Tetracycline-resistant coliforms in the effluent of the main sewage treatment plant in Hamilton, Ontario - do they have a common ancestral strain?

Sewage, a major source of bacterial contamination of the environment, can be an important health hazard. The presence of antibiotic-resistant bacteria in sewage can exacerbate this problem. The sources of antibiotic-resistant bacteria in sewage are, for this reason, worth identifying and addressing. The bacterial flora in the effluent of the Woodward Avenue Wastewater Treatment Plant (WAWTP) in Hamilton, Ontario, Canada, contains many antibiotic-resistant coliforms. Here we ask, are the antibiotic resistance genes in the coliforms in the effluent of WAWTP descended from a recent common ancestor strain? If so, the source could be identified and eliminated. If, on the other hand, the antibiotic resistance genes in the bacterial flora of the WAWTP have more than one origin, identification and elimination of the source(s) could be difficult. There was considerable diversity of antibiotic resistance patterns and antibiotic resistance genes among the effluent and influent coliform isolates of the WAWTP, suggesting multiple genetic ancestry. The patterns of horizontal transmissibility and sequence differences in the genes tetA and tetE among these coliform isolates also suggest that they have no one predominant ancestral strain. Using the same logic, the evidence presented here is not compatible with a single ancestral origin of the antibiotic resistance genes in the isolates described herein.

Effects of papaya seed extract and benzyl isothiocyanate on vascular contraction.

To investigate their potentially toxic effects on mammalian vascular smooth muscle, pentane extracts of papaya seeds and the chief active ingredient in the extracts, benzyl isothiocyanate (BITC), were tested for their effects on the contraction of strips of dog carotid artery. BITC and the papaya seed extract caused relaxation when added to tissue strips that had been pre-contracted with phenylephrine (PE). Incubation of the tissue with papaya seed extract or BITC caused inhibition of contraction when the strips were subsequently contracted with KCl or PE. This relaxation and inhibition of contraction did not appear to be endothelium-dependent, as endothelium-denuded rings showed the same degree of relaxation or inhibition of contraction in response to the preparations/drugs as those with the endothelium intact. The effects of both BITC and the extract were irreversible, i.e., the tissue did not recover to normal contractile ability after extensive washing. Exposure of the tissue to the papaya seed extract caused slower relaxation of the tissue, compared to controls, both after contraction with PE and subsequent addition of carbachol (CCh), and after contraction with KCl and then washing. Calcium imaging studies using cultured endothelial cells showed strong influxes of Ca2+ into the cells in response to addition of the papaya seed extract. We conclude that these extracts, when present in high concentration, are cytotoxic by increasing the membrane permeability to Ca2+, and that the vascular effects of papaya seed extracts are consistent with the notion that BITC is the chief bio-active ingredient.