Microbiology III Flashcards
1
Q
State 2 examples of gram-positive pathogenic bacteria.
A
Clostridium tetani
Meticillin resistant S.aureus
2
Q
State 3 examples of gram-negative pathogenic bacteria.
A
Salmonella enteritica
Pseudomonas aeruginosa
Proteus vulgaris
3
Q
A
4
Q
What type of bacteria is Streptococcus viridans?
A
commensal
normal microflora
(autochtone)
5
Q
What happens with most bacteria in humans?
A
Bacteria do not produce disease but they achieve a balance with the host that ensures the survival, growth and propagation of both the bacteria and the host.
6
Q
What happens with some bacteria eg. Salmonella typhi?
A
bacteria are clearly pathogenic but infection remains latent/subclinical and the host is a “carrier” of the bacteria.
7
Q
What is a pathogen?
A
A microorganism capable of causing disease.
8
Q
What is a non-pathogen?
A
A microorganism that does not cause disease. It may be part of the normal flora.
9
Q
What is an Opportunistic Pathogen?
A
An agent capable of causing disease only when the hosts resistance is impaired (eg. immunocompromised).
10
Q
What does “pathogenicity” refer to?
A
The ability of an infectious agent to cause disease.
11
Q
What is virulence?
A
The quantitative ability of an agent to cause disease. (virulent agents cause disease when they are introduced into the host in small numbers)
-> degree of pathogenicity
12
Q
What does virulence involve?
A
invasiveness and toxigenicity
13
Q
What is virulence measurable by?
A
LD50 or ID50
14
Q
What has been established in characterizing pathogenic microbes? (what unit?)
A
unit of virulence
15
Q
What is “Dlm”?
A
Dosis letalis minima
- the minimum number of live microbes which in a certain period of time bring about 95-97% death of the corresponding laboratory animals.
16
Q
What is “Dcl”?
A
Dosis certa letalis
the absolute lethal dose of pathogenic microbes which will kill 100% of the experimental animals.
17
Q
What may serve as an objective criterion for comparison with other units of virulence?
A
LD50 (the dose which is lethal to one half of the infected animals).
18
Q
What does ID50 represent?
A
the inoculum required to infect 50% of a population.
19
Q
What are the steps of a pathogenic infection?
A
exposure
adhesion
invasion
colonization
toxicity
tissue damage and disease
20
Q
What is the virulence of pathogenic microorganisms associated with?
A
adherence
invasiveness
capsule production
toxin production
aggressiveness
other factors
21
Q
What would happen to bacteria if they would not adhere to cells of a tissue surface?
A
they would be swept away by mucous and other fluids that bathe the tissue surface.
22
Q
What is the only step in the infectious process? What is it followed by?
A
step in infectious process: adherence
followed by:
- development of micro colonies
- subsequent complex steps in the pathogenesis of an infection
23
Q
What helps the pathogen infect the cell?
A
- Adhesin
- protein/glycoprotein
- found on the surface of the pathogen
- attaches to receptors on the host cell
24
Q
What type of pathogens are adhesions found on?
A
- bacterial
- fungal
25
State an example of a bacterial adhesin (eg. found in enterotoxigenic E.coli). where is it found?
type 1 fimbrial adhesin
(found on the tips of fimbriae)
26
What is the next step in pathogenesis after exposure and adhesion?
What does this step involve?
invasion
may involve enzymes and toxins
27
How do many pathogens invade the organism? Why is this effective?
blood stream
- blood vessels pass very close to every cell in the body
28
Define invasion.
The process whereby bacteria, parasites, fungi and viruses enter the host cell or tissues and spread in the body.
29
What term is used to describe the condition where toxins are found in the blood?
toxemia
30
What term describes the condition where bacteria are both present and multiplying in the blood?
septicemia
31
What is the ending used to describe the presence of pathogens in the bloodstream?
-emia
32
What term is used to describe the presence of bacteria in blood?
bacteremia
33
What term is used to describe bacteremia involving pyogens?
pyemia
34
what are pyogens?
pus-forming bacteria
35
What do some pathogens produce? What type of enzymes? What do they help in?
exoenzymes (extra cellular enzymes)
enable pathogens to invade host cells and deeper tissues.
36
What is the target of coenzymes?
a wide variety of targets
37
State examples of coenzymes as virulence factors.
Collagenase
Hyaluronidase
38
What is the function of collagenase?
degrades collagen, the major protein of fibrous connective tissue --> promotes the spread of infection in tissue
39
What is the function of hyaluronidase?
enables the pathogen to penetrate deep into tissues.
40
How do bacteria such as Clostridium penetrate deep into the host cell tissues?
use enzymes to dissolve collagen and hyaluronic acid, the protein and saccharides, that hold tissues together.
