Chapter 20: Serological and Molecular Detection of Bacterial Infections Flashcards
What are the different host-microbe relationships?
○ Symbiotic
○ Communalistic
○ Mutualistic
○ Parasitic
Symbiotic
○ Normal Flora, Host microbe live together long term
○ Interaction between them may/may not be beneficial
Communalistic
No benefit or harm to either organism
Mutualistic
Both host and microbe benefits
Parasitic
Microbes cause harm to host
Infectivity
Organisms ability to establish an infection
Pathogenicity
Ability of an organism to cause disease
Virulence
The extent of pathology caused by an organism when it infects host
Of the bacterial virulence factors which is a powerful stimulator of cytokines?
Endotoxins
What is the difference between pili and flagella?
○ Similarity they do adhere to host
○ Pili: helps microbe resist phagocytosis
○ Flagella: provides microbe with motility
What are exotoxins?
○ Potent toxic proteins released from living bacteria
○ Includes: Neurotoxins, cytotoxins, enterotoxins
Besides pili what helps block phagocytosis?
○ Capsule of bacteria
○ Also blocks antibody attachment
What are examples of innate immunity?
○ Intact skin and muscosal surfaces
○ Antimicrobial defense peptides (ie. Lysozymes)
○ Complement proteins, cytokines, acute-phase reactants
○ PAMPs, PRRs, TLRs
What are examples of adaptive immunity?
○ Antibody production-
○ Cell mediated immunity- CD4 T cells, T cytotoxic cells
What are ways bacterial evade immune system?
○ Inhibit chemotaxis
○ Block adherence of phagocytes to bacterial cells
○ Block digestion
○ Inhibiting complement
○ Cleaving IgA
How does labs detect bacterial detections?
○ Culture of causative agent: Growing on cultures, takes time
○ Microscope examinations: Gram or special stains
○ Detection of bacterial antigens: used by ELISA, LFA, or LA
○ Molecular detection of bacterial DNA or RNA
What are serological used for in bacterial detection?
detect and confirm infections
○ diagnose infections when symptoms aren’t specific
○ Current infection indicated by presence of IgM, a high IgG titer or a fourfold rise in antibody titer
○ To determine a past exposure (IgM–, IgG+)
What are the disadvantages of serological testing for bacteria?
○ Delay between start of infection and production of antibodies
○ Low antibody production by immunosuppressed patients
Group A Streptococci
○ Gram-positive cocci arranged in pairs or chains
○ Transmitted person to person
What can Group A strepococci manifest as?
○ Pharyngitis (“strep throat”)
○ Pyoderma (impetigo)
○ Scarlet fever
○ Toxic shock syndrome
○ Necrotizing fasciitis
Acute rheumatic fever
○ Develops 1 to 3 weeks after pharyngitis or tonsillitis in 2% to 3% of infected individuals
○ Most likely caused by immune responses to streptococcal antigens that cross-react with human heart tissue
What are the symptoms of Acute Rheumatic Fever?
fever, joint pain, inflammation of the heart
Poststreptococcal glomerulonephritis
May follow strep infection of the skin or pharynx
What can Poststreptococcal glomerulonephritis lead to?
○ Damages glomeruli
○ producing hematuria
○ Edema
○ Hypertension
○ Malaise
○ Backache
○ abdominal discomfort
○ impairment in renal function
How can one tell if they have an infection form Group A Streptococci?
○ Culture on sheep blood agar: Small translucent colonies surrounded by clear zone of beta hemolysis
○ Rapid assays to detect group A streptococcal antigens: LFA or Lateral Flow antigen test
What serological tests are there to detect Group A Strep?
○ Nephelometric methods to detect: Antistreptolysin O (ASO)
○ EIA to detect: Anti-DNase B
○ Streptozyme test: Detects antibodies to five streptococcal products
Helicobacter pylori (H. pylori)
○ Gram-negative
○ Transmission likely by fecal-oral route
What is H. pylori responsible for?
○ Major cause of gastric and duodenal ulcers
○ If untreated, can lead to gastric carcinoma or mucosa-associated lymphoid tumors
How can H. pylori survive in the stomach?
production of urease, which provides a buffering zone around the bacteria
How is H. pylori detected?
○ Detect urease in stomach biopsy
○ Urea breath test
Mycoplasma pneumoniae (M. pneumoniae)
○ Leading cause of respiratory infections
○ Tiny bacteria that lack a cell wall
○ Spread by respiratory droplets
What are some respiratory infections of M. pneumoniae?
○ “Walking pneumonia”: pneumonia present but not obvious
○ Raynaud syndrome
○ Stevens-Johnson syndrome in minority of cases: Top layer of skin dies and underlayer is exposed
Despite being the gold standard what is the issue with culture test for M. Pneumoniae?
organism is difficult to grow
What is the most useful diagnostic test for M. Pneumoniae?
○ Antibodies to M pneumoniae
○ IgM antibodies = recent infection
○ IgG antibodies = possible reinfection
Describe cold antigens
○ Present in about 50% of patients with M pneumoniae but not specific for the infection
○ Cause RBC agglutination at 4°C; reversible at 37°C
Rickettsial Infections
○ gram-negative bacteria
○ Spotted fever group- Rocky Mountain spotted fever
○ Typhus group
How is Rickettsial infections spread?
transmitted by arthropods (ticks, mites, lice, or fleas) through biting after feeding on an infected animal
Rocky Mountain Spotted Fever (RMSF)
○ Caused by R rickettsii
○ Transmitted by three species of ticks
○ Symptoms include headache, nausea, vomiting, diarrhea, skin rash; death
