Defective pgsA contributes to increased membrane fluidity and cell wall thickening in Staphylococcus aureus with high-level daptomycin resistance.

Daptomycin is a membrane-targeting last-resort antimicrobial therapeutic for the treatment of infections caused by methicillin- and/or vancomycin-resistant Staphylococcus aureus. In the rare event of failed daptomycin therapy, the source of resistance is often attributable to mutations directly within the membrane phospholipid biosynthetic pathway of S. aureus or in the regulatory systems that control cell envelope response and membrane homeostasis. Here we describe the structural changes to the cell envelope in a daptomycin-resistant isolate of S. aureus strain N315 that has acquired mutations in the genes most commonly reported associated with daptomycin resistance: mprF, yycG, and pgsA. In addition to the decreased phosphatidylglycerol (PG) levels that are the hallmark of daptomycin resistance, the mutant with high-level daptomycin resistance had increased branched-chain fatty acids (BCFAs) in its membrane lipids, increased membrane fluidity, and increased cell wall thickness. However, the successful utilization of isotope-labeled straight-chain fatty acids (SCFAs) in lipid synthesis suggested that the aberrant BCFA:SCFA ratio arose from upstream alteration in fatty acid synthesis rather than a structural preference in PgsA. Transcriptomics studies revealed that expression of pyruvate dehydrogenase (pdhB) was suppressed in the daptomycin-resistant isolate, which is known to increase BCFA levels. While complementation with an additional copy of pdhB had no effect, complementation of the pgsA mutation resulted in increased PG formation, reduction in cell wall thickness, restoration of normal BCFA levels, and increased daptomycin susceptibility. Collectively, these results demonstrate that pgsA contributes to daptomycin resistance through its influence on membrane fluidity and cell wall thickness, in addition to phosphatidylglycerol levels. IMPORTANCE: The cationic lipopeptide antimicrobial daptomycin has become an essential tool for combating infections with Staphylococcus aureus that display reduced susceptibility to ß-lactams or vancomycin. Since daptomycin's activity is based on interaction with the negatively charged membrane of S. aureus, routes to daptomycin-resistance occur through mutations in the lipid biosynthetic pathway surrounding phosphatidylglycerols and the regulatory systems that control cell envelope homeostasis. Therefore, there are many avenues to achieve daptomycin resistance and several different, and sometimes contradictory, phenotypes of daptomycin-resistant S. aureus, including both increased and decreased cell wall thickness and membrane fluidity. This study is significant because it demonstrates the unexpected influence of a lipid biosynthesis gene, pgsA, on membrane fluidity and cell wall thickness in S. aureus with high-level daptomycin resistance.

Defective pgsA contributes to increased membrane fluidity and cell wall thickening in S. aureus with high-level daptomycin resistance.

Daptomycin is a membrane-targeting last-resort antimicrobial therapeutic for the treatment of infections caused by methicillin- and/or vancomycin-resistant Staphylococcus aureus. In the rare event of failed daptomycin therapy, the source of resistance is often attributable to mutations directly within the membrane phospholipid biosynthetic pathway of S. aureus or in the regulatory systems that control cell envelope response and membrane homeostasis. Here we describe the structural changes to the cell envelope in a daptomycin-resistant isolate of S. aureus strain N315 that has acquired mutations in the genes most commonly reported associated with daptomycin-resistance: mprF, yycG, and pgsA. In addition to the decreased phosphatidylglycerol (PG) levels that are the hallmark of daptomycin-resistance, the mutant with high-level daptomycin resistance had increased branched-chain fatty acids (BCFAs) in its membrane lipids, increased membrane fluidity, and increased cell wall thickness. However, the successful utilization of isotope-labeled straight-chain fatty acids (SCFAs) in lipid synthesis suggested that the aberrant BCFA:SCFA ratio arose from upstream alteration in fatty acid synthesis rather than a structural preference in PgsA. RT-qPCR studies revealed that expression of pyruvate dehydrogenase (pdhB) was suppressed in the daptomycin-resistant isolate, which is known to increase BCFA levels. While complementation with an additional copy of pdhB had no effect, complementation of the pgsA mutation resulted in increased PG formation, reduction in cell wall thickness, restoration of normal BCFA levels, and increased daptomycin susceptibility. Collectively, these results demonstrate that pgsA contributes to daptomycin resistance through its influence on membrane fluidity and cell wall thickness, in addition to phosphatidylglycerol levels.

Making an Impact with E.M.P.A.C.T. Engage, Mentor Prepare, Advocate, Cultivate, and Teach: An Innovative Pilot Mentoring Program Evaluation for Students Underrepresented in Medicine.

Purpose: Medicine has yet to increase the representation of historically excluded persons in medicine to reflect the general population. The lack of support and guidance in the medical training of these individuals is a significant contributor to this disparity. The Engage, Mentor, Prepare, Advocate for, Cultivate, and Teach (EMPACT) Mentoring program was created to address this problem by providing support for learners who are historically underrepresented in medicine (URiM) as they progress through medical school. Methods: The EMPACT Pilot Program was formed and conducted during the 2019-2020 academic year. A total of 19 EMPACT mentorship groups were created, each consisting of two mentors and four medical student mentees. Additionally, four professional development workshops were held along with a final Wrap-up and Awards event. Pre and post pilot program surveys along with surveys after each workshop and focus groups were conducted with a random selection of program participants. Results: When compared to data from before and after the implementation of the EMPACT program, there were statistically significant differences (p < 0.05) in EMPACT mentees reporting they agree or strongly agree they felt ready to handle their clinical rotations (28% to 65%), felt the need to have an advocate (85% to 47%), possessed insight on day-to-day activities of an attending (26% to 56%) and felt a sense of community (79% to 94%). Mentors revealed an increase in their awareness of the concepts of microaggressions and imposter phenomenon. Finally, both groups felt an increase in their support system and sense of community at the school of medicine. Conclusion: Despite COVID-19 limitations, the EMPACT program met its goals. We effectively supported URiM medical students through mentorship, networking, and community.

