1. Mrs. Dalia Kamal Eldien Msc in Microbiology
Swabs culture
Mrs. Dalia Kamal Eldien
Msc in Microbiology
Lecture NO 11

2. Objectives Identify the different types of swabs
Method of collection the swab
Laboratory diagnosis of the different swab
Case study of patient suffering from tonsillitis
Case study of patient suffering from gas gangrene

3. Introduction
A swab can be taken from any area of the body that appears to have an infection. The microbiology laboratory attempt to culture (grow) a wide range of organisms (especially bacteria) from this sample, to determine which ‘germ’ is causing the infection.
Examples to the common swabs send to the microbiology lab
Throat swab
Nasal swab
Eye swab
Ear swab
High vaginal swab
Urethral swab
Wound swab
Skin swab

4. Method of collection:
A sterile cotton-wool swab, which is like an ear-bud, is used to collect a small amount of fluid from a wound or surface.
By rolling the swab in affected area.
The swab is transported in a special medium that encourages growth of bacteria.
For the throat swab In a good light and using the handle of a spoon to depress the tongue, examine the inside of the mouth. Look for inflammation, and the presence of any membrane, exudate, or pus, Swab the affected area

5. Swab

6. Collection of throat swab

7. Collection of Wound Swabs
Gentle cleansing of a skin wound prior to sample collection by sterile normal saline is recommended to reduce commensal flora.
Purulent exudates must be expressed onto swabs. Place the swab into the transport media.
Deep wound specimens (aspirates) are optimal as the predictive value of superficial swabs is low.
Investigation of deep wounds for anaerobes

8. Collection of the wound swab

9. Collection of Eye Swabs
Collect before topical or anesthetics are applied.
Swab pus or purulent discharge taken from the lower inverted lid.
Place the swab into the transport media.
Collection of Ear Swabs
Swab the external ear canal.

10. Urethral swab:
Express exudates from the urethra and collect it on a swab. If exudate is unavailable, insert an urethrogenital swab about 2 cm into the urethra, gently rotate it and remove.
Place the swab into the transport medium.
Vaginal swab
Wipe away any excessive amount of secretion.
Obtain secretions from the mucosal membrane with a swab.

11. Collection of Vaginal swab

12. Laboratory diagnosis Specimen Processing
Microbiologic testing should include both direct microscopic examination and culture of the specimen.
Clinical specimens should be inoculated onto both general purpose and selective media to maximize bacterial recovery.
Common media used are:
2 blood agar(earobic& anearobic)
MacConkey agar

13. Special media
Neomycin blood agar or kanamycin BA when anaerobic bacteria is suspected
Modified Tinsdale medium (MTM)or Tellurite blood agar (TBA) When Corynediphtheriae suspected
Crystal violet blood agar for streptococcus pyogen
LJ for M. tuberculosis
Modified New York City (MNYC) or Thayer Martin medium isolating Nisseria gonorrhoeae
Cooked meat medium (CMM)for Clostridium perfringens
Sabroud dextrose agar(SDA) for fungi

14. Bacterial Identification
The first step in culture evaluation is the visual examination of plated media.
Most bacteria produce visible colonies in 24 hr, although some require 48–72 hr. Inspection includes examination of colonial morphology, noting both types and numbers of colonies and any hemolytic reactions on blood-based agar.
Further classification is based on the presence or absence of growth on differential or selective media.
After the evaluation of plated media, examination of Gram stains made from each different colony type is performed.
Those reactions, combined with colonial morphology, may allow for the presumptive identification of organisms. If more than one colony type is present, subcultures of each are made.

15. Several microbial identification systems are commercially available
Several microbial identification systems are commercially available. Systems may be manual or automated.

16. Antimicrobial sensitivity test:
The agar disk diffusion method is more widely used for testing the common, rapidly growing aerobic to facultative anaerobic pathogenic bacteria.
The Kirby-Bauer method is based on the diffusion of an antimicrobial agent impregnated within a paper disk through an agar medium. Briefly, a suspension of actively growing test organism is standardized to a turbidity equivalent to 0.5 on the McFarland scale. Within 15 min of standardization, a sterile swab is dipped into the bacterial suspension and a dry Müller-Hinton agar plate is inoculated by streaking the swab over the entire surface 3 times. To ensure an even distribution of the inoculum, the plate is rotated ~60° each time. Antimicrobial disks are placed on the plate and are gently pressed down to ensure their close contact with the agar surface. Inverted plates are placed in an incubator at 35°C. Plates are examined after 18 hr of incubation.

17. Results:
Zones of complete inhibition are measured in millimeters using a ruler.
The zone sizes around each drug are compared to those published by the CLSI (Clinical and Laboratory Standards Institute ) in order to make an interpretation of susceptible, intermediate, or resistant for each agent tested.

18. CASE STUDY (1)
A 5-year-old boy presented to the hospital suffering from acute malaise, shivering and vague pains in his legs, sore throat and had vomited twice. He was febrile (temperature 40.2°C) with a tachycardia  . His pharynx, tonsils and buccal mucosa were red and inflamed and his tonsils were studded with white areas of exudate. He was diagnosed as having acute bacterial tonsillitis .proceed to identify the causative agent

19. BLOOD AGAR

20. Macconkey agar

23. CASE STUDY (2)
An 75-year-old diabetic man with swelling, blisters that contain gas bubbles near the area of infection, increased heart rate, and high fever. Skin in the affected area often turns from pale to brownish-red. Symptoms progress at a very rapid rate, the physician collect 2 wound swab and part of the necrotic tissue, proceed to identify the causative agent(s)

24. DIRECT MICROSCOPICAL EXAM

25. Blood agar and CMM

26. Gram stain

27. Gram stain

28. ?????

29. Spore stain

30. Nagler test

31. Litmus milk reduction test

32. Litmus milk reduction test