41
What are necrotizing enzymes?
- destroy cells and tissues
42
What is the best known example of necrotizing exoenzyme?
produced by Streptococcus pyogenes that causes fasciitis in humans.
43
What is the function of coagulase? How does it achieve that?
- facilitates clotting in a cell
- binds to prothrombin
- converts fibrinogen into fibrin
44
What bacteria use coagulase? Why?
Staphylococcus aureus:
- form a layer of fibrin around their cell
- protect against host defense mechanisms
45
What do hemolysins target?
erythrocytes (RBC)
46
What type of cytolysins do bacteria produce? What is their function?
hemolysins (dissolve erythrocytes)
leukocidins (dissolve leukocytes)
kill tissue cells
47
What -hemolytic can microorganisms be?
alpha-hemolytic
beta-hemolytic
gamma-hemolytic (non-hemolytic)
48
What is the signal for a positive coagulase test?
clot formation
49
What are the types of hemolysis?
beta: concentrated
alpha: further
gamma: none
50
What helpsicrobes resistantbto phagocytosis and antibodies increase their invasive properties?
the capsule
51
Why are capsular anthrax bacilli not subject to phagocytosis while other variants are easily phagocytized?
due to the protective capsule
52
Can microorganisms produce capsules?
yes! produce capsules in organisms, nutrient media, and animal and human bodies.
53
What is toxigenicity? What does it contribute to?
The ability of a pathogen to produce toxins to cause damage to host cells.
- contributes to the development of disease
54
What are toxins?
Biological poisons that assist in their ability to invade and cause damage to tissues.
55
How are toxins classified?
2 groups:
- exotoxins
- endotoxins
56
What is an 'endotoxin'?
The lipopolysaccharide (LPS) found on the outer membrane of gram-negative bacteria.
(During infection and disease, gram-negative bacterial pathogens release endotoxin either when the cell dies, resulting in the disintegration of the membrane, or when the bacterium undergoes binary fission. The lipid component of endotoxin, lipid A, is responsible for the toxic
properties of the LPS molecule.)
57
What are the main characteristics of endotoxins?
- stable at high temperatures (max 120*C)
- more firmly bind to the bacterial cell
- less toxic
- act on the organism in large doses
- latent period is estimated in hours
- selective action is poorly expressed
- produce gram negative bacteria
58
What are the main characteristics of exotoxins?
- heat liable! (due to their protein structure which is denatured above 41*C temperatures)
- majority are produced by gram positive bacteria (can be produce by gram negative)
59
What 3 categories are exotoxins grouped into? Based on what?
based on their target:
1) intracellular targeting
2) membrane disrupting
3) superantigens
60
What are the two types of membrane disrupting exotoxins? What do they do?
hemolysins and leukocidins
- form pores in cell membranes, causing leakage of the cytoplasmic contents and cell lysis.
61
Some strains of S. aureus produce leukocidins called what?
Panton-Valentine leukocidin (PVL)
62
What categories can exotoxins be divided into? What is it based on?
5 categories, based on the site affected:
1) **neurotoxins** (tetanotoxin, botulotoxin) C. tetani, C.botulinum, B. cereus, S. aureus;
2) **cytotoxins** (enterotoxins, dermatonecrotoxin) E. coli, Salmonella spp., Klebsiella spp.,C. perfringens;
3) **functional blocators** (cholerogen), V. cholerae
4) **membranotoxins** (hemolysins, leucocidin), S. aureus
5) **exfoliatin**- S. aureus.
63
What are the sources of the different toxins?
ENDO: gram-negative bacteria
EXO: gram-positive (primarily) and gram-negative bacteria
64
What is the composition of the different toxins?
ENDO: lipid A, liposaccharide
EXO: protein
65
What are the effects on hosts of the different toxins?
ENDO: general systemic symptoms of inflammation and fever
EXO: specific damage to cells dependent upon receptor-mediated targeting of cells and specific mechanisms of action
66
What are the heat tolerances of the different toxins?
ENDO: stable
EXO: most are heat liable, some are stable
67
What are the LD50 levels of the different toxins?
ENDO: high
EXO: low
68
What are the type of secretion of the different toxins?
EXO: Actively secreted by cells, diffuse into surrounding medium.
ENDO: form part of cell wall, do not diffuse into surrounding medium.
69
What are the ways of obtaining the different toxins?
EXO: Readily separable from cultures by physical means such as filtration.
ENDO: Obtained only by cell lysing
70
What are the ways of ACTION the different toxins?
EXO: often enzymatic
ENDO: no enzymatic action
71
What are the ways of ACTION (specific or non-specific) the different toxins?
EXO: specific
ENDO: non-specific
72
State examples of common exotoxins and their associated bacterial pathogens.
