Environmental Isolate Developing Antibiotic Resistance by Complementation

Antibiotic resistance is a growing concern within the scientific community.  With few new antibiotics being introduced and an increasing number of resistant microbes, routine bacterial infections are becoming more difficult to treat in clinics and hospitals. The purpose of this study is to compare the ability of two environmental isolates – Staphylococcus aureus (S. aureus) and Exiguobacterium undae (E. undae) to grow in solutions of increasing concentrations of tetracycline and ciprofloxacin. After the bacteria showed grow in the solutions, antibiotic susceptibility was tested by examining zones of inhibition on Trypticase Soy Agar (TSA) plates. Our results indicate both isolates were initially susceptible to each antibiotic. The isolates were grown individually and mixed to determine if the isolates could gain resistance to the antibiotics in either environment. Our results demonstrate that E. undae could grow and become resistant in mixed cultures when grown in the presence of S. aureus reflecting the ability of S. aureus to complement microbial growth. Along with the ability of S. aureus to complement the growth of E. undae, it was also able to develop resistance to both ciprofloxacin and tetracycline through repetitive exposure.