Infection Model and Infections on Surfaces Flashcards
What is an opportunist
A pathogen that invades a host when they are immunosuppressed
What patient factors influence infection
Patient
- Age
- Gender
- Physiological state
- Pathological state (co-morbidities)
- Social factors
Time
- Calender time
- Relative time- incubation time
Place
- Current
- Recent
What are the types of pathogens
Virus
Bacterium
Fungus- Yeast and Mould
Parasite- Protozoa and Helminth
Name the mechanisms of infection
Contiguous spread
Inoculation
Haematogenous
Ingestion
Inhalation
Vector
Vertical transmission
Describe the process of managment
Diagnosis- history, examination, investigations
Treatment- specific or supportive
Infection prevention- hospital and/or community
Describe the two types of treatment briefly
Specific treatment- using antimicrobials or surgery to target the infection directly. Surgery can be via three ways: drainage, debridement or dead space removal
Supportive treatment- giving symptom relief and physiological restoration. Supportive treatment aims to reduce the pain while figuring out the causative pathogen or disease
What surfaces can pathogens colonise on
Skin - epithelium, hair, nails
Mucosal surfaces - conjuctival, gastrointestinal, respiratory, genitourinary
Why do new strains of the same bacteria cause disease
Because the body cannot produce antibodies fast enough against the new strain of bacteria
What are the four ways patients get surface infections
Invasion
Migration
Innoculation
Haematogenous
Describe how endocarditis originates
Turbulent blood flow damages endothelium in the heart, causing sub-endothelial damage
This exposes fibronectin which bacteria can then bind to and colonise, eventually forming a vegitiation
This then results in endocarditis from the resulting immune response and inflammation
Why are artificial surfaces at risk of infection
They are avascular so are not protected by the immune system
Why is staph aureus different from other bacteria in relation to endocarditis
Staph aureus does not need any pre-existing valve damage to cause endocarditis unlike other bacteria
How are prosthetic joint infections treated
Joint is removed and there can then be: joint replacement, spaces in the joint or fusion of the joint
What is the process of infection on a surface and what is the hosts response
Adherence to host cells/surface - using pili or fimbriae
Biofilm formation
Invasion and multiplication
Response is either: pyogenic or granulomatous
What is a biofilm
A microbial community attached to a surface, encased in an extracellular matrix of microbial origin
What two bacteria are responsible for frequent nosocomial infections
Staphylococci
Enterococci
What are the stages in biofilm formation
Surface attachment
- Either reversible or irreversible
Microcolonies
- Cell proliferation
- Coaggregation
Macrocolonies
- Mushroom and tower-like structures
- Cell detachment
Why is it difficult to remove bacteria in biofilms by the immune system
The bacteria aggregate together making it harder for opsonisation and phagocytosis
What mechanism does a biofilm have against antibiotics
Matrix restricts penetration and diffusion of some antimicrobials
B-lactamase secretion
Expression of multi-drug resistance efflux pumps
Quorum-sensing systems and different concentrations of nutrients and waste contribute to resistance
What does quorum sensing control
Sporulation
Biofilm formation
Virulence factor secretion
What principles are involved in quorum sensing
Signalling molecules - autoinducers (AI)
Cell surface/cytoplasmic receptors
Gene expression - co-operative behaviour and more AI production
What is differential time positivity
The time for a blood culture to grow will depend on where the microbe was taken from as some areas will take a longer time to produce a culture than others
Give some examples of external natural surface infections
Cellulitis
Pharyngitis
Conjuctivitis
Gastroenteritis
UTI
Pneumonia
Give some examples of internal natural surface infections
Endovascular - endocarditis and vasculitis
Septic arthritis
Osteomyelitis
Empyema
Give some examples of prosthetic surface infections
Intravascular lines
Peritoneal dialysis catheters
Prosthetic joints
Cardiac valves
Pacing wires
Endovascular grafts
Ventriculo-peritoneal shunts
What are some causative organisms of prosthetic valve endocarditis, group the organisms
Native valve and >1 year prosthetic valve - viridans strep, enterococcus faecalis, staph aureus, candida, HACEK group
<1 year prosthetic valve - coagulase negative staph
Name some causative organisms of prosthetic joint infections
Coagulase negative staph
Staph aureus
Name some organisms which cause cardiac pacing wire endocarditis
Coagulase negative staph
Staph aureus
