[[Image:Staphylococcus aureus Gram.jpg|left|thumb|150px|Gram stain of ''S. aureus''.]]
''S. aureus'' is a [[Gram-positive]] [[coccus]], which appears as grape-like clusters when viewed through a microscope and has large, round, golden-yellow colonies, often with [[Hemolysis (microbiology)|hemolysis]], when grown on [[Agar plate|blood agar plate]]s.<ref name=Sherris>{{cite book | author = Ryan KJ; Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | publisher = McGraw Hill | year = 2004 | id = ISBN 0-8385-8529-9 }}</ref> The golden appearance is the [[etymology|etymological]] root of the bacteria's name: ''aureus'' means "golden" in [[Latin]].
''S. aureus'' is a [[Gram-positive]] [[coccus]], which appears as grape-like clusters when viewed through a microscope and has large, round, golden-yellow colonies, often with [[Hemolysis (microbiology)|hemolysis]], when grown on [[Agar plate|blood agar plate]]s.<ref name=Sherris>{{cite book | author = Ryan KJ; Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | publisher = McGraw Hill | year = 2004 | id = ISBN 0-8385-8529-9 }}</ref> The golden appearance is the [[etymology|etymological]] root of the bacteria's name: ''aureus'' means "golden" in [[Latin]].
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''S. aureus'' is [[catalase]] positive (meaning that it can produce the enzyme "catalase") and able to convert [[hydrogen peroxide]] (H<sub>2</sub>O<sub>2</sub>) to water and oxygen, which makes the catalase test useful to distinguish staphylococci from [[Enterococcus|enterococci]] and [[Streptococcus|streptococci]]. A large percentage of ''S. aureus'' can be differentiated from most other staphylococci by the [[coagulase|coagulase test]]: ''S. aureus'' is primarily coagulase-positive (meaning that it can produce the enzyme "coagulase" that causes clot formation) while most other ''Staphylococcus'' species are coagulase-negative.<ref name=Sherris /> However, while the majority of ''S. aureus'' are coagulase-positive, some may be atypical in that they do not produce coagulase. Incorrect identification of an isolate can impact implementation of effective treatment and/or control measures.<ref name="CNSA">{{cite journal | author=Matthews KR, Roberson J, Gillespie BE, Luther DA, Oliver SP | title=Identification and Differentiation of Coagulase-Negative Staphylococcus aureus by Polymerase Chain Reaction | journal=Journal of Food Protection | year=1997 | pages=686-8 | volume=60 | issue=6 |url = http://www.ingentaconnect.com/content/iafp/jfp/1997/00000060/00000006/art00015 }}</ref> It is medically important to identify ''S.aureus'' correctly as ''S.aureus'' is much more aggressive and likely to be antibiotic-resistant.
''S. aureus'' is [[catalase]] positive (meaning that it can produce the enzyme "catalase") and able to convert [[hydrogen peroxide]] (H<sub>2</sub>O<sub>2</sub>) to water and oxygen, which makes the catalase test useful to distinguish staphylococci from [[Enterococcus|enterococci]] and [[Streptococcus|streptococci]]. A large percentage of ''S. aureus'' can be differentiated from most other staphylococci by the [[coagulase|coagulase test]]: ''S. aureus'' is primarily coagulase-positive (meaning that it can produce the enzyme "coagulase" that causes clot formation) while most other ''Staphylococcus'' species are coagulase-negative.<ref name=Sherris /> However, while the majority of ''S. aureus'' are coagulase-positive, some may be atypical in that they do not produce coagulase. Incorrect identification of an isolate can impact implementation of effective treatment and/or control measures.<ref name="CNSA">{{cite journal | author=Matthews KR, Roberson J, Gillespie BE, Luther DA, Oliver SP | title=Identification and Differentiation of Coagulase-Negative Staphylococcus aureus by Polymerase Chain Reaction | journal=Journal of Food Protection | year=1997 | pages=686-8 | volume=60 | issue=6 |url = http://www.ingentaconnect.com/content/iafp/jfp/1997/00000060/00000006/art00015 }}</ref> It is medically important to identify ''S.aureus'' correctly as ''S.aureus'' is much more aggressive and likely to be antibiotic-resistant.
