Microbiological analysis of urine specimens Flashcards
composition of the urinary system
-two kidneys and two ureters
-one urinary bladder and one urethra
Which organs do not posses residential microbiota
kidneys, ureters, and bladder
-urine contains some antimicrobial proteins but if left at room temp urine can support bacterial growth
What keeps the urine sterile?
the movement of urine from the kidneys to the urinary bladder provides mechanical flushing that keeps urine sterile
What bacteria is found externally in females
lactobacillus
Where can residential microbiota be found
male/female external genitalia and lower urethra
What bacteria is found externally in males
-microbiota similar to those that colonize the epidermis of the skin
microbial antagonism
-our residential microbiota in this region can cause this
-it means to occupy space and block access to nutrients making it difficult for pathogens to colonize this region
ascending infection (pathway)
normal flora of the urethra/genitalia travel upwards through the urinary bladder to the kidneys
-bacteria will multiply in the urinary bladder and can travel through the ureter to infect the kidneys
-these infections occur more in females than males
Descending infection (pathway)
blood carries bacteria from a different infection site to the kidneys
-the bacteria travel with urine through the ureter to the bladder
-these infections are much less frequent than ascending
Urine produced from the kidneys will be?
sterile and free of microorganisms
when is flora introduced into urine?
-when the urine passes through the lower urethra
midstream voided urine sample
the first and last part of urine are not collected to avoid contamination by hands
-from health organisms will contain some microorganisms from their normal microbiota
What bacteria causes most urinary infections?
Enterobacteriaceae which is gram negative bacteria from the intestinal microbiota
What represents most enteric based UTIs
E.Coli represent about 70%
-Proteus and Klebsiella are also common
What represents most non-intestinal bacteria causing UTI infections
Pseudomonas and Staphylococcus
Yeast infection ( Candidiasis)
if candida albicans and other candida fungal species reach populations that are too high in this region they are called a UTI
What causes E.Coli to have virulence factors
- flagella permit E.Coli to swim through the ascending pathway
- fimbriae allow E.Coli to attach to the cells that line the urinary bladder
3.biofilms like substances help E.Coli evade our immune response
How are most urine sample collected?
clean midstream void
How can urine be collected directly from the bladder?
aseptic catherization, cystoscopy, and suprapubic aspiration
Where is urine stored and collected?
-collected in a sterile container and stored in a refrigerator
What media do we use to culture urine samples?
on MacConkey plate or sheep blood agar to determine the colony forming units (CFUs)
What do we use to transfer urine to the media plates?
calibrated loop
-allow you to streak an exact volume of urine typically 0.1 ml (100ul) or 0.01 ml (10 ul- yellow loop) or even smaller volumes .001 ml (1ul- blue loop)
How to determine CFUs?
counting the number of colonies that formed on the agar culturing the sample
How is the numbers of colonies per ml (CFU/ml) calculated?
multiplying the number of colonies counted by a conversion factor dependent on the initial volume used
If 0.01 ml (10 ul) was plated what do you multiply it by?
number of colonies * 100
If 0.001 ml (1 ul) was plated what do you multiply it by?
number of colonies * 1000
clean midstream void <10,000
negative for UTI
clean midstream void 10,000-100,000
suspicious or equivocal
clean midstream void > 100,000
positive for UTI
What are the instances where it is automatically positive for UTI?
-Aseptic catherization, cystoscopy, and suprapubic aspiration
Too numerous to count (TNTC)
if a bacterial lawn is grown on the media plate and unable to count individual colonies
What does MacConkey agar select for?
gram negative bacteria such as Enterobacteriaceae like E.Coli or Proteus or other UTI causative agents like Klebsiella and Pseudomonas
-Pseudomonas and E.Coli are both gram negative but can be differentiated based on if they ferment lactose
E.Coli test results on MacConkey agar
ferments lactose –> acidic/wine pink
Pseudomonas results on MacConkey agar
does not ferment lactose
What do the bile salts and crystal violet do
-inhibit most gram positive organisms
