W1 Infection, normal flora, infectious agents Flashcards
True or False:
Most microorganisms in nature and pathogenic
False!
Few microorganisms in nature are pathogenic.
Name 4 main types of pathogenic microorganisms
(a) Saprophytes
(b) Commensals
(c) Opportunistic pathogens
(d) True pathogens
Give examples of commensals (normal flora)
- Staphylococcus epidermidis
- Candida albicans
- Escherichia coli
Where on the body is staphylococcus epidermidis found?
Skin
Where on the body is Candida albicans found?
Upper respiratory tract
Where on the body is Escherichia coli found?
Large intestine
Give examples of opportunistic pathogens
- Staphylococcus epidermidis (device related infections)
- Candida albicans ( can cause oral thrush) overgrows when broad spectrum antibiotics are used (e.g. amoxicillin)
- E.Coli (UTI)
Give examples of true pathogens
- Staphylococcus aureus
- Neisseria Gonorrhoeae
- COVID-19
What is an infection?
A process of microbial invasion
Give examples of infections
- Common cold
- Tonsillitis
- Urinary tract infection
- Infected leg ulcer
What is an infectious disease?
Give examples
Communicable diseases. They are readily transmitted from person to person e.g. respiratory infections- TB, common cold, COIVD-19, gastrointestinal infections, Sexually transmitted infections (STI’s)
Infection in the 21st Century: Infectious diseases cause what percentage of all deaths?
Infectious diseases cause 25% of all deaths
Name some infections of concern in the developed world
-Pneumonia: HAP / CAP: UK deaths 30,000/PA
-Tuberculosis (10 million new cases) and drug-resistant TB (560,000 new cases) globally
UK 2018: 4,672
- Gastrointestinal infections (norovirus, campylobacter; Clostridium difficile (2018:13,286)
- Device-related infections (catheters, prosthetic joints)
-Healthcare associated infections (MRSA,
C. difficile, carbapenemase-producing Gram negative rods)
-Sexually transmitted infections (chlamydia, gonorrhoea, syphilis, herpes, genital warts, HIV)
What factors are facilitating the spread of infection in the 21st century?
- Ease of travel; ‘shrinking world-easy to travel’
- Medical interventions (ageing population; increased surgery)
- Overuse of antibiotics (antibiotic resistance; HAI)
- Contraceptive pill (STIs)
- Social: (alcohol, drugs, MSM, social networks: internet chat, geosocial networking apps - Grindr +Blendr – linked with increase in STIs)
Infection in the 21st Century: Developing Nations
Name some infections of concern in the developing world
Asia and Sub-Saharan Africa
- HIV: 70% the world’s HIV burden; 70% of all new HIV infections
- AIDS: 80% of AIDS related deaths
- Malaria: 90% of the global malarial burden
- TB: 40% of all new cases of TB
- Diarrhoeal disease (parasitic, bacterial, viral)
- Ebola
What factors are influencing the spread of infection in the 21st century? (developing nations)
- Poverty / overcrowding / malnutrition
- Weakened resources, infection control procedures and medical interventions (treatment, drugs, vaccination)
- Increased HIV incidence (secondary infections)
- Climate change; flooding
How do we classify infectious agents in clinical practice?
- Bacteria
- Parasites (helminths and protozoa)
- Fungi Fungi (moulds, yeasts)
- Viruses (DNA, RNA)
- Arthropods (direct / indirect causes of infection)
How are bacteria categorised in clinical practice?
- True bacteria
- Filamentous
- Spirochaetes
- Mycoplasmas
- Ricketssiae and Chalmydiae
How are true bacteria classified?
- Gram stain reaction (positive, negative)
- Shape (cocci, bacilli)
- Growth requirements (O2, ANO2)
Give some examples of Gram-positive cocci
- Staphylococcus eg. S. aureus, MRSA, S.epidermidis
- Streptococcus eg. S.pyogenes, S. pneumoniae,
Give examples of Gram-positive Bacilli
- Clostridium (anaerobic) eg. C. difficile
- Bacillus (aerobic) eg. B. anthracis
Give examples of gram negative cocci
Neisseria (N. gonorrhoeae)
Give examples of gram negative aerobic bacilli
- Enterobacteria eg. Escherichia coli
- Pseudomonads eg. Pseudomonas aeruginosa
- Parvobacteria (Small, Gram negative rods) eg. Haemophilus influenzae
- Vibrios (curved/spiral) eg. Campylobacter jejuni
Give an example of a gram negative anaerobic bacilli
Bacteroides sp
Give an example of a filamentous bacteria
Myobacterium
e.g. Myobacterium tuberculosis (high GC content in DNA)
Give an example of a spirochaete
Treponema
e.g. treponema pallidum
Give an example of a mycoplasma
Mycoplasma pneumoniae (causes atypical pneumonia)
No cell wall- can’t use beta lactam antiotics against them
Give an example of Ricketssia and Chlamydiae
Chlamydia and trachomatis (needs host cell to survive and growth)
PARASITES
What are the main characteristics of protozoa?
- Unicellular / Eukaryotic
- May exist as trophozoites or cysts eg. Giardia intestinalis
PARASITES
What are the main characteristics of helminths?
‘Worms’
-Multicellular / Eukaryotic eg. Ascaris lumbricoides (roundworm)
Parasites may be subdivided into:
Gastrointestinal (eg. Ascaris, Giardia)
Blood / tissue (eg. Plasmodium sp)
FUNGI
What are the main characteristics of moulds?
- Branching filaments (hyphae)
- Reproduce by forming spores
Give an example of a mould
Aspergillus fumigatus
FUNGI
What are the main characteristics of yeasts?
- Ovoid / Spherical
- Reproduce by budding
Give an example of a fungi
Candida albicans
What are viruses?
- Obligate intracellular parasites
- Strand of DNA or RNA encapsulated in a protein shell (capsid)
Give examples of RNA viruses
- Reoviruses (rotavirus)
- Retroviruses (HIV)
Give examples of DNA viruse
- Herpesviruses (Herpes simplex)
- Papovaviruses (Human papillomavirus)
What are arthropods?
Arguably the largest most successful single group of animals in the animal kingdom eg. louse, ticks, mites
How do arthropods cause disease directly?
By feeding on human blood/tissue eg. Phthirus pubis (crab louse: pubic lice, ‘crabs’)
How do arthropods cause disease indirectly?
By transmission of viruses/parasites to humans eg. Mosquitoes (malaria)
Why do we study infectious disease?
- Infectious disease in 21st century is common in developed and developing countries and is associated with significant morbidity and mortality
- Many factors facilitate the spread of infectious disease
- Commensal bacteria are widespread over many parts of the body and help to keep infectious disease at bay; may act as ‘opportunistic’ pathogens and cause disease; considered as ‘friend and foe’
Infectious agents can be conveniently categorised into 5 major groups:
- Bacteria
- Parasites
- Fungi
- Viruses
- Arthropods
Give examples of sterile parts of the body
Blood, muscle tissue and bladder
