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Pathogen of the month: Staphylococcus aureus

by Dr. Jaclynn Moskow

Staphylococcus aureus, 20,000X magnification
Staphylococcus aureus, 20,000X magnification. Courtesy of Frank DeLeo, NIAID

 

Staphylococcus aureus (S. aureus) is a facultative anaerobic, gram-positive coccus. S. aureus is part of the normal flora of the body, found in the skin, upper respiratory tract, gut, and genitourinary tract – and most commonly in the anterior nares. Twenty percent of individuals are persistent nasal carriers of S. aureus, and an additional thirty percent are intermittent carriers (1).

Under certain conditions, S. aureus can be pathogenic, causing a variety of infections, including skin conditions, pneumonia, gastroenteritis, endocarditis, osteomyelitis, septic arthritis, meningitis, bacteremia, and sepsis. Individuals at increased risk include patients with diabetes, cancer, HIV/AIDS, and other conditions that compromise the immune system. Intravenous drug users may introduce the bacteria into various tissues and/or the bloodstream. Hospitalization is in itself a risk factor for S. aureus infection.

 

Staphylococcus Aureus Skin infections

S. aureus can cause a diverse array of skin infections, including folliculitis, impetigo, furuncles, carbuncles, cellulitis, and abscesses. S. aureus is the most common cause of skin infection in individuals with eczema, and many presumed cases of “eczema” are, in fact, inflammatory reactions to colonization by S. aureus (2). 

S. aureus is the most common agent of surgical site infections (3), and a common cause of infection in burn patients. Animal bites, including bites from dogs and cats, can also lead to S. aureus skin infections.

Staphylococcal scalded skin syndrome, also known as “Ritter’s disease”, is caused by exotoxin-producing strains of S. aureus – and is characterized by diffuse erythematous cellulitis followed by extensive skin exfoliation (4). Fever is common, and patients are most often neonates, children, immunocompromised individuals, and individuals with severe renal disease. It is thought that the latter are at an increased risk due to a decreased ability to excrete the exotoxins in urine (5). Healthy adults rarely develop the syndrome, as a result of having antibodies to the exotoxins. Staphylococcal scalded skin syndrome is intraepidermal. Necrosis of the full epidermal layer may also occur as a result of S. aureus infection and is known as toxic epidermal necrolysis – a more severe form of the disease.

Various topical and systemic antibiotics can be used to treat S. aureus skin infections including beta-lactams, macrolides, and aminoglycosides. Treatment may be complicated by antibiotic resistance.

 

Staphylococcus Aureus Pneumonia 

S. aureus is identified in three percent of community-acquired bacterial pneumonias (6), and 18% of hospital-acquired pneumonias (7). S. aureus is a cause of secondary bacterial pneumonia associated with influenza, and influenza has been shown to increase the adherence of S. aureus to host cells (8). One study showed that 33% of children admitted to the PICU during the 2009 H1N1 pandemic had a secondary bacterial coinfection, with S. aureus being the most common pathogen (9). S. aureus is also frequently isolated from the respiratory tract of children with cystic fibrosis (10).

 

Doctor examining a lung radiography
Staphylococcus aureus is one of the etiological agents of bacterial pneumonia

 

S.aureus can cause necrotizing pneumonia, characterized by necrosis, liquefaction, and cavitation of the lung parenchyma (11) – often accompanied by empyema and bronchopleural fistulae. Necrotizing pneumonia caused by community-acquired methicillin-resistant S. aureus (MRSA) strains which produce Panton valentine leukocidin (PVL) toxin has a mortality rate of 60% (12).

Treatment of pneumonia caused by S. aureus is based on testing for antibiotic susceptibility. Nafcillin, oxacillin, and cefazolin are often used to treat methicillin-sensitive S. aureus (MSSA), while vancomycin or linezolid is often used to treat MRSA (13).

 

Food Poisoning From Staphylococcus Aureus 

S.aureus is one of the most common causes of food-borne disease worldwide (14). Illness is characterized by a short incubation period (2h-4h), nausea, vomiting, intestinal cramping, and profuse watery, non-bloody diarrhea (15). The condition is generally self-limited, and symptoms typically resolve within 12 to 24 hours.

 

Staphylococcal food poisoning, outbreak-related cases and rates in the United States, 1952 – 2010

Toxic Shock Syndrome From Staphylococcus Aureus

S.aureus is the most common cause of toxic shock syndrome, a life-threatening syndrome resulting from staphylococcal toxin-1 (TSST-1). It is characterized by fever, hypotension, myalgia, macular erythema, desquamation (particularly of the palms and soles), and acute vomiting or diarrhea (16). Most cases are associated with the use of “super absorbent” tampons or staphylococcal wound infection. Case fatality rates of 5 to 10% are reported. The condition is generally treated with vancomycin in combination with clindamycin.

 

Staphylococcus Aureus Endocarditis

S.aureus is the leading cause of acute bacterial endocarditis. Of infections caused by S. aureus, endocarditis accounts for the highest mortality rates (17). Populations at high risk include IV drug users and patients with implanted medical devices such as prosthetic heart valves, grafts, pacemakers, and hemodialysis catheters (18). Treatment varies and depends on several factors, including antibiotic susceptibility, site of infection (left side versus right side), IV drug abuse status, and if a prosthetic valve is present (19).

 

Other Infections Caused By Staphylococcus Aureus

Staphylococcus aureus can also cause mastitis, urinary tract infections, osteomyelitis, meningitis, septic arthritis, and many infections associated with medical devices and implants.

