INTRO-- BACTERIOLOGY

Question 1

The vast majority of resident bacteria are —
history of co-evolution and harmonious co-existence with the host.

Answer 1

commensals

Question 2

acquired soon after birth, are able to adhere to body surfaces.

Answer 2

COMMENSALS

Question 3

They form stable polymicrobial communities that are present throughout life as

Answer 3

‘normal microflora’

Question 4

The composition of the microbial communities tends

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to be host-specific
and, within hosts,
to be organ- specific.

Question 5

on the skin and in the hollow organs whose surfaces and
cavities are open to the environment.

Question 6

beneficial to the host in many ways

Answer 6

stable microflora

Question 7

The digestive system relies on the normal microflora to

Answer 7

to degrade ingested material in the rumen of cattle and sheep, in the caecum and colon of horses, and in the colon of pigs.

Question 8

The microflora of the rumen synthesizes

Answer 8

vitamin K and some of the vitamin B group,
as does the microflora of the intestine in non-ruminants

Question 9

a primes the immune system, facilitating a more efficient host response to challenge by
bacterial pathogens

Answer 9

normal microflora

Question 10

when that equilibrium is
disturbed or when the host is under severe stress, an indigenous member may escape from the restraining influences of the bacterial community and act as an

Answer 10

opportunistic pathogen

Question 11

This can occur in the

Answer 11

gastrointestinal tract following the
administration of oral antibiotics

Question 12

can exist as a commensal in the rumen but when it transfers to the liver of feedlot cattle it can act as a pathogen that causes hepatic abscesses

Answer 12

Fusobacterium necrophorum

Question 13

The ability of a microbe to damage a host is
called

Answer 13

pathogenicity

Question 14

the relative capacity of a pathogen to damage a host is the
degree of

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virulence

Question 15

The bacterial traits that confer pathogenicity are

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virulence factors

Question 16

virulence factors; these include

Answer 16

adhesins, toxins and capsules

Question 17

whose genes are
expressed only when their products are required in a process called

Answer 17

phase variation

Question 17

Many of the genes that encode virulence factors are
associated with mobile genetic elements:

Answer 17

bacteriophages, plasmids and
pathogenicity islands.

Question 18

arise when bacteria that live on the skin or mucous membranes as harmless commensals take advantage of impaired antimicrobial defenses of the host and behave as opportunistic pathogens.

Answer 18

Endogenous infections

Question 18

This is likely to happen
when

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-epithelial barriers are damaged,
-when immunity is weakened by drugs, -radiation or exogenous pathogens,
-when the ecological balance of the resident
-microbial community is disturbed by administration of antibiotics, or
-when the bacteria gain access to sites from which they are usually absent.

Question 19

are driven by microbial genes that express virulence factors and by host genes that are responsible for resistance to pathogens.

Answer 19

Subsequent interactions

Question 19

occur after direct or indirect transmission from an infected animal or from the environment

Answer 19

Exogenous infections

Question 20

Pathogens that
are able to survive within host cells are grouped into two categories:

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• strict (obligate) intracellular pathogens
  -facultative intracellular pathogens

Question 21

are obligate intracellular pathogens

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Chlamydiae and rickettsiae

Question 22

Among the facultative intracellular pathogens,

Answer 22

Mycobacterium species enter and replicate in phagocytic cells

Question 23

invade and replicate in non-phagocytic epithelial cells

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- Brucella species, - Uropathogenic E. coli, - Salmonella species, - Listeria monocytogenes

Question 24

The major virulence factors are

Answer 24

adhesins, capsules and toxins.

Question 25

to attach to host tissues and to resist the flushing action of body fluids

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adhesins

Question 26

play a significant role throughout the course of an infection

Question 27

The expression of adhesins is

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subject to phase variation in response to local conditions

Question 28

attach to the epithelial cells of the urinary bladder

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Type 1 fimbriae of uropathogenic E. coli a

Question 28

attach toepithelial cells in the kidney

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P fimbriae

Question 29

Adhesin–receptor interaction of enteropathogens with intestinal epithelium results in activation of signalling pathways that generate the release of n

Answer 29

nuclear factor-kappaB (NF-κB)

Question 30

a transcription factor that moves to the cell nucleus where it up-regulates the expression of a number of pro-inflammatory genes.

