Wound lecture

Question 1

Which organisms are associated with diabetes, cellulitis, post partum and burn infections?

Answer 1

1. Diabetes= staph, strep, OA, enterobacteriacea
2. Cellulitis as above but w GPCs
3. Post partum= as above but also H influenza, parainfluenzae, strep pyogenes
4. Burns= candida, filamentous fungi. enterobacteriacea, pseudomonas aeruginosa

Question 2

What are gardeners, fishermen, farmers, animal exposure and vets associated with?

Answer 2

gardeners= sporothrix schenckii, clostridia other fungi
fishermen= vibrio, myobacterium - slow growing GPB
farmers= clostridia, fungi
animal exposure= erysiopelothrix rhusiopathiae GPB
vet= all of the above

Question 3

What are associated with human, cat/dog, insect and spider bites?

Answer 3

human- mixed flora staph aureus, strep pyogenes, eikenella corrodens (GPB)
cat dog- Pasteurella multocida (GNB)
insect- s. aureus, strep pyogenes
spider- s. aureus, sporothrix schenckii

Question 4

What is associated with water?

Answer 4

Vibrio vulnificus, v. alginolyticus, Aeromonas hydrophila, Mycobacterium marinum

Question 5

Microscopy in wounds

Answer 5

Gram stain- look at leucocytes and report +/++, also bacteria seen and type of it and growth. correspond to growth, and SAB+C if see fungal/yeast cells if not seen don’t report anything

Question 6

What are the distinctive morphologies of anaerobes, actinomyes and streptomyces, nocardia, vibrio, fungi, erysiopelothrix rhusiopathiae

Answer 6

Anaerobes include Clostridium (GPB- perfingens large brick no spore don’t decolourise, others can decolourise like C tetanus an have spores), bacteroides- small pleomorphic GNB and fusobacterium and GNB with pointy ends
actinomyces and streptomyces are thin branching GPB like norcardia which is also and filamentous as well as acid fast (diff)
Vibrio- GNB comma shape grow on tcbs and can’t grow without salt
Fungi include moulds which have hyphae (red or pink), yeast with blastospores and pseudohypae (purple), with sporothrix schenckii elliptical cigar shaped.
erysiopelothrix rhusiopathiae GPB squiggly

Question 7

In ulcerative gingivitis which 2 bugs cant be cultured but are seen for it to be vincents angina and what other name does the disease have?

Answer 7

Fusobacterium and spirochetes and trenchmouth is the name

Question 8

Wound culture significance

Answer 8

Any pure culture from a sterile or closed lesion probably sig. Enterobacterales, P. aeurginosa, CoNS usually not sig in surface wound sites
most common wound isolate= S aureus and b haemolytic strep

Question 9

Which organisms are set up on plain sensitest in air for wounds

Answer 9

Staphylococcus, Acinetobacter, Enterobacterales, Vibrio, Aeromonas, Burkholderia, Psuedomonas sp.

Question 10

Which organisms are set up on BA sensitest in CO2 overnight

Answer 10

Strep and Enterococcus, Corynebacterium, Erysipelothrix, Listeria, Neiserria meningitidis and Moraxella catarrhalis

Question 11

Micrococcus, Kokuria, Kytococcus primary and secondary ID tests, primary and secondary habitat, and pathogenicity?

Answer 11

Primary tests- GPC catalase POS, obligate aerobe, microdase POS
Secondary tests- molecular and biochemical analysis
Primary habitat- mammalian skin and mucosa, secondary- meat dairy products soil disseminated from animals
Opportunistic pathogens in immunocompromised patients - intracranial abscesses, prosthetic valve endocarditis, Peritonitis in CAPD (which dec kidney function)

Question 12

What is CAPD?

Answer 12

Continuous Ambulatory Peritoneal Dialysis

Question 13

Which 2 sp of staphylococcus are catalase NEG?

Answer 13

S. saccharolyticus and S. aureus subsp anaerobius (virtually an OA) while most are facultative

Question 14

Where is staph aureus NF and what is its clinical significance?

Answer 14

Anterior nares in 20-40% people, skin, nasopharynx, perineal areas, often nosocomial infection. all isolates are clinically significant

Question 15

What are some infections caused by staph aureus?

Answer 15

Folliculitis, furuncles and carbuncles, impetigo (like group a strep), wound infections bacteremia pericarditis pyomyositis (inf of skeletal muscles)
food poisoning where exotoxins act as enterotoxins (rapid onset)
scalded skin- sloughing off superficial layer and depends on strain producing certain toxins
toxic shock syndrome multisystem illness

Question 16

How do the virulence factors of staph aureus - capsular polysaccharides, protein A, enzymes, haemolysins and toxins work?

Answer 16

1. Capsular polysaccharides inc resistance to phagocytosis by PMN and inc adherence properties
2. Protein A is present in cell wall of most stains and binds IgG (except IgG3) by Fc interfere w opsonisation phago
3. Enzymes - lipases help spread to cutaneous and subcutaneous tissue, B Lactamases, collagenases, coagulases, catalase etc
4. Haemolysins are toxic to host cells in vivo and lyse RBC in vitro - have a, b, gamma, delta. alpha is toxic to PMN RBC and has neurotoxic effect. different haemolysins compared to strep
5. toxins - epidermolytic cause scalded skin, enterotoxins w food poisoning

Question 17

Which staph aureus enterotoxins cause food poisoning and which cause toxic shock syndrome?

