Staphylococcus (2)

Staphylococcus

Eva L. Dizon, M.D.,FPPS,FPIDSP

Staphylococcus

Staphyle- Bunch of grapes0.5 to 1 umNon motileAerobic or Facultative AnaerobicCatalase positiveGrow in media containing 10% NaCl at temp 18 to 40 CPresent on the skin and mucuos membrane

Species S. aureus S. epidermidis S. saphrophyticus S. capitis S. haemolyticus Micrococcus sp Stomatococcus mucilaginosus Alloiococcus otitidis

Physiology and Structure

Structure

StructureCAPSULE- loose fitting polysaccharide layer (slime layer)

- protects bacteria by inhibiting chemotaxis and phagocytosis

- facilitates adherence of bacteria to catheters and synthetic materials

PEPTIDOGLYCAN- half of the cell wall

- consist of layers of glycan chains with alternating subunits of N –acetylmuramic acid and N- acetylglucosamine

- has endotoxin like activity

Structure

TEICHOIC ACID- phosphate containing polymers bound to peptidoglycan layer or to cytplasmic membrane

- mediates the attachment of staphylococcus to mucosal surfaces

S. aureus

Ribitol teichoic acid with N-acetylglucosamine ( Polysaccharide A)

S. epidermidis

glycerol teichoic acid with glucosyl residues (polysaccharide B)-

PROTEIN A- covalentlylinked to peptidoglycan

- has affinity to Fc receptor of Ig

- blocks opsonization and phagocytosis

Structure

CYTOPLASMIC MEMBRANE- osmotic barrier for the cell and provides an anchorage for the

biosynthetic and respiratory enzyme

COAGULASE and other SURFACE PROTEIN-Clumping factor or Bound coagulase binds fibrinogen convert to insoluble fibrin causing staphylococcus to

clump

- collagen , elastin and fibronectin binding protein

ToxinsA. 5 Cytolytic or membrane damage toxin

1. Alpha

2. Beta

3. Gamma

4. Delta

5. Panton Valentine

B. 2 Exfoliative toxin

C. 8 Enterotoxin

D. Toxic Shock Syndrome Toxin(TSST 1)

Cytotoxins

Lyse neutrophils release of lysosomal enzymes damage sorrounding tissues

Alpha toxin – disrupts the smooth muscle in blood vessels

- toxic to erythrocytes, hepatocytes, platelets, cultivated cells

- integrates to host cell membrane pores efflux of K and influx

of Na,Ca osmotic swelling cell lysis

- septic shock

Cytotoxin

Beta Toxin - Sphingomyelinase C

- specific for sphingomyelin and lysophosphatidylcholine

- toxic to RBC, WBC,Macrophage and fibroblast

- catalyze hydrolysis of membrane phospholipids in susceptible cells

- tissue destruction and abscess formation

Delta toxin- disrupts cell membrane

- toxic to variety of cells

Cytotoxin

Gamma toxin and Panton Valentine

-both damage membrane of susceptible cells

- lyze nuetrophils and macrophages

- cell lysis is mediated by pore formation

-Cause necrotizing skin infection

--PVL -potent leukotoxicity

Exfoliative toxin ETA - heat stable ETB – heat labile Serine protease Exposure splitting of desmosomes or

intercellular bridges in the stratum granulosum epidermis

Common in neonates – ETA and ETB binds to GM4 like glycolipids present in neonates

Enterotoxin A-E, G-I Stable to heating , resistant to

hydrolysis Enterotoxin A – most commonly

associated with disease Enterotoxin C and D- contaminated milk

products Enterotoxin B- Pseudomembranous

colitis Superantigens

TSST-1

Formerly pyrogenic exotoxin C and entertoxin F

Induce cytokine release from macrophage and T lymphocytes

Increase sensitivity to endotoxin Produce leakage of endothelial

cells Penetrate mucosal barrier

Staphylococcal enzymes

convert fibrinogen react with globulin plasma factor insoluble fibrin to form

staphylothrombin

Clumping

Cause formation of fibrin layer around abscess protecting staphylococcus from phagocytosis

Coagulase

Bound Free

Staphylococcal enzymes

Catalase- catalyze the conversion of toxic hydrogen peroxide to water and oxygen

Hyalurodinase- hydrolyzes hyaluronic acid in acellular matrix of connective tissue spread

Staphylococcal enzymes

Fibrinolysin- staphylokinase . Dissolve fibrin clot- aid in bacterial spreading

Lipases hydrolyse lipid to ensure survival in sebaceous areas of the body

Nuclease Penicillinase- plasmid Fatty acid modifying enzyme

(FAME)- antibacterial lipid- prolonged bacterial survival

Epidemiology

Transient colonizer of skin Nasal carriage – anterior

nasopharynx Persistent carrier – hospital

personnel Killed by high temperature and

disinfectant Direct contact, fomites Handwashing

Sites of infection

Ritters disease or SSSS

Perioral erythema spread body bullous desquamation

Nikolsky sign Bullous impetigo – localized form

of SSSS- localized blister - culture positive

SSSS

most commonly in children and neonates. Starts abruptly with perioral (around the mouth) erythema with sunburn-like rash rapidly turning bright red spreading to bullae (large vesicle appearing as a circumscribed area) in 2-3 days and desquamating (peeling) within 5 days.

Staphylococcal food poisoning

Ham , salted pork, custard, potato sald, ice cream

Hands, Nasal carriage I.P. – 4 hrs Vomiting, diarrhea, abd. pain

Toxic shock syndrome

Growth of organism in vagina or wound release of TSST-1

Fever, macular erythematous rashes, hypotension, multiorgan involvement, desquamation of palm and sole

TSS

Cutaneous infection

Impetigo Folliculitis Furuncle Carbuncle Wound infection

Folliculitis - superficial folliculitis is essentially a staphylococcal impetigo in which a small area of erythema develops around a hair follicle and subsequently becomes a dome-shaped pustule.

Carbuncle - a deep-seated pyogenic infection of the skin and subcutaneous tissues.

Impetigo - a contagious superficial pyoderma, caused by S. aureus and Streptococcus pyogenes, that begins with a superficial flaccid vesicle which ruptures and forms a thick yellowish crust, most commonly occurring in the face.

Others

Bacteremia Endocarditis Pneumonia Empyema Osteomyelitis Septic arthritis

Pneumonia

S.Epidermidis and CNS

Endocarditis- native or artificial valves

Catheter and shunt infection Prosthetic joint infection UTI

Laboratory diagnosisMicroscopy

Culture

Grow rapidly within 24 hours

Large, golden, smooth colonies

Blood Agar- hemolysis

Selective media- add NaCl 7.5%

Mannitol – fermented by S. aureus

Serology

Insensitive

Antibody against teichoic acid

Bacteremia. Endocarditis

After 2 weeks

Culture – S. aureus

S. epidermidis S. saphrophyticus

Coagulase test

Showing positive (upper tube) and negative (lower tube) coagulase tests.

Mannitol Salt Agar test

Identification

Biochemical testingCoagulase Heat stable nucleaseAlkaline phospatase

Mannitol fermentation test

Treatment and Prevention

Semisynthetic penicillinase resistant penicillin

Resistance ( mecgene A –codes for PBP 2’)