Answer 30

Nuclear factor-kappaB (NF-κB),

Question 31

interfere with opsonization, the binding of complement and antibody to the bacterial surface, thus protecting the bacterium from engulfment by phagocytes and from attack by antimicrobial agents.

Answer 31

capsules

Question 32

Encapsulated bacteria are often resistant to phagocytosis.

Question 33

During growth, encapsulated bacteria may stick together, forming a microcolony or a biofilm that is resistant to phagocytic cells because of its large size.

Question 34

Many capsules are composed of

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polysaccharides and are hydrophilic

Question 35

; thus, these capsules may help the bacterium to resist desiccation

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polysaccharides and are hydrophilic

Question 36

composed of polyglutamic acid;

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Bacillus anthracis

Question 37

; it is anti-phagocytic and is regarded as an essential virulence

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Polyglutamic acid;

Question 38

Traditionally, bacterial toxins have been considered to be of two types:

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exotoxins endotoxins

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produced and secreted by viable bacteria

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exotoxins

Question 40

integral constituents of the bacterial cell wall not released until the microorganisms are lysed.

Answer 40

endotoxins

Question 40

Toxicity resides in the lipid A portion.

Question 41

It is composed of three parts:

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- hydrophobic glycolipid (lipid A) - a hydrophilic polysaccharide composed of a core oligosaccharide and an Opolysaccharide (O antigen)

Question 41

is the lipopolysaccharide (LPS) of the outer leaflet of the outer membrane of Gram-negative bacteria.

Answer 41

Endotoxin

Question 42

Is released when bacterial cell walls are damaged by the complement system, phagocytes or antimicrobial drugs

Answer 42

Lipopolysaccharide

Question 42

LPS interacts with cells that have the toll-like receptor 4 (TLR-4):

Answer 42

mononuclear phagocytes neutrophils platelets dendritic cells and B lymphocytes

Question 43

High concentrations of circulating endotoxin greatly increase the release of

Answer 43

cytokines, notably interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-α)

Question 44

Released cytokines induce

Answer 44

fever, activate macrophages and clotting factor XII, and stimulate B cells to divide and produce antibodies

Question 45

stimulate the production of prostaglandins and leukotrienes which are mediators of inflammation

Answer 45

Cytokines

Question 46

responsible for the deposition of thrombi in small vessels (disseminated intravascular coagulation) and for a dramatic drop in blood pressure, giving rise to life-threatening endotoxic shock.

Answer 46

LPS

Question 47

ingested in contaminated food and produces systemic effects.

Answer 47

potent exotoxin, such as Clostridium botulinum toxin

Question 47

can be produced by either Gram-positive or Gram-negative bacteria.

Answer 47

Exotoxins

Question 48

are highly antigenic proteins that can induce the production of protective antitoxins.

Answer 48

toxins

Question 49

are produced within the host and they may exert their effects either locally or systemically

Answer 49

exotoxins

Question 50

Exotoxins have a two-subunit structure comprising an A subunit & B

Question 50

that possesses toxic enzymatic activity

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A subunit

Question 51

which acts on intracellular targets, does not become active until it is released in the cell.

Answer 51

enzymatic component

Question 51

that is responsible for binding the exotoxin to specific receptors on the host cell membrane and may help in the transfer of the B subunit across the cell membrane.

Answer 51

B subunit

Question 51

determines the host cell specificity of the toxin: if the cell does not have receptors for the B subunit, it is not vulnerable to the toxin.

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B subunit

Question 51

Categories of exotoxins:

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(i) toxins that act on the extracellular matrix; (ii) toxins that act on the plasma membrane of their target cells, where they interfere with transmembrane signalling pathways or alter membrane permeability; (iii) toxins that act inside the cells, where they modify signalling pathways or the activities of the cytoskeleton; and (iv) toxins that cause dysfunction of the immune system, so-called superantigens.

Question 52

Both tetanus toxin and botulinum toxin have the

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A–B subunit structure.

