Introduction to Microbes and Infection Flashcards
(28 cards)
What micro-organisms cause human disease?
- Bacteria
- Viruses
- Fungi
- Parasites
What is the Baltimore Classification of Viruses?
A way of classifying different types of virus.
There are 7 different classes of virus.
What are the three types of DNA virus?
1) Single-stranded, non-enveloped (Parovirus 19)
2) Double-stranded, non-enveloped (Adenovirus, HPV)
3) Double-stranded, enveloped (Herpes, Hep B)
What are the four types of RNA virus?
1) Single stranded, positive strand, icosahedral, non-enveloped (Norovirus, Hep A)
2) Single stranded, positive strand, icosahedral or helical, enveloped (HIV, Hep C, Rubella)
3) Single stranded, negative strand, helical, enveloped (Ebola, Lassa, Measles, Influenza, RSV)
4) Double stranded, icosahedral, non-enveloped (Rotavirus
What are the three main shapes of bacteria?
- Coccus (round)
- Spirillus (spiral)
- Bacillus (rods)
What arrangements can cocci be found in?
- Clusters
- Chains
What is the difference between Gram positive and negative?
- Gram positive = purple
- — Thick peptidoglycan layer
- Gram negative = pink
- – Thin peptidoglycan layer and has outer membrane made of lipopolysaccharide and protein
What are aerobes?
Can survive in the presence of oxygen
- Obligate aerobes require oxygen for survival
What are anaerobes?
Can survive in the absence of oxygen
- Obligate anaerobes require oxygen-free environment for survival (unless able to form spores)
What are some medically important Gram positive cocci?
- Staph Aureus
- Coagulase negative staph
- Alpha-haemolytic streptococci
- Beta-haemolytic streptococci (including Strep pyogenes)
- Streptococcus pneumoniae
- Enterococcus faecalis
What some medically important example of Gram negative cocci bacteria?
- Neisseria meningitidis
- Neisseria gonorrhoeae
- Moraxella catarrhalis
- Acinetobacter baumannii
What are some medically important examples of Gram positive bacilli bacteria?
- Listeria monocytogenes
- Bacillus anthracis
- Bacillus cereus
What are some medically important examples of Gram negative bacilli bacteria?
- Escherichia coli
- Proteus species
- Salmonella typhi
- Haemophilus influenzae
What are the main mechanisms of bacterial pathogenesis?
- Virulance factors
- – Host entry (eg. polysaccharide capsule)
- – Adherence to host cells (eg. pili and fimbriae)
- – Invasiveness (eg. enzymes such as collagenase)
- – Iron sequestration (siderophores)
- Toxins
- – Exotoxins (eg. diptheria toxin)
- – Endotoxins (lipopolysaccharide)
What are the two different types of fungi?
- Yeasts (single-celled)
- –> Candida albicans
- –> Cryptococcus neoformans
- –> Pneumocystis jiroveci
- Molds (multicellular)
- –> Aspergillus species
- –> Dermatophytes (ringworm, athlete’s foot)
What are the two different forms of Parasite?
- Protozoa (single-celled)
- –> Giardia lamblia
- –> Cryptosporidium parvum
- –> Plasmodium falciparum
- Helminths (worms, multi-cellular)
- –> Roundworms (eg. Enterobius vermicularis)
- –> Tapeworms (eg. Taenia saginata)
- –> Flukes (eg. Schistosoma mansoni)
What is an infection?
- Invasion of a host’s tissues by micro-organisms
What is disease caused by?
- Microbial multiplication
- Toxins
- Host response
How do people get infections (summary)?
- From source
- Via intermediary
- From environment (water, food, air, surface)
- From animals
- From microbiota
- Vertical transmission (mother-to-child)
How can the microbiota cause infection?
- Bacteria carried on skin and mucosal surfaces
- Normally harmless or even beneficial
- Infection occurs when commensals transferred to other sites
How can people get infections from source or intermediarys?
- Contact and intermediary may be infected or colonised
- Physical contact required for some infections, eg. sexually transmitted diseases
- Airborne spread from contacts, eg. chickenpox
- Vector may be necessary to spread some diseases from source, eg. malaria
How do people get infections from the environment?
- Transmission due to ingestion. of contaminated food or water
- Inhalation of air contaminated by environmental organisms
- Contact with contaminated surfaces
How do micro-organisms cause disease?
- Exposure
- Adherence
- Invasion
- Multiplication
- Dissemination
- Whilst releasing virulence factors (exotoxins, endotoxins) and causing host cellular damage (either direct or consequent to host immune response)
What are disease determinants?
Factors that determine how bad an infection will be for the patient
- Pathogen:
- virulence factors
- Inoculu, size
- antimicrobial resistance
- Patient
- Site of infection
- Co-morbidities
