Increased Acid Resistance Research Articles

Development of water vapor recovery membrane for efficient recycling system

Abstract In wastewater treatment at semiconductor plants separation operations are currently conducted mainly by distillation. Membrane distillation using ceramic surface-treated membranes is expected to provide more efficient separation. In this study, we investigated the improvement of acid resistance of surface-treated ceramic membranes by using four silicon alkoxides, Hexamethyldisiloxane(HMDS), Dimethyldimethoxysilane(DMDMOS), 3,3,3-Trifluoropropyltrimethoxysilane (TFPrTMOS), Tetramethoxysilane(TMOS) were used as surface treatment and it was performed in the gas phase. The water vapor permeance of the TFPrTMOS surface treated membrane was 2.35✕10−6 [mol m−2 s−1 Pa−1], and it maintained its functionality after immersion in a 10 wt% sulfuric acid solution under 60°C for 170 h. The membrane with multiple surface treatments with TFPrTMOS showed an increase in acid resistance to 491h, indicating that unreacted alkoxide affected the degradation. The water vapor permeance of the TFPrTMOS-DMDMOS treated membrane combined silicon alkoxides was 2.85✕10−6[mol m−2 s−1 Pa−1] and the acid resistance was 687 h. It is possible that DMDMOS acted as a cross-linker in modifying the unreacted alkoxide portion of the membrane, leading to improved resistance.

Increase acid resistance of teeth by 1000%

Increase acid resistance of teeth by 1000%

Mechanical properties of polyolefin and polypropylene fibers-reinforced concrete–An experimental study

Concrete, a widely used construction material, exhibits inherent brittleness and limited tensile strength. To address these shortcomings, the incorporation of fibers has gained prominence, with polyolefin and polypropylene fibers emerging as promising reinforcements. This study experimentally conducted and examined the mechanical characteristics of polyolefin and polypropylene fibers-reinforced concrete. The study involved conducting compressive strength tests and durability tests, including sulfate resistance, acid resistance, chloride ion penetration resistance, and abrasion tests. The results demonstrated a notable enhancement in the compressive strength of both cubic and cylindrical specimens with varying dimensions, owing to the inclusion of polyolefin fibers. Polyolefin fibers exhibited a greater reinforcing effect compared to polypropylene fibers, especially in larger cubic specimens and cylindrical specimens. The quantitative results show that specimens with polypropylene fibers exhibited a 9.67 % improvement in compressive strength, while those with polyolefin fibers showed a 30.47 % enhancement compared to specimens without fibers. The acid resistance test revealed that both types of fiber-reinforced specimens exhibited higher compressive strength in acidic environments compared to plain concrete specimens. In the chloride ion penetration resistance test, the polyolefin fiber-reinforced specimen demonstrated the highest resistance to degradation, while the plain concrete specimen exhibited the lowest resistance. Polyolefin demonstrated superior reinforcement compared to polypropylene, with a 35 % increase in acid resistance and better chloride ion resistance. In contrast, specimens without fibers weakened by 35.36 % in a chloride environment. The sulfate resistance test showed that the polyolefin fiber-reinforced specimen had the highest compressive strength in a sulfate environment, while the plain concrete specimen had the lowest. In sulfate and abrasion tests, polyolefin-fiber-reinforced specimens displayed the highest resistance and the lowest abrasion rate of 34.6 %. These findings highlight the potential of polyolefin fiber-reinforced concrete for enhancing mechanical properties and durability in various applications.

Efficient secreted expression of natural intracellular β-galactosidase from Bacillus aryabhattai via non-classical protein secretion pathway in Bacillus subtilis

In this study, the natural intracellular β-galactosidase (lacZBa) from Bacillus aryabhattai was expressed extracellularly in Bacillus subtilis. Sec and Tat signal peptides from different secretion pathways were incorporated to facilitate extracellular secretion of lacZBa, resulting in a yield of only 0.54 U/mL. Interestingly, it was discovered that lacZBa could be efficiently expressed and secreted in B. subtilis via a non-classical secretory pathway without the need for a signal peptide. The extracellular activity and secretion ratio were 5.3 U/mL and 65 %, respectively. Compared to E. coli, the expression of lacZBa in B. subtilis resulted in increased acid resistance and higher pH stability and thermostability, with a 1.7-fold increase in half-life at 50 °C and pH 6.0. Additionally, we combined single-factor experiments and response surface methodology to enhance extracellular expression of β-galactosidase in shake-flasks. The resulting optimal medium contained 4.46 % glucose, 1.47 % corn steep liquor, 1.5 % beef extract, 0.82 % CaCl2, and 0.1 % MgSO4. Under optimal conditions, the yield of extracellularly secreted β-galactosidase at the shake flask level was 17.41 U/mL, representing a 32.2-fold increase in initial extracellular enzyme activity. This study represents the first successful report of natural intracellular β-galactosidase being expressed through the non-classical secretory pathway in B. subtilis.

