A 65 year old man presenting with complaints of chest pain fever, cough with sputum. 0/E of sputum pus cells with gram positive cocci present. Blood agar showed positive result. How will you differentiate this from other gram positive cocci?
Bile solubility > 'b' i.e., Optochin sensitivity This question is about the differential diagnosis of streptococcus. Streptococcus can be broadly categorized into three groups. Alpha hemolytic group of streptococci Alpha hemolytic streptococci may be pathogens such as streptococcus pneumonia or a pa of the normal .flora of the upper respiratory tract i.e., Viridans streptococci. Collectively conzmensal streptococci are often called viridians streptococci which refers to their ahemolytic propey. - Viridans is the Latin for "green" and most of the viridians streptococci are alpha hemolytic, Not quite logically this term also includes few streptococci (e.g., the salivarius and mutans groups of streptococci that induce neither a nor fi hemolysis). Moreover - In common usage this term excludes streptococcus pneumonia although this species is also ahemylytic. Streptococcus pneumonia is the major cause of community acquired bacterial pneumonia and the most frequent cause of otitis media and bacteremia in infacts and children. - Thus it is impoant to distinguish streptococcus pneumonia from other alpha hemolytic streptococci which are commensuls. Two tests are commonly employed for distinguishing streptococcus pneumonia from the viridians streptococcus i.e., - Optochin sensitivity test - Bile solubility test Optochin sensitivity test Optochin (or ethylhydrocupreine) is a chemical used for distinguishing streptococcus pneumonia from other a hemolytic streptococci. - Streptococcus pneumoniae is sensitive to optochin i.e., it is lysed by optochin. - Other ahemolytic streptococci are resistant to (not killed by) optochin. Bacterias that are optochin sensitive will be inhibited to grow around optochin disc while the bacteria that are optochin resistant will be unaffected. Bile Solubility test Bile solubility test is used to distinguish streptococcus pneumoniae from other ahemolytic streptococci. - Bile will selectively lyse colonies of streptococcus pneumoniae while other streptococci are immune to bile's activity.
Bacitracin sensitivity
Optochin sensitivity
Bile solubility
Positive coagulase