STAPHYLOCOCCUS

AUREUS
Learning objectives
At the end of the session, the students will be able to
• Describe morphology including antigens
• Classify Staphylococci
• Describe virulence factors
• Describe clinical manifestations
• Decide appropriate lab tests and interpret the results
• Describe resistance patterns in Staphylococcus
Essentials of Medical Microbiology
History
• 1897 – Von Recklinghausen – first observed in pus
• 1880 – Louis Pasteur – First cultured in liquid medium

• Staphyle (Greek) – Bunch of grapes

• Kokkos - berry

Essentials of Medical Microbiology

General Feautures
• Gram positive cocci in grape-like
clusters
• Catalase positive

Essentials of Medical Microbiology

STAPHYLOCOCCUS AUREUS

Essentials of Medical Microbiology

 Virulence Factors..
Cell wall associated factors
Peptidoglycan Rigidity, Endotoxin
Teichoic acid Adhesion, Inhibit opsonisation
Cell surface adhesins-Clumping Adhesion, Clumping
factor
Protein A Anti-complementary
Chemotactic, Mitogenic, Inhibit
opsonisation
Induction of platelet damage
IgG Fc Co-agglutination

Capsule Inhibit phagocytosis

Essentials of Medical Microbiology
 Virulence Factors..
Toxins
Membrane active toxins
 Hemolysins-α,β,γ,δ
 Leucocidin F & S toxins + γ hemolysin hemolytic
and leucocidal (Synergohymenotropy)
Epidermolytic toxin Staphylococcal scalded-skin syndrome
Enterotoxins Serotype A- MC, Superantigen
Self limiting food poisoning IP<6 Hrs
Preformed toxin vagus stimulation
Toxic shock syndrome toxin Super antigen
Risk - abscesses, osteomyelitis, post-
surgical wound infection

Essentials of Medical Microbiology

Virulence Factors - Hemolysisns
hemolysin Inactivated at 70C reactivated at 100C
Lethal, leucocidal, dermonecrotic, cytotoxic and
neurotoxic
Lyses rabbit RBCs, but less active against sheep and
human RBCs.
βhemolysin Sphingomyelinase
Lyses sheep RBC, but not human or rabbit RBC
Exhibits hot-cold phenomenon
hemolysin Act together with leucocidin for hemolytic activity.
Lyses rabbit, sheep and human RBCs
hemolysin Surfactant action
Lyses rabbit, sheep, horse & human RBCs
Lethal, leucocidal and dermonecrotic

Essentials of Medical Microbiology

Virulence Factors..
Extracellular Enzymes
Coagulase + CRF prothrombin to thrombin
Tube coagulase test

