Urinary Tract Infection
Question 1. Enumerate the causative organism and laboratory diagnosis of
1. Urinary tract infection
2. Purulent meningitis
3. Sore throat
Answer:
1. Urinary tract infection
Enumeration of Causative Organisms:
- Bacterial agents:
- E. coli
- Proteus mirabilis
- Klebsiella spp.
- Staphylococcus aureus
- Staphylococcus saprophyticus
- Staphylococcus epidermidis
- Enterococci
- Salmonella spp.
- Pseudomonas aeruginosa
- Enterobacter spp.
- Citrobacter spp.
- Acinetobacter spp.
- Ureaplasma urealyticum
- Anaerobes such as Bacteroides fragilis
- Fungal agents:
- Candida albicans
- Cryptococcus neoformans.
Read And Learn More: Microbiology Question And Answers
Laboratory Diagnosis Of Urinary tract infection
- Microscopic examination:
- Wet mount: Urine is centrifuged and deposits should be examined under the microscope for detection of pus cells, epithelial cells, RBCs, bacteria, and crystals. 10 or more pus cells/mm3 of undiluted urine is indicative of bacteriuria.
- Gram Stain: If a Gram-stained smear demonstrates one or two bacteria per 2 to 3 microscopic fields of uncentrifuged urine or 5 bacteria per oil immersion field of centrifuged deposit, this is considered a significant bacteriuria.
- Chemical method:
- Triphenyl tetrazolium chloride test: It demonstrates the reduction of colorless soluble triphenyl tetrazolium chloride into pink to red insoluble compound known as triphenyl tetrazolium formazon due to the respiratory activity of growing bacteria.
- Enzymatic methods:
- Glucose oxidase test: It is based on the utilization of a small amount of glucose present in normal urine by bacteria, which leads to urinary tract infection.
- Leukocyte esterase test: It is a dipstick test that is used to detect pyuria. By this test, a pus cell count of more than 10 per mm3 can be done.
- Catalase test: It is based on the presence of catalase enzyme in pathogens, which is shown by hydrogen peroxide. The positivity of the test is demonstrated by effervescence.
- Griess nitrate test: It is based on the reduction of nitrate to nitrite with the help of nitrate reductase
- Culture: This method is an accurate and acceptable method of screening. In this method, both quantitative and semiquantitative methods are used.
- Quantitative methods: Quantitative methods used are the pour plate method, pipette dilution method, and simplified spread plate method. These methods are complicated, expensive, and impractical. So are indicated as reference methods only.
- Semiquantitative Methods:
- Calibrated loop method: In this, a loop delivering 0.001 mL of urine is used to inoculate blood agar. After incubating for 18 to 24 hours, plates are examined and colonies are counted. So the total number of bacteria per mL of urine is obtained as the Number of colonies × 1000.
- Dip-slide culture method: In this, commercially available plastic slides are coated with CLED agar over one side and McConkey’s agar on another side, these are inoculated by immersing in freshly pass urine. Slides should be kept in a plastic container and incubated. As incubation is over, colony counting is done.
- Filter paper strip technique: In this, the fitter paper should be dipped in urine and transferred to a conventional agar plate, as incubation gets over colony counting is done.
- Other screening methods:
- Automated screening test: Various commercially available kits are used for rapid screening of urine by light scatter photometry under 4 to 5 hours, for example of Vitek system and Pfizer’s autobac system.
- Interpretation of colony count (Kr ass Criteria):
- 100,000 or more bacteria per mL of urine indicate significant bacteriuria, a sensitivity test should be done.
- A count between 104/mL and 105/mL is doubtful significance, and the specimen should be repeated for culture.
- A count less than 104/mL indicates no significant growth and is considered contaminated.
- Bacterial identification:
- Bacteria is identified by colony characteristics, Gram staining, motility, biochemical reactions, and serological tests.
- Other investigations:
- Immunofluorescence test: It detects antibody-coated bacteria in urine, which determines whether the patient is suffering from a bladder infection or renal tissue infection.
- Antibody detection: Antibodies are detected in serum which is against infected microorganisms.