Ефективність використання червоного шламу при розробці кислотостійких гібридних лужних цементів

The use of secondary industrial products has long been an integral part of the construction industry. The most common man-made raw materials used in the production of building materials, in addition to slag, are fly ash and red mud.
 This work is devoted to the study of the effectiveness of using red mud as an additional source of an alumina silicate component of man-made origin in the production of alkali-activated cements with increased acid resistance.
 In conventional cement systems, the use of significant amounts of red mud is not possible due to the high content of alkali metal compounds and heavy elements, but this is not a problem for alkali-activated binders.
 Red mud obtained by processing bauxite ore using the Bayer process is highly alkaline, and its disposal and reusability are hampered by high sodium concentrations and high pH. That is why, according to the analysis of literature sources, research on the integrated use of red mud is mainly found in only a few areas, among which construction occupies a leading position.
 In the course of research, the parameters of dough of normal density, hardening terms and strength for the developed systems were determined. Direct determination of the acid resistance index was also carried out using two methods: accelerated and by long-term aging of samples. In this way, the main physical and mechanical characteristics of the developed compounds were determined and the results were analyzed.
 The obtained results of the study confirmed the possibility of partially replacing alumina silicate components with red mud to obtain acid-resistant alkaline cements. It was found that the introduction of up to 30% of red mud makes it possible to obtain material with an acid resistance coefficient (Ks) in the range of 0.8-0.95.

Probiotic Characteristics and Safety Assessment of Lacticaseibacillus casei KGC1201 Isolated from Panax ginseng.

Panax ginseng is one of the most important herbal medicinal plants consumed as health functional food and can be fermented to achieve better efficacy. Lacticaseibacillus, one of the representative genera among lactic acid bacteria (LAB), has also been used as a probiotic material for health functional foods due to its beneficial effects on the human body. To achieve a synergistic effect by using these excellent dietary supplement ingredients together, a novel LAB strain was isolated from the root of 6-year-old ginseng. Through similarity analysis of 16S rRNAs and whole-genome sequences, the strain was confirmed as belonging to the genus Lacticaseibacillus and was named L. casei KGC1201. KGC1201 not only met all safety standards as food, but also showed excellent probiotic properties such as acid resistance, bile salt resistance, and intestinal adhesion. In particular, KGC1201 exhibited superior acid resistance through morphological observation identifying that the cell surface damage of KGC1201 was less than that of the L. casei type strain KCTC3109. Gene expression studies were conducted to elucidate the molecular mechanisms of KGC1201's acid resistance, and the expression of the glycosyltransferase gene was found to be significantly elevated under acidic conditions. Exopolysaccharides (EPSs) biosynthesized by glycosyltransferase were also increased in KGC1201 compared to KCTC3109, which may contribute to better protection of KGC1201 cells from strong acidity. Therefore, KGC1201, with its increased acid resistance through molecular mechanisms and excellent probiotic properties, can be used in health functional foods to provide greater benefit to overall human health and well-being.

Prospects of development of acid–resistant hybrid cements on the basis of alkaline–activated binders

Quite often during operation, construction products and structures are exposed to aggressive environments, which leads to a decrease in their physical and mechanical characteristics and durability in general.
 To date, there is a wide range of options for eliminating the effects of structural failure, and new recommendations are being developed to prevent destructive processes that take place in the body of artificial cement stone. The issue of improving the acid resistance of building materials is no exception. Unfortunately, the existing acid–resistant materials, although characterized by high resistance to operation in acidic environments, but under the influence of water and with the change of environment to neutral or alkaline, they are also destroyed. This applies directly to acid–resistant materials based on liquid glass.
 An analysis of existing research has confirmed the effectiveness of using alkaline–activated binder systems as a basis for acid–resistant cements especially when comparing them with Portland cement. This is primarily due to the difference in the phase composition of their cement stone, which is characterized by the absence of highly basic hydrosilicates of calcium, etringite, free lime and the presence of alkaline and alkaline earth hydrosilicate and hydroaluminosilicate neoplasms. The latter, as research experience has shown, provide improved performance properties of materials based on alkaline–activated binders. They are also characterized by increased acid resistance. Thus, the main task of research is to determine the optimal ratio in the cement stone of the hybrid composition of the phases of the systems систем СaO – SiO2 – H2O; Na2O – CaO – Al2O3 – SiO2 – H2O and Na2O – Al2O3 – SiO2 – H2O, which will provide both hydrating properties of the binder and high acid resistance.
 The concept that clearly reflects the prospects of research is to consider the main factors influencing the formation of acid–resistant phases: "composition – properties – structure – technology". To study the physicochemical conditions of synthesis it is necessary to study model systems of different compositions of R2O – CaO – Al2O3 – SiO2 – H2O, as well as study of technological factors such as component composition, cooking conditions, curing conditions. As a raw material base, it is advisable to use man–made products of industrial production, which are generally represented by slag, ash, etc.

