Bicarbonate enhances the in vitro antibiotic activity of kanamycin in Escherichia coli

Physiological role of bicarbonate in microbes: A double-edged sword?

HCO3- is involved in pH homoeostasis and plays a multifaceted role in human health. HCO3- has been recognized for its antimicrobial properties and is pivotal in bacterial antibiotic susceptibility. Notably, the interconversion between CO2 and HCO3-, facilitated by the enzyme carbonic anhydrase (CA), is crucial in tissues infected by pathogens. Studies have highlighted the antimicrobial potency of CA inhibitors, emphasizing the importance of this enzyme in this area. The potential of HCO3- as an antibiotic adjuvant is evident; its ability to increase virulence in pathogens such as Enterococcus faecalis and Mycobacterium tuberculosis requires meticulous scrutiny. HCO3- modulates bacterial behaviours in diverse manners: it promotes Escherichia coli O157:H7 colonization in the human gut by altering specific gene expression and, with Pseudomonas aeruginosa, amplifies the effect of tobramycin on planktonic cells while promoting biofilm formation. These multifaceted effects necessitate profound mechanistic exploration before HCO3- can be considered a promising clinical adjuvant.

Bicarbonate Within: A Hidden Modulator of Antibiotic Susceptibility

Since its standardization, clinical antimicrobial susceptibility testing (AST) has relied upon a standard medium, Mueller-Hinton Broth/Agar (MHB/A), to determine antibiotic resistance. However, this microbiologic medium bears little resemblance to the host milieu, calling into question the physiological relevance of resistance phenotypes it reveals. Recent studies investigating antimicrobial susceptibility in mammalian cell culture media, a more host-mimicking environment, demonstrate that exposure to host factors significantly alters susceptibility profiles. One such factor is bicarbonate, an abundant ion in the mammalian bloodstream/tissues. Importantly, bicarbonate sensitizes methicillin-resistant Staphylococcus aureus (MRSA) to early-generation β-lactams used for the treatment of methicillin-susceptible S. aureus (MSSA). This "NaHCO3-responsive" phenotype is widespread among US MRSA USA300/CC8 bloodstream and skin and soft tissue infection isolates. Translationally, β-lactam therapy has proven effective against NaHCO3-responsive MRSA in both ex vivo simulated endocarditis vegetation (SEV) and in vivo rabbit infective endocarditis (IE) models. Mechanistically, bicarbonate appears to influence mecA expression and PBP2a production/localization, as well as key elements for PBP2a functionality, including the PBP2a chaperone PrsA, components of functional membrane microdomains (FMMs), and wall teichoic acid (WTA) synthesis. The NaHCO3-responsive phenotype highlights the critical role of host factors in shaping antibiotic susceptibility, emphasizing the need to incorporate more physiological conditions into AST protocols.

Effect of lysin EN4 in combination with sodium bicarbonate on reduction of Salmonella in chilled and thawed chicken meat

Lysin EN4 is a peptidoglycan-degrading enzyme. Like other lysins against Gram-negative bacteria, EN4 requires cell-wall destabilizing agents, such as ethylenediamine tetraacetic acid (EDTA) to facilitate it to the peptidoglycan layer. This study aimed to use EN4 in reducing Salmonella in chilled and thawed raw chicken meat. However, the use of EDTA is limited to some types of foods. An alternative to EDTA was explored. Sodium bicarbonate was identified as an effective alternative to EDTA. The combination of EN4 with 0.1 % NaHCO₃, pH 7.4 showed a wide lytic spectrum against Salmonella spp. The combination showed efficiency in reduction of Salmonella Enteritidis and Typhimurium in raw chicken meat during storage at 4 °C for 48 h, with the maximum reduction of 1.0-1.3log CFU/g. The efficiency of the combination against Salmonella was evaluated in frozen chicken meat during proper and improper defrosting. A significant reduction of Salmonella was observed in EN4-treated meat compared to the untreated control through 48 and 4 h of defrosting at 4 and 30 °C, respectively, with the greatest reduction of 1.2-1.6 log CFU/g. The results indicated that EN4 in combination with NaHCO₃ has a potential use for controlling growth of Salmonella in chilled and thawed chicken meat.

