Naturally occurring antibiotic resistance is common.  Genes for resistance to antibiotics, like antibiotics themselves, are ancient.   The genes that confer resistance are known as the environmental resistome .  These genes may be transferred from non-disease-causing bacteria to those that do cause disease, leading to clinically significant antibiotic resistance.  In 1952 it was shown that penicillin-resistant bacteria existed before penicillin treatment;  and also preexistent bacterial resistance to streptomycin .  In 1962, the presence of penicillinase was detected in dormant endospores of Bacillus licheniformis , revived from dried soil on the roots of plants, preserved since 1689 in the British Museum .    Six strains of Clostridium , found in the bowels of William Braine and John Hartnell (members of the Franklin Expedition ) showed resistance to cefoxitin and clindamycin .  Penicillinase may have emerged as a defense mechanism for bacteria in their habitats , such as the case of penicillinase-rich Staphylococcus aureus , living with penicillin-producing Trichophyton ; however, this may be circumstantial.  Search for a penicillinase ancestor has focused on the class of proteins that must be a priori capable of specific combination with penicillin .  The resistance to cefoxitin and clindamycin in turn was attributed to Braine's and Hartnell's contact with microorganisms that naturally produce them or random mutation in the chromosomes of Clostridium strains.  There is evidence that heavy metals and other pollutants may select for antibiotic-resistant bacteria, generating a constant source of them in small numbers. 
Maura Meade-Callahan, . , is a professor of biology at Allegheny College in Meadville, PA. There she teaches biology, microbiology, and antimicrobial agent resistance in bacteria. She earned her . in plant pathology at North Carolina State University. She is actively involved in a graduate research ethics project of the Association for Practical and Professional Ethics and in various aspects of undergraduate microbiology education through the American Society for Microbiology. She serves as a reviewer for several journals, textbooks, and web sites.