A DEVICE AND A METHOD FOR SPREADING MICROORGANISMS

Abstract: A device for the spreading of microorganisms consisting of an upper part (1) containing a magnet (6) and a lower part (2) in the shape of a bowl in which the upper part (1) can rotate when the two parts are put together (Fig. 3) and placed on a magnetic stirrer. An agar plate can be placed on the upper part. The device can preferably be made out of plastic. With the use of the device the spreading of microorganisms can be done on an agar plate which is placed on the upper part (1) and thereby rotates together with the upper part (1).

Description: A DEVICE AND A METHOD FOR SPREADING MICROORGANISMS The two most frequently used microbiological methods are the enumeration of microorganisms and the isolation of pure cultures from contaminated samples. Viable cells are enumerated by initially serially diluting in 10-fold steps and subsequently spreading an aliquot on an agar plate for determination of numbers of colony forming units. A spreader device of glass or plastic, is generally used to inoculate the plate. To avoid uneven distribution of colonies on the agar plate it is important that the plate be rotated during the spreading operation and that the plate be spread until the inoculum has been absorbed into the agar. Should this precaution not be observed, bacte¬ ria can continue to multiply in the fluid film and give rise to up to 10-fold higher counts. In most laboratories, this operation is completely manual, or at best, a manually operated turn table is used to rotate the plate. Pure cultures are obtained by serially diluting the ino- cula on agar plates to permit growth of individual colo- nies. Colony isolation is generally performed using wire, platinum or disposable polystyrene loops. Samples are sucessfully diluted on agar plates by the process known as a streak dilution method which involves numerous streak on the plate to sufficiently dilute the inoculum. A common difficulty with this methodology is to dilute sufficient¬ ly so as to yield single colonies without excess dilution, thereby obtaining very few individual colonies. Attempts to solve both these time consuming and tedious spreading operations by means of automated spreading de- vices for the enumeration of micro-organisms (1) and for colony isolation (2) have been reported. In addition, a rotating table on which the inoculated plate is placed and the inoculum manually spread by the operator with a bacteriological loop in a spiral mode has been described (3).It seems that although they are efficient and give reproducible results, most automated devices tend to be complicated, cumbersome and expensive to manufacture. In order to reduce the tedium associated with manual plate spreading for enumeration and isolation without excessive costs, a device was constructed in our laboratory which utilizes the principles reported by Frazer-Williams and Banbury 3. The device, the rotaplater, uses the stirring capacity of a magnetic stirrer to rotate the agar plate. The device will hold and rotate the agar plate during the spreading and colony isolation procedure. The rotaplater will be further described in the following drawings, where Fig 1 shows the upper part of the rotaplater, and Fig 2 Shows the lower part of the rotaplater, and Fig 3 shows both parts put together in one unit. Furthermore, we refer to five drawings, Fig. 4A-B and Fig 5A-C. Description The rotaplater consists of two parts, an upper part 1 and a lower part 2. The two parts put together in one unit 3 is shown in Fig. 3. This is the unit that is placed on a magnetic stirrer. The upper part 1 consists of a plate 4 and below this an attached part 5 containing the magnet 6. The upper part 1 can be made in one piece in which the magnet 6 is inserted. The lower part 2 is stabilised on the magnetic stirrer by double sided tape, alternatively, it can be made in a heavier material, which will exclude the use of the double sided tape. By the use of the magnet 6 mounted in the lower part 5, the upper part 1 rotates in the lower part 2. The rotaplater can be made in plastic. A suitable material is delrin. The rotating part 5 and the lower part 2 can preferably be made out of teflon or coated with teflon in order to reduce friction. The choice of material can be varied if due precaution is taken so that the friction between the rotating upper part 1 and the lower part 2 is low. It is possible to use metal in the lower part och plastic in the upper part or vice versa. The metal must in that case be unmagnetic. As examples on suitable dimensions, the plate 4 can be a circular bowl with an outer diameter of 88.5 cm and 6 mm high. The part 5 containing the magnet 6 can be a circular disc 59 mm in diameter and 11 mm high. The lower part 2 can be shaped like a circular bowl with outer diame¬ ter of 76 mm, inner diameter of 60 mm, outer height 10 mm and inner height (depth) 8 mm. Operation As mentioned in the introduction, the rotaplater can be used both for enumeration of microorganisms as illustra¬ ted in Fig. 4A and for colony isolation as illustrated in Fig. 4B. Methodology. Enumeration. After initial laboratory trials the rotapla¬ ter was tested by a four member team in a field trial spanning five weeks and yielding approximately 500 plates . per week. It was proposed that two members would use the rotaplater and two would serve as controls, and the opera- tors would alternate as control workers. Colony isolation. The plates were inoculated in two diffe¬ rent ways depending on whether the source of the inoculum was a liquid culture or a colony on an agar plate. A drop of liquid culture, 0,1 ml, was placed close to the centre of the plate and then a bacteriological loop was dragged from the inoculum towards the edge of the plate along the radius. Using the solid sample a drop of sterile buffer was placed close to the centre of the plate. Using a bac¬ teriological loop, a colony from another plate was εuspen- ded in the drop of buffer on the plate. The loop was then dragged as described for the liquid culture. Results. The four persons asked to evaluate the device during their routine laboratory work were all very pleased with the results. All continue to use the device on a regular basis. After the first of the five field trials, all members demanded rotaplaters and results comparing manual and rotaplater operations are only available from this one study. Operator A and operator B reduced the time taken to spread 60 plates by 50% and 40%, respectively. Operator C refused to act as a manual control. Operator D was very recently trained and was unaccustomed to spreading up to 150 plates per day. She suffered discomfort in the hand for several days after spreading all plates manually. Typical results from the field trial are illustrated in Fig. 5A. A uniform distribution of colonies was obtained for all dilutions thus enabling easy enumeration. The laboratory staff concluded that the plates which were spread by the rotaplater were much easier to count than plates from the control group. The results obtained from the colony isolation experiment are illustrated in Fig. 5B and C. The colonies isolated from the liquid culture are illustrated in Fig 5B and the colony shown in Fig 5C were isolated from a solid sample. The separation of colonies on the agar plate was completely acceptable and yielded higher numbers of individual colonies than the conventional streak dilution method, Conclusion It is concluded that this device filled a void for all microbiologists by providing a simple, time saving, in- expensive and easy to operate a apparatus which yields results comparable to or better than manual control results, References. (1) Jarvis, B., Lach, V.H., Wood, J.M. (1977) Evaluation of the spiral plate maker for the enumeration of Micro-orga- nisms in foods. J. Appl. Bact. 43, 149-157. (2) Trotman, R.E. (1971) The automatic spreading of bacte¬ rial cultures over a solid agar plate. J. Appl. Bact. 34, 615-616. (3) Fraser-Williams, R., Banbury, J.M. (1968) Mechanical rotary device for plating out bacteria on solid medium. J. Clin. Path. 21, 784. As a further development, the magnet 6 can be replaced with a core of a material that can rotate the upper part 1 in the lower part 2 under influence of a magnetic field. A suitable material is a core of iron instead of the mag¬ net 6. Other material can be used, provided it allows rotation under the influence of a magnetic field.

