Dual membrane-spanning anti-sigma factors regulate vesiculation in Bacteroides thetaiotaomicron

Bacteroidota are abundant members of the human gut microbiota that shape the enteric landscape by modulating host immunity and degrading dietary- and host-derived glycans. These processes are mediated in part by Outer Membrane Vesicles (OMVs). Here, we developed a high-throughput screen to identify genes required for OMV biogenesis and its regulation in Bacteroides thetaiotaomicron (Bt). We identified a family of Dual membrane-spanning anti-sigma factors (Dma) that control OMV biogenesis. We conducted molecular and multiomic analyses to demonstrate that deletion of Dma1, the founding member of the Dma family, modulates OMV production by controlling the activity of the ECF21 family sigma factor, Das1, and its downstream regulon. Dma1 has a previously uncharacterized domain organization that enables Dma1 to span both the inner and outer membrane of Bt. Phylogenetic analyses reveal that this common feature of the Dma family is restricted to the phylum Bacteroidota. This study provides mechanistic insights into the regulation of OMV biogenesis in human gut bacteria.

Comparative genomics reveals the correlations of stress response genes and bacteriophages in developing antibiotic resistance of Staphylococcus saprophyticus

IMPORTANCE

Staphylococcus saprophyticus is the second most common bacteria associated with urinary tract infections (UTIs) in women. The antimicrobial treatment regimen for uncomplicated UTI is normally nitrofurantoin, trimethoprim-sulfamethoxazole (TMP-SMX), or a fluoroquinolone without routine susceptibility testing of S. saprophyticus recovered from urine specimens. However, TMP-SMX-resistant S. saprophyticus has been detected recently in UTI patients, as well as in our cohort. Herein, we investigated the understudied resistance patterns of this pathogenic species by linking genomic antibiotic resistance gene (ARG) content to susceptibility phenotypes. We describe ARG associations with known and novel SCCmec configurations as well as phage elements in S. saprophyticus, which may serve as intervention or diagnostic targets to limit resistance transmission. Our analyses yielded a comprehensive database of phenotypic data associated with the ARG sequence in clinical S. saprophyticus isolates, which will be crucial for resistance surveillance and prediction to enable precise diagnosis and effective treatment of S. saprophyticus UTIs.

Uncharacterized and lineage-specific accessory genes within the Proteus mirabilis pan-genome landscape

Proteus mirabilis is a Gram-negative bacterium recognized for its unique swarming motility and urease activity. A previous proteomic report on four strains hypothesized that, unlike other Gram-negative bacteria, P. mirabilis may not exhibit significant intraspecies variation in gene content. However, there has not been a comprehensive analysis of large numbers of P. mirabilis genomes from various sources to support or refute this hypothesis. We performed comparative genomic analysis on 2,060 Proteus genomes. We sequenced the genomes of 893 isolates recovered from clinical specimens from three large US academic medical centers, combined with 1,006 genomes from NCBI Assembly and 161 genomes assembled from Illumina reads in the public domain. We used average nucleotide identity (ANI) to delineate species and subspecies, core genome phylogenetic analysis to identify clusters of highly related P. mirabilis genomes, and pan-genome annotation to identify genes of interest not present in the model P. mirabilis strain HI4320. Within our cohort, Proteus is composed of 10 named species and 5 uncharacterized genomospecies. P. mirabilis can be subdivided into three subspecies; subspecies 1 represented 96.7% (1,822/1,883) of all genomes. The P. mirabilis pan-genome includes 15,399 genes outside of HI4320, and 34.3% (5,282/15,399) of these genes have no putative assigned function. Subspecies 1 is composed of several highly related clonal groups. Prophages and gene clusters encoding putatively extracellular-facing proteins are associated with clonal groups. Uncharacterized genes not present in the model strain P. mirabilis HI4320 but with homology to known virulence-associated operons can be identified within the pan-genome. IMPORTANCE Gram-negative bacteria use a variety of extracellular facing factors to interact with eukaryotic hosts. Due to intraspecies genetic variability, these factors may not be present in the model strain for a given organism, potentially providing incomplete understanding of host-microbial interactions. In contrast to previous reports on P. mirabilis, but similar to other Gram-negative bacteria, P. mirabilis has a mosaic genome with a linkage between phylogenetic position and accessory genome content. P. mirabilis encodes a variety of genes that may impact host-microbe dynamics beyond what is represented in the model strain HI4320. The diverse, whole-genome characterized strain bank from this work can be used in conjunction with reverse genetic and infection models to better understand the impact of accessory genome content on bacterial physiology and pathogenesis of infection.

Evaluation of the NG-Test CARBA 5 Lateral Flow Assay with an IMP-27-Producing Morganella morganii and Other Morganellaceae

An isolate of Morganella morganii (MMOR1) that tested susceptible to 3rd/4th-generation cephalosporins and intermediate to meropenem was characterized as positive for NDM and IMP carbapenemases by NG-Test CARBA 5. Our objective was to further investigate this result, given the inconsistent susceptibility profile and unusual epidemiological profile for our region. The MMOR1 isolate was retested for antimicrobial susceptibilities and characterized for carbapenemase production. MMOR1 tested susceptible to ceftazidime, ceftriaxone, cefepime, aztreonam, and ertapenem, and intermediate to meropenem and imipenem. The isolate tested positive by carbapenem inactivation method (CIM) and CIM+EDTA (eCIM) testing, indicating metallo-β-lactamase production. The isolate tested negative for all carbapenemase genes on Xpert Carba-R, but positive for IMP on repeat testing of NG-Test CARBA 5. Whole-genome sequencing revealed MMOR1 contained blaIMP-27, but no other carbapenemase genes. Additional testing with NG-Test CARBA 5 revealed a false-positive NDM band when the assay was overloaded with test inoculum. Supplementary isolates were tested with an overloaded inoculum (n = 6 M. morganii; n = 1 P. mirabilis; n = 1 IMP-27-producing P. rettgeri; n = 1 IMP-1-producing E. coli; n = 1 K. pneumoniae), and two non-carbapenemase-producing carbapenem non-susceptible M. morganii also generated a false-positive NDM band; though, this was not universal among this species. A dual IMP+/NDM+ M. morganii is an unusual result that should prompt additional investigation, especially in nonendemic regions and when the susceptibility profile is incompatible. IMP-27 is not detected by Xpert Carba-R but is variably detected by NG-Test CARBA 5. The microorganism inoculum used for NG-Test CARBA 5 must be carefully controlled for accurate results. IMPORTANCE The detection of carbapenemase-producing carbapenem-resistant Enterobacterales (CP-CRE) is an important function of the clinical microbiology laboratory, where positive identifications have immediate implications for infection control and surveillance strategies in the inpatient setting and can inform appropriate selection of therapy among the various novel anti-CP-CRE agents. NG-Test CARBA 5 is a relatively new lateral flow assay used for detection of carbapenemases in CP-CRE. Here, we describe the characterization of a Morganella morganii isolate that generated a false-positive NDM carbapenemase detection by this assay, and perform bacterial test inoculum experiments with additional isolates to further investigate a cause of false-positive results using the NG-Test CARBA 5. While a lateral flow assay like the NG-Test CARBA 5 is a very desirable test format for clinical laboratories, there are pitfalls to avoid when performing this test and interpreting results, including recognizing an overloaded test assay, which could lead to false-positive results.

Outpatient Clonal Propagation and Rapid Regional Establishment of an Emergent Carbapenem-Resistant Acinetobacter baumannnii Lineage Sequence Type 499Pas

Eliminating carbapenem-resistant Acinetobacter baumannii (CRAb) disease requires comprehensive knowledge of how this noncommensal organism propagates among at-risk hosts. We molecularly characterized an ongoing surge of CRAb cases among patients in a Midwest US healthcare system, which coincided with sustained reductions in hospital-acquired CRAb infections and falloffs of cases associated with distinctly more resistant antibiotypes. Genome sequencing revealed surge isolates belonged to an emergent Pasteur scheme sequence type 499 and comprised multiple contemporaneous clonal clusters. Detailed query of health records revealed no consistent hospital source but instead identified various outpatient healthcare settings linked to cluster cases. We show that CRAb can rapidly establish a regional presence even without gains in breadth of antibiotic resistance and negligible contribution from sustained intrahospital transmission. As CRAb lineages may sidestep control efforts via outpatient epidemiological niches, our approach can be implemented to investigate outpatient CRAb propagation and inform subsequent local surveillance outside hospital settings.

