Staphylococci and streptococci

Transcription

1 Staphylococci and streptococci Prof. Marianna Murdjeva, MD, PhD Dept. Microbiology and Immunology Medical University Plovdiv Lecture course in microbiology for English-speaking medical students

2 Staphylococci - nomenclature family Micrococcaceae genus Staphylococcus Species many! Most important: S. aureus, S. epidermidis, S. saprophyticus

3 Morphology Shape: cocci Size: 1 m Arrangement: clusters (grape-shaped) Gram stain: (+) Additional structures: capsule (slime), no spores and flagella

4 Biology Respiration: facultative anaerobes Growth: 37 0 С, рн Culture: broth media: glucose broth agar: 5% blood agar Resistance: high

5 S. aureus culture on blood agar

6 Pathogenic factors А. Nontoxigenic coagulase and clumping factor (CF) protein А staphylokinase (fibrinolysin) hyaluronidase DNA-ase beta-lactamase urease catalase

7 Pathogenic factors B. Toxigenic hemolysins - leucocydine enterotoxins exfoliatin toxin of staphylococcus shock syndrome TSS

8 Pathogenesis of staphylococcal infections Transmission: via hands, aerosoles, blood, food Entry: skin and mucosa, wounds, mouth, vagina, urethra Dissemination via blood in many organs and submucosa

9 S. aureus diseases Non-toxin mediated (local or systemic) soft tissue infections: pyoderma, folliculitis,furuncles, carbuncles, abscesses pneumonia, endocarditis, osteomyelitis, sepsis Toxin-mediated (toxigenic) food poisoning toxic shock syndrome (TSS) wound or menstrual toxic epidermal necrosis staphylococcal scalded skin syndrome (SSSS)

10 Staphylococcus aureus pus-forming local infections Superficial pyoderma folliculitis furuncle carbuncle wound infections Profound abscessus arthritis osteomyelitis pneumonia otitis sinuitis sepsis Toxin-mediates syndromes (food poisoning, TSS, SSSS)

11 Microbiological diagnosis of S. aureus infections Materials: pus-forming exudates, nasal swabs, blood culture, CSF, urine, feces, swabs from hospital environment, hands of medical personnel Direct microscopy: only in CSF and primary sterile materials Direct /fast/ tests for Ag detection: latex-agglutination and/or coagglutination Culture Identification: morphological, cultural (golden pigmentation and beta-hemolysis), biochemical (catalase, coagulase). Automated systems. Phage typing, plasmid typing or ribotyping (fingerprinting of genomic DNA restriction fragments) in epidemics

12 CF and coagulase tests

13 S. epidermidisnormal flora of skin and mucosa But also can cause: Pyogenic local infections Endoplastitis (catheter-associated infection; slime adhesion) Endocarditis (infection of artificial valves) Peritonitis (peritoneal dialysis infection) Sepsis

14 S. epidermidis culture on blood agar

15 S. saprophyticus normal flora of skin and mucosa but can cause cystitis in young women

16 Prophylaxis and therapy of staphylococcal infections The worst wound enemy is doctor s hand Semmelweis Hand disinfection Skin disinfection Catheter hygiene Antibiotic treatment: Cloxacillin and Cephalosporins if MSSA Beta-lactamase inhibitors But they are ineffective in MRSA strains, which produce betalactamases due to mec-a gene. MRSA infections are treated with Glycopeptides (Vancomycin, Teicoplanin), Linezolid, Tigecycline, Clindamycin

17 Streptococci - nomenclature family Deinococcaceae genus Streptococcus spp. S. pyogenes, S. agalactiae, S. pneumoniae Streptococci classification: 1. According to hemolysis on BA - 2. Serological (Lancefield s) - A,B,C,D,G.. (Particularly useful for distinguishing β-haemolytic /pyogenic/ streptococci) 3. Ecological - pyogenic, oral, gut and anaerobic streptococci

18 Streptoccoci most important features! Gram positive round bacteria Arranged in chains Facultative anaerobes Catalase-negative Classification: hemolysis alpha-hemolytic example: S. viridans beta-hemolytic examples: S. pyogenes, S. agalactiae

19 Streptoccoci - morphology Shape cocci with slightly oval shape Arrangement chains Size m Gram stain - /+/ positive Additional structures - capsule (GAS, S. pneumoniae). No spores and flagella.

20 Streptococcus - Gram stain

21 Streptococci - biology Respiration: facultative anaerobes Growth: 18-24h. More fastidious than staphylococci need proteins, blood, serum Cultures: broth media: pellet and snowflake phenomenon in glucose broth agar media: 5% BA small, semitransparent colonies with hemolysis ( Catalase negative Resistance. Enterococci are resistant to bile, alkaline ph and salts.

22 Streptococcus viridans culture on blood agar

23 Pathogenic factors of Group A Streptococci (GAS): Associated with bacterial body: - М protein: antiphagocytic, antico and cytotoxic activity - F protein: fibronectin-binding adhesion factor - capsule and slime Hemolysins: - Streptolysin О. Induces Ab production (AST) - Streptolysin S

24 Exotoxins: Pathogenic factors of Group A Streptococci (GAS): - erythrogenin (produces in scarlet fever) - cardiohepatic toxin - streptokinase Enzymes: - hialuronidase - DNA-ase

25 Pathogenic factors of Group A Streptococci (GAS): А. Pyogenic: local - tonsillitis (complications: phlegmone, osteomyelitis), otitis, sinuitis, rhinitis, impetigo, cellulitis invasive (generalized) meningitis, scarlet fever, endocarditis, erysipelas, sepsis, necrotizing fasciitis В. Post-streptococcal complications (autoimmune) rheumatism acute glomerulonephritis

26 Streptococcal tonsillitis

27 Pharyngitis strep throat

28

29 Other streptococcal disease Group B streptococci (for example S. agalactiae): neonatal meningitis and neonatal pneumonia sepsis sexually-transmitted diseases: cervicitis, urethritis Alpha-hemolytic (viridans) streptoccoci: dental caries and focal infections subacute endocarditis Enterococci: subacute endocarditis, urine and genital infections

30 Streptococcus agalactiae pyogenic local infections Vaginal infection/ carriage Sepsis in newborns Meningitis in newborns

31 Materials: nasopharyngeal swabs, CSF, blood culture, urine, genital swabs pus, wounds Microbiological diagnosis of streptococcal infections Direct microscopy in primary sterile materials Culture BA, glucose broth Identificatiom: catalase /-/ for group A and B - presumptive: morphological, cultural hemolysis, bacitracin sensitivity - confirmative: hippurate hydrolysis, САМР test for viridans streptococci : differentiation from pneumococci: optochin test, bile sensitivity, inulin, inoculation in mouse For enterococci: esculine hydrolysis, growth in milk with methylene blue, 6.5% NaCl, 9.6 ph Serology: antistreptolysin titer in rheumatism (AST)

32 CAMP factor increases haemolysis in red cells pre-treated with S.aureus toxin Group A Group B

33 Prophylaxis of streptococcal infections The worst wound enemy is doctor s hand Semmelweis Hand disinfection

34 Specific prophylaxis of streptococcal infections no vaccine for GAS vaccines for dental caries in progress non-specific immune stimulators Imudon, Bronhovaxom Specific therapy of streptococcal infections All GAS are Penicillin sensitive - 10 days treatment of strep pharyngitis! Macrolides - Azithromycin, Clarithromycin Cephalosporines

35 You can read this topic from: 1. Baron s Medical Microbiology 2. Todar s online textbook of bacteriology