Intro to Infection & Microbes

Question 1

• define infection.

- how do people get infections?

Answer 1

• infection is invasion of a host’s tissues by micro organisms.
• via microbiota( microorganisms carried on skin & mucosal surfaces), physical contact eg STI’s, airborne transmission, vector eg mosquitoes, ingestion of contaminated food or water, contaminated surfaces, inhalation, vertical transmission eg mother to child

Question 2

• what are the steps in which a microorganism may cause disease?
• what are some disease determinants?

Answer 2

• exposure, adherence (to somewhere on body), invasion, multiplication, dissemination
• pathogen; virulence factors, inoculum size, anti microbial resistance, patients; co morbidities, site of infection

Question 3

What are supportive investigations used for? Give some examples

Answer 3

• to confirm there is an infection, NOT to find out what specifically the infection is
• full blood count(raised neutrophils= bacterial, raised lymphocytes= viral), C reactive protien (indicates presence of & degree of inflammation), liver & kidney function tests, imaging, histopathology

Question 4

What specific investigations would you do for a: bacterial infection, viral infection?

Answer 4

• bacteriology; specimens ie swabs, fluids, tissues, MC&S (microscopy-bacterial cells, gram stains, Culture, antibiotic susceptibility), antigen detection, nuclei acid detection
• virology; antigen detection, antibody detection, viral nuclei DNA or RNA

Question 5

Rank these microorganisms size from smallest to biggest; bacteria, fungi, prions, worms, viruses, yeasts
-give the basic structure of a virus and a bacteria.

Answer 5

• prions, viruses, bacteria, yeasts, worms
• virus= nucleus acid DNA or RNA, spikes for attachment, envelope, protein coat.
• bacteria= cell wall, capsule, nucleoid circular plasmid DNA, flagellum

Question 6

What are some classes of virus? Give examples.
What are the shapes of bacteria? Give examples.
Distinguish between gram positive and gram negative.

Answer 6

DNA viruses= double stranded non enveloped ie adenovirus, HOV, double stranded enveloped ie herpes, Hep B

• RNA viruses= ss, no envelops ie Hep A, ss enveloped ie rubella
• bacteria= coccus (circular), spirillus, bacillus (rod/ rectangle). Arranged clusters or chains.
• can be gram positive (thicker peptidoglycan & purple eg staph aureus, strep pneumoniae ), gram negative (thinner peptidoglycan and is decolourised by gram so pink eg salmonella, e-coli )

Question 7

Define the terms aerobes, obligate aerobes, anaerobes, obligate anaerobes
-give differences between prokaryotes and eukaryotes.

Answer 7

-aerobes can survive in the presence of oxygen, obligate aerobes require oxygen for survival, anaerobes can survive in the absence of oxygen, obligate anaerobes require oxygen free environments for survival (unless able to form spores).
-eukaryotes= multiple chromosomes, membrane bound nucleus, membrane bound organelles, carbs in pm, 80s ribosomes.
prokaryotes= 1 chromosome, no nuclear envelope, no membrane bound organelles, cell wall, no carbs, 70S ribosomes

Question 8

Describe

• fungi
• parasites

Answer 8

• fungi: yeasts (single celled, eg candida Albans natural yeast in vagina), mold eg athletes foot
• parasites: protazoa (single celled), helmiths (worms, multi-cellular)