SYNOPSISThe deoxyribonuclease (DNase) test is useful in classifying Serratia bacilli and in differentiating it from the Hafnia group, E. cloacae, and E. liquefaciens. It is recommended as a differential test in enteric bacteriology because of its specificity, the convenience of its use, and the rapidity with which it can be performed.Although the deoxyribonuclease (DNase) test has been used primarily as a test to determine potentially pathogenic staphylococci (Elston and Fitch, 1964;Fusillo and Weiss, 1959; Weckman and Catlin, 1957) it shows potential as a diagnostic tool in identifying Serratia species. This is particularly true of nonpigmented strains. Production of DNase has been associated mainly with pathogenic cocci (Brown, 1950;Cunningham, 1959;Fusillo and Weiss, 1959;Potter and Laskowski, 1959; Wannamaker, 1958; Weckman and Catlin, 1957) but a wide variety of microorganisms has been found to produce this enzyme. These have included Bacillus subtilis, Clostridium septicum, Corynebacterium, Pasteurella pestis, Pseudomonas, Achromobacter, Escherchia coli, and Serratia marcescens. In recent years, DNase production in Enterobacteriaceae has been investigated in greater detail (Lehman and Richardson, 1964;Rothberg and Swartz, 1965; Valu, 1966).From time to time reports have appeared in the literature of the isolation of Serratia from such clinical sources as abscesses, blood, sputa, urine, and wounds. Many of the Serratia strains recovered today are without pigmentation (pigments) and are late or nonlactose fermenters making cultural differentiation from some of the other enterobacteria difficult. Serratia are closely allied in their physiological behaviour with Hafnia species (Paracolobactrum aerogenoides) and some members of the Enterobacter (Aerobacter) group which may make a long series of biochemical procedures necessary to identify these organisms. A short set of routine tests, which includes DNase as a major differentiating factor, would be especially useful as a screening Received for publication 3 July 1967. procedure in characterizing Serratia in a short period of time.The present work was undertaken to explore further this potential. MATERIALS AND METHODSNinety-three different strains (isolates) were used. These strains consisted of 51 determined species of Serratia, 33 determined species of Hafnia, six Enterobacter cloacae, and three Enterobacter liquefaciens organisms. Eighty-seven strains were fresh isolates obtained by the authors, while four were received from other laboratories, and one E. cloacae, and one E. liquefaciens strain were from the American Type Culture Company.Routinely, Gram-negative bacilli isolated in our laboratory are subjected to six routine tests which form a basic combination helpful in determining other biochemical tests to be used in further identification of these organisms. These tests included: Kligler iron agar (Difco) used to determine the production of hydrogen sulphide, and the fermentation reaction on the slant (lactose) and in the butt (glucose) of the ...

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The Isolator system was compared with the large-volume centrifugation method for processing and recovering organisms from body fluids other than blood, cerebrospinal fluid, and urine. A total of 155 body fluid samples were processed for the recovery of clinically significant organisms. Of the 55 positive cultures, Isolator detected 94% and the large-volume centrifugation method detected 64%. The time necessary to indicate positivity was not significantly different in the two methods; however, in five cases, the Isolator system yielded clinically significant organisms 24 h sooner than the conventional method. The Isolator system was found to be a more sensitive alternative than the conventional large-volume centrifugation method.