Biology subjects

Bachta, K. E. R.

Publications and source records attributed to Bachta, K. E. R..

6 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↗

bioRxiv2024

Pseudomonas aeruginosa population dynamics in a vancomycin-induced murine model of gastrointestinal carriage

Pseudomonas aeruginosa is a common nosocomial pathogen and a major cause of morbidity and mortality in hospitalized patients. Multiple reports highlight that P. aeruginosa gastrointestinal colonization may precede systemic infections by this pathogen. Gaining a deeper insight into the dynamics of P. aeruginosa gastrointestinal carriage is an essential step in managing gastrointestinal colonization and could contribute to preventing bacterial transmission and progression to systemic infection. Here, we present a clinically relevant mouse model relying on parenteral vancomycin pretreatment and a single orogastric gavage of a controlled dose of P. aeruginosa. Robust carriage was observed with multiple clinical isolates, and carriage persisted for up to 60 days. Histological and microbiological examination of mice indicated that this model indeed represented carriage and not infection. We then used a barcoded P. aeruginosa library along with the sequence tag-based analysis of microbial populations (STAMPR) analytic pipeline to quantify bacterial population dynamics and bottlenecks during the establishment of the gastrointestinal carriage. Analysis indicated that most of the P. aeruginosa population was rapidly eliminated in the stomach, but the few bacteria that moved to the small intestine and the caecum expanded significantly. Hence, the stomach constitutes a significant barrier against gastrointestinal carriage of P. aeruginosa, which may have clinical implications for hospitalized patients. IMPORTANCEWhile P. aeruginosa is rarely part of the normal human microbiome, carriage of the bacterium is quite frequent in hospitalized patients and residents of long-term care facilities. P. aeruginosa carriage is a precursor to infection. Options for treating infections caused by difficult-to-treat P. aeruginosa strains are dwindling, underscoring the urgency to better understand and impede pre-infection stages, such as colonization. Here, we use vancomycin-treated mice to model antibiotic-treated patients who become colonized with P. aeruginosa in their gastrointestinal tracts. We identify the stomach as a major barrier to the establishment of gastrointestinal carriage. These findings suggest that efforts to prevent gastrointestinal colonization should focus not only on judicious use of antibiotics but also on investigation into how the stomach eliminates orally ingested P. aeruginosa.

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↗

bioRxiv2022

Genomic evaluation of a case of Lacticaseibacillus rhamnosus endocarditis: comparison with commercial yogurt isolates and examination of global population structure

Probiotics, including yogurt commonly containing bacteria of the Lactobacillus group, are widely used to promote microbiome health and to prevent gastrointestinal or other infections, especially in the setting of antibiotic use. Rarely, however, Lactobacillus bacteria have caused invasive or severe infections in patients. In this report, we present a patient with fatal Lacticaseibacillus bacteremia and endocarditis who frequently consumed yogurt. Whole genome sequencing identified the patients bloodstream isolate as Lacticaseibacillus (formerly Lactobacillus) rhamnosus, and sequencing of Lactobacillus isolates from selected commercial yogurt preparations revealed one isolate nearly identical to the patients isolate, differing by only one nucleotide (adenine to guanine substitution leading to a M1A amino acid change in the start codon of the nrdR gene). To place these sequences into broader context of L. rhamnosus strains, we compared them to 602 L. rhamnosus genome sequences publicly available through the National Center for Biotechnology Information repository. Both isolates belonged to a clade, identified in this report as clade YC, composed of mostly gastrointestinal isolates from healthy individuals, some of which also differed by only a single nucleotide from the patients isolate. Members of clade YC had only rarely been previously identified in invasive infections. In summary, the Lacticaseibacillus strain causing this patients infection may have originated from a commercial dairy product or from the commensal flora of his gastrointestinal tract. This study demonstrates that whole genome sequencing may be insufficient to reliably determine the source of invasive infections caused by L. rhamnosus. IMPORTANCEActive culture and probiotic foods and supplements are often used to promote gut health. Though largely considered safe for human consumption, there are rare reports of severe infections linked to bacterial species used in these products. Using whole genome sequencing, we examined a case of fatal infection with Lacticaseibacillus rhamnosus in the patients blood. By comparing the bacterial genome sequence from the patient to strains cultured from 4 commercial yogurt samples and 602 publicly available sequences of L. rhamnosus from around the world, we found that it was nearly identical to one of the yogurt strains and equally similar to other strains from both probiotics and healthy individuals gastrointestinal tracts. These findings show that even with whole genome sequencing it can be difficult to determine the source of an invasive L. rhamnosus infection, whether from recent consumption of a probiotic or dairy product versus from the gastrointestinal microbiome.

microbiology↗

bioRxiv2021

Functional and Structural Characterization of OXA-935, a Novel OXA-10-family β-lactamase from Pseudomonas aeruginosa

Resistance to antipseudomonal penicillins and cephalosporins is often driven by the overproduction of the intrinsic {beta}-lactamase AmpC. However, OXA-10-family {beta}-lactamases are a rich source of resistance in Pseudomonas aeruginosa. OXA {beta}-lactamases have a propensity for mutation leading to extended spectrum cephalosporinase and carbapenemase activity. In this study, we identified isolates from a subclade of the multidrug-resistant (MDR) high risk clonal complex CC446 with resistance to ceftazidime. Genomic analysis revealed that these isolates harbored a plasmid containing a novel allele of blaOXA-10, named blaOXA-935, which was predicted to produce an OXA-10 variant with two amino acid substitutions: an aspartic acid instead of glycine at position 157 and a serine instead of phenylalanine at position 153. The G157D mutation, present in OXA-14, is associated with resistance to ceftazidime. Deletion of blaOXA-935 restored sensitivity to ceftazidime and susceptibility profiling of P. aeruginosa laboratory strains expressing blaOXA-935 revealed that OXA-935 conferred ceftazidime resistance. To better understand the impact of the variant amino acids, we determined the crystal structures of OXA-14 and OXA-935. In OXA-14, one of two monomers contained the canonical carbamylated lysine-70 (K70). In contrast, both monomers of OXA-935 were decarbamylated at K70, and the F153S mutation conferred increased flexibility to the omega ({Omega}) loop. Compared to OXA-14, the catalytic efficiency of OXA-935 for nitrocefin was significantly reduced. Amino acid changes that confer extended spectrum cephalosporinase activity to OXA-10-family {beta}-lactamases are concerning given rising reliance on novel {beta}-lactam/{beta}-lactamase inhibitor combinations such as ceftolozane-tazobactam and ceftazidime-avibactam to treat MDR P. aeruginosa infections.

microbiology↗

bioRxiv2019

Systemic Infection Facilitates Transmission of Pseudomonas aeruginosa

Health care-associated infections such as Pseudomonas aeruginosa (PA) bacteremia pose a major clinical risk for hospitalized patients, and efforts to limit them are a priority. The fitness pressures accounting for PA virulence factors that facilitate bloodstream infections are unclear, as these infections are presumed to be a \"dead-end\" and have no impact on transmission. Here, we used a mouse model to show that PA spreads from the bloodstream to the gallbladder, where it replicates to extremely high numbers. Bacteria in the gallbladder then seed the intestines and feces, leading to transmission to uninfected cage-mate mice. The findings demonstrate that the gallbladder is critical for spread of PA from the bloodstream to the feces during bacteremia, a process that promotes transmission.

microbiology↗