Hold time study for the antibiotic oral suspension

During our R&D development, we have conducted a hold time study for antibiotic oral suspension, we got the results for antibiotic oral suspension study as below,

0 day 320 Cfu/g
3rd day 360 Cfu/g
7th day 330 cfu/g
10th day 420 cfu/g
15th day 460 cfu/g

from the above results there is little increase in the bacterial count but these results are within the factor of 2 from the first day result, how can we interpret these results?

It is meeting to the requirement of in the
As per the USP general chapter 51 the criteria given as, antimicrobial effectiveness is met if no increase defined as NMT 0.5 log10 unit more than value which is compared.

now please guide me,

NMT 0.5 log10 means how much percentage?
Can we take this criteria to conclude that there is no increase in my result?