Diagnosis and management of oral disease: microbiological tests

Question 1

Good sampling practice (3)

Answer 1

Wherever possible, collect the specimen prior to administration of antimicrobial therapy
Specimens must be from the actual infection site
-e.g. drainage from deeper site vs scab
Sample collection and transportation are critical
-results generated by lab are limited by quality of sample, which is affected by collection & transportation
-minimise introduction of contaminating microorganisms

Question 2

Processing samples (4)

Answer 2

Prompt processing is important
The quicker the specimen is processed the better
Pathogens may die in transit thus false negative results
If transport is delayed, a transport medium should be used

Question 3

Black top tube

Answer 3

Has transport medium in which keeps microorganisms alive

Black is activated charcoal to absorb any things the microorganisms produce

Question 4

Transport medium (1)

Answer 4

Transport media contain no growth supporting nutrients - objective is to maintain viability without supporting growth

Question 5

Transport medium: special purpose additives (3)

Answer 5

A reducing agent such as thioglycolate can be added to preserve anaerobes but allows aerobes to survive
CO2 can be included to support viability of certain pathogens (e.g. Neisseria gonorrhoeae and Streptococcus pneumoniae)
Charcoal, gelatin, or corn starch can be included to absorb toxic metabolic products of the host or the hosts normal microbes – most critical for particularly fastidious pathogens (e.g. Legionella)

Question 6

Vast majority of pathogens in oral cavity are

Answer 6

Anaerobes

Question 7

Pus samples (3)

Answer 7

Swabs
-clean mucosa prior to incision
-send in transport medium (water, isotonic salts, reducing agent, sometimes activated charcoal)
Aspirates
-leave in syringe
-make needle safe
Paper points: send in transport medium

Question 8

Mucosa and skin sample (2)

Answer 8

Swabs
-dry sites - moisten swab – standard
transport medium
-suspected viral – viral swab - viral transport medium
–>protein stabiliser, salts, gelatin, water, sometimes antibacterial agent
–>vesicle fluid – aspirate into a tuberculin syringe
Oral rinse
-10 ml sterile saline, rinse mucosa 30 seconds, spit into sterile bottle/tube
–>provides information on microbial load

Question 9

How to get samples to the lab (3)

Answer 9

Specimen request form
-state type of sample, where from, clinical signs and symptoms, provisional diagnosis
-ask for “culture and sensitivity”
-separate pocket of bag from specimen
Local lab: take ASAP
-same day or refrigerate if delay
Post
-label as ‘diagnostic specimen’ or ‘biological substance, category B’
-place in leak proof, rigid container (conforming with pi 650 - UN3373) - a primary receptacle, secondary packaging, outer packaging
Wrap aspirates in absorbent material in case of leakae
-e.g. cellulose wadding, paper towels
Itemise list of contents enclosed between secondary and outer packaging

Question 10

Category A (2)

Answer 10

Category A infectious substance is one which when exposure to it occurs, is capable of causing permanent disability, life-threatening or fatal disease to humans or animals
-HIV
-Hepatitis B or C
-Mycobacterium tuberculosis
This only applies to ‘cultures/concentrates’ - not swabs or aspirates from infected patients taken for diagnosis

Question 11

What to expect from the lab? (3)

Answer 11

Time for result? Preliminary possible after 24h but normally at least 48h required
-microscopy
-culture
Result will not give species (most times)
Will give sensitivity to common antibiotics: if in doubt telephone