Staph Infection (Staphylococcus Infection)

Staphylococcus bacteria (also termed staph) are responsible for a number of common infections. Staphylococcus is a genus of bacteria that is characterized by a round shape (coccus or spheroid shaped), Gram-stain positive, and found as either single cells, in pairs, or more frequently, in clusters that resemble a bunch of grapes. The genus name Staphylococcus is derived from Greek terms (staphyle and kokkos) that mean "a bunch of grapes," which is how the bacteria often appear microscopically after Gram-staining. In 1884, Rosenbach first described and named the bacteria. Two major divisions of the genus Staphylococcus are separated by the ability to produce coagulase, an enzyme that can clot blood. Most, but not all, human bacterial infections are caused by coagulase-positive Staphylococcus aureus strains. Staphylococcus epidermidis strains and other Staphylococcus species that are coagulase-negative produce slime that interferes with immune defenses. S. epidermidis are often associated with implanted devices (for example, catheters or prosthetic devices).

Almost any organ system can be infected by S. aureus. Most frequently, S. aureus strains first infect the skin and its structures (for example, sebaceous glands, hair follicles) or invade damaged skin (cuts, abrasions). Sometimes the infections are relatively limited (such as a sty, boil, furuncle, or carbuncle), but other times they may spread to other skin areas (causing cellulitis, folliculitis, or impetigo). Unfortunately, these bacteria can reach the bloodstream (bacteremia) and end up in many different body sites, causing infections (wound infections, abscesses, osteomyelitis, endocarditis, pneumonia) that may cause severe harm or even be fatal.

How do Staphylococcus aureus infections differ from Staphylococcus epidermidis infections?

• S. aureus strains also produce enzymes and toxins that likely cause or increase the severity of certain diseases. Such diseases include
  • food poisoning,
  • septic shock,
  • toxic shock syndrome, and
  • scalded skin syndrome.
• S. epidermidis strains, which usually do not cause infections, can cause infections in people whose immune system is suppressed. Patients who have any type of indwelling catheter or implanted device are also known to get S. epidermidis infections.

• Most staph infections that are visible usually have a reddish, swollen, itchy, and/or tender area at the site of infection.
• Often the site oozes pus or has some crusty covering with drainage.
• Sites of infection can be small like a pimple on someone's face or even in the nose, a boil on an extremity, or large like a carbuncle.
• Cellulitis (it most commonly appears on the legs) often shows redness and swelling of the involved area without pus, but impetigo shows a crusty weeping rash with an occasional blister.
• Scalded skin syndrome shows extensive skin redness with bullae (fluid- or pus-filled blisters).
• Infected catheters and other implanted devices usually show redness, pus, and tenderness at the skin entry site. Deep abscesses, pneumonia, osteomyelitis, and most other internal infections are only seen by X-ray and other imaging techniques or are not visible at all (for example, toxic shock, food poisoning) although nausea, vomiting, diarrhea and abdominal pain, chills, and fever may be present.

The appearances described above are only suggestive of staph infection; proof of infection depends on bacterial culture and subsequent identification of the infecting agent.

Staphylococci have the ability to synthesize and secrete many factors that either allow the bacteria to survive in the host or cause damage to host tissues. The list below summarizes these substances and their effects on the host:

• Surface proteins (for example, capsular polysaccharide, protein A) -- enhance attachment to host cells; others reduce phagocytosis (host immune cell's ability to ingest and kill bacteria)
• Membrane-altering toxins (for example, alpha, beta toxins plus leukocidin) -- all damage host cells by making holes in their membranes
• Exfoliatin toxins (exotoxins ETA and ETB) -- cause scalded skin syndrome (exfoliation of skin after erythematous cellulitis) in infants and children
• Enterotoxins (exotoxins secreted into the gastrointestinal tract termed SE-A, B, C, D, E, and G) -- cause nausea and vomiting associated with food poisoning
• Toxic shock syndrome toxin (TSST-1 toxin) -- syndrome of rapidly onset of fever (102 F or higher), low blood pressure (hypotension), watery diarrhea, muscle aches, weakness, and a rash after about 24 hours associated with staph infections. This occurs usually in females with tampons in place but occasionally occur in males and females with other staph infections such as wound infections.
• Coagulase -- possibly protects staph bacteria from host immune cells by causing bacterial aggregation
• Slime (a biofilm secreted by S. epidermidis) -- Coats and protects bacteria from host's immune cells, which make antibiotic treatment frequently complex. Please see the methicillin-resistant Staphylococcus aureus (MRSA) infection article for a more complete discussion of this complicated topic.

Other factors produced by these bacteria that may play a role in causing disease are hyaluronidase, kinases, clotting factor, and others, but their disease-causing potentials are still being evaluated.

Diagnosis of staph infections begins with attempting to culture the bacteria from an infected site. Any area with pus, crusty drainage, or blisters should be cultured. Blood from patients with sepsis, toxic shock syndrome, or pneumonia should be cultured. Standard microbiological techniques include a positive coagulase test to identify staph. S. aureus lyses red blood cells in blood agar plates (hemolytic staph) while S. epidermidis does not (nonhemolytic staph).

