Bacteria are single-celled microorganisms which can exist either as independent (free-living) organisms or as parasites (dependent upon another organism for life). They are about 0.5 to 2 micrometres in size. A grain of sand is 2 millimetres in size. This means you could fit 1000 bacterial cells into a single grain of sand. This means we can only see bacterial cells through the microscope.
Salmonella species are very similar to those of E.coli, if fact E.coli can be considered the big brother of Salmonella,