Laboratory Diagnosis of Urinary Tract Infections

This article discusses the laboratory diagnosis of urinary tract infections (UTIs) and the factors that can affect the accuracy of the diagnosis. It explores the different testing methods used, such as urine sample collection, specimen transportation, and specimen processing. The article also covers the treatment options for UTIs based on the antimicrobial sensitivity test.

Running head: HEALTH CARE
Health Care
Name of the Student
Name of the University
Author Note

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Answer 1
Urinary tract infections (UTIs) are regarded as common bacterial infections. The
detection of UTIs is challenging not because the diagnosis is not straight forward. Physicians
are required to distinguish UTIs from other diseases that might have identical clinical
presentations. Some form of UTIs are asymptomatic or are presented with atypical symptoms
on the other hand, the diagnosis of UTIs among the neutropenic patients (people who do not
have pyuria) might require different criteria for diagnosis in comparison to those of the
general population. Due these factors, the healthcare professionals mainly rely on the limited
number of imperfect laboratory diagnostic tests in order to augment clinical impressions even
when the overall clinical diagnosis is unequivocal. The healthcare professionals mainly order
for the laboratory tests in order to identify the cause and the infection and to provide the
isolated for the antimicrobial susceptibility testing (Mody and Juthani-Mehta 2014).
The first factor that might affect the laboratory diagnosis of UTIs is the process of
collection of the urine. The normal process of the urine sample collection for outpatient is
clean-catch midstream technique. This non-invasive technique has certain disadvantages like
urine sample passes through the distal urethra and thus can become contaminated with
commensal bacteria (Meister et al. 2013). The second factor that affects the laboratory
diagnosis of UTI is specimen transportation. Studies have highlighted that urine samples are
required to be plated within 2 hours of urine collection and then 24 hours after the collection.
The comparative results help to ascertain the UTIs. The urine collected from the outpatient or
even in in-hospital patients might get delayed to reach the laboratory unit letting to overall
delay in 2-hour time-point platting (Meister et al. 2013). The third factor affecting the
diagnosis of UTIs include specimen processing in the laboratory. The UTIs among the out-
patients are mainly caused by aerobic and facultative gram-negative bacteria and in

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hospitalised patients the main causative agents are enterococci. The problem in selection of
the culture medium might lead to the generation of false positive results (Meister et al. 2013).
The possible reasons for request of the second sample testing for the 19 year old girl
presented in the case study might be due to the eradication of the false positive or false
negative results. According to Kayalp et al. (2013) contamination of the urine culture in the
UTIs testing might lead to the generation of the false positive and false negative results.
Contamination mainly arises from the vaginal contaminants. Moreover, the girl was treated
with oral ampicillin for during four months before the hospital admission as she had a history
of UTI. Niranjan and Malini (2014) state that people are on the long-term medication of
antibiotics, the UTIs laboratory test might be mis-leading and such that second confirmatory
test is mandatory in order to detect the bacterial strength in the urine when the patient is not
under the antibiotic medication. Edlin et al. (2013) stated that after following the microscopy
of the bacterial culture of the urine sample, the antibiotic specificity of the bacteria is also
required to be undertaken. In this case, the girl might have developed ampicillin resistance for
long-term use. Determination of the antibiotic sensitivity in the second test will be helpful in
proper prescription of the medication. The second test will also be helpful in indentifying
single microbial species responsible for UTIs.
The procedure that can be used for the collection of urine for the UTIs testing include
invasive technique, suprapubic aspiration. It is the best method that can be used for the
collection of the urine sample in UTI diagnostic testing by avoiding contamination of bacteria
present in the urethra. In this process, urine is directly extracted into a syringe with the help
to the percutaneously inserted needle. Since the girl is 19 years old, she might feel
uncomfortable in this procedure. In that case straight catheter technique can be sued for the
process of urine collection with minimal contamination. (Hilt et al., 2014) Minimum of 10 ml
of urine is required in order to conduct the standard procedure of urinalysis (Hilt et al., 2014).

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The UTIs among the out-patients are mainly caused by aerobic and facultative gram-
negative bacteria and in hospitalised patients the main causative agents are enterococci. Thus
in case of the 19-year old girl in the case study, the chances of detection of the facultative
gram-negative bacteria and aerobic bacteria is high. The main clinical details that must be
highlighted while the collection of the urine sample include name, age, gender of the patients
along with the list of medications the patient is taking.
Answer 2
In case of the 19-year old girl, the tendency of developing gram-negative bacterial
infection in the urinary tract is higher. This is because, the study conducted by Kaye and
Pogue (2015) highlighted that UTI is the most common infectious diseases and is mainly
caused by gram-negative Escherichia coli. Women mainly the young adults are vulnerable
towards developing UTIs by gram-negative UTIs. The second most common uropathogenic
agent responsible for the disease includes Klebsiella pneumonia. The third most common
uropathogenic agents varied during the course of different seasons are Streptococcus sp
(separated from the Streptococcus D group), Pseudonomans aeruginosa, Staphylococcus
epidermidis and Enterococci (Kaye and Pogue 2015).
The preliminary detection of the bacterial load in the urine culture is done with the
help of dipsticks. It is the most commonly use instrument or tool used for the diagnostic
testing of the presence of the bacterial load in the urine sample of the patients suffering from
UTI (Tarchouna et al. 2013). In the majority of the cases, multistix procedure is used. This
procedure helps in the detection of nitrate, a metabolic by-product of bacterial pathogen
present in the urinary tract. It also helps in the detection of the leukocyte esterase, protein and
blood (blood is used as a marker for inflammation). The detection of nitrate in the urine
sample increases the probability of the urinary tract infection with a likelihood of 2.6 to 10.6.

