Collection of Samples

COLLECTION OF SAMPLES

  • Before collecting samples, careful consideration must be given to the desired purpose, the type and number of samples required to provide valid results. When samples are taken from live animals , care must be taken to avoid injury or distress to animal or danger to operators. Whenever handling biological material,from live or dead animals, the risk of zoonotic disease must be kept in mind and precautions taken to avoid human infection and environmental contamination.

Blood

  • Blood samples  for culture  or direct examination,  appropriate  anticoagulants,  such as heparin may be used.
  • Blood must be collected under aseptic conditions. Area over the vein should be shaved, throughly cleaned and sterilized with disinfectant.
  • The blood is added to a flask containing 50-100 ml of a rich nutrient medium that will permit growth of fastidious organisms or collected in specially designed blood culture tubes.
  • For direct examination of bacteria, it is necessary to make thick and thin smear from fresh blood.

Serum

  • Serum sample should be collected once early at the time of outbreak and the another on 14 to 21 days after the first collection for specific demonstration of increasing antibody titre. This is known as collection of paired serum samples.

Urine

  • Urine secreted in kidney and collected in bladder is sterile, when voided through urethra it may contaminate with normal urethral micro flora.
  • In small animals, urine is readily collected by means of cystocentesis.
  • In large animals, catheterization is the preferred method.
  • Collected urine should be placed immediately into a sterile test tube and culture as soon as possible.
  • If delayed of more than one hour then the urine should be refrigerated.

Fluids

  • Exudates from the pleural, peritoneal or synovial cavity must be aspirated using aseptic condition and transferred into sterile container.

Faeces

  • Faeces should be collected when freshly voided or directly from rectum and immediately placed in a sterile container.
  • In small animals it may be collected using faecal swab, it should be ascertained that swab carries faecal materials.
  • The faecal sample and swab should be dispatched to lab in a transport medium at 4ºc

Skin

  • The skin is normally preferred for vesicular diseases. Approximately 2 g of affected epithelial tissue should be collected and sent to lab in 5 ml of phosphate buffered glycerin or Tris buffer tryptose broth.
  • Vesicular fluid should be collected from unruptured vesicles aseptically using sterile syringe and needle.
  • Skin scrapings (from periphery of the lesion), and wool samples and hair (by plucking) are collected for fungal infection.
  • In birds, feather follicle can be collected for Marek’s disease.

Abscesses and wound

  • Pus may be collected from closed, undrained abscesses with a sterile syringe and needle after the area over the infection is disinfected.
  • Sterile cotton swab in test tubes offer the easiest method for specimen collection from open wound.
  • Care must be taken to avoid contamination from extraneous sources while taking swab.

Throat swab

  • The sterile swab must be extended to area to be examined without contaminating saliva, teeth, other fluids and swabbed on the area .
  • The swab from throat should be immediately soaked in sterile broth.

Genital tract infection

  • Semen should be collected using artificial vagina.
  • Vaginal and prepucial washing should be collected as samples in genital tract infection.
  • In case of endometritis and cervicitis specimen should be obtained using cultural swabs through vaginal speculum.

Eye

  • Suppurative material from an infected eye should be collected from the lower cul- de-sac or from the inner canthus by gently swabbing the surface.

Ear

  • Secretions and discharges from internal ear canal should be collected by gentle swabbing the canal with sterile cotton swab.

Nasal swab

  • Nasal secretions are collected in sterile cotton or gauze cloth. It should be transported to the lab in transport media at 4ºC.

Milk

  • Milk sample should be collected in sterile container after cleaning and drying of the tip of the teat.
  • The use of antiseptics should be avoided. The initial stream of milk should be discarded and next streams are collected in the tube.
  • Milk for serological tests should never be heated, frozen or subjected to violent shaking.  

Direct smears

The direct smear technique for detection of microorganisms is applicable in the examination of exudates, urine, cerebrospinal fluid, milk and tissue.

  • Urine
    • Direct microscopic examination of urine helps to detect the presence of microorganisms.
    • If urine is cloudy or opaque a drop of urine placed on slide and make a smear or if urine is clear centrifuge it take a small quantity of sediment with inoculating loop and make a smear and heat fix it and examine.
  • Cerebrospinal fluid
    • Direct smear can be prepared from fresh uncentrifuged CSF, which appears cloudy otherwise smear should be prepared from sediment of centrifuged CSF.
  • Milk
    • Milk placed on a slide, evenly spread over a predetermined area and heat fixed.
  • Tissue
    • Direct microscopic examination of impression smears from tissues will sometime reveal the presence of organisms. One centimeter square piece of tissue from an organ is to cut with sterile scissors and forceps, blot tissue to remove excess blood and carefully touch the cut surface of tissue on pre cleaned slide. Three or four such touch preparations may be made on a slide. After the slide is air dried and heat fixed stain with appropriate stain.
    • If firm nodules are present, they should be crushed between two microscopic slides, which are gently drawn apart. In certain diseases, smear should be examined in fresh state.
  • Exudates
    • Exudates collected in swab should be rolled or swabbed on surface of a pre cleaned microscope slide. If exudates have been collected with a syringe, a small drop is placed on a slide and spread using an inoculating loop. After the smear dried, it should be heat fixed.

Collection of sample from dead animals

  • From dead animals, tissues are collected for isolation of bacteria and for conducting histopathological or immuno histochemical techniques. Of late tissue samples from dead animals are also used for identification of protein or nucleic acid.
  • The collection of organs at the time of necropsy for subsequent microbial examination should be based on the history, clinical signs and necropsy lesions.
  • The tissue collection is determined largely by the predilection or affinity characteristics of the organisms.
  • The organs most commonly selected include the kidney, liver, spleen and heart. While collecting organs during necropsy, care must be taken to avoid contamination by extraneous microorganisms.
  • Easily sealed plastic bags are used for collection of organs. If the animal has been dead for several hours, bacteriologic examination of the tissue will be less reliable than examination of specimen obtained soon after death.
  • In large animals sufficient quantity of representative specimens including the site of lesions should be carefully removed and placed in a container.
  • In smaller animals the entire organ is to be collected. If immediate microbial examination is impossible, the specimen should be refrigerated or frozen.
  • For histopathlogy, the specimens must be sent in 10% buffered formal saline.
Last modified: Saturday, 24 September 2011, 10:45 AM