Reassessment of the cefaclor breakpoint for Streptococcus pneumoniae

Impact of Cu(II)-doping on the vulnerability of Escherichia coli ATCC 10536 revealed by Atomic Force Microscopy

E. coli strain is a gram-negative bacterium known to induce both extra-intestinal infections and intestinal infections. For survival of microbes, metal intake and accessibility should be according to their physiological requirements. Peculiarly, copper homeostasis is critical for E. coli survival and growth. Therefore in this study, an extensive work is conducted to investigate the impact of Cu(II)-doping on the susceptibility of Escherichia coli ATCC 10536 against Cu(II)-selective Cefaclor-silver nanoconjugates (i.e., Cf-AgNPs) and its organic precursor (i.e. Cefaclor). At first, the maximal non-cytotoxic dose of Cu(II) that was sub-lethal for Escherichia coli was determined by MTT assay and was found to be 100 μg/L. Afterwards, MICs of Cf-AgNPs and Cefaclor against controlled and Cu(II)-doped E. coli cells were determined by using Agar well diffusion method. The susceptibility of E. coli cells against Cf-AgNPs was increased upon Cu(II) doping, whereas the bactericidal activity of Cefaclor against Cu(II)-doped E. coli cells was retarded due to hydrolysis. In addition, morphological changes induced in controlled and Cu(II)-doped samples of E. coli after treatment with Cefaclor and Cf-AgNPs were also monitored by Atomic force microscopy (AFM). The obtained results from both Agar well diffusion method and AFM confirmed that Cf-AgNPs are more effective against Cu(II)-doped Escherichia coli. Moreover, thermal profile of Cu(II)-selective Cf-AgNPs was also demonstrated by TGA and DSC. This study can be an important part of the relevant state-of-the-art. Indeed, further clinical studies are necessary to determine the relevant role of Cf-AgNPs compared with that of the Cefaclor now available.

Reassessment of cefaclor breakpoints for Haemophilus influenzae

We previously reported that standard methods overestimate cefaclor minimum inhibitory concentrations (MICs) for Streptococcus pneumoniae due to in vitro chemical instability. This study aimed to ascertain if standard methods accurately measure cefaclor MICs to Haemophilus influenzae. Cefuroxime was used as a comparator. Standard NCCLS broth microdilution and E-Test MICs were determined for eight isolates of H. influenzae. Kill curves determined the "bacteriostatic" MIC, defined as the concentration showing no significant growth or kill over six hours taking into account cefaclor instability. On average, cefaclor and cefuroxime bacteriostatic MICs were 0.2 x MIC and 0.6 x MIC determined by NCCLS methodology respectively. The mean MIC determined by NCCLS methodology was 3.0 mg/L for cefaclor and 0.8 mg/L for cefuroxime. Cefaclor MICs by NCCLS methodology were overestimated due to chemical instability over 18-24 hours. The bacteriostatic MICs by kill curve were not significantly different from those of cefuroxime.