Peptidoglycan Cross-Linking Activity of l,d-Transpeptidases from Clostridium difficile and Inactivation of These Enzymes by ß-Lactams.

In most bacteria, the essential targets of ß-lactam antibiotics are the d,d-transpeptidases that catalyze the last step of peptidoglycan polymerization by forming 4→3 cross-links. The peptidoglycan of Clostridium difficile is unusual since it mainly contains 3→3 cross-links generated by l,d-transpeptidases. To gain insight into the characteristics of C. difficile peptidoglycan cross-linking enzymes, we purified the three putative C. difficile l,d-transpeptidase paralogues LdtCd1, LdtCd2, and LdtCd3, which were previously identified by sequence analysis. The catalytic activities of the three proteins were assayed with a disaccharide-tetrapeptide purified from the C. difficile cell wall. LdtCd2 and LdtCd3 catalyzed the formation of 3→3 cross-links (l,d-transpeptidase activity), the hydrolysis of the C-terminal d-Ala residue of the disaccharide-tetrapeptide substrate (l,d-carboxypeptidase activity), and the exchange of the C-terminal d-Ala for d-Met. LdtCd1 displayed only l,d-carboxypeptidase activity. Mass spectrometry analyses indicated that LdtCd1 and LdtCd2 were acylated by ß-lactams belonging to the carbapenem (imipenem, meropenem, and ertapenem), cephalosporin (ceftriaxone), and penicillin (ampicillin) classes. Acylation of LdtCd3 by these ß-lactams was not detected. The acylation efficacy of LdtCd1 and LdtCd2 was higher for the carbapenems (480 to 6,600 M-1 s-1) than for ampicillin and ceftriaxone (3.9 to 82 M-1 s-1). In contrast, the efficacy of the hydrolysis of ß-lactams by LdtCd1 and LdtCd2 was higher for ampicillin and ceftriaxone than for imipenem. These observations indicate that LdtCd1 and LdtCd2 are inactivated only by ß-lactams of the carbapenem class due to a combination of rapid acylation and the stability of the resulting covalent adducts.

Does the ICU Requirement Score allow the poisoned patient to be safely managed without admission to the intensive care unit? - a validation cohort study.

BACKGROUND: The Intensive care unit (ICU) Requirement Score (IRS) has been defined as identifying poisoned patients on hospital admission who do not require ICU referral, in an effort to reduce health expenses. However, this score has been poorly validated. We aimed to evaluate the IRS in a large cohort of poisoned patients. METHODS: We performed a single-center retrospective cohort study. IRS was calculated using clinical parameters obtained on admission including age, systolic blood pressure, heart rate, Glasgow coma score, intoxication type, co-morbidities (i.e., arrhythmia, cirrhosis, and respiratory insufficiency), and the combination of the intoxication with another reason for ICU admission. We evaluated the ability of IRS < 6 determined on admission to predict the lack of need for ICU treatment, defined as the need for mechanical ventilation, vasopressors, and/or renal replacement therapy in the first 24 h post-admission and/or death during the hospital stay. This score was compared to the usual prognostic scores, i.e., SAPS II and III, SOFA score, and PSS. RESULTS: During the 10-year study period, 2,514 poisoned patients were admitted, 1,011 excluded as requiring ICU treatment on admission, and 1,503 included. Among these patients, 232 met the endpoint whereas only 23/510 patients with IRS < 6 (4.5%) presented the endpoint and one patient died. The area under the curve of the IRS ROC curve was 0.736 (95% confidence interval (CI), 0.702-0.770). The negative predictive value of IRS < 6 was 95% (95% CI, 93-97), sensitivity 89% (95% CI, 85-93), specificity 38% (95% CI, 36-41), and positive predictive value 21% (95% CI, 18-24). IRS performance was similar to those of the other tested scores, which are however not readily available on admission. CONCLUSION: Our data demonstrate the excellent negative predictive value of the IRS, allowing the exclusion of ICU requirements for poisoned patients with IRS < 6. IRS usefulness should be confirmed based on a prospective multicenter cohort study before extensive routine use.

Cytological patterns of bronchoalveolar lavage fluid in mechanically ventilated COVID-19 patients on extracorporeal membrane oxygenation.

