THE SLOW GROWING GRAM NEGATIVE PIGMENTED WATER BACTERIA

Abstract

Bacteria, producing yellow to orange pigmented colonies on the surface of natural and artificial media, can be found in virtually every segment of the environment. They can be isolated from the soil, from fresh and salt water, from rain and snow, as well as from man, animals, birds, fish and plants. The majority of pigmented organisms are slow growing and can best be seen on the surface of agar plates and membrane filter pads, but usually only after extended incubation of 5-15 days at room temperatures, Some species appear to be chlorine tolerant and can be readily isolated from domestic water supply outlets such as taps, spigots and drinking fountain heads. They also grow readily in static water holding units such as tanks, water baths and special equipment, commonly noted in laboratories and hospitals. Although most of the yellow pigmented bacterial colonies can be classified as harmless microorganisms, occurring in most natural water supplies; infections can and do occur among infants, debilitated patients, surgical patients and patients on immunosupressive drug therapy, chiefly through careless handling of water supplies contaminated with these organisms, The use and abuse of our natural fresh water supplies is an ever increasing worldwide problem. Not only are the lakes and streams polluted by chemicals, fertilizers, and insecticides from surface waters, but the sewage disposal practices encourage the survival and growth of many undesirable species of microbes. Bayliss /2/ in 1930 foresaw the coming events when he stated, "It is easy to remove microorganisms and avoid other particles by filtration, but it is not easy to reduce the organic content of many waters to the point where it will not support microbial growth." The truth of this statement was verified many times over a period of twenty years of microbiological analyses of water samples in a hospital and research facility. The samples came from many sources such as dynamic and free flowing and static or stored water supplies especially in dead end or little used pipe lines, water baths, reservoirs, tank and storage units. Most samples at one time or another, contained viable mold spores, yeast cells, acid fast bacilli, aerobic and anaerobic spore formers, micrococci, streptococci and diptheroids in addition to many species of pigmented and nonpigmented gram negative rods /14/—some of which still remain to be classified as this symposium is attempting to demonstrate. Our attention was first drawn to this problem when four open heart surgery patients developed a bacteremia during their convalescent period /4/. Environmental studies demonstrated a similar organism in a water bath for tempering blood in the surgical area, and in the watér cooling system of the heart lung machine used on the four patients, as was isolated from blood cultures of these patients. Subsequent environmental studies showed that various species of pigmented gram negative bacteria could be readily isolated from the water from virtually every area, in varying numbers, of the research complex. Since water is the "almost universal" solvent, it is able to extract both beneficial and harmful components from the soil or surfaces over or through which it flows and percolates that give it flavor, odor, color, hardness, acidity, alkalinity, and the nutrients that support and encourage microbial growth before, during and after routine use and handling. Chambers and Clarke /7/ describe it clearly, "the extent to which water can serve as a bacterial growth medium is one of the least recognized facets of microbiology." The typical water bacteria, i.e., the pigmented gram-negative, non-fermenting, slow growing species require somewhat different conditions for optimum development. Pigment is most readily produced on the surface of agar plates incubated at room temperature for 5-15 days. The slow growth is not limited to artificial media, since samples of water held at room temperature show a slow but steady increase in numbers, while the levels of coliforms or other non-pigmented species usually decrease during similar holding periods.