What Is Staphylococcus aureus?

Staphylococcus aureus

Staphylococcus aureus (Gk. staphyle = bunch of grapes; Lat. coccus = spherical bacterium, aureus = golden) or golden staph (pronounced ‘staff’) is the most common species of staphylococcus bacteria causing infections in human.

Lab Tests for Staph
Staph Epidemiology

Staph Infections

S.aureus lives as a part of the normal skin flora in the nose or on the skin in 20-30% of healthy people (staph carriers), (1). However, in even slightly injured skin or mucosa, staph may cause styes, pimples, folliculitis, furuncles, boils (Picture 1), swimmer’s ear, sinusitis, epiglotitis, whitlow, breast infection, impetigo, cellulitis, genital infection, scalded skin syndrome or other staph infections. Infections of internal organs include urinary tract infections, arthritis, pneumonia, infection of veins (thrombophlebitis), lymph nodes (lymphadenitis) or lymph vessels (lymphangitis), bone infection (osteomyelitis) (Picture 2), or life threatening  sepsis (staph blood invasion), infection of heart valves (endocarditis),  meningitis, “flesh eating bacteria” infection (necrotizing fasciitis) and toxic shock syndrome. S.aureus enterotoxins may cause food poisoning.

S.aureus and S.epidermidis are among the most common causes of hospital-acquired infections, like bloodstream infections, infections of surgical wounds or pneumonia (2). Staph may also appear in vascular and urinary catheters, prosthetic joints and heart valves.

Staph skin infection usually appears as a red, warm, painful swelling with a blister, ulcer, or crust, and a drainage (Picture 1). Infection may spread into the deeper tissues, like the bones (Picture 2).

Staph Boil Staph osteomyelitis in the shin bone (tibia)
Picture 1.
A boil on the upper arm
Picture 2.
X-ray of child’s legs:
osteomyelitis in shin bones (grey patches)

How Widespread and How Dangerous is Staph?

Staph does not just float around in the air. A close skin contact, sharing towels, sport equipment and other fomites with an infected person or staph carrier, is needed to catch the infection. In an otherwise healthy persons staph usually causes only localized skin infections, which heal on their own within a few weeks (3). In heavily ill or immunodeficient patients, staph may cause deadly sepsis.

Staph Antibiotic Resistance

In 1942, only two years after introducing penicillin into infection treatment, staph resistance to penicillin was recognized in hospitals (4). In 1960, methicillin (later replaced by oxacillin) was used to treat penicillin resistant staph. Over 90% of staphylococci now contain enzyme penicillaze (which breaks down penicillin), so they have to be treated with penicillase-resistant penicillins, cephalosporins or other antibiotics (5).

MRSA

Methicillin Resistant S.aureus (MRSA) is resistant to most antibiotics derived from penicillin, including methicillin, so it has got a nickname ‘superbug’. MRSA was first detected in Britain in 1961 and is now increasingly recognized in the community worldwide (4). MRSA still mainly occurs in hospitals and nursing homes, but has lately spread to general community (Community Associated MRSA or CA-MRSA). It is impossible to distinguish MRSA from the “common” S.aureus (MSSA = Methicillin Susceptible S.aureus) only from symptoms (6). MRSA itself is not more “powerful” than MSSA, but it can be dangerous when it is not recognised as MRSA and not treated with appropriate antibiotics.

VISA and VRSA

In 1996, in Japan, S.aureus that was resistant to to an usual dose of vancomycin, was recognized. The terms Vancomycin Intermediate S.aureus (VISA) and Vancomycin Resistant S.aureus (VRSA) are now used, when 8-16 µg/ml or > 32 µg/ml of vancomycin respectively, is needed to inhibit staph growth during antibiotic susceptibility test (7). VISA and VRSA are not more powerful than other staphylococci, but they should be recognised as such, otherwise the treatment may not be successful. At present, VISA may be treated with larger doses of vancomycin and VRSA by some other antibiotics. VRSA is still rare: only seven cases were identified in United States between y. 2002-2006 (8).

Taxonomy of Staphylococcus aureus

Taxonomy (Gk. taxis = arrangement; -nomia= method) is classification of organisms in groups, according to their presumed natural relationships. In the “Bergey’s Manual of Systematic Bacteriology” Staphylococcus aureus is placed into:

Kingdom Bacteriae,
Phylum (Division) XIII. ‘Firmicutes (Lat.: firmus = strong, cutis= skin, referring to the cell wall),
Class I. ‘Bacilli‘,
Order I. ‘Bacillales‘,
Family.VIII ‘Staphylococcaceae‘,
Genus I. ‘Staphylococcus
Species ‘Staphylococcus aureus’ (9).

