Presented by Dr zena makkie abd-alkareem

Transcription

1 Presented by Dr zena makkie abd-alkareem

2 staphylococci Introduction The staphylococci are derived from Greek word STAPHYLO (bunch of grape) gram-positive spherical cells, usually arranged in grape-like irregular clusters Some are members of the normal flora of the skin and mucous membranes of humans; others are pathogenic They grow readily on many types of media, ferment CHO and producing pigments varying from white to deep yellow The pathogenic staphylococci often hemolyze blood, coagulate plasma, and produce a variety of extracellular enzymes and toxins.

3 Staphylococci has at least 35spps Can be classified into two main types: Coagulase +ve staph. Staph.aureus(pyogenic). Coagulase ve staph. Staph.albus(epidermedis). Staph.citreus(saprophyticus).

4 The coagulase-negative staphylococci are normal human flora and sometimes cause infection, often associated with implanted appliances and devices, especially in very young, old, and immunocompromised patients. Approximately 75% of these infections caused by coagulase-negative staphylococci are due to S epidermidis

5 Morphology & Identification Typical Organisms Staphylococci are spherical cells about 1 Mm in diameter arranged in irregular clusters Single cocci, pairs, tetrads, and chains are also seen in liquid cultures. Young cocci stain strongly gram-positive; on aging, many cells become gram-negative. Staphylococci are nonmotile and do not form spores. Micrococcus spp often resemble stap.they are found free_living in the enviroment and form regular pakets of four or eight cocci,micrococcus spp can cause disease in immunocompramized pt.

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7 culture Staphylococci grow readily on most bacteriologic media under aerobic and facultative anaerobic conditions. They grow most rapidly at 37 C but form pigment best at room temperature (20 25 C).. Colonies on solid media are round, smooth, raised, glistening and pigmented, pigments appear only on nutrient agar. S aureus usually forms golden yellow colonies. S epidermidis form white on primary isolation; many colonies develop pigment only upon prolonged incubation S saprophyticus forms lemon yellow colonies.. No pigment is produced anaerobically or in broth. Various degrees of hemolysis are produced by S aureus and occasionally by other species Some staph are anaerobic like staph.sacroleticus&staph.aureus sub spp anaerobus but they don't produce Catalase.

8 GROUTH CHARECTARESTICS The staphylococci produce catalase, which differentiates them from the streptococci.. Staphylococci slowly ferment many carbohydrates, producing lactic acid but not gas.. Proteolytic activity varies greatly from one strain to another. Staphylococci are relatively resistant to drying, heat they withstand 50 C for 30 minutes and 9% sodium chloride

9 are readily inhibited by certain chemicals, eg, 3% hexachlorophene. Staphylococci are variably sensitive to many antimicrobial drugs and resistance falls into several classes: resistant to many penicillins like: penicillin G, ampicillin, ticarcillin, piperacillin, and similar drugs due to B lactemase production under plasmid control,the plasmids are transmitted by transduction and perhaps also by conjugation,there are 4 types of β_lactemase enz.

10 Resistance to nafcillin, methicillin and oxacillin is independent of B-lactamase production its under chromosomal control through special gene known as mec A gene. The resistance is related to the lack of certain PBPs in the organisms. Resistance to vancomycin Staphylococci are suseptable to vancomycin if the (MIC) is 2 g/ml; of intermediate susceptibility if the MIC is 4 8 g/ml; and resistant if the MIC is 16 g/ml. Strains of S aureus with intermediate susceptibility to vancomycin have been isolated in Japan. These are often known as vancomycinintermediate S aureus, or "VISA." They generally have been isolated from patients with complex infections who have received prolonged vancomycin therapy.. The mechanism of is associated with increased cell wall synthesis and alterations in the cell wall and is not due to the van genes found in enterococci. resistance

11 vancomycin-resistant S aureus (VRSA) strains were isolated from patients in the United States. The isolates contained the vancomycin resistance gene vana from enterococci.. Plasmid-mediated resistance to tetracycline's, erythromycins, aminoglycosides, and other drugs is frequent in staphylococci A Tolerance" implies that staphylococci are inhibited by a drug but not killed by it ie, there is great difference between minimal inhibitory and minimal lethal concentrations of an antimicrobial drug. Patients with endocarditis caused by a tolerant S aureus may have a prolonged clinical course compared with patients who have endocarditis caused by a fully susceptible S aureus. Tolerance can at times be attributed to lack of activation of autolytic enzymes in the cell wall.

