Pneumococci producing beta hemolysis on agar

Streptococcus pneumoniae produces a second haemolysin that is distinct from pneumolysin

Pneumococci are described as alpha-haemolytic but under certain circumstances they produce zones of beta-haemolysis on blood-containing medium. This observation was investigated using wild type strains and a genetically-modified strain unable to produce the haemolytic toxin, pneumolysin. beta-haemolysis was produced by all pneumococci tested. It was not inhibited by anti-pneumolysin antibody but could be inactivated by cholesterol. These data confirm that pneumococci elaborate a second haemolysin, distinct from pneumolysin.

False no-growth blood cultures in pneumococcal pneumonia

The growth of Streptococcus pneumoniae in commercial media containing 14C-labeled substrates was studied experimentally; the results of blood cultures that were positive for S. pneumoniae over a 14-month period were analyzed to explain no-growth but radiometrically positive blood cultures from four patients with clinically diagnosed pneumococcal pneumonia. The growth of S. pneumonoiae in aerobic blood culture vials resulted in a chocolate color in the medium. S. pneumoniae grew rapidly in both aerobic and anaerobic media, but 14CO2 evolved from the metabolism of the labeled substrates was detected only in the aerobic culture vials. Radiometric detection lagged behind growth of the organisms and was accompanied by visual changes in the media. By 24 h, the viability of the culture was on the decline; radiometric readings remained positive even when the culture had died.

Disk test for the differentiation of pneumococci from other alpha-hemolytic streptococci

One hundred twenty-five strains of Diplococcus pneumoniae and one hundred twenty-five strains of other alpha-hemolytic streptococci were planted on horse red cell-Brucella agar, and a disk of methicillin was placed on each inoculated plate. All strains were incubated anaerobically at 37 C for 24 h and then exposed to air at 6 C for 48 h. All strains of pneumococci produced a ring of beta-hemolysis surrounding the zone of inhibition produced with the methicillin disk, whereas no strain of alpha-hemolytic streptococci produced beta-hemolysis. It is suggested that this new criterion is useful for the differentiation of pneumococci from other alpha-hemolytic streptococci in those cases where other characteristics were insufficient for an unequivocal identification.

Pneumococcal beta hemolysin produced under the effect of antibiotics

The relationship between exposure of pneumococci to antibiotics and appearance of beta hemolysis (rather than the usual alpha hemolysis) was studied in 100 isolates. All strains were capable of producing beta hemolysis. This occurred at the edge of inhibition zones produced by methicillin and other antibiotics, but only if grown anaerobically and subsequently exposed to air at reduced temperatures. Autolysis of the pneumococci was necessary for the beta hemolysis to be produced. Beta hemolysis was optimal at pH 6.8; none occurred at pH 7.4. The concentration of red cells influenced the reaction: at 4% the extent of beta hemolysis was drastically reduced, which suggests that the lysin is not an enzyme.