Microbiology

• Active space
• Infections


  • Skin/wound infections
  • Multi drug resistance organisms (MRSA, VRE)
  • Diarrhoeas due to- E.coli O157, Shigella, C. difficile, Noroviruses, Rotavirus
  • Localized Herpes zoster
• Droplet precautions


  • Single patient space or room
  • Don mask on entry into patient room/space & discard mask just after exiting area
• Diseases requiring droplet precautions

  • Meningococcal disease
  • Strep pharyngitis
  • Pneumonic plague
  • Diphtheria
  • Pertussis
  • Mumps
  • Rubella
  • Fifth disease
  • Epiglottitis
• Contact precautions


  Add contact precautions - RSV, Adenovirus, Influenza, Ebola, Lassa, marburg viruses
• Airborne precautions


  • Airborne infection isolation room with negative pressure
  • N-95 respirator just before entry to a shared air space & discard respirator just after exiting area
• Diseases requiring airborne precautions

  • Measles
  • TB
• Contact precautions + eye protection

  Add contact precautions + eye protection - SARS
• Category A bioterrorism agents / Tier I
• Category A bioterrorism agents / Tier I

  • Bacillus anthracis
  • Botulinum toxin
  • Plague (Yersinia pestis)
  • Smallpox (variola major)
  • Tularemia (Francisella tularensis)
  • Viral hemorrhagic fevers, including: Filoviruses (Ebola, marburg), Arenaviruses (Lassa, machupo)
• Mnemonic: Francis is playing with bottles that are filled with small ants
• Category B bioterrorism agents / Tier 2 select agents
• Category B bioterrorism agents / Tier 2 select agents

  • Brucellosis (Brucella species)
  • Epsilon toxin of Clostridium perfringens
  • Food safety threats (Salmonella spp, E. coli O157:H7, Shigella)
  • Glanders (B. mallei)
  • Melioidosis (B. pseudomallei)
  • Psittacosis (c. psittaci)
  • Q fever (c. burnetii)
  • Ricin toxin
  • Staph enterotoxin B, Typhus fever (R. prowazekii)
  • Viral encephalitis (such as εEE, WEE, VEE)
  • Water safety threats (V. cholerae, Cryptosporidium parvum)
• Category C bioterrorism agents / Tier 3 select agents
• Emerging pathogens that could be engineered for mass dissemination in future because of availability, ease of dissemination. Potential high morbidity and mortality rates and major public health and social disruption
• Hendra virus
• Wear thing
• Systemic bacteriology
• Staphylococcus


  40 spp.
• Types of Staphylococcus


  • S. aureus
  • CONS
• S. aureus


  • Free & bound Coagulase +
  • Mannitol fermentation +
  • B-hemolytic on blood agar
  • Golden pigment
• CONS


  • Coagulase- (both/bound/free)
  • Mannitol fermentation -
  • Non-hemolytic
  • Pigment -
• Protein A


  • Present in its cell wall
  • Binds to Fc part of Ig G antibody (antiphagocytic)
  • Used in coagglutination tests which are used for detection of soluble antigens
  • Strain rich in Protein A: Cowan I strain
• Toxin mediated syndromes of S. aureus

  • Enterotoxins
  • Exfoliatins A & B / Epidermolytic toxins
  • Superantigens/T-cell mitogens
• Enterotoxins


  • Heat stable (100°C x 10-40 mins)
  • Preformed
  • Stimulation of vomiting
• Exfoliatins A & B / Epidermolytic toxins

  Proteolyse Dsg-1 stratum granulosum of epidermis leading to mid-epidermal split
• Superantigens/T-cell mitogens


  • TSST-I, SE-B, SE-C
  • Activate 5-20% Th cells
  • Cytokine storm
• Toxic shock syndrome


  • Menstrual: Associated with vaginal colonisation by toxin producing S. aureus
  • Non-menstrual
  • CDC criteria: Fever, hypotension, generalised skin blisters associated with desquamation, involvement ≥ 3 organ systems
• • Superantigens do not need processing by the APCs
  • They directly bind to the MHC-II of the APC at a site lateral to usual antigen presenting groove
  • Recognised by the vẞ TCR
• Infections by S. aureus

  • Surgical site infections
  • Folliculitis
  • Impetigo
  • Bullous impetigo
  • Botryomycosis (mycetoma)
  • Tropical pyomyositis
  • Osteomyelitis
  • Infective endocarditis
  • Native valve Infective endocarditis (NVE)
  • Acute Infective endocarditis
  • Early Prosthetic valve endocarditis (CONS)
  • Late Prosthetic valve endocarditis (Viridans group)
  • Hospital acquired pneumonia
  • Ventilator acquired pneumonia
• 1. lactams


  Bind transpeptidases/Penicillin Binding Protein's (crosslink the murine monomers)
• Resistance to B-lactams


  • Penicillinase (hydrolytic enzyme)
  • Altered PBP 2a
• MRSA


  • Resistance to B-lactams
  • Chromosomally mediated: mecA gene
• VRSA


  • Altered precursors of cell wall where vancomycin acts
  • Due to vanA gene
• S. aureus carriage


  • Nose
  • Vagina
  • Hair
• CONS


  • Resistant to Novobiocin
  • Cause of Honeymoon cystitis
• S. lugdunensis


  • Bound coagulase + (slide coagulase test positive)
  • Fulminant Native valve endocarditis
  • Skin soft tissue infections
• S. epidermidis


  • Present as normal skin flora
  • Bacteremia in IV catheterized (mcc)
  • Surgical site infections
  • Dialysis associated peritonitis
  • Early Prosthetic valve endocarditis
  • Orthopedic implant infections
  • Multidrug resistant organism (treatment: Vancomycin)
• Catalase positive
• Catalase negative