Gram positive pyogenic cocci

(1)

Gram positive pyogenic

cocci

(2)

(3)

Staphylococci

•

Gram positive cocci

•

Arranged in grape like clusters.

•

Ubiquitous

•

Commonest cause of Suppurative lesions in human

beings.

•

Able to develop resistance to Penicillin & other

antibiotics.

•

Hence important in Hospital Acquired Infections

(4)

Morphology

Staph vs. Strep

Gram-positive cocci in

clusters

Morphology

• Gram positive, non spore forming cocci

• _{Nonmotile, Facultatively anaerobic, Arranged in grape like clusters.} • _Ubiquitous

• _{Can exist on dry surfaces for a long period}

• _{Relatively heat-resistant; temperature range from 18° to 40° C for} growth

•_{Able to grow in media containing 10% NaCl}

(5)

Staphylococcus

•

1. Coagulase positive Staphylococci

–

Staphylococcus aureus

•

2. Coagulase negative Staphylococci

–

Staphylococcus epidermidis

(6)

(7)

Gram stain smear showing Gram Positive

Violet colour Cocci arranged in clusters

Clinical importantance:

Important human pathogen

Causes both relatively minor and serious diseases

- Commonest cause of Suppurative lesions in human beings. - Able to develop resistance to Penicillin & other antibiotics.

(8)

Nosocomial Infections –

•

Staphylococci

are one of the important causative

(9)

(10)

Hemolytic bacteria

•

(alpha)

α

-hemolysis: Cause a biochemical

change in the hemoglobin of red blood

cells results in green color around the

colonies

•

(beta)

β

-hemolysis: Cause gross

hemolysis of the red blood cells in blood

agar

•

(Gamma)

γ

– no hemolysis or change in

(11)

Growth characteristics

On Blood agar

• Similar to those on Nutrient agar. • Gives β-Haemolysis

• Haemolysis best seen on sheep or rabbit blood agar plate.

COLONIES ON MAcCONKEY’S agar Very small & pink due to lactose

(12)

MANNITOL SALT AGAR –

Selective & indicator medium contain – Nutrient agar with 1% mannitol 7.5% NaCl and Phenol red. Due to Mannitol fermentation Yellow colonies formed.

 MILK AGAR –

Contains Nutrient agar & sterilized milk. Staphylococcal strains produce various pigments for e.g. Golden yellow,

(13)

BIOCHEMICAL REACTIONS

BASED ON ENZYME PRODUCTION -

• Catalase test (+ve) • Coagulase test (+ve)

• Production of Phosphatase (+ve) • Production Deoxyribonuclase (+ve) • Production of Lecithinase (+ve)

BASED ON FERMENTATION –

• Ferments number of sugars with the production of acid

but no gas.

• But are of no diagnostic value.

(14)

Slide Catalase Test

Catalase On The Plate

Catalase +ve Catalase -ve

(15)

TUBE CATALASE TEST Sterile Glass Rod Sterile Test tube with 3% H₂O₂

Test isolated colony from NA Plate

Break down of H₂O₂ by enzyme

(16)

Coagulase Test

•

Test used to identify

Staph. aureus

which

produces the enzyme coagulase.

•

To differentiate from

Staph. epidermidis.

•

Principle –

•

Coagulase causes plasma to clot by converting

fibrinogen to fibrin.

•

Two types of coagulase are produced by most of

the strains.

(17)

Fibrinogen



Fibrin

Staph aureus +ve

(18)

(19)

Virulence Factors

(associated with cell wall of the bacteria

1. Capsule or slime layer (glycocalyx)

2. Teichoic acid is covalently linked to (peptidoglycan)

S. aureus ribitol teichoic acid (polysaccharide A)

S. Epidermidis glycerol teichoic acid (polysaccharide B)

(20)

Enzyme production (virulence factors)

•

Haemolysis on Blood Agar plate.

•

Gelatin liquefaction test.

•

Coagulase activity.

•

Lipolytic activity.

•

Production of Urease.

(21)

Most constant association found between

virulence & production of enzyme “Coagulase”

(22)

DISEASES

•

Due to direct effect of organism

–

Local lesions of skin

–

Deep abscesses

–

Systemic infections

•

Toxin mediated

–

Food poisoning

(23)

Staph. aureus

can cause skin

infections.

These usually remain localized;

the collection of pus is called a

furuncle

(=boil)

-or causes Carbuncle. This one is

at a typical site on the back of the

neck.

(24)

Exotoxins –

A. Haemolysins –

Four antigenically distinct types called Alpha (а), Beta (ß), Gamma (γ), Delta (δ).

Food poisoning

Toxin production

B. Enterotoxin –

• Responsible for staphylococcal food poisoning. • Eight antigenically distinct enterotoxins.

A, B, C1, C2, C3, D, E, & H.

The toxin can be detected by serological tests such as latex agglutination tests & ELISA.

The source staphylococcal food poisoning:

(25)

Toxic Shock Syndrome Toxin (TSST)

Toxin production

• _{This condition is characterized by:}

• _{Fever, hypotension, vomiting, diarrhoea & an}

erythematous rash.

• _{Most TSST producing strains belongs to}

bacteriophage group-I

It means: (not chromosome encoded).

TSS widely known to be in association with use of tampons by menstruating women but it occurs in other conditions also.

(26)

Exfoliative (

Epidermolytic

) Toxin

Toxin production

-Two types of exfoliative toxin, A & B

1. Type A- Heat stable, its production is under chromosomal control (chromosome encoded)

2. Type B- Heat labile, production is plasmid mediated. they Lead to epidermal splitting

producing Staphylococcal Scalded Skin Syndrome (SSSS).

Severe form of SSSS is known as Ritter’s disease

(27)

Deep abscesses

& systematic infection

•

Bacteremia

•

Osteomyelitis

bone infection

•

Pulmonary

(28)

Laboratory Diagnosis



Specimens –

 Pus – Suppurative lesions.

 Sputum – Respiratory infections.

 Blood – Septicemia or PUO (Pyrexia of unknown origin)  Urine – UTI.

 CSF – Meningitis.

 Faeces – Food Poisoning.

(29)

Laboratory Follow Up –

 Culture –Blood Agar/ Nutrient Agar/ MacConkey agar/ Mannitol

Salt Agar/ Milk Agar etc.

 Direct Smear – Gram’s Stain.

 Colony morphology studies and staining.

 Biochemical Reactions - Enzyme detection & fermentation of sugars.

Antibiotic Sensitivity testing.

 Bacteriophage typing.

(30)

Resistance:

–

Plasmid-borne (hydrolysis of ß-lactam

ring)

–

Chromosomal—change in structure of

penicillin-binding proteins (PBP)

•

MRSA (“Methicillin-resistant

Staph aureus

”)

–

resistant to all β-lactams

•

Vancomycin normally used for MRSA

•

VRSA have appeared, still rare – genes

(31)

Divided into two groups on the basis of fermentation of

mannitol.

•

Group I –

•

Mannitol fermenters (Anaerobically).

•

Coagulase production.

•

Usually pathogenic in nature.

•

Group II –

•

Mannitol non fermenters.

•

Coagulase test negative.

•

Usually non pathogenic but cause opportunistic infections.

(32)

•

Skin microfloral

•

Infection associated with prosthetic

material like heart valves, shunts

•

Causes urinary tract infection in

cathetarised patients

(33)

Stapylococcus saprophyticus

•

Skin commensal

•

Cause of UTI in sexually active young

women

•

Usually sensitive to wide range of