Staphylococcus aureus is a Gram-positive, round-shaped bacterium, a member of the Firmicutes, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is the leading cause of skin and soft tissue infections such as abscesses (boils), furuncles, and cellulitis. Although most staph infections are not serious, S. aureus can cause serious infections such as bloodstream infections, pneumonia, or bone and joint infections.

1. Staphylococcus aureus
By Vanshika Varshney
18081564015 (4621)
Medical Microbiology
BSc (H) Microbiology

2. ● Gram positive Cocci.
● 1 micrometer diameter.
● Family : Micrococcaceae
● Genus : Staphylococcus
● “Staphylococcus” derived from greek word
which means ‘Bacteria occurring in grapes
like clusters or berry’.
● Frequently found in upper respiratory tract
& on the skin.
● Non motile, non sporing & few strains are
encapsulated.

4. Habitat

5. ● The natural habitat is mammalian body surfaces.
● They are normal flora of the skin and mucous membrane.
● Also present in the nose / the anterior nares.
● They can also be found in Pharynx.
● Found in stratified epithelial cells or mucous or serum constituents
associated with these cells.
● Found in skin/nasal passage and axillae of humans.
● They act as a benign or symbiotic relationship with the hosts.
● Enterogeneric strains of S. aureus are found in various food products.
● They may survive on dry skin.
● Thirty percent (30%) of the normal human healthy population is affected
by S. aureus as it is asymptomatically colonized on the skin of the human
host.

6. The History

7. ● Robert Koch (1878)
● Louis Pasteur (1880)
● Alexander Ogston (1881)
First to cultivate in liquid medium.
First to see Staphylococci in pus specimen.
Named the bacteria as “Staphylococcus”

8. Classification
1. Based on Pigment Production:
S. aureus - Golden yellow colonies
S. albus - White colonies
S. citreus - Lemon yellow colonies
1. Based on Pathogenicity:
Pathogenic - S. aureus
Non pathogenic - S. epidermidis, S. saprophyticus,
S. albus, S. citreus etc.
1. Based on Coagulase production:
Coagulase positive - S. aureus
Coagulase negative - S. epidermidis, S.
saprophyticus

9. Culture

10. ● Staphylococci grow readily on most bacteriologic media
aerobic or microaerophilic conditions.
● They grow most rapidly @ 37°C but the pigment best at
RT.
● Colonies on solid media are round, smooth, raised and
glistening.
● S. aureus usually forms gray to deep golden yellow
colonies.
● Optimum pH for growth is 7.5
● On Nutrient Agar :
Golden yellow & opaque colonies with smooth glistening
surface, 1-2 mm in diameter (Max. pigment production
@ 22°C).

11. ● On Blood agar :
Golden yellow colonies, surrounded
by a clear zone of hemolysis (ꞵ-
hemolysis).
● On MacConkey agar :
Smaller colonies than those on NA
(0.1-0.5 mm) & are pink colored
due to lactose fermentation.
● On Mannitol Salt agar :
S. aureus ferments mannitol and
appear as yellow colonies.

12. Biochemical Properties

13. ● Indole test = Negative
● Methyl Red test = Positive
● Voges Proskauer test = Positive
● Urease test = Positive
● Phosphatase = Positive
● DNAse test = Positive
● Coagulase test = Positive
● Catalase test = Positive
● Citrate test = Positive
● Gas = Negative
● Gram staining = Positive
● Nitrate reduction = Positive
● Glucose/ Lactose/ Sucrose fermentation = Positive

14. Virulence factor

16. S. aureus expresses many potential virulence factors:
(1) surface proteins that promote colonization of host tissues
(2) invasins that promote bacterial spread in tissues (leukocidin, kinases,
hyaluronidase)
(3) surface factors that inhibit phagocytic engulfment (capsule, Protein A)
(4) biochemical properties that enhance their survival in phagocytes (carotenoids,
catalase production)
(5) immunological disguises (Protein A, coagulase)
(6) membrane-damaging toxins that lyse eukaryotic cell membranes (hemolysins,
leukotoxin, leukocidin
(7) exotoxins that damage host tissues or otherwise provoke symptoms of disease
(SEA-G, TSST, ET)
(8) inherent and acquired resistance to antimicrobial agents.

