Antimicrobial susceptibility profile of soil isolates of Nocardia asteroides from Kuwait.
OBJECTIVE
To find the antimicrobial susceptibility profile of 42 soil isolates of Nocardia asteroides against 14 antimicrobial agents representing beta-lactams, aminoglycosides, ciprofloxacin, minocycline, erythromycin and third generation cephalosporins.


METHODS
The antimicrobial susceptibility was determined by the disk diffusion method using Mueller-Hinton agar medium. A homogeneous suspension giving an inoculum of 106-108 CFU/mL was used to streak the plates. The zone of inhibition was read after 36-48 h of incubation at 37 degrees C.


RESULTS
All the soil isolates of N. asteroides were susceptible to amikacin, imipenem and tobramycin. Susceptibility to cephalosporins was quite variable; 86% of the isolates were susceptible to cefotaxime, 57% to ceftriaxone and 40% to cefamandole. Fifty-seven per cent of the isolates showed intermediate susceptibility to cefamandole, 33% to ceftriaxone and 5% to cefotaxime. Ninety-three per cent of the isolates were resistant to sulfamethoxazole alone or in combination with trimethoprim.


CONCLUSIONS
The study reports a wide variation in the antimicrobial susceptibility profile of soil isolates of N. asteroides originating from a single geographical area. Of interest is the finding that over 90% of N. asteroides isolates were resistant to sulfamethoxazole without any previous exposure to this drug. This may have serious therapeutic implications as sulphonamides or the combination of trimethoprim-sulfamethoxazole is the therapy of choice for nocardiosis. Demonstration of resistance to beta-lactam antibiotics may be attributed to the presence of beta-lactamases which was detectable in > 90% of the soil strains of N. asteroides. The study underscores the importance of antimicrobial susceptibility testing for clinical isolates of Nocardia since individual strains show considerable differences in their susceptibility patterns necessitating therapeutic adjustments.
Khan
Z
Z
Department of Microbiology and Surgery, Faculty of Medicine, Kuwait University, Kuwait. ziauddin@hsc.kuniv.edu.kw
Al-Sayer
H
H
Chugh
T D
TD
Chandy
R
R
Provost
F
F
Boiron
P
P
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004352:Drug Resistance, Microbial; D007730:Kuwait; D008826:Microbial Sensitivity Tests; D009616:Nocardia asteroides / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology / Q000302:isolation & purification; D012988:Soil Microbiology; D001618:beta-Lactamases / Q000378:metabolism
D000900:Anti-Bacterial Agents; D001618:beta-Lactamases