As Christina pointed out, metabolic pathways are very similar in a wide variety of organisms. Further, resistance genes are routinely transferred between species, including bacteria to microsporidan transfer, as reported below. What this means is that the feeding of antibiotics to livestock for the sole purpose of raising productivity can have the unwanted side effect of creating resistant organisms which can pass their resistance genes to other pathogens, including those that affect humans. This is why we need to take a stand against using antibiotics in the absence of a clear need for them. 

Through their action in decomposing reactive oxygen
species, catalases can help pathogens overcome host
defense mechanisms. The potential advantages conferred
by the acquisition of foreign catalases have been extensively
studied in pathogenic bacteria. In fungi, a
recent transfer of a bacterial catalase has been described in
the microsporidian pathogen Nosema locustae.

Interestingly, another plant pathogen Pseudomonas syringae
is placed among the possible bacterial donors of this
gene, which suggests the transfer of potential virulence
factors among pathogens.

Multiple transfers of functionally-related enzymes are
remarkable because they can provide the recipient species
with a novel metabolic pathway. Our analyses found, in
similar sets of Aspergillus species, the first three enzymes
of the bacterial peptidoglycan biosynthesis pathway:
MurA, MurB and MurC. Recipient species included
Aspergillus terreus, Aspergillus oryzae, Aspergillus flavus,
Aspergillus fumigatus

SOURCE:
Marcet-Houben, M., & Gabaldón, T. (2010). Acquisition of prokaryotic genes by fungal genomes. Trends in Genetics, 26(1), 5-8.

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