In
Figures 1 to
4, the bar indicates the mean of the log difference, and the error bars indicate SD. A negative value on the
y-axis indicates log reduction, a positive value on the
y-axis indicates growth, and the
x-axis represents the three (6, 10, and 24 hours) different time points.
A significant (
P ≤ 0.001) log reduction for the MicroBlock compared with the other lens cases was clearly revealed in
Figures 1,
2, and
4 against the test strains
P. aeruginosa ATCC 9027,
S. marcescens ATCC 13880,
Delftia acidovorans 001, and
F. solani ATCC 36031 after 24 hours of storage at all the challenged inocula. As can be seen in
Figures 1 and
2, MicroBlock exhibited complete kill effect at lower inocula (
Figs. 1A,
1B) after 24 hours of storage against
P. aeruginosa ATCC 9027 at 10
3 and 10
4 CFU/mL and
S. marcescens ATCC 13880 at 10
3 CFU/mL (
Fig. 2A). Additionally, at higher inocula (
Figs. 1C,
1D,
2C,
2D), these cases showed a log reduction of 3.2 ± 1.4 (mean ± SD) and 2.4 ± 0.5 against
P. aeruginosa ATCC 9027 at 10
5 and 10
6 CFU/mL and 3.8 ± 0.3, 4.2 ± 1.3, 3.3 ± 0.9 against
S. marcescens ATCC 13880 at 10
4, 10
5, and 10
6 CFU/mL, respectively, after 24 hours of storage. Noticeably, after 6 and 10 hours of storage, MicroBlock demonstrated significantly (
P < 0.001;
Fig. 4) higher activity than the other storage cases against
D. acidovorans 001 and
F. solani ATCC 36031, and log reductions of 2.8 ± 0.1 and 0.5 ± 0.2 were observed, respectively, after 24 hours of storage. In addition, these cases revealed significant (
P < 0.02;
Fig. 3) activity against
S. aureus ATCC 6538 compared with CIBA control by showing log reductions of 1.3 ± 0.9 at 10
3 and 2.4 ± 1.1 at 10
6 CFU/mL after 24 hours' storage. MicroBlock showed no effect on
S. maltophilia 002 (
Fig. 4).
Interestingly, i-clean was more effective against
S. aureus ATCC 6538 (
P < 0.007) than other cases at all the inocula after 24 hours (
Fig. 3). In addition, log reductions of 2.8 ± 1.5, 3.7 ± 1.9, and 5.4 ± 1.1 were observed at 10
4 CFU/mL, 10
5 CFU/mL, and 10
6 CFU/mL, respectively, after 24 hours. Against this test strain, at the lowest challenge inocula, i-clean cases demonstrated significantly greater (
P ≤ 0.02) activity when compared with the other cases at 6 hours and 10 hours, with further complete bactericidal activity after 24 hours. There are no noteworthy observations with i-clean against
P. aeruginosa ATCC 9027,
S. marcescens ATCC 13880,
C. albicans ATCC 36031,
F. solani ATCC 36031,
D. acidovorans 001, and
S. maltophilia 002.
The Nano-case showed significant (P < 0.02) activity against S. maltophilia 002 compared with other cases at 24 hours, with a small log reduction of 0.2 ± 0.3. Nano-case showed no appreciable activity against all other strains.
Figure 5a shows the silver release data for 3 cases tested at 6, 10, and 24 hours, and
Figure 5b shows the silver release over a month at 7, 14, 21, and 28 days. MicroBlock, with a range of 16–45 μg/L over 28 days, was the only storage case to demonstrate measurable release of silver into the DPBS.