SEROLOGY PART 2 (P1)

group a streptococci

• gram positive cocci

• arranged in chains or pairs

• non-motile

• non- spore forming

• catalase negative

• produces beta hemolysis (complete hemolysis) on blood agar

m protein

• inhibits phagocytosis

streptolysin o and s

• hemolysins that destroy rbcs

streptokinase

• dissolves clots

hyaluronidase

• spreads infection in tissues

dnase

• breaks down dna

pyrogenic exotoxins

• responsible for rash and toxic shock

lipoteichois acid

• adheres to epithelial cells, induces infection

protein f

• adheres to epithelial cells

culture method

• gold standard

• diagnosis of acute infection is usually done by doing this by getting specimens from the infected site

antistreptolysin o (aso) test

• detects antibodies agains streptolysin o, a toxin that lyses rbcs

• indicates recent streptococcal infection and useful in patients suspected of: rheumatic fever and post streptococcal glomerulonephritis

streptozyme test

• a slide agglutination screening test detecting antibodies to multiple streptococcal antigens

• sheep rbcs are coated with: streptolysisn, streptokinase, hyaluronidase, dnase, nadase

• patient serum + coated rbcs

anti-dnase b test

• useful when aso is negative, especially in skin infections

• dnase b is produced mainly by streptococcus pyogenes

• detects infection in patients with: post streptococcal glomerulonephritis, rheumatic fever with negative aso

helicobacter pylori

• curved or spiral shaped, sometime s shaped or helical

• gram negative

• urease, catalase, oxidase positive

• microaerophilic

urease

• neutralizes stomach acid

flagella

• motility through mucus

adhesins

• allow attachment to gastric epithelial cells

cytotoxin

• damage gastric mucosa and contribute to ulcers and carcinogensis

culture (invasive method)

• most specific test for h. pylori

• sensitivity is lower because the bacteria are unevenly distributed in gastric tissue

histological examination invasive method

• microscopic evaluation lf gastric biopsy tissue to visualize h pylori

biopsy urease test invasive method

• detects urease enzyme produced by h pylori

• urease breaks down urea to ammonia and bicarbonate which raises the ph making a change in color in test

• rapid results (within 2 hours) simple to use, ideal for quick diagnosis

urea breath test noninvasive method

• patient ingest urea labeled with 14c or 13c

• h pylori metabolizes urea → labeled co2 detected in breath

• high sensitivity and specificity, can monitor eradication after therapy

• 14c involved radioactivity, 13c uses mass spectrometry

fecal antigen test noninvasive method

• detects h pylori antigens in stool using enzyme labeled monoclonal antibodies

• sensitivity 84-95%, specificity: 97%

• mainly used to confirm eradication after treatment

molecular tests noninvasive method

• detect h pylori dna via pcr (standard or real time/taqman)

• can determine bacterial load and antibiotic resistance

• cannot distinguish between live and dead bacteria

mycoplasma pneumoniae

• formerly known as “eaton agent”

• associated with a dry nonproductive cough “primary atypical pneumonia”

• they do not have cell wall

p1 adhesin protein

• allows attachment to respiratory epithelial cells

cytotoxic activity

• produces reactive oxygen species that damage host cells

immune evasion

• antigenic variation helps avoid host immune response

superantigen-like effects

• can trigger inflammatory responses

rickettsial infections

• short rods or coccobacilli, obligate intracellular, gram-negative bacteria

• two main groups: spotted fever group and typhus group

spotted fever group

• rickettsii and japonica

• ticks (most), sometimes mites

• accidental

• rocky mountain spotted fever, japanese spotted fever

• ~ 7 days after tick bite

typhus group

• typhi and prowazekii

• fleas (typhi) and lice (prowazekii)

• accidental (prowazekii can spread human to human via lice)

• endemic typhus, epidemic thypus

• ~ 1-2 weeks after exposure

weil-felix reaction (classical agglutination test)

• based on cross-reactivity between patient antibodies and proteus antigens

• historical test; largely replaced by ifa, elisa, and pcr

ox19

• epidemic typhus (prowazekii). endemic typhus (typhi)

• patients with typhus group rickettsiae

ox2

• rocky mountain spotted fever (rickettsii)

• patients infected with spotted fever group rickettsiae

oxk

• scrub typhus (orientia tsutsugamushi)

• patients infected with scrub typhus