Variability of cutaneous and nasal population levels between patients colonized and infected by multidrug-resistant bacteria in two Brazilian intensive care units

Exploring the metabolic profile of A. baumannii for antimicrobial development using genome-scale modeling

With the emergence of multidrug-resistant bacteria, the World Health Organization published a catalog of microorganisms urgently needing new antibiotics, with the carbapenem-resistant Acinetobacter baumannii designated as "critical". Such isolates, frequently detected in healthcare settings, pose a global pandemic threat. One way to facilitate a systemic view of bacterial metabolism and allow the development of new therapeutics is to apply constraint-based modeling. Here, we developed a versatile workflow to build high-quality and simulation-ready genome-scale metabolic models. We applied our workflow to create a metabolic model for A. baumannii and validated its predictive capabilities using experimental nutrient utilization and gene essentiality data. Our analysis showed that our model iACB23LX could recapitulate cellular metabolic phenotypes observed during in vitro experiments, while positive biomass production rates were observed and experimentally validated in various growth media. We further defined a minimal set of compounds that increase A. baumannii's cellular biomass and identified putative essential genes with no human counterparts, offering new candidates for future antimicrobial development. Finally, we assembled and curated the first collection of metabolic reconstructions for distinct A. baumannii strains and analyzed their growth characteristics. The presented models are in a standardized and well-curated format, enhancing their usability for multi-strain network reconstruction.

Acinetobactin-Mediated Inhibition of Commensal Bacteria by Acinetobacter baumannii

Acinetobacter baumannii is an important hospital-associated pathogen that causes antibiotic resistant infections and reoccurring hospital outbreaks. A. baumannii’s ability to asymptomatically colonize patients is a risk factor for infection and exacerbates its spread. However, there is little information describing the mechanisms it employs to colonize patients. A. baumannii often colonizes the upper respiratory tract and skin. Antibiotic use is a risk factor for colonization and infection suggesting that A. baumannii likely competes with commensal bacteria to establish a niche. To begin to investigate this possibility, we cocultured A. baumannii and commensal bacteria of the upper respiratory tract and skin. In conditions that mimic iron starvation experienced in the host, we observed that A. baumannii inhibits Staphylococcus epidermidis, Staphylococcus hominis, Staphylococcus haemolyticus and Corynebacterium striatum. Then using an ordered transposon library screen we identified the A. baumannii siderophore acinetobactin as the causative agent of the inhibition phenotype. Using mass spectrometry, we show that acinetobactin is released from A. baumannii under our coculture conditions and that purified acinetobactin can inhibit C. striatum and S. hominis. Together our data suggest that acinetobactin may provide a competitive advantage for A. baumannii over some respiratory track and skin commensal bacteria and possibly support its ability to colonize patients.

IMPORTANCE The ability of Acinetobacter baumannii to asymptomatically colonize patients is a risk factor for infection and exacerbates its clinical spread. However, there is minimal information describing how A. baumannii asymptomatically colonizes patients. Here we provide evidence that A. baumannii can inhibit the growth of many skin and upper respiratory commensal bacteria through iron competition and identify acinetobactin as the molecule supporting its nutritional advantage. Outcompeting endogenous commensals through iron competition may support the ability of A. baumannii to colonize and spread among patients.

Pathogens and Prognosis of Deep Neck Infection in End-Stage Renal Disease Patients

OBJECTIVES/HYPOTHESIS

To examine the pathogenic bacterial spectra and prognosis of deep neck infection (DNI) in end-stage renal disease (ESRD) patients.

STUDY DESIGN

Retrospective study.

METHODS

Patients diagnosed with DNI between 2004 and 2015 in Chang Gung Memorial Hospital were enrolled and divided into three groups, namely ESRD-DNI, chronic kidney disease (CKD)-DNI, and non-CKD-DNI. Differences in pathogenic bacteria, treatment, and prognosis were compared across the three groups.

RESULTS

The bacterial spectra differed among the three groups. The main three facultative anaerobic or aerobic bacteria causing ESRD-DNIs were methicillin-resistant Staphylococcus aureus (MRSA; 25.4%), methicillin-susceptible S. aureus (MSSA; 14.1%), and Klebsiella pneumoniae (KP; 12.7%). For CKD-DNIs, they were KP (23.5%), Viridans streptococci (VS; 23.5%), and MSSA (14.7%). For non-CKD-DNIs, they were VS (31.7%), KP (17.2%), and coagulase-negative staphylococci (8.0%). Compared with the other groups, the ESRD-DNI group had higher white blood cell and C-reactive protein levels, longer hospital stays, more frequent admissions to the intensive care unit, more mediastinal complications, and a significantly higher mortality rate.

CONCLUSIONS

The ESRD-DNI group exhibited more severe disease activity and higher mortality compared with those of the CKD-DNI and non-CKD-DNI groups. MRSA was the leading pathogen for patients with ESRD-DNI. Physicians must implement strategies for the early detection of MRSA to accurately prescribe antibiotics and prevent nosocomial transmission.

LEVEL OF EVIDENCE

4 Laryngoscope, 2021.

Activity of antimicrobial peptides and conventional antibiotics against superantigen positive Staphylococcus aureus isolated from patients with atopic dermatitis

Introduction

Staphylococcus aureus causes a diverse array of diseases, ranging from relatively harmless localized skin infections to life-threatening systemic conditions. It secretes toxins directly associated with particular disease symptoms.

Aim

To determine the prevalence of methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) colonization among patients with atopic dermatitis and to assess the antimicrobial susceptibility to conventional antibiotics and selected antimicrobial peptides among toxin-producing strains and nonproducing strains.

Material and methods

One hundred patients with atopic dermatitis and 50 healthy people were microbiologically assessed for the carriage of S. aureus. Antimicrobial susceptibility tests were performed using the broth microdilution method for conventional antibiotics and antimicrobial peptides (CAMEL, Citropin 1.1, LL-37, Temporin A). Detection of genes lukS/lukF-PV, tst, sea-sed, eta and etb by multiplex PCR was performed.

Results

Staphylococcus aureus strains were isolated from the majority of patients, from either the skin (75%) or the anterior nares (73%). Among the conventional antibiotics tested, the highest rates of resistance were observed for ampicillin, daptomycin, lincomycin and erythromycin. Antimicrobial peptides did not show significant diversity in activity. Among MSSA strains greater differentiation of secreted toxins was observed (sec, eta, pvl, tsst, etb, seb), while in the group of MRSA strains secretion of 3 toxins (pvl, eta, seb) was noted.

Conclusions

Antimicrobial resistance continues to evolve. It is important to monitor S. aureus infections. The profile of toxins produced by S. aureus strains is an important consideration in the selection of an antimicrobial agent to treat infections.