Heat stable thermonuclease specific to S.aureus

Deoxyribonuclease specific to S.aureus
Lipase
Protease
Staphylokinase(fibrinolysin)
Hyaluronidase
Essentials of Medical Microbiology
Pathogenesis
• Colonization-anterior nares, axilla and perineal skin
• Introduction into the tissue- minor abrasions or
instrumentation adhere to tissue
• Invasion- with help of enzymes
• Evasion of host defence mechanisms
- Anti-phagocytic -microcapsule and Protein A
- Inhibition of leukocyte migration
- Intracellular survival -formation of small colony variants
• Metastatic spread- hematogenous
Essentials of Medical Microbiology
Clinical Manifestations
 Skin & Soft tissue infections
• Folliculitis, Furuncle
• Carbuncle, Impetigo
• Mastitis and breast abscess
• Surgical site wound
infections
• Cellulitis 
• Hidradenitis suppurativa
• Botryomycosis Essentials of Medical Microbiology
Clinical Manifestations...
Musculoskeletal Respiratory Tract
Infections Infections
• Septic arthritis • Ventilator associated
• Osteomyelitis pneumonia in adults
• Pyomyositis in HIV • Septic pulmonary emboli
• Psoas abscess • Post viral pneumonia
• Epidural abscess • Empyema and
Pneumothorax
• Pneumatocele in neonates
Essentials of Medical Microbiology
Bacteremia and its
Complications
• Sepsis, septic shock
• Central line associated blood stream
infection
• Metastasis - kidney, joints, bone and lung
• Native-valve endocarditis
• Prosthetic-valve endocarditis
• Intravenous drug use associated
endocarditis
Essentials of Medical Microbiology
 Clinical Manifestations
 UTI(Urinary tract  Infections Associated
infection)- secondary to with CA-MRSA
bacteremia • Necrotizing pneumonia
 Toxin-Mediated Illnesses • Purpura fulminans
• Toxic shock syndrome • Necrotizing fasciitis
• Food poisoning
• Staphylococcal scalded-
skin syndrome
Essentials of Medical Microbiology
Staphylococcal Gastroenteritis
• Enterotoxin - expressed by 50% of S.aureus
• preformed heat stable toxin and resistant to gastric
juice
• Serotypes(A–E, G–I, R-T and V). Type A – Most
common
• Site of action- Stimulates the vagus nerve and the
vomiting center. Stimulation of intestinal peristaltic
activity Essentials of Medical Microbiology
Staphylococcal Gastroenteritis
• incubation period – 16 Hrs
• Symptom- nausea, vomiting and occasionally
diarrhea, hypotension, and dehydration. No fever.
Selflimiting within 8–10 hour.
• Source - food handler
• Food items - milk products, bakery food,custards,
potato salad, or processed meats.
Essentials of Medical Microbiology
 Staphylococcal scalded-skin syndrome (SSSS)
• Epidermolytic/exfoliative toxin –
• Two proteins- ET-A (chromosomal and heat stable), ET- B
(plasmid coded, heat labile).
• More common in newborns and children
• Clinical Features-
- May vary from localized tender blisters& bullae formation
to exfoliation & separation of outer epidermal layer
leaving denuded underlying skin (Nikolsky's sign).
Essentials of Medical Microbiology
Staphylococcal scalded-skin syndrome (SSSS)
• Milder form - pemphigus neonatorum and bullous
impetigo
• Ritter’s syndrome - Severe form in newborns
- Fever, lethargy, and irritability with poor feeding.
- S.aureus bacteriophage group II

Essentials of Medical Microbiology

 TOXIC SHOCK SYNDROME
• Toxic shock syndrome toxin (TSST)- Enterotoxin F, a
superantigen
• Risk factors- vaginal tampons, abscesses,
osteomyelitis and post-surgical wound infection.
• Pathogenesis- TSST absorbed into circulation - non-
specifica T cells stimulation - excessive cytokine
production -multisystem disease.
Essentials of Medical Microbiology
 TOXIC SHOCK SYNDROME
• Clinical features- Fever, hypotension, mucosal
hyperemia, vomiting, diarrhea, confusion, myalgia,
abdominal pain and erythematous rashes  rapid
involvement of liver, kidneys, GIT and/or CNS.
• Diagnosis-
- Detection of TSST - latex agglutination test and ELISA
- TSST genes 1 and 2 - PCR
• Treatment- Clindamycin (MSSA), vancomycin (MRSA)
Essentials of Medical Microbiology
LABORATORY DIAGNOSIS..
Infection Specimen
Suppurative Pus, wound swab
lesion
Respiratory Sputum
Infections
Urinary tract Mid ­stream urine
infection
PUO, Bacteremia Blood
Food poisoning Feces, vomitus, food
Carriers Nasal & perianal swab

Essentials of Medical Microbiology

 LABORATORY DIAGNOSIS..
• MICROSCOPY
• Gram staining -Gram
positive cocci in clusters

Essentials of Medical Microbiology

 LABORATORY DIAGNOSIS- CULTURE
• Aerobe, facultative
anaerobe, Non-
fastdious
• Nutrient agar – Golden
yellow

• Blood agar – beta

hemolytic Essentials of Medical Microbiology
 LABORATORY DIAGNOSIS..
• MacConkey agar- Small pink
• Liquid medium - uniform turbidity
• Selective media
- Mannitol salt agar – yellow
colonies -mannitol fermentation 
- Salt milk agar
- Ludlam’s medium
Essentials of Medical Microbiology
 LABORATORY DIAGNOSIS- Biochemical Tests
 Coagulase test
o Tube coagulase
o Clumping factor
 Heat stable thermo nuclease test
 DNase test
 Phosphatase (also produced by S.epidermidis) • S.aureus positive
 Golden yellow pigmentation and CoNS mostly
 Hemolysis on blood agar negative
 Mannitol fermentation
 Black coloured colonies on potassiumtellurite
agar
 Gelatin liquefaction
 Protein A detection Essentials of Medical Microbiology
 LABORATORY DIAGNOSIS..
Tube coagulase Slide coagulase
Due to coagulase enzyme Due to clumping factor
Requires CRF in plasma Does not require CRF in
plasma
Done in tube Done in slide
Positive if clot is formed Positive if clumps are formed