Claims: CLAIMS 1. A device for spreading microorganisms on a surface, preferably on an agar plate, c h a r a c t e r i s e d in that the device con¬ sists of an upper part (1) containing a magnet (6), the function of the upper part (1) being to support a plate, preferably an agar plate, and rotate in a lower part (2) under the influence of a magnetic field. 2. A device according to claim 1, c h a r a c t e r i s e d in that the upper part (1) consists of a circular plate (4) in the shape of a bowl in which an agar plate can be placed and a bel w that plate (4) mounted circular plate (5) containing a magnet (6) . 3. A device according to claim 2, c h a r a c t e r i s e d in that the upper part (1) is made out of one piece. 4. A device according to claim 1, c h a r a c t e r i s e d in that the lower part (2) has the shape of a circular bowl so constructed that it accomodates the plate (5) thereby enabling the plate (5) to rotate in the lower part (2). 5. A device according to claim 1-4, c h a r a c t e r i s e d in that the device is made in plastic. 6. A device according to claim 5, c h a r a c t e r i s e d in that the device is made out of delrin. 7. A device according to claim 5, c h a r a c t e r i s e d in that part (5 ) and the lower part (2) is made out of teflon or coated with teflon. 8. A device according to claim 1-4, c h a r a c t e r i s e d in that the device is partly made out of metal, preferably in such way that the lower part is made in an unmagnetic metal material and the upper part out of a plastic mate- rial or vice versa. 9. A method for the spreading of microorganisms with the use of a device according to claims 1-7, c h a r a c t e r i s e d in that a plate, prefe¬ rably an agar plate is placed on the circular plate (4), and that the upper part of the device (1) is placed in the lower part (2), which is stabilised on a magnetic stirrer so that the upper part (1) of the device is brought to rotation with the help of a magnetic stirrer and the agar plate is inocu¬ lated during the rotation. 10. A method according to claim 9, c h a r a c t e r i s e d in that during the ino¬ culation of the rotating agar plate an inoculation loop is dragged from the centre of the plate towards the edge of the plate along the radius. 11. A method according to claim 9, c h a r a c t e r i s e d in that spreading of microorganisms on the agar plate is done with a spreader in that a small part of the bacterial sus¬ pension is placed in the centre of the agar plate and that the spreader first is placed in the centre of the plate and then moved backwords and forwards on the surface of the agar plate. 12. A device according to claim 1, c h a r a c t e r i s e d in that the device con¬ sists of an upper part (1) containing a core of a material that can bring the upper part (1) to rotation in the lower part (2) during the influence of a magnetic field. 13. A device according to claim 12, c h a r a c t e r i s e d in that the core is made out of iron.

Inventors: CONWAY PATRICIA, WRANGSTAD MICHAEL, CONWAY, PATRICIA, WRANGSTAD, MICHAEL
Applicants: BIOINVENT INT AB, BIOINVENT INTERNATIONAL AB
Application year: 1988
Main classification: C12M1
IPC codes: C12M1, C12N1