THE STAPHYLOCOCCI II MBBS Dr Bansal V P

THE STAPHYLOCOCCI II MBBS Dr Bansal V. P.

Overview n Many species are medically important 1. S. aureus – n n 2. 3. most virulent species Most common cause of bacterial infections, food poisoning & toxic shock syndrome S. epidermidis – important cause of prosthetic implant infections S. saprophyticus – UTI, especially cystitis in women Dr Bansal V P

Staphylococci – General features n Gram +ve cocci arranged in grape like cluster n Facultative anaerobes n Produce catalase n Major component of normal flora in humans n n n Skin Nose Mucosal membranes Dr Bansal V P

Culture n n n NA – Moist, buterous, pigmented, opaque. BA – B hemolysis. MCA: No growth or tiny LF Selective media: Manitol Salt Agar Lithium chloride Polymyxin Tellurite Milk Agar Dr Bansal V P

Staphylococcus aureus – General features n n n n n Coagulase positive Ferments mannitol Beta hemolytic colonies on BA Produces golden yellow pigment Produces phospahatse Reduces tellurite producing black colonies Highly resistant non sporing bacteria Can grow in the presence of 10 – 15% Na. Cl. Resistance to Penicillin Dr Bansal V P

S. aureus - Epidemiology n Colonise skin, mucosa of anterior nares and vagina n Source of infection – human patients & carriers n n About 10 -30% of healthy persons carry staphylococci in the nose, about 10% in the perineum and hair. Vaginal carriage is about 5 -10%, which rises during menses. Modes of transmission – by direct contact or through fomites, by dust or by airborne droplets. Common cause of postoperative wound infection & other hospital cross infections – multidrug resistant strains. Dr Bansal V P

Staphylococcus aureus n Diseases produced by S. aureus can be due to 1. 2. 3. Infection – cocci gain access to damaged skin, mucosa or tissue, colonise at the site, multiply & cause damage Intoxication – bacterial toxins produced either in the host or preformed invitro Combination of infection & intoxication. Dr Bansal V P

Virulence Factors n The virulence of S. aureus depends on a number of factors. These can be: 1. Cell associated polymers and surface proteins, 2. Enzymes & 3. Toxins – cytolytic & superantigen exotoxins Dr Bansal V P

1. Cell associated polymers & surface proteins n n n Teichoic acid: - promotes colonization of host tissues, complement mediated opsonisation. Capsule (slime layer): - inhibits phagocytosis Protein A: - major component of cell wall, has many biological properties: Ø Antiphagocytic Ø Anticomplementary Ø Platelet injury Ø Binds to the Fc part of Ig. G Ø Role in coagglutination – for streptococcal grouping & gonococcal typings (Coagglutination test) Dr Bansal V P

1. Cell associated polymers & surface proteins n Clumping factor – Ø Ø a surface protein Also called “Bound Coagulase” Responsible for “slide coagulase test” – routinely used for the presumptive identification of S. aureus strains Saline suspension of S. aureus + drop of human plasma – clumping of cocci Dr Bansal V P

2. Enzymes n Coagulase – Clotting of human or rabbit plasma in the presence of ‘coagulase reacting factor’ (CRF) Ø Binds to prothrombin in the plasma & results in the conversion of fibrinogen to fibrin Ø Responsible for “tube coagulase test” – standard criterion for the identification of S. aureus Ø Eight types have been identified. Ø Most human strains form coagulase type A. Ø No evidence that it is a virulence factor Ø Dr Bansal V P

2. Enzymes n n n Staphylokinase (Fibrinolysin) – lysis fibrin clots, spread of infection Hyaluronidase – breaks down the connective tissue, initition & spread of infection Lipase – infection of skin & subcutaneous tissue Nuclease – degrades DNA Catalase – Ø enhance their survival in phagocytes by inactivating toxic H 2 O 2 & free radicals released after the ingestion of staphylococci. Dr Bansal V P

3. Toxins Cytolytic exotoxins: hemolysins (alpha, beta, gamma & delta), leucocidins - membrane active substances A. Alpha hemolysin I. n Leucocidal, cutotoxic, dermonecrotic, neurotoxic, lethal on IV innoculation in rabits. Toxic to macrophages, muscle tissue, renal cortex, & circulatory system Beta hemolysin II. n Sphingomyelinase - damages membranes rich in this lipid Leucocidin (PVL) III. n important factor in necrotizing skin infections. Dr Bansal V P

3. Toxins Superantigen exotoxins B. I. III. Enterotoxin: Eight antigenic types - A, B, C 1 to 3, D, E and H & I causes food poisoning Toxic shock syndrome toxin (TSST) Exfoliative (epidermolytic toxin): Type A &B Dr Bansal V P

Pathogenicity (staphylococcal diseases) Dr Bansal V P

Pathogenicity Skin & soft tissue infections 1. n n Localized skin infection - Folliculitis, furuncle (boil), carbuncle, abscess (particularly in breast), wound infection (surgical, traumatic), impetigo Deep, localized infections – Osteomyelitis (S. aureus is the most common cause), arthritis (septic arthritis in children) Respiratory tract infections 2. n bronchopneumonia, tonsillitis, pharyngitis, sinusitis, lung abscess, empyema Dr Bansal V P

Pathogenicity 3. CNS infections – abscess, meningitis, intracranial thrombophlebitis 4. Endovascular – bacteremia, septicemia, pyemia, endocarditis 5. Urinary tract infection often in association with local instrumentation, implants or diabetes 6. Nosocomial infections – wound infection, catheter associated bacteremia. Dr Bansal V P