19. Antigenic structure

20. ● Staphylococci contain antigenic polysaccharides & proteins as well as other substances
important in cell wall structure.
● Peptidoglycan, a polysaccharide polymer containing linked subunits, provides the rigid
exoskeleton of the cell wall.
● Peptidoglycan is destroyed by strong acid or exposure to lysozyme.
● Teichoic acids, which are polymers of polyribitol–phosphate, are cross-linked to the
peptidoglycan and can be antigenic.
● Protein A is a cell wall component of S aureus strains and is a bacterial surface protein
that has been characterized among a group of adhesins called Microbial Surface
Components Recognizing Adhesive Matrix Molecules (MSCRAMMS).
● Protein A binds to the Fc portion of IgG molecules except IgG3. The Fab portion of the
IgG bound to protein A is free to combine with a specific antigen.
● Most S. aureus strains of clinical importance have polysaccharide capsules, which inhibit
phagocytosis by polymorphonuclear leukocytes unless specific antibodies are present.

22. Enzymes & Toxins

23. ● Staphylococci can produce disease both through their ability to multiply and
spread widely in tissues and through their production of many extracellular
substances.
● Some of these substances are enzymes: others are considered to be toxins.
A) Catalase :
H2O2 H2O + O2
Catalase test differentiates the staphylococci, which are positive, from the
streptococci, which are negative.

24. B) Coagulase & Clumping factor :
S.aureus produces coagulase, an enzyme-like protein that clots oxalated or citrated
plasma. It binds to prothrombin and together they become enzymatically active and
initiate fibrin polymerization. Coagulase production is considered synonymous with
invasive pathogenic potential.
Clumping factor is another example of MSCRAMM that responsible for adherence of
the organism to fibrogen and fibrin. S. aureus forms clumps. Clumping factor
distinct from coagulase.

25. C) Other Enzymes :
Include a hyaluronidase, or spreading factor; a Staphylokinase resulting in
fibrinolysis but acting much more slowly than streptokinase; proteinases; lipases; &
ꞵ- lactamase.
D) Hemolysis :
α-Hemolysis is a heterogeneous protein that acts on a broad spectrum of eukaryotic
cell membranes. The ꞵ-toxin degrades Sphingomyelin & therefore is toxic for many
kinds of cells, including human RBC. The δ-toxin is heterogeneous and dissociates
into subunits in nonionic detergents. The 𝛾 hemolysis is a leukocidin that lyses WBC
and is composed of two proteins designated S & F.

27. E) Panton- Valentine Leukocidin ;
The toxin of S. aureus has 2 components. The 2 components designated as S & F
act synergistically on the WBC membrane. This toxin is an important virulence
factor in CA- MRSA infections.
F) Exfoliative Toxins :
These epidermolytic toxins of S. aureus are 2 distinct proteins of the same molecular
weight. Exfoliative toxin A is encoded by eta located on a phage and is heat stable.
Exfoliative toxin B is plasmid mediated and heat labile. The toxins are
superantigens.

28. G) Toxic shock syndrome toxin :
Most S. aureus strain isolated from patients with toxic shock syndrome produce a
toxin called toxic shock syndrome toxin-1 (TSST-1), which is same as the
enterotoxin F. It’s the prototypical superantigen. TSST-1 binds to MHC Ⅱ
molecules, yielding T-cell stimulation,which promotes the protein manifestation of
the syndrome.
H) Enterotoxins :
There are multiple enterotoxins that, similar to TSST-1, are superantigens.
Enterotoxins are heat stable and resistant to the action of gut enzymes.

