Containers and Swabs Used for Collection of Specimens | Microbiology

Let us make an in-depth study of the containers and swabs used for collection of specimens.

Containers used for microbiological investiga­tions should be sterile, leak-proof and strong. Each container should bear the name of the patient, from whom the specimen was collected and his case reg­ister number. The investigation requisition form should also accompany the specimen indicating the investi­gation required along with the probable clinical diag­nosis and current chemotherapy. Details of previous immunization should be furnished for serological in­vestigation.

Glass Tubes and Universal Containers:

Specimens of exudate, pus, blood, cerebrospinal fluid, urine and faeces should be collected in strong, sterile, corked glass test tubes (4 x 3/8 inch). Before collection of samples, test tubes with loosely fitted cotton plug, or bark corks can be sterilised in hot air oven and then the corks should be pressed in.

Universal Container:

Screw capped bottle is a strong moulded glass bottle (3.1 /4 in height x 1.1 /8 in diameter) of one oz. (28 ml) capacity with a flat base and wide mouth. It is sterilised with loose cap and then tightened. It cannot be sterilised in the hot air oven as the rubber washer will not withstand the temperature.

The screw capped universal container has many advantages over the glass test tubes. It is strong, the mouth of the container is sterile because of the screw cap; whereas in case of stoppered glass test tubes, the dust may collect at the rim of the test tube. The content of a container will not leak and will not be contaminated.

It is quite stable at the base of the con­tainer and it is very convenient for collection of the sample at the bed side and it is very suitable for the collection of serous fluids, e.g., pleural or peritoneal fluids. The collection of the fluids that may be coagulable on standing can be done in the container to which 0.3 ml of a 20 per cent solution of sodium citrate is added prior to the autoclaving. This method of collecting fluid may be useful in performing cell count or centrifuging procedures.

Blood may be collected in a sterile universal screw capped container or test tube fitted with cot­ton plug for serological investigation. The streptoki­nase digested or minced blood clot may be cultured in a selective medium, e.g., for enteric organisms (Sal­monella) or blood for culture may be collected and submitted to the bacteriological laboratory in a spe­cial blood culture bottle containing bile salt broth. Serum from clotted blood can be transmitted to the laboratory while preserved in sodium azide or merthiolate (1: 10,000) in a sterile polystyrene or polypropylene plastic container.

Faeces:

May be collected in a small bottle of about 2 oz capacity or in a glass specimen tube or by a rectal swab. If the laboratory is situated at a far off place, the container may be transmitted with all pre­cautions by post; the package should be labelled as “Pathological specimen” If there is a delay of some hours before laboratory cultivation can be performed, neutral glycerol saline should be added to the faeces.

Rice water stool from cholera patient should be col­lected on a leaf or paper, but not in disinfected bed pan; because disinfectants can kill Vibrio cholerae. Specimen should be sent in transport medium, e.g., alkaline peptone water or Venkatraman-Ramakrishnan (VR) medium.

Urine—:

For the diagnosis of urinary tract infec­tion, the urine, if required in small quantity, can be collected in a universal container; complete early morning specimens (large quantities of urine) can be collected in a 20 oz screw capped bottles.

Disposable Specimen Containers:

Sterile screw capped waxed cartoons of 2 oz. capacity (such as used for ice-cream) are suitable for the collection of sputum or faeces. These waxed car­toons cannot be sent through post because of postal regulations. Plastic polystyrene or polypropylene con­tainers of variable size are suitable for urine, faeces, pus, blood etc. Recently, disposable plastic specimen containers have become available from various manu­facturers. All disposable containers should be de­stroyed in a furnace after use.

Swab—A swab consists of a piece of wooden (bamboo or broom) stick of about 6. 1/2 in long. Around one end of the stick a thin pledget of absorb­ent cotton wool is tightly wrapped for about 3/4 in. The stick is placed in a test tube (5 in x 1/2) and the top of the tube is plugged with a cotton-wool.

This has the advantage that the stick can be broken off ‘short when the swab has to be placed in transport medium in a screw-capped container. Besides col­lection of specimens, the swab can also be useful in the laboratory for seeding of medium for antibiotic disk sensitivity tests. A variety of disposable swabs (Plain, serum coated, charcoal coated) in plastic tubes are available. They can be destroyed in a furnace after use or sterilised in autoclave before discarding.

Swabs are useful in collecting specimen from:

(i) Throat:

In cases of suspected diphtheria, tonsillitis;

(ii) Wound:

Specimen from surgical condi­tions (fistula, sinus) or discharging ears can be collected by swabs;

(iii) Postnasal or Naso-Pharyngeal Space:

Specimens from suspected meningococ­cal carriers and whooping cough can be collected by using sterile postnasal swab which is made from a flexible copper wire or Nichrome (0.51 mm diameter), its terminal end (1/4 in) bent back through an angle of 45 degrees is tightly wrapped with a thin pledget of absorbent cotton wool. For the diagnosis of whooping cough, a prenasal swab is preferable to the postnasal swab.

(iv) Rectum:

Rectal swabs are very useful in bacillary dysentery in young children.

(v) Cervix Uteri:

A longer sterile stick or wire, 9 in, is preferable for the specimens in gonorrhea and puerperal infections. In conditions where delicate pathogens are concerned, e.g., meningococcus, gonococcus or Bordetella pertussis, it is preferable to place the swab in a sterile Bijou bottle containing transport medium, e.g., neutral glycerol saline. For blood culture, medical flat bottle is used.