<br>
[[Image:Staphylococcus aureus Gram.jpg|left|150px|Gram stain of S. aureus]]
<br><br><br><br><br>
==Role in disease==
==Role in disease==
''S. aureus'' may occur as a [[commensal]] on human [[skin]]; it also occurs in the nose frequently (in about a third of the population)<ref name="third">{{cite book |last=Whitt |first=Dixie D. |coauthors=Salyers, Abigail A. |title= Bacterial Pathogenesis: A Molecular Approach |origyear=2002 |edition=2nd edition |publisher=ASM Press |location=USA |isbn=1-55581-171-X |chapter=14 }}</ref> and throat less commonly. The occurrence of ''S. aureus'' under these circumstances does not always indicate infection and therefore does not always require treatment (indeed, treatment may be ineffective and re-colonisation may occur). It can survive on domesticated animals such as dogs, cats and horses, and can cause [[bumblefoot (infection)|bumblefoot]] in chickens. It can survive for some hours on dry environmental surfaces, but the importance of the environment in spread of ''S. aureus'' is currently debated. It can host [[phage]]s, such as the [[Panton-Valentine leukocidin]], that increase its virulence.
''S. aureus'' may occur as a [[commensal]] on human [[skin]]; it also occurs in the nose frequently (in about a third of the population)<ref name="third">{{cite book |last=Whitt |first=Dixie D. |coauthors=Salyers, Abigail A. |title= Bacterial Pathogenesis: A Molecular Approach |origyear=2002 |edition=2nd edition |publisher=ASM Press |location=USA |isbn=1-55581-171-X |chapter=14 }}</ref> and throat less commonly. The occurrence of ''S. aureus'' under these circumstances does not always indicate infection and therefore does not always require treatment (indeed, treatment may be ineffective and re-colonisation may occur). It can survive on domesticated animals such as dogs, cats and horses, and can cause [[bumblefoot (infection)|bumblefoot]] in chickens. It can survive for some hours on dry environmental surfaces, but the importance of the environment in spread of ''S. aureus'' is currently debated. It can host [[phage]]s, such as the [[Panton-Valentine leukocidin]], that increase its virulence.
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These tests suggest that the yellow pigment may be key to the ability of ''S. aureus'' to survive immune system attacks. Drugs that inhibit the bacterium's production of the [[carotenoid]]s responsible for the yellow coloration may weaken it and renew its susceptibility to antibiotics.<!--
These tests suggest that the yellow pigment may be key to the ability of ''S. aureus'' to survive immune system attacks. Drugs that inhibit the bacterium's production of the [[carotenoid]]s responsible for the yellow coloration may weaken it and renew its susceptibility to antibiotics.<!--
--><ref name="JExpMed2005-Liu">{{cite journal | author=Liu GY, Essex A, Buchanan JT, Datta V, Hoffman HM, Bastian JF, Fierer J, Nizet V | title=Staphylococcus aureus golden pigment impairs neutrophil killing and promotes virulence through its antioxidant activity | journal=J Exp Med | year=2005 | pages=209–15 | volume=202 | issue=2 | id=PMID 16009720 | url=http://www.jem.org/cgi/content/full/202/2/209}}</ref>
--><ref name="JExpMed2005-Liu">{{cite journal | author=Liu GY, Essex A, Buchanan JT, Datta V, Hoffman HM, Bastian JF, Fierer J, Nizet V | title=Staphylococcus aureus golden pigment impairs neutrophil killing and promotes virulence through its antioxidant activity | journal=J Exp Med | year=2005 | pages=209–15 | volume=202 | issue=2 | id=PMID 16009720 | url=http://www.jem.org/cgi/content/full/202/2/209}}</ref>
==Diagnosis==
Depending upon the type of infection present, an appropriate specimen is obtained accordingly and sent to the laboratory for definitive identification by using biochemical or enzyme-based tests. A [[Gram stain]] is first performed to guide the way, which should show typical gram-positive bacteria, cocci, in clusters. Secondly, culture the organism in [[Mannitol Salt Agar]], which is a selective medium with 7–9% [[Sodium chloride|NaCl]] that allows ''S. aureus'' to grow producing yellow-colored colonies as a result of salt utilization and subsequent drop in the medium's [[pH]]. Furthermore, for differentiation on the species level, [[catalase]] (positive for all species), [[coagulase]] (fibrin clot formation), [[DNAse]] (zone of clearance on nutrient agar), [[lipase]] (a yellow color and rancid odor smell), and [[phosphatase]] (a pink color) tests are all done. For staphylococcal food poisoning, phage typing can be performed to determine if the staphylococci recovered from the food to determine the source of infection.
