Survival, and Protection against Chlorination, of Human Enteric Pathogens in Free-Living Nematodes Isolated from Water Supplies

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  • Robert A. Taft Sanitary Engineering Center, Bureau of State Services, Public Health Service, U. S. Department of Health, Education, and Welfare, Cincinnati, Ohio

Summary and Conclusions

The findings gathered in this investigation are summarized as follows:

  1. a)The D. nudicapitatus and C. quadrilabiatus readily ingested Salmonella and Shigella organisms on plate cultures and could even ingest small amounts of Coxsackie and Echo viruses in a fluid suspension.
  2. b)About 5 to 6% of the ingested S. typhosa or Sh. sonnei and about 12 to 16% of the ingested S. paratyphi or Coxsackie A9 virus survived for 24 hours; but the survivals of these were reduced to about 0.1% and 1% respectively after 48 hours. There was no evidence of excretion of viable pathogens.
  3. c)These nematodes are so highly resistant to the destructive action of free chlorine in water that they were not affected by 2.5–3.0 ppm of chlorine in a 120-minute exposure or by 15 to 45 ppm of chlorine in a 1-minute exposure when the water temperature was 25° C, pH 6.6–7.2, and the chlorine residuals were only slightly lower than initials. Even with an initial chlorine as high as 95–100 ppm, 50–60% of these nematodes survived a 5-minute contact and 10–20% survived a 15-minute contact. The C. quadrilabiatus appeared to be somewhat more resistant than the D. nudicapitatus, but the difference was reduced as the chlorine dosage was increased from 15 to 95–100 ppm.
  4. d)The ingested pathogens were protected by the carrier nematodes to the extent that they had a complete survival even when about 90% of the worms were immobilized by the free chlorine.

It is concluded that nematodes of the Rhabditidae family and of sewage-treatment origin may be potential carriers of human enteric bacteria and viruses. Although a majority of the ingested pathogens may disappear in 1 to 2 days after ingestion, 5 to 16% may remain viable if the worms are carried to the water supply within 24 hours after departure from their habitat and will survive routine chlorination as practiced in the field.