30. Pathogenesis

31. ● Nasal carriage of S. aureus occurs in 20-50% of humans.
● It's also found regularly on clothing, bed linens and other fomites in human
environments.
● The pathogenic capacity of a given strain of S. aureus is the combined effect of
extracellular factors and toxins together with the invasive properties of the
strain.
● Pathogenic, invasive S. aureus produces coagulase and tends to produce a
yellow pigment and to be hemolytic.

33. ● Three species are pathogenic in humans : Staphylococcus aureus ,
Staphylococcus epidermidis and Staphylococcus saprophyticus.
● Most staphylococcal infections are caused by Staphylococcus aureus, which
grows especially well on skin and mucous membranes but can infect any part of
the body.
● Staphylococcus aureus causes a wide variety of suppurative diseases, including
among others abscesses of the skin (impetigo, boils, styes, carbuncles, breast
abscesses, botryomycosis), abscesses of bone (osteomyelitis) and other deep
organs, infections of burns and surgical and other wounds, infections of the
upper and lower respiratory tracts (pharyngitis, bronchopneumonia , empyema),
purulent arthritis, septicemia, acute endocarditis and meningitis.
● Staphylococcus aureus releases several exotoxins : enterotoxins, (enteritis and
food poisoning) ; exfoliative toxin (exfoliative skin disease); and pyrogenic toxin
(toxic shock syndrome).

34. ● Staphylococcus epidermidis causes only minor skin lesions, except in patients
who have surgically inserted prostheses or are immunodeficient.
● Staphylococcus saprophyticus is responsible for bladder infections.

35. Infection of the Skin:
● Staphylococcal infections cause a variety of cutaneous and systemic infections,
including Impetigo, Furuncles (boils), subcutaneous abscess, staphylococcal
scalded skin syndrome, Toxic Shock Syndrome and neonatal toxic shock
syndrome-like exanthematous disease, in association with microbial virulence
factors.
● Staphylococcal scalded skin syndrome: The exfoliative toxin of S. aureus causes
the “scalded skin syndrome”. A painful, brick-red rash begins on the face, neck,
axilla, and groin, and then becomes generalized. The rash leads to blisters or
bullae, and the upper dermis is shed in large sheets. Breast abscesses usually
arise within a few weeks after delivery, when staphylococci are transmitted
from an infant with neonatal sepsis to the skin glands in the breasts of the
nursing mother.

37. Abscesses of Bone (Osteomyelitis):
● Acute staphylococcal osteomyelitis most commonly afflicts boys between 3 to
10 years of age, most of whom have a history of infection or trauma.
● The bones of the legs are involved in most patients.
● Many patients have an underlying bacteremia (S. aureus) with systemic
symptoms.
● Osteomyelitis may become chronic if not properly treated.
● Adults after 50 years of age are more frequently afflicted with osteomyelitis of
the vertebra.
● The onset of localized back pain is usually abrupt, but may follow
staphylococcal infection of the skin or urinary tract, prostatic surgery, infected
abortion, puerperal infection, or a surgical procedure such as pinning a fracture.

39. Acute and Chronic Bacterial Arthritis:
● S. aureus is the causative organism in half of all cases of septic arthritis. Most
of those who have the disease are adults, 50 to 70 years old, and usually only a
single joint is involved.
● Rheumatoid arthritis and steroid therapy are common predisposing conditions.
● The acute onset of staphylococcal arthritis is marked by severe, throbbing pain,
often worse at night, which is accompanied by shaking chills and fever.
● Acute staphylococcal arthritis may be confused with an acute episode of
rheumatoid arthritis.

41. Septicemia:
● Septicemia with S. aureus occurs in patients with lowered resistance who are in
the hospital for other diseases or conditions.
● Some having underlying staphylococcal infections (for example, osteomyelitis or
septic arthritis), some have had surgery (especially transurethral resection of
the prostate), and some have infections from an indwelling intravenous
catheter.
● Staphylococcal septicemia is associated with the common symptoms of
bacteremia, such as shaking chills and fever.
● Miliary abscesses and staphylococcal endocarditis are serious complications.