===Rapid Diagnosis and Typing===
Diagnostic microbiology laboratories and reference laboratories are key for identifying outbreaks and new strains of ''S. aureus''. Recent genetic advances have enabled reliable and rapid techniques for the identification and characterization of clinical isolates of ''S. aureus'' in real-time. These tools support infection control strategies to limit bacterial spread and ensure the appropriate use of antibiotics. These techniques include [[Real-time PCR]] and [[Quantitative PCR]] and are increasingly being employed in clinical laboratories.<ref name= FrancoisP >{{cite book |chapterurl=http://www.horizonpress.com/staph|author= Francois P and Schrenzel J|year=2008|chapter=Rapid Diagnosis and Typing of Staphylococcus aureus|title=Staphylococcus: Molecular Genetics|publisher=Caister Academic Press|id=[http://www.horizonpress.com/staph ISBN 978-1-904455-29-5]}}</ref><ref name=Mackay>{{cite book | author = Mackay IM (editor). | title = Real-Time PCR in Microbiology: From Diagnosis to Characterization | publisher = Caister Academic Press | year = 2007 | url=http://www.horizonpress.com/rtmic | id = [http://www.horizonpress.com/rtmic ISBN 978-1-904455-18-9 ]}}</ref>
==Treatment==
===Antimicrobial Regimen===
* '''Staphylococcus aureus'''<ref name="pmid19489710">{{cite journal| author=Mermel LA, Allon M, Bouza E, Craven DE, Flynn P, O'Grady NP et al.| title=Clinical practice guidelines for the diagnosis and management of intravascular catheter-related infection: 2009 Update by the Infectious Diseases Society of America. | journal=Clin Infect Dis | year= 2009 | volume= 49 | issue= 1 | pages= 1-45 | pmid=19489710 | doi=10.1086/599376 | pmc=PMC4039170 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19489710 }} </ref>
:::* Preferred regimen: [[Vancomycin]], 15 mg/kg IV q12h {{or}} [[Daptomycin]], 6–8 mg/kg per day IV, or [[Linezolid]] IV; {{or}} [[Vancomycin]] IV {{and}} ([[Rifampicin]] IV or [[Gentamycin]] IV); or [[TMP-SMZ]] IV alone (if susceptible).
:::* Pediatric dose
::::* [[Linezolid]]
:::::* Neonates
::::::* 0–4 weeks of age and birthweight <1200 g: 10 mg/kg every 8–12 h (note: use every 12 h in patients <34 weeks gestation and <1 week of age).
::::::* <7 days of age and birthweight >1200 g, 10 mg/kg every 8–12 h (note: use every 12 h in patients <34 weeks gestation and <1 week of age).
::::::* 7 days and birthweight >1200 g, 10 mg/kg every 8 h.
:::::* Infants and children <12 years of age: 10 mg/kg every 8 h Children 12 years of age and adolescents: 10 mg/kg every 12 h.
