Survey of Free‐Living Nematodes and Amebas in Municipal Supplies

Abstract

The persistent occurrence of free‐living nematodes in a city water supply was reported in May 1959, and has led to the speculation that the presence of nematodes in municipal water supplies may be more common than has been generally realized. A survey of a representative group of large city water supplies in the United States has, therefore, been conducted. A search for viable cysts of free‐living amebas in the finished waters has also been made. Arrangements for collection and shipment of one raw‐ and one finished‐water sample were made either directly with the water utility, water commissioners, state health departments, or through the regional offices of the U.S. Public Health Service (USPHS). All samples were collected in 2 1/2‐liter plastic bottles and shipped without refrigeration or preservatives. Upon receipt of the samples, the entire volume of each sample was filtered through a SS type (3 μ pore size) membrane filter, and the concentrate was examined in the manner described in the previous article. When nematodes were observed under the microscope, the whole concentrate was pipeted into a centrifuge tube and centrifuged at 500 rpm for 5 min. The sediment thus obtained was used in preparing stained specimens for identification. When a concentrate showed a worm population of more than 10 per gallon, half of the sediment was used in identification and the other half in cultivation by the technique described in another report. When a raw‐water sample had a high turbidity and, consequently, a poor filterability, 500‐1,000 ml was filtered through 2‐4 membranes. The concentrate was washed from each membrane and examined separately to avoid the possibility of overlooking nematodes hidden by particulate matter. When amebic cysts were shown to be present in a finished‐water sample, 2‐3 drops of the sediment, after centrifuging, were placed on a buffered sucrose nitrate agar plate preseeded with Proteus mirabilis for viability and identification.