Antibiotic dependence in clinical isolates has been reported, albeit rarely, such as
vancomycin-dependent enterococcus and
beta-lactam-dependent Staphylococcus saprophyticus. We report herein a clinical isolate of
beta-lactam-dependent Bacillus cereus. A 16-yr-old female was admitted on 8 September 2005 with neutropenic
fever during
chemotherapy following surgical removal of
peripheral neuroectodermal tumor. She had had an indwelling chemoport since August 2004 and experienced B. cereus
bacteremia three times during the recent 3-month period prior to the admission; the
bacteremias were treated with
cefepime-based
chemotherapy. On hospital days 1 and 3, B. cereus was isolated from blood drawn through the chemoport. The isolates were resistant to
penicillin,
ceftriaxone, and
erythromycin, and susceptible to
vancomycin and
ciprofloxacin. The isolate of hospital day 3 grew only nearby the
beta-lactam disks including
penicillin and
ceftriaxone on disk diffusion testing. The
beta-lactam-dependent isolate required a minimum of 0.064 microg/mL of
penicillin or 0.023 microgram/mL of
cefotaxime for growth, which was demonstrated by E test (AB Biodisk, Sweden). Light microscopy and transmission electron microscopy revealed a marked elongation of the dependent strain compared with the non-dependent strain. Prolonged
therapy with
beta-lactams in the patient with an indwelling intravenous
catheter seemed to be a risk factor for the emergence of
beta-lactam-dependence in B. cereus.