Laser irradiation prevents root caries: Microhardness and scanning electron microscopy analysis.

A promising option for the prevention of dental caries is the use of laser irradiation. Evaluate the effects of Er:YAG, Nd:YAG, and CO2 laser irradiation, associated or not to 2% sodium fluoride (2% NaF), on root caries prevention. One hundred and four human root dentin samples were divided in eight groups (n = 13). A 9-mm2-area on each dentin sample was delimited and treated as follows: G1: no treatment (control); G2: 2% NaF; G3: Er:YAG; G4: 2% NaF + Er:YAG; G5: Nd:YAG; G6: 2% NaF + Nd:YAG; G7: CO2; G8: 2% NaF + CO2. When used, the 2% NaF was applied before irradiation for 4 min. The samples were subjected to a 2-week cariogenic challenge, consisted of daily immersion in de-remineralizing solutions for 6 h and 18 h, respectively. Knoop hardness (KHN) were evaluated (10 g and 20 s) at different depths from the dentin surface. The samples (n = 3) were prepared for scanning electron microscopy (SEM). Microhardness data were analysed by one-way analysis of variance (ANOVA) and Fisher's test (α = 5%). The Er:YAG laser group (KHN = 41.30) promoted an increase in acid resistance of the dentin (P < 0.05) when compared to all groups. There was no synergism between laser irradiation and 2% NaF application. Morphological changes were observed after irradiation with all lasers; carbonization and cracks were also observed, except when Er:YAG were used. Er:YAG laser irradiation can safely increase the acid resistance of the dentin surface of the root, since it promoted a significant increase in surface hardness. The application of 2% NaF did not result in a synergistic effect.

New method for the protection and restoration of calcareous cultural heritage stones by polyelectrolytes and hydroxyapatite nanocrystals

We have investigated the feasibility of a new two-step protocol for the restoration of marbles. The process employs a polyelectrolyte multilayer film that enhances the chemical affinity between the treated stone and restorative material (hydroxyapatite nanocrystals), through functionalization, while at the same time it attributes an acid resistant property to the resulting system. Surface functionalization and material deposition is achieved through spraying; a simple and versatile application method suitable for objects of various sizes and geometries. Polyelectrolyte (polyethylenimine and polyacrylic acid) deposition was examined through Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy (ATR-FTIR) and Atomic Force Microscopy (AFM), and tested through contact angle, water absorption and dissolution experiments. The hydroxyapatite nanocrystals were studied by ATR-FTIR, z-potential, AFM and Scanning Electron Microscopy (SEM), and characterized via contact angle and color alteration measurements. Our results show that the polyelectrolyte multilayer was stable in an aqueous environment with increased acid resistance (up to 46% decrease in mass weight loss when compared with untreated samples) and decreased water absorption (up to 39%). Color measurements of the outer hydroxyapatite layer showed a minimal color alteration for one type of the tested substrates showing low color difference values (ΔΕ* < 5). The results suggest that the proposed method holds great potential for marble restoration as it attributes multi-functionality and is easy to apply.

Effect of recycled aggregate and flyash on glass fiber reinforced concrete

The main purpose of this study was to evaluate fresh properties and mechanical characteristics of Glass fiber reinforced concrete (GR) containing Recycled aggregate and Fly Ash. It was utilized to replace Ordinary Portland Cement material at different percentages of 5, 10, 15, 20, and 25%. Glass fibers (6 mm length) have been incorporated in two different volume fractions of 0.5 and 1%. Experimental results proved that the addition of flyash in concrete mixes decreased compressive strength test results at early ages; on the other hand, strength increased at later ages with reference mixes. The replacement of flyash also showed decreased sorptivity, water absorption value, and increased acid resistance compared to control mixes. incorporation of glass fiber improved compressive strength test results of GR; however, fiber inclusion decreased fresh properties of GR mixes. Besides, Scanning Electronic Microscopic analysis studies of GR with optimum fiber content and flyash recommended development of C-S-H gel and cementitious compounds as an effect of reaction between flyash, recycled aggregate, and cement. experimental results showed that utilization of concrete prepared with flyash and recycled aggregate is more suitable for sustainable construction & green concrete block production industry beyond economic benefits.

