in the anterior nares).
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8
Q

What are the virulence factors of Staphylococcus aureus?

A
  • Cell wall-associated proteins and polymers

- Enzymes and toxins produced by S. aureus

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9
Q

What are the cell wall-associated proteins and polymers of staphylococcus aureus?

A

Capsular polysaccharide:
 Inhibits phagocytosis and chemotaxis

Protein A:
 The major protein in the cell wall.
 It binds to the Fc portion of IgG.
 It inhibits opsonization

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10
Q

What are the enzymes of staphylococcus aureus?

A

“CCS - OTHER ENZYMES”

Coagulase: Causes clotting plasma to clot by converting prothrombin to thrombin which converts fibrinogen to fibrin coats the bacterial cell interferes with opsonization and phagocytosis.

Staphylokinase.

Catalase: Inactivates toxic H2O2 inside phagocytes enhance survival of S. aureus in phagocytes.

Other enzymes: Proteases, lipase, and DNase.

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11
Q

What are staphylococcus aureus exotoxins?

A

Membrane damaging toxins: Haemolysin and leucocidin.

Enterotoxins: Cause food poisoning when ingested, Heat and acid-stable

Toxic shock syndrome toxin (TSST-1): Causes toxic shock
syndrome.

Epidermolytic (exfoliative) toxin: Causes scalded skin syndrome in neonates.

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12
Q

What are the types of diseases caused by Staphylococcus aureus?

A

Suppurative (pus-forming) infections

Toxigenic diseases

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13
Q

What are suppurative infections caused by Staph aureus?

A

✓ Skin lesions: Boils, styes and furunculosis.

✓ Invasive infections: Pneumonia, meningitis, UTI, bacteremia, endocarditis, etc.

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14
Q

What are toxigenic diseases caused by staph Aureus

A

Scalded skin syndrome

Food poisoning

Toxic shock syndrome (TSS)

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15
Q

What is a clinical picture of scaled skin syndrome?

A

Widespread blistering and loss of the epidermis in neonates.

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16
Q

What is the type of food that causes food poisoning with staph aureus? And what is the incubation period?

A

Diary milk products, 1-6 hours

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17
Q

What is the clinical picture of food poisoning with staph aureus?

A

Nausea, vomiting, and slight diarrhea, but no fever.

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18
Q

Where does toxic shock syndrome occur?

A

Occurs in young females on using tampons

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19
Q

What is the clinical picture of toxic shock syndrome?

A

Fever, vomiting, diarrhea, desquamation of skin and

hypotension.

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20
Q

What are the samples used for the diagnosis of staphylococcus aureus?

A

Differ according to the site of infection (swabs, pus, sputum, C.S.F, blood, …).

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21
Q

Direct film of Staph aureus

A

Stained with Gram stain for characteristic morphology.

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22
Q

Culture of staph aureus

A
  • Facultative anaerobes, optimum temperature: 37 °C, normal atmospheric CO2
  • Can grow on ordinary media.
  • S. aureus produce golden yellow endopigments.
  • S. aureus causes β-hemolysis on blood agar.
  • Selective media is mannitol salt agar, where S.aureus ferments mannitol and salt inhibits other normal flora.
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23
Q

How are colonies of staph aureus identified?

A
  • Film stained by Gram for characteristic morphology.
  • Biochemical reactions:
    ✓ All staphylococci are catalase positive.
    ✓ S. aureus is coagulase and DNAase positive and ferment mannitol.
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24
Q

What are the methods of diagnosis of Staph aureus?

A
  • Direct film
  • Culture
  • Identification of colonies
  • Antimicrobial susceptibility: to select the effective drug.
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25
Q

What is the Treatment of staph aureus?

A

Penicillinase-resistant β-lactams.

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26
Q

What are coagulase-negative staphylococci (CONS)?

A
  • S. epidermidis

- S. saprophyticus

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27
Q

What is the habitat of S. epidermis?

A

Normal flora of the skin, nonpathogenic.

