Staphylococci and streptococci Prof. Marianna Murdjeva, MD, PhD Dept. Microbiology and Immunology Medical University Plovdiv Lecture course in microbiology for English-speaking medical students
Staphylococci - nomenclature family Micrococcaceae genus Staphylococcus Species many! Most important: S. aureus, S. epidermidis, S. saprophyticus
Morphology Shape: cocci Size: 1 m Arrangement: clusters (grape-shaped) Gram stain: (+) Additional structures: capsule (slime), no spores and flagella
Biology Respiration: facultative anaerobes Growth: 37 0 С, рн - 7.2-7.4 Culture: broth media: glucose broth agar: 5% blood agar Resistance: high
S. aureus culture on blood agar
Pathogenic factors А. Nontoxigenic coagulase and clumping factor (CF) protein А staphylokinase (fibrinolysin) hyaluronidase DNA-ase beta-lactamase urease catalase
Pathogenic factors B. Toxigenic hemolysins - leucocydine enterotoxins exfoliatin toxin of staphylococcus shock syndrome TSS
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
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)
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)
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
CF and coagulase tests
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
S. epidermidis culture on blood agar
S. saprophyticus normal flora of skin and mucosa but can cause cystitis in young women
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
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
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
Streptoccoci - morphology Shape cocci with slightly oval shape Arrangement chains Size - 0.5-1 m Gram stain - /+/ positive Additional structures - capsule (GAS, S. pneumoniae). No spores and flagella.
Streptococcus - Gram stain
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.
Streptococcus viridans culture on blood agar
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
Exotoxins: Pathogenic factors of Group A Streptococci (GAS): - erythrogenin (produces in scarlet fever) - cardiohepatic toxin - streptokinase Enzymes: - hialuronidase - DNA-ase
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
Streptococcal tonsillitis
Pharyngitis strep throat
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
Streptococcus agalactiae pyogenic local infections Vaginal infection/ carriage Sepsis in newborns Meningitis in newborns
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)
CAMP factor increases haemolysis in red cells pre-treated with S.aureus toxin Group A Group B
Prophylaxis of streptococcal infections The worst wound enemy is doctor s hand Semmelweis Hand disinfection
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
You can read this topic from: 1. Baron s Medical Microbiology www.ncbi.nlm.nih.gov/books 2. Todar s online textbook of bacteriology www.textbookofbacteriology.net/staph.html