43. Bacterial Endocarditis:
● Acute and subacute bacterial endocarditis are complications of septicemia
caused by S. aureus (as well as by S. epidermidis).
● Endocarditis may develop spontaneously on normal valves or on valves
damaged by rheumatic fever.
● It may also follow insertion of prosthetic valves or other intracardiac surgery.
● Those with intravenous heroin addiction also have an increased risk of
endocarditis from infection with S. aureus.
● In addition to the symptoms of septicemia, a heart murmur is usual, with or
without evidence of embolization to other organs.

45. Staphylococcal Food Poisoning:
● Staphylococcal food poisoning is caused by the ingestion of preformed
staphylococcal enterotoxin in prepared food.
● This commonly involves food eaten in a restaurant (not industrially processed
food), especially unrefrigerated meats, milk, or custard and other milk products.
● At least six enterotoxins are produced by some of the coagulase +ve strains of
S. aureus, and enterotoxins are also produced by by a few coagulase -ve strains.
● Enterotoxins are resistant to heat and withstand cooking for 20-60 minutes.
● Usually, nausea and vomiting begin within a few hours of ingesting the toxin.
● Patients with more severe food poisoning have bloody mucus in the vomitus and
stools, as well as muscle cramps, headache, and sweating.
● The acute phase commonly lasts 4-6 hours, and recovery is complete within 1-2
days.

46. Prevention

49. Diagnostic Laboratory
Tests

50. A. Specimens
Surface swab pus or aspirate from an abscess, blood, tracheal aspirate, or spinal
fluid for culture, depending on the localization of the process, are all appropriate
specimens for testing. The anterior nares are frequently swabbed to determine nasal
colonization, either by culture or nucleic acid amplification tests, for epidemiological
purposes.
B. Smears
Typical staphylococci appear as gram-positive cocci in clusters in Gram-stained
smears of pus or sputum. It is not possible to distinguish saprophytic (S epidermidis)
from pathogenic (S aureus) organisms on smears.

51. C. Culture
Specimens planted on blood agar plates give rise to typical colonies in 18 hours at
37°C, but hemolysis and pigment production may not occur until several days later
and are optimal at RT. S. aureus but not other staphylococci ferment mannitol.
Specimens contaminated with a mixed flora can be cultured on media containing
7.5% NaCl; the salt inhibits most other normal microbiota but not S. aureus.
Mannitol salt agar or commercially available chromogenic media are used to screen
for nasal carriers of S aureus and patients with cystic fibrosis.
D. Catalase Test
This test is used to detect the presence of cytochrome oxidase enzymes. A drop of
3% hydrogen peroxide solution is placed on a slide, and a small amount of the
bacterial growth is placed in the solution. The formation of bubbles (the release
of oxygen) indicates a positive test result.

52. E. Coagulase Test
Citrated rabbit (or human) plasma diluted 1:5 is mixed with an equal volume of
broth culture or growth from colonies on agar and incubated at 37°C. A tube of
plasma mixed with sterile broth is included as a control. If clots form in 1–4 hours,
the test result is positive. Coagulase +ve staphylococci are considered pathogenic
for humans; however, coagulase +ve staphylococci of dogs (Staphylococcus
intermedius) and dolphins (Staphylococcus delphini) rarely cause disease in humans.
Infections of prosthetic devices can be caused by organisms of the coagulase -
negative S epidermidis group.
F. Serologic and Typing Tests
S. epidermidis isolates from blood cultures represent bacteremia caused by the same
strain, seeded by a nidus of infection. Molecular typing techniques have been used to
document the spread of epidemic disease-producing clones of S. aureus. Pulsed-field
gel electrophoresis and multilocus sequence typing are highly discriminatory.

