>> Antibiotic use certainly *could have* a detrimental effect on beneficial
micro-organisms. However, no one has shown that it does.

On the other hand:

> Antibiotics are a crucial line of defense against bacterial infections.
Nevertheless, several antibiotics are natural products of microorganisms
that have as yet poorly appreciated ecological roles in the wider
environment. We isolated hundreds of soil bacteria with the capacity to grow
on antibiotics as a sole carbon source. Of 18 antibiotics tested,
representing eight major classes of natural and synthetic origin, 13 to 17
supported the growth of clonal bacteria from each of 11 diverse soils. 

> Bacteria subsisting on antibiotics are surprisingly phylogenetically
diverse, and many are closely related to human pathogens. Furthermore, each
antibiotic-consuming isolate was resistant to multiple antibiotics at
clinically relevant concentrations. This phenomenon suggests that this
unappreciated reservoir of antibiotic-resistance determinants can contribute
to the increasing levels of multiple antibiotic resistance in pathogenic
bacteria. 

"Bacteria Subsisting on Antibiotics" Gautam Dantas et al

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