I&I Lab Tests
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A previously well 23 year-old female patient presented to her GP
with frequency and dysuria. The patient was instructed to collect a
clean catch, mid-stream urine specimen, which was sent to the diagnostic
microbiology laboratory. The laboratory reported a WBC count of 5x107/L and 108/L Escherichia coli present in the urine specimen.
The number of bacteria in the urine sample was determined because:
It distinguishes infection from contamination.
Leukocyte casts in a urine specimen indicate:
There is inflammation in the kidneys
Which of the following in a mid-stream urine specimen is NOT an indicator of a urinary tract infection in a symptomatic patient:
A. ≥ 106 /L Staphylococcus species
B. A leukocyte count of ≥ 107 /L of urine
C. Presence of squamous epithelial cells
D. ≥ 108 /L Escherichia coli
E. Excess protein and positive nitrite dipstick test
A 26 year-old female sex-worker presented to
her GP with an abnormal vaginal discharge. Clinical samples
(endocervical swab, vaginal swab and first pass urine) were collected
and sent to the diagnostic microbiology laboratory.
The endocervical swab was collected specifically for laboratory diagnosis of:Select one:
A. Bacterial vaginosis
D. Chlamydia infection
A suitable clinical sample/test combination for the diagnosis of Chlamydia trachomatis infection is
First pass urine/ligase chain reaction.
- Chlamydia trachomatis has an intracellular lifestyle so
- infected cells are required for laboratory diagnosis. While these can be
- collected using vaginal or urethral swabs, a first-pass urine specimen is recommended as urethral epithelial cells are concentrated in the first part of the urine stream. Chlamydia cannot be cultured or Gram stained so a DNA based method is recommended for detection.
Rapid Plasma Reagin (RPR) test for syphilis is
a test for lipoidal antibodies
Besides sexually transmitted pathogens,
other microbes associated with an abnormal vaginal discharge include all
of the following EXCEPT:
A. Gardneralla vaginalis
B. Candida albicans
D. Trichomonas vaginalis
A five year-old child has
developed an itchy, scaly, red, ring-like lesion about 2 cm in diameter
on his arm (photograph Case 3 skin lesion). There were no other symptoms
and the child was healthy. Skin scrapings were collected and sent to
the diagnostic microbiology laboratory. The laboratory report indicated a
fungal infection. What is it?
- Dermatophyte fungi invade keratinised epithelium producing ring-like
- lesions. Healing occurs in the centre and inflammation on the periphery
- with flaking of the skin.
Young children are often infected with Enterobius vermicularis (photograph). This is
Also known as Threadworm.The correct answer is: An intestinal nematode
The correct specimen to take for the diagnosis of Enterobius vermicularis is
A sticky paddle applied to the anus in the morning
A patient undergoing a vaginal hysterectomy developed a
post-operative wound infection and is febrile. She has a history of
recurrent bacterial vaginosis. Blood cultures reveal she is infected
with Bacteroides fragilis. B. fragilis, staphylococci and streptococci
are isolated from the wound swab.
The most likely source of the Bacteroides fragilis is:
- B. fragilis
- is an obligate anaerobe associated with bacterial vaginosis and is
- present in the colon as part of the normal microflora. It is unlikely to
- survive for long on fomites, surgical instruments or skin due to the
- presence of oxygen. In the wound, anaerobic conditions are created by
- staphylococci and streptococci which preferentially use up the oxygen
- before switching to anaerobic metabolic pathways.The correct answer is: The patient’s vaginal microflora
All of the following may form part of the normal human microflora EXCEPT:
A. Streptococcus Groups A & B
B. Staphylococcus aureus
C. Streptococcus viridans
D. Staphylococcus epidermidis
E. Legionella pneumophila
- Legionella pneumophila is an environmental species which does not
- colonise body surfaces. The other species are part of the normal
- microflora but may also cause various types of infections.
Legionellosis was included in the
differential diagnosis for the two athletes with severe lower
respiratory tract symptoms. All of the following are compatible with a
diagnosis of legionellosis EXCEPT:
A. Normal neutrophil count
B. Positive Ziehl-Neelsen sputum stain
C. Patients were over 55 years of age
D. Low serum sodium
E. Fever and diarrhoea
A positive ZN stain indicates the patient has tuberculosis.
Pseudomonas aeruginosa and E. coli were cultured from the swab of the infected heel. All of the following statements about these bacteria are true EXCEPT:
A. They can both cause wound infections
B. E. coli is a Gram negative rod which colonises the colon
C. P. aeruginosa is susceptible to a wide range of antibiotics
D. They may be present in contaminated environmental sites such as lakes
E. Oxidase and oxidation/fermentation are distinguishing laboratory tests
Both species are Gram negative rods. P. aeruginosa is essentially an environmental microorganism; it is found in the colon less frequently than E. coli. P aeruginosa is oxidase positive and oxidises glucose whereas E. coli is oxidase negative and ferments glucose. P. aeruginosa is inherently resistant to a number of commonly used antibiotics.
Giardia and Cryptosporidium are:
Protozoa which cause diarrhea
What is the work up and empiric first line treatment for uncomplicated UTI?
- - Midstream urine sample
- - urinalysis (+WBC, +nitrates, +RBC +proteinuria)
- - urine microscopy (WBC quantitative count to differentiate between contamination and infection)
- - identification by culture and biochemical tests
First line treatment: single high dose of trimethoprim or nitrofurantoin
What is the treatment for asymptomatic bacteriuria in a pregnant woman?
Amoxycillin if susceptible otherwise nitrofurantoin
What is the empiric treatment for acute pyelonephritis and what is its MOA?
IM/IV gentamicin which is an aminoglycoside that inhibits bacterial protein synthesis by binding to ribosomes
OR ciprofloxacin which is a fluoroquinolone that inhibits bacterial DNA replication by inhibition of the enzyme DNA gyrase
What is the most likely etiological agent and treatment for:
a) community acquired UTI
b) hospital acquired UTI
c) community acquired pneumonia
d) atypical pneumonia
- a) E Coli, nitrofurantoin or trimethoprim
- b) S faecalis, nitrofurantoin or trimethoprim
- c) streptococcus pneumoniae, co-amoxyclav + erythromycin/ceftriaxone
- d) mycoplasma, legionella or chlamydia pneumoniae, erythromicin
What is the work up and treatment for suspected chlamydia infection?
- Endocervical swab or urethral swab for direct fluorescent antibody test
- First pass urine for LCR/PCR
Azithromycin (macrolide) or Ceftriaxone (cephalosporin)
What is the work up and treatment for suspected gonorrhea infection?
Endocervical swab or urethral swab for culture and biochemical tests
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