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Chapter 5
5.2. Methods
5.2.1. Colony morphology on congo red agar
I. The test organisms were streaked onto Luria Bertani (LB) agar and
incubated at 37°C.
II.
Congo red (CR) agar was made in batches of 15 plates on two
consecutive days. The CR agar consisted of LB agar without sodium
chloride (LB w/o NaCl) which consists of bacto-tryptone (10 g/L),
yeast extract (5 g/L) and agar (15 g/L). The agar was sterilized by
autoclave before the addition of the dye agents:
o Congo Red (40 µg/ml) and coomassie brilliant blue R (20
µg/ml).
III.
IV.
The CR plates were streaked with colonies from the nutrient plate
and incubated for 48 hours.
The CR plates were examined and categorised as rdar, bdar, pdar,
sbam or saw accordingly (see table 5.1).
V. The experiments were performed twice on all 13 strains.
VI.
The S. Typhimurium strain LT2 was used as a positive control for the
rdar morphology. As stains previously characterised as bdar, pdar
and saw morphotypes were not available the colony morphology
produced by each strain was compared to the published images (of
colony morphology) provided by Römling et al. [77, 167] and
Malcova et al. [86].
5.2.2. Microtitre plate method
I. The test organism was streaked onto LB agar and XLD Agar and
incubated overnight at 37°C.
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