12 ANTIGENIC STRUCTURE OF STAPHYLOCOCCI capsule some S aureus strains have capsules, which inhibit phagocytosis by PMN cells unless specific antibodies are present Peptidoglycan a polysaccharide polymare provide a rigide exoskeleton but it is destroyed by strong acid or exposure to lysozyme, It elicits production of interleukin-1 (endogenous pyrogen) and opsonic antibodies by monocytes, and it can be a chemoattractant for PMN Teichoic acids which are polymers of glycerol or ribitol phosphate, are linked to thepeptidoglycan and can be antigenic.

13 continue Protein A is a cell wall component of many S aureus strains that binds to the Fc portion of IgG molecules except IgG 3 Clummping factor(coagulase) most strain of S.aureus have coagulase on the cell wallsurface coagulase binds nonenzymatically to fibrinogen, yielding aggregation of the bacteia ENZ&TOXINS Staph. can produce disease both through their ability to multiply and spread widely in tissues and through their production of many extracellular substances. Some of these substances are enzymes; others are considered to be toxins like:

14 Toxins: Pore-forming toxins create channels to disturb cellular homeostasis Exotoxins include several toxins: Alpha toxin is apotent hemolysin Beta toxin is atoxic to many kind of cells including RBC those toxins &the other Gamma;Delta are antigeniticly distinct

15 Exfoliative Toxins These epidermolytic toxins of S aureus are two distinct proteins of the same molecular weight. Epidermolytic toxin A is a chromosomal gene product and is heat-stable (resists boiling for 20 minutes). Epidermolytic toxin B is plasmidmediated and heat-labile. The epidermolytic toxins yield the generalized desquamation of the staphylococcal scalded skin syndrome by dissolving the mucopolysaccharide matrix of the epidermis. The toxins are superantigens Leukocidin: This toxin of S aureus has two components. It can kill white blood cells of humans and rabbits. The two components act synergistically on the white blood cell membrane. This toxin is an important virulence factor in community associated methicillin resistant S aureus infections

16 Toxic Shock Syndrome Toxin Most S aureus strains isolated from patients with toxic shock syndrome produce a toxin called toxic shock syndrome toxin-1 (TSST-1), which is the same as enterotoxin F. TSST-1 is the prototypical superantige. The toxin is associated with fever, shock, and multisystem involvement, including a desquamative skin rash. The gene for TSST-1 is found in about 20% of S aureus isolates

17 Enterotoxins There are at least 6(A-F)soluble toxins produced by about50% of S.aureus strains.like TSST-1, the enterotoxins are superantigens. The enterotoxins are heat-stable and resistant to the action of gut enzymes. An important cause of food poisoning, enterotoxins are produced when S aureus grows in carbohydrate and protein foods. Ingestion of 25 g of enterotoxin B results in vomiting and diarrhea. The emetic effect of enterotoxin is probably the result of central nervous system stimulation (vomiting center) after the toxin acts on neural receptors in the gut

18 Enzymes Catalase all staph produce catalase Coagulase S aureus produces coagulase, an enzyme-like protein that clots oxalated or citrated plasma. Coagulase may deposit fibrin on the surface of staphylococci, perhaps altering their ingestion by phagocytic cells.there are 2 serological distinct types of coagulase free&clumping factor(acell bounding coagulase) Staphylokinase resulting in fibrenolysis Lipase Hyalorodinase(spreading factor) B lactemase Proteinases