INTRODUCTION: Coronavirus disease-2019 (COVID-19) may lead to acute respiratory distress syndrome requiring extracorporeal membrane oxygenation (ECMO). Patterns of inflammatory bronchoalveolar cells in COVID-19 patients treated with ECMO are not well described. OBJECTIVE: We aimed to describe inflammatory cell subpopulations in blood and bronchoalveolar lavages (BALs) obtained in critically ill COVID-19 patients shortly after ECMO implementation. METHODS: BAL was performed in the middle lobe in 12 consecutive ECMO-treated COVID-19 patients. Trained cytologists analyzed peripheral blood and BAL cells using flow cytometry and routine staining, respectively. Data were interpreted in relation to dexamethasone administration and weaning from ECMO and ventilator. RESULTS: High neutrophil proportions (66% to 88% of total cells) were observed in the absence of bacterial superinfection and more frequently in dexamethasone-free patients (83% [82-85] vs. 29% [8-68], P = 0.006), suggesting that viral infection could be responsible of predominantly neutrophilic lung inflammation. Successful weaning from ECMO/ventilator could not be predicted by the peripheral white blood and BAL cell pattern. CONCLUSION: High neutrophil proportions can be observed in critically ill COVID-19 patients despite the lack of microbiological evidence on BAL of bacterial superinfection. Dexamethasone was associated with lower neutrophil proportions in BAL. Our study was probably underpowered to provide BAL cell pattern helpful to predict weaning from ECMO/ventilator.

Factors associated with prolonged intensive care stay among self-poisoned patients.

CONTEXT: Since recovery or death is generally observed within a few days after intensive care unit (ICU) admission of self-poisoned patients in the developed countries, reasons for the prolonged ICU stay are of interest as they have been poorly investigated. We aimed to identify the characteristics, risk factors, outcome, and predictors of death in self-poisoned patients requiring prolonged ICU management. METHODS: We conducted an eight-year single-center cohort study including all self-poisoned patients who stayed at least seven days in the ICU. Patients admitted with drug adverse events and chronic overdoses were excluded. Using multivariate analyses, we investigated risk factors for prolonged ICU stay in comparison with a group of similar size of self-poisoned patients with <7day-ICU stay and studied risk factors for death. RESULTS: Among 2,963 poisoned patients admitted in the ICU during the study period, the number who stayed beyond seven days was small (398/2,963, 13.1%), including 239 self-poisoned patients (125 F/114M; age, 51 years [38-65] (median [25th-75th percentiles]); SAPSII, 56 [43-69]). Involved toxicants included psychotropic drugs (59%), cardiotoxicants (31%), opioids (15%) and street drugs (13%). When compared with patients who stayed <7days in the ICU, acute kidney injury (odds ratio (OR), 3.15; 95% confidence interval (1.36-7.39); p = .008), multiorgan failure (OR, 8.06 (3.43-19.9); p < .001), aspiration pneumonia (OR, 8.48 (4.28-17.3); p < .001), and delayed awakening related to the persistent toxicant effects, hypoxic encephalopathy and/or oversedation (OR, 8.64 (2.58-40.7); p = .002) were independently associated with prolonged ICU stay. In-hospital mortality rate was 9%. Cardiac arrest occurring in the prehospital setting and during the first hours of ICU management (OR, 27.31 (8.99-158.76); p < .001) and delayed awakening (OR, 14.94 (6.27-117.44); p < .001) were independently associated with increased risk of death, whereas exposure to psychotropic drugs (OR, 0.08 (0.02-0.36); p = .002) was independently associated with reduced risk of death. CONCLUSION: Self-poisoned patients with prolonged ICU stay of ≥7days are characterized by concerning high rates of morbidities and poisoning-attributed complications. Acute kidney injury, multiorgan failure, aspiration pneumonia, and delayed awakening are associated with ICU stay prolongation. Cardiac arrest occurrence and delayed awakening are predictive of death. Further studies should focus on the role of early goal-directed therapy and patient-targeted sedation in reducing ICU length of stay among self-poisoned patients.

Impact of Early Limitation of Therapeutic Effort in Elderly COVID-19 Patients Admitted to the Intensive Care Unit-A Cohort Study.

