Lecture 2- Bacterial Diseases Flashcards
What are the two potential routes of infection by bacteria?
Extrinsic
Intrinsic
Name some of the intrinsic sources of infection
- Nasal cavity and sinuses
- mouth
- upper respiratory tract
- stomach
- small intestine
- large intestine
- lower genital tract
- skin
What are expected and unexpected portals of entry?
Expected= normal micobiota entering through an expected route (newborn and maternal microbiota)
Unexpected= normal microbiota entering an unusual site or entry of pathogenic microbes
How are pathogens targeting the upper respiratory tract usually acquired?
Extrinsically
- droplets or airborne
- hand to hand transmission as intermediate
Give some example of viruses which enter through the upper respiratory tract
Influenza Parainfluenza Rhinovirus Measles VZV Herpes viruses
Give some examples of bacteria which enter through the upper respiratory tract
- streptococcus spp
- strep pneumoniae
- strep pyogenes
- neisseria meningitidis
- staph aureus
What are the consequences of bacterial pathogens acquired by the upper respiratory tract?
1) upper respiratory tract infection
- pharyngitis
- tonsillitis
- sinitis
2) spread to adjacent tissue
- meningitis
- brain abscess
- middle ear infection
3) lower resp tract infection
- bronchitis
- pneumonia
4) spread to bloodstream
- bacteraemia
What are the intrinsic sources of infection through the urogenital tract? Give examples
Bacteria landing here from the large intestine
- e.coli
- klebsiella
- enterobacter spp.
- candida/ yeast
- strep B
What are extrinsic sources of bacteria affecting the urogenital tract?
1) Nonsocomial transmission by catheters
- E. Coli
- Klebsiella
2) sexually transmitted
- Neisseria gonorrhoea
- Chlamydia trachomatis
- Syphilis
- HIV/ HSV
Skin is a portal of entry, how might pathogens enter through the skin?
- surgery/ wound
- skin disease (varicella, eczema)
- IVDA
- insect bites
- bites (human and animal)
- cannula
Name some bacteria which enter through broken skin
1) bacteria originally found in the mouth
- staph aureus
- strep pyogenes
2) hospitals
- pseudomonas
- MRSA
What are some of the consequences of infections via broken skin?
- superficial infection
- cellulitis
- abscess (pus filled pocket)
- fasciitis
- myositis (infection of muscle)
- gangrene/ necrosis (cell death under superficial layer)
- bacteraemia
Name some bacteria that enter through the GI tract
E. Coli Campylobacter jejuni Shigella (dysentery) Vibrio cholerae Salmonella enterica Salmonella typhi Listeria C. Difficile
Name some viruses that enter through the GI tract
Hep A
Hep E
Norovirus
Other than viruses and bacteria, what could have a pathogenic effect on the GI tract?
Toxins (enterotoxins, botulinum toxins)
Parasites
What are the consequences of bacterial infections acquired through the GI tract
Diarrhoea
Vomiting
Dysentery (bloody stools)
Bacteraemia
What are true pathogens
Bacteria which can cause disease in normal people e.g. Staph aureus
What are opportunistic pathogens?
Pathogens which can only cause disease when they are given a chance (when immunocompromised) e.g. Staph epidermis
Define the term pathogenicity
Ability to cause disease
What are commensalism?
Bacteria which do not cause disease
What are the two factors which affect pathogenicity?
Infectivity- ability to get into the host system and establish themselves
Virulence- features that enhance disease causation ( whodunnits enhance the symptoms)
What are the factors involved in infectivity?
- transmission to host
- ability to colonise host
- ability to find unique niche
- ability to replicate
- immune evasion
What are the four factors that affect virulence?
1) Toxins (pneumocystis forms pores in lungs)
2) Enzymes (hyaluronan lyase)
3) Interference with host cell function (superantigens from S.aureus interfere with T cells)
4) Complete immune evasion- S. aureus leukocidins= neutrophil death
Define the term infectious dose
The number of bacteria required to initiate an infection
What can affect the infectious dose?
Route of transmission (stomach acid)
Ability to colonise host
Tropism and motility- cholera have flagella
Replication speed
Immune evasion at site (TB survives inside macrophages)
Describe the pathogenicity of vibrio cholera
- massive infective dose
- flagella to penetrate mucus
- makes 2 component toxins (A+B)
- binds to gut
- triggers cAMP
- Cl- efflux
- Na+ and H20 follow
- diarrhoea
Which disease originates from the GI tract, moves down to the urogenital tract and is passed onto neonates?
Strep B
