Clostridium difficele

 

     Selective pressures from antibiotic treatment have contributed to horizontal gene transfer events largely responsible for the spread and acquisition of antibiotic resistance in bacteria. Tetracycline resistance is commonly found in bacteria of the human gut. We identified a candidate horizontal transferring protein (CSBG_03569) from the strain Clostridium difficile using parametric analysis that relied on characteristic GC content of the organism genome (10.07560881 standard deviations from mean). This protein was identified as tetracycline resistant protein, class C (TetC), of 219 amino acids long.

     Further analysis of the same amino acid sequence with DarkHorse identified TetC, 396 amino acids long, from Chlamidya suis as a horizontal gene transfer candidate (lineage probability index (LPI) of 0.504). Low LPI scores suggest a large phylogenetic distance between the amino acid sequence tested and the closest matched sequence selected from taxonomy databases. Therefore, the existence of this protein, 100% identical to the gene found in Clostridium difficile, would suggest a horizontal transfer event between these different strains. The resistance found in Chlamidya suis is mobilized by genomic islands containing the TetC allele. DarkHorse provided evidence to where this transfer event originated and what elements were most likely responsible for this transfer event. Our results provided a match for Chlamidya suis TetC in Helicobacter pullorum (LPI of 0.504). This organism was also recognized by the parametric method as HPMG_01968 (standard deviation from mean of 7.584459956). Helicobacter pullorum is a gram-negative pathogen prevalent in the human intestine and a considered a possible food-borne pathogen. Although the amino acid sequences between these strains were not identical, this result would suggest that antibiotic resistant genes are commonly transferred between unrelated organisms in the gut microbiome due to their protective function that provides a selective advantage to the organism. The recurrence of horizontal gene transfer of TetC is consistent with recent research identifying the human gut as a major antibiotic resistant reservoir. When compared with other genes, antibiotic resistance was found to be more prevalent in gram positive (Proteobacteria) bacteria than gram negative (Bacteriodetes).

     Clostridium difficile is a spore-forming gram-positive bacillus that is responsible for most nosocomial diarrheic disease. This organism is considered a member of the normal gut microflora which is composed of a high density of bacteria and abundant nutrients. Bacteriodes account for 25% of the human gut microbiome and have gained increasing resistance to antibiotics acquired in host diet. The prevalence of transmission of antibiotic resistance determinants is known to increase with a diet that favors survival of strains that maintain this newly acquired resistant elements. This has created public concern for food safety. Antibiotic resistant bacteria in food can cause life-threatening infections if such gut microflora as Clostridium difficile, escape into other more susceptible body sites.