Evaluation of Variability in Interpretation of Disk Diffusion Testing for Cefiderocol Using Different Brands of Mueller-Hinton Agar

BACKGROUND

Cefiderocol is a new antibiotic used to treat infections with antibiotic resistant Gram-negative bacilli. The impact of differences between Mueller-Hinton agar (MHA) brands on susceptibility testing is underexplored. Compounding the implementation of cefiderocol susceptibility testing is a lack of harmonization between different regulatory body breakpoint criteria.

METHODS

We performed Kirby-Bauer disk diffusion using BD, Hardy, and Remel MHA, in addition to broth microdilution for Acinetobacter baumannii (n = 25), Enterobacterales (n = 25), Stenotrophomonas maltophilia (n = 24), and Pseudomonas aeruginosa (n = 23). We analyzed disk diffusion diameters and minimum inhibitory concentrations using interpretive criteria from the Clinical and Laboratory Standards Institute (CLSI), US Food and Drug Administration (FDA), and the European Committee on Antimicrobial Susceptibility Testing (EUCAST).

RESULTS

Breakpoint criteria impacted interpretation of susceptibly testing results, for example with the broth microdilution we found 8% (2/25) of A. baumannii isolates change interpretation between CLSI and EUCAST and 32% (8/25) change between CLSI and FDA, 12% (3/25) of Enterobacterales change between CLSI and EUCAST, 13% (3/23) of P. aeruginosa interpretations change between CLSI and FDA, and 4% (1/25) S. maltophilia change between CLSI and FDA. There was a significant difference between the zone disk diffusion diameters for P. aeruginosa and S. maltophilia between Hardy and BD; which changed interpretation (using CLSI criteria) for 8.7% (2/23) for P. aeruginosa but 0% (0/24) for S. maltophilia.

CONCLUSIONS

Breakpoint criteria impact cefiderocol susceptibility testing interpretation for broth microdilution and disk diffusion. Choice of MHA brand can also affect result interpretation.

E. coli catheter-associated urinary tract infections are associated with distinctive virulence and biofilm gene determinants

Urinary catheterization facilitates urinary tract colonization by E. coli and increases infection risk. Here, we aimed to identify strain-specific characteristics associated with the transition from colonization to infection in catheterized patients. In a single-site study population, we compared E. coli isolates from patients with catheter-associated asymptomatic bacteriuria (CAASB) to those with catheter-associated urinary tract infection (CAUTI). CAUTI isolates were dominated by a phylotype B2 subclade containing the multidrug-resistant ST131 lineage relative to CAASB isolates, which were phylogenetically more diverse. A distinctive combination of virulence-associated genes was present in the CAUTI-associated B2 subclade. Catheter-associated biofilm formation was widespread among isolates and did not distinguish CAUTI from CAASB strains. Preincubation with CAASB strains could inhibit catheter colonization by multiple ST131 CAUTI isolates. Comparative genomic analysis identified a group of variable genes associated with high catheter biofilm formation present in both CAUTI and CAASB strains. Among these, ferric citrate transport (Fec) system genes were experimentally associated with enhanced catheter biofilm formation using reporter and fecA deletion strains. These results are consistent with a variable role for catheter biofilm formation in promoting CAUTI by ST131-like strains or resisting CAUTI by lower-risk strains that engage in niche exclusion.

Genomic Surveillance of Clinical Pseudomonas aeruginosa Isolates Reveals an Additive Effect of Carbapenemase Production on Carbapenem Resistance

Carbapenem resistance in Pseudomonas aeruginosa is increasing globally, and surveillance to define the mechanisms of such resistance in low- and middle-income countries is limited. This study establishes the genotypic mechanisms of β-lactam resistance by whole-genome sequencing (WGS) in 142 P. aeruginosa clinical isolates recovered from three hospitals in Islamabad and Rawalpindi, Pakistan between 2016 and 2017. Isolates were subjected to antimicrobial susceptibility testing (AST) by Kirby-Bauer disk diffusion, and their genomes were assembled from Illumina sequencing data. β-lactam resistance was high, with 46% of isolates resistant to piperacillin-tazobactam, 42% to cefepime, 48% to ceftolozane-tazobactam, and 65% to at least one carbapenem. Twenty-two percent of isolates were resistant to all β-lactams tested. WGS revealed that carbapenem resistance was associated with the acquisition of metallo-β-lactamases (MBLs) or extended-spectrum β-lactamases (ESBLs) in the blaGES, blaVIM, and blaNDM families, and mutations in the porin gene oprD. These resistance determinants were found in globally distributed lineages, including ST235 and ST664, as well as multiple novel STs which have been described in a separate investigation. Analysis of AST results revealed that acquisition of MBLs/ESBLs on top of porin mutations had an additive effect on imipenem resistance, suggesting that there is a selective benefit for clinical isolates to encode multiple resistance determinants to the same drugs. The strong association of these resistance determinants with phylogenetic background displays the utility of WGS for monitoring carbapenem resistance in P. aeruginosa, while the presence of these determinants throughout the phylogenetic tree shows that knowledge of the local epidemiology is crucial for guiding potential treatment of multidrug-resistant P. aeruginosa infections. IMPORTANCE Pseudomonas aeruginosa is associated with serious infections, and treatment can be challenging. Because of this, carbapenems and β-lactam/β-lactamase inhibitor combinations have become critical tools in treating multidrug-resistant (MDR) P. aeruginosa infections, but increasing resistance threatens their efficacy. Here, we used WGS to study the genotypic and phylogenomic patterns of 142 P. aeruginosa isolates from the Potohar region of Pakistan. We sequenced both MDR and antimicrobial susceptible isolates and found that while genotypic and phenotypic patterns of antibiotic resistance correlated with phylogenomic background, populations of MDR P. aeruginosa were found in all major phylogroups. We also found that isolates possessing multiple resistance mechanisms had significantly higher levels of imipenem resistance compared to the isolates with a single resistance mechanism. This study demonstrates the utility of WGS for monitoring patterns of antibiotic resistance in P. aeruginosa and potentially guiding treatment choices based on the local spread of β-lactamase genes.

Multiplatform Assessment of Saliva for SARS-CoV-2 Molecular Detection in Symptomatic Healthcare Personnel and Patients Presenting to the Emergency Department

BACKGROUND

Saliva has garnered great interest as an alternative specimen type for molecular detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Data are limited on the relative performance of different molecular methods using saliva specimens and the relative sensitivity of saliva to nasopharyngeal (NP) swabs.

METHODS

To address the gap in knowledge, we enrolled symptomatic healthcare personnel (n = 250) from Barnes-Jewish Hospital/Washington University Medical Center and patients presenting to the Emergency Department with clinical symptoms compatible with coronavirus disease 2019 (COVID-19; n = 292). We collected paired saliva specimens and NP swabs. The Lyra SARS-CoV-2 assay (Quidel) was evaluated on paired saliva and NP samples. Subsequently we compared the Simplexa COVID-19 Direct Kit (Diasorin) and a modified SalivaDirect (Yale) assay on a subset of positive and negative saliva specimens.

RESULTS

The positive percent agreement (PPA) between saliva and NP samples using the Lyra SARS-CoV-2 assay was 63.2%. Saliva samples had higher SARS-CoV-2 cycle threshold values compared to NP swabs (P < 0.0001). We found a 76.47% (26/34) PPA for Simplexa COVID-19 Direct Kit on saliva and a 67.6% (23/34) PPA for SalivaDirect compared to NP swab results.

CONCLUSION

These data demonstrate molecular assays have variability in performance for detection of SARS-CoV-2 in saliva.

A Visual Interactive Narrative Intervention (VINI) for aphasia education: Can digital applications administer augmented input to educate stroke survivors with aphasia?

OBJECTIVE

Persons with aphasia (PWA) face additional barriers to proper healthcare due to inadequate patient education by health professionals unequipped to use augmentative and alternative communication (AAC). The current study examines a digital application that evokes and sustains health information processing through AAC specifically aimed at increasing comprehension with augmented input (AI).

METHODS

A digital application designed to educate PWA about their health condition was compared to a video-recorded doctor providing oral-only education. Sixteen PWA received both education interventions in a crossover manner. Health information processing was assessed through heart rate (HR) and skin conductance levels (SCL), which were collected continually during each administration of education interventions.

RESULTS

PWA demonstrated greater cognitive processing of health information via HR and SCL indices during the digital application compared to the typical oral-only education intervention. The oral-only intervention led PWA to disengage with health information.

CONCLUSION

By combining visuographic materials and adapted language into a customizable narrative structure, digital applications can utilize AI to educate PWA about basic health information (i.e., diagnosis and prognosis).

