Bacteria from conventional chicken and from people who ate the chicken became resistant to Synercid, a strong antibiotic used to treat antibiotic-resistant bacteria, more often than from vegetarians or antibiotic-free chicken. In fact, the study found it was rare to find resistant bacteria among antibiotic-free chicken, while the majority of bacterial isolates from conventional poultry were resistant.
The bacteria studied was a gut bacteria that is causing increasing numbers of infections in hospitals, and the study indicates that the use of antibiotics in poultry (in this case the antibiotics were used to promote growth) may harm humans' health in the long-term.
Aside from the antibiotic problem, conventional chickens eat feed that is laced with pesticides, which may then be transferred to you. This gives you all the more reason to seek out organic, free-range chicken (and other meats). Organic, antibiotic-free chicken is less contaminated with bacteria, is free from pesticides, antibiotics and hormones, and is raised more humanely than conventional chicken.
The Journal of Infectious Diseases November 2006;194:1200-1208 (Free Full-Text Article)
Science Blog October 10, 2006