Staphylococcus aureus Characteristics

S.aureus is a spherical (coccus) Gram-positive bacterium, about 1 micrometer in size, with the thick cell wall and thin capsule. It does not form spores, but it can still survive outside the body, for example, on bed lining or computer keyboards from few days to several weeks (10). It is a facultative anaerobe – it grows in the air, but can also thrive in anaerobic conditions. It is an opportunistic pathogen – it may be present in the body without causing any harm, but in lowered immunity or injury, it may cause a disease. Staph bacteria have no flagella, so they are immobile. They grow in pairs, short chains or clusters (Picture 3).

Staphylococcus aureus

Picture 3. Grape-like clusters of S.aureus, electron micrograph, Magnitude. ~ 5000x;
(source: phil.cdc.gov)

S.aureus has ability to clot plasma – it is coagulase positive. Bacteria are resistant to temperatures as high as 122 °F (50°C), to high salt concentrations (<10%), and to drying (11). Colonies are usually 6-8 mm in diameter, rounded and smooth, golden yellow or pale yellow to orange (Picture 6).

Staphylococcus aureus Cell Wall Structure

A S.aureus wall consists from three layers: an outer polysaccharide capsule, peptidoglycan (murein) layer, and inner cytoplasmic membrane. Into this structure, proteins and teichoic acid are embedded and protrude from the cell wall on its outer side, forming a “fuzzy coat” (Picture 4), (12). Capsule is thin and may be seen only under the electron microscope. Sometimes more bacteria share one capsule and form a slime layer or biofilm, mostly found on the inner wall of venous and urinary catheters (13).

S. aureus Cell Wall Structure

Picture 4. S.aureus cell wall structure

Virulence Factors of Staphylococcus aureus

A term ‘virulence’ refers to microbe’s “ability to invade the tissues of the host”, or “the potential to cause a disease”. Virulence factors of S.aureus include:

  1. Surface proteins that promote attachment of staphylococci to the damaged host tissues;
  2. Inhibitors of phagocytosis: capsule; Protein A that binds IgG molecules the wrong way and thus disrupt phagocytosis (14); polysaccharides secreted by staph aureus may form a biofilm or slime layer on indwelling medical devices (13); yellow pigment made of carotenoids protect bacteria against free radicals, and catalase breaks down peroxide (phagocytes use free radicals and peroxide to kill bacteria) (15);
  3. Bound coagulase – “clumping factor”, which causes coagulation of plasma and bacteria clumping, and free coagulase, which also triggers plasma coagulation (14);
  4. Invasins, which promote bacterial spread in tissues: kinases, hyaluronidases (destroy hyaluronic acid in the connective tissue), and fatty acid modifying enzyme (FAME);
  5. Cytotoxinsthat lyse cell membranes: hemolysins (lysis of erythrocites), leukotoxin and Panton-Valentine leukocidin – PVL (lysis of leukocytes);
  6. Exfoliatin Toxin – ET(in scalded skin syndrome), and superantigen toxins, which may trigger massive non-specific T-cell response: enterotoxins SEA-G (in food poisoning), and TSST-1 (in Toxic Shock Syndrome) (14);
  7. Antibiotic resistance – inherited and acquired. More details about S. aureus virulence factors.

NOTE: amount of virulence factors may differ among individual S.aureus bacteria considerably.

Prevention of Staphylococcus aureus Infections

Staph infection may be prevented on many levels:

  1. Hands washing and regular bathing.
  2. Skin wounds should be cleaned and covered.
  3. Food workers should be tested for staphylococci and being treated, even if they have no active infection. Staph carriers should not work in food preparation.
  4. Surfaces in hospitals can be cleaned with alcohol, quaternary ammonium or iodine compounds, which are effective to both MSSA and MRSA (20). Effective sprays for air disinfection also exist (16).
  5. Cows should be regularly checked for mastitis, and milk tested for S.aureus or its toxins. Only pasteurized or cooked milk should be used.
  6. Human and bovine vaccines against S.aureus have been developing.

What is NOT NEEDED to prevent staph infections: antibacterial soaps, wearing masks, washing linens of staph infected persons separately from others, using disposal dishes, disinfecting surfaces with hypochlorite, denying patients from using whirlpools or foot baths, work restrict staff members who are MRSA carriers, unless they have skin lesions or active nasal infection (20).

Treatment of Staphylococcus Aureus Infections

Staph colonization may be treated with mupirocin (Bactroban) nasal gel, and daily Hibiclens skin cleanser baths (17).

Local skin infections are treated with antibacterial ointments. In more extensive infections, S.aureus has to be tested for antibiotic sensitivity, and then usually oral antibiotics are used. Skin abscesses often have to be drained, and deep abscesses may require surgical drainage. In systemic infection, hospitalization and intravenous antibiotics are needed. Artificial heart valves and vein catheters often need to be removed or replaced.