PRACTICE IMPLICATIONS

The current study's AAC requires minimal training and can be used as an aided support in conjunction with other techniques that increase PWA's access to health information.

Genomic Prediction of Antimicrobial Resistance: Ready or Not, Here It Comes!

BACKGROUND

Next-generation sequencing (NGS) technologies are being used to predict antimicrobial resistance. The field is evolving rapidly and transitioning out of the research setting into clinical use. Clinical laboratories are evaluating the accuracy and utility of genomic resistance prediction, including methods for NGS, downstream bioinformatic pipeline components, and the clinical settings in which this type of testing should be offered.

CONTENT

We describe genomic sequencing as it pertains to predicting antimicrobial resistance in clinical isolates and samples. We elaborate on current methodologies and workflows to perform this testing and summarize the current state of genomic resistance prediction in clinical settings. To highlight this aspect, we include 3 medically relevant microorganism exemplars: Mycobacterium tuberculosis, Staphylococcus aureus, and Neisseria gonorrhoeae. Last, we discuss the future of genomic-based resistance detection in clinical microbiology laboratories.

SUMMARY

Antimicrobial resistance prediction by genomic approaches is in its infancy for routine patient care. Genomic approaches have already added value to the current diagnostic testing landscape in specific circumstances and will play an increasingly important role in diagnostic microbiology. Future advancements will shorten turnaround time, reduce costs, and improve our analysis and interpretation of clinically actionable results.

IL-7 Immunotherapy in a Nonimmunocompromised Patient With Intractable Fungal Wound Sepsis

A nonimmunocompromised patient developed life-threatening soft tissue infection with Trichosporon asahii, Fusarium, and Saksenaea that progressed despite maximum antifungal therapies and aggressive debridement. Interleukin-7 immunotherapy resulted in clinical improvement, fungal clearance, reversal of lymphopenia, and improved T-cell function. Immunoadjuvant therapies to boost host immunity may be efficacious in life-threatening fungal infections.

Evaluation of PCR cycle threshold values by patient population with the quidel lyra SARS-CoV-2 assay

The Lyra SARS-CoV-2 assay was the primary method for molecular testing performed at Barnes-Jewish Healthcare System in St. Louis, Missouri during the initial COVID-19 surge from mid-March to late-April 2020. We performed a retrospective analysis of 1,043 positive Lyra SARS-CoV-2 results during these 36 days to investigate associations between cycle threshold (C_T)  value and patient characteristics. Total RNA were extracted from NP or OP swabs using either the EasyMag or KingFisher automated extraction systems and quantified with RotorGene Q (Qiagen) or Applied Biosystems 7500 Fast Dx thermocyclers respectively. Notably, we found lower a significant median lower C_T for samples tested on the KingFisher-ABI 7500 fastDX (KF/ABI) system compared to the EasyMag/RotorGene (EM/RGQ) platform. Since 77.5% of our tests were ran on the EM/RGQ pipeline we then perform additional analysis on these values and found that C _T values in outpatient care settings compared to samples obtained in the emergency department or inpatient had significantly lower C _T values. These collective findings suggests a difference in viral load amongst various patient populations.

Phenotypic and genotypic characterization of linezolid-resistant Enterococcus faecium from the USA and Pakistan

OBJECTIVES

Linezolid is an important therapeutic option for the treatment of infections caused by VRE. Linezolid is a synthetic antimicrobial and resistance to this antimicrobial agent remains relatively rare. As a result, data on the comparative genomics of linezolid resistance determinants in Enterococcus faecium are relatively sparse.

METHODS

To address this knowledge gap in E. faecium, we deployed phenotypic antibiotic susceptibility testing and Illumina WGS on hospital surface (environmental) and clinical isolates from the USA and Pakistan.

RESULTS

We found complete concordance between isolate source country and mechanism of linezolid resistance, with all the US isolates possessing a 23S rRNA gene mutation and the Pakistan isolates harbouring two to three acquired antibiotic resistance genes. These resistance genes include the recently elucidated efflux-pump genes optrA and poxtA and a novel cfr-like variant. Although there was no difference in the linezolid MIC between the US and Pakistan isolates, there was a significant difference in the geometric mean of the MIC between the Pakistan isolates that had two versus three of the acquired antibiotic resistance genes. In five of the Pakistan E. faecium that possessed all three of the resistance genes, we found no difference in the local genetic context of poxtA and the cfr-like gene, but we identified different genetic contexts surrounding optrA.

CONCLUSIONS

These results demonstrate that E. faecium from different geographical regions employ alternative strategies to counter selective pressure of increasing clinical linezolid use.

Genomic Characterization of Antibiotic Resistant Escherichia coli Isolated From Domestic Chickens in Pakistan

Poultry husbandry is important for the economic health of Pakistan, but the Pakistani poultry industry is negatively impacted by infections from Escherichia coli. We performed Illumina whole genome sequencing on 92 E. coli isolates obtained from the livers of deceased chickens originating in five Pakistani geographical regions. Our analysis indicates that the isolates are predominantly from the B1 and A clade and harbor a diverse number of antibiotic resistance and virulence genes, with no linkage between phylogeny and antibiotic resistance gene presence but some association between phylogeny and virulence gene and SNP presence for the B1 and E phylogroups. The colistin resistance gene mcr-1 and the quinolone resistance gene qnrS1 were both found in 13/92 isolates. Alarmingly, 82/92 of the E. coli strains characterized in this study are multidrug resistant with 100% (92/92) resistance to lincomycin, 81.5% (75/92) to streptomycin, 79.3% (73/92) to ampicillin and 66.3% (61/92) to ciprofloxacin. These results provide a high-resolution analysis of poultry-associated E. coli isolates in an area with a high endemic burden of antibiotic resistance. Surveillance of antibiotic resistance in poultry associated E. coli isolates is an important pillar of the One Health concept to integrate analysis of potential pathogens in human, animal, and environmental niches.

In Silico Analysis of Gardnerella Genomospecies Detected in the Setting of Bacterial Vaginosis

BACKGROUND

Gardnerella vaginalis is implicated as one of the causative agents of bacterial vaginosis, but it can also be isolated from the vagina of healthy women. Previous efforts to study G. vaginalis identified 4 to 6 clades, but average nucleotide identity analysis indicates that G. vaginalis may be multiple species. Recently, Gardnerella was determined to be 13 genomospecies, with Gardnerella piottii, Gardnerella leopoldii, and Gardnerella swidsinkii delineated as separate species.

METHODS

We accessed 103 publicly available genomes annotated as G. vaginalis. We performed comprehensive taxonomic and phylogenomic analysis to quantify the number of species called G. vaginalis, the similarity of their core genes, and their burden of their accessory genes. We additionally analyzed publicly available metatranscriptomic data sets of bacterial vaginosis to determine whether the newly delineated genomospecies are present, and to identify putative conserved features of Gardnerella pathogenesis.

RESULTS

Gardnerella could be classified into 8 to 14 genomospecies depending on the in silico classification tools used. Consensus classification identified 9 different Gardnerella genomospecies, here annotated as GS01 through GS09. The genomospecies could be readily distinguished by the phylogeny of their shared genes and burden of accessory genes. All of the new genomospecies were identified in metatranscriptomes of bacterial vaginosis.

CONCLUSIONS

Multiple Gardnerella genomospecies operating in isolation or in concert with one another may be responsible for bacterial vaginosis. These results have important implications for future efforts to understand the evolution of the Gardnerella genomospecies, host-pathogen interactions of the genomospecies during bacterial vaginosis, diagnostic assay development for bacterial vaginosis, and metagenomic investigations of the vaginal microbiota.

Spatiotemporal dynamics of multidrug resistant bacteria on intensive care unit surfaces

Bacterial pathogens that infect patients also contaminate hospital surfaces. These contaminants impact hospital infection control and epidemiology, prompting quantitative examination of their transmission dynamics. Here we investigate spatiotemporal and phylogenetic relationships of multidrug resistant (MDR) bacteria on intensive care unit surfaces from two hospitals in the United States (US) and Pakistan collected over one year. MDR bacteria isolated from 3.3% and 86.7% of US and Pakistani surfaces, respectively, include common nosocomial pathogens, rare opportunistic pathogens, and novel taxa. Common nosocomial isolates are dominated by single lineages of different clones, are phenotypically MDR, and have high resistance gene burdens. Many resistance genes (e.g., blaNDM, blaOXA carbapenamases), are shared by multiple species and flanked by mobilization elements. We identify Acinetobacter baumannii and Enterococcus faecium co-association on multiple surfaces, and demonstrate these species establish synergistic biofilms in vitro. Our results highlight substantial MDR pathogen burdens in hospital built-environments, provide evidence for spatiotemporal-dependent transmission, and demonstrate potential mechanisms for multi-species surface persistence.

