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Carbapenenemase producers, particularly the metallo-β-lactamase (MBL) types in Pseudomonas aeruginosa, have emerged as an urgent threat in health care settings. MBLs require zinc at their catalytic site and can be inhibited by dimercaptosuccinic acid (DMSA), a metal chelator known for the treatment of lead and mercury intoxication. Isogenic strains of wild-type and OprD-deleted P. aeruginosa PA14, were constructed, producing the MBLs VIM-2, NDM-1, SPM-1, IMP-1, and AIM-1, or the non-MBL carbapenemases, GES-5 and KPC-2. In addition, 59 previously characterized clinical isolates of P. aeruginosa producing different ß-lactamases (including carbapenemases), and with known outer-membrane porin OprD status, were utilized. Minimal inhibitory concentrations values of imipenem and meropenem, and DMSA combinations were determined, and time-kill assays were performed with PA14 expressing VIM-2. Results indicated a significant additive effect of DMSA (most effective at 3 mM) and carbapenems in recombinant and clinical strains of P. aeruginosa expressing MBLs, in particular against VIM producers, which are the most prevalent carbapenemases in P. aeruginosa. This effect was best evidenced with meropenem and in strains without OprD modification. DMSA shows promising efficacy, particularly in combination therapy with meropenem, for treating infections caused by MBL-producing P. aeruginosa. [ABSTRACT FROM AUTHOR]

Tigecycline (Tgc), a third-generation tetracycline is found as the last line of defense against multi-drug resistant bacteria. Recent increased rate of resistance to tgc, a human-restricted agent among animal bacteria poses a significant global health challenge. Overuse of first generation tetracyclines (Tet) and phenicols in animals have been suggested to be associated with Tgc resistance development. In the current study we aimed to determine the effect of tetracycline (Tet) and chloramphenicol (Chl) overexposure on Tgc susceptibility. A Tet and Chl-susceptible isolate of K. pneumoniae and E. coli were exposed to successively increasing concentrations of tetracycline and chloramphenicol separately until a ≥4 times increase in Tet and Chl MICs was observed. Susceptibility changes to several antimicrobial agents were tested using disk diffusion and broth dilution methods. The genetic alterations of genes coding for major AcrAB regulators including acrR (repressor of acrAB), ramR (repressor of ramA), soxR (repressor of soxS) in K. pneumoniae and lon (proteolytic degradation of MarA), marR (repressor of marA), acrR and soxR in E. coli were investigated. The expression level of acrB was measured using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) method. The excessive exposure (15 to 40 selection cycles) of studied bacteria to both antibiotics significantly decreased susceptibility of Tet-resistant (R) and Chl-R variants of E. coli (n = 6) and K. pneumoniae (n = 6) to several groups of antibiotics including tigecycline (4–16 and 8–64 times respectively) and quinolones. About 58% of variants (n = 7) carried genetic alterations in AcrAB regulators including ramR (frameshift mutations/locus deletion), MarR (L33R, A70T, G15S amino acid substitutions) and Lon (L630F change, frameshift mutation) which were associated with acrB upregulation. Our study demonstrated the capacity of chloramphenicol and tetracycline exposure for selection of mutants which revealed tigecycline resistance/decreased susceptibility mostly mediated by active efflux mechanism. Unaltered acrB expression level in some strains indicates possible contribution of other efflux pumps or non-efflux-based mechanisms in the development of multiple- antibiotic resistance phenotype. [ABSTRACT FROM AUTHOR]

Membrane fouling is a major hindrance that restricts the application of membrane bioreactors (MBRs). Bdellovibrio-and-like organisms (BALOs), as obligatory parasitic bacteria, prey upon various bacteria. In this study, the BALO mixtures were screened and found more effective in membrane fouling mitigation compared to the single BALO species and extended the membrane filtration period by as long as 33.3%. The higher BALO diversity reduced the potential foulants generation in the activated sludge by decreasing the sludge viscosity as high as 13.8 ± 0.6% than the pure culture of BALO. Meanwhile, the mixed BALOs demonstrated superior biofilm predation capabilities, with the content of soluble microbial products and extracellular polymeric substances on the biofilm decreasing by 26.1 ± 0.5% and 38.3 ± 0.2% as the most compared to the single BALO species involved system. Additionally, the BALO mixtures expanded the single strains' host lysis spectrum of both the activated sludge and biofilm. The abundance of membrane-fouling-related bacteria such as Flavobacterium, Rhodobacter, and Labilithrix and pioneer bacteria such as Sphingorhabdus and Pseudomonas was significantly reduced. In summary, this study disclosed the significantly better membrane fouling mitigation effects of the BALOs with higher diversity, suggesting that the expansion of the host range is crucial for the further application of BALOs to enhance the anti-fouling performance of the MBR system. [ABSTRACT FROM AUTHOR]

