S7 L2 - Infections on surfaces, Endocarditis Flashcards
What is the surface?
Give examples
- *Surface** – interface between a solid and either a liquid or gas
- *Example:** Skin (epithelial, hair, nails), mucosal surface (conjunctival, gastrointestinal, respiratory, genitourinary)
- *Skin microbiota e.g.**
- Viruses
- Bacteria - gram positive
- Bacteria - gram negative
- Fungi
- Parasites
Skin microbiota:
Viruses: Herpes simplex, papilloma
Bacteria (gram positive): Staph. Aureus, Staph. Epidermis, coagulase negative staphylococci (e.g. Staph. Epidermis)
Bacteria (gram negative): Enterobacteriases e.g. E.coli USUALLY BELOW THE WAIST
Fungi: Candida albicans
Parasites: Mites
- *Microbiota:**
- Nares
- Nasophranyx
- Mouth
- Stomach
- Intestine
- Urethra
- Vagina
Microbiota:
- Nares: Staph. Aureus
- Nasophranyx: NHS Neisseria Meningitidis, Haemophilus Influenzae, Streptococcus pneumoniae
- Mouth: Streptococcus mutans, Candida Albicans
- Stomach: Helicobacter
- Intestine: E.coli, C.difficile
- Urethra: Lactobacilli
- Vagina: Lactobacilli, Candida Albicans
How do people get infected?
4 ways
- Invasion (contiginous spread) e.g. Strep pyogenes pharyngitis
- Migration e.g. Escherichia coli urinary tract infection
- Inoculation e.g. coagulase negative staphylococcus prosthetic joint infection
- Haematogenous e.g. Veridians Streph endocarditis
- *Examples of natural surface infections**
- External infections
- Internal infections
- Example of prosthetic surface infections
Examples of natural surface infections:
- External: cellulitis, pharyngitis, conjunctivitis, gastroenteritis, urinary tract infection, pneumonia
- Internal: Endocarditis, vasculitis, empyema (infection of the pleurae space), septic arthiritis, osteomyelitis
Examples of prosthetic surface infections:
Prone to infections by skin bacteria
- Intravascular lines
- Peritoneal dialysis catheters
- Prosthetic joints
- Cardiac valves
- Pacing wires
- Ventriculo-peritoneal shunts
(organisms may be growing on these surfaces for many months or years, before symptoms…)
Prosthetic heart valve endocarditis - Microorganisms
Prosthetic joint infections - Microorganisms
Cardiac pacing wire electrodes - Microorganism
- *Processes of pathogenesis of infection at surface**
- includes biofilm formation etc…
- Adherence to host cells or prosthetic surface (by pilli or fimbriae)
- Biofilm formation (colony of bacteria – number of bacteria together, signal to each other called quorum sensing, showing lots of them are there, this switches on different metabolic pathways, then bacteria secrete substances that cover them extracellularly, covering the bacteria with a protective layer called biofilm (also can form spores, and other virulence factors too), very challenging to treat as the biofilm prevents human host response by complement, antibodies etc. Biofilms are also very impervious to antibiotics)
- Invasion and multiplication
- Host response (innate and adaptive)
- *Management of infections on surfaces**
- Diagnosis
- Challenges with biofilm
Diagnosis -
- Identify infecting organism and its antimicrobial susceptibilities
- Challenges: Biofilms – Poor penetration of antibiotics into biofilms, Low metabolic state so a challenge to treat with antibiotics, dangers of new infection if surgery is required
- Blood cultures (depends on the infection)
- Tissue culture (depends on the infection) e.g. heart valve is removed and then sent to the lab, to find the culture on it
- *Management of infections on surfaces**
- Treatment
Aim – sterilise tissue, reduce bioburden
Aim is achieved through:
- Antibacterial
- Remove prosthetic material
- Surgery (resect infected material)
- *Prevention**
- Natural surface
- Prosthetic surface
Natural surface -
Maintain surface integrity (e.g. keeping skin intact), prevent bacterial surface, removing surface colonisation, Oral hygiene (reduces chances of endocarditis)
Prosthetic surface -
Prevent contamination at the time of putting the prosthetic surface into the body, removing surface colonisation e.g. disinfectant of skin at time of surgery/intravascular lines…, remove intravascular lines etc.. straight away when not needed, prophylaxis medication before surgery
- *Endocarditis**
- Hallmark of endocarditis
- Three explanations of symptoms in endocarditis
- Infective endocarditis - what does this mean? What happens here?
Hallmark of endocarditis: formation of vegetation that binds to valves or mural endocardium, leads to a collection of fibrin, platelets and inflammatory cells
- *Three explanations of symptoms in endocarditis:**
1. Symptoms due to cytokines
2. Local spread of infection causing destruction of the myocardium
3. Distal blood borne septic embolism (superficial bacterial colonies tend to embolise – i.e. lodge and obstruct digitally)
Infective Endocarditis:
Microorganisms that enter the blood stream from the skin, mucosa and other sites of local infection, bind to the vegetation and cause local infection leading to a pro-coagulative state. Further fibrin deposition, platelet aggregation and bacterial invasion lead to an infection cascade causing infective endocarditis
- *Endocarditis:**
- Pathogen
- Patient at risk (3 main reasons)
- Prevention
- Clinical features
- Mechanism of infection
- Infection (explain the process)
Duke criteria for diagnosing endocarditis includes…
Reminder:
- Prosthetic Joint infections (Device-associated infections)
- Cardiac pacing wire electrode (Device-associated infections)
