Reliability of transport medium in the laboratory evaluation of corneal ulcers.
OBJECTIVE
To compare the microbiological yield of corneal ulcer cultures established by direct inoculation of culture media vs indirect inoculation by means of transport medium (Amies without charcoal).


METHODS
Single masked, prospective clinical trial.


METHODS
Scrapings were obtained for Gram and potassium hydroxide (KOH) stains from eyes with presumed infectious keratitis and cultured by direct plating onto standard media. Samples were also held in transport media (Amies without charcoal) at room temperature and then plated after 4 and 24 hours. Yields from direct plating vs cultures by means of transport media were compared.


RESULTS
Of 100 consecutive eyes examined with presumed infectious keratitis, Gram or KOH stain revealed a bacterial or fungal agent in 69 cases (69%). Of these, 26 were bacterial and 43 fungal. Twenty-two bacterial infections produced positive cultures by direct plating, and all produced the same organism with Amies medium after 4 and 24 hours, respectively. For 43 fungal infections identified by KOH stain, 29 (67%) yielded a positive result after 4 hours in Amies transport medium and 27 (63%) after 24 hours in Amies medium. A total of three cases (7%) that showed fungal infection on KOH stain but did not yield organisms by direct plating did so after inoculation with Amies transport medium. For all comparisons, there was no difference in recovery rates by means of transport medium compared with direct plating (McNemar exact P > .05).


CONCLUSIONS
In the clinical setting, Amies transport medium may be a useful alternative to direct inoculation onto blood agar for the laboratory evaluation of infectious keratitis.
McLeod
Stephen D
SD
Department of Ophthalmology at the University of California at San Francisco, 10 Koret Way, San Francisco, CA 94143, USA. mcleods@itsa.icsf.edu
Kumar
Abha
A
Cevallos
Vicky
V
Srinivasan
Muthaiah
M
Whitcher
John P
JP
D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D001419:Bacteria / Q000254:growth & development / Q000302:isolation & purification*; D001431:Bacteriological Techniques / Q000295:instrumentation*; D015169:Colony Count, Microbial; D003320:Corneal Ulcer / Q000175:diagnosis / Q000188:drug therapy / Q000382:microbiology*; D003470:Culture Media; D015818:Eye Infections, Bacterial / Q000175:diagnosis / Q000188:drug therapy / Q000382:microbiology*; D015821:Eye Infections, Fungal / Q000175:diagnosis / Q000188:drug therapy / Q000382:microbiology*; D005260:Female; D005658:Fungi / Q000254:growth & development / Q000302:isolation & purification*; D006801:Humans; D008297:Male; D011446:Prospective Studies; D015203:Reproducibility of Results; D016037:Single-Blind Method
D000900:Anti-Bacterial Agents; D003470:Culture Media