Genotypic and Phenotypic Characterization of Antimicrobial Resistance in Neisseria gonorrhoeae: a Cross-Sectional Study of Isolates Recovered from Routine Urine Cultures in a High-Incidence Setting

The objectives of this study were to perform genomic and phenotypic characterization of antimicrobial resistance in Neisseria gonorrhoeae isolates recovered from urine samples from patients in St. Louis, MO, USA. Sixty-four clinical isolates were banked over a 2-year period and subjected to antimicrobial susceptibility testing (AST) by Kirby-Bauer disk diffusion (penicillin, tetracycline, cefuroxime, and ciprofloxacin) and gradient diffusion (tetracycline, doxycycline, azithromycin, ceftriaxone, cefixime, ciprofloxacin, gemifloxacin, and delafloxacin). The medical records for the patients were evaluated to determine the demographics, location, and prescribed treatment regimen. Isolate draft genomes were assembled from Illumina shotgun sequencing data, and resistance determinants were identified by ResFinder and PointFinder. Of the 64 isolates, 97% were nonsusceptible to penicillin, with resistant isolates all containing the blaTEM-1b gene; 78 and 81% of isolates were nonsusceptible to tetracycline and doxycycline, respectively, with resistant isolates all containing the tet(M) gene. One isolate was classified as non-wild-type to azithromycin, and all isolates were susceptible to ceftriaxone; 89% of patients received this combination of drugs as first-line therapy. Six percent of isolates were resistant to ciprofloxacin, with most resistant isolates containing multiple gyrA and parC mutations. Correlation between disk and gradient diffusion AST devices was high for tetracycline and ciprofloxacin (R2 > 99% for both). The rates of N. gonorrhoeae antibiotic resistance in St. Louis are comparable to current rates reported nationally, except ciprofloxacin resistance was less common in our cohort. Strong associations between specific genetic markers and phenotypic susceptibility testing hold promise for the utility of genotype-based diagnostic assays to guide directed antibiotic therapy.IMPORTANCENeisseria gonorrhoeae causes the sexually transmitted infection gonorrhea, which is most commonly diagnosed using a DNA-based detection method that does not require growth and isolation of N. gonorrhoeae in the laboratory. This is problematic because the rates of antibiotic resistance in N. gonorrhoeae are increasing, but without isolating the organism in the clinical laboratory, antibiotic susceptibility testing cannot be performed on strains recovered from clinical specimens. We observed an increase in the frequency of urine cultures growing N. gonorrhoeae after we implemented a total laboratory automation system for culture in our clinical laboratory. Here, we report on the rates of resistance to multiple historically used, first-line, and potential future-use antibiotics for 64 N. gonorrhoeae isolates. We found that the rates of antibiotic resistance in our isolates were comparable to national rates. Additionally, resistance to specific antibiotics correlated closely with the presence of genetic resistance genes, suggesting that DNA-based tests could also be designed to guide antibiotic therapy for treating gonorrhea.

Urinary tract colonization is enhanced by a plasmid that regulates uropathogenic Acinetobacter baumannii chromosomal genes

Multidrug resistant (MDR) Acinetobacter baumannii poses a growing threat to global health. Research on Acinetobacter pathogenesis has primarily focused on pneumonia and bloodstream infections, even though one in five A. baumannii strains are isolated from urinary sites. In this study, we highlight the role of A. baumannii as a uropathogen. We develop the first A. baumannii catheter-associated urinary tract infection (CAUTI) murine model using UPAB1, a recent MDR urinary isolate. UPAB1 carries the plasmid pAB5, a member of the family of large conjugative plasmids that represses the type VI secretion system (T6SS) in multiple Acinetobacter strains. pAB5 confers niche specificity, as its carriage improves UPAB1 survival in a CAUTI model and decreases virulence in a pneumonia model. Comparative proteomic and transcriptomic analyses show that pAB5 regulates the expression of multiple chromosomally-encoded virulence factors besides T6SS. Our results demonstrate that plasmids can impact bacterial infections by controlling the expression of chromosomal genes.

Acinetobacter baumannii is generally considered an opportunistic pathogen. Here, Di Venanzio et al. develop a mouse model of catheter-associated urinary tract infection and show that a plasmid confers niche specificity to an A. baumannii urinary isolate by regulating the expression of chromosomal genes.

Draft Genome Sequence of a bla NDM-1- and bla PME-1-Harboring Pseudomonas aeruginosa Clinical Isolate from Pakistan

We performed Illumina whole-genome sequencing on a carbapenem-resistant Pseudomonas aeruginosa strain isolated from a cystic fibrosis patient with chronic airway colonization. The draft genome comprises 6,770,411 bp, including the carbapenemase bla NDM-1 and the extended-spectrum beta-lactamase bla PME-1 This isolate harbors 3 prophages, 14 antibiotic resistance genes, and 257 virulence genes.

Multidrug-resistant plasmids repress chromosomally encoded T6SS to enable their dissemination

Acinetobacter baumannii (Ab) is a nosocomial pathogen with one of the highest rates of multidrug resistance (MDR). This is partially due to transmissible plasmids. Many Ab strains harbor a constitutively active type VI secretion system (T6SS) that is employed to kill nonkin bacteria. T6SS and plasmid conjugation both involve cell-to-cell contact. Paradoxically, successful conjugation requires the survival of the recipient, which is the target of the T6SS. Thus, an active T6SS in either the donor or the recipient poses a challenge to plasmid conjugation. Here, we show that large conjugative MDR plasmids heavily rely on their distinctive ability to repress the T6SS of their hosts to enable their own dissemination and the conjugation of other plasmids, contributing to the propagation of MDR among Acinetobacter isolates.

The Impact of Cognitive Load on the Cardiac Orienting Response to Auditory Structural Features during Natural Radio Listening Situations

Previous research has shown that structural features such as voice changes, jingle onsets, and production effects in a radio broadcast elicit cardiac orienting responses. In fact, the voice change has been shown to reliably elicit orienting without habituation after several repetitions. However, repeated onsets of two other auditory structural features-jingles and production effects-did result in habituation when the participant was exposed to them embedded in an audio production absent a central cognitive task. This article presents two experiments testing the possibility that adding a central task prevents the development of a robust neural model of the auditory structural features necessary for habituation. In both studies, results show that adding a primary cognitive task eliminated habituation to jingles and production effects. However, varying the cognitive load of the primary task across two levels of difficulty had no significant effect on habituation.

Superficieibacter electus gen. nov., sp. nov., an Extended-Spectrum β-Lactamase Possessing Member of the Enterobacteriaceae Family, Isolated From Intensive Care Unit Surfaces

Two Gram-negative bacilli strains, designated BP-1(T) and BP-2, were recovered from two different Intensive Care Unit surfaces during a longitudinal survey in Pakistan. Both strains were unidentified using the bioMerieux VITEK MS IVD v2.3.3 and Bruker BioTyper MALDI-TOF mass spectrometry platforms. To more precisely determine the taxonomic identity of BP-1(T) and BP-2, we employed a biochemical and phylogenomic approach. The 16S rRNA gene sequence of strain BP-1(T) had the highest identity to Citrobacter farmeri CDC 2991-81(T) (98.63%) Citrobacter amalonaticus CECT 863(T) (98.56%), Citrobacter sedlakii NBRC 105722(T) (97.74%) and Citrobacter rodentium NBRC 105723(T) (97.74%). The biochemical utilization scheme of BP-1(T) using the Analytic Profile Index for Enterobacteriaceae (API20E) indicated its enzymatic functions are unique within the Enterobacteriaceae but most closely resemble Kluyvera spp., Enterobacter cloacae and Citrobacter koseri/farmeri. Phylogenomic analysis of the shared genes between BP-1(T), BP-2 and type strains from Kluyvera, Citrobacter, Escherichia, Salmonella, Kosakonia, Siccibacter and Shigella indicate that BP-1(T) and BP-2 isolates form a distinct branch from these genera. Average Nucleotide Identity analysis indicates that BP-1(T) and BP-2 are the same species. The biochemical and phylogenomic analysis indicate strains BP-1(T) and BP-2 represent a novel species from a new genus within the Enterobacteriaceae family, for which the name Superficieibacter electus gen. nov., sp. nov., is proposed. The type strain is BP-1(T) (= ATCC BAA-2937, = NBRC 113412).

blaIMP-27 on transferable plasmids in Proteus mirabilis and Providencia rettgeri

OBJECTIVES

A carbapenem-resistant Providencia rettgeri (PR1) isolate was recovered from a wound infection in Missouri, USA. This isolate possessed an EDTA-inhibitable carbapenemase that was unidentified using the Xpert CARBA-R assay. Our objective was to elucidate the molecular determinant of carbapenem resistance in this isolate. We then sought to test the transmissibility of bla_IMP-27 loci in clinical P. rettgeri and Proteus mirabilis isolates.

