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Overview of Gram-Positive Bacteria

By

Larry M. Bush

, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University

Last full review/revision Mar 2021| Content last modified Mar 2021
Click here for the Professional Version

Gram-positive bacteria are classified by the color they turn after a chemical called Gram stain is applied to them. Gram-positive bacteria stain blue when this stain is applied to them. Other bacteria stain red. They are called gram-negative. Gram-positive and gram-negative bacteria stain differently because their cell walls are different. They also cause different types of infections, and different types of antibiotics are effective against them.

Some Gram-positive bacteria cause disease. Others normally occupy a particular site in the body, such as the skin. These bacteria, called resident flora Resident Flora Healthy people live in harmony with most of the microorganisms that establish themselves on or in (colonize) nonsterile parts of the body, such as the skin, nose, mouth, throat, large intestine... read more , do not usually cause disease.

Gram-positive bacilli cause certain infections, including the following:

Gram-positive cocci cause certain infections, including the following:

Gram-positive bacteria are increasingly becoming resistant to antibiotics. For example, methicillin-resistant Staphylococcus aureus (MRSA) Methicillin-resistant Staphylococcus aureus (MRSA) Staphylococcus aureus is the most dangerous of all of the many common staphylococcal bacteria. These gram-positive, sphere-shaped (coccal) bacteria (see figure How Bacteria Shape Up) often cause... read more Methicillin-resistant Staphylococcus aureus (MRSA) bacteria are resistant to most antibiotics that are related to penicillin. Methicillin is a type of penicillin Penicillins Penicillins are a subclass of antibiotics called beta-lactam antibiotics (antibiotics that have a chemical structure called a beta-lactam ring). Carbapenems, cephalosporins, and monobactams... read more . MRSA strains are commonly involved in infections acquired in health care facilities and can cause infections acquired outside health care facilities (community-acquired infections).

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