Staphylococcus aureus was first described and characterized in the 1880's by Rosenbach. Soon, by means of Koch's postulates, the bacterium was determined to be the cause of many types of dangerous and deadly skin, subcutaneous, blood, bone and systemic infections. Staphylococcus aureus are Gram-positive cocci which divide and multiply rapidly and, unless treated by effective and appropriate antibiotics, infected patients my die with a few hours or days from the start of the infection.
Ecology and Microbiology of Staphylococcus aureus
Staphylococcus aureus bacteria are common to the skin and mucocutaneous membranes of many people. In fact, about 5 to10% of people may be nasal carriers of these simple bacteria. Staphylococci can tolerate high concentrations of salt (up to about 10%) and this accounts for their ability to colonize, grow and multiply on sweat-laden areas of the body such as the head, neck, groin, buttocks and folded or axillary areas of the skin.
Staphylococcal bacteria usually are not an infectious disease problem unless there is damage or injury to tissue such as a wound or cut or abrasion. What contributes to the actual start of staph infectious is often an underlying condition such as diabetes, corticosteroid or immunosuppressant therapies or patient treatments that involve IV lines, dialysis or surgery. Staphylococcus outbreaks are common in hospitals, nursing homes, dialysis centers, jails and exercise and health facilities.
Occasionally, participation in athletic or sports activities with the associated sweating and abrasions may cause staph infectious disease. Even inadequately- or improperly-disinfected (chlorine- or bromine-treated) hot tubs or spas have been shown to be causes of different types of bacterial infections in these communal bathing environments.
Staph infections, including MRSA ("methicillin-resistant Staphylococcus aureus" which is commonly called or pronounced "MeRSA"), occur most often among persons in hospitals and healthcare facilities such as nursing homes and dialysis centers. In these environments persons who have weakened immune systems may acquire MRSA infections. Pimples and boils are common general staphylococcal infections in the many community populations in general. Nevertheless, even a small lesion may progress and expand rapidly with severe and damaging consequences. No infection should be left unattended and immediate qualified medical attention should be sought.
Pathogenic Factors of Staphylococcus aureus
Staphylococcus aureus produces various exotoxins or superantigens. These biochemical products of staph have significant effects on the organisms that they infect and cause disease in:
- coagulase, causes the plasma of infected to coagulate and form clots
- hemolysins, lyse red blood and release nutrients of value for staphylococcal nutrition
- Protein A, is a very unique protein that is attached to the surface of the S. aureus and causes antibody to attach to the protein by the Fc component of antibody. This disguises and protects staphylococci.
- leukocidins, inactivate or kill white blood cells
- TSST-1, toxic shock syndrome toxin, causes fever, flushing of the skin and hypotension (low blood pressure). Several cases of death by TSS have been documented. An infamous epidemic of TSS related to the commercial introduction of ultra-absorbent tampons that permitted staph to grow, multiply and produce TSS. Several women lost their lives related to the initial introduction of that product. Since that time issues related to tampons have not occurred.
- enterotoxins produce by certain staphylococci cause food poisoning in milk and egg based foods. Many a picnic has been ruined by S. aureus-contaminated cole slaw or potato or egg salads. The enterotoxin is excreted by the staph into the food and the signs include vomiting and fever.
Identification and Treatment of Staphylococcus aureus Infectious Disease
The diagnosis of staphylococcal infections is based on the nature of the physical signs and symptoms of the disease (e.g. boils, abscesses, carbuncles, furuncles, septicemia, osteomyelitis, etc.) and the isolation of the pathogen from the clinical specimen.
Pus, exudates, blood, biopsies are typical clinical specimens submitted for analysis. Staphylococcus aureus typically has a characteristic growth and colony appearance on blood agar plates and selective agars such as mannitol-salt agar. Gram stains of small portions of typical colonies reveals Gram-positive cocci which test as coagulase positive and confirm the isolate as S. aureus.
The treatment of Staphylococcus aureus requires a rapid, adequate and thorough medical response. Small pimples or abscess can develop into severe systemic disease within a few hours or days with septicemia (e.g., staph in the blood) and toxemia (toxins in the blood). Therefore, increasing signs and symptoms of disease such as the enlarging size and redness of lesions, with or without fever, are examples of events that require immediate medical attention.
Antibiotic treatments are usually effective, but because of the increased incidence of MRSA antibiotic testing and evaluation is done to determine the most effective antibiotic(s) to use. The figure below shows the Kirby-Bauer disk test for evaluation of antibiotic effectiveness.
Thorough and proper handwashing is an important and effective means of controlling the spread of infectious disease organisms such as bacteria and viruses.
Source
Bannister, B. A.., N. T. Begg, S. H. Gillespie. 2000. Infectious Disease. Blackwell Science Inc., Malden, MA.
Disclaimer: This article is presented for informational purposes only. A qualified physician/medical doctor should always be seen as soon as possible to attend to these and other infectious disease problems whenever they arise.
Donald Reinhardt - Think, read, write & live well always. DJR has a PhD in Biology/Microbiology & is a Fellow & Diplomate, ASM Amer Acad Micro.
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