Part of Thermo Fisher Scientific
OXOID SIGNAL® BLOOD CULTURE SYSTEM
The following section describes briefly the Oxoid SIGNAL Blood Culture System, the principles of its function and the equipment required for its optimal performance. For full details of the usage of the System the product insert should be consulted.
Principle of the Test
Blood samples are collected from patients, using strict aseptic technique and sterile equipment. The samples are inoculated into the blood culture bottles and mixed with the medium.
The formulation of the medium encourages the growth of aerobic, anaerobic and micro-aerophilic organisms. The medium is also designed to create pressure in the sealed bottle when organisms are growing.
The detection of positive pressure is by means of a growth indicator device which is connected to the bottle after the blood sample is added. A positive pressure in the bottle displaces a quantity of blood/broth mixture into the chamber as a sign of microbial activity.2,3,4
A positive result is indicated when the blood/broth mixture rises above the green locking sleeve of the growth indicator device.
Blood Culture Bottles plus
20 plus 20
Tryptone Soya Broth
Sodium polyanethol sulphonate
Sodium polyanethol sulphonate (SPS), 0.03% is added because it inhibits clotting5, neutralises the bactericidal effect of human serum6, prevents phagocytosis7 and partially inactivates certain antibiotics (streptomycin, kanamycin, gentamicin and polymyxin B)8,9. SPS may be inhibitory to some strains of Peptostreptococcus anaerobius, Neisseria meningitidis and Neisseria gonorrhoeae; therefore gelatin is added to the medium to neutralise this inhibition.10,11 When human blood is added to this medium, CO2 produced can be detected at 2.5 to 5% v/v in the bottle head-space4.
Materials required but not provided
1 Sterile syringe or other means of obtaining blood.
2 Alcohol solutions, or other suitable skin disinfection material.
3 Culture media and other equipment for subcultures.
4 Incubator equipment to maintain 36 ± 1°C.
5 Orbital shaker (for optimal results)
Method of Use (for full details see current product insert)
A. Inoculation Procedure
1 Examine the bottle of broth before taking the blood sample and discard it if any evidence of contamination can be seen.
2 Prepare the bottle for inoculation before taking the blood sample. Remove the green plastic `flip-off’ cap and disinfect the exposed part of the rubber stopper.
3 Aseptically inject a maximum volume of 10 ml of blood through the central ring of the rubber stopper. (The partial vacuum in the bottle will accept 12 ml of blood.)
4 Thoroughly mix the blood with the broth in the bottle.
5 Write the patient’s name and identification details on the bottle label.
6 Immediately transfer the inoculated blood culture bottle to the laboratory. In the event of the laboratory being closed or transportation being delayed, the bottle should be incubated at 36 ± 1°C, and the `Laboratory Procedure’, detailed below, carried out at the earliest opportunity (within 24 hours).
B. Laboratory Procedure
1 Place the inoculated bottle in an incubator at 36 ± 1°C for approximately 1 hour.
2 Remove from the incubator and place the bottle in an incubation tray.
3 Disinfect the rubber stopper of the bottle by swabbing, e.g. with alcohol.
4 Remove the growth indicator device from its sterile package and ensure that the needle and cap are fully tightened. (Hold the clear plastic body of the device with the covered needle pointing downwards. Tighten the needle by turning the needle cover anti-clockwise. Tighten the cap by turning it clockwise.)
5 Slide the plastic shield from the needle. Do not touch the needle.
6 Aseptically insert the needle through the centre of the rubber stopper. Push the needle shaft as far as it will go through the rubber stopper.
7 Slide the green locking sleeve of the growth indicator device downwards until it fully locks on to the neck of the blood culture bottle. Press down the chamber to ensure full contact with the rubber seal of the bottle.
8 For optimal results shake the system for approximately 24 hours at 150 orbits/minute, using a shaker placed in the incubator, or a bench top integrated shaker/incubator, at 36 ± 1°C. (If use of a shaker in the first 24 hours is impossible the system should be manually shaken as often as possible (at least 4 times) during this period.)
9 Examination of the system for a positive result should be carried out at least twice daily.
10 At the end of the 24 hour period, remove the system from the shaking apparatus and place on the shelf of an incubator preset at 36 ± 1°C.
11 Examine the system on the incubator shelf twice daily and if positive remove for further examination. Vigorously agitate the negative systems to resuspend the erythrocytes in the broth and return to the incubator shelf. A total incubation period of at least 7 days is recommended concluding with a terminal subculture.
12 POSITIVES - mix the contents of the chamber, unscrew the green cap and aseptically remove a sample of blood/broth mixture for subculture, microscopy and susceptibility testing. The vent in the cap contains a 0.2 micron hydrophobic membrane which ensures that the chamber is not under pressure. After sampling replace the cap on the chamber.
A positive blood culture, indicating growth of micro-organisms is recognised by the appearence of the blood/broth mixture in the transparent growth indicator device above the level of the locking sleeve. A visual inspection is also reccommended for lysis, turbidity or the appearence of colonies on the interface of the blood layer as these may become apparent before the blood/broth mixture appeares above the locking sleeve.
The following organisms are used by Oxoid as part of the quality assurance of the product. The total inoculum challenge for each test organism per bottle is 10 to 50 colony forming units (CFU’s).
User Quality Assurance
1 Examine the bottles of broth for turbidity and/or change of colour before adding any blood. Discard any bottles showing abnormal characteristics.
2 If further user quality control is required, it is recommended that 3 aerobes and 1 anaerobe from the above list be used.
1. Finegold S. M. and Martin W. J. (1982) Diagnostic Microbiology 6th Edn. Published C. V Mosby Co. St Louis. p.42.
2. Hinder S. M., Sawhney D. and Swaine D. 2nd European Congress of Clinical Microbiology 1985, Abstract 12/2.
3. King A., Bone G. and Phillips I. 2nd European Congress of Clinical Microbiology 1985, Abstract 12/4.
4. King A., Bone G. and Phillips I. (1986) J. Clin. Pathol. 39. 661-665.
5. Sawhney D., Hinder S., Swaine D. and Bridson E. Y. (1986) J. Clin. Pathol. 39. 1259-1263.
6. Van Haebler T. and Miles A. A. (1938) J. Path. Bact. 46. 245-252.
7. Lowrance B. L. and Traub W. H. (1969) Appl. Microbiol. 17. 839-842.
8. Rosner R. (1972) Amer. J. Clin. Path. 57. 220-227.
9. Traub W. H. (1969) Experientia 25. 206-207.
10. Traub W. H. and Lowrance B. L. (1969) Experientia 24. 1184-1185.
11. Eng J. and Holten E. (1977) J. Clin. Microbiol. 6. 1-3.
OXOID and OXOID SIGNAL are trademarks.