Daptomycin is a lipopeptide antibiotic that has recently been approved for treatment of gram-positive bacterial infections. The mode of action of daptomycin is not yet entirely clear. To further understand the mechanism transcriptomic analysis of changes in gene expression in daptomycin-treated Staphylococcus aureus was carried out. The expression profile indicated that cell wall stress stimulon member genes (B. J. Wilkinson, A. Muthaiyan, and R. K. Jayaswal, Curr. Med. Chem. Anti-Infect. Agents 4:259-276, 2005) were significantly induced by daptomycin and by the cell wall-active antibiotics vancomycin and oxacillin. Comparison of the daptomycin response of a two-component cell wall stress stimulon regulator VraSR mutant, S. aureus KVR, to its parent N315 showed diminished expression of the cell wall stress stimulon in the mutant. Daptomycin has been proposed to cause membrane depolarization, and the transcriptional responses to carbonyl cyanide m -chlorophenylhydrazone (CCCP) and nisin were determined. Transcriptional profiles of the responses to these antimicrobial agents showed significantly different patterns compared to those of the cell wall-active antibiotics, including little or no induction of the cell wall stress stimulon. However, there were a significant number of genes induced by both CCCP and daptomycin that were not induced by oxacillin or vancomycin, so the daptomycin transcriptome probably reflected a membrane depolarizing activity of this antimicrobial also. The results indicate that inhibition of peptidoglycan biosynthesis, either directly or indirectly, and membrane depolarization are parts of the mode of action of daptomycin.

Listeria monocytogenes is a Gram-positive foodborne pathogen responsible for a severe disease occurring in immuno-compromised populations. Foodborne illness caused by L. monocytogenes is a serious public health concern because of the high associated mortality. Study of the closely related, but nonpathogenic Listeria innocua has accounted for a better understanding of the behavior of L. monocytogenes in environments beyond the laboratory. Traditionally, the ecological co-habitation, genomic synteny, and physiological similarity of the two species have supported use of L. innocua for predicting the behavior of L. monocytogenes in farm and food processing environments. However, a careful review of the current literature indicates that in a given situation it may not be prudent to use L. innocua as a surrogate for L. monocytogenes without prior confirmation of their similar phenotypes, as an increasing number of studies have arisen demonstrating differences in L. monocytogenes and L. innocua stress response, and furthermore, there are differences among the L. monocytogenes subgroups. Future research should take into consideration that multiple surrogates might be required to accurately model even a single condition depending on the L. monocytogenes subgroup of interest.

Listeria monocytogenes is an opportunistic human pathogen that causes listeriosis, a disease that mainly affects the immunocompromised, the elderly, infants, and pregnant women. Listeriosis has become increasingly common in the last 25 years since the first foodborne outbreak was noted. Treatment for listeriosis currently consists primarily of supportive therapy in conjunction with the use of intravenous antibiotics. Antibiotics have been commercially available for over 60 years for treatment of a myriad of clinical diseases. Bacteria resistant to antibiotics have been developing over this same period. This review seeks to elucidate the extent of antibiotic resistance in L. monocytogenes, the possible transmission mechanisms, and contributing factors to distribution of antibiotic resistance among Listeria species, and possible control strategies.

Aims: The objectives of this study were to evaluate the antistaphylococcal effect and elucidate the mechanism of action of orange essential oil against antibiotic‐resistant Staphylococcus aureus strains. Methods and Results: The inhibitory effect of commercial orange essential oil (EO) against six Staph. aureus strains was tested using disc diffusion and agar dilution methods. The mechanism of EO action on MRSA was analysed by transcriptional profiling. Morphological changes of EO‐treated Staph. aureus were examined using transmission electron microscopy. Results showed that 0·1% of terpeneless cold‐pressed Valencia orange oil (CPV) induced the cell wall stress stimulon consistent with the inhibition of cell wall synthesis. Transmission electron microscopic observation revealed cell lysis and suggested a cell wall lysis–related mechanism of CPV. Conclusions: CPV inhibits the growth of Staph. aureus, causes gene expression changes consistent with the inhibition of cell wall synthesis, and triggers cell lysis. Significance and Impact of the Study: Multiple antibiotics resistance is becoming a serious problem in the management of Staph. aureus infections. In this study, the altered expression of cell wall‐associated genes and subsequent cell lysis in MRSA caused by CPV suggest that it may be a potential antimicrobial agent to control antibiotic–resistant Staph. aureus.