With every dose of antibiotics a person receives, the microbes that survive the medicine will be “antibiotic resistant.” These antibiotic resistant microbes can then be passed to other people and even a fetus. A person may have never had a course of antibiotics in their entire life, yet harbor many antibiotic resistant pathogens. These resistant bacteria are transmitted in three ways:
- Consumption of animal products (such as meat, eggs, and milk)
- Close contact with animals or humans who harbor antibiotic resistant microbes
- Through the environment, as in water contaminated with animal or human waste
Our modern food supply in which farm animals are routinely administered antibiotics for prevention of illnesses rife in crowded factory farm conditions and also for growth promotion, not only produces animal products that contain antibiotic resistant pathogens, but they are released into the environment and used as fertilizers on on food crops.
A bit of evidence that improper use of naturally produced antibiotic signalling molecules alone are responsible for the antibiotic resistance we are seeing comes from an unlikely source: syphilis. Once considered an untreatable disease, syphilis was studied extensively in the early 1900s and soon an effective “antibiotic” was discovered. Arsenic made the sufferer of syphilis wish he was dead, but it cured the disease by rupturing the cell walls of the offending microbe known as Treponema pallidum. This treatment was used for decades with no resistance to the arsenic ever noted. In 1952, researchers were optimistic that this meant we had won the battle over our germs:
“Syphilis has now been treated with arsenicals for about 40 years without any indications of an increased incidence of arsenic-resistant infections, and this work gives grounds for hoping that the widespread use of penicillin will equally not result in an increasing incidence of infections resistant to penicillin.”
Ironically, Treponema pallidum is still being treated with penicillin and has not yet become resistant to it’s effects, but many other pathogenic bacteria have, including the particularly profuse Escherichia coli and the equally harmful Klebsiella pneumoniae which have become not only resistant to the original formula of penicillin, but also to semi-synthetic penicillin, cephalosporins, and the newer carbapenem antibiotics.
From the Proceedings of the National Academy of Sciences, 2006:
“An unexpected residual excess of teleological thinking has influenced the evolution of biological sciences during the last few decades. Although this approach can contribute to the establishment of potential scenarios of research, it frequently leads to wrong interpretations when applied to the experimental results. Antibiotics have been searched on purpose as inhibitors (either bactericidal or bacteriostatic) of bacterial growth, and we have tended to consider that microbes are using them to play the same function in nature. The automatic application of a classic Darwinian view supported the idea that such bacterial killer compounds could play an important role in the fight between microbial competitors for colonizing the same niche. It is obvious that many primary or secondary metabolites, not only antibiotics, might exert different effects at different concentrations. For instance, antibiotics that inhibit bacterial topoisomerases might, at low concentrations, produce changes in DNA supercoiling. Because DNA supercoiling regulates expression of virulence determinants in some bacterial species, a general change in the virulent properties in the presence of subinhibitory concentrations of these antibiotics might be expected.”  
Special thanks to Dr. Grace Liu, PHARMD, from Animal Pharm for contributions to this article.
 "Non-therapeutic Use of Antibiotics in Animal Agriculture ..." 2013. 3 May. 2014 <http://www.cgdev.org/article/non-therapeutic-use-antibiotics-animal-agriculture-corresponding-resistance-rates-and-what>
 "Food and Agriculture Organization of the United Nations World." 2005. 3 May. 2014 <http://www.who.int/foodsafety/publications/micro/en/amr.pdf>
 Aminov, Rustam I. "A brief history of the antibiotic era: lessons learned and challenges for the future." Frontiers in microbiology 1 (2010).
 "Emergence of a new antibiotic resistance mechanism in ..." 2010. 2 May. 2014 <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2933358/>
 Dorman, CHARLES J. "DNA supercoiling and environmental regulation of gene expression in pathogenic bacteria." Infection and immunity 59.3 (1991): 745.