METHODS

In October 2016 the novel ambler Class B carbapenemase bla_IMP-27, was reported in two different Proteus mirabilis (PM185 and PM187) isolates. Broth mating assays for transfer of carbapenemase activity were performed for the three clinical isolates with recipient sodium azide-resistant Escherichia coli J53. Antibiotic susceptibility testing and phenotypic carbapenemase activity testing were performed on the clinical isolates, J53 and transconjugants using the Kirby-Bauer disc diffusion method according to CLSI guidelines. Plasmid DNA from PM187, PR1 and their transconjugants were used as input for Nextera Illumina sequencing libraries and sequenced on a NextSeq platform.

RESULTS

PR1 was resistant to both imipenem and meropenem. PM187 and PR1 could transfer resistance to E. coli through plasmid conjugation (pPM187 and pPR1). pPM187 had a virB/virD4 type IV secretion system whereas pPR1 had a traB/traD type IV secretion system.

CONCLUSION

Two of three bla_IMP-27-bearing clinical isolates tested could conjugate resistance into E. coli. The resulting transconjugants became positive for phenotypic carbapenemase production but did not pass clinical resistance breakpoints. bla_IMP-27 can be transmitted on different plasmid replicon types that rely on distinct classes of type IV secretion system for horizontal transfer.

The rapid spread of carbapenem-resistant Enterobacteriaceae

Carbapenems, our one-time silver bullet for multidrug resistant bacterial infections, are now threatened by widespread dissemination of carbapenem-resistant Enterobacteriaceae (CRE). Successful expansion of Enterobacteriaceae clonal groups and frequent horizontal gene transfer of carbapenemase expressing plasmids are causing increasing carbapenem resistance. Recent advances in genetic and phenotypic detection facilitate global surveillance of CRE diversity and prevalence. In particular, whole genome sequencing enabled efficient tracking, annotation, and study of genetic elements colocalized with carbapenemase genes on chromosomes and on plasmids. Improved characterization helps detail the co-occurrence of other antibiotic resistance genes in CRE isolates and helps identify pan-drug resistance mechanisms. The novel β-lactamase inhibitor, avibactam, combined with ceftazidime or aztreonam, is a promising CRE treatment compared to current colistin or tigecycline regimens. To halt increasing CRE-associated morbidity and mortality, we must continue quality, cooperative monitoring and urgently investigate novel treatments.

Cotransfection of heme oxygenase-1 prevents the acute inflammation elicited by a second adenovirus

The acute inflammatory response elicited by adenovirus vectors results in loss of gene expression and tissue injury in the target organ. This acute inflammation is now believed to be the major limiting factor for the use of adenovirus vectors in gene therapy. While exploring the level of acute inflammation caused by the adenovirus encoding the gene for the anti-inflammatory enzyme heme oxygenase-1, we discovered that this adenovirus not only did not elicit acute inflammation, but could prevent the inflammation caused by a second adenovirus. Here we describe a new approach to gene therapy, which uses the encoding of the potent anti-inflammatory enzyme heme oxygenase-1 to prevent early host inflammatory responses normally associated with adenovirus vectors.

Role of leukocyte accumulation and oxygen radicals in ischemia-reperfusion-induced injury in skeletal muscle

The role of leukocytes and nonleukocyte-derived reactive oxygen metabolites (ROMs) in reperfusion-induced skeletal muscle injury was determined. Male rats received 2 h no-flow hindlimb ischemia-reperfusion (I/R, n = 6) or were rendered neutropenic via antineutrophil serum (ANS) before I/R (I/R + ANS, n = 5). Oxygen radicals in the absence of neutrophils were tested by administration of dimethylthiourea (DMTU) (I/R + ANS + DMTU, n = 5). Perfused capillaries (CD(per)) and rolling (L(r)), adherent (L(a)), and extravasated leukocytes (L(e)) in the extensor digitorum longus muscle were measured every 15 min during 90 min of reperfusion using intravital microscopy. The vital dyes bisbenzimide (BB) and ethidium bromide (EB) provided direct measures of tissue injury (EB/BB). CD(per) decreased immediately on reperfusion in the I/R and I/R + ANS groups. CD(per) in the I/R + ANS + DMTU group remained at baseline throughout reperfusion. L(a) increased in the I/R group; however, EB/BB was the same between I/R and I/R + ANS groups. Injury in the I/R + ANS + DMTU group did not differ from other groups > or =60 min, after which EB/BB became significantly lower. L(e) did not differ between groups and was highly correlated to tissue injury. The results suggest that L(e) lead to parenchymal injury, and ROMs lead to perfusion deficits during the early reperfusion period after ischemia.

Kupffer cell-initiated remote hepatic injury following bilateral hindlimb ischemia is complement dependent

Intravital fluorescence microscopy was applied to the livers of male Wistar rats to test the hypothesis that complement mobilization stimulates Kupffer cells and subsequently initiates hepatic injury after hindlimb ischemia/reperfusion (I/R). Following 3 h of limb reperfusion, hepatocellular viability (serum levels of alanine transaminase and cell death via propidium iodide labeling) decreased significantly from levels in sham-operated animals. Inhibition of complement mobilization with soluble complement receptor type 1 (20 mg/kg body wt) and interruption of Kupffer cell function with GdCl(3) (1 mg/100g body wt) resulted in significant hepatocellular protection. Although the effects of hindlimb I/R on hepatic microvascular perfusion were manifest as increased heterogeneity, both complement inhibition and suppression of Kupffer cell function resulted in marked improvements. No additional hepatocellular protection and microvascular improvements were provided by combining the interventions. Furthermore, inhibition of complement mobilization significantly depressed Kupffer cell phagocytosis by 42% following limb reperfusion. These results suggest that the stimulation of Kupffer cells via complement mobilization is necessary but is not the only factor contributing to the early pathogenesis of hepatic injury following hindlimb I/R.

Cytokines contribute to early hepatic parenchymal injury and microvascular dysfunction after bilateral hindlimb ischemia

PURPOSE

Hepatic dysfunction may contribute to death from multiple organ dysfunction after abdominal aortic surgery. Several factors are likely responsible, and the purpose of this study was to determine whether the cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin 1 (IL-1) are involved in initiating this remote hepatic injury.

METHODS

In a normotensive rat model of 4-hour bilateral hindlimb ischemia/reperfusion (I/R), we measured systemic TNF-alpha and IL-1 levels throughout the I/R period. Rats were randomly assigned to either the 3-hour control group, the 3-hour I/R group, or the I/R group with administration of a polyclonal antibody (PAb) to TNF-alpha (I/R + TNF-alpha PAb). Direct evidence of lethal hepatocyte injury through the labeling of nuclei by propidium iodide (per 10(-1)mm(3)) and altered microvascular perfusion were assessed by using intravital microscopy.

RESULTS

Systemic TNF-alpha peaked at 83.97 pg/mL (P <.05, n = 5) at 30 minutes of reperfusion and returned to baseline in 60 to 90 minutes. No significant change in systemic IL-1 was detected (P <.05, n = 4). Alanine aminotransferase increased 2.5-fold in the I/R group through 3 hours of reperfusion (P <.05, n = 4), and TNF-alpha PAb did not attenuate this alanine aminotransferase increase (P <.05, n = 6). Lethal hepatocyte injury increased by 8-fold in the I/R group compared with the control group (P <.05, n = 5), whereas TNF-alpha PAb significantly reduced this injury (P <.05, n = 4). No regional differences in injury were noted within the acinus. Total perfusion within the microvascular unit did not drop; however, significant flow heterogeneity was observed. The proportion of continuously perfused sinusoids declined in the I/R group after 3 hours of reperfusion in both periportal (62.0 +/- 2.2, P <.05) and, to a lesser, although significant, degree, in the pericentral regions (73. 2 +/- 1.73, P <.05).

