Biology subjects

Nozick, S.

Publications and source records attributed to Nozick, S..

4 recordsLinked to original sources

bioRxiv2026

Comparison of Galleria mellonella, Epithelial Cell Cytotoxicity, and Mouse Model of Bacteremia to Measure Pseudomonas aeruginosa Virulence

Considerable effort has focused on identifying alternatives to mouse models in research studies. In the field of bacterial pathogenesis, Galleria mellonella and epithelial cell lines have been widely used for this purpose, but the concordance of these models with mice remains unclear. To begin to address this knowledge gap, we used 105 clinical isolates of Pseudomonas aeruginosa for which the virulence had been previously determined in a mouse bacteremia model. A semistrong correlation was observed between G. mellonella median time to 50% mortality and mouse 50% pre-lethal dose (LD50) values (Spearmans rank correlation coefficient [{rho}] = 0.75), whereas percent A549 epithelial-like cell lysis during co-culture showed a weak correlation to mouse LD50 values ({rho} = -0.47). Given the stronger correlation between G. mellonella and mouse virulence, we next examined whether G. mellonella could substitute for mice when asking questions about the virulence of large numbers of P. aeruginosa isolates. Results from mice indicated that isolates with resistance to more antibiotics were significantly less virulent, and the use of G. mellonella identified the same inverse correlation. Furthermore, both models found no evidence for the existence of hypervirulent clonal lineages. In particular, isolates belonging to sequence types defined as high-risk clones were not consistently more virulent than other isolates, despite the known association of high-risk clones with poor clinical outcomes. These findings suggest that G. mellonella can serve as an adequate substitute for mice when addressing specific population-based virulence questions, although conclusions should be confirmed in mice. Author SummaryWe found that virulence measurements in a G. mellonella infection model showed a semistrong correlation with those from a mouse bacteremia model and that this insect larval model adequately detected population-level trends similarly to mice. In contrast, A549 epithelial-like cell lysis during bacterial co-culture correlated less well with mouse virulence. Together, these results support the use of G. mellonella as a scalable, low-cost, and humane first-line model for assessing P. aeruginosa virulence but also indicate that conclusions should be validated in mice.

microbiology↗

bioRxiv2026

A novel mechanism of ceftolozane-tazobactam resistance in Pseudomonas aeruginosa mediated by L2 β-lactamase

The prevalance of non-susceptibility to ceftolozane-tazobactam (C/T) among Pseudomonas aeruginosa remains low but novel mechanisms of C/T resistance are of concern. Herein, we describe a novel Pseudomonas aeruginosa genotype associated with high-level C/T resistance (>256/4 {micro}g/mL) in a single patient. Whole genome sequencing of the isolate was compared to that of a susceptible isolate cultured from the same patient two months earlier. Analysis of the sequences revealed two different P. aeruginosa high-risk clones: ST111 followed by ST235. The C/T-resistant ST235 isolate contained five copies of a genetic element comprised of an L2 {beta}-lactamase gene (blaL2) and a truncated ampRL2 transcriptional regulator gene, which are commonly found together in Stenotrophomonas maltophilia strains and have not been reported to mediate resistance to C/T. Comparative genomic analysis with other P. aeruginosa isolates failed to identify alternative explanations for the observed C/T resistance. We found that exogenous expression of blaL2 modestly increased C/T MICs in genetically distinct P. aeruginosa strains. A screen of our archived isolates identified two P. aeruginosa clinical isolates, PS2045 and PS2046, with one and two copies, respectively, of the genetic element containing blaL2 and truncated ampRL2. Interestingly, disruption of the gene blaL2 but not the truncated ampRL2 in PS2045 led to a significant decrease in C/T MIC. Thus, we report a novel mechanism of C/T resistance in P. aeruginosa mediated by an L2 {beta}-lactamase independently of its canonical regulator AmpRL2.

microbiology↗

bioRxiv2023

Genome-wide screens reveal shared and strain-specific genes that facilitate enteric colonization by Klebsiella pneumoniae