::::* [[Gentamycin]]
:::::* Neonates
::::::* Premature neonates and <1000 g, 3.5 mg/kg every 24 h; 0–4 weeks and <1200 g, 2.5 mg/kg every 18–24 h.
::::::* Postnatal age 7 days: 2.5 mg/kg every 12 h.
::::::* Postnatal age 17 days and 1200–2000 g, 2.5 mg/kg every 8–12 h.
::::::* Postnatal age 17 days and 12000 g, 2.5 mg/kg every 8 h.
::::::* Once daily dosing for premature neonates with normal renal function, 3.5–4 mg/kg every 24 h.
::::::* Once daily dosing for term neonates with normal renal function, 3.5–5 mg/kg every 24 h.
:::::* Infants and children <5 years of age: 2.5 mg/kg every 8 h; once daily dosing in patients with normal renal function, 5–7.5 mg/kg every 24 h.
:::::* Children >5 years of age: 2–2.5 mg/kg every 8 h; once daily dosing in patients with normal renal function, 5–7.5 mg/kg every 24 h.
::::* [[TMP-SMZ]]
:::::* Infants 12 months of age and children: mild-to-moderate infections, 6–12 mg TMP/kg/day in divided doses every 12 h; serious infection, 15–20 mg TMP/kg/day in divided doses every 6–8 h.
:*'''Coagulase-negative staphylococci'''
::* [[Methicillin]] susceptible
:::* Preferred regimen: [[Nafcillin]], 2 g IV q4h {{or}} [[Oxacillin]], 2 g IV q4h.
:::* Alternative regimen: First-generation [[Cephalosporin]] {{or}} [[Vancomycin]] {{or}} [[TMP-SMZ]].
::* Methicillin resistant
:::* Preferred regimen: [[Vancomycin]], 15 mg/kg IV q12h.
:::* Alternative regimen: [[Daptomycin]] 6 mg/kg per day IV {{or}} [[linezolid]] IV.
continue here
==Prophylaxis==
===Antimicrobial Regimen===
* Staphylococcus aureus
:* '''CABG-associated acute mediastinitis'''<ref name="pmid22070836">{{cite journal| author=Hillis LD, Smith PK, Anderson JL, Bittl JA, Bridges CR, Byrne JG et al.| title=2011 ACCF/AHA Guideline for Coronary Artery Bypass Graft Surgery. A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Developed in collaboration with the American Association for Thoracic Surgery, Society of Cardiovascular Anesthesiologists, and Society of Thoracic Surgeons. | journal=J Am Coll Cardiol | year= 2011 | volume= 58 | issue= 24 | pages= e123-210 | pmid=22070836 | doi=10.1016/j.jacc.2011.08.009 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=22070836 }} </ref>
:::* Preferred regimen: A first- or second-generation [[Cephalosporin]] is recommended for prophylaxis in patients without methicillin-resistant Staphylococcus aureus colonization.
:::* Preferred regimen: [[Vancomycin]] alone or in combination with other antibiotics to achieve broader coverage is recommended for prophylaxis in patients with proven or suspected methicillin-resistant S. aureus colonization
:::: Note (1): Preoperative antibiotics should be administered to all patients to reduce the risk of mediastinitis in cardiac surgery.
:::: Note (2): The use of intranasal [[Mupirocin]] is reasonable in nasal carriers of S. aureus.
Staph infection that is not antibiotic resistant can be treated in about a month (depending on severity) using antibiotics.