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However, the level of overall sensitivity is low. In comparison to this, leucocyte esterase
uplifts the overall probability to a minimal degree. The presence of blood in the urine sample
provides high level of sensitivity along with low specificity (Tarchouna et al. 2013).
Vitek MS test can be used for the confirmatory detection of the gram negative
bacteria in the urine sample (≥105 CFU/mL). In this process, the urine specimens are Gram
stains followed by microscopic analysis of the bacterial culture. The urine specimen, which
showed a single morphotype by Gram staining was then processed by culturing matrix-
assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS).
Vitek MS is used to successfully differentiate between gram negative bacteria, glucose non-
fermenting gram negative bacteria and other yeast cultures (Kim et al. 2015). This approach
helps in proper differentiation of the gram-negative Escherichia coli and gram-negative
Klebsiella and Acinetobacter spp, Bacilli and Staphylococcus aureus.
Answer 3
The interpretation of the results would have been different if the sample is from the
sterile site as the bacterial colony count will directly indicate the bacterial load of the
causative agent of the UTIs. However, the urine sample contains contamination of the
commensal bacterial present at the urethra or at the vaginal surface. Thus the detection of the
bacteria causing the UTIs or and its subsequent characterization will require elimination of
the commensal bacteria. This can be achieved by culturing the urine sample in differential
media which will promote selective growth of the bacteria causing UTIs while eliminating
the commensal strains (Picozzi et al. 2013).
The wide diversity of bacterial nucleases provides a rich source of enzymes. The
bacterial nuclease activity provides a rich source of enzymes that could be exploited in the
form of the signal amplifying biomarkers in order to promoted selective, rapid detection of

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the bacterial species. Micrococcal nuclease activity helps in the rapid detection of the
Staphylococcus aureus. On the other hand endonuclease I is a robust biomarker for the
detection of the E.coli under rpid ultrasensitive assay (Flenker et al. 2017). Endonuclease I is
predominant DNase present in the E. coli lysates. It is detected through immunoblot and
activity assays mainly in the uropathogenic strains of the E. coli. The oligonucleatide probe
of the endonuclease I helps in the rapid and accurate detection of the presence of the E.coli in
the urine samples under only 3 hours of turn-around time. This time limit is shorter in
comparison to the culture-based methods used in urinalysis (Flenker et al. 2017).
Answer 4
The appropriate treatment will be determined in the laboratory with the help of the
antimicrobial sensitivity test. After the detection of the bacterial strain antimicrobial
sensitivity test is performed in order to detect the drug resistance in the common pathogens
and to assure the susceptibility of the drugs of choice for the particular infections. The
commonly used testing methods for the anti-microbial sensitivity include broth microdilution
or rapid automated instrument methods. Both the methods employ commercially marketed
materials and devises. Detection of the microbial strain along with the detection of the drug
resistance will help in determination of the treatment procedure in the laboratory (Álvarez-
Fernández et al. 2013).
If the laboratory detection of the urine sample indicate uncomplicated cystitis caused
by the E.coli then antibiotic treatment will be initiated. Nitrofurantoin
monohydrate/macrocrystals is a common bactericidal antibiotic administered with a dosage
of 100 mg orally twice a day. The antibiotic inhibits the protein, DNA, RNA and cell wall
biosynthesis of the bacteria. The antibiotic is found of inflict low rate of bacterial resistance
and has lower risks of the adverse effects (Barber et al. 2013). Trimethoprim –

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sulfamethoxazole is another class of antibiotic. It is also bactericidal in nature and it inhibits
the synthesis of nucleic acid by inhibiting the folate synthesis. It is given at the dosage of 160
mg/ 800 mg twice a day for 3 days. However, this antibiotics can only be used if the patient is
free from the sulfa drug allergies (Barber et al. 2013). The third antibiotic that can be used for
the treatment of the UTIs is the Fosfomycin trometamol. It is also bactericidal in nature as it
blocks the cell-wall biosynthesis by inactivation of the enolpyruvyl transferase. However, the
antibiotic cast a risk of collateral damange and is inferior in efficacy in comparison to the
other antibiotics. It is given as a single dosage with a strength of 3 grams (Barber et al. 2013).
The fourth antibiotics include Pivmecillinam. This bactericidal antibiotic disrupts the
synthesis of the bacterial cell wall by inhibiting the cross-linkage of the peptidoglycan layes.
It is given at a dosage of 400 mg per day at 3 days to one week. The antibiotic is found to
have low resistance and low risk of adverse effects (Barber et al. 2013).
In some cases women are treated with nitrofurantoin (100 mg per day) or cephaexin
(250 mg per day) or trimethoprim – sulfamethoxazole ( 40 to 200 mg per day). Thes are
broad spectrum antibiotics however, only found to produce symptomatic relief and
subsequent protection against the recurrent infection (Barber et al. 2013).
According to the randomized control double-blinded trial conducted by Wagenlehner
et al. (2015), in order to treat complicated urinary tract infections among the young adults
girls or the adolescents girls, ceftolozane – tazobactum is found to generate promising
response in comparison to the higher dosage of the levofloxacin. Thus, in order to reduce the
chances of developing antibiotic resistance and to get a comprehensive recovery, ceftolozane
– tazobactum.
Other advanced therapies for the treatment of the UTIs, which are in their initial
stages of development include vaccines. The vaccine molecules are designed targeting the

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bacterial co-factors that are important for the initial attachment of the bacterial in the human
cells in order to propagate the disease progression. The main bacterial co-factor that are the
target molecules for the production of vaccines include adhesions, bacterial toxins, proteases
and siderophores and other small molecule inhibitors that prevents the bacterial adhesions
and host cell receptors interactions (Flores-Mireles et al. 2015).

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