Answer 17

A to D,E,H,I= food poisoning- heat stable.
A to D, H,I, toxic shock syndrome toxin-1 (TSST-1)= toxic shock

Question 18

How to ID staph aureus from staph?

Answer 18

Perform coagulase test (5% stains can be neg) or phadebact staph (which tests for clumping factor as well as protein A and capsular polysaccharides)
POS= presumptive s. aureus, confirm with slide coagulase being POS and dark blue colonies on Brilliance staph

Question 19

What is the principle of coagulase test for s aureus?

Answer 19

Coagulase is an enzyme that staph aureus has that reacts with fibrinogen.
there are 2 tests for cell bound coagulase (use slide test- clumping factor test) and free coagulase (tube test- staphylocoagulase)
In each use EDTA plasma as citrated plasma= false pos.

Question 20

Slide coagulase test is _______ for _______ _________ (95% strains pos), reacts directly with ___________ in the plasma and causes it to precipitate on staph cell wall. Emulfisy test colony in water and use straight wire of plasma. All neg results should be tested with ______ coagulase as may produce free coagulase.

Answer 20

rapid, clumping factor, fibrinogen, tube

Question 21

Tube coagulase detects _____ coagulase which reacts with coagulase reacting factor (prothromin) to form a complex. this activated CRF reacts with fibrinogen to form a _______ ______. what is the method?

Answer 21

free, fibrin clot.
Emulsify 2-3 colonies in plasma incubate at 35 degrees for 4hrs, check for clot formation. if neg- incubate overnight at RT (prolonged at 35 will prod false neg result as strain can produce fibrinolysis)

Question 22

When is staph epidermidis clinically significant?

Answer 22

If it is pure, in a sterile environment lot of it clinical history of surgery etc. CoNS most likely nosocomial infections- coagulase negative staph most common is epidermidis

• primarily as a result of practices and procedures esp. implantation of medical devices e.g. shunts, catheters, cardiac valves, prosthetic joints
• Surgery, instrumentation, implants allow invasion of organism
• Clinical relevance should be substantiated before ID and reporting CoNS- seen in smear, purity, quantity of growth site of infection, Hx- not always clinically sig like s aureus

Question 23

What are the virulence factors of staph epidermidis? (3)

Answer 23

1. capsular polysaccharide adhesin (forms biolayer, slime- adhere to plastic and prov conditions inhibitory to antibiotic and host defence actions)
2. Propensity to acquire antimicrobial resistance - survival in hospital setting
3. It is v common - NF around everywhere

Question 24

How can we ID coag neg staph?

Answer 24

Novobiocin S but check inn urine, commercial ID panels, MALDI TOF

Question 25

What is the 2nd most encountered CoNS?

Answer 25

S. haemolyticus - native valve endocarditis

Question 26

Staph slide and tube coag test result

S. schleiferi subsp. coagulans
* S. schleiferi subsp. schleiferi
* S. sciuri subsp. carnaticus
* S. sciuri subsp. rodentium

Answer 26

S. schleiferi subsp. coagulans – tube coagulase positive, slide coagulase variable
* S. schleiferi subsp. schleiferi – tube coagulase variable, slide coagulase positive
* S. sciuri subsp. carnaticus – slide coagulase variable, tube coagulase negative
* S. sciuri subsp. rodentium – slide coagulase positive, tube coagulase negative

Question 27

Clostridium sp. (probably not perfringens as decolourised cells with spores present) Middle: Abscess: C. perfringens, S. epidermidis, Enterococcus sp. Isolated
Right: Bacteroides fragilis group – typical vacuolated GNB circled

Answer 27

b

Question 28

Which staph is cat neg?

Answer 28

Catalasepositive
- Exceptions: S. saccharolyticus, S. aureus subsp. anaerobius

Question 29

General Staphylococcus Epidemiology

Answer 29

Commensal inhabitants of skin and mucous membranes in humans and animals - Some species are only found in animals (e.g., S. delphini, S. simiae)
* Occasionally they can be isolated from humans i.e., dog bite
* Zoo workers, farmers, vets
* Infections frequently caused by endogenous colonising strains - Trauma/abrasion to skin, mucosal surface or sterile site
- Can be an unnoticed event - rubbing eyes or ears, scratch
- Commonly isolated from wounds, eyes, ears
* Strains can be transmitted from person to person - Direct skin contact
- In the air (dispersed from clothing, linen)
- Contact with inanimate objects (fomites)
- Can become part of normal flora of the recipient
- Direct transmission to a sterile site by healthcare workers
* during surgery - surgeon/nurse - hands/instruments/air
* dressing of wounds - hands/in the air
* poor aseptic technique - dirty hands, needles
- Very significant in hospitals and the community if strains have acquired antimicrobial resistance…e.g., MRSA