Acid Resistance of Glass Ionomer Cement Restorative Materials.

In view of the need for aesthetics, restorations of teeth will typically be completed using tooth colored restorative materials. With the advent of biomimetic restorative materials, such as glass ionomer cements (GIC), much greater emphasis is now being placed on how well such materials can resist the challenge of acids that are present in foods and drinks, or gastric contents that are regurgitated. This laboratory study compared the dissolution and behavior of five GIC materials (GC Fuji® VII, GC Fuji® Bulk, GC Fuji® IX Fast, Fuji® IX Extra and GC Equia® Forte Fil) when exposed to three acids (citric acid, phosphoric acid and lactic acid), versus ultrapure deionized water, which was used as a control. Discs of each material GIC were submerged in solutions and percentage weight changes over time determined. Subsequently, the GIC materials were also placed as a part of standardized Class II sandwich restorations in bovine teeth (n = 20), and submerged in the solutions, and the extent of GIC dissolution and protection of the adjacent tooth was scored. Weight loss increased with time and with acid concentration. Overall, the most soluble material was GC Fuji® IX Extra, while GC Fuji® IX Fast and GC Fuji® Bulk were less soluble, and the least soluble material was GC Equia® Forte Fil. The most destructive solution for both the discs and for GIC restorations in teeth was 10% citric acid, while the least destructive acid was 0.1% lactic acid. The more recent GIC materials GC Fuji® Bulk and GC Equia® Forte Fil showed increased acid resistance over the older GIC materials, and this further justifies their use in open sandwich Class II restorations in more hostile environments.

Mechanical properties of alkali-activated mortar in organic acid environment

Ingression of acid into the concrete results in early degradation by microstructural alteration of phases leading to mass changes, weakening of mechanical properties and increase in porosity due to calcium leaching. This paper discusses the resistance of geopolymer composites (GP) and conventional concrete system (OPC) in 0.125M and 0.25M concentrations of acetic acid medium by investigating the changes in the mechanical properties of mortar. The results of the study reveal that the GP samples display increased resistance to acetic acid attack not only in terms of mass and strength loss but also with reference to the variation in ultrasonic pulse velocity and relative dynamic modulus of elasticity. The results also manifest that blends of ground granulated blast furnace slag (GGBS) and fly ash (class F) (FA) with red mud (RM) offer increased acid resistance due to the nature of the main binder gel produced in GP systems.

Degradation kinetics of alkali-activated pastes in acetic acid

Growing urban and industrial activities globally are found to be the sources of rising acidic environment. These acidic environments ensue early degradation of concrete in terms of microstructural alteration of phases formulating to mass changes, weakening of mechanical properties, and increase in porosity due to calcium leaching. This paper probes into the acetic acid resistance of geopolymer composites (GP) and its comparison with conventional concrete system (OPC) in 0.125M and 0.25M concentrations of acetic acid medium. The GP samples displayed increased resistance to acetic acid attack in terms of mass and thickness loss. It was also found that blends of ground granulated blast furnace slag (GGBS) and fly ash (class F) (FA) with red mud (RM) offered increased acid resistance due to the nature of the main binder gel produced in GP systems.

Degradation kinetics of alkali-activated mortar in aggressive citric acid environment

Acid attack is a complex phenomenon arising in construction industries worldwide as it is responsible for the deterioration of concrete in acidic environments resulting in premature degradation with regard to mass changes, weakening of mechanical properties, and increase in porosity due to calcium leaching. This paper investigates the citric acid resistance of geopolymer composites (GP) and its comparison with conventional concrete system (OPC) in lower and higher concentrations of acid medium. The GP samples displayed increased resistance to citric acid attack than OPC system in terms of mass and strength loss. It was also found that geopolymer mortar made with a blend of ground granulated blast furnace slag (GGBS) and red mud (RM) offered increased acid resistance based on the parameters studied in the degradation kinetics