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28
Q

What are the diseases caused by S. epidermidis?

A

It may cause infections in immunocompromised individuals & infections on prosthetic implants such as heart valves and hip joints.

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29
Q

What are the diseases caused by S. saprophyticus?

A

Causes UTI in young females.

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30
Q

What are the differences between Staphylococcal species?

A

S. Aureus is positive to “AEH CDM” protein A, exotoxin production, hemolysis production, coagulase, DNase, and mannitol fermentation.

While S. Epidermedis and S. saprophyticus are negative to all of them

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31
Q

How to differentiate between S. Epidermedis and S. saprophyticus?

A

S. saprophyticus tests positive to resistance to novobiocin.

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32
Q

What is the definition of an antigen?

A

Substance recognized by immune system which may be:
✓ Simple or complex
✓ Carbohydrate, lipid, protein, nucleic acid, phospholipids

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33
Q

What type of antigens are recognized by B cells and T cells?

A
  • B cell recognize any biological Ag

- T cell recognize peptide Ag presented on MHC

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34
Q

What is the definition of epitopes (antigenic determinant)?

A

Smallest part on Ag which bind with BCR & T cell receptors

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35
Q

What is an antigen with multiple epitopes?

A

it is called multivalent Ag

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36
Q

What are the types of antigens – epitopes and what are they classified according to?

A

Depending on the nature of immune responses they trigger, antigens/epitopes are divided into 3 fuctional types:

  • Immunogens
  • Haptens
  • Tolerogens “all the body” “cells that attack them are killed”
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37
Q

What is the definition of immunogens?

A

Large Ag with epitopes capable of binding with immune receptor & inducing immune response.
(Notice that not all antigens are immunogens)

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38
Q

What is the definition of Haptens?

A
  • A small Ag with epitopes capable of binding with immune receptor & without inducing immune response
  • BUT can produce immune response only when conjugated with large carrier molecule (as a protein) → immune response against epitopes of hapten & carrier.
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39
Q

What is the definition of Tolerogens?

A

Self Ag (MHC) normally “but may cause in pathological cases” not stimulate immune system

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40
Q

What are the factors that influence immunogenicity?

A

size:- Proteins > 10 KDs are more immunogenic

Complexity:- Complex proteins with numerous, diverse epitopes are more to induce an immune response than are simple peptides that contain only one or few epitopes.

Conformation and accessibility:- Epitopes must be “seen by” and be accessibile to the immune system. “Particles in the eye are not accessible”

Chemical properties:
✓ A protein is good immunogens.
✓ Many charbohydrates, steroids, and lipids are poor immunogens.
✓ Amino acids and haptens are, by themselves, not immunogenic

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41
Q

What are the types of Antigens according to dependency on T-cells?

A
  • T-cell independent Ag (TI): Activate B cells without help from T cell; e.g. polysaccharides (Pneumococcal polysaccharide, LPS)
  • T-cell dependent Ag: Requires T cell help for B cell activation, e.g. proteins (microbial proteins & non-self or altered-self proteins).
42
Q

what are the steps of production and distribution of antibodies?

A
  • In lymph node → Ag stimulation of B cells with help of T helper cytokines → B cell proliferate → differentiate into plasma cell which secrete antibodies → enter circulation → site of infection
  • Also mature B cell in Bone Marrow express membrane bound antibodies (BCR)
  • So antibodies are produced in lymphoid tissue & bone marrow
43
Q

What are the forms of antibodies?

A

Secreted: “99%”
✓ In plasma & mucosa & interstitial fluids of tissues

Membrane-bound Ig:
✓ Expressed on B cell surface (IgM & IgD) as BCR for Ag
✓ If bind with Ag, initiate B cell response

44
Q

What is the structure of antibodies?

A
  • Y shaped molecules of 4 polypeptide chains
  • 2 identical heavy chain (1 variable domain (VH) and 3 or 4 constant domains (CH)
  • 2 identical light chain (1 variable domain (VL) and 1 constant domain (CL)
  • Each variable domain (VL or VH) contains 3 hypervariable regions called complementary determining repeats (CDR)
  • Disulfide bonds connect heavy chain with light chain & heavy chain with heavy chain.
45
Q

What are the regions of antibodies according to proteolytic fragments?