Antibiotic resistance in ''S. aureus'' was almost unknown when penicillin was first introduced in 1943; indeed, the original petri dish on which [[Alexander Fleming]] observed the antibacterial activity of the [[Penicillium notatum|penicillium]] mould was growing a culture of ''S. aureus''. By 1950, 40% of hospital ''S. aureus'' isolates were penicillin resistant; and by 1960, this had risen to 80%.<ref name="EmergInfectDis2001-Chambers">{{cite journal | author=Chambers HF | title=The changing epidemiology of Staphylococcus aureus? | journal=Emerg Infect Dis | year=2001 | pages=178–82 | volume=7 | issue=2 | id=PMID 11294701 | url= http://www.cdc.gov/ncidod/eid/vol7no2/chambers.htm}}</ref>
===Mechanisms of antibiotic resistance===
Staphylococcal resistance to [[penicillin]] is mediated by [[penicillinase]] (a form of [[beta-lactamase|β-lactamase]]) production: an enzyme which breaks down the β-lactam ring of the penicillin molecule. Penicillinase-resistant penicillins such as [[methicillin]], [[oxacillin]], [[cloxacillin]], [[dicloxacillin]] and [[flucloxacillin]] are able to resist degradation by staphylococcal penicillinase.
The mechanism of resistance to methicillin is by the acquisition of the mecA gene, which codes for an altered [[penicillin-binding protein]] (PBP) that has a lower affinity for binding β-lactams ([[penicillin]]s, [[cephalosporin]]s and [[carbapenem]]s). This confers resistance to all β-lactam antibiotics and obviates their clinical use during [[MRSA]] infections.
Glycopeptide resistance is mediated by acquisition of the vanA gene. The vanA gene originates from the [[Enterococcus|enterococci]] and codes for an enzyme that produces an alternative [[peptidoglycan]] to which [[vancomycin]] will not bind.
Today, ''S. aureus'' has become [[antibiotic resistance|resistant]] to many commonly used antibiotics. In the UK, only 2% of all ''S. aureus'' isolates are sensitive to [[penicillin]] with a similar picture in the rest of the world, due to a [[penicillinase]] (a form of [[β-lactamase]]). The β-lactamase-resistant [[penicillin]]s ([[methicillin]], [[oxacillin]], [[cloxacillin]] and [[flucloxacillin]]) were developed to treat penicillin-resistant ''S. aureus'' and are still used as first-line treatment. [[Methicillin]] was the first antibiotic in this class to be used (it was introduced in 1959), but only two years later, the first case of [[methicillin resistant staphylococcus aureus|methicillin-resistant ''S. aureus'']] ('''MRSA''') was reported in England.<ref name="BMJ1961-Jevons">{{cite journal | author=Jevons MP | title=Celbenin-resistant staphylococci | journal=BMJ | volume=1 | year=1961 | pages=124–5}}</ref>
Despite this, MRSA generally remained an uncommon finding even in hospital settings until the 1990s when there was an explosion in MRSA prevalence in hospitals where it is now [[Endemic (epidemiology)|endemic]].<!--
--><ref name="JAntimicrobChemother2001-Johnson">{{cite journal | author=Johnson AP, Aucken HM, Cavendish S, Ganner M, Wale MC, Warner M, Livermore DM, Cookson BD | title=Dominance of EMRSA-15 and -16 among MRSA causing nosocomial bacteraemia in the UK: analysis of isolates from the European Antimicrobial Resistance Surveillance System (EARSS) | journal=J Antimicrob Chemother | year=2001 | pages=143–4 | volume=48 | issue=1 | id=PMID 11418528 |url = http://jac.oxfordjournals.org/cgi/content/full/48/1/143 }}</ref>
MRSA infections in both the hospital and community setting are commonly treated with non-β-lactam antibiotics such as [[clindamycin]] (a lincosamine) and [[co-trimoxazole]] (also commonly known as trimethoprim/sulfamethoxazole). Resistance to these antibiotics has also led to the use of new, broad-spectrum anti-Gram positive antibiotics such as [[linezolid]] because of its availability as an oral drug. First-line treatment for serious invasive infections due to MRSA is currently [[glycopeptide]] antibiotics ([[vancomycin]] and [[teicoplanin]]). There are number of problems with these antibiotics, mainly centred around the need for intravenous administration (there is no oral preparation available), toxicity and the need to monitor drug levels regularly by means of blood tests. There are also concerns that glycopeptide antibiotics do not penetrate very well into infected tissues (this is a particular concern with infections of the brain and [[meninges]] and in [[endocarditis]]). Glycopeptides must not be used to treat methicillin-sensitive ''S. aureus'' as outcomes are inferior.<!--