CONCLUSION

By scavenging extracellular TNF-alpha with a PAb, we provide direct evidence that TNF-alpha contributes to, but is not solely responsible for, early remote hepatocellular injury and microvascular dysfunction. The administration of TNF-alpha PAb reduced lethal hepatocyte injury in both regions of the acinus and also improved perfusion in the periportal region (76.8 +/- 5.41, P <.05), but not in the pericentral region. This suggests that TNF-alpha released during reperfusion mediates early remote hepatocellular injury and microvascular dysfunction after a remote ischemic insult.

Microcirculatory perfusion deficits are not essential for remote parenchymal injury within the liver

A normotensive model of hindlimb ischemia-reperfusion in Wistar rats was used to test the hypothesis that microvascular perfusion deficits contribute to the initiation of remote hepatic injury during a systemic inflammatory response. Animals were randomly assigned to one of three groups: 4 h of ischemia with 6 h of reperfusion (I/R-6; n = 4), 4 h of ischemia with 3 h of reperfusion (I/R-3; n = 5), or no ischemia (naive; n = 5). With intravital fluorescence microscopy, propidium iodide (PI; 0.05 mg/100 g body wt) was injected for the in vivo labeling of lethally injured hepatocytes (number/10(-1) mm(3)). PI-positive hepatocytes increased progressively over the 6-h period (naive 32.9 +/- 7.8 vs. I/R-3 92.8 +/- 11.5 vs. I/R-6 232 +/- 39.2), with no difference between periportal and pericentral regions of the lobule. Additionally, a significant decrease in continuously perfused sinusoids (naive 70.0 +/- 1.5 vs. I/R-3 65.0 +/- 1.0 vs. I/R-6 48.8 +/- 0.9%) was measured. Regional sinusoidal perfusion differences were only observed after 3 h of limb reperfusion. Indirect measures of hepatocellular injury using alanine transaminase levels support the progressive nature of hepatic parenchymal injury (0 h 57.8 +/- 6.5 vs. 3 h 115.3 +/- 20.7 vs. 6 h 125.6 +/- 19.5 U/l). Evidence from this study suggests that remote hepatic parenchymal injury occurs early and progresses after the induction of a systemic inflammatory response and that microvascular perfusion deficits are not essential for the initiation of such injury.

Initiation of remote hepatic injury in the rat: interactions between Kupffer cells, tumor necrosis factor-alpha, and microvascular perfusion

Severe trauma may initiate a systemic inflammatory response, which in turn may result in remote organ injury. After limb ischemia/reperfusion (I/R), intravital fluorescence microscopy was applied to the livers of normotensive rats to investigate the initiation of remote injury to the liver. Additionally, we determined whether Kupffer cell activation and tumor necrosis factor-alpha (TNF-alpha) were involved, via perfusion deficits, in such injury. TNF-alpha, measured by immunoassay, peaked at 30 minutes of reperfusion, but returned to baseline within 60 minutes. Limb I/R resulted in significant increases to global hepatocellular injury measured by alanine transaminase (ALT) and lethal hepatocyte injury as seen with intravital fluorescence microscopy. Although the number of perfused sinusoids went unchanged, a significantly augmented perfusion heterogeneity was measured. After 1.5 hours of reperfusion, both TNF-alpha and Kupffer cells were shown to contribute to global hepatocellular injury (e.g., ALT). After 3 hours, TNF-alpha was no longer essential for this injury, suggesting that some other mechanism(s) activated Kupffer cells and initiated hepatocellular injury. Using propidium iodide and fluorescence microscopy, we found that both TNF-alpha and Kupffer cell activation were necessary to drive hepatocytes toward lethal injury. No additional benefits were observed with a combination of TNF-alpha inhibition and Kupffer cell suppression. These results not only implicate both Kupffer cells and TNF-alpha in the initiation of remote hepatic injury, but suggest that sinusoidal perfusion deficits are not essential for the initiation of such injury. Other mechanism(s) are likely involved in the pathogenesis of remote hepatic parenchymal injury.

Microvascular perfusion deficits are not a prerequisite for mucosal injury in septic rats

Our major objective was to investigate whether injury to the mucosa of the small intestine occurred in a normotensive model of sepsis and whether such injury was associated with microvascular perfusion deficits. Using fluorescence intravital microscopy, we show direct evidence of cell injury within the mucosa (pneumonia 12.4 +/- 2.6 cells/field, sham 2.2 +/- 0.7 cells/field), whereas use of 51Cr-labeled EDTA showed evidence of increased mucosal permeability (pneumonia 1.90 +/- 0.67 ml. min-1. 100 g-1; sham 0.24 +/- 0.04 ml. min-1. 100 g-1), 48 h following induction of pneumonia. Despite such injury the capillary density in the ileal mucosa and submucosa of pneumonic rats (1,027 +/- 77 and 1,717 +/- 86 mm2) was not significantly different compared with sham (998 +/- 63 and 1,812 +/- 101 mm2). However, a modest albeit significant decrease in capillary perfusion was measured in the muscularis layer of pneumonia (11.0 +/- 1.3 mm) compared with sham (13.9 +/- 0.63 mm) and appeared to be associated with leukocyte entrapment. Pretreatment using low doses of endotoxin to induce endotoxin tolerance not only increased muscularis capillary density but reduced the number of leukocytes trapped within the microvasculature, decreased myeloperoxidase activity within the ileum in pneumonic rats, and prevented mucosal injury. In conclusion, we have shown that pneumonia results in remote injury to the mucosa of the ileum and that such injury was not associated with concurrent mucosal perfusion deficits.

The effect of mannitol versus dimethyl thiourea at attenuating ischemia/reperfusion-induced injury to skeletal muscle

OBJECTIVE

Mannitol is used as a treatment for skeletal muscle ischemia/reperfusion (I/R) injury in humans, despite the fact that its effectiveness in vivo is still disputed. The purpose of this study was to determine the efficacy of mannitol in attenuating I/R injury at the microcirculatory level.

METHODS

The study was designed as an experimental study with male Wistar rats. The main outcome measures were intravital microscopy, which was used to measure capillary perfusion, capillary and venular red blood cell velocity (VRBC), and leukocyte-endothelial interactions in the extensor digitorum longus muscle of the rat hind limb before and after ischemia. In addition, tissue injury was assessed during reperfusion with the fluorescent vital dyes bisbenzimide and ethidium bromide. Dimethyl thiourea (DMTU), a highly effective therapeutic agent of experimental I/R injury, was used as a positive control.

RESULTS

No-flow ischemia (2 hour) resulted in a 40% drop in capillary perfusion, a decline in capillary and venular VRBC, and increased leukocyte venular adherence and tissue infiltration. Tissue injury increased to a constant level during reperfusion. Mannitol attenuated capillary malperfusion during the first 60 minutes of reperfusion and prevented a decline in capillary VRBC. However, mannitol did not reduce tissue injury or leukocyte adherence and infiltration during reperfusion. By comparison, DMTU not only prevented the perfusion deficits and the increases in leukocyte venular adherence and tissue infiltration but significantly reduced the magnitude of tissue injury.

CONCLUSION

Our findings suggest that mannitol may be of limited value for the prevention of early reperfusion-induced injury after no-flow ischemia in skeletal muscle. By comparison, DMTU was highly efficacious by not only reducing microvascular perfusion deficits but by also reducing leukocyte-endothelial cell interactions and the incidence of cellular injury.

Ischemic tolerance in skeletal muscle: role of nitric oxide

We tested the hypothesis that ischemic preconditioning (PC) of skeletal muscle provided tolerance to a subsequent ischemic event 24 h later, and that such protection was due to nitric oxide (NO). Male Wistar rats, anesthetized with halothane, were randomly assigned to groups: ischemic (no PC; n = 11), PC (n = 11), PC + N-nitro-L-arginine methyl ester (L-NAME; 100 micromol/l; n = 5), PC + N-nitro-D-arginine methyl ester (100 micromol/l; n= 4), PC + aminoguanidine (AMG; 100 micromol/l; n = 4), ischemic + L-NAME (n= 4), or ischemic + AMG (n = 4). PC consisted of 5x 10 min of ischemia and reperfusion, and, 24 h later, 2 h of ischemia were induced by a tourniquet applied to the limb. With the use of intravital microscopy, the number of perfused capillaries (Npc) in the extensor digitorum longus (EDL) muscle was measured over a 90-min reperfusion period. The ratio of ethidium bromide- to bisbenzimide-labeled nuclei was used to estimate tissue injury. PC preserved Npc (23.6 +/- 2.5) following 2 h of ischemia compared with sham muscles (11.5 +/- 5.1), significantly elevating inducible NO synthase (iNOS) activity (81% increase), but did not afford protection to the parenchyma. L-NAME and AMG prevented ischemia-reperfusion-induced reduction in Npc in muscles without PC. However, after 90 min of reperfusion, L-NAME (Npc = 15.0 +/- 1.7), but not AMG (Npc = 22.8 +/- 3.1), significantly reduced the microvascular protection afforded by PC. We conclude that PC of the EDL muscle resulted, 24 h later, in protection to microvascular perfusion only, and that such protection was due to NO from sources other than iNOS.

