STAPHYLOCOCCI

Definition: Gram +ve cocci arranged in clusters.

All Catalase test +ve # [ streptococci] .All Oxidase negative #

[Neisseria]

2

Gram positive cocci in clusters staphylococci

MSA NA BA

White colonies Pigmented golden yellow

1COLONIAL

MORPHOLOGY

Pigmented colonies of staph on NA

Complete ( β )2

HEAMOLYSIS

Hemolytic staphylococci on BA

Hemolytic staphylococci on BA

Ferment mannitol

(yellow color)

Don’t Ferment mannitol (red

color )

3FERMENTATION

Staphylococci on mannitol salt agarpathogenic (F+) non pathogenic(F-)

Staphylococci on mannitol salt agar pathogenic (F+)

Oxidase Catalase-ve +ve

4BIOCHEMICAL

REACTION

Catalase

2H2O2 O2 + 2H2OStreptococci vs. Staphylococci

Differential Characteristics

Catalase POS

Staphylococcus

Catalase NEG

S. aureus

Coagulase

Fibrinogen Fibrin

Differential Characteristics

Coagulase NEG

Coagulase POS

Staphylococcus aureus

COAGULASE TEST

Staphylococci

Coagulase +ve

(pathogenic)

Coagulase –ve

(non-pathogenic)

Staph. aureusStaph.

epidermidis

Staph.

saprophyticus

Pathogenic Non-pathogenic

1- coagulase +ve 1- Coagulase –ve.

Culture media 2- Pigmented golden yellow on NA 2- White colonies.

3- Haemolysis on BA. 3- No hemolysis on BA

4- Ferment mannitol on MSA . 4- Don not ferment

mannitol.

Biochemical reactions of staphylococci

Coagulase +ve Coagulase –veMannitol fermentation +ve Mannitol fermentation –ve

1-Novobiocin sensitive.* S. epidermidis.

2-Nov. resistant* S. saprophyticus.

Difference between pathogenic and non pathogenic

Novobiocin testStaph epidermidis ---S Staph saprophytics ---R

Staph. aureus has several cell wall components and antigens: 1- Peptidoglycan polymer. 2- Telchoic acids that mediate adherence of the organism to mucosal cells.

3- Protein A: 90% of staph. aureus posses this antigen. It is antiphagocytic. Protein A binds IgG molecule non-specifically through Fc portion leaving specific Fab sites free to combine with specific antigen. When suspension of such sensitized staphylococci is treated with homologous (test) antigen, the antigen combines with free Fab sites of IgG attached to staph cells leading to visible clumping of staphylococci within two minutes. It is known as “coagglutination”.

Antigenic structure

4- Clumping factor: which binds to fibrinogen yielding aggregation of the bacteria.

5- Capsular polysaccharide: A few strains of staph. aureus are encapsulated and tend to be more virulent that non capsulated strains.

6- Surface receptors: for specific bacterial phages, permit phage typing for epidemiological purposes.

Antigenic structure

Toxins and Enzymes produced by Staph. aureus

Toxins :

Hemolysin

Leucocidin

Toxic shock syndrome

toxin-1 (TSST-1)

Exfoliative toxin

Enterotoxin

Enzymes :

Coagulase enzyme

Staphylokinase

Hyaluronidase

B- lactamase

(penicillinase )

DNAase

25

Diseases produced by Staph. aureus

Pyogenic infection (enzymes)DisseminatedFocal

Toxin mediated: Food poisoning .Toxic shock syndrome .Scalded skin syndrome.

Staphylococcal Disease

27

Range from localized to systemicLocalized cutaneous infections – invade skin

through wounds, follicles, or glandsfolliculitis – superficial inflammation of hair follicle;

usually resolved with no complications but can progress

furuncle – boil; inflammation of hair follicle or sebaceous gland progresses into abscess or pustule

carbuncle – larger and deeper lesion created by aggregation and interconnection of a cluster of furuncles

impetigo – bubble-like swellings that can break and peel away; most common in newborns

28

Nonbullous Lesions of Impetigo

Figure 21.4

Staphylococcal Disease

30

Systemic infections osteomyelitis – infection is established in

the metaphysis; abscess formsbacteremia - primary origin is bacteria

from another infected site or medical devices; endocarditis possible

31

Figure 23.4

Bacterial Endocarditis

Staphylococcal Disease

33

Toxigenic disease food intoxication – ingestion of heat stable

enterotoxins; gastrointestinal distressstaphylococcal scalded skin syndrome –

toxin induces bright red flush, blisters, then desquamation of the epidermis

toxic shock syndrome – toxemia leading to shock and organ failure

Lesions of Skin Syndrome

Figure 21.5

35

Staphylococcal Food Poisoning

Pathogen Staphylococcus aureusSymptoms Nausea, vomiting, and

diarrhea

Intoxication/Infection IntoxicationEnterotoxin (superantigen)

Diagnosis Phage typingTreatment None

Events in Staphylococcal Food Poisoning

Figure 25.6

Importance in hospital infection:· Carriage of staph. by medical personnel→hospital

infection (nosocomial infection of patients) or food poisoning.

Carriage in : Nose.§Hands.

Tracing the source of infection = (epidemiological study of the isolated strains)phage typing. Detection of carriers nasal or skin swabblood agar. staph (identification).

Carriers of Staph. aureus

40

Phage typing

Figure 10.13

Phage Typing

Methicillin-resistant Staph.aureus (MRSA)

Resistant to all beta lactam antibiotics. resistant to other drugs (aminoglycosides).

sensitive to vancomycin.

Other Staphylococci

45

Coagulase-negative staphylococcus; frequently involved in nosocomial and opportunistic infections

S. epidermidis – lives on skin and mucous membranes; endocarditis, bacteremia, UTI

S. saprophyticus – infrequently lives on skin, intestine, vagina; UTI

Coagulase-Negative Staphylococci

Staphylococcus epidermidis

S. saprophyticus

Novobiocin testStaph epidermidis ---S Staph saprophytics ---R

Staph. saprophytics:urinary tract infections in

young females

Staphylococcal Biofilms

Figure 21.3