A

Hinge region:
• Flexible region lies between Fab & Fc to give mobility to both Fab to accommodate different Ag

Fc (fragment crystalline)
• Tend to crystallize in solution
• 1 in number
• Contain remaining of both heavy chains C domain.
• Effector & biological function.

Fab = Fragment antigen binding

  • Contain whole light+VH+ CH1
  • 2 in number
  • Ag recognition and binding
46
Q

What are immunoglobulin classes (isotypes)?

A
  • Immunoglobulins →divided into five different classes → according to the difference in structure in constant domains of heavy chain
 Gamma heavy chains → IgG
 Alpha heavy chains → IgA 
 Mu heavy chains → IgM
 Epsilon heavy chains → IgE 
 Delta heavy chains → IgD
  • Different classes and subclasses of antibodies perform different effector functions
47
Q

What are the types of light chains of antibodies?

A
  • There are two types of light chains, called κ (kappa) and λ (lambda).
  • An antibody has either two κ or two λ light chains.
48
Q

What is heavy chain class switching?

A
  • Is the switch from one Ig isotype to another.
  • After activation of B lymphocytes, a specific clone of B cells proliferate and differentiate into progeny that secrete antibodies; some of the progeny secrete IgM, and other progeny produce antibodies of different isotypes
49
Q

What are the subtypes of IgA?

A

IgA 1 and IgA 2

50
Q

What is the heavy chain of IgA?

A

Alpha-1 and alpha-2

51
Q

What is the serum content of IGA?

A

3.5mg/ml

52
Q

What is the Secreted form of IGA?

A

Monomer, dimer and trimer

53
Q

What are the functions of IGA?

A

Mucosal immunity

54
Q

What is the heavy chain of IgD?

A

Delta

55
Q

What is a Serum content of IGD?

A

Traces.

56
Q

What is the secreated form of IgD?

A

None

57
Q

What are the functions of IgD?

A

B-cell receptor

58
Q

what is the heavy chain of IGE?

A

Epsilon

59
Q

What is a Serum content of IGE?

A

0.05

60
Q

What is the secreted form of IGE?

A

Monomer

61
Q

What is the function of IGE?

A
  • Parasite

- allergy

62
Q

What are the subtypes of IgG?

A

IgG1 – IgG4

63
Q

What is the heavy chain of IgG?

A

Gama 1,2,3,4

64
Q

What is the serum content of IgG?

A

13.5

65
Q

What is the secreted form of IgG?

A

Monomer

66
Q

What are the functions of IgG?

A
  • Opsonization
  • Complement
  • ADCC
67
Q

What is a heavy chain of IGM?

A

Mu

68
Q

What is the serum content of IGM?

A

1.5

69
Q

What is a Secrete form of IgM?

A

Pentamer

70
Q

What are the functions of IgM?

A

B-cell receptor and compliment

71
Q

What is the definition of monoclonal antibodies?

A
  • Identical monospecific antibodies that are produced by one type of immune cell that are all clones of a single parent cell.
72
Q

What are antibodies obtained from the blood of an immunized host called?

A
  • In contrast, antibodies obtained from the blood of an immunized host are called polyclonal antibodies.
73
Q

What are the steps of production of monoclonal antibodies? (Hybridoma technology)

A
  • A mouse is immunized with the antigen
  • B cells are isolated from the spleen of the mouse.
  • B cells (Anibody-producing cell) are then fused with myeloma cells (malignant cell) in vitro by using a fusion agent as poly-ethylene glycol, a virus.
  • The cell fusion forms an antibody-producing cell “hybridoma”.
  • Hybrids (fused cells) are selected for growth in special culture media
  • The B cells that fuse with another B cell or do not fuse at all die because they do not have the capacity to divide indefinitely.
  • Only hybridomas between B cells and myeloma cells survive.
  • Hybridomas, secrete a large amount “and indefinitely” of mAbs.
74
Q

What are the applications of monoclonal antibodies?