Severe staph infections require treatment with parenteral penicillinase-resistant penicillin like nafcillin and oxacillin, or cephalosporins of 1st or 2nd generation (e.g. cephalexin, cefuroxime) plus clindamycin. Vancomycin is reserved for MRSA and clindamycin resistant strains or for life-threatening infections. Staph food poisoning usually heals on its own. List of antibiotics that can be used in Staphaureus infections (5, 11):

  • Amoxycillin;
  • Cefazolin, Cephalexin, Cephalotin;
  • Ciprofloxacin;
  • Clindamycin;
  • Cloxacillin;
  • Daptomycin;
  • Dicloxacillin;
  • Erythromycin (only for minor skin infections, since it is only bacteriostatic)
  • Flucloxacillin (side effect: hepatic cholestasis);
  • Linezolid (C);
  • Methycillin (common adv. effects: hypersensitivity, interstitial nephritis);
  • Minocycline (D);
  • Mupirocin;
  • Nafcillin;
  • Oxacillin;
  • Quinupristin/dalfopristin (Synercid) (C);
  • Penicillin G (Benzylpenicillin), Penicilin V (Phenoxymethylpenicillin);
  • Retapamulin;
  • Rifampin (C);
  • Tigecycline (D);
  • Trimethoprim-sulfamethoxazole (C);
  • Vancomycin.

NOTE: safety of group C antibiotics in pregnancy is not confirmed; group D antibiotics are unsafe in pregnancy.

Detailed intravenous and oral antibiotic treatment regimes in staph infections

Literature about Staphylococcus aureus:

Books:

  • Staphylococcus: Molecular Genetics
    Publisher: Caister Academic Press
    Edited by: Jodi Lindsay Department of Cellular and Molecular Medicine, St George’s, University of London, UK
    Publication date: May 2008
    ISBN: 978-1-904455-29-5
  • Staphylococcus aureus Infections
    Author: Lisa Freeman-Cook and Kevin D. Freeman-Cook
    Publisher: Facts on File (September 01, 2005)
    ISBN: 9780791085080
  • Methicillin-Resistant Staphylococcus Aureus (MRSA) Protocols
    Author: Yinduo Ji
    Publisher: Humana Pr Inc (December 30, 2007)
    ISBN: 9781588296559
  • Bergey’s Manual of Determinative Bacteriology, 9th ed.,
    Author: Williams & Wilkins.
    ISBN 0-683-00603-7

Research papers:

  • Research papers and Staphylococcus aureus (Google Scholar links)

Online literature about Staphylococcus aureus:

  1. Bergey’s Taxonomic Outline
  2. Staphylococcus aureus Articles
  3. List of Microbiology Links (by Louis B. Caruana, Ph.D., professor of clinical laboratory science)

Related Articles:

References:

  1. Staph infections  (Merck.com)
  2. Hospital acquired infections  (Emedicine.com)
  3. For how long does staph infection last?  (Kidshealth.org)
  4. S. Aureus antibiotic resistance  (Emedicine.com)
  5. Antibiotics for stapgh infection  (Antimicrobe.org)
  6. MSSA and MRSA cannot be distinguished clinically  (Garetthealth.org)
  7. VRSA (Utah.gov)
  8. VRSA incidence  (Ncbi.nlm.nih.gov/pubmed)
  9. Taxonomy of S.aureus, Bergey’s manual  (Bergeys.org)
  10. MRSA survival time on surfaces  (Livescience.com)
  11. Staph salt and temperature resistance  (Emedicine.com)
  12. S. Aureus – cell wall structure  (Pubmedcentral.nih.gov)
  13. Staph biofilm  (CDC.gov)
  14. Staph virulence factors, superantigen toxins  (Utmb.edu)
  15. A yellow pigment as a virulence factor  (Newscientist.com)
  16. Sprays for air disinfection  (BBC.co.uk)
  17. Staph colonization treatment (Tenet.edu)
About Jan Modric (249 Articles)
Health writer

Ask a Doctor Online Now!

