Skin flora & infection

Question 1

what microbial nutrients are in the secretions of sebaceous glands

Answer 1

Urea, amino acids, salts, lactic acid and lipids

Question 2

what area of the skin are microbes primarily associated

Answer 2

with the sweat ducts and hair follicles

wihtin the superficial layers of the epidermis and upper parts of the hair follicles

Question 3

what is the pH of human secretions

Answer 3

always acidic, between 4 and 6

Question 4

what pathogens are most skin infections due to

Answer 4

Most skin infections due to Staphylococcus aureus, Streptococcus pyogenes and Pseudomonas aeruginosa

Question 5

what is the only gram negative bacterium commonly found in the skin

Answer 5

Acinetobacter johnsonii

Question 6

why are gram negative usually only minor constituents of normal skin flora

Answer 6

• 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.

Question 7

give some examples of gram positive bacteria normally found on the skin

Answer 7

Staphylococcus epidermis, Streptococcus mitis and Micrococcus sp.,
(and a variety of both aerobic and anaerobic corynebacteria)

Question 8

how many bacterial species live upon the skin

Answer 8

~1000 bacterial species

Question 9

how does y-proteo P aeruginosa act as a mutualistic bacterium

Answer 9

offers benefits: pseudomonic acid (mupirocin) inhibits staph and strep tRNA synthetases; other factors inhibit fungi an opportunist. (can produce antibiotic)
but can cause disease

Question 10

what species are mainly found in sebaceous areas

Answer 10

Propionibacteria and Staphylococcus species

Question 11

what species of bacteria are mainly found in moist areas of the skin

Answer 11

Corynebacteria and Staphylococci

Question 12

what species are mainly found in dry areas

Answer 12

Mixture of species but beta-Proteobacteria and Flavobacteriales dominate

Question 13

ecologically why do sebaceous areas have greater species richness

Answer 13

due to the sebaceous fluid being produced form the glands

Question 14

hat surgical revisions are available to treat infected hip replacements

Answer 14

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%).

Question 15

what is 18F-Fluoro-deoxyglucose positron emission tomography (18F-FDG PET)

Answer 15

a procedure used to detect problems with hip implants by illuminating the Activated inflammatory cells that accumulate FDG with high concentraion

Question 16

what two types of catheters are common sites of infection

Answer 16

vascular catheters and intravenous catheters

Question 17

what is the standard catheter called (most commonly deployed medical device)

Answer 17

Foley catheters (100 million used annually worldwide)

Question 18

what is the chemical makeup of struvite stones

Answer 18

magnesium ammonium phosphate

Question 19

how do struvite stones from and what bacteria are capable of forming them

Answer 19

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.

Question 20

what strategies are used against struvite formation around catheters

Answer 20

lower urine pH (citrus drinks); increase fluid intake; if antibiotics fail, surgically remove bladder stones

Question 21

why does replacing the catheter after urinary infection cause recurrence

Answer 21

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

Question 22

what serious kidney and bloodstream infections can be caused by ascending reflux of alkaline urine containing bacteria and aggregates of crystals

Answer 22

pyelonephritis, septicaemia and endotoxic shock.

Question 23

what are uncomplicated UTIs

Answer 23

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)

Question 24

what are complicated UTIs

Answer 24

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)

Question 25

in bladder infections what biofilm like defence do E.coli form inside the bladder epithelium

Answer 25

Intracellular bacterial communities (IBC): produce ‘pod’ in which they hide and become dormant in. and are activated by infection with another species (causing the epithelial wall to die and fall away)

Question 26

why are E.coli more virulent in presence of other bacteria (potentially)

Answer 26

when they form Intracellular bacterial communites, the cells inside the pod are activated by infection with another species which causes epithelial wall to start to die and fall away creating a perfect entry point for bacteria to come (eg Gardnerella vaginalis )

Question 27

what are three signatures of Ecoli biofilms

Answer 27

(type 1) pili, antigen 43 and EPS formation

Question 28

what are langerhans cells

Answer 28

a unique population of tissue-resident macrophages that form a network of cells across the epidermis of the skin, but which have the ability to migrate from the epidermis to draining lymph nodes (LN). Their location at the skin barrier suggests a key role as immune sentinels.