Animal models for blood transfusion: a model for sterile blood sampling in the rat

Rat blood is frequently used for experimental transfusion. However, no data are available concerning the quality of the blood used, although bacterial contamination could severely alter results. To obtain large quantities of sterile rat blood for a transfusion study, we tested carotid artery cannulation, known as a standard procedure. Blood cultures from the collected blood showed polymicrobial overgrowth even after sterility measures were improved. In contrast, the puncture of the abdominal aorta proved to be a simple and reliable method for the collection of sterile blood. We conclude that studies using blood collected from donor rats should be controlled and the quality of such blood be tested before transfusion.

Leukocyte activation and flow behavior in rat skeletal muscle in sepsis

In animal models of endotoxemia, sepsis is associated with the accumulation of leukocytes and altered microvascular perfusion. In order to test the hypothesis that bacterial sepsis upregulates leukocyte-endothelial adhesion, we used intravital microscopy to examine the flow behavior of leukocytes in the postcapillary venules (PCV) of rats made septic by cecal ligation and perforation (CLP). Animals were randomized to CLP or sham study groups and studied 6 h, 24 h, or 48 h later. In postcapillary venules of the extensor digitorum longus muscle, we found that: (1) over the course of the study, leukocyte adhesion and extravasation increased in both experimental groups (analysis of variance [ANOVA], significant time effect: adhesion, p < 0.001; extravasation, p < 0.05); (2) leukocyte adhesion was decreased by CLP treatment (ANOVA, sepsis effect, p = 0.05), particularly after 24 to 48 h of sepsis (ANOVA, sepsis x time interaction, p < 0.05); and (3) the reduction in leukocyte adhesion in CLP animals was associated with a decrease in leukocyte extravasation (ANOVA, sepsis effect, p < 0.01). After correction for the reduction in systemic leukocyte count associated with CLP, the effect of sepsis on leukocyte adhesion and extravasation no longer reached statistical significance. These findings suggest that chronic (6 to 48 h) bacterial sepsis does not upregulate leukocyte adhesion in a manner similar to that seen in models of acute endotoxemia. These data suggest that the increased microcirculatory flow heterogeneity seen in this and other models of bacterial sepsis may not be explained by leukocyte entrapment in postcapillary venules.

Transfusing red blood cells stored in citrate phosphate dextrose adenine-1 for 28 days fails to improve tissue oxygenation in rats

OBJECTIVE

To determine whether the time that red blood cells are stored in citrate phosphate dextrose adenine-1 solution before transfusion alters the ability to improve tissue oxygenation.

DESIGN

Prospective, randomized, controlled study.

SETTING

University research institute laboratory.

SUBJECTS

Male Sprague-Dawley rats (350 to 450 g).

INTERVENTIONS

Twenty-four hours after randomization to sham laparotomy (n = 21) or cecal ligation and perforation (n = 16)1 supply-dependency of systemic oxygen uptake (VO2) was induced in rats by isovolemic hemodilution. Rats were then re-randomized to receive either rat red blood cells stored in citrate phosphate dextrose adenine-1 for 3 days ("fresh" n = 17) or rat red blood cells stored in citrate phosphate dextrose adenine-1 for 28 days ("old" n = 20).

MEASUREMENTS AND MAIN RESULTS

Changes in systemic VO2 were measured for 90 mins to determine the efficiacy of the treatment. Statistical analysis included a fully factorial repeated-measures, generalized linear model. No significant interaction was found between cecal ligation and perforation or sham animals and transfusion with fresh or old red blood cells. However, comparing the combined groups of animals receiving either fresh or old red blood cells, we found that after the transfusion of old red blood cells, systemic VO2 was not significantly improved (after hemodilution 1.68 +/- 0.27 mL/100 g/min, after transfusion 1.86 +/- 0.17 mL/100 g/min; p > .05). In contrast, transfusion with fresh red blood cells acutely increased systemic VO2 (after hemodilution 1.62 +/- 0.06 mL/100 g/min, after transfusion 2.10 +/- 0.09 mL/100 g/min; p = .049).

CONCLUSION

Storage of rat red blood cells for 28 days in citrate phosphate dextrose adenine-1 impaired their ability to improve tissue oxygenation when transfused into either control or septic rats placed into supply dependency of systemic VO2.

Microcirculatory changes in rat skeletal muscle in sepsis

The aim of this study was to confirm that microvascular perfusion was abnormal during the early phases of normotensive sepsis and to determine whether these changes were due to the development of tissue edema. Skeletal muscle red blood cell (RBC) flow was studied in rats made septic by cecal ligation and perforation (CLP). After anesthesia with halothane, arterial and venous cannulae were inserted and, in the treatment group, a CLP performed. At 6, 24, and 48 h after entry into the study, the incidence of microcirculatory absence of flow in the extensor digitorum longus muscle (EDL) was examined with intravital microscopy. The number of capillaries containing RBCs were counted over a 60-s interval, and the flow status of each capillary was recorded. A significant increase in the number of stopped-flow capillaries was observed in the CLP group (p < 0.01) as compared with time-matched controls. In both groups the number of capillaries with stopped flow was greater than in naive animals. The severity of absence of flow was negatively correlated with the systemic hemoglobin concentration. These changes were not associated with an increase in tissue wet/dry weight ratio or albumin flux. This study shows that sepsis was associated with increased RBC flow heterogeneity. These changes, which occur within 24 h of the septic insult, are a persistent feature of the evolving septic process in the absence of tissue edema. These observations support the view that extrinsic compression of the microcirculation by tissue edema is not the primary cause of alterations in microcirculatory flow in sepsis.

Intestinal mucosal permeability to 51Cr-ethylenediaminetetraacetic acid is increased after bilateral lower extremity ischemia-reperfusion in the rat

BACKGROUND

Despite successful revascularization of ischemic extremities, multiorgan dysfunction syndrome develops in some patients. Mechanisms responsible for this are not known; however, the gastrointestinal tract has been implicated as a possible mediator. Our objective was to demonstrate increased intestinal mucosal permeability after bilateral hindlimb ischemia-reperfusion (I-R) in a rodent model.

METHODS

Sixteen male Wistar rats were randomized either to 4 hours of bilateral hindlimb tourniquet ischemia and 24 hours of reperfusion (n = 8) or control groups (n = 8). The animals received 10 MuCi 51Cr-ethylenediaminetetraacetic acid (EDTA) by gavage, and excretion was measured in urine collected every 8 hours in 16 animals and every 4 hours in 8 animals. Arterial blood pressure was monitored continuously. Intravenous normal saline solution (3 ml/hr) with fentanyl (2 microgram/100 gm/hr) was continuously administered. Immediately before death complete blood count and levels of arterial lactate, creatinine, and urea were obtained. Mesenteric lymph nodes were harvested from the ileocecal region and cultured. Distal small bowel and proximal colon were preserved for histologic analysis. An additional 11 rats, six experimental and five control, were evaluated for mesenteric lymph node cultures only.

RESULTS

Urinary excretion of 51Cr-EDTA was significantly greater in the I-R group between 0 and 8 hours (p < 0.02) and 8 to 16 hours (p < 0.0002) of reperfusion. This increase occurred as early as 4 to 8 hours of reperfusion (p < 0.0001). Urine volume in the I-R group was significantly reduced during 0 to 4 hours of reperfusion (p < 0.002). Hemoglobin and lactate level were significantly different in the I-R group. Leukocyte and platelet counts, levels of creatinine and urea, and colony counts from mesenteric lymph nodes were similar in I-R and control groups. Blinded histologic analysis of bowel segments did not reveal morphologic differences.

CONCLUSIONS

Bilateral hindlimb I-R produces remote intestinal mucosal injury shown by significantly increased permeability to 51Cr-EDTA. Such increased mucosal permeability may be important in the development of multiorgan dysfunction syndrome in patients who sustain lower extremity I-R injury.

