Introduction to Infection and Microbes Flashcards
Define infection
An invasion of a host’s tissues by microorganisms causing a disease (pathological change/damage)
What causes the disease in an infection?
Microbial multiplication
Toxins
Host response
Define zoonoses
Infectious diseases of animals that can naturally be transmitted to humans
What are the 3 ways of horizontal transmission?
Contact (direct, indirect, vectors)
Inhalation (droplets, aerosols)
Ingestion (faecal-oral)
What is vertical transmission?
Transmission of an infection from mother to child before or after birth (eg. HIV)
Give some examples of types of exotoxins
Cytolytic
AB toxins
Super antigens
Enzymes
What are the 4 types of microbe?
Viruses
Bacteria
Parasites
Fungi
What is the key characteristic of all microbes?
They multiply
What is a viral envelope made of?
Lipopolysaccharides and lipids
What is the difference between gram positive and gram negative bacteria?
Gram positive bacteria have a very thick peptidoglycan wall whereas gram negative have a thinner peptidoglycan wall and 2 membranes. Gram positive bacteria hold the gram stain.
What are obligate anaerobes?
Microbes that require oxygen free environments to survive
How do we name bacteria?
Linnaean taxonomy
Genus then species eg. Staphylococcus aureus
Give an example of gram positive cocci
Staphylococcus aureus
Streptococcus pneumoniae
Enterococcus faecalis
Give an example of gram negative cocci
Neisseria meningitidis
Mortadella catarrhalis
Give an example of gram positive bacilli
Listeria monocytogenes
Bacillus cereus
Give an example of gram negative bacilli
Escherichia coli (E-coli) Klebsiella pneumoniae Salmonella typhi Pseudomonas aeruginosa Haemophilus influenzae
Name a yeast
Candida albicans (thrush) Cryptococcus neoformans (meningitis)
Name a mould (fungi)
Aspergillus species (lung infection)
Name a protozoa (single celled) parasite
Giardia lamblia
Plasmodium falciparum
Name a helminth (worm, multicellular)
Roundworms
Tapeworms
Flukes
What are the beneficial effects of normal flora?
Sheer number in bowel make it hard for invading pathogen to compete for nutrients and site
Some produce antimicrobials
Helps develop the immune system
Can provide nutrients (vitamin K)
Can aid in digestion and absorption of nutrients
What are mycoplasma?
Small, prokaryotic organisms with no peptidoglycan in their cell walls
Have a single plasma membrane
Extremely small so frequently pass through filters
Describe chlamydiae
Small bacteria that are obligate intracellular parasites
Grow in cytoplasmic vacuoles
Have 2 lipid bilayers
Describe rickettsia
Small, rod-like or coccobacillary shaped
Double layered, gram negative cell wall
Transmitted by arthropods (eg. Fleas)
What does positive RNA mean?
Directly encodes for mRNA
What does negative RNA mean?
Does not directly encode for mRNA
Why is HPV linked to cervical cancer?
Direct carcinogen as it express E6 and E7 proteins that inhibit p53 and pRB protein function (important for cell proliferation)
What is the normal range for CRP?
< 5
What bacteria causes cellulitis?
Staph aureus
Strep pyogenes
Briefly describe strep pyogenes
Gram positive
Group A streptococcus
Beta haemolytic (complete destruction of RBCs on blood agar)
What is the sweep test?
Performed when looking for necrotising fasciitis
If the fascia is dead then there will be no resistant to sweeping the finger around in a small surgical incision
What is the treatment for necrotising fasciitis?
Supportive care - IV fluids, analgesia, antypyretics
Antibiotics
ITU referral - high mortality condition
Surgery - drain pus, remove infected source, amputation
Why can’t necrotic tissue recover?
Lack of blood supply
What do we think about when choosing an Abx?
Severity of infection
Site of infection
Likely pathogen(s)
Route of administration
Possible adverse effects - allergy, interactions with other drugs, renal/hepatic impairment
Ecological impact - don’t select for other organisms
What is the likely bacterial cause of NF?
Strep pyogenes
Group A beta haemolytic
Describe alpha haemolysis and bacteria that do it
Produces a green appearance on agar
Strep viridans group
Strep pneumoniae
Describe the virulence factors of strep pyogenes
M proteins - antiphagocytic Exotoxins - streptolysin for cell lysis Streptokinase - lysis of clots Streptodornase - DNAases to promote spread C5a peptidase - inactivate complement
Which Abx are active against streptococci?
Beta lactams (penicillins, cephalosporins, carbapenems) Glycopeptides (vancomycin)
What is toxin-mediated disease treatment?
Anti-toxin therapy - high dose immunoglobulin
Interfere with toxin production - Abx that inhibit protein synthesis
What is the empiric treatment for strep infections?
Tazocin and clindamycin
If group A strep is identified, which Abx do we use?
Benzylpenicillin and clindamycin
Name some group A strep diseases (other than cellulitis and NF)
Acute pharyngitis/tonsillitis
Scarlet fever
Impetigo
Erysipelas
Puerperal sepsis ('childbed fever')What are some consequences post-strep infections?
Acute rheumatic fever - cross reaction between heart/joint tissue and strep antigens - valve damage/pericarditis/endocarditis etc
Acute glomerulonephritis - antigen-antibody complexes on basement membrane
Which bacteria falls under non-haemolytic ‘strep’?
Enterococcus faecalis
Name some common staph skin infections
Impetigo
Furuncle (boil) - hair follicles
Surgical wound infection
Is staph aureus coagulase positive or negative?
Positive
What colours do coagulase positive and negative tests produce?
Positive = gold Negative = white
Describe some features of coagulase negative bacteria
Low violence
Generally don’t cause infections in otherwise healthy people
Can create biofilms
Which of staph and strep is typically localised and which is spreading?
Staph = localised Strep = spreading
What Abx do we use for staph?
Flucloxacillin
Beta lactam combinations eg. Coamoxiclav and tazocin
Vancomycin for flucloxacillin resistant strains
Why is flucloxacillin generally a good choice?
Resistant to staph beta lactamase