All staph should be further tested to see if the bacteria are resistant to the antibiotic methicillin (and other antibiotics) and thus determine if the organisms are MRSA. This test is important as MRSA organisms are resistant to many antibiotics usually prescribed for staph infections.

There are two main types of treatment for staph infections, surgical and antibiotic treatment.

In most patients who require surgical treatment, antibiotic treatment is also required. Incision and drainage of pus is the main surgical treatment; however, surgical removal of sources of infection (for example, intravenous lines, artificial grafts, heart valves, or pacemakers) may be required. Other sites of infection, such as joint infections (especially in children), osteomyelitis, or postoperative abscesses, may require surgery. Any tissue site that continues to harbor the bacteria may require surgical intervention and placement of a surgical drain.

There are many antibiotics that are effective against staph if the bacteria are shown to be non-MRSA staph including 

• nafcillin [Nallpen, Unipen],
• cefazolin [Ancef, Kefzol],
• dicloxacillin [Dycill,Dynapen],
• clindamycin [Cleocin T, Clindagel, ClindaMax, ClindaReach Pledget, Evoclin], or
• trimethoprim-sulfamethoxazole [Bactrim, Bactrim DS, Septra, Septra DS, SMZ-TMP DS, Sulfatrim Pediatric],
• doxycycline [Oracea].

However, MRSA organisms usually require other antibiotics;

• minor skin infections may be treated topically with Bacitracin (Baciguent) or mupirocin (Bactroban), but
• serious MRSA infections are usually treated with two or more antibiotics (for example, vancomycin [Vancocin HCl Pulvules], linezolid [Zyvox], rifampin [Rifadin], sulfamethoxazole-trimethoprim, and others).

In addition, there are other types of multiple drug-resistant staph, such as VRSA (vancomycin-resistant staph, for example).

• Although many simple staph infections can be treated by a person's primary-care provider (including internal medicine and family medicine specialists) or pediatrician,
• more complicated infections are usually treated by emergency-medicine physicians, infectious-disease consultants and, if the patient is hospitalized, critical-care and/or lung specialists.
• In addition, a surgeon may need to be involved if an extremity or a deep-tissue infection needs to have infected or dead or dying tissue removed.

Staph bacteria are frequently present in healthy humans. Areas where the bacteria can be found include the sebaceous (sweat) glands, nose, and other skin areas. Because of this colonization of healthy people, it is almost impossible to prevent contact with the bacteria. Most staph bacteria are transmitted by person-to-person contact, but viable staph on surfaces of clothing, sinks, and other objects can contact skin and cause infections. As long as a person has an active infection, the organisms are contagious. However, reducing risk factors such as skin scratches, abrasions, or puncture wounds -- or if they occur, immediately cleaning and treating them appropriately with antibacterial compounds -- helps prevent staph and other types of infections.

Home remedies like good hygiene, especially hand washing, prevents many infections. Individuals who live in crowded or unsanitary conditions, play contact sports, or share towels or clothing have a higher risk of getting staph infections. Individuals who work in hospitals can reduce their infection risk by wearing protective garments (for example, masks, gloves, and gowns). Any conditions that suppress a person's immune response create a higher risk for infection. Hospitalized people have a high risk of infection because of skin penetration by such things as intravenous lines, surgical incision sites, and implanted devices. Keeping penetrated skin sites clean and protected (covered with sterile dressings) helps prevent infections.

Home remedies for staph infections are numerous and can be found easily on the Internet. One such article offers 17 home remedies for staph infections on the face, leg, and other body parts. Home remedies range from using colloidal silver to items such as tea tree oil, apple cider vinegar, onions, sea salt, and many others. Although many are listed, most sources of this information do not supply data to show effectiveness in treating staph infections or symptoms of staph infections. Anecdotal reports are the basis of most of these home remedies. Before trying such home remedies to treat staph infections, individuals should discuss their use with their doctor.

If a staph infection is treated early with appropriate antibiotics and, if necessary, surgical drainage, the patient's prognosis is excellent. However, the U.S. National Institutes of Health (NIH) warns that the outcome of a MRSA infection varies both with the severity of the infection and the general condition of the person who has the infection. MRSA pneumonia and sepsis (infection of the blood) have high death rates; the calculated death rate of invasive MRSA is about 20%. HA-MRSA (hospital-acquired MRSA) infections are a growing problem; it is reported that about 19,000 deaths per year in the U.S. are due to HA-MRSA, which is more deaths than HIV causes per year. However, with better hospital and home care, the U.S. Centers for Disease Control and Prevention (CDC) notes the number of deaths are declining. Fortunately, people who have good general health and have mild CA-MRSA (community-acquired MRSA) that is appropriately treated recover in almost every case.

"Methicillin-Resistant Staphylococcus aureus (MRSA) Infections," CDC

"Staphylococcal Infections," Medscape.com