Is new

• Infectivity


  An organism's ability to establish an infection. The proportion of individuals exposed to a pathogen through horizontal transmission who will become infected
• Pathogenicity


  The inherent capacity of an organism to cause disease. A qualitative trait determined by its genetic makeup
• Virulence


  A quantitative trait that refers to the extent of damage, or pathology, caused by the organism
• Plasmids


  Self-replicating genetic elements located in the bacteria's cytoplasm that contain a limited number of genes. The location where the genetic information needed to produce virulence factors is found
• Bacterial Evasion Mechanisms


  • Avoiding antibodies by altering antigens (antigenic variation)
  • Blocking phagocytosis by inhibiting binding of neutrophils and macrophages
  • Blocking/inactivating complement activation
• Methods to detect causative agent of bacterial infection


  • Culture or growth of the causative agent
  • Microscopy
  • Detection of bacterial antigens in the clinical sample
  • Molecular detection of bacterial DNA or RNA
  • Serology, or detection of antibodies produced in response to the infection
• Serology disadvantage


  Delay between start of infection and production of antibodies
• Serology for Group A Streptococci


  1. Culture or rapid screening methods are useful for acute pharyngitis diagnosis

  2. Serological diagnosis must be used to identify rheumatic fever and glomerulonephritis
• Streptococcal antigen detection


  Rapid assays like lateral flow immunochromatographic assays (LFA) are used to detect Group A streptococcal antigens directly from throat swabs
• Streptozyme Kit Testing


  Sheep RBCs are coated with streptococcal antigens so antibodies to any of them can be detected by hemagglutination
• Anti-DNase Testing


  1. Classic Neutralization method - Anti-DNase B antibodies neutralize reagent DNase B, preventing DNA depolymerization

  2. Nephelometry method - Immune complexes between antibodies and DNase B reagent generate light scatter
• Anti-Streptolysin O (ASO)


  Presence of antibodies indicates recent streptococcal infection. ASO titers usually do not increase with skin infections
• Traditional/Classic ASO titer tube method


  Involves dilution of patient serum, addition of streptolysin O reagent, and indicator RBCs. No hemolysis indicates presence of anti-streptolysin O antibody
• Helicobacter pylori is now recognized as a major cause of both gastric and duodenal ulcers
• Helicobacter pylori virulence factors


  • Production of CagA protein, vacuolating cytotoxin (VacA)
  • Production of large amounts of urease to protect against stomach acid
• Methods to detect Helicobacter pylori


  • Invasive techniques: endoscopy, biopsy
  • Noninvasive techniques: serological analysis, fecal antigen detection, urea breath tests
• Real-time PCR (RT-PCR)


  Can detect presence of H. pylori in fecal samples, but cannot distinguish between living and dead bacteria
• Urea Breath Test


  Patient ingests urea labeled with radioactive or nonradioactive carbon. Measures exhaled labeled carbon dioxide to detect H. pylori infection
• Serological testing for H. pylori


  Measures IgG antibodies, which are the primary antibody found in chronic infections. ELISA is the method of choice
• CLOtest


  Detects urease activity in gastric mucosal biopsies. Turns pink in presence of urease, indicating H. pylori infection
• Mycoplasma pneumoniae infections are referred to as "atypical pneumonia" because the organism lacks a cell wall and cannot be treated with penicillin
• Mycoplasma pneumoniae is a leading cause of community-acquired pneumonia, often referred to as "walking pneumonia"
• Mycoplasma pneumoniae infections are associated with dermatological manifestations
• Yellow gel


  Turns hot pink color due to increase in pH in the presence of urease
• Gel


  Remains yellow if urease is not present
• Majority of the tests will turn positive within 20 minutes
• Test should be held and reexamined after 24 hours to allow time for detection of a low-level infection
• Test


  Easy to use and ideal for rapid diagnosis of H pylori infections
• Pneumonia caused by M pneumoniae


  Originally referred to as "atypical pneumonia" because the infection could not be treated with penicillin
• M pneumoniae lacks the cell wall to which penicillin is directed against
• M pneumoniae


  A leading cause of community acquired pneumonia
• Infection caused by M pneumoniae


  Often referred to as "walking pneumonia" because individuals often do not stay home from work or school and still participate in their daily activities
• Dermatological manifestations associated with M pneumoniae infection


  • Stevens–Johnson syndrome, or erythema multiforme major
  • Raynaud syndrome
• M. pneumoniae is associated with a cold agglutinin that is directed against altered I antigens (I blood group system) in the RBCs
• Laboratory means of detecting Mycoplasma infection


  • Culturing of the organism
  • Detection of M pneumoniae-specific antibodies in serum
  • Detection of M pneumoniae-specific antigens or nucleotide sequences directly in patient specimens
• Culture


  Considered as the gold standard for diagnosis
• Growth of M pneumoniae in culture


  Produces a "mulberry" colony with a typical "fried egg" appearance
• Serology


  Detection of M pneumoniae-specific IgM immunoglobulin is the most useful diagnostic test
• Enzyme-linked immunoassays


  The most widely used methods for antibodies and can detect IgM or IgG directed against M pneumonia
• Cold agglutinin titer test is no longer recommended because the development of cold agglutinins occurs in other circumstances, including some viral infections and collagen vascular diseases