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toxins that cause dysfunction of the immune system,

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superantigens

Question 54

The cells of the innate immune system express various --- capable of detecting conserved molecular ‘patterns’ that are unique to microorganisms and are not expressed by the hosts

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pattern-recognition receptors (PRRs

Question 55

Although these microbial ‘patterns’ are present in commensals and pathogens alike, they are known as

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pathogen-associated molecular patterns (PAMPs)

Question 56

– rather than ‘molecular patterns’ that are recognized in most instances.

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It is molecules – specific, individual molecules

Question 57

that are expressed constitutively in a variety of host immune cells, such as macrophages, dendritic cells, neutrophils, mast cells, B cells, and specific types of T cells.

Question 57

Mammals possess a family of transmembrane PRRs, called

Answer 57

toll-like receptors (TLRs

Question 58

They are expressed also in some non-immune cells, such as epithelial cells, endothelial cells and fibroblasts

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toll-like receptors (TLRs)

Question 59

detect the molecular signatures of microbial pathogens, they orchestrate the innate immune responses, and they help to initiate the adaptive immune response

Answer 59

TRLs

Question 60

If an enteric pathogen, such as Salmonella Dublin in cattle or S. Typhi in humans, is sequestered in the gall bladder or in lymph nodes and is not excreted in the faeces, the host is described as a

Answer 60

latent carrier

Question 61

In stressful situations, latent carriers can become active carriers, asymptomatic hosts that contaminate the environment and infect other susceptible animals.

Question 61

if the pathogen is shed in faeces, either continuously or intermittently, the host is considered an a

Answer 61

active carrier

Question 61

In cattle herds, ---- can establish long-term residence in both latent carriers and active carriers.

Answer 61

Salmonella Dublin

Question 62

is common amongst pathogens, there are exceptions

Answer 62

‘restrained virulence'

Question 63

These bacteria produce highly lethal toxins that kill the host, which then becomes an anaerobic substrate in which the bacteria multiply and from which they can be disseminated as spores

Answer 63

Clostridium species

Question 64

Some pathogens are not invasive and do not spread systemically, yet they release toxins and other signals that pose challenges to homeostasis, local or systemic.

Question 64

contaminate a wound in any region of the body, producing a neurotoxin.

Answer 64

Clostridium tetani

Question 64

secretes a number of toxins that degrade the epithelial barrier and allow the opportunistic pathogen to enter the subepithelial tissues.

Answer 64

Pseudomonas aeruginosa

Question 64

There are two routes by which invasive pathogens can breach the epithelial barrier: b

Answer 64

- through the intercellular spaces (the paracellular route), or by - passage through the epithelial cells (the transcellular route).

Question 65

The paracellular route can be taken by bacteria that are able to disrupt the intercellular tight junctions: for example,

Answer 65

-Enteropathogenic E. coli, -Listeria monocytogenes, -Helicobacter pylori, -some Clostridium species and -some Salmonella serovars

Question 66

may pass through the paracellular route when tight junctions are opened by emigrant neutrophils responding to chemotactic stimuli from pathogens present on the epithelial surface.

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Shigella species

Question 67

There are two major types of induced uptake

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- a ‘zipper’ mechanism and - a ‘trigger’ mechanism

Question 67

induced by specific ligand–receptor interactions at the cell membrane

Answer 67

Zipper mechanism

Question 67

During bacteraemia, bacteria are present transiently in the bloodstream without replicating,

Question 67

induced by effector molecules delivered into the cell by a type III secretory system

Answer 67

trigger mechanism

Question 68

whereas, during septicaemia, pathogenic organisms multiply and persist in the bloodstream, producing systemic disease.

Question 69

Bacterial infections can be conveniently categorized as

Answer 69

acute, subacute, chronic or persistent.

Question 70

usually have a short severe clinical course, often a matter of days, and the invading bacteria are usually cleared from the body by the host’s immune response.

Answer 70

Acute infections

Question 70

produce clinical effects of less intensity

Question 70

tend to occur when the host fails to eliminate the pathogen.

Answer 70

Chronic infections

Question 70

occurs in certain sites such as the uriniferous tubules and the CNS in which the effects of cell-mediated and humoral immunity are minimal.

Answer 70

Persistence

Question 71

shedding may occur from some of these sites as in bovine leptospirosis, in which leptospires may be shed in urine for more than a year.

Answer 71

Persistent