Saminathan Ratnapandian

Dye (10 g/l)	Thar (A. catechu)
Caspian (A. nilotica)
Mordant		CuSO4.5H2O (15 g/l)	FeSO4.7H2O (5 g/l)	CuSO4.5H2O (15 g/l)	FeSO4.7H2O (5 g/l)
Washing test		3–4	3–4	3–4	3–4
Light fading		4–5	3–4	4–5	3–4
Rubbing	Dry	5	5	5	5
	Wet	5	5	5	5

4. Antibacterial evaluation results

In accordance with the test specifications in Section 2.2.3.4, the agar plates for the different dilutions for the control swatch were examined after incubation. The plates containing 10⁰ and 10¹ times dilutions had uncountable colonies, while the plate with 10³ times dilution had too few colonies. These plates were therefore discarded. The
plate with 10² dilutions with 253 Colony Forming Units (CFU) was selected to compare the control and test swatches.
Both dyes, when tested on their own, were found to be inactive, with uninhibited growth of bacteria (>500 CFU) in the agar plates (Figure 5.9). This is in agreement with the results published by Singh et al. [101], who reported that the dyes derived from the Acacia family do not possess intrinsic antibacterial functionality.

Figure 5.9 Bacterial growth on agar plates for Thar (A) and Caspian (B) dyes

All fabric samples pad-dyed in the presence of chitosan were completely effective against E. coli. The 10² dilutions from these samples did not show any bacterial colonies after incubation and thereby exhibited 100% reduction in CFU% as calculated by Equation 2.2.

where
( X  Y ) _100%
X

Equation 2.2

X= average number of bacterial colonies in the agar plate from control
Y = average number of bacterial colonies in the agar plates from fabric dyed in the presence of chitosan

Figure 5.10 shows representative photographs of biocidal activity in the agar plates corresponding to the control fabric (A) with 253 CFU of E. coli and the test sample dyed in the presence of 0.05% chitosan (B) with no bacterial growth. The results are in agreement with earlier research, which reported antimicrobial properties of cotton fabrics treated first with chitosan by exhaust dyeing and then dyed by exhaust or padding methods [96, 176, 190, 191].The above results are summarised in Table 5.3.

Figure 5.10 Agar plates control (A) and fabric dyed with Thar and 0.05% chitosan (B)
Table 5.3 Antimicrobial testing results