A
  • Identification of phenotypic markers:
    They have been used to define clusters of differentiation (CD markers) “4-8” on lymphocytes.
  • Immunodiagnosis:
    The diagnosis of many infectious and systemic diseases relies on the detection of specific antigens or antibodies in the circulation or tissues by use of mAbs.
  • Tumor diagnosis:
    Tumor-specific monoclonal antibodies are used for detection of tumors by imaging techniques.
  • Therapy: “Drug associated with monoclonal antibodies for specific target”
    A number of mAbs are used therapeutically today: Anti-CD3 for immunosuppression and prevention of graft rejection
75
Q

What are the types of adaptive immunity?

A

1) Humoral (Antibody - Mediated) Immunity.

2) Cell-Mediated Immunity.

76
Q

What is humoral immunity mediated by?

A

mediated by secreted antibodies

77
Q

What is the function of humoral immunity?

A

Its physiologic function is defense against extracellular microbes and microbial toxins

78
Q

What are the functions of antibody isotypes?

A

1) Neutralization of microbes and microbial toxins
2) Opsonization and phagocytosis
3) Antibody-dependent cell-mediated cytotoxicity (ADCC)
4) Activation of the complement by IgG and IgM “pathogen—> no reaction. Pathogen with AB —-> Reaction”
5) Functions of antibodies at special sites

79
Q

What is the naturalization function of microbes and microbial toxin by antibodies?

A
  • Antibodies blocks and prevent binding of microbe to cells i.e. prevent infection of cells. “So that we don’t even need cell mediated immunity”
  • Antibodies inhibit the spread of microbes from an infected cell to an adjacent cell.
  • Antibodies block binding of toxin to cellular receptors, and thus inhibit pathologic effects of the toxin.
80
Q

What is the opsonization and phagocytosis function of antibodies?

A

Antibodies of IgG isotype opsonize (coat) microbes

81
Q

What is ADCC function of antibodies?

A
  • IgG bind to infected cells by the Fab regions, and bind by Fc to Fc receptors on NK cells.
  • The NK cells are activated and kill the cells.
  • IgE “+IgG” bind to helminthic parasites by the Fab regions, and bind by Fc-to-Fc receptors on eosinophils.
  • The eosinophils are activated to release their granule contents, which kill the parasites.
82
Q

What are the functions of antibodies at special sites?

A

Mucosal immunity

Neonatal immunity

83
Q

What is the function of antibodies in mucosal immunity?

A
  • IgA is the major class that is produced by the mucosa-associated lymphoid tissues (MALT) in the GIT and RT and transported to the lumens of organs.
  • In mucosal secretions, IgA binds to microbes and toxins present in the lumen and neutralize them by blocking their entry.
84
Q

What is the function of antibodies in neonatal immunity?

A
  • neonates are protected from infection by maternal antibodies (IgG) “produced by mother” transported across the placenta into the fetal circulation and by antibodies in ingestd milk transported across the gut epithelium of newborns.

“But they are passive antibodies which last for six months”

“Newborns have good immunity to most infections that have have infected the mother”

85
Q

What are the characteristics of the primary immune response?

A
  • When we are exposed to an antigen for the first time:

a) There is a lag of several days (10 days) before a specific antibody becomes detectable.
b) This antibody is IgM.
c) After a short time , the antibody level declines.

86
Q

What are the characteristics of the secondary immune response?

A

If at a later date we are re-exposed to the same antigen, there is

a) more rapid appearance of antibody, greater amount.
b) IgG class.
c) remains detectable for months or years.

87
Q

What happens if we are re-exposed to an antigen while we are exposed to a different antigen for the first time?

