220 Modern Food Microbiology
Figure 10–1 Special counting grid for spiral plater (A); growth of organisms on an inoculated spiral plate (B);
and areas of plate enumerated (C). In this example, the inoculum volume was 0.0018 ml counts for the two areas
shown were 44 and 63, and the averaged count was 6.1 × 10
4 bacteria per milliliter. Courtesy of Spiral System
Instruments, Bethesda, Maryland.
on milk samples showed that the spiral plater compared favorably with the SPC. A standard deviation
of 0.109 was obtained by using the spiral plater compared to 0.110 for the SPC.
94 In another study,
the spiral plater was compared with three other methods (pour, surface plating, and drop count), and
no difference was found among the methods at the 5% level of significance.
62 In yet another study,
the spiral plate maker yielded counts as good as those by the droplet method.
51 Spiral plating is an
official Association of Official Analytical Chemists (AOAC) method.
Among the advantages of the spiral plater over standard plating are the following: less agar is used;
fewer plates, dilution blanks, and pipettes are required; and three to four times more samples per hour
can be examined.
69 Also, 50–60 plates per hour can be prepared, and little training is required for its
operation.
62 Among the disadvantages is the problem that food particles may cause blocking in the
dispensing stylus. It is more suited for use with liquid foods such as milk. A laser-beam counter has
been developed for use with the plater. Because of the expense of the device, it is not likely to be
available in laboratories that do not analyze large numbers of plates. The method is further described
in reference 36.
MEMBRANE FILTERS
Membranes with a pore size that will retain bacteria (generally 0.45 µm) but allow water or diluent
to pass are used. Following the collection of bacteria upon filtering a given volume, the membrane is
placed on an agar plate or an absorbent pad saturated with the culture medium of choice and incubated
Figure 10–1 Special counting grid for spiral plater (A); growth of organisms on an inoculated spiral plate (B);
and areas of plate enumerated (C). In this example, the inoculum volume was 0.0018 ml counts for the two areas
shown were 44 and 63, and the averaged count was 6.1 × 10
4 bacteria per milliliter. Courtesy of Spiral System
Instruments, Bethesda, Maryland.
on milk samples showed that the spiral plater compared favorably with the SPC. A standard deviation
of 0.109 was obtained by using the spiral plater compared to 0.110 for the SPC.
94 In another study,
the spiral plater was compared with three other methods (pour, surface plating, and drop count), and
no difference was found among the methods at the 5% level of significance.
62 In yet another study,
the spiral plate maker yielded counts as good as those by the droplet method.
51 Spiral plating is an
official Association of Official Analytical Chemists (AOAC) method.
Among the advantages of the spiral plater over standard plating are the following: less agar is used;
fewer plates, dilution blanks, and pipettes are required; and three to four times more samples per hour
can be examined.
69 Also, 50–60 plates per hour can be prepared, and little training is required for its
operation.
62 Among the disadvantages is the problem that food particles may cause blocking in the
dispensing stylus. It is more suited for use with liquid foods such as milk. A laser-beam counter has
been developed for use with the plater. Because of the expense of the device, it is not likely to be
available in laboratories that do not analyze large numbers of plates. The method is further described
in reference 36.
MEMBRANE FILTERS
Membranes with a pore size that will retain bacteria (generally 0.45 µm) but allow water or diluent
to pass are used. Following the collection of bacteria upon filtering a given volume, the membrane is
placed on an agar plate or an absorbent pad saturated with the culture medium of choice and incubated