semen id and detection Flashcards
what is semen
male reproductive fluid
production starts at puberty 8-17 yrs old
spermatozoa + seminal fluid = semen
biological characteristics of semen
typical ejaculate is 2-5 mL
water soluble
normal sperm count ranges from 10^7 - 10^ 8 spermatozoa per mL
principle cell in semen is spermatozoa
pH is 7.2 - 7.8 so ~ 7.5
slightly basic
75 - 90% semen is contributed by accessory glands
20% prostate
60% seminal vesicle
Cowper’s gland
urethral galnds
seminal fluid
combined secretions of several accessory glands
seminal fluid is thick because it contains mucus and proteins
fructose, citric acid, creatine, spermine, choline, urea
also contains epithelial cells and WBCs (source of DNA)
seminal vesicle fluid
contains proteins that play a role in coagultion
contains flavin which causes semen to fluoresce under UV light
prostatic fluid, contributed by the prostate
contain high concentrations of acid phosphatase (AP) and prose-specidic antigen (PSA)
used to screen for semen
anatomy
sperm are created in the testes, mature in the epididymis, traverse the vas deferent. and ejaculatory dict to enter the urethra
accessory glands: seminal vesicle, prostate, Cowper’s gland, urethral glands provides the bulk of semne
emission - movement of semen into the urethra by contraction of the smooth muscles of the vas deferents and seminal vesicles
ejaculation - semen is propelled out of the urethra by contraction of the bulbocavernosus muscle
muscle of the perneum
acid phosphates (AP)
primary screening test, colorimetric
the prostate is the most abundant source of AP
not specific for seminal fluid
found in lower concentration in other bodily fluids
fecal stains vaginal secretions blood
seminal fluid AP conc is 20-400 times greater than other bodily fluids
elevated levels of prostatic AP are present in serum of males with prostate cancer used to diagnose
also can be found in fungi bacteria and many plants
AP levels are not affected by vasectomies because it is generated by the prostate
not testes
can use to screen for seminal fluid (semen)
prostate specific antigen (PSA)
has molecular weight of 30 kDa so also known as P30, interchangeable with PSA
present in seminal fluid in concentrations of 0.5 to 2.0 mg/mL
produced in the prostate epithelium and secreted into the semen
responsible for hydrolyzing semenogelin which mediates gel formation in semen
can also be found in the paraurethral glands, perianal glands, aprocrine sweat glands, and mammary glands
not prostate specific, not sex specific
not as specific for the prostate as once thought
detected in low levels in urine fecal material sweat and breast milk breast tumors amniotic fluid
abnormally high P30 levels in blood serum can be associated with prostate cancer as well
presumptive identification of semen stains
dried semen stains are typically off white to yellow in color
can appear crust or you can feel them
problems can occur in locating semen stains on clothing items that are thick or coarse or the color could make it difficult too
dried semen stains fluoresce bluish white on most substrates with UV excitation (ALS)
innate fluorescent compounds (flavins)
fluorescent compounds elaborated by bacteria
pseudomonas fluorescens
note taking: document document document
document color appearence whether it fluoresces what wavelength, etc
can circle stains under ALS to view in ambient light if stain is positive, document size of stain color
if visible under ambient, etc
UV fluorescence under UV or ALS
white cotton in underpants commonly fluoresces under ALS, document any observations, may need to continue with additional screening tests
light sources for semen search
using a handheld UV light, semen stains will appear bluish in color
DNA can be detrimentally affected by brief high intensity UV exposure
using an ALS (430-470 nm wavelength range) semen stains will be visible as a yellow-colored stain
crime lite
ALS is not specific for semen
other bodily fluids will fluoresce
some detergents and other chemicals have fluorescent properties
when using all you always use a filter to render the emitted light as a single wavelength colored goggles
saliva and urine fluoresce
identification process of semen stains from clothing
semen stain
presumptive tests - ALS => AP
confirmatory tests - microscopic ID of semen
stop if sperm is seeen
if not seen, P30
positive P30, possible vasectomy, possible low conc sperm
at LASD, positive P30 was semen indicated
P30 isn’t as specific as once thought
AP presumptive test for semen
semen contains high levels of acid phosphatase which is produced by prostate gland
the enzyme has optimal pH of 5.4, acidic and liberates inorganic phosphate from phosphoric esters
sodium α-Naphthyl phosphate is used as the substrate
Naphthyl liberated in the reaction couples with an ago dye (brentamin Fast Blue B) to form an insoluble colored product
colorimetric test
2-step test
time sensitive 20 sec
in presence of semen the result is a color change to purple
can test directly or indirectly
you can cut sample directly and perform in test tube (more sensitive) or swab stain and use taco method with filter paper
chemistry of AP and Fast Blue b
the enzyme has optimal ph of 5.4 and liberates inorganic phosphate from phosphoric esters
sodium α-Naphthyl phosphate is used as substrate
AP false positives may have weak reactions
fecal stains
vag secretions
plants, cauliflower sprouts
yeasts react with brentamine dye
bacteria can be present in vagina due to pregnancy or infection
contraceptive creams react with brentamine dye
combination of solutions can be delivered backwards to make more specific
fast blue B is added 1st to eliminate false positives
add dye first, color change - substrate α-Naphthyl not added yet therefore false positive
different types of colorimetric screening tests for AP
test strips were found to detect semen down to a 1/2000 dilution whereas comparative testing with two other AP tests and a zinc test showed that their limit of detection was 1/150 - 1/300
simply moisten stain, remove protective test cover and either collect swab and apply to test paper or press test paper on stain
return test cover and in approx 1 min a positive result is indicated by a deep purple color
AP mapping
blotting paper dampened with water
use mister of spray bottle
not too wet to dilute stain
place on fabric
press
remove and AP reagents are sprayed onto the blotting paper
prostate specific antigen P30 identification
immunochromatographic assays
Seratec PSA semi quant, One step ABA card PSA
used as screening test for semne
utilizes antibody-antigen relationship
3 lines indicates positive for P30 2 is negative because semi quant line
line used for detecting prostate cancer
not forensic
Enzyme linked immunoabsorbent Assay (ELISA)
antibody sandwich ELISA in which an antibody-antigen-antibody sandwich complex is formed
intensity of the signal is detected and proportional to amount of bound antigen
time consuming therefore bad for screening
Sertec PSA semiquant
cartridge technology replaced CIE (crossover immunoelectrophoresis)
more sensitive less time
specificity
shows no cross reactivity with other seminal fluids
shows no cross reactivity with neat breast milk, female urine, or female serum samples
no cross reactivity with other animal seminal fluid, except higher primates apes
sensitivity 1ng/uL
can suffer from high dose hook effect
false negative oversaturated with P30 PSA
dilute sample and run again
competitive binding
served p30 cards
free gold labeled mouse monoclonal anti-P30 antibodies just upstream of test zone, in sample well
immobilized mouse monoclonal anti-p30 antibodies in T zone
polyclonal anti-mouse antibodies present at the control region and internal standard line
when p30 present it forms fold labeled mouse anti p30 antibody - p30 antigen - mouse anti p30 antibody sandwich at test site
