Microbiologie

• Taxonomy


  The study of general principles of scientific classification and naming organisms
• Classification


  Organisation of organisms into progressively more inclusive groups (taxons) by either phenotypic similarities or evolutionary relationships
• Nomenclature


  Systematic naming of organisms based on international rules according to its characteristics
• Identification


  Refers to the practical use of a classification scheme
• Taxonomic levels


  • Family
  • Genus
  • Species
  • Subspecies
  • Strain
• Genus


  Written in upper case
• Species


  Written in lower case
• Genus and species should be written in italics or underlined (if handwritten)
• Staphylococcus genus


  • Staphylococcus aureus
  • Staphylococcus epidermidis
  • Staphylococcus saprophyticus

  
• Coagulase


  • Positive
  • Negative (CNS)
• Staphylococcus aureus


  • Very virulent
  • Multiple pathogenicity factors
  • Resistant to desiccation, temperature, salt, despite not forming spores
  • Colonizers of our skin and mucous membranes (moist environments: nose, armpits)

  
• Broken barriers are essential in the pathogenesis of Staphylococcus aureus

  
• Staphylococcus aureus


  • Gram-positive cocci
  • Grouped in tetrads or clusters
  • Facultative anaerobes
  • Growth in standard media (nonselective) such as blood agar at 37°C
  • Golden colonies (aureus)
  • Beta-hemolysis on blood agar. Complete hemolysis

  
• Coagulase


  Transforms fibrinogen into fibrin
• Coagulase can be negative or positive
• Staphylococcus aureus


  • Golden colonies
  • Complete hemolysis on blood agar

  
• Normal microbiota (skin and mucosas)


  Pathogenicity favored by: Broken mucocutaneous barriers, Impaired immunity (diabetes, chemotherapy, corticosteroids)
• Structural virulence factors of Staphylococcus aureus

  • Teichoic acids
  • Capsule (in some cases)

  
• Toxins produced by Staphylococcus aureus

  • Cytotoxins α, β, γ, δ (β-hemolysis in blood agar)
  • Panton-Valentine Leukocidin
  • Thermostable Enterotoxins (Gastroenteritis/Food poisoning)
  • Exfoliatin (Scalded Skin Syndrome)
  • Toxic Shock Syndrome Toxin (TSST-1)
• Enzymes produced by Staphylococcus aureus

  • Coagulase
  • Hyaluronidase
  • Catalase
  • DNase
  • Lipase
• Purulent infections caused by Staphylococcus aureus

  • Folliculitis
  • Furuncle
  • Hydradenitis
  • Paronychia
  • Impetigo
  • Cellulitis
  • Wound infection

  
• Systemic infections caused by Staphylococcus aureus

  • Bacteremia
  • Sepsis
  • Endocarditis
  • Pneumonia
  • Arthritis/Osteomyelitis
  • Meningitis
• Manifestations caused by Staphylococcus aureus toxins

  • Staphylococcal Food Poisoning (Gastroenteritis)
  • Staphylococcal Scalded Skin Syndrome (SSSS)
  • Toxic Shock Syndrome (TSST)

  
• Coagulase-Negative Staphylococci


  • Gram-positive cocci
  • Grouped in tetrads or clusters
  • Facultative anaerobes (oxidative and fermentative metabolism)
  • Growth in standard media (nonselective) such as blood agar at 37°C
  • White or gray colonies. Non hemolytic on blood agar
  • No coagulase enzyme (Coagulase -)
  • Production of catalase (catalase +)
• Coagulase-Negative Staphylococci


  Less virulent than S. aureus
• Transmission of Coagulase-Negative Staphylococci


  • Hands (normal microbiota) and fomites
  • Staphylococcus epidermidis: Adhesion to plastics (infection of catheters, prostheses), Infection of intravenous lines, urinary catheters, prosthetic heart valves (endocarditis, bacteremia)
• Key factors for Coagulase-Negative Staphylococci infection

  • Presence of foreign bodies
  • Immunodeficiency
• If there is pus, drainage is required. Plastic or prosthesis should be removed (S. epidermidis). Urinary infection by S. saprophyticus requires liquid treatment.
• Coagulase-Negative Staphylococci may be multidrug resistant and can be contaminants as they live on our skin.

  
• Treatment for Staphylococcus aureus infections

  • No penicillins, more than 95% of strains have beta-lactamases (penicillinases)
  • Cloxacillin (semisynthetic penicillin, type of penicillin modified to be resistant to beta-lactamases) is the empirical treatment of choice
  • Alternatives: quinolones, aminoglycosides, macrolides, lincosamides etc.
  • Some S. aureus have become resistant to methicillin (MRSA), treated with glycopeptides (vancomycin, teicoplanin) or linezolid

  
• Treatment for Coagulase-Negative Staphylococci infections

  • Similar to S. aureus but are often more resistant to cloxacillin and other families of antibiotics
  • Empirically: Vancomycin or Teicoplanin (almost all gram-positive are sensitive to these antibiotics)
  • Later adjustment for sensitivity testing

  
• Although Coagulase-Negative Staphylococci are less virulent than S. aureus they are often more resistant

  
• Staphylococci in dentistry


  • S. aureus and S. epidermidis are the most frequently isolated staphylococci in the oral cavity (in saliva of 1/3 of the population but in small quantities)
  • Not normal oral microbiota, only transient guests
  • Possible opportunistic pathogens if they find the chance
  • Isolated from polymicrobial infectious processes where the significance as a pathogen is unknown
  • Found in dental plaque of immunocompromised or patients with prosthesis

  
• Staphylococcal infections in the oral cavity

  • Root caries, periapical infections
  • Glossitis
  • Gingivitis and periodontitis
  • Maxillary osteitis, periimplant osteitis
  • Abscess of tonsils
  • Cavernous sinus thrombosis
  • Facial malignant staphylococcal infection
• Outside the oral cavity:
• Endocarditis


  Caused by dental instrumentation
• In neutropenic patients


  Serious infections
• They are not clear pathogens in other infectious diseases (opportunistic)
• Encompass many species sometimes difficult to distinguish and to classify
• Streptococcus mutans group


  • S. mutans
  • S. sobrinus
  • S. cricetus
  • S. ratti