An Overview of Pumice Stone as a Cementitious Material – the Best Manual for Civil Engineer

Pumice stone is a natural sponge-like lightweight aggregate formed during the rapid cooling and solidification of molten lava. After suitable preparation, it can be used as an aggregate to produce lightweight concrete or as a cementitious material to produce blended cement or geopolymer. This article focused on the influence of pumice powder (PP) on fresh properties and hardened properties of conventional cementitious materials and geopolymers. Additionally, different modification methods carried out to modify some properties of conventional cementitious materials containing PP have been included. This review showed that the incorporation of PP in the traditional cement matrix has some benefits such as increasing thermal and acoustic insulation, increasing fire resistance, increasing abrasion resistance, decreasing unit weight, decreasing hydration heat, decreasing drying shrinkage, decreasing autoclave expansion, increasing sulfate resistance, increasing seawater resistance, increasing acid resistance, increasing electrical resistivity, decreasing alkali silica reaction (ASR) expansion, decreasing porosity, water absorption and permeability. On the other hand, it has a negative effect on workability, mechanical strength and increasing carbonation rate. This review also confirmed that PP has a promising future in the field of alkali-activated and geopolymer materials.

Amino acids other than glutamate affect the expression of the GAD system in Listeria monocytogenes enhancing acid resistance

The Glutamate Decarboxylase (GAD) system is important for survival of L. monocytogenes and other microorganisms under acidic conditions. Environmental conditions influence the function of the GAD system. Until now, the only conditions known to lead to increased transcription of the GAD system are the stationary phase in rich media and anoxic conditions. Previously, we showed that transcription of the GAD system requires unidentified compounds other than glutamate present in rich media. Following a test looking at various compounds we identified for first time that peptone, tryptone and casamino acids activate the GAD system under oxic conditions suggesting that amino acid(s) other than glutamate and/or peptides are important for the above process. The defined medium, where the GAD system is inactive, once it is supplemented with the above compounds results in an active intracellular and extracellular GAD system and increased acid resistance. Through functional genomics we show that these compounds are required for GadD2 activity and although we previously showed that GadD3 is active part of the intracellular GAD system, the supplementation did not activate this gene. The above is explained by the fact that only gadD2 transcription was upregulated by these compounds while the transcription of gadD1 and gadD3 remained unaffected. Together our results show that the L. monocytogenes GadD2 decarboxylase is activated in the presence of amino acids or peptides other than glutamate, a finding that has important implications for acid tolerance and food safety.

Engineering viable foot-and-mouth disease viruses with increased acid stability facilitate the development of improved vaccines

Foot-and-mouth disease virus (FMDV), the most acid-unstable virus among picornaviruses, tends to disassemble into pentamers at pH values slightly below neutrality. However, the structural integrity of intact virion is one of the most important factors that influence the induction of a protective antibody response. Thus, improving the acid stability of FMDV is required for the efficacy of vaccine preparations. According to the previous studies, a single substitution or double amino acid substitutions (VP1 N17D, VP2 H145Y, VP2 D86H, VP3 H142D, VP3 H142G, and VP1 N17D + VP2 H145Y) in the capsid were introduced into the full-length infectious clone of type O FMDV vaccine strain O/HN/CHN/93 to develop seed FMDV with improved acid stability. After the transfection into BSR/T7 cells of constructed plasmids, substitution VP1 N17D or VP2 D86H resulted in viable and genetically stable FMDVs, respectively. However, substitution VP2 H145Y or VP1 N17D + VP2 H145Y showed reverse mutation and additional mutations, and substitution VP3 H141G or VP3 H141D prevented viral viability. We found that substitution VP1 N17D or VP2 D86H could confer increased acid resistance, alkali stability, and thermostability on FMDV O/HN/CHN/93, whereas substitution VP1 N17D was observed to lead to a decreased replication ability in BHK-21 cells and mildly impaired virulence in suckling mice. In contrast, substitution VP2 D86H had no negative effect on viral infectivity. These results indicated that the mutant rD86H carrying substitution VP2 D86H firstly reported by us could be more adequate for the development of inactivated FMD vaccines with enhanced acid stability.

