Microbiology: Principles

Question 1

How do pathogens escape the host immune response?

Answer 1

Using:
O-antigen
Capsule
Fc binding proteins
Leukotoxins
Inhibition of phagolyzozome
Escape from phagolyzozome
Antigenic mimicry/variation
Coagulase

Question 2

What is O-antigen?

Answer 2

TheO antigen, consisting of many repeats of an oligosaccharide unit, is part of the lipopolysaccharide (LPS) in the outer membrane of Gram-negative bacteria

Question 3

What is the bacterial capsule?

Answer 3

The bacterialcapsule is a polysaccharide layer that lies outside the cell envelope, and is thus deemed part of the outer envelope of a bacterial cell.

Question 4

What are Fc binding proteins

Answer 4

AnFc receptoris a protein found on the surface of certain cells– including, among others,B lymphocytes,follicular dendritic cells,natural killer cells,macrophages,
neutrophils,eosinophils,basophils, humanplatelets, andmast cells– that contribute to the protective functions of theimmune system.

Fc receptors bind to antibodies that are attached to infected cells or invadingpathogens. Their activity stimulatesphagocyticorcytotoxiccells to destroymicrobes, or infected cells byantibody-mediatedphagocytosisorantibody-dependent cell-mediated cytotoxicity

Question 5

What are leukotoxins?

Answer 5

Leukotoxinsare a group of exotoxins that produce their primary toxic effects against leukocytes, especially polymorphonuclear cells (PMNs).

Question 6

Which organisms inhibit the phagolysozome?

Answer 6

Inhibition ofphagolysosomefusion represents a major intracellular survival strategy for a number of intracellular bacteria, includingM. tuberculosis, Francisellaspp.,Brucellaspp., andL. monocytogenes. After engulfment, these pathogens manipulate the endocytic fate of the phagosome that contains them.

Question 7

Which organisms escape the phagolysosome?

Answer 7

LegionellaandBrucella

Question 8

What is coagulase?

Answer 8

A bacterial enzyme which brings about the coagulation of blood or plasma and is produced by disease-causing forms of staphylococcus.

Question 9

What is non-specific (innate) immunity

Answer 9

Anatomical structures
Inhibitory secretions 
Lysozyme
Complement 
Defensins 

Cells: Macrophages, DC, neutrophils, eosinophils NK cells

Question 10

What is specific immunity?

Answer 10

T-Lymphocytes
B- lymphocytes

Cytokines and antibodies

Question 11

Define Latent

Answer 11

Anasymptomaticinfectioncapableofmanifestingsymptomsunderparticularcircumstancesorifactivated

Question 12

Define carrier

Answer 12

Anindividualwhoharboursthespecificorganismsofadiseasewithoutmanifestsymptomsandiscapableof transmittingtheinfection;
theconditionofsuchanindividualisreferredtoasthecarrierstate.

Question 13

What colour are gram +ve bacteria with gram staining?

Answer 13

Positive stain purple as they retain the crystal violet dye

Question 14

How would you describe an acid fast bacteria?

Answer 14

Acid-fast organisms likeMycobacteriumcontain large amounts of lipid substances within their cell walls called mycolic acids. These acids resist staining by ordinary methods such as a Gram stain.

Question 15

How would you describe a Mycoplasma?

Answer 15

Mycoplasmais a genus of bacteria that lack a cell wall around their cell membrane. Without a cell wall, they are unaffected by many common antibiotics such as penicillin or other beta-lactam antibiotics that target cell wall synthesis

Question 16

What is toxic shock?

Answer 16

Toxicshocksyndrome(TSS)isanuncommon,butpotentiallyserious,illnessthatoccurswhenpoisonoussubstances(toxins)producedbystreptococcus aureus enterthebloodstream.
Gram –ve release lipid-A as they die.

Question 17

What is an exotoxin?

Answer 17

An exotoxin is a toxin that is produced by a bacterium and then released from the cell into the surrounding environment. The damage caused by an exotoxin can only occur upon release. As a general rule, enterotoxins tend to be produced by Gram-positive bacteria rather than by Gram-negative bacteria.

Question 18

What is an enterotoxin?

Answer 18

Anenterotoxinis aproteinexotoxinreleased by amicroorganismthat targets theintestines

Question 19

What is an endotoxin?

Answer 19

WhereasEndotoxinsare bacterial toxins consistingoflipids that are located within a cell.

Question 20

What produces enterotoxin?

Answer 20

Staphylococcus aureus andStreptococcus pyogenes

Question 21

What produces endotoxin?

Answer 21

Gram-negative bacteria, such asNeisseriaspp. andHaemophilusspp.

Question 22

How do enterotoxins work?

Answer 22

These toxins share the ability tobindto themajor histocompatibility complexproteins of their hosts. Enterotoxins are frequentlycytotoxicand kill cells by altering the apical membranepermeabilityof the mucosal (epithelial) cells of the intestinal wall.

Question 23

How do endotoxins work?

Answer 23

largemoleculesconsisting of alipidand apolysaccharidecomposed of O-antigen, outer core and inner core joined by acovalent bond; they are found in theouter membrane ofGram-negative bacteria.

Question 24

What are the stages (steps) of viral infection?

Answer 24

Initial acquisition – binds to the receptor on a cell
Enters the cell
Replication of nucleic acid and proteins
Release from cell