Pathogenicity Staphylococcal food poisoning 7. n n n n Occurs 1 to 6 hrs after consumption of food contaminated with preformed toxins (enterotoxins – very fast acting) Nausea, vomiting, abdominal cramps & diarrhoea Self limiting condition, 1 to 3 days Toxins are resistant to heat, resistant to cooking Highest risk of contamination: sliced meat, puddings, pastries, sandwiches, milk & cheese Source of infection – food handler Type A enterotoxin is responsible for most cases Dr Bansal V P

Pathogenicity Toxic shock syndrome 8. n n Caused by TSST-1 (formerly known as Enterotoxin F): responsible for 75% of TSS, including all menstrual (tampon related TSS) cases Fatal multisystem disease Dr Bansal V P

Tampon - Associated with outbreak of toxic shock syndrome. Dr Bansal V P

Signs And Symptoms : TSS n n n n High grade fever and/or chills Hypotension Nausea and/or vomiting Profuse watery diarrhea with abdominal pain Mucosal hyperemia (vaginitis, conjunctivitis) & erythematous rash which desquamates in 1 -2 weeks Myalgias and/or arthralgias Headache Confusion (more common with staphylococcal TSS than with streptococcal TSS) Dr Bansal V P

Pathogenicity Staphylococcal scalded skin syndrome (SSSS) 9. n n Exfoliative skin disease – outer layer of epidermis gets separated. Severe form of SSSS is 1. 2. n “Ritter’s Disease” in newborns and Toxic epidermal necrolysis in older patients Milder forms are 1. 2. Pemphigus neonatorum Bullous impetigo Dr Bansal V P

SSSS n Signs And Symptoms: n n n Fever Generalized erythema skin slips off with gentle pressure leaving wet red areas (Nikolsky sign) exfoliation or desquamation painful skin Treatment: n n Fluid rehydration Topical wound care: saline AND topical antibiotic ointment Dr Bansal V P

Laboratory diagnosis n Specimen – depends on type of lesion 1. 2. 3. 4. 5. n Pus - Suppurative lesion Sputum – respiratory tract infection Feces & remains of food – food poisoning Blood – septicemia Nasal swab – detection of carriers Microscopy n Gram stain – gram +ve cocci in clusters Dr Bansal V P

Laboratory diagnosis n Culture – specimens are plated on 1. 2. 3. NA - golden yellow colony BA – hemolytic colonies Selective media – Ludlam’s media, Mannitol salt agar (MSA) MSA Dr Bansal V P

Laboratory diagnosis Biochemical tests n 1. Catalase test – using 3% H 2 O 2 : all Staphylococci are catalase positive, gives effervescence Dr Bansal V P

Laboratory diagnosis Biochemical tests n 2. n Coagulase test – S. aureus is coagulase +ve Done by two methods n n n Slide coagulase test – detects bound coagulase (clumping factor) Tube coagulase test – detects free coagulase Bacteriophage typing - for epidemiological purposes Dr Bansal V P

Staphylococcus aureus Coagulase POS Coagulase NEG Dr Bansal V P

Coagulase-negative Staphylococci (CONS) n n n S. epidermidis S. saprophyticus S. haemolyticus S. hominis S. capitis Dr Bansal V P

General features of CONS n n n Important agents of nosocomial infections Associated with increased use of implants such as CSF shunts, IV lines, cardiac valves, pacemakers, artificial joints, urinary catheters Morphologically similar to S. aureus, however they form white colonies, and are coagulase negative. Dr Bansal V P

S. epidermidis Dr Bansal V P

Disease Caused By Coagulasenegative Staphylococci n n Prosthetic valve endocarditis Meningitis Peritonitis UTI in pregnant women (S. saprophyticus) Dr Bansal V P

Differences between the major species of Staphylococci Characters S. aureus S. epidermidis S. saprophyticus Coagulase + - - Mannitol fermentation + - - Novobiocin sensitivity S S R Phosphatase + + - Dr Bansal V P

Treatment n Drain infected area n Deep/metastatic infections n n n Endocarditis n n n semi-synthetic penicllins cephalosporins erythromycin clindamycin semi-synthetic penicillin + an aminoglycoside Life threatening staphylococcal infections, Vancomycin is the drug of choice However, the appropriate antibiotic should be chosen based on AST. Dr Bansal V P

Drug Resistance in Staphylococci First developed resistance against Penicillin Resistance to penicillin can be due to: n n 1. 2. 3. 4. 5. Mutation in chromosomal genes Acquisition of resistance genes as extrachromosomal plasmids, transducing particles, transposons, or other types of DNA inserts. Production of penicillinases Changes in bacterial surface receptors Development of tolerance Dr Bansal V P

Drug Resistance in Staphylococci n To combat resistance due to penicillinase, Methicillin was developed & now methicillin resistant strains have evolved due to n n Chromosomal acquisition of gene coding for a modified PBP Plasmid borne resistance to erythromycin, tetracyclines, aminoglycosides and almost all clinically useful antibiotics Dr Bansal V P

MRSA (Methicillin resistant S. aureus) n n had a medical procedure HA- MRSA (such as dialysis, surgery, catheters) community-associated (CA)-MRSA infections skin infections: abscesses, boils, and other pus -filled lesions Dr Bansal V P

MRSA Reservoirs n n In hospitals, the most important reservoirs of MRSA are infected or colonized patients HOSPITAL PERSONNEL: commonly identified as a link for transmission between colonized or infected patients. Dr Bansal V P

Mode Of Transmission: MRSA n via hands (especially health care workers') which may get contaminated by contact with 1. 2. 3. colonized or infected patients colonized or infected body sites of the personnel themselves, devices, items, or environmental surfaces contaminated with body fluids containing MRSA. Dr Bansal V P

Treatment: MRSA n Glycopeptides 1. 2. Vancomycin Teicoplanin Dr Bansal V P

Thank You Dr Bansal V P