Innovative Strategies to Overcome Antimicrobial Resistance and Tolerance

Antimicrobial resistance and tolerance are natural phenomena that arose due to evolutionary adaptation of microorganisms against various xenobiotic agents. These adaptation mechanisms make the current treatment options challenging as it is increasingly difficult to treat a broad range of infections, associated biofilm formation, intracellular and host adapted microbes, as well as persister cells and microbes in protected niches. Therefore, novel strategies are needed to identify the most promising drug targets to overcome the existing hurdles in the treatment of infectious diseases. Furthermore, discovery of novel drug candidates is also much needed, as few novel antimicrobial drugs have been introduced in the last two decades. In this review, we focus on the strategies that may help in the development of innovative small molecules which can interfere with microbial resistance mechanisms. We also highlight the recent advances in optimization of growth media which mimic host conditions and genome scale molecular analyses of microbial response against antimicrobial agents. Furthermore, we discuss the identification of antibiofilm molecules and their mechanisms of action in the light of the distinct physiology and metabolism of biofilm cells. This review thus provides the most recent advances in host mimicking growth media for effective drug discovery and development of antimicrobial and antibiofilm agents.

Bicarbonate Effects on Antibacterial Immunity and Mucus Glycobiology in the Cystic Fibrosis Lung: A Review With Selected Experimental Observations

The primary defect in cystic fibrosis (CF) is abnormal chloride and bicarbonate transport in the cystic fibrosis transmembrane conductance regulator (CFTR) epithelial ion channel. The apical surface of the respiratory tract is lined by an airway surface liquid layer (ASL) composed of mucin comprising mainly MUC5A and MUC5B glycoproteins. ASL homeostasis depends on sodium bicarbonate secretion into the airways and secretion deficits alter mucus properties leading to airway obstruction, inflammation, and infections. Downstream effects of abnormal ion transport in the lungs include altered intrinsic immune defenses. We observed that neutrophils killed Pseudomonas aeruginosa more efficiently when it had been exposed to sodium bicarbonate, and formation of neutrophil extracellular traps (NETs) by neutrophils was augmented in the presence of increasing bicarbonate concentrations. Physiological levels of bicarbonate sensitized P. aeruginosa to the antimicrobial peptide cathelicidin LL-37, which is present in both lung ASL and in NETs. Sodium bicarbonate has various uses in clinical medicine and in the care of CF patients, and could be further explored as a therapeutic adjunct against Pseudomonas infections.

Study of Antibacterial Chemical Substances and Molecular Investigation among Sulfamethoxazole-trimethoprim (SXT)-Resistant Escherichia coli Isolates

Background

Escherichia coli (E. coli) remains one of the leading agents of urinary tract infection (UTIs), it has become resistant to many drugs. Current work aimed to evaluate some chemical substances as antibacterial agents and molecular study of virulence factors associated with UTIs.

Methods

This work involved 133 urine specimens obtained from females' patients suffering from UTIs, Methods of well diffusion and disk diffusion were achieved to assay the effect of some chemical substances and antibiogram profiles toward Sulfamethoxazole-trimethoprim (SXT)-resistant E. coli respectively. Virulence genes were done based on the technique of Polymerase Chain Reaction (PCR).

Results

The results recorded 49/133 (36.84%) E. coli among women suffering UTIs, 28/49 (57.14%) were resistant to SXT drug. imipenem, meropenem, and nitrofurantoin were recorded more effectively. Chemicals substances at the concentration 0.3 (g/ml) recorded percentages of inhibition, reaching 9.143±1.442, 15.36±0.5914, and 21.82±0.8699 for NaHCO3, Ch4c, and Viroxide Super™ respectively. PCR demonstrated that 28/28 (100%) of SXT-resistant E. coli isolates were harbored Sul-2, FeoB and PapC genes, while 14/28 (50%), 15/28 (53.57%), 19/28 (67.85%) and 26/28 (92.85%) in U250 (pet), FumC, Sul-1 and IutA genes, respectively. Sul-3 gene was not observed.

