Enterococcus

CASE 1

• A 24 year old woman has had recurrent urinary tract infections for the past 5 years. The infections usually begin with a sense of urinary urgency and increased frequency of voiding. Then, the patient develops dysuria (pain with urination) and suprapubic discomfort. During past episodes, the symptoms responded promptly to treatment with cotrimoxasole (sulfamethoxazole-trimethoprim). With this episode, this antibiotic resulted in no improvement, and the symptoms improved only partially after treatment with ciprofloxacin (a fluoroquinolone).

• A urine Gram stain showed Gram-positive cocci in pairs and chains with numerous neutrophils. The patient was placed on amoxicillin (which is converted to ampicillin in the body), and the symptoms responded promptly. A urine culture was performed before taking the amoxicillin grew >100,000 colonies of Enterococcus faecalis per ml.

Questions:

1. What characteristics or tests distinguish Enterococcus from Streptococcus in culture? In what culture conditions do Enterococci grow but Streptococci do not.
2. Where in the human body are Enterococci found normally?
3. Why did previous urinary infections respond to co-trimoxasole, but this one did not? Are Enterococci ever sensitive to this antibiotic? If not, why not?

CASE 2

• A 72 year old man has mild fevers, decreased appetite, and night sweats for for the past 4 months. His health has been otherwise good, except for the the long-standing complaint of difficulty starting his urinary stream and some dribbling afterward. He also awakens from sleep to urinate 3-4 times every night.

• On physical examination, the temperature is 38 degrees, and the patient is found to have a new systolic ejection heart murmur. There are peripheral signs of endocarditis, including splinter hemorrhages of several fingernails and a conjunctival hemorrhage (see below). A rectal examination reveals a prostate gland that is twice normal size. A blood culture is obtained.

• The attending physician astutely recognizes the signs and symptoms of an enlarged prostate. To investigate this further, he passes a catheter into the patient's bladder after he has voided completely. 500ml of urine are obtained (suggesting a chronic bladder outlet obstruction). A culture of the catheter urine is obtained, and the catheter is removed.

• An echocardiogram (ultrasound of the heart) shows evidence of degenerative disease of the aortic valve and a 2cm vegetation on the coronary cusp of the valve.

• After 24 hours, both the blood and urine cultures grow Enterococcus faecalis. The patient is treated with intravenous ampicillin, but his symptoms improve only slightly, and new hemorrhages appear in his nailbeds and new petechiae are seen in his conjunctivae and oral mucosa.

Questions:

1. Does this patient have endocarditis? If so, where is the source?
2. What characteristic of Enterococci explains why he does not improve completely with intravenous ampicillin?