Skin flora & infection Flashcards
what microbial nutrients are in the secretions of sebaceous glands
Urea, amino acids, salts, lactic acid and lipids
what area of the skin are microbes primarily associated
with the sweat ducts and hair follicles
wihtin the superficial layers of the epidermis and upper parts of the hair follicles
what is the pH of human secretions
always acidic, between 4 and 6
what pathogens are most skin infections due to
Most skin infections due to Staphylococcus aureus, Streptococcus pyogenes and Pseudomonas aeruginosa
what is the only gram negative bacterium commonly found in the skin
Acinetobacter johnsonii
why are gram negative usually only minor constituents of normal skin flora
• 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.
give some examples of gram positive bacteria normally found on the skin
Staphylococcus epidermis, Streptococcus mitis and Micrococcus sp.,
(and a variety of both aerobic and anaerobic corynebacteria)
how many bacterial species live upon the skin
~1000 bacterial species
how does y-proteo P aeruginosa act as a mutualistic bacterium
offers benefits: pseudomonic acid (mupirocin) inhibits staph and strep tRNA synthetases; other factors inhibit fungi an opportunist. (can produce antibiotic)
but can cause disease
what species are mainly found in sebaceous areas
Propionibacteria and Staphylococcus species
what species of bacteria are mainly found in moist areas of the skin
Corynebacteria and Staphylococci
what species are mainly found in dry areas
Mixture of species but beta-Proteobacteria and Flavobacteriales dominate
ecologically why do sebaceous areas have greater species richness
due to the sebaceous fluid being produced form the glands
hat surgical revisions are available to treat infected hip replacements
Surgical revision involves
prosthesis removal and debridement with either immediate (one-stage; 30%) or
delayed (two-stage; 2-12 months; 64% (leave wound open with the joint and just treat the infection) joint replacement or
with excision (Girdlestone procedure; 6%).
what is 18F-Fluoro-deoxyglucose positron emission tomography (18F-FDG PET)
a procedure used to detect problems with hip implants by illuminating the Activated inflammatory cells that accumulate FDG with high concentraion
what two types of catheters are common sites of infection
vascular catheters and intravenous catheters
what is the standard catheter called (most commonly deployed medical device)
Foley catheters (100 million used annually worldwide)
what is the chemical makeup of struvite stones
magnesium ammonium phosphate
how do struvite stones from and what bacteria are capable of forming them
Due to urease hydrolysing urea, leading to the formation of ammonium and carbonate ions and an increase in urinary pH.
As the urine becomes alkaline, magnesium and calcium phosphate crystals are precipitated
Organisms splitting urea are Proteus, Pseudomonas, Klebsiella, Staphylococcus, and Mycoplasma.
what strategies are used against struvite formation around catheters
lower urine pH (citrus drinks); increase fluid intake; if antibiotics fail, surgically remove bladder stones
why does replacing the catheter after urinary infection cause recurrence
new catheters are placed directly into alkaline urine containing bacteria and aggregates of crystals. Consequently, crystalline biofilms readily form on the new catheters and patients are prone to recurrent catheter blockage.
The crystalline aggregates also form stones in the bladder; antibiotic treatment will not clear the bacteria from the urinary tract. Bacteria embedded in the biofilm of the bladder stones are also protected from antibiotics
what serious kidney and bloodstream infections can be caused by ascending reflux of alkaline urine containing bacteria and aggregates of crystals
pyelonephritis, septicaemia and endotoxic shock.
what are uncomplicated UTIs
occurs in patients who have a normal, unobstructed genitourinary tract, who have no history of recent instrumentation, and whose symptoms are confined to the lower urinary tract. (uropathogenic E.coli)
what are complicated UTIs
infection associated with factors increasing colonization and decreasing efficacy of therapy. Due to underlying medical conditions or other risk factors such as age, anatomical differences and indwelling devices. (P.mirabilis)
