Staphylococci - Prac. Microbiology
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Gram positive cocci
(streptococci catalase –ve)
Catalase: +ve Coagulase:
+ve: S. aureus-ve: CoNS
Coagulase enzyme FibrinVisible Clot
3 Incubate at 37oC, observe for formation of visible clot.
1 ml dil. citrated plasma1
(coagulase +ve staphylococci)
Gram positive cocci
CultureNutrient agar (golden yellow endopigment)
Blood agar (ß-haemolysis)
Mannitol-Salt agar (MSA)
• Selective, differential medium.
• 7.5% sodium chloride + mannitol sugar.
S. aureus (ferment)
• Mannitol Acid
CoNS (No fermentation)
• Mannitol No acid
Virulence Factors for Pyogenic Diseases
A- Localized Skin infectionsPYOGENIC DISEASES
B- Staphylococcal Pneumonia
C- Invasive Infections
• Bacteremia.• Osteomyelitis.• Acute bacterial endocarditis.• Meningitis.• Septicemia.
Diagnosis of Pyogenic Diseases
Abscess ----- pus Endocarditis ----- blood
Meningitis --- CSF, blood Pneumonia ----- sputum
UTI ----- urine
2 -Direct detection
Other than blood
(pus, CSF, urine)
A- Colony Morphology
C- Biochemical Reactions
1-Coagulase 2-Clumping factor
A- SSS Exfoliatin
B- TSS TSST-1
C- Food poisoning Enterotoxins
A- Staph. Scalded Skin Syndrome
B- Toxic Shock Syndrome Predisposing factors:- First observed in Menstruating females using tampons )tampon retained in vagina for 4-5 days(- Any staphylococcal lesion can predispose to TSS.
Virulence factor: TSST-1
Diagnosis: clinical picture.culture: for isolation & identification.
ELISA: for toxin detection in blood
C- Staph. aureus food poisoning
I.P: 1- 6 hrs.
Clinical picture:Colic, vomiting, mildDiarrhea, but no fever
Diagnosis:1. Specimen: food, vomitus, stools.
2. Culture: on MSA.
3. ELISA: for toxin detection in sample or in isolated organism.
4. Strain typing: to trace source of infection )e.g. phage typing(.
• Phage typing.• Colony morphology.• Biotyping.• Plasmid profile.• Ribotyping.• Chromosomal
Treatment1 -Penicillin-resistant S.aureus
Coagulase negative Staphylococci (CoNS)
• General Characters:– Non-hemolytic on blood
agar– Coagulase negative– Mannitol non-fermenter
• Diseases: S. epidermidis:– Device-related infections
(prosthetic valve endocarditis, shunt infections, … etc…)
– Urinary tract infection– Wound infection
S. saprophyticus: UTI )honeymoon( cystitis
Case 1 A man underwent an emergency operation for
perforated appendix. He required admission to the Intensive Care Unit. On the 5th day of hospitalization he developed fever, and the wound was erythematous, swollen, with purulent discharge )Surgical site infection “SSI”(. The surgeon requested bacteriological examination )culture and sensitivity( of the wound pus
Surgical site infection
• Wound swabs were obtained.
• Gram staining & Microscopy Gram-positive cocci arranged in clusters amongst pus cells.
On nutrient agar →
Golden yellow pigment
On Blood agar →Beta-hemolysis
On MSA →Yellow colonies
Identification:Film from colonies Gram-positive cocci in clusters
Catalase +ve Coagulase +ve Clumping factor +ve
Which organism is causing this condition?
• Gram-positive cocci in clusters, catalase positive
• β-hemolysis , golden yellow pigment, yellow colonies on MSA and coagulase positivity
Antimicrobial susceptibility “Disc diffusion” the organism is resistant: to oxacillin, penicillin,erythromycin, & gentamicin but sensitive to: vancomycin.
How do you interpret the susceptibility data?
The organism is multi-resistant, including oxacillin-resistant
methicillin-resistant S. aureus (MRSA).
Name other diseases caused by this organism.
1. Pyogenic infections a. Localized skin infections, e.g. folliculitis, furuncles,
abscess. b. Staph pneumonia c. Invasive staph. infections, e.g. endocarditis, cellulitis,
osteomyelitis, and septic arthritis
2. Toxin-mediated diseases a. Toxic shock syndrome , b. Scalded skin syndrome,
c. Food poisoning.
A group of people shared a carbohydrate- rich meal. 1-6 hours later, they manifested vomiting, diarrhea but no fever. The condition was mild and self- limited.a( What could be the clinical diagnosis?b( What is the possible causative organism?c( What is the virulence factor responsible for this condition?d( What is the mechanism of action of such virulence factor?e( What is the laboratory test that is used to trace the source of this outbreak?
1. All the following are characteristic features of staphylococci except:
a) Gram positive cocci.b) Arranged in clusters.c) Catalase negative .d) Usually grow on simple media.e) Usually inhabit skin and mucosa.
2. The following medium is used to isolate S. aureus from specimens contaminated by other bacteria: a) Nutrient agar. b) MacConkey's agar. c) Blood agar . d) Mannitol salt agar. e) Chocolate agar
3. The localized nature of S. aureus lesions is due to:a) Adhesins. b) Protein A.c) Staphylocoagulase d) Staphylokinasee) Exfoliatin
4. S. aureus growth can be identified by the following characters except:a) Colony on blood agar is golden yellow.b) Colony on blood agar is surrounded with a clear zone. c) Colony on Mannitol salt agar is rose pink.d) Protein A positive. e) Coagulase test positive.
5. One of the following is a S. aureus toxin-mediated disease: a) Folliculitis b) Staphylococcal pneumonia. c) Toxic shock syndrome. d) Osteomyelitis e) Carbuncles
6. Staphylococcal strain typing is used :
a) To diagnose staphylococcal pyogenic diseases.
b) To differentiate between coagulase -ve and coagulase +ve staphylococci.
c) To differentiate between staphylococci & streptococci.
d) To trace the source of outbreaks of S. aureus in the epidemiological studies.
e) To identify enterotoxin-producing strains of S. aureus.