Culture plate temperature and delayed incubation effect on bacterial recovery.
OBJECTIVE
To discover if initial culturing conditions (plate temperature and time delay to incubation) adversely influence the recovery of organisms associated with bacterial keratitis.


METHODS
The rate of temperature equilibration of culture plates taken from a refrigerator and placed in an incubator and left on the desk was evaluated with a digital thermometer. A standard inoculum for each of five organisms (S. aureus, S. pneumoniae, P. aeruginosa, E. aerogenes, K. oxytoca) isolated from human bacterial keratitis was spread evenly on blood agar plates at refrigerator (Tcold; 4 degrees C), room (Troom; 24 degrees C), and incubator (Twarm; 37 degrees C) temperatures. The plates were then kept at room temperature for 0, 1, 3, 5, and 8 hours before overnight incubation at 37 degrees C (S. pneumoniae under microaerophilic conditions), and the number of colony-forming units was counted.


RESULTS
Cold plates took at least 15 minutes in an incubator to attain room temperature, and up to an hour when left on the desk. Increased organism recovery was found comparing both Twarm and Troom plates (6.2 to 24.8% and 7.0 to 14.7%, respectively, P<0.001) to Tcold plates for all organisms except S. pneumoniae (P=0.057). Comparing Twarm plates to Troom plates demonstrated an increased recovery (P<0.001) for S. aureus. Delayed incubation resulted in decreased recovery for S. pneumoniae (P<0.001).


CONCLUSIONS
Culture plates should preferably be warmed at least to room temperature before inoculation, as well as promptly incubated to increase bacterial recovery from cases of septic keratitis.
Department of Ophthalmology, Loma Linda University, California, USA.
Nathan J
NJ
Rudometkin
Izak F
IF
Wessels
Rudy S
RS
Hedayi
Joyce E
JE
Choe
Richmond E
RE
Roeske
D001419:Bacteria / Q000302:isolation & purification*; D001424:Bacterial Infections / Q000382:microbiology*; D001431:Bacteriological Techniques / Q000295:instrumentation*; D006801:Humans; D007634:Keratitis / Q000382:microbiology*; D013696:Temperature; D013997:Time Factors