--><ref name="ArchInternMed2002-Blot">{{cite journal | author=Blot SI, Vandewoude KH, Hoste EA, Colardyn FA | title=Outcome and attributable mortality in critically Ill patients with bacteremia involving methicillin-susceptible and methicillin-resistant Staphylococcus aureus | journal=Arch Intern Med | year=2002 | pages=2229–35 | volume=162 | issue=19 | id=PMID 12390067 | url=http://archinte.ama-assn.org/cgi/content/full/162/19/2229 }}</ref>
Because of the high level of resistance to penicillins, and because of the potential for MRSA to develop resistance to vancomycin, the [[Centers for Disease Control and Prevention]] have published [http://wonder.cdc.gov/wonder/prevguid/m0039349/m0039349.asp guidelines]for the appropriate use of vancomycin. In situations where the incidence of MRSA infections is known to be high, the attending physician may choose to use a glycopeptide [[antibiotic]] until the identity of the infecting organism is known. When the infection is confirmed to be due to a methicillin-susceptible strain of ''S. aureus'', then treatment can be changed to [[flucloxacillin]] or even [[penicillin]] as appropriate.
[[Vancomycin-resistant Staphylococcus aureus|Vancomycin-resistant ''S. aureus'']] ('''VRSA''') is a strain of ''S. aureus'' that has become resistant to the glycopeptides.
The first case of '''vancomycin-intermediate ''S. aureus''''' ('''VISA''') was reported in Japan in 1996;<!--
Spread of ''S. aureus'' (including [[methicillin-resistant Staphylococcus aureus|MRSA]]) is through human-to-human contact, although recently some vets have discovered that the infection can be spread through pets, with environmental contamination thought to play a relatively unimportant part. Emphasis on basic [[hand washing]] techniques are therefore effective in preventing the transmission of ''S. aureus''. The use of disposable aprons and gloves by staff reduces skin-to-skin contact and therefore further reduces the risk of transmission. Please refer to the article on [[infection control]] for further details.
Recently, there have been a myriad of reported cases of S. aureus in hospitals across America. The incredibly hardy pathogen has had facilitated transportation in medical facilities mainly because of poor doctor hygiene. S. aureus is an incredibly hardy bacterium, as was shown in a study where it survived on a piece of polyester for just under three months,polyester being the main material used in hospital privacy curtains.
The bacterium is able to transport itself on the hands of doctors who, for instance, get the bacteria from a seemingly healthy patient carrying a "benign" or commensal strain of the pathogen, and then going into surgery and infecting the open incision with staphylococcus. Such introduction of the bacterium into the bloodstream can lead to various complications including, but not limited to, endocarditis, meningitis, and, if it is widespread, sepsis - toxins infecting the entire body.
Because of these infections in hospitals, as of February 14th, 2008, all California medical facilities must now report S. aureus infections that are checked into the hospitals, in the hope of starting a trend to aid disease trackers and pathologists in their search for a cure.
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[[Alcohol]] has proven to be an effective topical sanitizer against MRSA. [[Quaternary ammonium]] can be used in conjunction with alcohol to increase the duration of the sanitizing action. The prevention of [[nosocomial infection]]s involve routine and [[terminal cleaning]]. Nonflammable alcohol vapor in [[carbon dioxide|CO<sub>2</sub>]] [[NAV-CO2]] systems have an advantage as they do not attack metals or plastics used in medical environments, and do not contribute to antibacterial resistance.
