Using this flow chart, a species that is alpha-hemolytic and catalase-negative is Streptococcus pyogenes Streptococcus pneumoniae Enterococcus faecalis This diagram depicts the classification of Gram-Positive Bacteria, focusing primarily on cocci and bacilli.### Gram-Positive Bacteria1. **Cocci** - **Staphylococcus (catalase-positive)** - **S. aureus (coagulase-positive)** - **Coagulase-negative Staphylococcus** - **S. epidermidis (Novobiocin-sensitive)** - **S. saprophyticus (Novobiocin-resistant)** - **Streptococcus (catalase-negative)** - **β-hemolytic (clear)** - Group A: **S. pyogenes** - Group B: **S. agalactiae** - **γ-hemolytic (non-hemolytic)** - **Enterococcus** - **E. faecalis** - **E. faecium** - **α-hemolytic (green)** - **S. pneumoniae** - **Viridans group**2. **Bacilli** - Includes: - **Corynebacterium** - **Clostridium** - **Listeria** - **Bacillus**### Explanation- **Cocci** are spherical bacteria, further classified into catalase-positive (Staphylococcus) and catalase-negative (Streptococcus) groups.- **Staphylococcus** species are differentiated by their coagulase reaction and novobiocin sensitivity.- **Streptococcus** species are categorized based on their hemolytic properties: β-hemolytic (clear), γ-hemolytic (non-hemolytic), and α-hemolytic (green).- **Bacilli** are rod-shaped bacteria and include several genera that are important medically, such as Corynebacterium and Clostridium. This classification helps in identifying the properties and potential pathogenic nature of these bacteria, which is crucial in medical microbiology.

In this question, we are given a dichotomous key for identification of bacteria on the basis of the observations obtained by biochemical tests. We have to determine a species of bacteria which is both coagulase negative and alpha-hemolytic. According to the key, all members of Streptococcus genera are coagulase negative. There are only two species of bacteria which are both catalase negative and alpha-hemolytic. Alpha-hemolytic species are mentioned in the image as a branch of catalase negative Streptococcus. These two species are: Streptococcus pneumoniae and Streptococcus viridans. Hence out of the given species, it is Streptococcus pneumoniae which is both catalase negative and alpha-hemolytic. Other options are incorrect because Streptococcus pyogenes is beta-hemolytic according to dichotomous key and Enterococcus faecalis is gamma-hemolytic. Correct answer: Streptococcus pneumoniae.