Bexkens, M. L. | Search bioRxiv

bioRxiv2024

Stability of four carbapenem antibiotics in discs used for antimicrobial susceptibility testing

In low-to middle-income countries, microbiological laboratories often use disc diffusion for antimicrobial susceptibility testing (AST). Reliable AST of carbapenem antibiotics is crucial for treatment decisions and surveillance purposes. Transport and storage conditions of materials used for AST are critical and may be challenging in some settings, where temperature cannot always be controlled. This study aimed to test the stability of four carbapenems in discs for AST under unfavourable conditions, i.e., at room temperature and 35{degrees}C for up to 72 hours. Imipenem, meropenem, ertapenem, and doripenem discs from three brands, Oxoid, Becton Dickinson, and HiMedia, containing 10 g of antibiotic were included. Discs were exposed to six unfavourable conditions and the recommended storage-condition as control. Subsequently, disc diffusion testing following the EUCAST guidelines was performed with four well-defined strains of Escherichia coli with different susceptibility profiles to carbapenems. The inhibition zone diameters were measured after 16-18 hours of incubation at 35{+/-}2{degrees}C. All experiments were executed in triplicate. In parallel, the carbapenems degradation was observed using a spectrophotometric method. Our study revealed that carbapenem discs were generally stable for AST although the concentration of most carbapenem antibiotics in discs decreased over time. Overall, imipenem (Oxoid and Becton Dickinson) discs were the most stable. Meropenem discs were less stable when exposed to 35{degrees}C than at room temperature. Concentrations of carbapenems in HiMedia discs were higher than those in Oxoid and Becton Dickinson. For carbapenem AST using disc diffusion in a rural area, we recommend using imipenem discs from Oxoid or Becton Dickinson. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=82 SRC="FIGDIR/small/599257v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@1ca4d5aorg.highwire.dtl.DTLVardef@9c54bborg.highwire.dtl.DTLVardef@17ee220org.highwire.dtl.DTLVardef@12fcfc0_HPS_FORMAT_FIGEXP M_FIG C_FIG HIGHLIGHTSO_LIIn remote areas, transportation conditions of AST discs may be challenging C_LIO_LIDiscs with four carbapenems from three brands were tested using six conditions C_LIO_LICarbapenem discs were generally stable for AST C_LIO_LIIn unfavourable conditions, concentrations in the discs degraded over time C_LIO_LIImipenem (Oxoid and Becton Dickinson) discs were the most stable C_LI

microbiology↗

bioRxiv2018

Schistosoma mansoni does not and cannot oxidize fatty acids, but these are used for biosynthetic purposes instead

Adult schistosomes, parasitic flatworms that cause the tropical disease schistosomiasis, have always been considered to be homolactic fermenters and in their energy metabolism strictly dependent on carbohydrates. However, more recent studies suggested that fatty acid {beta}-oxidation is essential for egg production by adult female Schistosoma mansoni. To address this conundrum, we performed a comprehensive study on the lipid metabolism of S. mansoni. Incubations with [14C]-labelled fatty acids demonstrated that adults, eggs and miracidia of S. mansoni did not oxidize fatty acids, as no 14CO2 production could be detected. We then re-examined the S. mansoni genome using the genes known to be involved in fatty acid oxidation in six eukaryotic model reference species. This showed that the earlier automatically annotated genes for fatty acid oxidation were in fact incorrectly annotated. In a further analysis we could not detect any genes encoding {beta}-oxidation enzymes, which demonstrates that S. mansoni cannot use this pathway in any of its lifecycle stages. The same was true for S. japonicum. Absence of {beta}-oxidation, however, does not imply that fatty acids from the host are not metabolized by schistosomes. Adult schistosomes can use and modify fatty acids from their host for biosynthetic purposes and incorporate them in phospholipids and neutral lipids. Female worms deposit large amounts of these lipids in the eggs they produce, which explains why interference with the lipid metabolism in females will disturb egg formation, even though fatty acid {beta}-oxidation does not occur in schistosomes. Our analyses of S. mansoni further revealed that during the development and maturation of the miracidium inside the egg, changes in lipid composition occur which indicates that fatty acids deposited in the egg by the female worm are used for phospholipid biosynthesis required for membrane formation in the developing miracidium.

biochemistry↗