An important and previously unrecognized means of community-associated methicillin-resistant S. aureus colonization and transmission is during sexual contact.<!--
--><ref name="CDI2007">{{cite journal |author=Cook H, Furuya E, Larson E, Vasquez G, Lowy F |title=Heterosexual transmission of community-associated methicillin-resistant Staphylococcus aureus |journal=Clin Infect Dis |volume=44 |issue=3 |pages=410–3 |year=2007 |id=PMID 17205449 | url=http://www.journals.uchicago.edu/cgi-bin/resolve?CID40836}}</ref>
Staff or patients who are found to carry resistant strains of ''S. aureus'' may be required to undergo "eradication therapy" which may include antiseptic washes and shampoos (such as [[chlorhexidine]]) and application of topical antibiotic ointments (such as [[mupirocin]] or [[neomycin]]) to the anterior [[nares]] of the nose.
In March 2007, BBC reported that a vaporizer spraying some essential oils into the atmosphere reduced airborne bacterial counts by 90% and kept MRSA infections at bay and may hold promise in MRSA infection control.<ref>{{cite news |author= |title=Essential oils 'combat superbug' |url=http://news.bbc.co.uk/2/hi/uk_news/england/manchester/6471475.stm |publisher=BBC News |date=20 March 2007 |accessdate=2008-04-15}}</ref>
Staphylococcus aureus (Template:PronEng, literally "Golden Cluster Seed" and also known as golden staph, is the most common cause of staph infections. It is a spherical bacterium, frequently living on the skin or in the nose of a person. Approximately 20–30% of the general population are "staph carriers".[1]Staphylococcus aureus can cause a range of illnesses from minor skin infections, such as pimples, impetigo (may also be caused by Streptococcus pyogenes), boils, cellulitis folliculitis, furuncles, carbuncles, scalded skin syndrome and abscesses, to life-threatening diseases, such as pneumonia, meningitis, osteomyelitis endocarditis, Toxic shock syndrome (TSS), and septicemia. Its incidence is from skin, soft tissue, respiratory, bone, joint, endovascular to wound infections. It is still one of the four most common causes of nosocomial infections, often causing postsurgical wound infections. Abbreviated to S. aureus or Staph aureus in medical literature, S. aureus should not be confused with the similarly named (and also medically relevant) species of the genusStreptococcus.
S. aureus was discovered in Aberdeen, Scotland in 1880 by the surgeon Sir Alexander Ogston in pus from surgical abscesses.[2] Each year some 500,000 patients in American hospitals contract a staphylococcal infection.[3]
Microbiology
S. aureus is a Gram-positivecoccus, which appears as grape-like clusters when viewed through a microscope and has large, round, golden-yellow colonies, often with hemolysis, when grown on blood agar plates.[4] The golden appearance is the etymological root of the bacteria's name: aureus means "golden" in Latin.
S. aureus is catalase positive (meaning that it can produce the enzyme "catalase") and able to convert hydrogen peroxide (H2O2) to water and oxygen, which makes the catalase test useful to distinguish staphylococci from enterococci and streptococci. A large percentage of S. aureus can be differentiated from most other staphylococci by the coagulase test: S. aureus is primarily coagulase-positive (meaning that it can produce the enzyme "coagulase" that causes clot formation) while most other Staphylococcus species are coagulase-negative.[4] However, while the majority of S. aureus are coagulase-positive, some may be atypical in that they do not produce coagulase. Incorrect identification of an isolate can impact implementation of effective treatment and/or control measures.[5] It is medically important to identify S.aureus correctly as S.aureus is much more aggressive and likely to be antibiotic-resistant.
Gram stain of S. aureus
Role in disease
S. aureus may occur as a commensal on human skin; it also occurs in the nose frequently (in about a third of the population)[6] and throat less commonly. The occurrence of S. aureus under these circumstances does not always indicate infection and therefore does not always require treatment (indeed, treatment may be ineffective and re-colonisation may occur). It can survive on domesticated animals such as dogs, cats and horses, and can cause bumblefoot in chickens. It can survive for some hours on dry environmental surfaces, but the importance of the environment in spread of S. aureus is currently debated. It can host phages, such as the Panton-Valentine leukocidin, that increase its virulence.
