NAME: The Tryptone Task
TYPE: Designed experiment
SIZE: 30 observations, 9 variables
DESCRIPTIVE ABSTRACT:
Bacteria are cultured in medical laboratories to identify them so patients can be treated
correctly. The tryptone dataset contains measurements of bacteria counts following the
culturing of five strains of Staphylococcus aureus. There are many strains of
Staphylococcus aureus; five were used by the experimenter. They are identified by numbers
in the data because their names are too complicated to be useful as identifiers. The
dataset also contains the time of incubation, temperature of incubation and concentration
of tryptone, a nutrient. The protocols for culturing this bacteria, set the time at 24
hours, the temperature at 35 degrees and the tryptone concentration at 1.0%. The question
is whether the conditions recommended in the protocols for the culturing of these strains
are optimal. The task is to find the incubation time, temperature and tryptone concentration
that optimises the growth of this Bacterium.
SOURCE:
The data was collected by Gavin Cooper at the Auckland University of Technology. This was
done for a project for his Bachelor of Applied Science entitled 'The Efficiency of the
Recovery of Methicillin Resistant Staphylococcus aureus from Salt Enrichment Broth'.
VARIABLE DESCRIPTIONS:
Line 1
Columns
1 - 6 Row this is the case number
7 - 14 Count1 Bacteria counts for strain 1. Units are millions of Colony Forming Units
15 - 22 Count2 Ditto for Strain2
23 - 30 Count3 Ditto for Strain 3
31 - 38 Count4 Ditto for Strain 4
39 - 46 Count5 Ditto for Strain 5
47 - 53 Time Time in Hours, takes the values 24 and 48
54 - 60 Temperature Temperature of incubation in degrees Celcius, may be 27, 35 or 43
61 - 64 Concentration The concentration of the nutrient Tryptone as a percentage, it may be 0.6, 0.8, 1.0, 1.2 or 1.4
Values are aligned and delimited by blanks.
There are no missing values
STORY BEHIND THE DATA:
Bacteria are cultured by growing them in a nutrient broth. The current protocols have Time
of culture 24 hours, Temperature of incubation 35 degrees and Concentration of tryptone 1.0%,
which are suspected of not being optimal. The experimenter has varied these conditions
hoping to find conditions that will better suit the bacteria Staphylococcus aureus. For
each set of conditions and for each strain he has measured the bacteria count after
incubation.
PEDAGOGICAL NOTES:
This data may be explored by students at several levels. Graphical methods can be used to
investigate the relationship between the variables. Suitable graphs are dot-plots, box-plots,
scatter-plots, multiple scatter-plots, interaction plots and main effects plots. ANOVA can
be used with one-way, two-way and factorial models with interactions, to identify significant
factors. Multiple polynomial regression methods can be used to model the data, with optimal
conditions estimated by partial differentiation. Comparing the results for the five strains
will suggest the conditions most likely to be close to optimal whatever strain is present.
These conditions are to be compared with the current protocols.
SUBMITTED BY:
Neil S. Binnie
Department of Applied Mathematics
Auckland University of Technology
Private Bag 92006, Auckland 1020, New Zealand
Ph 649-917-9999 x8528
neil.binnie@aut.ac.nz