Effects of commercial enzymes on the adhesion of a marine biofilm-forming bacterium

Microbial enzymes as powerful natural anti-biofilm candidates

Bacterial biofilms pose significant challenges, from healthcare-associated infections to biofouling in industrial systems, resulting in significant health impacts and financial losses globally. Classic antimicrobial methods often fail to eradicate sessile microbial communities within biofilms, requiring innovative approaches. This review explores the structure, formation, and role of biofilms, highlighting the critical importance of exopolysaccharides in biofilm stability and resistance mechanisms. We emphasize the potential of microbial enzymatic approaches, particularly focusing on glycosidases, proteases, and deoxyribonucleases, which can disrupt biofilm matrices effectively. We also delve into the importance of enzymes such as cellobiose dehydrogenase, which disrupts biofilms by degrading polysaccharides. This enzyme is mainly sourced from Aspergillus niger and Sclerotium rolfsii, with optimized production strategies enhancing its efficacy. Additionally, we explore levan hydrolase, alginate lyase, α-amylase, protease, and lysostaphin as potent antibiofilm agents, discussing their microbial origins and production optimization strategies. These enzymes offer promising avenues for combating biofilm-related challenges in healthcare, environmental, and industrial settings. Ultimately, enzymatic strategies present environmentally friendly solutions with high potential for biofilm management and infection control.

Thermothelomyces thermophilus exo- and endo-glucanases as tools for pathogenic E. coli biofilm degradation

The escalating prevalence of drug-resistant pathogens not only jeopardizes the effectiveness of existing treatments but also increases the complexity and severity of infectious diseases. Escherichia coli is one the most common pathogens across all healthcare-associated infections. Enzymatic treatment of bacterial biofilms, targeting extracellular polymeric substances (EPS), can be used for EPS degradation and consequent increase in susceptibility of pathogenic bacteria to antibiotics. Here, we characterized three recombinant cellulases from Thermothelomyces thermophilus: a cellobiohydrolase I (TthCel7A), an endoglucanase (TthCel7B), and a cellobiohydrolase II (TthCel6A) as tools for hydrolysis of E. coli and Gluconacetobacter hansenii biofilms. Using a design mixture approach, we optimized the composition of cellulases, enhancing their synergistic activity to degrade the biofilms and significantly reducing the enzymatic dosage. In line with the crystalline and ordered structure of bacterial cellulose, the mixture of exo-glucanases (0.5 TthCel7A:0.5 TthCel6A) is effective in the hydrolysis of G. hansenii biofilm. Meanwhile, a mixture of exo- and endo-glucanases is required for the eradication of E. coli 042 and clinical E. coli biofilms with significantly different proportions of the enzymes (0.56 TthCel7B:0.44 TthCel6A and 0.6 TthCel7A:0.4 TthCel7B, respectively). X-ray diffraction pattern and crystallinity index of E. coli cellulose are comparable to those of carboxymethyl cellulose (CMC) substrate. Our results illustrate the complexity of E. coli biofilms and show that successful hydrolysis is achieved by a specific combination of cellulases, with consistent recurrence of TthCel7B endoglucanase.

Exploring fishery waste potential as antifouling component

Marine biofouling is a global issue with economic and ecological implications. Existing solutions, such as biocide-based antifouling paints, are toxic for the environment. The search for better antifouling agents remains crucial. Recent research focuses on eco-friendly antifouling paints containing natural compounds like enzymes. This study evaluates enzymatic extracts from fishery residues for antifouling potential. Extracts from Pleoticus muelleri shrimp, Illex argentinus squid, and Lithodes santolla king crab were analyzed. Proteolytic activity and thermal stability were assessed, followed by bioassays on mussel byssus thread formation and barnacle cypris adhesive footprints. All three extracts demonstrated proteolytic activity and 24-h stability at temperate oceanic temperatures, except I. argentinus. P. muelleri extracts hindered cyprid footprint formation and mussel byssus thread generation. Further purification is required for L. santolla extract to assess its antifouling potential activity. This study introduces the use of fishery waste-derived enzyme extracts as a novel antifouling agent, providing a sustainable tool to fight against biofouling formation.

