1. Diagnostic Microbiology Laboratory -2015-
Introduction to Diagnostic Microbiology
*Lecture 1*
Diagnostic Microbiology Laboratory
-2015-

2. Introduction to Bacterial Identification
Accurate and definitive microorganism identification, including bacterial identification and pathogen detection, is essential for correct disease diagnosis, treatment of infection and trace-back of disease outbreaks associated with microbial infections.
Bacterial identification is used in a wide variety of applications including microbial forensics, criminal investigations, bioterrorism threats and environmental studies.

3. Approach to Laboratory Diagnosis
The laboratory diagnosis of infectious diseases involves two main approaches:
Bacteriological approach; in which the organism is identified by: microscopic observation, macroscopic identification, biochemical reactions and molecular diagnosis techniques.
Immunological (serological) approach; in which the organism is identified by detection of antibodies against the organism in the patient’s serum.

4. Diagnostic approaches
Macroscopic identification
Microscopic observation
Biochemical tests
Molecular diagnosis techniques
Serological tests

5. Cultural Characteristics
Microorganisms may show distinguishing gross morphologies when cultured on different media.
This macroscopic appearance of bacteria (characteristic growth patterns which can be observed with the naked eye) is often used in their identification.

6. Cultural Characteristics are observed according to
1. Observe the amount of growth
none = 0
slight = +
moderate = ++
abundant = +++
2. Coloration- Two types of pigmentation may occur:
a. pigmentation occurring within the organism itself; or
b. water soluble pigment that diffuses into the surrounding medium.
Most organisms will lack chromogenesis (pigment production), exhibiting a white, beige, or gray growth. Pigmentation within the organism may be red, yellow, violet, or other colors.
Soluble pigments may be blue, green, yellow, brown, or other colors. Hold the plate up to the light to examine for diffusible pigments. It may be helpful to compare the color of the agar with an uninoculated media.

7. 3. Opacity- Surface growth can be termed as opaque, as transparent, or as translucent (partial transparency) depending on the degree of growth.
4. Form- The gross or macroscopic appearance of the growth from the single streak inoculation is described by:
a. filiform - uniform growth along the line of inoculation.
b. echinulate- margins of growth have a toothed appearance.
c. beaded- separate or semi confluent colonies.
d. effuse- growth is thin, veil-like, unusually spreading.
e. arborescent- branched, tree-like growth.
f. rhizoid- root-like appearance

9. Morphology and staining
There are many different ways to stain bacteria so that they can be more easily visualized under the microscope. Some stains can also be used to identify and classify bacteria.
1. Gram stain
2. Acid fast Stain
Other stains used to visualize bacterial structure
Spore stain
Flagellar stain
Capsule stain

10. Biochemical Characteristics
1. Fermetation & oxidation.
2. IMVIC tests.
3. Biochemical tests.
4. API 20 E.

11. Other techniques
1. PCR 2. Phage typing 3. Other molecular techniques

12. Serological characteristics
To Identify several strains of the same type of bacteria we need to perform serotyping of them such as:
1. Widal test
2. Lancefield grouping
3. Protien A latex
4. others

13. How to handle microbiological sample
All samples should be treated as infectious ones.
Some samples will demonstrate microbial growth and require further laboratory analysis to identify the contaminants. When growth is detected, the sample should be taken from the clean section of the laboratory to the live culture section without undue delay.
Subculturing, staining, microbial identification, or other investigational operations should be undertaken in the live culture section of the laboratory. If possible, any sample found to contain growing colonies should not be opened in the clean zone of the laboratory.
Careful segregation of contaminated samples and materials will reduce false- positive result..

14. How to handle microbiological sample
Soo it necessary to ensure:
1. Proper collection of the sample
2. Adequate amount
3. Requisitions
4. Tightly capped container

15. How to handle microbiological sample
When needed, a written test request must include the following information:
1. Hospital No.
2. Full name
3. Gender
4. Date of birth
5. Address
6. Social security no.
7. For female pregnant/ lactating
8. Date of illness
9. Signs/ symptoms
10. Date of onset
11. Recent travel history
12. Immunization

16. Identification of samples
1. Type of specimen
2. Collection date and time
3. Laboratory number
4. Test requested
5. Ordering physician
6. Laboratory findings

17. Specimen handling and storage
Samples should be delivered to microbiology central processing area, within the specified period and then CPA will
1. Check requisition for completeness.
2. Store the sample until they are picked up to microbiology staff.
When STAT requests are received, the CPA staff should inform the microbiology supervisor.

18. Specimen rejection criteria
1. The information in the label doesn’t match the information on the request form.
2. The specimen was transported in improper container or at wrong temperature.
3. Leaking specimen.
4. The quantity of specimen is insufficient.

19. Comments
1. Blood received in blood culture is unsuitable for fungal isolation.
2. Saliva is unacceptable for culture.
3. Multiple samples sent with the same request should be noticed.

20. Samples not satisfactory for culturing
1. Sample in fixative
2. Dried out swab
3. 24hrs urine or sputum
4. Urine still more than 2hrs at room temperature.
5. Antibiotic medicated patient
6. Anaerobic culture for vaginal, cervical, or urine samples
7. Stool samples from more than 5 days inpatient.

21. Media Classification Consistency Nutritional component Functional use
Solid
Semisolid
Liquid –Broth-
Simple
Complex
Synthetic or Chemically Defined Media: Exact chemical composition is known
Basic-General- media
Selective
Differential
Enriched
Enrichment
Transport

22. End of Lecture