On 2013 Nov 05, Fiona Walsh commented:

The beta-lactams in our study were not 'catabolised' but were digested by the antibiotic resistance enzymes, the beta-lactamases. We used the same strains as the Dantas study i.e. two beta-lactam catabolising bacteria and also identified that the degradation of the beta-lactams was due to the beta-lactamases. These bacteria were either Pseudomonas or Burkholderia species, both of which contain chromosomal beta-lactamases. We identified bacteria which presented with a streptomycin or trimethoprim 'catabolising' phenotype, which we isolated from soil (the original strains from Dantas et al., study with such phenotypes were lost). However, the HPLC experiments clearly showed that these antibiotics were not degraded over 28 days, we concluded based on these and other results that the bacteria did not catabolise the antibiotics. The Dantas study described the HPLC/ chemical degradation studies only for the beta-lactams (carbenicillin and penicillin) and extrapolated these results to all other classes of antibiotics described in the study.

On 2013 Nov 04, Laura Williams commented:

Walsh F, 2013 recently investigated the central claim of this article, which is that many soil bacteria are able to grow using different classes of antibiotics as a single carbon source. Contrary to the findings of Dantas et al., Walsh et al. were only able to confirm catabolism of beta-lactam antibiotics, rather than catabolism of multiple classes of antibiotics. Their paper points to the presence of EDTA in the minimal medium used in the original study as a possible source of carbon sufficient for bacterial growth, which would suggest that growth in the media+antibiotic condition is not a indication of catabolism of the antibiotic, but simply antibiotic resistance.

On 2013 Nov 04, Laura Williams commented:

Walsh F, 2013 recently investigated the central claim of this article, which is that many soil bacteria are able to grow using different classes of antibiotics as a single carbon source. Contrary to the findings of Dantas et al., Walsh et al. were only able to confirm catabolism of beta-lactam antibiotics, rather than catabolism of multiple classes of antibiotics. Their paper points to the presence of EDTA in the minimal medium used in the original study as a possible source of carbon sufficient for bacterial growth, which would suggest that growth in the media+antibiotic condition is not a indication of catabolism of the antibiotic, but simply antibiotic resistance.

On 2013 Nov 05, Fiona Walsh commented:

The beta-lactams in our study were not 'catabolised' but were digested by the antibiotic resistance enzymes, the beta-lactamases. We used the same strains as the Dantas study i.e. two beta-lactam catabolising bacteria and also identified that the degradation of the beta-lactams was due to the beta-lactamases. These bacteria were either Pseudomonas or Burkholderia species, both of which contain chromosomal beta-lactamases. We identified bacteria which presented with a streptomycin or trimethoprim 'catabolising' phenotype, which we isolated from soil (the original strains from Dantas et al., study with such phenotypes were lost). However, the HPLC experiments clearly showed that these antibiotics were not degraded over 28 days, we concluded based on these and other results that the bacteria did not catabolise the antibiotics. The Dantas study described the HPLC/ chemical degradation studies only for the beta-lactams (carbenicillin and penicillin) and extrapolated these results to all other classes of antibiotics described in the study.