19 Pathogenesis Staphylococci, particularly S epidermidis, are members of the normal flora of the human skin and respiratory and gastrointestinal tracts. Nasal carriage of S aureus occurs in 20 50% of humans. Staphylococci are also found regularly on clothing, bed linens, and other fomites in human environment Sites of carrying staph. Are nose, skin fold,axilla,vagina&perinum The pathogenic capacity of a given strain of S aureus is the combined effect of extracellular factors and toxins together with the invasive properties of the strain. At one end of the disease spectrum is staphylococcal food poisoning, attributable solely to the ingestion of preformed enterotoxin; at the other end are staphylococcal bacteremia and disseminated abscesses in all organs. Pathogenic, invasive S aureus produces coagulase and tends to produce a yellow pigment and to be hemolytic. Nonpathogenic, noninvasive staphylococci such as S epidermidis are coagulase-negative and tend to be nonhemolytic. Such organisms rarely produce suppuration but may infect orthopedic or cardiovascular prostheses or cause disease in immunosuppressed persons. S saprophyticus is typically nonpigmented, novobiocin-resistant, and nonhemolytic; it causes urinary tract infections in young women

20 Diseases cauced by staph.aureus 1.Superficial infections: charecterized by intense suppuration,local tissue necrosis &followed by local abscess formation. Impetigo(pyoderma): Skin infection caused by staph aureus,but may also be caused by staph epidermidis&sterptococci.it characterized by formation of vesicles filled with serious or mucinus fluid.later on these lesions dry out with scabs form over the vesicles. Folliculitis,furuncle(boil),styes: Hair follicles infection,if the infection is limited called folliculitis,but if ther is involvment that may required local drinage called furencles.when the infection involve the eyelid is called stye Carbuncles: when multiple interconected abcesses involving hair follicles,sebacious gland &the surrowending tissues. postoperative staphylococcal wound infection or infection following trauma (chronic osteomyelitis subsequent to an open fracture, meningitis following skull fracture).

21 2.Deep infections: Osteomylitis: Blood born infection. Dissemenated infection&bacteremia endocarditis,. Meningitis,mltiple brain abscess. pulmonary infection,multiple lung infection.

22 Toxin mediated infection 1 Food poisoning due to staphylococcal enterotoxin short incubation period (1 8 hours); violent nausea, vomiting, and diarrhea; and rapid convalescence. Self limited disease. There is no fever. Recovery in 24 hr. 2 Toxic shock syndrome abrupt onset of high fever, vomiting, diarrhea, myalgias, a rash, and hypotension with cardiac and renal failure in the most severe cases. It often occurs within 5 days after the onset of menses in young women who use tampons but it also occurs in children or in men with staphylococcal wound infections. The syndrome can recur.

23 Scalded skin syndrom (sss) Caused by s.aureus that produce exfoleative toxin Involve neonate and children less than 5 y blisters rupture dermis exposure skin peels Disease caused by coagulase ve staph. 1. Community acquired s.saprophyticus =UTI in women,staph.saprophyticus has tissue tropism to UTI epth (uroepithelal &priurithral tissue)in greater %than other tissue 2. Hospital acquired s.epidermedis =colonization of prosthesis (heart valve). 3. There is staph.intermedus that isolate from several type of infection in dogs & man can get infection from direct contact with infected dogs through a wound or bite cutanus or even internal or systemic infection 4. Staph.Lutrae can cause infection in domestic animal like dogs &cats human gets infection through direct contact with infected animal like zoo workers,veteranien &farmers

24 Factors that predispose individual to serious staph.aureus infection 1. Defect in opsonization by antibody 2. Complement component deficiency like C3&C5 3. Defect in leukocyte chemotact factors either congenital like down syndrome or acquired like D.M,R.A 4. Defect in intracellular killing of bacteria following phagocytosis due to inability to activate membrane bounding system result in absence of peroxides &superoxidase killing enz from phacocytic vacuoles like in chronic granulomotus diseases & in lymphoblastic lymphoma 5. Skin injury like in eczima,burn &trauma 6. Presence of foreign body 7. Viral or bacterial infections as a complication 8. Chronic underlying disease like malignancy, heart disease,alcohlic person 9. Prophylactic or therapeutic antimicrobial administration

25 Virulence factors of staph. epidermis These bacteria produce a cell surface &extracellular macromolecules that initiate subsequent adherence to plastic surface of foreign body to form abiofilm mediated by capillary polysaccharide adhesion called(ps/a)also able to protect m.o from complement mediated phagocytic killing Other attachment mechanism is there ability to interact with different plasma or tissue component of the host that constitute the initial step in tissue colonization& establishment of infection in absence of foreign body

