Disclosed herein are methods and compositions related to probiotic formulas. These formulas comprise the bacterial strain Lactobacillus crispatus WZ-12 or a derivative thereof. Other strains which can be included in the composition include, but are not limited to, Lactobacillus salivarius 1-14, or Lactobacillus reuteri 2-2, and derivatives thereof. These compositions can be used in a variety of methods to treat and/or ameliorate diseases, such as colonization of antibiotic-resistant bacteria in the host organism. Also disclosed herein are methods of treating those subjects in need thereof by administering the compositions disclosed herein.