Gastrointestinal (GI) colonization by Klebsiella pneumoniae is a risk factor for subsequent infection as well as transmission to other patients. Additionally, colonization is achieved by many strain types that exhibit high diversity in genetic content. Thus, we aimed to study strain-specific requirements for K. pneumoniae GI colonization by applying transposon insertion sequencing to three classical clinical strains: a carbapenem-resistant strain, an extended-spectrum beta-lactamase producing strain, and a non-epidemic antibiotic-susceptible strain. The transposon insertion libraries were screened in a murine model of GI colonization. At three days post-inoculation, 27 genes were required by all three strains for colonization. Isogenic deletion mutants for three genes/operons (acrA, carAB, tatABCD) confirmed colonization defects in each of the three strains. Additionally, deletion of acrA reduced bile tolerance in vitro, while complementation restored both bile tolerance in vitro and colonization ability in vivo. Transposon insertion sequencing suggested that some genes were more important for colonization of one strain than the others. For example, deletion of the sucrose porin-encoding gene scrY resulted in a colonization defect in the carbapenemase-producing strain but not in the extended-spectrum beta-lactamase producer or the antibiotic-susceptible strain. These findings demonstrate that classical K. pneumoniae strains use both shared and strain-specific strategies to colonize the mouse GI tract. IMPORTANCEKlebsiella pneumoniae is a common cause of difficult-to-treat infections due to its propensity to express resistance to many antibiotics. For example, carbapenem-resistant K. pneumoniae (CR-Kp) has been named an urgent threat by the United States Centers for Disease Control and Prevention. Gastrointestinal colonization of patients with K. pneumoniae has been linked to subsequent infection, making it a key process to control in prevention of multidrug-resistant infections. However, the bacterial factors which contribute to K. pneumoniae colonization are not well understood. Additionally, individual strains exhibit large amounts of genetic diversity, begging the question of whether some colonization factors are strain-dependent. This study identifies the enteric colonization factors of 3 classical strains using transposon mutant screens to define a core colonization program for K. pneumoniae as well as detecting strain-to-strain differences in colonization strategies.

microbiology↗

bioRxiv2020

Novel Immunoassay for Diagnosis of Ongoing Clostridioides difficile Infections Using Serum and Medium Enriched for Newly Synthesized Antibodies (MENSA)

BACKGROUNDClostridioides difficile infections (CDI) have been a challenging and increasing serious concern in recent years. While early and accurate diagnosis is crucial, available assays have frustrating limitations OBJECTIVEDevelop a simple, blood-based immunoassay to accurately diagnose patients suffering from active CDI. MATERIALS AND METHODSUninfected controls (n=95) and CDI patients (n=167) were recruited from Atlanta area hospitals. Blood samples were collected from patients within twelve days of a positive CDI test and processed to yield serum and PBMCs cultured to yield medium enriched for newly synthesized antibodies (MENSA). Multiplex immunoassays measured Ig responses to ten recombinant C. difficile antigens. RESULTSSixty-six percent of CDI patients produced measurable responses to C. difficile antigens in their serum or MENSA within twelve days of a positive CDI test. Fifty-two of the 167 CDI patients (31%) were detectable in both serum and MENSA, but 32/167 (19%) were detectable only in MENSA, and 27/167 (16%) were detectable only in serum. DISCUSSIONWe describe the results of a multiplex immunoassay for the diagnosis of ongoing CDI in hospitalized patients. Our assay resolved patients into four categories: MENSA-positive only, serum-positive only, MENSA- and serum-positive, and MENSA- and serum-negative. The MENSA positive-only patients accounted for 30% and may be attributed to nascent antibody secretion in MENSA prior to seroconversion. Conversely, the serum positive-only subset may have been more advanced in their disease course. Immunocompromise and misdiagnosis may have contributed to the 34% of CDI patients who were not identified using MENSA or serum immunoassays. IMPORTANCEWhile there was considerable overlap between patients identified through MENSA and serum, both methods detected additional, unique patients. The combined use of both MENSA and serum to detect CDI patients resulted in the greatest identification of CDI patients. Together, longitudinal analysis of MENSA and serum will provide a more accurate evaluation of successful host humoral immune responses in CDI patients.

microbiology↗