Leukocyte activity and tissue injury following ischemia-reperfusion in skeletal muscle

Few studies have correlated the occurrence of leukocytes with the time course of ischemia-reperfusion (I-R)-induced tissue injury in skeletal muscle. The goal of this study was to test the hypothesis that leukocytes were responsible for not only the onset, but progression of parenchymal cell injury within skeletal muscle following no-flow ischemia. Thirteen male Wistar rats (150-250 g) were randomly allocated to either a control (no I-R; n = 3), I-R (n = 5), or a leukopenic I-R group (n = 5). Under halothane anesthesia, the extensor digitorum longus muscle was prepared for intravital microscopy to allow video recording of microvascular perfusion and leukocyte flow behavior following 3 hr no-flow ischemia of the hindlimb. Tissue injury was assessed as the ratio of ethidium bromide (impermeant dye)-labeled nuclei to bisbenzimide (permeant dye)-labeled nuclei (E/B). During reperfusion, the I-R group showed a progressive decline in the number of perfused capillaries (N(C)) (from 19.37 +/- 0.04 to 3.34 +/- 1.18), while leukopenic and control rats were not significantly different. In the I-R group, the number of rolling leukocytes increased from 4.05 +/- 1.93 to 14.77 +/- 1.33 at the onset of reperfusion and remained stable throughout the reperfusion period. The number of stuck leukocytes, in the I-R group, progressively increased from 1.41 +/- 0.01 prior to ischemia to 4.66 +/- 0.01 at the onset of reperfusion to 11.96 +/- 0.01 after 90 min. The index of tissue injury (EIB) increased asymptotically from 0.60 +/- 0.02 to 0.95 +/- 0.01 after 90 min of reperfusion in the I-R group, while leukopenia significantly reduced both the magnitude of tissue injury (i.e., 35% reduction from untreated I-R group) and the onset of such injury. In spite of the benefit afforded by leukopenia, evidence of tissue injury persisted (20% above control baseline level). We conclude that although leukocytes were responsible for the onset of parenchymal injury in skeletal muscle following 3 hr no-flow ischemia they are not the sole mediators of such injury.

Measurement of tissue viability using intravital microscopy and fluorescent nuclear dyes

Intravital microscopy used with fluorescent vital stains provides the opportunity to measure the temporal and spatial extent of tissue injury following disease processes. However, this assumes that prolonged exposure to such dyes does not alter microvascular perfusion or cellular viability. To test this hypothesis, the extensor digitorum longus (EDL) muscle in 24 male Wistar rats, anesthetized with sodium pentobarbital (Somnotal, 65 mg/kg, ip), were prepared for microscopy. The EDL was either bathed continuously (n = 6) in Krebs solution containing bisbenzimide (5 micrograms/ml; labels nuclei of all cells) and ethidium bromide (5 micrograms/ml; labels nuclei of injured cells) or had dyes topically applied 1 hr (n = 4) and 4 hr (n = 4) following dissection of the muscle. Noxious stimuli (i.e., hypoxia:FiO2 of 8-10% (n = 3), 95% ethanol (n = 3), and 2 hr ischemia followed by 90 min reperfusion (n = 4) were used to test the ability of ethidium bromide, when used in conjunction with intravital microscopy, to differentiate injured tissue. Video recordings at the surface of the EDL muscle were made every 30 min for 5 hr from which the number of perfused capillaries was counted (NCper). The numbers of bisbenzimide- and ethidium bromide-labeled nuclei were counted at the surface of the muscle and at two to three additional locations within the muscle (to a maximum depth of approximately 120-160 microns). The average NCper (19.05 +/- 1.7) remained constant over 5 hr, while the number of nuclei stained by bisbenzimide increased linearly with time from an initial value of 1218 +/- 125.(ABSTRACT TRUNCATED AT 250 WORDS)

Capillary network morphology and capillary flow

This paper examines the authors' research on capillary network morphology and the heterogeneity of capillary red cell (RBC) perfusion in skeletal muscle with the aim of demonstrating that capillary network structure plays a major role in determining flow distribution. Capillary network morphology was examined by quantifying the heterogeneity of capillary diameters, path and segment lengths, as well as the changes in configuration that occur as vessels accommodate themselves to continual changes of fiber length. Because of the network complexity and the two-phase nature of the perfusing blood, both spatial (i.e. among capillaries) and temporal heterogeneity of capillary perfusion were predicted to result. By means of computer analysis of video images of the microcirculation in vivo, we have demonstrated that more than 70% of the total spatial heterogeneity of capillary RBC perfusion arises from the capillary network as opposed to the arterioles, and that RBC flow continuously redistributes among capillaries. The spatial heterogeneity increases substantially as the arteriolar input to the network falls, and the data predict that during low-flow states, the network will fail to distribute blood properly among its constituent vessels. Thus passive rheological mechanisms and capillary network morphology are important determinants of functional capillary density.

Skeletal muscle injury induced by ischemia-reperfusion

OBJECTIVE

To study the temporal progression of injury in skeletal muscle after ischemia-reperfusion insult by means of intravital videomicroscopy and nuclear fluorescent dyes.

DESIGN

A controlled study in an animal model.

SETTING

A vascular research laboratory at a university-affiliated hospital.

SUBJECTS

Eight male Wistar rats, for each of which the extensor digitorum longus muscle of the hind limb was exposed and prepared.

INTERVENTIONS

Two hours of complete no-flow ischemia followed by 90 minutes of reperfusion in five of the rats; the other three rats acted as controls and underwent the same surgical procedure but not ischemia. During the reperfusion period the fluorescent vital dyes bisbenzimide, which permeates all cells, and ethidium bromide, which permeates cells with damaged membranes, were applied. Recordings to videotape were made with the intravital microscope very 15 minutes during the reperfusion period.

MAIN OUTCOME MEASURES

The number of perfused capillaries crossing three straight lines on the video monitor were counted as a measure of microvascular dysfunction. An index of tissue injury was calculated as the ratio of the number of nuclei stained by ethidium bromide to the number stained by bisbenzimide (E/B). The number of stuck and rolling leukocytes and the velocity of the rolling leukocytes were determined in postcapillary venules.

RESULTS

The mean number of perfused capillaries (and standard error of the mean) fell from 20.71 (1.64)/mm before ischemia to 11.69 (1.18)/mm during reperfusion in the experimental group but remained constant in the control group. In the experimental group E/B progressed from 0.43 (0.05) at the onset of reperfusion to 0.87 (0.03) at the end of reperfusion, the number of rolling leukocytes increased from a preischemia mean of 4.00 (1.90) to 14.80 (1.30)/1000 microns2, and the number of stuck leukocytes increased from 1.42 (0.20) to 9.20 (0.70)/1000 microns2. The velocity of the rolling leukocytes did not differ between the control and the experimental groups.

CONCLUSIONS

Although microvascular perfusion decreased quickly to a constant level after 2 hours of noflow ischemia plus reperfusion, a progressive increase in tissue injury occurred, which may correlate with the number of stuck leukocytes.

Effect of superoxide dismutase and 21-aminosteroids (lazaroids) on microvascular perfusion following ischemia-reperfusion in skeletal muscle

Intravital video microscopy was used to test superoxide dismutase and a lazaroid analogue, U-74389F, as a pretreatment for ischemia-reperfusion-induced microvascular dysfunction in skeletal muscle. Twenty-two male Wistar rats (350-400 g), anesthetized with sodium pentobarbital (65 mg/kg i.p.), were divided into groups to test the lazaroid analogue U-74389F (3 mg/kg; n = 8), a citric acid/citrate mixture (CS-4; n = 4) used as the vehicle for the lazaroid analogue, superoxide dismutase (SOD, 10 mg/kg; n = 5), and saline (n = 5). Normothermic ischemia of the extensor digitorum longus muscle was induced for 3 h by tightening a tourniquet placed around the limb above the muscle. Measurements of the number of perfused capillaries (CDper; mm-1) and capillary red blood cell velocity (VRBC; mm/s) were made after 30, 60 and 90 min of reperfusion. Thirty minutes following release of the tourniquet, all test groups showed a significant drop in CDper. The extent of this reduction was maximal in SOD treated muscles, while it was minimized in the lazaroid-treated muscles following 90 min reperfusion. Hyperemia occurred only in muscles treated with saline or lazaroid. The hyperemia was of limited duration in saline-treated muscles, but lasted the entire reperfusion period following lazaroid treatment. An index of microvascular flow, estimated from the product of VRBC and CDper, indicated that flow was significantly greater in muscles treated with lazaroids as compared with all other groups following the 90-min reperfusion. We conclude that whereas SOD was detrimental, the lazaroid analogue U-74389F improved microvascular perfusion following 3 h of no-flow ischemia and 90 min reperfusion.