Wednesday, August 24, 2011

Proper Sampling in Clinical Microbiology Laboratory

Collection of good quality specimens:
Depends on
1- The optimal time of specimen collection .
2- The correct type of specimen
3- Well collected specimens with minimum contamination from normal flora of the patient or the person collecting the specimen.
4- Adequate amounts of each specimens and appropriate no. of specimens
5- Clearly labeled safe specimens
1- Optimal time of collection of collection of specimens:
-specimens for the culture of bacteria collected before the start of anttibiotic therapy
-Blood cultures and blood films for malarial parasites are best collected just as the patient’s temp. starts to starts to rise, however, when infective endocorditis is suspected , three blood culture sets collected with 24 hour irrespective of patient temp.
- Specimens for virus isolation are most likely to give positive results when collected during the most acute stages of the disease
-Serology is satisfactary when four fold or greater rising antibody titre is demonstrated in pained sera.
The 1st serum sample as early as possible in the disease course. Second in the convalescent stage
2-Correct types of specimens:
Bacterial meningitis blood cultures CSF collated
Suspected gonorrhea cervical, wretheral and rectsl swab should be collected rather than high regional subs.
3-Well collected specimens with minimum contamination from the normal flora:
Poor quality speeimens include saliva instead of sputum or a salirary – mucoid sputum sample instead of a muco purulent sputum.
-Mid stream urine reed careful collection to a void excess contamination by genital flora.
-A thoat swab should not touch the buccal mucosa and the tongue depressed by a spatula.
-Vaginal speculum should not be wet with antiseptic solution during collection of high vaginal swabe with care not to touch the lower ragin or perineium
-Strict septic and antiseptic techniques are used for blood and CSF cultures to avoid cantaminstion from Skin flora or from the dactor.
4-Adeqate amounts of appropriate number of specimens:
The volume of blood for culture from adult
-5-10 ml per bottle and in children and neonates 1-5ml per bottle.
-Collection of early moring sputum speceimens, and collection of adequate amount of early morning urine specimen for 3 successive days is required for the isolation of M.T.B.
-Patients with diarrhea at least 2 specimens of faeces is collected for culture of salmonellae or shigellae.
-Serological investigations usually require paired sera.
5-Clearly labeled and safe specimens:
Specimens for microbiological investigations should be placed in leak – proof containers, and each container should be enclosed in aplastic bag.
The hazards to staff handling leaking contaiver s include aquiring enteric infection from feces, T.B. from sputum of an open case of pulm. T.B. and riruse s such as HCV , HBV, HIV, from leaking blood.
Transport of specimens to the laboratory
Many potheyenic organisms don’t survive for long inclinical specimens kept at room temp. Examples include gonococci, Haemophilus, Bacteroides, oraerobic coccic and most virusea.
On the othen hand, some organisms contaminating specimens from the normal flora such as coliform and coagulase –ve staphylo cocci, may rapidly grow in specimeny Kept at room temp.
-Urine or sputum speeimens should reach the loboatory within 2h.of collection when even possible. If delay are expected immediately inoculated into transport media .
-Transport media used.
Stuart’s transport media for pus or swbs for bacterial cultue when deloys in in transport.>1/2h or when neisseria infections ore suspectecd.Howrver the inoculated tronspot media should be sent to the laboratory within 4h.
The investigation of eye,genital tract is best carried at the bed side when suitable culture media are directly inoculated.
-CSF not refrigested since othenwise meningococci may rapidly die.
-Viral transport media is necessary for virus isolation, and also for chlamydia isolation .
Specimens for virus isolation are kept at –70ÂșC till time of transferring the appropriate cell line which support growth of the possible virus or chlamydia.

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