Survey of Gram Positive Bacteria (Staphylococcus)

Gram Positive Bacteria

Have a cell wall that contains a thick out layer of peptidoglycan laced with lipoteichoic acid and teichoic acid. Feature staphylococcus, streptococcus, enterococcus, bacillus, and clostridium. Mostly cause disease from secreted toxins

Low G and C Bacteria

Low amount of Guanine-Cytosine nucleotide base pairs versus Adenine-Thymine nucleotide base pairs

High G and C Bacteria

High amount of Guanine-Cytosine nucleotide base pairs versus Adenine-Thymine nucleotide base pairs

Staphylococcus

Many are normal members of residential microbiota. Under certain conditions can become opportunistic pathogens, resulting in minor to life threatening conditions. They are facultative Anaerobes, nonmotile (lack flagella), and are spheres in grape like arrangement

Facultative Anaerobe

Prefer to grow in an environment with oxygen for aerobic respiration but can grow and survive in environments without oxygen (staphylococcus)

Salt

Staphylococcus are able to survive on the epidermis that has this deposited on it from sweat glands because it is tolerant of it

Catalase

Staphylococcus contains this enzyme and will bubble and release O2 when exposed to hydrogen peroxide

Desiccation, Radiation, and Heat

Staphylococcus can tolerate harsh environment conditions like this which allows them to survive for a long time on environmental surfaces outside the human body

Staphylococcus aureus

More virulent strain causing a wide variety of disease conditions and symptoms depending on site of infection. Will ferment mannitol causing the pH to become acidic. This causes the pH indicator phenol red to turn yellow and changes the media color on an MSA plate

Staphylococcus epidermidis

Normal microbiota of the human skin but can cause opportunistic infections in very rare cases. Will not ferment mannitol on an MSA plate and leaves the media a pink color

Mannitol Salt Agar

Can be used to identify S. aureus and S. epidermidis. They grow because they can tolerate salt

Pathogenicity of Staphylococcus

Infection results when they breach the body’s skin or mucus membrane to reach the blood. Only takes a few hundred to cause disease, results from extracellular enzymes, antiphagocytic structures, and toxins

Cell-Free Coagulase

Causes blood clotting, reacts with prothrombin, causing the inactive fibrinogen to convert to the active fibrin. Fibrin causes red blood cells to clot

Staphylokinase

Dissolves fibrin causing blood clots to breakdown or dissolve, allows S. aureus to free itself from clots and spread through blood vessels

Hyaluronidase

Skin cells in the epidermis are tightly backed and glue together by hyaluronic acid. Allows the bacteria pass between cells in the epidermis by breaking down hyaluronic acid

Lipases

Breaks down lipids/oil for energy on the skin, allowing staphylococci to grow on the surface of the skin and in cutaneous oil glands

B Lactamase

Gives antibiotic resistance as this enzyme breaks open and destroys the beta lactam ring found in all beta lactam antibiotics such as penicillin

Protein A

Aureus. staphylococcus coats their cells with this. B cells release antibodies that bind to the surface of the bacteria where phagocytes can grip. This makes it easier for phagocytes to adhere to and engulf the bacteria. This binds to antibodies, blocking the location where phagocytes grab on to the antibodies during phagocytosis

Slime Layer

Inhibits leukocyte chemotaxis and phagocytosis, also has a capsule

Cytolytic Toxins

This binds and weakens/destroys the plasma membrane

Leukocidin Toxin

Specifically binds to and destroy all leukocytes

Exfoliative Toxins

These breakdown desmosomes, causing skin cells to separate and slough off

Enterotoxins

Stimulates intestinal contraction, nausea, and intense vomiting (food poison symptoms). These enzymes are very heat stable, meaning they do not breakdown at high temperatures

Epidemiology

The study of the incidence, distribution, and control of disease

Staphylococcus epidermidis

Found everywhere on human skin. Grow in the upper respiratory, gastrointestinal, and urogenital tracts of humans. Transmitted by direct contact or fomites, can be prevented by aseptic techniques and handwashing.

Staphylococcus aureus

Usually only found in moist skin folds. Grow in the upper respiratory, gastrointestinal, and urogenital tracts of humans. Transmitted by direct contact or fomites, can be prevented by aseptic techniques and handwashing.

Noninvasive Disease

Food poisoning due to the ingestion of enterotoxins left in contaminated food NOT bacteria growth. Food left at room temperature for several hours allows bacteria to grow long enough to produce enterotoxins. These toxins are stable at high temperatures, you can kill the bacteria when reheating food but not the enterotoxins

Scalded Skin Syndrome

Blistering and peeling of skin due to exfoliative toxins. These spread through the blood stream and bind to target proteins on the epidermis, layers of the epidermis peel off in sheets

Impetigo

Formation of red sores that eject fluid and leave an amber colored scab. These red sores are filled with bacteria, pus, and leukocytes

Toxic Shock Syndrome

Some Staphylococcus strains produce this toxin inside wounds. The toxin is absorbed and spread through the blood producing fever, vomiting, rash, and low blood pressure. This can be fatal if blood pressure drops so low that vital organs do not get enough oxygen to function

Bacteremia

Presence and spreading of the bacteria in the blood

Endocarditis

The bacteria attack and damage to the lining of the heart. This causes the amount of blood pumped by the heart to drop rapidly

Pneumonia

Inflammation of the lungs, empyema occurs when pus fills the lungs

Osteomyelitis

Inflammation of bone and blood marrow

Treatment of Staphylococcus

Due to beta lactamase, these bacteria are resistant to penicillin. Semisynthetic penicillin-methicillin is commonly used, some strains are resistant to this called methicillin-resistant Staphylococcus aureus (MRSA).

Vancomycin is used for infections that does not respond to penicillin-methicillin