BK - Skin & Indwelling Device Infections Flashcards
What are some common implant infections and the associated organisms? (9)
- Contact Lenses: Pseudomonas aeruginosa, Staphylococcus epidermidis (Keratitis)
- Dentures: Candida albicans (Oral Thrush)
- Urinary Catheters: Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, Proteus mirabilis (Bacteriuria)
- Intravascular Catheters: Staphylococcus epidermidis, Staphylococcus aureus (Septicemia, Endocarditis)
- Endotracheal Tube: Pseudomonas aeruginosa, Escherichia coli, Staphylococcus epidermidis, Staphylococcus aureus (Pneumonia)
- Voice Prostheses: Streptococci, Staphylococci (Prosthesis Failure)
- Prosthetic Valve: Staphylococcus epidermidis, Streptococcus sanguis (Prosthetic Valve Endocarditis)
- Joint Replacement: Staphylococcus epidermidis, Staphylococcus aureus (Septicemia, Device Failure)
- Total Artificial Heart: Pseudomonas aeruginosa, Staphylococcus epidermidis, Staphylococcus aureus (Septicemia, Device Failure)
What are the two main classifications of normal skin flora?
Normal skin flora can be classified as:
- Transients: Bacteria that are constantly being deposited on the skin but cannot multiply and eventually die.
- Residents: Bacteria that can multiply and establish themselves on the skin
What are some characteristics of the secretions from skin glands that influence the skin flora?
Skin gland secretions provide nutrients for microbes and have an acidic pH (between 4 and 6), which helps to:
- Favor the growth of certain bacteria.
- Limit the growth of harmful pathogens.
What are some common bacteria found in normal skin flora according to conventional wisdom? (2)
Traditionally, culture recovery focused on:
- Gram-positive bacteria: Staphylococcus epidermis, Streptococcus mitis, Micrococcus sp.
- Corynebacteria: Propionibacterium acnes (can cause acne)
How are gram-negative bacteria related to the skin flora? (3)
- Gram-negative bacteria almost always minor constituents of the normal flora, even E. coli continually inoculated from faecal contamination.
- Acinetobacter johnsonii is the only other Gram-negative bacterium commonly found on the skin.
- Originally thought lack of success of Gram-negative bacteria is due to their inability to compete with Gram-positive organisms that are better adapted to the skin. If the latter are eliminated by antibiotic treatment, the Gram-negative bacteria can flourish.
What are 4 features of the skin microbiome?
Skin Microbiome
- 2 square metres of human skin
- ~1000 bacterial species upon human skin from 19 phyla
- Total number of bacteria estimated at 1012
- Most are found in the superficial layers of the epidermis and the upper parts of hair follicles
What 3 regions can specific bacterial communities exist in?
Sebacious (hair, chest)
- Mainly Propionibacteria (Cutibacteria) and Staphylococcus species
Moist (joints, groin, arm pits)
- Mainly Corynebacteria and Staphylococci
Dry (arms, legs)
- Mixture of species but beta-Proteobacteria and Flavobacteriales dominate
How is a prosthetic hip infection treated? (2)
Surgical revision is the primary treatment for prosthetic hip infections. It involves removing the prosthesis and infected tissue (debridement). Two main approaches exist:
One-stage revision (30%): Involves immediate implantation of a new prosthesis during the same surgery.
Two-stage revision (64%): Considered more effective but costlier. Involves:
- Debridement in the first surgery.
- Implantation of a new prosthesis in a second surgery (2-12 months later).
- Sometimes a spacer implant is used in the interim.
How can 18F-FDG PET help diagnose prosthetic hip infection?
18F-Fluoro-deoxyglucose positron emission tomography (18F-FDG PET) is an imaging technique that detects areas of inflammation.
- FDG accumulates in activated immune cells, and its presence in the hip joint can indicate infection
How do vascular catheters increase the risk of UTIs?
Vascular catheters breach the skin barrier, creating a direct pathway for bacteria to enter the urinary system
What are the 2 different catheters and how can they cause UTIs?
Central line catheters: Enter the bloodstream and travel to the urinary system.
Foley catheters: Have a balloon to prevent leakage but can:
- Increase urine pH (become more alkaline) due to a bacterial enzyme (urease).
- Contribute to crystal formation (struvite) that can block the catheter and damage the urinary tract lining.
How does urease from Proteus mirabilis contribute to UTIs?
Similar to the stomach bacterium H. pylori, Proteus mirabilis produces urease, an enzyme that breaks down urea in urine to ammonia. This can:
- Increase urine pH (alkaline environment).
- Damage the protective lining of the urinary tract, making it more susceptible to infection.
Why can simply replacing a blocked catheter lead to recurrent UTIs? (2)
Replacing a blocked catheter without addressing the underlying cause (crystals and bacteria) can lead to recurrent infections:
- New catheters placed in alkaline urine with bacteria and crystals.
- Crystals can form biofilms on new catheters, making them more prone to blockage
How can UTIs from catheters lead to serious complications? (3)
UTIs from catheters can have serious consequences if left untreated:
- Ascending reflux of urine: Urine flows backward into the kidneys, potentially causing pyelonephritis (kidney infection).
- Septicemia: Bacteria enter the bloodstream, causing a life-threatening infection.
- Endotoxic shock: A severe inflammatory response to bacterial toxins.
How are UTIs from catheters treated if antibiotics fail? (2)
If antibiotics fail to clear the infection due to biofilms in bladder stones:
- Strategies to lower urine pH (e.g., citrus drinks, increased fluid intake).
- Surgical removal of bladder stones may be necessary.
