16. Microbial Infections II

What are the different types of microbes? Which are too small to visualize?

B
F
P
V
P

• bacteria

• fungus

• protozoa

• viruses

• prions

viruses and prions

How are microbes commonly encountered?

A
S
I
S

• aspirates

• scrapings

• impressions

• smears

What can be useful in recognize the type of microbe?

morphology

In most cases, what information about the microbe will provide enough information to diagnose it as a bacterium, fungus, or protozoan?

S
S
S

• size

• shape structure

What is the pathogenicity of a bacterium regulated by?

its virulence factors

What might virulence factors be used by microbes to do?

A
K
B
E
B
I
E

• attach to cells

• kill phagocytic cells

• block phagocytosis

• evade fusion with lysosomes

• block killing within phagocytes

• inhibit the host’s immune response

• enhance replication within phagocytes

molecules derived from bacterial genes

virulence factors

How are microbes able to cause disease?

I
A
C
I
T

• initial encounters at portals of entry

• adhesion

• colonization

• invasiveness

• toxigenesis

process of bacteria attaching to cells, tissue, and biologic substances

adhesion

adherence, multiplication, and establishment of bacteria

colonization

ability of bacteria to invade tissues

invasiveness

ability of bacteria to produce toxins

toxigenesis

Living bacteria (Gram-positive) secrete what?

exotoxins

Dead Gram-positive bacteria release what?

lipoteichoic acid

Dead Gram-negative bacteria release what?

endotoxins

What do these toxins activate?

large variety of biochemical cascades involving cell membrane systems and organelles that result in cell dysfunction and or death and destruction of ECM

secreted from viable bacteria, usually Gram-positive bacteria, and are potent toxins

exotoxins

Surface-acting exotoxins bind to ________ ________ and form ________ through which cell ________ occurs.

cell membranes; pores; lysis

also located in the cell wall of Gram-positive bacteria like S. aureus and behaves as a Gram-positive endotoxin because its actions mimic LPS

lipoteichoic acid

Gram-negative bacteria can release ________ into ________ tissues when they die. This is a general term used to characterize any ________ ________-associated toxin of the cell.

endotoxins; vascularized; outer membrane

Endotoxin typically refers to what?

LPS complex

What is the toxicity of LPS attributable to? What is immunogenicity attributable to?

the lipid A component of LPS; polysaccharide components of LPS

What does the membrane function to do?

I
F
P

• impede phagocytosis by macrophages

• facilitate colonization of target cells

• participate in the process of genomic variation in which the outer membrane acquires variant polysaccharide components and evades host innate and acquired immune responses

When are endotoxins released?

following destruction of the bacterial cell wall

True or false: Endotoxins are toxic to most animal cells, especially endothelial cells, platelets, and macrophages, tissues, and organs, and can be lethal if large quantities are absorbed by or released into the circulatory system.

true

What can occur if large quantities of endotoxins are absorbed by or released into the circulatory system? What does this outcome lead to?

activation of proinflammatory cytokines and nitric oxide (NO) from macrophages and endothelial cells; endotoxic shock characterized by fever, hypoglycemia, thrombosis (DIC, hypotensive shock, and death)

What are other virulence factors of bacteria?

S
S
B
C

• secretion systems

• siderophores

• biofilms/intracellular bacterial communities

• capsules

bacterial organelles that secrete or inject bacterial-derived toxins into the cytoplasm of target cells

secretion systems

virulence factors that mediate the release of iron from intracellular iron stores

siderophores

Some bacteria require ________ for colonization of mucosa. It is plentiful in cells but ________ to bacteria because it is tightly bound in ________, ________, ________, or ________ molecules.

iron; unavailable; heme; ferritin; transferrin; lactoferrin

How does biofilm serve as a virulence factor?

bacteria embedded in them are not susceptible to phagocytosis by macrophages, and they can become resistant to antibiotics

virulence factors that protect bacteria from phagocytosis by cells such as neutrophils and macrophages during acute inflammatory and adaptive immune response

capsules

Capsules are secreted by the ________ and are tightly adhered to the bacterial ________ ________. They also aid with ________ to mucosa and skin and are a reserve of ________, including ________.

bacterium; cell wall; adhesion; nutrients; water

What is the causative bacteria of wooden tongue?

actinobacillus lignieresii

normal commensal bacterium of mucosa of the oral cavity of cattle and sheep

Actinobacillus lignieresii

In which species does Wooden Tongue commonly occur in?

cattle and sheep

What is the portal of entry for Actinobacillus lignieresii?

during chewing, the bacterium is carried through the mucosa into the submucosal connective tissues via penetrating wounds such as those caused by sharp foreign bories

What are the target cells of Actinobacillus lignieresii?

submucosal connective tissue

What are the virulence factors of Actinobacillus lignieresii?

LPS and others

What is the inflammatory response of Actinobacillus lignieresii?

pyogranulomatous

Is there a potential for systemic spread with Actinobacillus lignieresii?

regional lymph nodes and rarely disseminates to other organs

What is this?

Actinobacillus lignieresii (Wooden Tongue)

What are the 6 key steps in the viral replication cycle?

