Infection Model and Introduction

Question 1

What is an infection?

Answer 1

An infection is the invasion of a host’s tissues by microorganisms that then cause disease by microbial multiplication, toxins and host response.

Question 2

Where do infection come from?

Answer 2

People get infections from other people, animals, environment (air, water, food and surfaces) and intermediary carriers.

Question 3

What is horizontal and vertical transmission?

Answer 3

Horizontal transmission – spread from person to person or via vectors

Vertical transmission – from mother to child before or at birth

Question 4

In general terms how does a disease occur from initial exposure?

Answer 4

Exposure, adherence, invasion multiplication and then dissemination

Question 5

What causes the host cellular damage?

Answer 5

Host cellular damage can be direct or as a consequence of the host immune response.

Question 6

How do we test for infections?

Answer 6

Histopathology – take a sample and culture then use detection methods to specifically name the organisms causing the infection e.g. microscopy, Gram stains, antigen detection and nucleic acid detection.

Virology – must detect the antigen of the virus or antibodies to those antigens. Also detecting viral DNA or RNA.

Question 7

What is a virus?

Answer 7

Virus – protein coat and envelope (also protein but could be lipopolysaccharide) surrounding any type of nucleic acid (very small amounts of genetic code. On the outside attached to the protein envelope are different spikes that allow for attachments to specific cell surfaces (and antigens).

RT refers to reverse transcriptase. All viruses hijack the mRNA machinery to go on to create proteins.

Question 8

What are bacteriophages?

Answer 8

Bacteriophages – viral infections of bacteria – transmission of antibiotic resistance.

Question 9

What are the two different type of bacteria?

Answer 9

Two different types of bacteria – Eubacteria and Archaebacteria.

Question 10

Describe a typical bacteria

Answer 10

Typical bacteria – central DNA looped genome, sometimes extra =chromosomal DNA which are smaller circles – transferable i.e antibiotic resistance (plasmid). Free floating ribosomes, cytoplasm, plasma membrane, Cell wall and cell capsule. Pili poke through the envelope structure, flagellulm.

Question 11

What different shapes can bacteria be in?

Answer 11

Bacterial shapes – coccus is round (cocci plural), spirillus (spiraled) and bacillus also known as rods (plural bacilli) can be arranged in clusters or chains.

Question 12

Describe some common virulence factors?

Answer 12

Host entry such as polysacchirde capsule, Adherence such as pili and fimbriae, Invasiveness such as enzymes like collagenase, Iron sequestration (iron used as metabolite) such as siderophores.

Question 13

What’s the difference between endo and exotoxins?

Answer 13

Toxins – exotoxins are released out into the host (diphtheria toxin) and endotoxins (not secreted but released when the cell is disrupted) e.g. lipopolyacharies.

Question 14

Discuss fungi

Answer 14

Fungi – Fungi include mould and yeasts and can be distinguished from other infectious organisms such as bacteria and viruses because they are eukaryotes. They have a membrane enclosed nucleus and other organelles. The fungal cell wall and cell membrane are fundamentally different from bacteria. Fungal cell walls are composed largely of chitin. They are therefore unaffected by antibiotics that commonly are targeted at bacterial cell walls (which are composed of peptidoglycan).

Question 15

What are protozoa

Answer 15

Protozoa – single celled

Question 16

What are Helminths

Answer 16

Helminths – worms, multicellular

Question 17

Describe the difference between Prokaryotes and eukaryotes

Answer 17

Prokaryotes: Circulate DNA, plasmids, no nuclear envelope, no membrane bound organelles, cell wall +/- peptidoglycan and 70 s ribosomes.

Eukaryote: Multiple chromosomes, membrane bound nucleus, membrane bound organelles present, cell wall only in plants and 80s ribosomes (70s in organelles)

Question 18

What factors influence a patients likelihood of infection?

Answer 18

(epi)genetics, age (change over time in what infections are likely to affect you), gender, physiological state (pregnancy, menstrual cycle), pathological state (nutritional, hygiene, co-morbidities) and social factors. Other factors are the calendar time – seasons.

Question 19

How does premature birth affect immune the system?

Answer 19

Premature birth results in a defective immune system as the immune system is developed later in the pregnancy.

Question 20

How can infections be spread?

Answer 20

There are different ways that an infection can spread: continuous or direct spread from one part of your body to another, inoculation (i.e. an item used on you that is infected), haematogenous, ingestion, inhalation, vectors and vertical transmission.

Question 21

How does an infection lead to cellular damage?

Answer 21

Once an infection is established and attached to the host cells (or invasion) there are 2 mechanisms by which damage is caused: interaction with the host defences leading to inflammation and eventual damage or production of toxins leading to host damage.

Question 22

What is an endotoxin?

Answer 22

Endotoxin – released when bacterial cell breaks down causing an inflammatory response (such as lipopolysaccharide in gram negative), exotoxin released by bacteria on purpose.

Question 23

In general terms how do we treat infections?

Answer 23

Specific – antimicrobials, surgery such as drainage, debridement (removal of dead tissue) and dead space removal after this (space left after debridement).
Supportive – symptom relief and physiological restoration