2. Purulent Meningitis
Enumeration of Causative Organism:
- In children and adults:
- Nasser meningitidis
- Streptococcus pneumoniae
- Haemophilus influenza
- Staphylococcus aureus
- Listeria monocytogenes
- E.coli
- Organisms that are occasionally seen:
- Proteus spp.
- Klebsiella spp.
- Citrobacter spp.
- Enterobacter spp.
- Serratia
- In neonates and infants:
- E. coli
- Group B streptococci
- Staphylococcus aureus
- H. influenza
- Listeria monocytogenes
- Streptococcus pneumoniae
- Klebsiella spp.
Laboratory Diagnosis Purulent Meningitis:
- Rapid diagnostic methods:
- Direct wet preparation: Wet mount of cerebrospinal fluid is seen for cytological studies which show dominant neutrophils in purulent or pyogenic meningitis.
- Quellung reaction: It is indicated in identification of H. influenza type b, pneumococci and meningococci.
- Gram stain: Gram staining smear of CSF sediment is used to demonstrate bacteria and cells.
- Direct immunofluorescence test: They detect antigens by using specific antibodies and fluorescent dyes.
- Countercurrent immunoelectrophoresis: In CSF, it is used to detect soluble antigens of meningococcal, pneumococci, Group B streptococci, H. influenza, E. coli, etc.
- Latex agglutination test: It detects antigens in CSF in pneumococcal, meningococcal, Group B streptococcal, and H. influenza. ELISA: This is used to detect an antigen.
- Culture:
- Centrifuged CSF deposit should be inoculated on blood agar, chocolate agar, MacConkey’s agar, and thioglycollate broth.
- A part of CSF should be mixed with an equal volume of glucose broth and incubated for extended culture.
- One blood agar plate should be incubated anaerobically, and another blood agar plate and chocolate agar plate is incubated in a candle jar.
- Another blood agar plate and another media should be incubated aerobically at 37 °C. Incubation should be for 72 hours.
- As soon as incubation is completed, plates should be observed for growth, colony morphology is studied and each colony is reported and identified by using standard biochemical and serological procedures
3. Sore Throat:
Enumeration of Causative Organisms:
The following agents lead to sore throat:
- Bacteria:
- Streptococcus pyogenes
- Corynebacterium diphtheriae
- Staphylococcus aureus
- Beta-hemolytic streptococci—Group C and G
- Borrelia vincentii
- Nasser gonorrhea
- Mycoplasma pneumonia
- Fusobacterium spp.
- Fungus:
- Candida albicans
- Virus:
- Adenovirus
- Influenza virus
- Para influenza virus
- Coxsackie virus
- Rhinovirus
- Coronavirus
- Respiratory syncytial virus
Laboratory Diagnosis Of Sore Throat:
- Direct Microscopy:
- Gram stain: This staining method is useful only in the demonstration of Vincent’s organism and Candida albicans. When staining with Gram stain is done, Borrelia Vincent appears as a gram-negative spirochaete and fusiform bacilli appear as gram-negative bacilli. Candida appears as a gram-positive oval budding yeast cell.
- Albert staining: It is useful in the presumptive diagnosis of C. diphtheriae. Bacilli appear as green-colored and V or L-shaped bacilli with bluish-black metachromatic granules.
- Culture:
- Following are the media which are used for the culture:
- Blood agar: All organisms can grow on this medium.
- Crystal violet blood agar: Selective medium for S. pyogenes. S. pyogenes appear as pinpoint, round, or convex colonies with entire margins with β-hemolysis.
- Potassium telurite blood agar: Selective medium for growing C. diphtheriae. It appears as black-colored round colonies.
- Sabouraud’s dextrose agar: It is used when candida is suspected. Candida appears as a white, colored, or cream-colored colony.
- The above media are incubated at 37 °C for overnight. In the case of potassium tellurite blood agar, incubation is done for 48 hours.
- Identification:
- S. pyogenes: It is seen as pinpoint, round, or convex colonies with an entire margin with β hemolysis
- C. diphtheriae: On potassium tellurite blood agar, it is seen as black-colored round colonies. Candida albicans: It appears as white or cream-colored colonies.
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