(1) Background: Admission to the ICU and intensity of care provided to elderly COVID-19 patients are difficult choices guided by the expected patient-centered benefits. However, the impact of an early discussion of limitation of therapeutic effort (LTE) has been poorly investigated. (2) Methods: We performed a single-center retrospective cohort study including all ≥70-year-old COVID-19 patients admitted to the ICU. Factors associated with early LTE discussion (defined as before or up to 2 days post-ICU admission) and in-hospital mortality were evaluated. (3) Results: Eighty-two patients (59 M/23 F; 78 years (74−82) [median (interquartile range)]; 43/82 with LTE) were included. The in-hospital mortality rate was 55%. Early LTE was decided upon for 22/82 patients (27%), more frequently in older (p < 0.001) and frailer patients (p = 0.004). Using a multivariable logistic regression model including clinical frailty scale grade ≥4, hospital acquisition of COVID-19, ventilation support modality and SOFA score on admission, early LTE was not associated with mortality (adjusted odds ratio = 0.57 (0.15−2.00), p = 0.39). LTE resulted in less frequent invasive mechanical ventilation (23% versus 65%, p = 0.001), renal replacement therapy (5% versus 27%, p = 0.03) and norepinephrine infusion (23% versus 60%, p = 0.005), and shorter ICU stay (6 days (2−12) versus 14 days (7−24), p = 0.001). (4) Conclusions: In this small sample exploratory study, we were unable to demonstrate any increase in in-hospital mortality associated with early LTE discussion in elderly COVID-19 patients while reducing the use of organ support techniques. These findings require confirmation in larger studies.

Dismal Survival in COVID-19 Patients Requiring ECMO as Rescue Therapy after Corticosteroid Failure.

(1) Background: COVID-19 may lead to refractory hypoxemia requiring venovenous extracorporeal membrane oxygenation (ECMO). Survival rate if ECMO is implemented as rescue therapy after corticosteroid failure is unknown. We aimed to investigate if ECMO implemented after failure of the full-recommended 10-day corticosteroid course can improve outcome. (2) Methods: We conducted a three-center cohort study including consecutive dexamethasone-treated COVID-19 patients requiring ECMO between 03/2020 and 05/2021. We compared survival at hospital discharge between patients implemented after (ECMO-after group) and before the end of the 10-day dexamethasone course (ECMO-before group). (3) Results: Forty patients (28M/12F; age, 57 years (51-62) (median (25th-75th percentiles)) were included, 28 (70%) in the ECMO-before and 12 (30%) in the ECMO-after group. In the ECMO-before group, 9/28 patients (32%) received the 6 mg/day dexamethasone regimen versus 12/12 (100%) in the ECMO-after group (p < 0.0001). The rest of the patients received an alternative dexamethasone regimen consisting of 20 mg/day during 5 days followed by 10 mg/day during 5 days. Patients in the ECMO-before group tended to be younger (57 years (51-59) versus 62 years (57-67), p = 0.053). In the ECMO-after group, no patient (0%) survived while 12 patients (43%) survived in the ECMO-before group (p = 0.007). (4) Conclusions: Survival is poor in COVID-19 patients requiring ECMO implemented after the full-recommended 10-day dexamethasone course. Since these patients may have developed a particularly severe presentation, new therapeutic strategies are urgently required.

Tryptophan Fluorescence Quenching in ß-Lactam-Interacting Proteins Is Modulated by the Structure of Intermediates and Final Products of the Acylation Reaction.

In most bacteria, ß-lactam antibiotics inhibit the last cross-linking step of peptidoglycan synthesis by acylation of the active-site Ser of d,d-transpeptidases belonging to the penicillin-binding protein (PBP) family. In mycobacteria, cross-linking is mainly ensured by l,d-transpeptidases (LDTs), which are promising targets for the development of ß-lactam-based therapies for multidrug-resistant tuberculosis. For this purpose, fluorescence spectroscopy is used to investigate the efficacy of LDT inactivation by ß-lactams but the basis for fluorescence quenching during enzyme acylation remains unknown. In contrast to what has been reported for PBPs, we show here using a model l,d-transpeptidase (Ldtfm) that fluorescence quenching of Trp residues does not depend upon direct hydrophobic interaction between Trp residues and ß-lactams. Rather, Trp fluorescence was quenched by the drug covalently bound to the active-site Cys residue of Ldtfm. Fluorescence quenching was not quantitatively determined by the size of the drug and was not specific of the thioester link connecting the ß-lactam carbonyl to the catalytic Cys as quenching was also observed for acylation of the active-site Ser of ß-lactamase BlaC from M. tuberculosis. Fluorescence quenching was extensive for reaction intermediates containing an amine anion and for acylenzymes containing an imine stabilized by mesomeric effect, but not for acylenzymes containing a protonated ß-lactam nitrogen. Together, these results indicate that the extent of fluorescence quenching is determined by the status of the ß-lactam nitrogen. Thus, fluorescence kinetics can provide information not only on the efficacy of enzyme inactivation but also on the structure of the covalent adducts responsible for enzyme inactivation.