Introduction of a mini-gene encoding a five-amino acid peptide confers erythromycin resistance on Bacillus subtilis and provides temporary erythromycin protection in Proteus mirabilis

Novel Antibiotic Resistance Determinants from Agricultural Soil Exposed to Antibiotics Widely Used in Human Medicine and Animal Farming

Antibiotic resistance has emerged globally as one of the biggest threats to human and animal health. Although the excessive use of antibiotics is recognized as accelerating the selection for resistance, there is a growing body of evidence suggesting that natural environments are "hot spots" for the development of both ancient and contemporary resistance mechanisms. Given that pharmaceuticals can be entrained onto agricultural land through anthropogenic activities, this could be a potential driver for the emergence and dissemination of resistance in soil bacteria. Using functional metagenomics, we interrogated the "resistome" of bacterial communities found in a collection of Canadian agricultural soil, some of which had been receiving antibiotics widely used in human medicine (macrolides) or food animal production (sulfamethazine, chlortetracycline, and tylosin) for up to 16 years. Of the 34 new antibiotic resistance genes (ARGs) recovered, the majority were predicted to encode (multi)drug efflux systems, while a few share little to no homology with established resistance determinants. We characterized several novel gene products, including putative enzymes that can confer high-level resistance against aminoglycosides, sulfonamides, and broad range of beta-lactams, with respect to their resistance mechanisms and clinical significance. By coupling high-resolution proteomics analysis with functional metagenomics, we discovered an unusual peptide, PPP^{AZI 4}, encoded within an alternative open reading frame not predicted by bioinformatics tools. Expression of the proline-rich PPP^{AZI 4} can promote resistance against different macrolides but not other ribosome-targeting antibiotics, implicating a new macrolide-specific resistance mechanism that could be fundamentally linked to the evolutionary design of this peptide.IMPORTANCE Antibiotic resistance is a clinical phenomenon with an evolutionary link to the microbial pangenome. Genes and protogenes encoding specialized and potential resistance mechanisms are abundant in natural environments, but understanding of their identity and genomic context remains limited. Our discovery of several previously unknown antibiotic resistance genes from uncultured soil microorganisms indicates that soil is a significant reservoir of resistance determinants, which, once acquired and "repurposed" by pathogenic bacteria, can have serious impacts on therapeutic outcomes. This study provides valuable insights into the diversity and identity of resistance within the soil microbiome. The finding of a novel peptide-mediated resistance mechanism involving an unpredicted gene product also highlights the usefulness of integrating proteomics analysis into metagenomics-driven gene discovery.

Accelerated transformation and deactivation of erythromycin in superheated water. 2. Transformation reactions and bioassays

The work presented in this second part of a two-part series on the accelerated transformation of erythromycin in superheated water focuses on the chemical nature and resultant antimicrobial implications of the overall reaction observed. Analyses of reactor effluents employing infrared spectroscopy and liquid chromatography/mass spectrometry indicated that the initial step in the decomposition pathway is one of dehydration. Subsequent hydrolysis in the presence of an acetate buffer appeared to result in the loss of the sugar cladinose. Chemical transformation under superheated conditions was tied to the loss of antibiotic function by an agar dilution test. The sensitivity of this test was verified by determination of the minimum inhibitory concentration (MIC) of erythromycin corresponding to each of two test microorganisms. MIC values for the selected strains of Escherichia coli and Bacillus subtilis were 35 and 0.5 mg/L, respectively. To relate the loss of antimicrobial activity to increased reaction temperature and thus to increased extent of parent compound transformation to microbially benign intermediates, bioassays using E. coli as test microorganism were performed on flow reactor effluents resulting from reaction of initial erythromycin concentrations of 75-150 mg/L.

Short peptides conferring resistance to macrolide antibiotics

Translation of specific short peptides can render the ribosome resistant to macrolide antibiotics such as erythromycin. Peptides act in cis upon the ribosome on which they have been translated. Amino acid sequence and size are critical for peptide activity. Pentapeptides with different consensus sequences confer resistance to structurally different macrolide antibiotics, suggesting direct interaction between the peptide and the drug on the ribosome. Translation of resistance peptides may result in expulsion of the macrolide antibiotics from the ribosome. The consensus sequence of peptides conferring erythromycin resistance is similar to the sequence of the leader peptide involved in translational attenuation of erythromycin resistance genes, indicating that a similar type of interaction between the nascent peptide and antibiotics can occur in both cases.