What is the minimum titre of typhoid that can cause damage internally, which are the organs that are prone to get affected by this?
The minimum infectious dose for a disease like typhoid is hard to obtain, because the most controlled method of obtaining this information is via human challenge studies, and those are essentially no longer performed due to some ethical issues. That means one must look at older data or observational studies, which have some methodological drawbacks.
A somewhat older review suggests the necessary dose to provoke clinical disease was <10^3 organisms. Public Health Canada characterizes the infectious dose for enteric fever (which is another name for typhoid fever) as ~ 10^5 organisms.
In terms of which organs can be effected - in the most severe cases, complications can be fairly systemic, with the most dangerous complication being haemorrhage due to intestinal perforation.