Staphylococcus aureus References : Ananthnarayan and Panikers Textbook of Microbiology Apurba Sankar Sastry and Sandhya Bhat - Essentials of Medical Microbiology-Jaypee Brothers Medical Publishers Textbook of Microbiology – Dr. C.P. Baveja

1. Staphylococcus aureus
Deepashree Sah

2. Note
• All cocci are Gram positive
• Except
Moraxella
Neisseria
Veillonella

3. Classification of GPC
• Gram Positive Cocci
• Micrococcaceae
• Staphylococcus
• Micrococcus
• Strepcococcaceae
• Streptococcus
• Enterococcus
• Pneumococcus

4. Gram Positive Cocci (GPC)
• Gram-positive cocci are classified into two families Micrococcaceae
and Strepcococcaceae, differentiated by the catalase test.
• Micrococcaceae are catalase positive, gram-positive cocci arranged in
tetrads or clusters
• Where as Strepcococcaceae are catalase negative gram positive cocci,
arranged in pairs or chains.

5. • Staphylococcus species are arranged in clusters, show fermentative
pattern in oxidative fermentative test
• Among Staphylococcus species, S. aureus is the most pathogenic; it
produces an enzyme coagulase which forms the basis of coagulase
test
• Whereas, other species do not produce coagulase and are called as
coagulase-negative Staphylococcus (CoNS).

6. Family – Micrococeae
Genus – Staphylococcus
Classification
A. Based on pigment production
• Staphylococcus aureus – Golden yellow
• Staphylococcus albus – White colonies
• Staphylococcus citrus – Lemon yellow colonies
B. Based on pathogenicity
• Pathogenic – Staphylococcus aureus
• Non-Pathogenic – S. epidermidis, S. albus
C. Based on Coagulase production
• Coagulase positive – S.aureus
• Coagulase negative – S.epidermidis, S. saprophyticus

7. Staphylococcus aureus
Morphology, Antigenic structure, growth requirements and cultural characteristics,
biochemical properties, lab diagnosis & treatment

8. Staphylococcus
• Staphyle means bunch of grapes

9. Morphology
• Gram-positive, singly, in pairs, or in a short chain of 3-4 bacteria.
• Irregular clusters of cells in 3 dimensional plane
• 1 um in diameter
• Spherical colonies in clusters in two planes.
• Cell wall- very thick peptidoglycan layer
• Non-Flagellated
• Non-Motile
• Non-Sporing
• Non-capsulated (Few strains posses capsules especially young cultures
• Grapes like clusters arrangement.
• Facultative anaerobes

10. Antigenic structure / Virulence factor
Cell associated factors
1. Capsule
Some strains of Staph. aureus possess capsule and inhibit
phagocytosis. The capsule is composed of polysaccharide. Capsulated
strains tend to be more virulent.

11. 2. Peptidoglycan
 Peptidoglycan is a polysaccharide polymer that provides rigidity to the cell
wall. It activates complement and evokes production of inflammatory
cytokines.
3. Teichoic Acid
It is a major antigenic determinant of all strains of Staph. aureus. It is the
group specific ribitol teichoic acid of the cell wall. It facilitates adhesion of
the cocci to the host cell surface and protects them from complement
medicated opsonisation. It is associated with the peptidoglycan in an
insoluble form. It is absent in Staph. epidermidis. The latter contains glycerol
teichoic acid.

12. 4. Protein A
It is a cell wall component of most strains of Staph. aureus (especially
Cowan I strain). It is chemotactic antiphagoocytic, anticomplementary
and elicits platelet injury. Protein A has ability to bind the Fc portion of
immunoglobulin G (IgG). Binding IgG in this manner can block
phagocytosis. Cowan I strains coated with any IgG antiserum will be
agglutinated if mixed with its corresponding antigen. This procedure is
known as Coagglutination. i.e. role in Co-agglutination test.

13. Extracellular factors (Cytolytic toxins)
1. Toxins
membrane active substances
Four types of haemolysins are produced by staphylococci
i. Alpha haemolysin
• most important protein inactivated at 70°C but reactivates at 100°C
• lyses rabbit erythrocytes, but is less active against sheep & human red cells
• It is also leucocidal, Cytotoxic, dermonecrotic (on intradermal inoculatios in rabbits), neurotoxic and lethal
• Toxic to macrophages, Lysosomes, muscle tissues & renal cortex.
ii. Beta hemolysin
• Sphingomyelinase C, hemolytic for Sheep cells, but not human or rabbit erythrocytes.
• lysis is initiated at 37°c but it is evident only on cold temperature so, is named as hot-cold phenomenon.
• Produced both aerobically as well as anaerobically.
iii. Gamma lysin
• Acts on human, sheep and rabbit erythrocytes
iv. Delta lysin
• lytic to human, sheep and rabbit red blood cells.

