Staphylococcal infection

Coagulase-positive

The main coagulase-positive staphylococcus is Staphylococcus aureus, although not all strains of Staphylococcus aureus are coagulase positive. These bacteria can survive on dry surfaces, increasing the chance of transmission. S. aureus is also implicated in toxic shock syndrome; during the 1980s some tampons allowed the rapid growth of S. aureus, which released toxins that were absorbed into the bloodstream. Any S. aureus infection can cause the staphylococcal scalded skin syndrome, a cutaneous reaction to exotoxin absorbed into the bloodstream. It can also cause a type of septicaemia called pyaemia. The infection can be life-threatening. Problematically, methicillin-resistant Staphylococcus aureus (MRSA) has become a major cause of hospital-acquired infections. MRSA has also been recognized with increasing frequency in community-acquired infections. The symptoms of a staphylococcal infection include a collection of pus, such as a boil or furuncle, or abscess. The area is typically tender or painful and may be reddened or swollen.

Coagulase-negative

• S. epidermidis, a coagulase-negative staphylococcus species, is a commensal of the skin, but can cause severe infections in immune-suppressed patients and those with central venous catheters.
• S. saprophyticus, another coagulase-negative species that is part of the normal vaginal flora, is predominantly implicated in uncomplicated lower genitourinary tract infections in young sexually active women.
• Other staphylococcal species have been implicated in human infections, notably S. lugdunensis, S. schleiferi, and S. caprae.

Causes

Staph infections have a multitude of different causes, such as:

• Open wounds – This is by far the biggest cause of staph infection. Any open wound, even ones as small as a paper cut, are vulnerable to being infected. Staph bacteria will enter the body through any open wound, so it is important to properly treat, disinfect, and bandage any wounds.
• Contact with infected persons or surfaces – Staph infections are very contagious when in contact with a person that is already infected. A person with staph infection is contagious until the bacteria are completely out of their body, and any wounds from the infection are healed. It is common to see the spread of staph in contact sports; i.e. wrestling, through contact in locker rooms, or by sharing any equipment.
• Weakened immune system – Anyone with a weakened immune system for any reason can be more easily affected by staph bacteria, because their bodies are unable to defend against infectious bacteria as well.
• Unwashed linens – Staph bacteria are very resistant under harsh conditions, and they will cling to objects where they can create a niche. Unwashed bath towels, blanket, bed sheets, and clothes can create a great environment for these bacteria to grow. This is important to recognize, because every single day people use linens in their daily lives.
• Infection after surgery – Hospitals are a very common place for staph bacteria to contaminate. This becomes problematic when people are in surgery, because in some cases staph can be introduced to a person's body when an incision is opened.
• Invasive devices – Medical devices that have any connection to organs to the outside of the body are very problematic, because they allow an easy open pathway into the body. Examples of these devices are; catheters, dialysis tubing, feeding tubes, breathing tubes, etc.

Signs and symptoms

Staph infection is typically characterized by redness, pus, swelling, and tenderness in areas of the infection. But, each type of skin infection caused by staph bacteria is different.

A few common skin infections caused by staph bacteria are:

• Boils – Boils are the most common type of staph infection, they are pockets of white pus that start where a hair follicle or oil gland is. The boil is tender and red where the infection is located on the skin.
• Impetigo – Impetigo is most prominent among children, and is usually located around their mouth, nose, hands, and feet. It shows up like a rash of painful blisters, will eventually produce pus that is yellowish in color.
• Cellulitis – Cellulitis is also rash-like; the skin that is infected will be red, swollen, and usually warm to the touch. Cellulitis commonly infects the lower legs, but can also, less commonly, affect the face and arms.
• Staphylococcus scalded skin syndrome – Staphylococcus scalded skin syndrome is caused by toxins produced when a staph infection gets too severe. It is characterized by a fever, rash, and blisters.
• Methicillin-resistant Staphylococcus aureus (MRSA) – MRSA is one of the most common antibiotic-resistant strains of staph bacteria. It is more difficult to treat than other staph infections. MRSA causes rashes, boils, sores, and other abscesses.

Bacterial identification

In the microbiology lab, Staphylococcus is mainly suspected when seeing Gram-positive cocci in clusters.

Treatment

Treatment for staph infection varies depending on the type and severity of infection. Common treatments are antibiotics, topical creams, and drainage/cleaning of infectious wounds.

Etymology

The generic name Staphylococcus is derived from the Greek word "staphyle", meaning bunch of grapes, and "kokkos", meaning granule. The bacteria, when seen under a microscope, appear like a branch of grapes or nuts.

Epidemiology

Staphylococcus bacteria is one of the leading community-acquired bacteria. According to the CDC, after a push from hospitals to better prevent staph infections, the percentage of people affected has dropped dramatically. However, staph infections are still prominent and a cause for concern among healthcare professionals, especially new antibiotic-resistant strains. In the U.S., the incidence of staph infection is around 38.2 to 45.7 per 100,000 person-years, whereas other First World countries have an average incidence rate of 10 to 30 per 100,000 person-years.