Food-borne bacteria are the primary cause of spoilage and food poisonings. Thriving in moist, low-acid environments where lots of protein is present, pathogens like Salmonella, Campylobacter and E. coli live with the bird during its life and stay with its meat after slaughter; likewise, other bacteria, such a Acinetobacter and Pseudomonads fluroescens, putida or fragi, thrive on the meat after it’s processed. Given chicken’s somewhat unique qualities, quick spoilage is inevitable, and can only be mitigated by careful attention to time, temperature and moisture.
Source: The Science of Why Chicken Goes Bad So Quickly
It also depends on whether the chicken is organic, or Portland organic and whether it was able to take another chicken under it’s wing. Always look at the chicken’s dossier before making your final decision. And count its fingers!
Some are reporting a trend to sell “Chicken without salmonella” and “eggs without salmonella”. From research, it shows that 99,99% of eggs is salmonella-free these days (without extra work, straight from the chicken) and Salmonella is killed at 75°C, so if you, by bad luck, have a salmonella infested piece of chicken or egg, just cooking it thoroughly already kills the virus.