14. 2. P-V Toxin / Leucocidin
Panton–Valentine
3. Epidermolytic / Exfoliative Toxin
Cause scalded skin syndrome
Toxic epidermal necrolysis (TEN)
Ritter’s syndrome
4. Enterotoxins
Responsible for food poisoning
Incubation period of 1-6 hrs
(Can be because of S.aureus from milk, bakery product or poultry)
Can be because of B.cereus from Chinese food)
Act on vagus nerve and act on vomiting centre

15. Types of Enterotoxin
• From A to I but no F
• From R to T and last one V

16. 5. TSST (Toxic shock syndrome toxin)
It is Enterotoxin F
It is superantigen
Risk Factor or Classical history : Vaginal tampons
Clinical features : Rash, Fever, low BP
And if not treated then multi organ failure
Diagnosis : Latex agglutination test , RIA, ELISA

17. Extracellular factors (Cytolytic toxins)
1. Enzymes
i. Catalase
ii. Free Coagulase
iii. Thermonuclease (Heat stable)
iv. Phosphatase
v. DNAase
vi. Lipases
vii. Hyaluronite
viii. Nuclease
ix. Staphylokinase (fibriolysin)
x. Protease

18. Growth requirements
• Aerobes and facultative anaerobes
• Temperature range 10-42°C
• Optimum Temperature for growth = 37°C (35°C – 37°C)
• Optimum pH for growth = 7.5 (7.4 – 7.6)
• Grow on ordinary media

19. Cultural characteristics
Media used
1. Non-selective Media
• Nutrient agar
• Blood agar
• Mac Conkey agar
2. Selective media
• SALT-Milk agar (8-10% NaCl)
• Lundlam’s Medium

20. Nutrient agar
• Colonies : Large (2-4mm in diameter), Circular, Convex, Smooth, Shiny, Opaque,
Easily emulsifiable
• On nutrient agar slope, confluent growth presents a characteristic Oil paint
appearance
• Most strains produce golden-yellow
pigment, though some may be white,
orange or yellow. The pigment doesn’t
diffuse into the medium. Pigment
production occurs optimally at 22°C and
only in aerobic cultures. Pigment
production is enhanced when 1% glycerol
monoacetate or milk is incorporated. in the
medium.

21. Note
• Golden yellow due to production of pigment known as
staphyloxanthin (belongs to beta carotene group)
• Require 22°C , aerobic condition
• Non-diffusible pigment

22. Blood agar
• Colony characteristic are same as on Nutrient agar
• Most strain are β-hemolytic when incubate under 20-25% CO2
• Sheep, rabbit blood (and weak on horse blood) shows marked hemolysis
• Human blood is not used as it contain antibody or other inhibitors

23. MacConkey agar,
• They produce smaller colonies that appear pink due to lactose fermentation.

24. • Liquid media
The growth appears as uniform turbidity.
• Selective Media
Needed for isolating from specimen such as Feces
8-10% NaCl may be added to nutrient agar, Salt agar or Milk agar (Salt-milk
agar)
Mannitol salt agar
Lithium chloride & Tellurite agar
Ludlam’s medium
Polymyxin

25. Biochemical properties
• Catalase positive, Oxidase negative
• Coagulase positive: the presence of free and /or bound coagulase
• OF (oxidative-fermentative)test – fermentative
• Indole negative, Gas negative, Hydrogen sulfide negative
• Methyl red positive, VP positive
• Nitrate reduction positive (Nitrate to nitrite)
• Gelatin hydrolysis positive
• Citrate positive, Urease positive
• PYR negative
• DNA-ase test positive
• Phosphatase positive
• Phage typing

26. Resistance
• more resistant among non-sporing bacteria
• They survive in dried pus for 2-3 months.
• Most Staphylococci are killed at 62°C for 30 minute
• But hour some may require 80°C for one hour
• Most strains grow in presence of 10% NaCl
• Staphylococci are resistant to 1% phenol for 15 minutes while
mercury per chloride (1%) solution kills in 10 minutes.
• Staphylococci and resistant to lysozyme sensitive to lysostaphin.

27. Pathogenicity
• Source of infection
Exogenous : patient or carrier
Endogenous : from colonized site
• Mode of Transmission
Contact : direct/indirect through fomites
Inhalation : Air borne droplets

28. CLINICAL FEATURES
• S – Soft tissue infections i.e. folliculitis, impetigo
• O – Osteomyelitis , musculoskeletal infections
• F – Food poisoning
• T – TSST, TEN
• P – Pneuminia
• A – Acute endocarditis
• I – Infective arthritis
• N – Necrotising fascitis
• S - Sepsis

29. Acute endocarditis
• (if person <12month= S.epidermidis & >12 month = S.viridians)
• In I.V drug abusers then right side of heart –S. aureus & left side of
heart – Enterococcus

30. 1. Cutaneous Infections
• Folliculitis
Inflammation of hair follicle
Small red bump or pimple develops at infection sites of hair follicle

31. • Furuncle/boils
Furuncle is deep seated infection, originating from folliculitis, (if infection extends from
follicle to neighbour tissue.
Causes redness, Swelling, Severe pain.
Commonly found on the neck, armpit and groin regions (between two thigh).
• Carbuncle
Carbuncle is an aggregation of infected furuncles. Carbuncles may form large
abscesses.
It is a large area of redness, Swelling aud bain, Punctuated by several sites of drainage
pus

32. • Impetigo
A very Superficial Skin infection Common in Children, usually produces
blisters or Sores on the face, neck, hand and diapers area.
It is characterized by watery bristles, Which become pustules and then honey
Coloured Crust.