Coagulase enzyme has eight Clumping factor has one

serotypes serotype
S.lugdunensisgives a negative S.lugdunensisgives a positive
result result
Both tube and slide coagulase positive for S.aureus,
S.hyicus, and S.intermedius
Essentials of Medical Microbiology
Typing of S.aureus
• Phenotypic methods
- Bacteriophage typing
- Antibiogram typing.
• Genotypic methods - PCR-RFLP

Essentials of Medical Microbiology

DRUG RESISTANCE IN S.aureus
1. Production of β lactamase enzyme
2. By alteration of PBP – MRSA
• mec A gene – chromosomal – PBP-2a - resistant to all β lactam
antibiotics
• Detection of MRSA-
- Disc diffusion test - oxacillin/cefoxitin discs
- Oxacillin screening agar
- PCR detecting mecA gene
Essentials of Medical Microbiology
DRUG RESISTANCE IN S.aureus
• Treatment of MRSA
- Vancomycin - DOC
- Alternative drugs - teicoplanin, linezolid, daptomycin and
quinupristin/dalfopristin
- Other non-beta-lactams if sensitive by AST

3. Resistance to vancomycin (VRSA and VISA)

Essentials of Medical Microbiology
CONTROL MEASURES
• Proper hand washing
• Screening of MRSA carriers
• Treatment of carriers
• Stoppage ofantibiotic misuse
• Bundling

Essentials of Medical Microbiology

COAGULASE NEGATIVE STAPHYLOCOCCUS
(CONS)
Essentials of Medical Microbiology
 CONS
• Mostly harmless • Important species:
commensals - S. epidermidis
• Less virulent than - S.saprophyticus
S.aureus - S.lugdunensis
• Recently their role as - S.schleiferi
pathogens is
increasingly been
reported
Essentials of Medical Microbiology
STAPHYLOCOCCUS EPIDERMIDIS
• Most common CONS (75-80%)
• Normal flora - skin, oropharynx and
vagina
• Risk - prosthetic devices
• Pathogenesis-
- Initial adhesion
- Colonization (Biofilm)
Essentials of Medical Microbiology
STAPHYLOCOCCUS EPIDERMIDIS
• Infections:
- Prosthetic-device related infections
endocarditis with insertion of
valvular prosthesis and ventricular
shunt infections
- Stitch abscess

Essentials of Medical Microbiology

CoNS..
Staphylococcus saprophyticus
• UTI in sexually active young women
• Unlike other Staphylococci resistant
to novobiocin
• S.lugdunensis and S.schleiferi
- Native-valve endocarditis and
osteomyelitis
Essentials of Medical Microbiology
ASSESSMENT

Essentials of Medical Microbiology

 MCQs
• Staphylococcal scalded skin • Staphylococcus aureus
syndrome is caused by – causes vomiting in 6-8
a) Hemolysin hours. The mechanism of
b) Coagulase action is:
c) Enterotoxin a. Stimulation of cAMP
d) Epidermolytic toxin b. Vagal stimulation
c. Stimulation of cGMP
d. Acts through ganglioside
GM receptor
Essentials of Medical Microbiology
 MCQs
• All can be given in • All are true about S.aureus except:
MRSA except? A. Most common source of infection
A. Cotrimoxazole – cross infection from infected
B. Cefaclor persons in hospital
C. Vancomycin B. 30% of general population is
D. Ciprofloxacin healthy carriers
C. TSS and enterotoxins are
superantigens
D. MRSA- chromosomally mediated
Essentials of Medical Microbiology
 MCQs
• A patient has prosthetic valve replacement and he
develops endocarditis 8 months later. Organism
responsible is?
A. Staphylococcus aureus
B. Streptococcus viridans
C. Staphylococcus epidermidis
D. HACEK
Essentials of Medical Microbiology
THANK YOU..!

Essentials of Medical Microbiology