Likewise,both nonpathogenic and pathogenic species occur in the Gram- negative cocci of the genus Neisseria.For example,Neisseria meningitidis and Neisseria gonorrhoeae are the causative agents of meningitis and gonorrhea. respectively Differentiating between these groups of cocci is easy.Neisseria are oxidase- positive,Gram-negative,kidney bean-shaped cells often found in pairs. Staphylococcus are Gram-positive,catalase-positive cocci usually found singly or in clusters.Streptococcus are Gram-positive,catalase-negative cocci often found in chains.Differentiating between the species within a genus is more complex,but obviously necessary for proper diagnosis of disease.In this exercise,we will isolate cocci from the human body and identify some of the isolates. BIOCHEMICAL REACTIONS USED FOR IDENTIFICATION OF GRAM- POSITIVE COCCI CATALASE During aerobic respiration,microorganisms produce hydrogen peroxide (H2O2).This compound is toxic,and accumulation of the substance will result in death of the organism unless it can be enzymatically degraded to water and oxygen. 2H02→2H0+O, Catalase is the enzyme responsible for degradation of hydrogen peroxide.To determine the catalase activity of a bacterial culture,a solution of dilute H2O,is added to a bacterial smear on a glass slide.The formation of bubbles (0.)is evidence of catalase activity.Catalase is invariably present in aerobes and is also present in some facultative organisms.As a differential test,the catalase test is used to distinguish between streptococci(catalase negative)and staphylococci (catalase positive). 5353 Likewise, both nonpathogenic and pathogenic species occur in the Gram￾negative cocci of the genus Neisseria. For example, Neisseria meningitidis and Neisseria gonorrhoeae are the causative agents of meningitis and gonorrhea, respectively. Differentiating between these groups of cocci is easy. Neisseria are oxidase￾positive, Gram-negative, kidney bean-shaped cells often found in pairs. Staphylococcus are Gram-positive, catalase-positive cocci usually found singly or in clusters. Streptococcus are Gram-positive, catalase-negative cocci often found in chains. Differentiating between the species within a genus is more complex, but obviously necessary for proper diagnosis of disease. In this exercise, we will isolate cocci from the human body and identify some of the isolates. BIOCHEMICAL REACTIONS USED FOR IDENTIFICATION OF GRAM￾POSITIVE COCCI CATALASE During aerobic respiration, microorganisms produce hydrogen peroxide (H2O2). This compound is toxic, and accumulation of the substance will result in death of the organism unless it can be enzymatically degraded to water and oxygen. 2 H2O2
2 H2O + O2 Catalase is the enzyme responsible for degradation of hydrogen peroxide. To determine the catalase activity of a bacterial culture, a solution of dilute H2O2 is added to a bacterial smear on a glass slide. The formation of bubbles (O2) is evidence of catalase activity. Catalase is invariably present in aerobes and is also present in some facultative organisms. As a differential test, the catalase test is used to distinguish between streptococci (catalase negative) and staphylococci (catalase positive)