Question

A chain of coccoid bacterial cells is
A. Staphylococcus
B. Monococcus
C. Diplococcus
D. Streptococcus

Answer 1

Streptococcus is a genus of gram-positive coccus or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Firmicutes. A diplococcus is a round bacterium (a coccus) that typically occurs in the form of two joined cells. Examples of gram-positive diplococci are Streptococcus pneumoniae and Enterococcus.

Complete step by step answer: Cell division in Streptococci occurs along a single axis, so as they grow, they form pairs or chains that may appear bent or twisted. They are spherical-shaped bacteria that occur in clusters. Whereas, Staphylococci divide along multiple axes, thereby generating irregular, grape-like clusters of cells. Most Streptococci are oxidase-negative, catalase-negative and many are facultative anaerobes. Species of Streptococcus are classified based on their hemolytic properties. Alpha-hemolytic species cause oxidation of iron in haemoglobin molecules within red blood cells, giving it a greenish colour on blood agar. Beta-hemolytic species cause a complete rupture of red blood cells. On blood agar, this appears as wide areas clear of blood cells surrounding bacterial colonies. Gamma-hemolytic species cause no hemolysis. Natural genetic transformation involves the transfer of DNA from one bacterium to another through the surrounding medium. Transformation is a complex process dependent on the expression of numerous genes.
Hence, the correct answer is option D.

Note: In addition to streptococcal pharyngitis, certain Streptococcus species are responsible for many cases of pink eye, meningitis, bacterial pneumonia, endocarditis, erysipelas and necrotizing fasciitis. However, many streptococcal species are not pathogenic and form a part of the commensal human microbiota of the mouth, skin, intestine and the upper respiratory tract.