Polysaccharase Activity in Streptococcus agalactiae (Group B Streptococci)

Abstract

1381 ~~ ~~Of 300 recently isolated strains of Streptococcus agalactiae from human sources, 97 % degraded starch. Representative strains also degraded glycogen, pullulan, amylopectin and amylose. The polysaccharase activity is easily detected by clearing around growth on Columbia agar base medium. The activity is weaker than that of some S. pyogenes strains, and it does not appear to produce fermentable products but is inhibited by the presence of easily used sugars. I N T R O D U C T I O NWhile working with Streptococcus agalactiae strains we noticed that growth on Columbia agar base, without blood, resulted in clearing of the slightly opaque medium. The opacity appeared to be due to corn starch. Streptococcus agalactiae is described in the literature as negative in starch hydrolysis tests (Buchanan & Gibbons, 1974) and acid production from starch tests (Simmons & Keogh, 1940). This paper describes comparative results for S. agalactiae and other bacteria in simple tests for the degradation of polysaccharides. M E T H O D SBacteria. Three hundred strains of S. agalactiae recently isolated from human sources were maintained by freeze-drying. Five serotype strains of S. agalactiae were taken from lyophilized stock in the University of Queensland Microbiology Department Culture Collection (UQM 1737, 1738, 1739, 1740 and 1744 representing serotypes Ia, Ib, Ic, I1 and 111, respectively). The identity of all S. agalactiae strains was confirmed serologically and by CAMP and hippurase reactions. Ten strains of Group D streptococci freshly isolated from human faeces and sewage on bile-aesculin agar were identified serologically. Ten strains of viridans streptococci were freshly isolated from human saliva on mitis-salivarius agar by selecting colonies of the Streptococcus sanguis and S . salivarius type. Escherichia coli (UQM 70), Enterobacter aerogenes (UQM 427), Streptococcus pyogenes (UQM 1897), Corynebacterium diphtheriae var. gravis (UQM 890), Corynebacterium diphtheriae var. intermedius (UQM 896) and Listeria monocytogenes (UQM 3691) were obtained from the University of Queensland Microbiology Department Culture Collection. All the bacteria were maintained by subculture on 5 % horse blood agar and in cooked-meat medium (Oxoid CM439). Substrate degradation tests(a) Agar plate method. Maize starch, potato starch, soluble starch, oyster glycogen, dextrin (BDH), amylose, amylopectin and pullulan (Sigma) were added to 100 ml lots of blood agar base no. 2 (Oxoid CM271) to give 0 -2 % (w/v) final concentration, sterilized at 12 1 *C for 15 min, mixed well and poured as top layers on prepoured layers of 0.9% (w/v) saline agar in 9 cm Petri dishes; 100 ml of substrate medium gave 12 plates. Controls without substrate and double-layer plates of Columbia agar base (CAB, Gibco) were also prepared. The plates were spot inoculated (four strains per plate) with about 30 pl of 24 h cultures in Todd-Hewitt broth (THB, Gibco), delivered with Pasteur pipettes. All of the 33 1 strains were tested on CAB. Nine strains of S. agalactiae (i...