**Intracellular-tageting toxins**
Tetanus toxin - Clostridium tetani
Botulinum toxin - Clostridium botulinum
Streptolysin - Streptococcus pyogenes
**Membrane-disrupting toxins**
Pneumolysin - Streptococcus pneumoniae
Alpha-toxin - Staphylococcus aureus
Toxic shock syndrome toxin - Staphylococcus aureus
73
How do some athogens evade phagocytosis or leukocyte microbidical mechanisms?
1) by adsorbing normal host componets to their surfaces
2) have surface factors that impede phagocytosis
74
What is an antibiotic?
Medicines that fight infections caused by
bacteria in humans and animals by either killing the bacteria or making it difficult for the bacteria to grow and multiply.
75
WHta is the main problem of antibiotics?
They cause side effects and contribute to antibiotic resistance.
76
How do antibiotics work against bacteria?
Antibiotics disrupt essential processes or structures in the bacterial cell. This either kills the bacterium or slows down bacterial growth. Depending on these effects an antibiotic is said to be bactericidal or bacteriostatic.
77
What is a bactericidal antibiotic?
kills bacteria
78
What is a bacteriostatic antibiotic?
supresses bacterial growth
79
What are the three maun antibiotic targets in bacteria?
1.The cell wall or membranes that surrounds the bacterial cell
2.The machineries that make the nucleic acids DNA and RNA
3.The machinery that produce proteins (the ribosome and associated proteins).
80
What rae the main types of antibiotics?
**Penicillins** for example, amoxicillin.
**Cephalosporins**- for example, cefaclor, cefadroxil and cefalexin.
**Tetracyclines**- for example, tetracycline, doxycycline.
**Aminoglycosides**- for example, gentamicin and tobramycin.
**Macrolides**- for example, erythromycin, azithromycin and clarithromycin.
**Sulfonamides** and **trimethoprim**- for example, co-trimoxazole.
**Quinolones**- for example, ciprofloxacin, and norfloxacin.
**Nitrofurantoin**- used for urinary infections.
81
What causes AMR?
The main cause of antibiotic resistance is antibiotic use. When we use antibiotics, some bacteria die but resistant bacteria can survive and even multiply. The overuse of antibiotics makes resistant bacteria more common.
82
What is antibiotic resistance?
AMR occurs when microorganisms, such as bacteria, viruses, parasites, or fungi, become resistant to antimicrobial treatments to which they were previously susceptible.
The more microbes are exposed to pharmaceuticals, such as antibiotics, the more likely they are to adapt to them.
83
How does AMR develop?
1) Microbes naturally evolve in response to changes in their environment. This includes contact with antimicrobial drugs. The more we use antimicrobials, the faster resistance will develop.
For example, just like any other bacteria, resistant bacteria can be spread through the food chain
in uncooked meat, produce that was contaminated by water or soil, prepared food.
Contaminated through surfaces, or in the environment through animal or human waste.
2) poor infection prevention and control in health care,
3) through contact between people in the community.
84
What are the 2 types of resistance?
1) Inherent (natural) resistance
2) Acquired resistance
85
What is inherent (natural) resistance?
Bacteria may be inherently resistant to an antibiotic.
eg. an organism lacks a transport system for an
antibiotic, or an organism lacks the target of the antibiotic molecule
(as in the case of Gram-negative bacteria, the cell
wall is covered with an outer membrane that establishes a permeability barrier against the antibiotic)
86
What is acquired resistance?
- modification of existing genetic material or the
acquisition of new genetic material from another source
87
What is teh most common mode of acquired resistance?
enzymatic inactivation of the antibiotic
88
89
What is vertical gene transfer?
The transfer of genetic information, including any genetic mutations, from a parent to its offspring.
90
What is genetic information encoded into in humans?
chromosomes
91
What is horizontal gene transfer?
The process by which bacteria acquire and/or exchange genetic material.
92
What are the antibiotic resistance genes carried on?
plasmids, transposons or integrons
93
What is the most common way for bacteria to become resistant to antibiotics?
By acquiring resistance genes from other bacteria.
94
What is used to test antibiotic susceptibility in bacteriostatic antibiotics?
**Minimum inhibitory concentration (MIC)**
Lowest concentration that results in inhibition of visible growth (colonies on a plate or turbidity of liquid culture).
95
What is used to test antibiotic susceptibility in bactericidical antibiotics?
**Minimum bactericidal concentration (MBC)**
Lowest concentration that kills 99.9% of the original inoculum.
96
What test is used to measure antibiotic susceptibility?
Kirby - Bauer method (Disk Diffusion Test)
97
What is the Epsilon test?
Etest (previously known as the Epsilometer test) is a way of determining antimicrobial sensitivity by placing a strip impregnated with antimicrobials
onto an agar plate.