1. A

2. E

3. S

4. R

5. A

6. S

1. attachment

2. entry (penetration)

3. spread (uncoating)

4. replication

5. assembly

6. shedding (release or egress)

Viruses are approximately a ________ times ________ than bacteria.

hundred; smaller

Viruses are unable to produce ________ and contain a limited number of ________. Therefore, they are completely ________ on ________ ________ for such resources and thus are ________ ________ parasites.

energy; enzymes; dependent; target cells; obligate intracellular

True or false: Viruses are of insufficient size to be observed and diagnosed using cytologic and histologic techniques.

true

Some diseases caused by viruses can be diagnosed using what?

inclusion bodies

aggregates of viral organisms within the cell’s cytoplasm and or nucleus

inclusion bodies

term used to express the relative severity of disease, clinical signs, and lesions caused by viruses

viral pathogenicity

What is viral pathogenicity determined by>

E
O

• expression of viral genes used to produce structural or functional proteins

• other molecules needed to sustain or enhance replication of the virus

In viruses, what do the actions of virulence factors focus on?

A
P

• attachment to, replication in, and shedding from target cells

• processes of modulating and or evading host defense mechanisms

During viral replication, the pathogenicity of a disease and the survival of target cells are determined by what?

H
H

• how the virus uses and or alters the functions of cell organelles and the transcriptional and translational processes

• how it escapes from target cells such as by lysis

microbes that are common in the environment and as microflora of mucosa

fungi

Fungi exist as ________ or as ________ ________ ________ or ________ (_________).

yeasts; branched filamentous pseudohyphae; hyphae (molds)

Fungi contain a variety of complex molecules that are arranged to form ________ ________ and ________ that aid in ________ of tissues and to ________ the microbe against ________ and other defense mechanisms.

cell walls; capsules; colonization; protect; phagocytosis

Because of this complexity, these molecules and cell walls cannot be completely ________ and removed by ________ ________. The response rapidly progresses to ________ ________.

degraded; acute inflammation; granulomatous inflammation

What substances often act to block phagocytosis? What happens when they are phagocytized?

glucans and glycoproteins; often difficult to degrade

What is the life span of macrophages? Why is this significant?

short (6 to 16 days); since it is short, these nondegraded materials are released from dead macrophages into tissues and lead to the recruitment of additional macrophages into tissues to remove the debris

Macrophages that phagocytize this debris are ________, resulting in the synthesis and secretion of ________ and ________ that recruit additional ________ from the vascular system into the site of inflammation.

activated; chemokines; cytokines; macrophages

This is results in recurring cycles of __________ in macrophages, ________ of macrophages, and ________ of fungi and fungal debris and antigens, and ________ of these materials by newly recruited and naive macrophages.

replication; death; release; phagocytosis

this disease is often initiated by farm management practice such as diets high in grains such as corn

mycotic rumenitis (followed by mycotic hepatitis)

Feedlot cattle are fed ________ quantities of corn that serve as a ________ source for ruminal ________, which convert it, in part, to ________ ________.

increasing; carbohydrate; microflora; lactic acid

What does excessive grain in the diet (diet overload) cause? What can happen, especially if some animals are deprived of water? What does this outcome result in?

increase in the quantity of lactic acid (lactic acidosis) in the rumen; lactic acid can accumulate and result in a drop of the pH of fluids covering ruminal mucosa; acid burns followed by loss of the epithelium and exposure of the basement membrane and subjacent vascularized connective tissue of the lamina propria and ECM tissues

What type of fungi are able to invade and colonize the injured mucosa and invade the vasculature of the ECM, and then spread regionally to other organ systems such as the liver?

angioinvasive fungi

What protozoa are ciliates?

balantidium coli (Balantidiasis)

What protozoa are flagellates?

giardia spp. (Giardiasis)

What protozoa are apicomplexans?

C
E
C
N
S
T

• cryptosporidium parvum (Cryptosporidiosis)

• eimeria and isospora spp (Coccidiosis)

• cytauxzoon felis

• neospora caninum

• sarcocystis neurona

• toxoplasma gondii

When do viruses, fungi, and protozoa all replicate their nucleic acid genomes?

during their infection cycle

transmissible protein aggregation disease and lack an infectious genome

prion diseases

True or false: Prion particles are of insufficient size to be observed and diagnosed using cytologic and histologic techniques. However, specific lesions can be diagnostic of prior diseases.

true

What is the mechanism of injury in transmissible spongiform encephalopathies (TSEs)?

metabolic dysfunction of neurons and neural cells caused by the conversion of normal cellular prion protein (PrPC, encoded by the host PRNP gene) to an abnormal form (PrPSc) and the accumulation of PrPSc in neurons, and extracellulary within the neuropil

Gross lesions are not observed except when? What may occur?

in chronic cases; atrophy of the brain

What microscopic lesions are characteristic of injury?

I
N
G
A

• intracytoplasmic vacuoles in neurons and neuropil (spongiform change)

• neuronal loss

• gliosis

• absence of leukocytic inflammation

What are some of the prion diseases in animals?

S
B
C
T
F
U

• scrapie (sheep and goats)

• bovine spongiform encephalopathy (BSE, aka mad cow disease)

• chronic wasting disease (CWD) in cervids

• transmissible mink encephalopathy

• feline spongiform encephalopathy

• ungulate spongiform encephalopathy