Friday, 7 December 2007

Elaine Blog2: case 1 Khong Fay seah

The entrobacteriaceae are heterogeneous group of gram-negative rods whose natural habitat is the intestinal tract of humans and animals. The family includes: Escherichia, shigella, salmonella, enterobacter, klebsiella, serratia.

E.coli form circular, convex, smooth colonies with distinct edges. Klebsiella colonies are large and very mucoid and tend to coalesce with prolonged incubation.
Salmonella and shigellae produce colonies similar to E.coli but they do not ferment lactose. However, salmonella and shigellae do not appear in the urinary tract.

E.coli is the most common cause of UTI and accounts for approximately 90% of first urinary tract infections in young women. The symptoms and signs include urinary frequency, dysuria, hematuria, and pyuria. However, none of these symptoms or signs is specific for E.coli.


  • Urine collected from clean-catch mid-stream or one obtained by bladder catherterization or suprapubic.

  • common causative: E.coli; Enterobacteriaceae; other gram-negactive rods

  • usual microscope: gram-negative rods seen on stained smear of uncentrifuged urine indicate more than 105/mL

  • culture on blood agar and macConkey

  • Comments: gray colonies that are B-hemolytic and give a positive spot indole test are usually E.coli; other require further biochemicsl tests

E.coli--> colonies show metallis on EMB agar

Klebsiella pneumoniae--> has large mucoid capsule and hence viscous colonies

Proteus mirabilis--> motility causes "swarming" on agar; produce urease

Pseudomonas aeruginosa--> blue-green pigment and fruity odor produced; causes nonsocomial infections and often drug-resistant

If unknown-form of colonies are observed (other than E.coli) , biochemical tests should be done to differentiate each micro-organism from each other.

Diagnosis: Biochemical Reaction:

IMViC (Indole Methy Re€d Voges-Proskauer simmons's Citrate) plus lactose fermentation & TSI


  1. E.coli ++--+ acid slant/acid butt with gas production

  2. Pseudomonas Aeruginosa -+--- alkaline slant/alkaline butt plus positive oxidation fermentation

  3. Klebsiella Pneumoniae +-+++ acid slant/acid butt with gas production

  4. Proteus Mirabilis -+++- alkaline slant/acid butt with H2S production

Other possible bacteria and tests required:

5. Enterococcus Faecalis

  • growth in the presence of bile, hydrolyze esculin

  • Alpha-hemolytic

  • growth in 6.5% NaCl, PYR-positive

6. Staphylococcus Saprophyticus

  • -ve mannitol

  • -ve coagulase

  • -ve Novobiocin sensitivity

  • -ve alpha toxin

7. Neisseria Gonorrhoeae

  • +ve glucose

  • -ve maltose

  • -ve Lactose

  • -ve Sucrose

8. Mycoplasma Genitalium

  • culture is difficult.

  • Data obtained from PCR, molecular probes, serologic tests

9. Ureaplasma Urealyticum

  • It required 10% urea for growth

Antibiotic Susceptibility Testing:

Escherichia coli (gram -ve rods enteric and related organisms)
drug choice: Cefotaxime, Fluoroquinolones, nitrofurantoin

Pseudomonas aeruginosa (gram -ve rods aerobic)
drug choice: Aminoglycoside, pencillin

klebsiella pneumoniae (gram -ve rods enteric and related organisms )
drug choice: A cephalosporin

proteus mirabilis (gram -ve rods enteric and related organisms)
drug choice: Ampicillin

Staphylococcus saprophyticus (gram +ve cocci)
drug choice: penicillin, tetracycline, vancomycin, gentamicin, rifampin

Neisseria gonorrhoeae (gram -ve cocci)
drug choice: ceftriaxone, ciprofloxacin, gatifloxacin,

Enterococcus faecalis (Pos cocci)
drug choice: Ampicillin, gentamicin

Mycoplasma genitalium (wall-less cells)
drug choice: erythromycin (ERY), clarithromycin (CLR), ciprofloxacin hydrochloride (CIP)

Ureaplasma urealyticum
drug choice: ciprofloxacin and ofloxacin, tetracycline and doxycycline, roxithromycin, erythromycin


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