Neighborhood deprivation and severe maternal morbidity in a medicaid-Insured population in Georgia.

BACKGROUND: Despite growing acceptance of the role of context in shaping perinatal risk, data on how neighborhood factors may identify high-risk obstetric patients is limited. In this study, we evaluated the effect of neighborhood deprivation and neighborhood racial composition on severe maternal morbidity (SMM) among persons delivered in a large public health system in Atlanta, Georgia. METHODS: We conducted a population cohort study using electronic medical record data on all deliveries at Grady Memorial Hospital during 2011-2020. Using residential zip codes, we calculated neighborhood deprivation index based on data from the US Census. We used log-binomial regression with generalized estimating equations to estimate crude and adjusted relative risks (aRR) and 95% confidence intervals (CI) for the association between tertile of neighborhood deprivation and SMM, adjusting for demographic, clinical, and neighborhood-level (racial composition, food desert, and transit access) covariates. RESULTS: Among 25,257 deliveries, 6.2% (1566) experienced SMM. Approximately 24.0%, 32.0%, and 44.0% of women lived in the lowest, middle, and highest tertile of neighborhood deprivation, respectively and 64.9% lived in a neighborhood with majority non-Hispanic Black residents. After adjustment, there was no association between neighborhood deprivation and SMM (aRR: 1.0 (0.8, 1.1)) or residence in a majority Black neighborhood and SMM (aRR:1.0 (0.9, 1.2)). CONCLUSION: In this safety-net hospital, residence in a high deprivation or majority Black neighborhood did not predict SMM at or following delivery. Individual-level social determinants may better explain variation in risk, particularly in high-burden populations.

Revealing Fatty Acid Heterogeneity in Staphylococcal Lipids with Isotope Labeling and RPLC-IM-MS.

Up to 80% of the fatty acids in Staphylococcus aureus membrane lipids are branched, rather than straight-chain, fatty acids. The branched fatty acids (BCFAs) may have either an even or odd number of carbons, and the branch position may be at the penultimate carbon (iso) or the antepenultimate (anteiso) carbon of the tail. This results in two sets of isomeric fatty acid species with the same number of carbons that cannot be resolved by mass spectrometry. The isomer/isobar challenge is further complicated when the mixture of BCFAs and straight-chain fatty acids (SCFAs) are esterified into diacylated lipids such as the phosphatidylglycerol (PG) species of the S. aureus membrane. No conventional chromatographic method has been able to resolve diacylated lipids containing mixtures of SCFAs, anteiso-odd, iso-odd, and iso-even BCFAs. A major hurdle to method development in this area is the lack of relevant analytical standards for lipids containing BCFA isomers. The diversity of the S. aureus lipidome and its naturally high levels of BCFAs present an opportunity to explore the potential of resolving diacylated lipids containing BCFAs and SFCAs. Using our knowledge of lipid and fatty acid biosynthesis in S. aureus, we have used a stable-isotope-labeling strategy to develop and validate a 30 min C18 reversed-phase liquid chromatography method combined with traveling-wave ion mobility-mass spectrometry to provide resolution of diacylated lipids based on the number of BCFAs that they contain.

Recent applications of mass spectrometry in bacterial lipidomics.

The popularity of mass spectrometry-based lipidomics has soared in the past decade. While the majority of the lipidomics work is being performed in mammalian and other eukaryotic systems, there is also a growing rise in the exploration of bacterial lipidomics. The lipids found in bacteria can be substantially different from those in eukaryotic systems, but they are equally important for maintaining the structure of the bacteria and providing protection from the surrounding environment. In this article, recent applications of lipidomics in combination with molecular biology and applications in microbial strain identification and antibiotic susceptibility are highlighted. The authors' perspectives on current challenges facing the field and future directions are also provided.

Rationally designed phenanthrene derivatized triazole as a dual chemosensor for fluoride and copper recognition.

A 1,2,3-triazole chemosensor containing phenanthrene and phenol moieties (PhTP) was efficiently synthesized via copper (I)-catalyzed azide-alkyne cycloaddition, "click chemistry". PhTP is a dual analyte sensor for fluoride and copper (II) ions in homogeneous medium. Deprotonation of the phenolic OH proton by the fluoride ion is responsible for a change in fluorescence color from blue (PhTP) to yellowish-orange (PhTP-fluoride adduct), while a charge transfer between the triazole nitrogen of the chemosensor and Cu2+ revealed a turn-off fluorescence output. The detection capability of PhTP was analyzed with a series of anions (F-, Cl-, Br-, I-, H2PO4-, ClO4-, OAc-, BF4-) and cations (Fe3+, Fe2+, Cu2+, Ag+, Cr3+, Al3+, Co2+, Ni2+, Cd2+, Zn2+). With anions, competitive fluorescence responses under UV lamp were observed for acetate and dihydrogen phosphate anions, but maximum response from fluoride ion was substantiated from steady state absorption and fluorescence experiments. With cations, PhTP displayed a selective and sensitive recognition towards Cu2+ ion through spectral modulation in absorption spectroscopy and a turn-off fluorescence response. Nuclear magnetic resonance (NMR) spectroscopic titration studies supported the results obtained through photophysical studies and provided evidence for the ion-binding sites on the probe.