The effects of the morphological response of Enterobacteriaceae to cephalosporins on PAE and CERT.
PAE and CERT values of cefaclor, loracarbef and cefuroxime (0.1-100 x MIC) were established for 8 E. coli, 3 K. pneumoniae and 2 P. mirabilis isolates. Cell enumeration was by impedance (IMP) monitoring in combination with either bioluminescence (BIOL) or viable counting (VC). Morphology was determined by interference contrast microscopy. After 2 h exposure to cefaclor, loracarbef and cefuroxime; concentration-dependent differences in counts were seen by BIOL and VC, varying from a mean value of 0.07 x log10 after exposing the P. mirabilis isolates to 0.1 x MIC cefaclor to a mean value of 2.24 x log10 after exposing the E. coli strains to 100 x MIC cefuroxime. Higher concentrations gave rise to fragile morphological forms including spheroplasts and lower concentrations to less fragile forms such as long bacilli. The longest PAE and CERT values were obtained after exposing the E. coli strains to 100 x MIC cefaclor with mean values of 4.07 and 4.87 h, respectively. Corresponding values were PAE and CERT values of 2.17 and 2.60 h for 100 x cefuroxime and 3.45 and 2.91 h for 100 x MIC loracarbef. By the Student's t-test, PAE values determined by IMP/BIOL and IMP/VC were found to be significantly different, whereas CERT values were found not to be significantly different. PAE and CERT are concentration dependent and vary with specific antibiotic/organism combinations.
Mackenzie
F M
FM
Department of Medical Microbiology, Aberdeen Royal Infirmary, Foresterhill, UK.
Milne
K E
KE
Gould
I M
IM
D002433:Cefaclor / Q000494:pharmacology; D002444:Cefuroxime / Q000494:pharmacology; D002511:Cephalosporins / Q000494:pharmacology*; D015169:Colony Count, Microbial; D003470:Culture Media; D017097:Electric Impedance; D004755:Enterobacteriaceae / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development*; D008163:Luminescent Measurements; D008826:Microbial Sensitivity Tests
D002511:Cephalosporins; D003470:Culture Media; C054920:loracarbef; D002433:Cefaclor; D002444:Cefuroxime