A

the properties of the specific response to this antigen are those of the primary response

88
Q

Compare between secondry response and primary response according to:-

Onset
Magnitude
Lifetime
Isotype

A

Onset: rapid - slow

Magnitude: High - low

Lifetime: long - short

Isotype: IgG (Or IgA, or IgE) - IgM

89
Q

Why does secondary immune response happen?

A
  • because the immune system possesses specific immunologic memory for antigens.
  • During the primary response, some B lymphocytes, become memory cells which are long lived.
90
Q

What phenomenon is required in the secondary response?

A

Thus we can see that the secondary response requires the phenomen known as class switching (IgM to IgG).

91
Q

What is the function of cell mediated immunity?

A

Eradicates infections by intracellular microbes.

92
Q

What are the steps of activation of cell mediated immunity?

A
  • Consist of the activation of naïve T cells to proliferate and differentiate into effector cells (CD4+ T helper cells and CD8+ cytolytic cells; CTLs) and the elimination of the intracellular microbes
93
Q

What are the types of cell mediated immunity?

A

CD4+ T cells:

Differentiate into 2 effector cells according to cytokine production by antigen presentig cell:
 IL-12 leads to Th1
 IL-4 leads to Th2
 Th1 secrets IFN-g activates phagocytes to kill microbes.
 Th2 secrets IL-4 and IL-5 which stimulate eosinophil and mast cell degranulation in allergy and helminthic infection

CD8+ T cells:

kill any cell containing microbes or microbial proteins in the cytoplasm (intracellular) by direct cell cytotoxicity,; eliminating the reservoir of infection .

94
Q

How are T cells activated? “T-helper”

A

Activated by two signals
- The 1st signal: peptide + MHC on the surface of APCs recognized by TCRCD3.

  • The 2nd co-stimulatory signal: is the interaction of B7 molecule on APCs with CD28 on T cells.
95
Q

What happens in case of absence of the second signal inactivation of T cells?

A

exposure of T cells to antigen lead to anergy (unresponsiveness)

96
Q

What are the steps of killing infected cells by CD8 - CTLs?

A

1) CTLs recognize class I MHC + peptides on the surface of infected “target” cell”.
2) Formation of tight adhesions “conjugates” with these cells.
3) CTLs are activated by IL-2 & IFN-γ to release their granule contents toward the target cell i.e. granule exocytosis.

4) The granules contents include:
- Perforin, which form pores in the target cell membrane
- Granzymes enter the target cells through these pores and induce apoptosis through the activation of caspases.

5) Detachment of CTL from target cells to kill other target cell.
6) Death of target cell.

97
Q

What is the definition of MHC?

A
  • Group of genes on short arm of chromosome 6 which produce MHC molecules present on cell surfaces and responsible for display of protein Ag to T cell Also called human leucocytic Ag = HLA
98
Q

What is the classification of genes of MHC?

A

1) Class I MHC genes → HLA-A “human leucocytes antigen” & HLA-B & HLA-C → role in Ag presentation to Tc
2) Class II MHC genes → HLA-D region (HLA-DR & HLA-DP & HLADQ) → role in Ag presentation to Th
3) Class III MHC genes → lies between class I & II & not produce MHC but produce some complement components & TNF-α.

99
Q

What is the structure and distribution of MHC molecules?

A
  • Are membrane proteins expressed on cells.
  • Each class I & II molecule consist of extracellular part, a transmembrane and a cytoplasmic part to anchore the molecule to the cell.
100
Q

What is the structure and function of class 1 MHC molecules?

A
  • polypeptide chains, α chain formed of 3 domains (α1, α2, α3), attached to a polypeptide chain called β2 microglobulin encoded by a gene outside MHC.
  • α1 and α2 domains form the cleft or groove which bind peptide.
  • Present antigen to CD8+ cells.
  • Class I molecules are expressed on all nucleated cells.
101
Q

What is the structure and function of class 2 MHC molecules?

A
  • 2 polypeptide chains α chain (α1 & α2) and β chain (β1 & β2).
  • α1 and β1 domains form the peptide binding cleft.
  • Present antigen to CD4+ cells.
  • Class II is expressed on APCs only.

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