Abstract

Axenic cultures of Klebsiella pneumoniae, Escherichia coli and Staphylococcus aureus obtained from the Medical Microbiology Laboratory of the Delta State University Teaching Hospital, Oghara, were inoculated into ten-fold serial dilutions of 10-1 to 10-7 in sterile Nutrient broth and incubated in water bath at 37°C for 18 h initially. The turbid broth cultures of 10-5, 10-6 and 10-7 dilutions were subcultured aseptically on sterile MacConkey agar, Nutrient agar and Blood agar plates and incubated at 37°C for 18 h. Antibiotic sensitivity testing was done using gentamycin, nalidixic acid, nitrofurantoin, ofloxacin, cotrimoxazole, tetracycline, amoxicillin and amoxicillin/clavulanic acid on isolates from the last three dilutions selected and results were recorded as before temperature treatment. Serial dilutions were repeated and the last three dilutions were subcultured on same media as before treatment and all inoculated plates were incubated at 30, 35, 40 and 45°C in the water bath for 18 h. Antibiotic sensitivity testing was then carried out using the same drugs and results were recorded as after treatment. Mean±standard error zones of inhibition (ZI) recorded for 10-5, 10-6 and 10-7 E. coli broth dilutions at 37°C by gentamycin, nalidixic acid, nitrofurantoin and ofloxacin were 13.8±10.0, 16.8±11.0, and 14.0±8.1 mm, respectively. Same broth dilutions of K. pneumoniae recorded 17.6±9.5, 14.4±6.0 and 13.8±9.3 mm ZI, respectively to same drugs. Similarly, same broth culture dilutions of S. aureus recorded 3.4±7.1, 2.8±6.9 and 2.8±5.7 mm ZI, respectively to same antibiotics. There was resistance reduction (RR) of 76.2±11.6 and 57.0±14.3% by 10-6 and 10-5 broth dilutions of E. coli at 30 and 40°C, respectively. In all three broth culture dilutions of K. pneumoniae, there was a less than 30% RR at all tested temperatures. S. aureus broth dilutions of 10-5, 10-6 and 10-7 recorded 173.9±6.4, 150.0±7.3 and 87.0±6.2% RR, respectively to ofloxacin at 30°C.  At 35°C, 10-7 S. aureus broth dilution recorded 87.0±4.3% RR. There was more than 50% RR in 10-5 and 10-6 S. aureus broth dilutions at 40°C and more than 50% RR in all three dilutions at 45°C. Vertically, the three pathogens in 10-7 broth dilution and at 40°C recorded a common RR of 58.1±11.2% against gentamicin. Broth culture dilutions of 10-5 and 10-6 of all pathogens produced RR of 74.6±22.2 and 74.6±21.0%, respectively against ofloxacin with no significant RR against the other drugs at the temperatures tested. The implications of these findings are discussed.

Key words: Elevated, temperature, resistance reduction, clinical pathogens.