53. Treatment

54. ● In acne, lipases of staphylococci and corynebacteria liberate fatty acids from
lipids and thus cause tissue irritation. Tetracyclines are used for long-term
treatment.
● Abscesses and other closed suppurating lesions are treated by drainage. Many
antimicrobial drugs have some effect against staphylococci in vitro. However, it
is difficult to eradicate pathogenic. It is also difficult to eradicate the S aureus
carrier state.
● In chronic and recurrent osteomyelitis, surgical drainage and removal of dead
bone is accompanied by long-term administration of appropriate drugs, but
eradication of the infecting staphylococci is difficult.
● Bacteremia, endocarditis, pneumonia, and other severe infections caused by S
aureus require prolonged intravenous therapy with a β-lactamase-resistant
penicillin. Vancomycin is often reserved for use with nafcillin-resistant
staphylococci.

55. ● S. epidermidis infections are difficult to cure because they occur in prosthetic
devices where the bacteria can sequester themselves in a biofilm. S. epidermidis
is more often resistant to antimicrobial drugs than is S. aureus; approximately
75% of S. epidermidis strains are nafcillin resistant.
● Penicillin G–resistant S aureus strains from clinical infections always produce
penicillinase. They constitute more than 95% of S aureus isolates in
communities in the United States.
● They are often susceptible to β-lactamase–resistant penicillins,
cephalosporins, or vancomycin. Nafcillin resistance is independent of β-
lactamase production.

56. Epidemiology &
Control

57. ● Staphylococci are ubiquitous human parasites. Contact spread of infection has
assumed added importance in hospitals, where a large proportion of the staff
and patients may carry antibiotic-resistant staphylococci in the nose or on the
skin.
● Aerosols (eg, glycols) and ultraviolet irradiation of air have little effect.
● In hospitals, the areas at highest risk for severe staphylococcal infections are
newborn nurseries, intensive care units operating rooms, and cancer
chemotherapy wards.
● Patients who test positive by culture or PCR are placed on contact precautions
to minimize spread on the hands of health care workers. Health care workers
should strictly adhere to infection control policies by wearing gloves and
washing hands before and after patient contact.

60. Articles based on current
research on Staphylococcus
aureus

61. ● Staphylococcus aureus in Agriculture: Lessons in Evolution from a
Multispecies Pathogen
● Sustained Coinfections with Staphylococcus aureus and Pseudomonas
aeruginosa in Cystic Fibrosis
● Fractional methicillin-resistant Staphylococcus aureus infection model
under Caputo operator
● SOCS-1 inhibition of type I interferon restrains Staphylococcus aureus
skin host defense
● Staphylococcus aureus lipoproteins promote abscess formation in mice,
shielding bacteria from immune killing
● Staphylococcus aureus binds to the N-terminal region of corneodesmosin
to adhere to the stratum corneum in atopic dermatitis

62. ● Photodynamic Therapy for Treating Staphylococcus aureus Infections
● M13 phage-based nanoprobe for SERS detection and inactivation of
Staphylococcus aureus
● Novel Research Models for Staphylococcus aureus Small Colony
Variants (SCV) Development: Co-pathogenesis and Growth Rate
● Intracellular Staphylococcus aureus persisters upon antibiotic exposure
● Development of a vaccine against Staphylococcus aureus invasive
infections: Evidence based on human immunity, genetics and bacterial
evasion mechanisms

63. https://scholar.google.com/scholar?start=50&q
=staphylococcus+aureus&hl=en&as_sdt=2007
&as_ylo=2021

66. References
● https://microbiologyinfo.com/biochemical-test-and-identification-of-
staphylococcus-aureus/
● http://textbookofbacteriology.net/staph_2.html
● Ananthanarayan R. and Paniker C.K.J. (2009) ‘Textbook of Microbiology’ 8th
edition University Press Publication.
● Brooks G.F., Carroll K.C., Butel J.S. and Morse S.A. (2013) ‘Jawetz, Melnick
and Adelberg’s Medical Microbiology’ 26th edition. McGraw Hill Publication.