Racial Disparities in COVID-19 Severity Are Partially Mediated by Chronic Stress-Evidence from a Large Integrated Healthcare System.

BACKGROUND: Racial and ethnic minorities have experienced a disproportionate burden of severe COVID-19. Whether chronic stress, also disproportionately experienced by racial and ethnic minorities, explains this excess risk is unknown. METHODS: We identified 9577 adults (≥ 18 years) diagnosed with COVID-19 from January 1, 2020, through September 30, 2021, enrolled in Kaiser Permanente Georgia (KPGA) with complete biomarker data. Self-reported race (Black or White) was defined from electronic medical records. Chronic stress, defined as allostatic load (AL), a composite score (scale 0-7) based on seven cardio-metabolic biomarkers, was categorized as below (low AL) or above (high AL) the median. Severe COVID-19 was defined as hospitalization or mortality within 30 days of COVID-19 diagnosis. The association between race, AL, and severe COVID-19 was assessed using multivariable Poisson regression. The mediating effect of AL was assessed using the Valeri and VanderWeele method. All results were expressed as risk ratios (RRs) with 95% confidence intervals. RESULTS: Overall, Black (vs. White) KPGA members had an 18% excess risk of AL (RR: 1.18, 95%CI: 1.14-1.23) and a 24% excess risk of severe COVID-19 (RR: 1.24, 95%CI: 1.12, 1.37). AL explained 23% of the Black-White disparities in severe COVID-19. CONCLUSIONS: In our study, chronic stress, characterized by AL, partially mediated Black-White disparities in severe COVID-19 outcomes.

Mutagenesis and structural analysis reveal the CTX-M ß-lactamase active site is optimized for cephalosporin catalysis and drug resistance.

CTX-M ß-lactamases are a widespread source of resistance to ß-lactam antibiotics in Gram-negative bacteria. These enzymes readily hydrolyze penicillins and cephalosporins, including oxyimino-cephalosporins such as cefotaxime. To investigate the preference of CTX-M enzymes for cephalosporins, we examined eleven active-site residues in the CTX-M-14 ß-lactamase model system by alanine mutagenesis to assess the contribution of the residues to catalysis and specificity for the hydrolysis of the penicillin, ampicillin, and the cephalosporins cephalothin and cefotaxime. Key active site residues for class A ß-lactamases, including Lys73, Ser130, Asn132, Lys234, Thr216, and Thr235, contribute significantly to substrate binding and catalysis of penicillin and cephalosporin substrates in that alanine substitutions decrease both kcat and kcat/KM. A second group of residues, including Asn104, Tyr105, Asn106, Thr215, and Thr216, contribute only to substrate binding, with the substitutions decreasing only kcat/KM. Importantly, calculating the average effect of a substitution across the 11 active-site residues shows that the most significant impact is on cefotaxime hydrolysis while ampicillin hydrolysis is least affected, suggesting the active site is highly optimized for cefotaxime catalysis. Furthermore, we determined X-ray crystal structures for the apo-enzymes of the mutants N106A, S130A, N132A, N170A, T215A, and T235A. Surprisingly, in the structures of some mutants, particularly N106A and T235A, the changes in structure propagate from the site of substitution to other regions of the active site, suggesting that the impact of substitutions is due to more widespread changes in structure and illustrating the interconnected nature of the active site.