33. 2. Deep Infections
• Osteomyelitis
Inflammation of bone
Bacteria can get to the bone via blood stream,
following an injury
Clinical feature : Pain, swelling, defective healing ,
in some case pus flow.
Diagnosis : X-ray, MRI, bone aspirates

34. • Periostitis
Inflammation of periosteum.
Clinical Features - Fever, Localized pain,
leucocytosis.
Diagnosis - Needle aspiration of subperiosteal
fluid.
• Endocarditis
It is an inflammation of the inner layer of the
heart, the Endocardium.
Endocarditis occurs when bacteria enter blood
stream, travel to heart, and lodge on abnormal
heart valves or damaged heart tissue.

35. 3. Exfoliate Disease
• Exfoliate = scaling off tissues in layers
• Also known as Staphylococcal skin scalded syndrome
• Epidermal toxin produced by S.aureus at skin and is
carried by blood stream to epidermidis, where it causes a
split in a cellular layer i.e. this toxin separates outer layer
of epidermis from underlying tissue.

36. Types of SSSS:
Severe form Milder form
In new born - Ritter’s disease - Pemphigus neonatorum
In older patients - Toxic epidermal - Bullous ,necrolysis,
impetigo

37. 4. Toxic Shock Syndrome
• Caused when Toxic shock syndrome toxin (TSST) liberated by S.aureus enters
blood stream
• It is multisystem illness characterized by (see fig)

38. 2) Staphylococcal Toxic shock syndrome (STSS):
• STSS is associated with infection of mucosal or sequestered sites by
TSST( formerly known as enterotoxin type F) producing S.aureus.
• It is fatal multisystem disease presenting with fever, hypotension,
myalgia, vomiting, diarrhea, mucosal hyperemia and erythematous
rash which desquamates subsequently.

39. 2 types of STSS known:
i) Menstrual associated STSS: Here colonization of S.aureus occurs in
the vagina of menstruating woman who uses highly absorbent vaginal
tampons.
ii) Non menstrual associated STSS: Here colonization of S.aureus occurs
in other sites like surgical wound.

40. 5. Staphylococcal Food Poisoning
• Caused when consuming food in which S.aureus has multiplied and
formed endotoxin.
• Symptoms : Nausea, vomiting, Severe abdominal cramp, Diarrhoea,
Sweating, Headache etc.
• Mode of Transmission : Person with lesions, Air borne droplets,
Asymptomatic carrier, Cross-Infection

41. Epidemiology
• Human patients and carriers are the commonest source of infection.
• In hospital, more than 50% of nursing staff are carriers of
Staphylococcus aureus.
• Staphyloccal disease may be exogenous & endogenous.
• Staphylococci are the commonest cause of hospital cross infection.

42. Prevention
• Isolation & treatment of MRSA patients
• Detection of carriers among hospital staff, their isolation &
treatment.
• Avoid indiscriminate usage of antibiotics.
• Stop misuse of antibiotics.

43. Treatment
• Drug resistance is common.
• Benzyl penicillin most effective antibiotic, if the strain is sensitive.
• Cloxacillin or methicillin used against B-Lactamase.
• Vancomycin is used in treatment of infection with MRSA. (Harboring
vanA & me CA).
• Tolerance to penicillin.

44. Laboratory Diagnosis
• Hematological Investigation
TLC ( Normal = 4,000 – 10,000 cells/mm3
, In infection >10,000 cells/mm3
)
DLC (Normal = 80%, Infection = >80%)
• Bacteriological Investigation
Specimens
o Pus : from wound or abscess or burns
o Nasal swab : from suspected carrier
o Food : To diagnose staphylococcal intoxication
o Blood : To diagnose endocarditis and bacteremia
o Sputum : To diagnose lower respiratory tract infection
o Urine : UTI
o CSF : meningitis
o Feces : Food poisoning
o Food or vomit : Food poisoning

45. Collection & Transport
Direct Microscopy
Culture
Colony morphology & Gram staining
Biochemical rxns
oCatalase – positive , Cagulase – positive
oMannitol fermentation – Acid production without gas
oGelatin liquefaction – positive
oTellunite reduction – positive
oProduction of enzyme phosphatase
oOxidase – Negative
oDNAse – Positive
Bacteriophage typing

46. References
• Ananthnarayan and Panikers Textbook of Microbiology
• Apurba Sankar Sastry and Sandhya Bhat - Essentials of Medical
Microbiology-Jaypee Brothers Medical Publishers
• Textbook of Microbiology – Dr. C.P. Baveja

47. THANK YOU