Chapter 20: Serological and Molecular Detection of Bacterial Infections

Question 1

What are the different host-microbe relationships?

Answer 1

○ Symbiotic
○ Communalistic
○ Mutualistic
○ Parasitic

Question 2

Symbiotic

Answer 2

○ Normal Flora, Host microbe live together long term
○ Interaction between them may/may not be beneficial

Question 3

Communalistic

Answer 3

No benefit or harm to either organism

Question 4

Mutualistic

Answer 4

Both host and microbe benefits

Question 5

Parasitic

Answer 5

Microbes cause harm to host

Question 6

Infectivity

Answer 6

Organisms ability to establish an infection

Question 7

Pathogenicity

Answer 7

Ability of an organism to cause disease

Question 8

Virulence

Answer 8

The extent of pathology caused by an organism when it infects host

Question 9

Of the bacterial virulence factors which is a powerful stimulator of cytokines?

Answer 9

Endotoxins

Question 10

What is the difference between pili and flagella?

Answer 10

○ Similarity they do adhere to host
○ Pili: helps microbe resist phagocytosis
○ Flagella: provides microbe with motility

Question 11

What are exotoxins?

Answer 11

○ Potent toxic proteins released from living bacteria
○ Includes: Neurotoxins, cytotoxins, enterotoxins

Question 12

Besides pili what helps block phagocytosis?

Answer 12

○ Capsule of bacteria
○ Also blocks antibody attachment

Question 13

What are examples of innate immunity?

Answer 13

○ Intact skin and muscosal surfaces
○ Antimicrobial defense peptides (ie. Lysozymes)
○ Complement proteins, cytokines, acute-phase reactants
○ PAMPs, PRRs, TLRs

Question 14

What are examples of adaptive immunity?

Answer 14

○ Antibody production-
○ Cell mediated immunity- CD4 T cells, T cytotoxic cells

Question 15

What are ways bacterial evade immune system?

Answer 15

○ Inhibit chemotaxis
○ Block adherence of phagocytes to bacterial cells
○ Block digestion
○ Inhibiting complement
○ Cleaving IgA

Question 16

How does labs detect bacterial detections?

Answer 16

○ 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

Question 17

What are serological used for in bacterial detection?

Answer 17

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+)

Question 18

What are the disadvantages of serological testing for bacteria?

Answer 18

○ Delay between start of infection and production of antibodies
○ Low antibody production by immunosuppressed patients

Question 19

Group A Streptococci

Answer 19

○ Gram-positive cocci arranged in pairs or chains
○ Transmitted person to person

Question 20

What can Group A strepococci manifest as?

Answer 20

○ Pharyngitis (“strep throat”)
○ Pyoderma (impetigo)
○ Scarlet fever
○ Toxic shock syndrome
○ Necrotizing fasciitis

Question 21

Acute rheumatic fever

Answer 21

○ 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

Question 22

What are the symptoms of Acute Rheumatic Fever?

Answer 22

fever, joint pain, inflammation of the heart

Question 23

Poststreptococcal glomerulonephritis

Answer 23

May follow strep infection of the skin or pharynx

Question 24

What can Poststreptococcal glomerulonephritis lead to?

Answer 24

○ Damages glomeruli
○ producing hematuria
○ Edema
○ Hypertension
○ Malaise
○ Backache
○ abdominal discomfort
○ impairment in renal function

Question 25

How can one tell if they have an infection form Group A Streptococci?

Answer 25

○ 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

Question 26

What serological tests are there to detect Group A Strep?

Answer 26

○ Nephelometric methods to detect: Antistreptolysin O (ASO)
○ EIA to detect: Anti-DNase B
○ Streptozyme test: Detects antibodies to five streptococcal products

Question 27

Helicobacter pylori (H. pylori)

Answer 27

○ Gram-negative
○ Transmission likely by fecal-oral route

Question 28

What is H. pylori responsible for?

Answer 28

○ Major cause of gastric and duodenal ulcers
○ If untreated, can lead to gastric carcinoma or mucosa-associated lymphoid tumors

Question 29

How can H. pylori survive in the stomach?

Answer 29

production of urease, which provides a buffering zone around the bacteria

Question 30

How is H. pylori detected?

Answer 30

○ Detect urease in stomach biopsy
○ Urea breath test

Question 31

Mycoplasma pneumoniae (M. pneumoniae)

Answer 31

○ Leading cause of respiratory infections
○ Tiny bacteria that lack a cell wall
○ Spread by respiratory droplets

Question 32

What are some respiratory infections of M. pneumoniae?

Answer 32

○ “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

Question 33

Despite being the gold standard what is the issue with culture test for M. Pneumoniae?

Answer 33

organism is difficult to grow

Question 34

What is the most useful diagnostic test for M. Pneumoniae?

Answer 34

○ Antibodies to M pneumoniae
○ IgM antibodies = recent infection
○ IgG antibodies = possible reinfection

Question 35

Describe cold antigens

Answer 35

○ 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

Question 36

Rickettsial Infections

Answer 36

○ gram-negative bacteria
○ Spotted fever group- Rocky Mountain spotted fever
○ Typhus group

Question 37

How is Rickettsial infections spread?

Answer 37

transmitted by arthropods (ticks, mites, lice, or fleas) through biting after feeding on an infected animal

Question 38

Rocky Mountain Spotted Fever (RMSF)

Answer 38

○ Caused by R rickettsii
○ Transmitted by three species of ticks
○ Symptoms include headache, nausea, vomiting, diarrhea, skin rash; death