![]() The partial decomposition of the hemoglobin of the erythrocytes by a weaker hemolysin.This is designated as beta (β)-hemolysis. Complete lysis of the erythrocytes in the vicinity of the growing colony.Hemolysis is the lysis of the sheep erythrocytes within the agar by bacterial toxins (hemolysins) that are produced by the different genera of Gram-positive cocci. Slide 5: Hemolysis on sBAPĪs mentioned, the type of hemolytic reaction produced on sBAP is a major clue toward the identification of the genus. Typical colonies are often described as gray to white, moist or glistening. These families of bacteria produce colonies which are variable both in size, consistency, and the type of hemolysis produced on sBAP. The third image represents the colony morphology of many of the streptococci and enterococci. The majority of staphylococcal species produce non-pigmented colonies with smooth margins, as opposed to the important pathogen, Staphylococcus aureus, which produces the characteristic colonies seen here. Next, we see an image of a mixed bacterial culture which displays the white, creamy, non- hemolytic colonies of Staphylococcus epidermidis mixed with the golden, hemolytic colonies of Staphylococcus aureus. Note the bright yellow, non-diffusable colony pigment which is a defining characteristic of M. Micrococcus luteus, a commonly found member of the Micrococcaceae, produces round colonies which are convex (curving outward) with smooth, entire margins. Slide 4: Differentiation of Gram-positive Cocci Culture MorphologyĮxamples of the colony morphology associated with each family is represented on this slide. These four tests will, as we shall see, allow for the differentiation of the families of organisms and will guide the laboratorian to other more definitive tests for the identification of the organism. The categorization of the Gram-positive cocci based on their possession of the enzyme catalase, a quality which can be easily assayed in the lab.The microscopic morphology of the organisms as visualized using the Gram’s stain can give initial clues as to the possible identification of the organism.Included in the observation of the morphology of the colony is the effect that the bacterial growth has on the sheep erythrocytes in the agar medium.Growth can produce colonies of a certain size and consistency, as well as pigmentation. ![]() Colony morphology, the elucidation of the characteristics of the growth of the bacterium on agar medium, in most cases trypticase soy agar containing 5% sheep blood (sBAP).The differentiation of the Gram-positive cocci encompasses 4 main exercises used to compare and contrast the characteristics of each family: Slide 3: Differentiation of Gram-positive Cocci This presentation will focus on the laboratory tests useful for the differentiation among the families as opposed to the more complicated differentiation and identification of the organisms within the different genera. Although many of the members of these families have low pathogenicity and are classified as causes of opportunistic infections, those organisms most often cited as pathogens are listed on this slide. The previous classification of these organisms was much simpler however, with the use of more advanced genetic sequencing methods, these gram-positive cocci have expanded into 4 separate families and their associated genera. These organisms range in virulence potential from commensal organisms found on the skin and mucous membranes to pathogens associated with serious infections. The two unifying characteristics of these four families are their coccoid shape and the fact that they stain purple in the Gram’s method for visualizing bacteria microscopically. In this presentation, we will discuss the fundamentals of the primary identification of those microorganisms that are members of four main families of Gram-positive cocci, the Micrococcaceae, the Staphylococcaceae, the Streptococcaceae, and the Enterococcaceae.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |