**Question:** True about streptococcus is

A. It is a Gram-positive coccus
B. It is universally susceptible to penicillin
C. It is the most common cause of bacterial pneumonia
D. It is related to tetanus

**Core Concept:** Streptococcus is a group of Gram-positive bacteria that can cause various infections in humans. These bacteria are classified into different serotypes, and some are more pathogenic than others. Penicillin is a widely used antibiotic to treat streptococcal infections, but some strains have developed resistance. Streptococcus pneumoniae is a common cause of bacterial pneumonia, while Streptococcus pyogenes is associated with pharyngitis (strep throat) and scarlet fever. Streptococcus tetani, on the other hand, is the causative agent of tetanus.

**Why the Correct Answer is Right:**

Streptococcus is a Gram-positive coccus, meaning it is a small, spherical bacterium that stains purple under the Gram staining technique. This is highlighted in option A.

However, the second part of the question is incorrect. While penicillin is effective against some streptococcal infections, antibiotic resistance has emerged, making some strains resistant to penicillin. This is why option B is not entirely true.

Streptococcus pneumoniae is a significant cause of bacterial pneumonia, hence option C is relevant. Streptococcus pyogenes is responsible for causing pharyngitis (strep throat) and scarlet fever. This is why option D is also correct.

**Why Each Wrong Option is Incorrect:**

Option A is partially correct, as streptococci are Gram-positive cocci, but it fails to address penicillin resistance.

Option B is incorrect because penicillin resistance has emerged, making some streptococcal strains resistant to penicillin.

Option C is partially correct, as Streptococcus pneumoniae is indeed a common cause of bacterial pneumonia. However, it is essential to note that not all streptococcal infections are caused by this bacterium.

Option D is partially correct, as Streptococcus pyogenes is indeed responsible for causing pharyngitis (strep throat) and scarlet fever. However, it is essential to note that not all streptococcal infections are caused by this bacterium, leaving option D incomplete.

**Clinical Pearl:**

In treating streptococcal infections, it is crucial to consider the potential antibiotic resistance and choose an appropriate alternative antibiotic. Additionally, various streptococcal species can cause different infections, so knowing the specific pathogens involved is essential for accurate diagnosis and treatment.