Conclusion

Observed a high percentage of E. coli that were resistant to SXT drug, and having several virulence genes, poses a real threat, it requires a real pause to create substitutions to limit the spreading of this threat.

Nonviral Expression of LL-37 in a Human Skin Equivalent to Prevent Infection in Skin Wounds

Inefficient autologous tissue recovery in skin wounds increases the susceptibility of patients to infections caused by multidrug resistant microorganisms, resulting in a high mortality rate. Genetic modification of skin cells has become an important field of study because it could lead to the construction of more functional skin grafts, through the overexpression of antimicrobial peptides that would prevent early contamination and infection with bacteria. In this study, we produce and evaluate human skin equivalents (HSEs) containing transfected human primary fibroblasts and keratinocytes by polyplexes to express the antimicrobial peptide LL-37. The effect of LL-37 on the metabolic activity of normal HSEs was evaluated before the construction of the transfected HSEs, and the antimicrobial efficacy against Pseudomonas aeruginosa and Staphylococcus aureus was evaluated. Subsequently, the levels of LL-37 in the culture supernatants of transfected HSEs, as well as the local expression, were determined. It was found that LL-37 treatment significantly promoted the cellular proliferation of HSEs. Furthermore, HSEs that express elevated levels of LL-37 were shown to possess histological characteristics close to the normal skin and display enhanced antimicrobial activity against S. aureus in vitro. These findings demonstrate that HSEs expressing LL-37 through nonviral modification of skin cells are a promising approach for the prevention of bacterial colonization in wounds.

Bicarbonate Alters Bacterial Susceptibility to Antibiotics by Targeting the Proton Motive Force

The antibacterial properties of sodium bicarbonate have been known for years, yet the molecular understanding of its mechanism of action is still lacking. Utilizing chemical-chemical combinations, we first explored the effect of bicarbonate on the activity of conventional antibiotics to infer on the mechanism. Remarkably, the activity of 8 classes of antibiotics differed in the presence of this ubiquitous buffer. These interactions and a study of mechanism of action revealed that, at physiological concentrations, bicarbonate is a selective dissipater of the pH gradient of the proton motive force across the cytoplasmic membrane of both Gram-negative and Gram-positive bacteria. Further, while components that make up innate immunity have been extensively studied, a link to bicarbonate, the dominant buffer in the extracellular fluid, has never been made. Here, we also explored the effects of bicarbonate on components of innate immunity. Although the immune response and the buffering system have distinct functions in the body, we posit there is interplay between these, as the antimicrobial properties of several components of innate immunity were enhanced by a physiological concentration of bicarbonate. Our findings implicate bicarbonate as an overlooked potentiator of host immunity in the defense against pathogens. Overall, the unique mechanism of action of bicarbonate has far-reaching and predictable effects on the activity of innate immune components and antibiotics. We conclude that bicarbonate has remarkable power as an antibiotic adjuvant and suggest that there is great potential to exploit this activity in the discovery and development of new antibacterial drugs by leveraging testing paradigms that better reflect the physiological concentration of bicarbonate.

Importance of bicarbonate transport in pH control during amelogenesis - need for functional studies

Dental enamel, the hardest mammalian tissue, is produced by ameloblasts. Ameloblasts show many similarities to other transporting epithelia although their secretory product, the enamel matrix, is quite different. Ameloblasts direct the formation of hydroxyapatite crystals, which liberate large quantities of protons that then need to be buffered to allow mineralization to proceed. Buffering requires a tight pH regulation and secretion of bicarbonate by ameloblasts. Many investigations have used immunohistochemical and knockout studies to determine the effects of these genes on enamel formation, but up till recently very little functional data were available for mineral ion transport. To address this, we developed a novel 2D in vitro model using HAT-7 ameloblast cells. HAT-7 cells can be polarized and develop functional tight junctions. Furthermore, they are able to accumulate bicarbonate ions from the basolateral to the apical fluid spaces. We propose that in the future, the HAT-7 2D system along with similar cellular models will be useful to functionally model ion transport processes during amelogenesis. Additionally, we also suggest that similar approaches will allow a better understanding of the regulation of the cycling process in maturation-stage ameloblasts, and the pH sensory mechanisms, which are required to develop sound, healthy enamel.