26 Diagnostic Laboratory Tests Specimens Surface swab pus, blood, tracheal aspirate, or spinal fluid,sputum&urine. Smears Typical staphylococci appear as gram positive cocci in clusters in Gram-stained smears of pus or sputum. It is not possible to distinguish saprophytic (S epidermidis) from pathogenic (S aureus) organisms on smears. Culture planted on blood agar plates give rise to typical colonies in 18 hours at 37 C, but hemolysis and pigment production may not occur until several days later and are optimal at room temperature. Specimens contaminated with a mixed flora can be cultured on media containing 7.5% NaCl; the salt inhibits most other normal flora but not S aureus. Mannitol salt agar or commercially available chromogenic media are used to screen for nasal carriers of S aureus and patients with cystic fibrosis Phenyl ethyl alcohol agar inhibit the growth of G-ve bacteria &allow the growth of G+ve bacteria

27 Testes used for identification of staphylococci Catalase Test: this test used to diferentiate staph +ve from streptococcus&pneumococcus _ve This test is used to detect the presence of cytochrome oxidase enzymes. A drop of 3% hydrogen peroxide solution is placed on a slide, and a small amount of the bacterial growth is placed in the solution. The formation of bubbles (the release of oxygen) indicates a positive test. Coagulase Test: this test used to diferentiate S aureus from other staphylococci The test is done by using citrated rabbit (or human) plasma diluted 1:5 is mixed with an equal volume of broth culture or growth from colonies on agar and incubated at 37 C. A tube of plasma mixed with sterile broth is included as a control. If clots form in 1 4 hours, the test is positive.

28 Susceptibility Testing Broth microdilution or disk diffusion susceptibility testing should be done routinely on staphylococcal isolates from clinically significant infections. Resistance to penicillin G can be predicted by a positive test forb - lactamase; approximately 90% of S aureus produce -lactamase. Resistance to nafcillin (and oxacillin and methicillin) occurs in about 35% of S aureus and approximately 75% of S epidermidis isolates. The gene coded for nafcillin resistance can be detected by PCR.

29 Serological&typing tests Serologic tests for diagnosis of S aureus infections have little practical value. Antibody to tecioc acid can be detected in prolonged deep infection(staph endocarditis) Molecular typing techniques have been used to document the spread of epidemic disease-producing clones of S aureus

30 Treatment 1 Tetracyclines are used for long-term treatment. In (acne, furunculosis) occur most often in adolescents. Similar skin infections occur in patients receiving prolonged courses of corticosteroids In acne, lipases of staphylococci and corynebacteria liberate fatty acids from lipids and thus cause tissue irritation. 2 (penicillin &cephalosporin).with drainage. Abscesses and other closed suppurating lesions. 3 Acute hematogenous osteomyelitis responds well to antimicrobial drugs. In chronic and recurrent osteomyelitis, surgical drainage and removal of dead bone is accompanied by long-term administration of appropriate drugs. 4 Bacteremia, endocarditis, pneumonia, and other severe infections due to S aureus require prolonged intravenous therapy with a B-lactamase-resistant penicillin 5. Vancomycin is often reserved for use with nafcillin-resistant staphylococci. 6 If the infection is found to be due to non--lactamase-producing S aureus, penicillin G is the drug of choice, but only a small percentage of S aureus strains are susceptible to penicillin G. 7 S epidermidis infections are difficult to cure because they occur in prosthetic devices where the bacteria can hides them selves also staph epidermidis more resistant to antibiotics than staph aureus

31 Epidemiology &control staph. Are colonizers of skin and mucosal surface they get entrance through trauma to skin &mucosal surface Direct transmission from person to other through direct contact &fomites of infected persons The mode of spread is imp in the hospitals where large proportions of medical staff and patients carry antibiotic resistant staph in their nose or skin Application of topical anti septic to nasal or per anal carriage site Pt of active staph lesions &carriers should be excluded from ICU,operating room&cancer chemotherapy areas Rifampicin coupled with oral antistaph drug sometimes provide long term supression&possibly cure of nasal carriage.

32 Thank you