Two immunological methods, a sialidase-inhibition test and an ELISA, had been developed for a species-specific detection of sialidases (EC 3.2.1.18) secreted by growing cells of Clostridium perfringens, C. septicum, and C. sordellii. These assays were applied to samples from the infected tissues and cotton wool plugs soaked with wound exudate from patients suspected to be suffering from gas gangrene. The results from 72 patients were compared with bacteriological investigations of 67 homologous samples. From these, 35 patients were found to be infected with one or two of the clostridial species: thirty patients contained C. perfringens, six samples showed an immunologically positive reaction for C. septicum and eight for C. sordellii. In the case of C. perfringens, a high degree of coincidence between the immunological and the bacteriological analyses was obtained. However, in infections with C. septicum or C. sordellii the bacteriological and immunological tests did not agree well. The simple and rapid sialidase inhibition test or the slightly more time-consuming ELISA, which even detects low quantities of sialidase, can be applied for the specific diagnosis of infections caused by C. perfringens, thus allowing a species-specific detection of this bacterial species in two or six hours, respectively, even at an early stage of infection. This early diagnosis is a prerequisite for a specific and life-saving therapy of this severe disease.

In order to improve the diagnosis of gas gangrene, especially at an early stage of infection, new ways for the detection of the responsible Clostridia were investigated. Sialidase, known to be excreted in large amounts by the most frequently occurring myonecrotizing clostridial species, Clostridium perfringens, Clostridium septicum, and Clostridium sordellii, was isolated. With polyclonal antibodies raised against these enzymes, two immunological assays were established, which are directed against the sialidase activity (sialidase inhibition test) and the enzyme protein (‘sandwich’-ELISA), respectively. Using these assays, species-specific information about the presence of clostridial sialidase was obtained within 50 min or 6 h. Animal tests revealed that both assays are applicable 8–12 h after clostridial infection, using resected tissues or wound fluids for estimations. The assays allow specific, sensitive, and quantitative measurement of clostridial sialidases, and no significant interference by sialidases from other microbes or from host tissues occurred. The applicability of the new assays for an early diagnosis of gas gangrene in human patients is discussed.

As the present classification (19) of Clostridium sordellii and C. bifermentans is based on properties which are not conclusive for most of our strains, we investigated 80 strains from various origin of this group regarding 30 selected properties. Four of these properties were correlative and therefore particularly important for a distinct differentiation of the strains investigated: urease activity (U), growth inhibition by 1% mannose (M), arginine deaminase activity (A), and sialidase (EC 3.2.1.18) activity (S). Concerning these four characters three clusters were formed: cluster I was positive for U, M, A, and S and comprised 36 strains including C. sordellii type strain (ATCC 9714T); cluster II was positive for M and S and negative for U and A and comprised twelve strains including strain ATCC 35392; and cluster III was positive for A and negative for U, M, and S and comprised 32 strains including C. bifermentans type strain (ATCC 638T). Only two of the correlative properties (U and S, U and A, A and M, or A and S) needed to be tested to determine the affiliation of any strain of the C. sordellii/bifermentans group to one of the three clusters. Clusters I and II, representing two phenotypes of C. sordellii, can now clearly be distinguished from C. bifermentans. Sialidase formed by cluster I and II strains was inhibited by antibodies produced against cluster I strain sialidase. No cross reaction was found with other clostridial sialidases. Pathogenicity, hitherto considered as one of the distinctive properties of C. sordellii and C. bifermentans, was found with various strains of all the three clusters. Therefore, in the case of an infection caused by these two species, care should be taken as to the pathogenicity especially of C. bifermentans and treatment should be accordingly.

The origin and nature of gas gangrene can be diagnosed exactly only by time-consuming bacteriological tests. In order to improve the diagnostic procedures, rabbits were infected with strains of Clostridium perfringens, Clostridium septicum or Clostridium sordellii. Sialidase activity was found to increase rapidly in serum; elevated creatine kinase activities were observed, too. High sialidase concentrations were found in sera (up to 1.6 mU/ml) and in tissues of wounded regions (up to 110 mU/g) of patients diagnosed to be infected with C perfringens. By inhibition of enzyme activity with antibodies specific for the sialidase from this Clostridium species, it was possible to identify the clostridial origin of the sialidase activities. In the same material from other patients supposed to suffer from gas gangrene, but where no Clostridia could be detected, significant sialidase activity was not found. Thus, sialidase may be a useful tool for the diagnosis of myonecrosis due to clostridial infection.