A new emerging serotype of Vibrio parahaemolyticus in China is rapidly becoming the main epidemic strain

ObjectivesDuring surveillance, we found a new type of Vibrio parahaemolyticus named ‘O4:KUT-recAin’ and studied the phenotypic, pathogenic and epidemiological characteristics of O4:KUT-recAin. MethodsV. parahaemolyticus were isolated from acute diarrhoeal patients in coastal hospitals of China. Serum agglutination test, specific PCR assay, growth curves under different conditions and rabbit diarrhoeal models were using to characterize O4:KUT-recAin. ResultsThe O4:KUT-recAin strain has a new type of K antigen and a 25 043-bp-large fragment encoding 20 proteins inserted in the housekeeping gene recA. Retrospective analysis found that only one O4:KUT-recAin strain was detected in 563 V. parahaemolyticus strains in 2014; then the proportion increased rapidly and reached 17.8% (105/590) in 2016 and 31.1% (224/721) in 2017, making O4:KUT-recAin the second dominant serotype following O3:K6. O4:KUT-recAin strains (100%, 14/14) exhibited increased acid resistance and could reproduce in medium at pH 4.9, while 92.9% (13/14) of the O3:K6 strains could not grow at this pH value. O4:KUT-recAin could cause diarrhoea and small intestinal tissue lesions in infant rabbits, but its diarrhoeal (93.1%, 27/29) and mortality (78.6%, 22/28) rates were slightly lower than those of O3:K6 (100% 16/16, 100% 16/16). Based on diarrhoea patients, there were no significant differences in the two groups for most clinical symptoms and laboratory results, except media age, haemoglobin and the number of red blood cells in stool samples. ConclusionsO4:KUT-recAin had enhanced acid resistance, was capable of causing infectious diarrhoea in both rabbits and humans, and has become widespread during a short period of time in China.

Highly effective immobilization of Pb and Cd in severely contaminated soils by environment-compatible, mercapto-functionalized reactive nanosilica

Soils contaminated with Pb and Cd greatly threaten the health of humans. With a view to decrease the environmental risk of Pb and Cd in the soil, we design and prepare a type of immobilization material possessing high stability and high immobilization efficiency towards Pb and Cd. Nanosilica which has good compatibility with soils is chosen as the matrix and functional groups (mercapto) are loaded on the nanosilica surface via the covalently bonding between 3-mercaptopropyl-trimethoxysilane (denoted as MPTS) and nanosilica. The as-prepared MPTS/nano-silica is characterized, and its immobilization efficiency towards Pb and Cd in contaminated soil as well as the stability of the immobilized Pb and Cd under acidic condition is evaluated. Results demonstrate that the as-prepared nanosilica has spherical or spheroidal shape and exhibits a diameter of 20–30 nm. In the meantime, MPTS/nano-silica selectively reacts with Pb and Cd to reduce the content of bioavailable-Pb and bioavailable-Cd from 1193.54 mg/kg and 12.46 mg/kg to 10.34 mg/kg and 0.22 mg/kg, respectively, providing an immobilization rate of 99.12% and 98.23% for Pb and Cd. The results of chemical species analysis of Pb/Cd indicate that the nanosilica can transform most Pb/Cd from unstable species into more stable species. More importantly, MPTS/nano-silica exhibits low impact on soil and the Pb- and Cd-species immobilized by MPTS/nano-silica exhibit greatly increased acid resistance, which could be significant for the long-term remediation of the heavy-metal-contaminated soils.

Immunogenicity and protective efficacy of a novel foot-and-mouth disease virus empty-capsid-like particle with improved acid stability

Foot-and-mouth disease virus (FMDV) is the etiological agent of a highly contagious disease that affects cloven-hoofed animal species. The FMDV capsid is highly acid labile and viral particles lose their immunogenicity when they disassemble at mildly acidic pHs. The viral capsid of FMDV serotype O is more sensitive than those of other serotypes, making it more difficult to acquire enough empty-capsid-like particles in the acidic insect cell environment for research. In this study, novel FMDV mutants with increased acid resistance were isolated using BHK-21 cell cultured under low-pH conditions. Amino acid substitutions Q25R, K41E, and N85A in the VP1 capsid protein and K154Q in the VP3 capsid protein were detected in all six mutants. Based on these amino acid replacements, empty-capsid-like particles of FMDV serotype O, which were resistant to the acid-induced dissociation of the capsid into pentameric subunits, were produced in insect cells. We characterized the protective immunity induced by these acid-resistant empty capsid particles. Significant humoral and cellular immune responses were elicited in mice after immunization with the acid-resistant empty capsid particles. The acid-resistant empty-capsid-like particles also induced strong neutralizing antibodies in guinea pigs and protected all the guinea pigs from FMDV challenge. Our results suggest that these acid-resistant empty-capsid-like particles have potential utility as a vaccine against serotype O FMDV infection.