Please note that any information or feedback on this website is not intended to replace a consultation with a health care professional and will not constitute a medical diagnosis. By using this website and the comment service you agree to abide by the comment terms and conditions as outlined on this page

  • Pingback: Staph Epidemiology | HealthHype.com()

  • Pingback: Lab Tests for Staph | HealthHype.com()

  • Pingback: Staph Skin Infections | HealthHype.com()

  • Pingback: Staph Infection Symptoms | HealthHype.com()

  • Pingback: Staphylococcus Aureus - Coagolase Negative Staphylococci | HealthHype.com()

  • Pingback: Vancomycin Resistant Staphylococcus Aureus ~ VRSA (and VISA) | Current Health Articles 2008()

  • Pingback: Itchy Eyelids - Causes and Treatment | Current Health Articles 2008()

  • Pingback: Itchy Eyes - Causes and Treatment | Current Health Articles 2008()

  • Pingback: Can Piercing Cause Staph Infection? | Current Health Articles 2009()

  • medicallibta@yahoo.com

    prevalance of muli-resistant staphylococcus in hospital environmental

  • Jan Modric

    Medicallibta, for the answer search for HA-MRS (Hospital acquired MRSA).

  • Pingback: Bacterial Diarrhea Due to Food Poisoning - Symptoms, Causes & Cure | Current Health Articles 2009()

  • Pingback: Itchy Scalp - Pictures, Causes and Treatment | Current Health Articles 2009()

  • chessfer

    IS THE STAPHILO AUREOUS TRANSMITED BY KISSING YOUR LOVE ONES?

  • Jan Modric

    To chessfer.

    Yes, Staphylococcus aureus may be transmitted by kissing, since some people have these bacteria in their mouth. But, if the person, you’re kissing, is only a carrier of S. aureus, and doesn’t have an active infection with symptoms like sore throat, it is possible you will acquire S. aureus, but it is not likely you’ll get an active infection.

    But if your mouth mucosa is injured from some reason (ulcers…) you may get infected even by a person without active infection…

    S. aureus is mainly transmitted by skin-to-skin contact with a person with an obvious skin infection (boil, pemphigus…), and not so easy like, for example, the flu.

  • Pingback: What Causes Diarrhea After Eating? | Current Health Articles 2009()

  • Pingback: Complications of Breast Augmentation - Implants, Enhancement | Current Health Articles 2009()

  • Pingback: Infection - Definition, Causes, Transmission, Symptoms, Signs | Current Health Articles 2009()

  • Pingback: Microorganisms - Types, Harmful Effects on Human Body, Pictures | Current Health Articles 2009()

  • Pingback: Folliculitis | Current Health Articles 2009()

  • SLEY FAME

    WHAT IS THE MOST CURRENT, EFFECTIVE AND ERADICATION DRUG FOR STAPHYLOCOCCUS AUREUS AS IT REGARDS (URINARY TRACT INFECTION)

    REGARDS
    KINGSLEY

  • Jan Modric

    To SLEY FAME.

    In staph infection, antibiotics are chosen on the basis of results of (urinary) culture and antibiotic sensitivity tests, as you can read in lab tests for staph. So, antibiotic choise depends on exact subtype (strain) of S. aureus found in the urine.

  • Pingback: Itchy Legs - Causes and Treatment | Current Health Articles()

  • Faith

    WHAT DOES STAPYLOCOCUS AEURUS CAUSE IN THE MOUTH?

  • Jan Modric

    Faith,

    staph cellulitis (infection spreading under the mouth mucosa with reddened and swollen mucosa) and staph tonsillitis (like we say strep throat (from streptococcal tonsillitis) there can be a staph throat infection). These are two examples of staph infections in the mouth.

  • smart.77

    please ineed more hnformation

  • Jan Modric

    smart.77,

    what information do you need?

  • ML

    Hello,
    Question about MRSA symptoms: if one’s teeth get yellow in a fairly short period of time with light-colored slimy things on the tongue (latter part when one wakes up in the morning), and joints hurt, can these alone be MRSA symptoms?
    Thanks,
    ML

  • Jan Modric

    ML,

    I can’t exclude MRSA infection from symptoms you’ve mentioned. The term MRSA only tells a type of bacteria, I mean MRSA infection can cause anything from no symptoms to a severe disease. Yellow teeth and “slimy things” (mucus) on the tongue sounds like a gastrointestinal issue to me. Joint pains are also a common symptom in certain gastrointestinal disorders. A gastroenterologist can say more.

  • jeanny

    sorry have one last question cause ive built up a resistant to nix and lindane cream for a follucitis infection, is that gonna cause the effect of other weaker, bacterial soaps? cause i notice even though i just used lindane, then when it didnt work, i tried nix, different ingrediants and that didnt matter it still did not work…why is that?? thanks

  • julietta

    Hi , i would like to know what your source is to the study for VRSA in the united states? Because you put (8) but i can’t find the source of it. Can you tell me please !!
    Thanks you very much
    Julie Lagden.

  • Hi Julietta. This article was first published in 2008 and last reviewed in 2013. So links to reference articles on other websites may have changed. This is out of our control. If you are looking for the most recent statistics then we would advise to you to look at the CDC website or emedicine.medscape.com under the epidemiology section. Those are the main consistent online sources for health stats in the United States.