Background: One of the main issues facing public health with microbial infections is antibiotic resistance. Nanoparticles (NPs) are among the best alternatives to overcome this issue. Silver nanoparticle (AgNPs) preparations are widely applied to treat multidrug-resistant pathogens. Therefore, there is an urgent need for greater knowledge regarding the effects of improper and excessive use of these medications. The current study describes the consequences of long-term exposure to sub-lethal concentrations of AgNPs on the bacterial sensitivity to NPs and the reflection of this change on the bacterial genome. Results: Chemical methods have been used to prepare AgNPs and gamma irradiation has been utilized to produce more stable AgNPs. Different techniques were used to characterize and identify the prepared AgNPs including UV-visible spectrophotometer, Fourier Transform Infrared (FT-IR), Dynamic light scattering (DLS), and zeta potential. Transmission electron microscope (TEM) and Scanning electron microscope (SEM) showed 50–100 nm spherical-shaped AgNPs. Eleven gram-negative and gram-positive bacterial isolates were collected from different wound infections. The minimum inhibitory concentrations (MICs) of AgNPs against the tested isolates were evaluated using the agar dilution method. This was followed by the induction of bacterial resistance to AgNPs using increasing concentrations of AgNPs. All isolates changed their susceptibility level to become resistant to high concentrations of AgNPs upon recultivation at increasing concentrations of AgNPs. Whole genome sequencing (WGS) was performed on selected susceptible isolates of gram-positive Staphylococcus lentus (St.L.1), gram-negative Klebsiella pneumonia (KP.1), and their resistant isolates St.L_R.Ag and KP_R.Ag to detect the genomic changes and mutations. Conclusions: For the detection of single-nucleotide polymorphisms (SNPs) and the identification of all variants (SNPs, insertions, and deletions) in our isolates, the Variation Analysis Service tool available in the Bacterial and Viral Bioinformatics Resource Center (BV-BRC) was used. Compared to the susceptible isolates, the AgNPs-resistant isolates St.L_R.Ag and KP_R.Ag had unique mutations in specific efflux pump systems, stress response, outer membrane proteins, and permeases. These findings might help to explain how single-nucleotide variants contribute to AgNPs resistance. Consequently, strict regulations and rules regarding the use and disposal of nano waste worldwide, strict knowledge of microbe-nanoparticle interaction, and the regulated disposal of NPs are required to prevent pathogens from developing nanoparticle resistance. [ABSTRACT FROM AUTHOR]

Background: Increasing trend and spread of multidrug-resistant Pseudomonas aeruginosa (MDR-PA) in clinical settings is a great challenge in managing patients with infections caused by this pathogen. Objective: To determine the risk factors and outcomes of MDR-PA acquisition in the northeastern state of Malaysia. In addition, this study also reported on the susceptibility pattern and common resistant genes among MDR-PA. Materials and Methods: MDR-PA isolates obtained between March 2021 and February 2022 from all four major hospitals in the state of Kelantan, Malaysia, were submitted for susceptibility and resistant genes identification. The clinical data of the patients with MDR-PA were retrospectively reviewed. The risk factors and outcomes of MDR-PA acquired patients were analyzed by comparing with patients who acquired susceptible-PA while admitted to the same hospital during the study time. Results: A total of 100 MDR-PA and 100 susceptible-PA cases were included. Ceftolozane–tazobactam was susceptible in 41.3% of MDR-PA compared to only 4%–8% with other β-lactams. About half (46%) of the MDR-PA isolates harbored the bla -NDM-1 gene, but none had the bla -OXA-48 gene. Factors independently associated with MDR-PA acquisitions were age (OR: 1.02; P = 0.028), genitourinary disorder (OR: 6.89; P = 0.001), and central venous catheter (OR: 3.18; P = 0.001). In addition, MDR-PA acquisitions were found to be associated with antimicrobial treatment failure (41.1% vs. 25.0%; P = 0.001) and mortality (40.0% versus 6.0%; P <0.001). Conclusion: Most of the MDR-PA strains in Kelantan tertiary hospitals harbored the bla -NDM-1 gene, which is easily transmissible and can lead to an outbreak. Nonetheless, a significant number of the MDR-PA isolates were still susceptible to ceftolozane–tazobactam. [ABSTRACT FROM AUTHOR]

Paramount to human health, symbiotic bacteria in the gastrointestinal tract rely on the breakdown of complex polysaccharides to thrive in this sugar-deprived environment. Gut Bacteroides are metabolic generalists and deploy dozens of polysaccharide utilization loci (PULs) to forage diverse dietary and host-derived glycans. The expression of the multi-protein PUL complexes is tightly regulated at the transcriptional level. However, how PULs are orchestrated at translational level in response to the fluctuating levels of their cognate substrates is unknown. Here, we identify the RNA-binding protein RbpB and a family of noncoding RNAs as key players in post-transcriptional PUL regulation. We demonstrate that RbpB interacts with numerous cellular transcripts, including a paralogous noncoding RNA family comprised of 14 members, the FopS (family of paralogous sRNAs). Through a series of in-vitro and in-vivo assays, we reveal that FopS sRNAs repress the translation of SusC-like glycan transporters when substrates are limited—an effect antagonized by RbpB. Ablation of RbpB in Bacteroides thetaiotaomicron compromises colonization in the mouse gut in a diet-dependent manner. Together, this study adds to our understanding of RNA-coordinated metabolic control as an important factor contributing to the in-vivo fitness of predominant microbiota species in dynamic nutrient landscapes. Gut Bacteroides deploy several polysaccharide utilization loci (PULs) to forage diverse dietary and host-derived glycans. Here, the authors identify the RNA-binding protein RbpB and a family of noncoding RNAs as key players in post-transcriptional PUL regulation, further showing that ablation of RbpB in Bacteroides thetaiotaomicron compromises colonization in the mouse gut in a diet-dependent manner. [ABSTRACT FROM AUTHOR]