| Much of what is known about the frequency and distribution of antibiotic resistance is based on bacteria isolated from clinical settings. Far less is known about resistance that evolves and segregates in bacteria obtained from the environment. This study indicates that phenotypic measurements of resistance in nature were equivalent or greater to what is found in clinical isolates, not lower as would be expected. In addition, TEM, SHV, OXY and ampC-type beta-lactamases were PCR amplified and the DNA sequences determine for a total of 104 environmental isolates of enteric bacteria. Among those strains a total of 30 strains encoded blaTEM, 12 encoded blaSHV, 15 encoded blaOXY and 53 encoded species-specific blaampC. In this small sample of bacteria 5 novel beta-lactamase alleles were identified, as were two novel ampC-like genes. The sequence information obtained was compared to housekeeping genes from a similar set of environmental isolates, as well as to clinical data provided in GenBank. The similar nucleotide diversity levels found in clinical and environmental isolates suggest that resistance is derived from the same pool. Given that resistance to classical antibiotics preceded it's mass-market production, it is likely that this pool is located in nature and that subsequent clinical resistance is derived from that reservoir. This work suggests the need for additional analysis of environmental isolates to gain a broader perspective of the antibiotic resistance problems found in hospitals. |
