Laboratory method in identification of microorganisms

Sputum

The patient is instructed to take a deep breath and cough up sputum directly into a wide mouth sterile container.Saliva and postnasal discharge should be avoided.A minimum of 1 ml sputum should be collected.

Urine

For microbiological analysis, the midstream urine is the preferred sample.. This is the ideal specimen for culture and sensitivity testing because of the reduced microbial contamination.This method of collection can be conducted at any time of the day or night.Following is the procedure of collection of urine specimen.

Patient are advised to first cleanse the urethra.

The patient should then void the first portion of the urine stream.

The urine midstream is then collected into a clean container provided to them.

Blood

Blood is usually collected for the identification of bacteria in case of bacteremia.Following are the recommended volume of blood collected aseptically for its culture.

Venous blood

Infant 0.5 to 2 ml 

Children 2 to 5 ml 

Adult 5 to 10 ml 

Cerebrospinal fluid

The CSF is collected by lumbar puncture.A spinal needle is inserted between the third and fourth lumbar vertebrae to collect the CSF.The CSF is collected in sterile tubes in aseptic condition.Normally a clinician who is trained in lumbar puncture collect the CSF.

Faeces

Freshly passed stool sample are collected in sterile or clean container.Bedpan specimen should be avoided.

Throats swab 

First hold the tongue away with a tongue depressor.Using a sterile swab rub back and forth the area of inflammation and exudate in the posterior pharynx, tonsillar region of the throat behind the uvula.The swabbing should not be done on the soft palate and tongue.

Transport medium

The specimen collected is normally stored in a sterile container or in a sterile syringe.If the specimen is collected in a hospital attached with a clinical laboratory it can be immediately transported to the same without any delay.If the transport of specimen is delayed,the specimen can be transported by a transport device or by a transport medium.Transport medium is used for the temporary storage of specimen for transport to the laboratory for cultivation.It helps the micro organisms to survive until it reaches the laboratory for its processing.It is non nutritive and does not allow organisms to multiply.Thus, the transport media contain only buffer and salt.The lack of carbon, nitrogen and organic growth factor prevent the multiplication of micro organisms.