 

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References 

(1) Wertheim HF, Melles DC, Vos MC, van Leeuwen W, van Belkum A, Verbrugh HA, Nouwen JL. The role of nasal carriage in Staphylococcus aureus infections. Lancet Infect Dis. 2005 Dec;5(12):751-62. doi: 10.1016/S1473-3099(05)70295-4.

(2) Nakamura Y, Oscherwitz J, Cease KB, Chan SM, Muñoz-Planillo R, Hasegawa M, Villaruz AE, Cheung GY, McGavin MJ, Travers JB, Otto M, Inohara N, Núñez G. Staphylococcus δ-toxin induces allergic skin disease by activating mast cells. Nature. 2013 Nov 21;503(7476):397-401. doi: 10.1038/nature12655. 

(3) Mellinghoff SC, Vehreschild JJ, Liss BJ, Cornely OA. Epidemiology of Surgical Site Infections With Staphylococcus aureus in Europe: Protocol for a Retrospective, Multicenter Study. JMIR Res Protoc. 2018 Mar 12;7(3):e63. doi: 10.2196/resprot.8177.

(4) “Staphylococcal scalded skin syndrome”, GIDEON Informatics, Inc, 2021. [Online]. Available: https://app.gideononline.com/explore/diseases/staphylococcal-scalded-skin-syndrome-12245

(5) Ross A, Shoff HW. Staphylococcal Scalded Skin Syndrome. 2020 Oct 27. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan–. 

(6) Hageman JC, Uyeki TM, Francis JS, Jernigan DB, Wheeler JG, Bridges CB, Barenkamp SJ, Sievert DM, Srinivasan A, Doherty MC, McDougal LK, Killgore GE, Lopatin UA, Coffman R, MacDonald JK, McAllister SK, Fosheim GE, Patel JB, McDonald LC. Severe community-acquired pneumonia due to Staphylococcus aureus, 2003-04 influenza season. Emerg Infect Dis. 2006 Jun;12(6):894-9. doi: 10.3201/eid1206.051141.

(7) Kollef MH, Micek ST. Staphylococcus aureus pneumonia: a “superbug” infection in community and hospital settings. Chest. 2005 Sep;128(3):1093-7. doi: 10.1378/chest.128.3.1093.

(8) Morris DE, Cleary DW, Clarke SC. Secondary Bacterial Infections Associated with Influenza Pandemics. Front Microbiol. 2017 Jun 23;8:1041. doi: 10.3389/fmicb.2017.01041.

(9) Randolph AG, Vaughn F, Sullivan R, Rubinson L, Thompson BT, Yoon G, Smoot E, Rice TW, Loftis LL, Helfaer M, Doctor A, Paden M, Flori H, Babbitt C, Graciano AL, Gedeit R, Sanders RC, Giuliano JS, Zimmerman J, Uyeki TM; Pediatric Acute Lung Injury and Sepsis Investigator’s Network and the National Heart, Lung, and Blood Institute ARDS Clinical Trials Network. Critically ill children during the 2009-2010 influenza pandemic in the United States. Pediatrics. 2011 Dec;128(6):e1450-8. doi: 10.1542/peds.2011-0774.

(10) Hurley MN. Staphylococcus aureus in cystic fibrosis: problem bug or an innocent bystander? Breathe (Sheff). 2018 Jun;14(2):87-90. doi: 10.1183/20734735.014718.

(11) Nicolaou EV, Bartlett AH. Necrotizing Pneumonia. Pediatr Ann. 2017 Feb 1;46(2):e65-e68. doi: 10.3928/19382359-20170120-02.

(12) Gillet Y, Vanhems P, Lina G, Bes M, Vandenesch F, Floret D, Etienne J. Factors predicting mortality in necrotizing community-acquired pneumonia caused by Staphylococcus aureus containing Panton-Valentine leukocidin. Clin Infect Dis. 2007 Aug 1;45(3):315-21. doi: 10.1086/519263.

(13) Clark SB, Hicks MA. Staphylococcal Pneumonia. 2020 Oct 1. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan–. 

(14) Kadariya J, Smith TC, Thapaliya D. Staphylococcus aureus and staphylococcal food-borne disease: an ongoing challenge in public health. Biomed Res Int. 2014;2014:827965. doi: 10.1155/2014/827965.

(15) “Staphylococcal food poisoning”, GIDEON Informatics, Inc, 2021. [Online]. Available: https://app.gideononline.com/explore/diseases/staphylococcal-food-poisoning-12260

(16) “Toxic shock syndrome”, GIDEON Informatics, Inc, 2021. [Online]. Available: https://app.gideononline.com/explore/diseases/toxic-shock-syndrome-12360

(17) Fernández Guerrero ML, González López JJ, Goyenechea A, Fraile J, de Górgolas M. Endocarditis caused by Staphylococcus aureus: A reappraisal of the epidemiologic, clinical, and pathologic manifestations with analysis of factors determining outcome. Medicine (Baltimore). 2009 Jan;88(1):1-22. doi: 10.1097/MD.0b013e318194da65.

(18) Fowler VG Jr, Miro JM, Hoen B, Cabell CH, Abrutyn E, Rubinstein E, Corey GR, Spelman D, Bradley SF, Barsic B, Pappas PA, Anstrom KJ, Wray D, Fortes CQ, Anguera I, Athan E, Jones P, van der Meer JT, Elliott TS, Levine DP, Bayer AS; ICE Investigators. Staphylococcus aureus endocarditis: a consequence of medical progress. JAMA. 2005 Jun 22;293(24):3012-21. doi: 10.1001/jama.293.24.3012. 

(19) Bille J. Medical treatment of staphylococcal infective endocarditis. Eur Heart J. 1995 Apr;16 Suppl B:80-3. doi: 10.1093/eurheartj/16.suppl_b.80.

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