S. aureus can infect other tissues when normal barriers have been breached (e.g., skin or mucosal lining). This leads to furuncles (boils) and carbuncles (a collection of furuncles). In infants S. aureus infection can cause a severe disease Staphylococcal scalded skin syndrome (SSSS).[7]
S. aureus infections can be spread through contact with pus from an infected wound, skin-to-skin contact with an infected person by producing hyaluronidase that destroy tissues, and contact with objects such as towels, sheets, clothing, or athletic equipment used by an infected person.
Deeply situated S. aureus infections can be very severe. Prosthetic joints put a person at particular risk for septic arthritis, and staphylococcal endocarditis (infection of the heart valves) and pneumonia, which may be rapidly spread.
Atopic dermatitis
S. aureus is extremely prevalent in atopic dermatitis patients, who are less resistant to it than other people. It often causes complications. The disease is most likely found in fertile active places including, the armpits, hair and scalp. Large pimples in those areas, when popped will cause the worst of the infection.
Toxic shock syndrome
Some strains of S. aureus produce toxic shock syndrome toxin, which are the causative agent for toxic shock syndrome. Some strains that produce an enterotoxin are the cause of staphylococcal food poisoning.
Mastitis in cows
S. aureus is one of the causal agents of mastitis in dairy cows. Its large capsule protects the organism from attack by the cow's immunological defenses.[8]
Virulence factors
Toxins
Depending on the strain, S. aureus is capable of secreting several toxins, which can be categorized into three groups. Many of these toxins are associated with specific diseases.
Pyrogenic toxin superantigens (PTSAgs) have superantigen activities that induce toxic shock syndrome (TSS). This group includes the toxin TSST-1, which causes TSS associated with tampon use. The staphylococcal enterotoxins, which cause a form of food poisoning, are included in this group.
Exfoliative toxins are implicated in the disease staphylococcal scalded-skin syndrome (SSSS), which occurs most commonly in infants and young children. It also may occur as epidemics in hospital nuseries. The protease activity of the exfoliative toxins causes peeling of the skin observed with SSSS.
Staphylococccal toxins that act on cell membranes include alpha-toxin, beta-toxin, delta-toxin, and several bicomponent toxins. The bicomponent toxin Panton-Valentine leukocidin (PVL) is associated with severe necrotizing pneumonia in children. The genes encoding the components of PVL are encoded on a bacteriophage found in community-associated MRSA strains.
Role of pigment in virulence
The vivid yellow pigmentation of S. aureus may be a factor in its virulence. When comparing a normal strain of S. aureus with a strain modified to lack the yellow coloration, the pigmented strain was more likely to survive dousing with an oxidizing chemical such as hydrogen peroxide than the mutant strain was.
Colonies of the two strains were also exposed to human neutrophils. The mutant colonies quickly succumbed while many of the pigmented colonies survived. Wounds on mice were swiped with the two strains. The pigmented strains created lingering abscesses. Wounds with the unpigmented strains healed quickly.
These tests suggest that the yellow pigment may be key to the ability of S. aureus to survive immune system attacks. Drugs that inhibit the bacterium's production of the carotenoids responsible for the yellow coloration may weaken it and renew its susceptibility to antibiotics.[9]
References
↑Heyman, D. Control of Communicable Diseases Manual (2004) 18th Edition. Washington DC: American Public Health Assocation.
↑Ogston A (1984). ""On Abscesses". Classics in Infectious Diseases". Rev Infect Dis. 6 (1): 122–28. PMID 6369479.
↑ 4.04.1Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed. ed.). McGraw Hill. ISBN 0-8385-8529-9.CS1 maint: Extra text: authors list (link) CS1 maint: Extra text (link)
