Streptococci on Vegetation and Insects

GELDREICH E. E. (Division of Water Supply and Pollution Control, U.S. Public Health Service, Cincinnati, Ohio), B. A. KENNER, AND P. W. KABLER. Occurrence of coliforms, fecal coliforms, and streptococci on vegetation and insects. Appl. Microbiol. 12:63-69. 1964.-This study considers the sanitary significance of coliforms, fecal coliforms, and streptococci isolated from 152 species of plants and 40 samples of insects. These specimens were collected from various ecological environments and grouped into several categories. Results indicate that typical coliforms of the warm-blooded animal gut contribute a relatively small percentage of the organisms associated with vegetation (14.1%) and insects, (14.9%G). A total of 1,203 coliform strains from vegetation and 1,084 coliform strains from insects were classified as to IMViC type and fecal coliform. No type was predominant in either the vegetation or insect groupings. The biochemical results for 646 streptococci from vegetation and 226 cultures from insects were reported. The predominant group, Streptococcus fecalis, as defined by Sherman criteria, constituted a majority of all strains from vegetation and insects. The "Completed Coliform Test" is recommended for the examination of plant and insect specimens to eliminate the many anaerobic and aerobic sporeforming bacteria that frequently produce false positive reactions by the "Confirmed Test" procedure. These findings support the current interpretation of the significance of the fecal coliform test for stream investigations or for surface water quality evaluations. The sanitary significance of a bacterial indicator of pollution is determined from accurate information on its probable sources and quantitative distribution in nature. Interpretation of this significance for the coliform group and the fecal coliform segment within the group has been, and currently is, a controversial subject. Much the same case can be made for the fecal streptococcus group. The coliform group and the fecal streptococcus group are composed of many species, of which some predominate in warm-blooded animal feces, and others may predominate in soil and on vegetation. During periods of rainfall, pollution indicators that might be associated with vegetation would enter the surface waters by way of storm water drainage. Wilson et al. (1935) found the coliform content of grass, hay, and straw to be relatively small except on samples subjected to soil contamination. Thomas and M\IcQuillin (1952) reported these microorganisms abundant in grass from both ungrazed herbage and intensively grazed pasture. Coliform bacteria were reported by Thomas and Hobson (1955) as normal inhabitants on ears and panicles of cereal crops. They also noted 2.7% of the 148 strains as capable of gas production at 44 C. Fraser et al. (1956) reported that coliform bacteria were seldom found on foliage of a wide variety of garden plants, trees and shrubs, and field plants. These authors stated that exceptions were a result of possible contamination by insects, animals, or dust. Many of the earlier investigations related to occurrence of coliform bacteria were based on temperatures other than 35 and 45 C and on media or methods lacking selectivity and sensitivity. Sherman (1937) reported that Streptococcus fecalis and S. liquefaciens types were rather common on plants, but gave no further information. Mundt, Johnson, and Khatchikian (1958) examined leaves, flowers, and shoots of plants grown in cultivated and uninhabited areas for "enterococci" and coliform bacteria. They reported "the enterococci group" were isolated from 58.5 % of 106 samples including 63 plant species, and coliform bacteria were isolated from 67.0 % of these samples. In another study, i\lundt (1961) reported "enterococci" from 27% of the flowers sampled and 6.8 %o of the buds from the same plants. Totals of 34, 32.2, and 10.4 %, respectively, of the flowers from nonagricultural, agricultural, and grass plants contained "enterococci." Data reported on "enterococci" per gram of corn flowers indicated corn tassel samples contained iMlinimal Probable Number (MPN) densities to a maximum of 300,000 per g. Recently, Mundt (1963) described the occurrence of "enterococci" on plants from the Great Smoky AiJountains. "Enterococci" were obtained from 14.2 % of 2,169 flowers and 3.4% of 440 samples of leaves, buds, shoots, fruits, and seeds, but he found no evidence of plant-specific species or variants of the "enterococci." These reports of pollution indicators on vegetation may, in part, be derived from insect contact. Steinhaus (1941) isolated 11 strains of coliform bacteria from the alimentary tract of two Orthoptera, one Hemiptera, one Coleoptera, and two Lepidoptera. S. fecalis was isolated in five insect species (one Orthoptera, one Hemiptera, one Homoptera, and two Lepidoptera). Fecal streptococci were reported by West (1951) to be present in the housefly (1Iusca 63 on Jne 1, 2017 by gest ht://aem .sm .rg/ D ow nladed fom GELDREICH, KENNER, AND KABLER APPL. MICROBIOL.