Marine antifouling properties of enzyme modified polyaniline coated stainless steel surface

On solid surfaces immersed in a liquid medium, a biofilm layer which is called biofouling formed over time by organic molecules and microorganisms. It is important to produce new eco-friendly ideas can prevent this undesired phenome. In this study, we focused on the antifouling performance of polyaniline (PANI), whose anticorrosive properties have been already known. The main purpose of this study was to immobilize hydrolytic enzymes that could break down biomolecules and microorganisms and how this would contribute to the antifouling performance of the PANI coating. When α-amylase, DNAse, glucose oxidase, α-chymotrypsin, lipase and pectinase enzymes immobilized into PANI that was synthesized in ammonium oxalate (PANIAO) and sodium salicylate (PANISS) electrolytes, α-amylase containing film (PANISS-A) showed the highest performance (76.5% antifouling activity). The surface properties after keeping in the Mediterranean Sea for 12 days were compared by digital photography, Scanning Electron microscope (SEM) and fluorescence microscope images, also with Energy Dispersive X-Ray (EDX) analysis and crystal violet staining. Carbohydrate and protein amounts and CFU (Colony Forming Units) values of biofilms formed on the surface for bare, PANISS and PANISS-A coupons after keeping 12 days in the Mediterranean Sea were determined. Vibrio species (V.harveyi, V.alginolyticus, V.parahaemolyticus) were detected in the biofilms by Matrix- Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) analysis.

Wirelessly Powered Drug-Free and Anti-Infective Smart Bandage for Chronic Wound Care

We present a wirelessly powered ultraviolet-C (UVC) radiation-based disinfecting bandage for sterilization and treatment in chronic wound care and management. The bandage contains embedded low-power UV light-emitting diodes (LEDs) in the 265 to 285 nm range with the light emission controlled via a microcontroller. An inductive coil is seamlessly concealed in the fabric bandage and coupled with a rectifier circuit to enable 6.78 MHz wireless power transfer (WPT). The maximum WPT efficiency of the coils is 83% in free space and 75% on the body at a coupling distance of 4.5 cm. Measurements show that the UVC LEDs are emitting radiant power of about 0.6 mW and 6.8 mW with and without fabric bandage, respectively, when wirelessly powered. The ability of the bandage to inactivate microorganisms was examined in a laboratory which shows that the system can effectively eradicate Gram-negative bacteria, Pseudoalteromonas sp. D41 strain, on surfaces in six hours. The proposed smart bandage system is low-cost, battery-free, flexible and can be easily mounted on the human body and, therefore, shows great promise for the treatment of persistent infections in chronic wound care.

Development and Control of Biofilms: Novel Strategies Using Natural Antimicrobials

Separation membranes have a wide application in the food industry, for instance, in the clarification/fractionation of milk, the concentration/separation of selected components, and wastewater treatment. They provide a large area for bacteria to attach and colonize. When a product comes into contact with a membrane, it initiates bacterial attachment/colonization and eventually forms biofilms. Several cleaning and sanitation protocols are currently utilized in the industry; however, the heavy fouling of the membrane over a prolonged duration affects the overall cleaning efficiency. In view of this, alternative approaches are being developed. Therefore, the objective of this review is to describe the novel strategies for controlling membrane biofilms such as enzyme-based cleaner, naturally produced antimicrobials of microbial origin, and preventing biofilm development using quorum interruption. Additionally, it aims to report the constitutive microflora of the membrane and the development of the predominance of resistant strains over prolonged usage. The emergence of predominance could be associated with several factors, of which, the release of antimicrobial peptides by selective strains is a prominent factor. Therefore, naturally produced antimicrobials of microbial origin could thus provide a promising approach to control biofilms. Such an intervention strategy could be implemented by developing a bio-sanitizer exhibiting antimicrobial activity against resistant biofilms.

Spray-Drying Hydrophobic Cellulose Nanocrystal Coatings with Degradable Biocide Release for Marine Antifouling

With increasing awareness about the ecological environment, increased attention has been paid to the application of eco-friendly materials in the field of marine antifouling. In this work, a novel coating having good mechanical strength and static marine antifouling characteristics was fabricated using cellulose nanocrystals (CNCs) as the skeleton material, with in situ growth of SiO₂ as the basic superhydrophobic material and introducing hexadecyl trimethyl ammonium bromide (CTAB) and 4-bromo2-(4-chlorophenyl)-5-(trifluoromethyl)-1H-pyrrole-3-carbonitrile (Econea) into the coating. Due to the high strength and rod structure of CNCs, the coating maintained super-hydrophobicity after 50 cycles of abrasion tests. Moreover, the addition of CTAB during the synthesis of SiO₂ led to the hydrolysis and polycondensation of tetraethyl orthosilicate at the micellar interface. Econea was fully mixed with SiO₂ nanoparticles, thus slowing down the rate of release of Econea. Meanwhile, the adhesion between the coating and the substrate reached 1.9 MPa, which can meet the application requirements for marine environments. The bioassay using bacteria (Escherichia coli) and diatoms (Nitzschia closterium) showed that the rate of inhibition of the coating on bacteria and diatoms could reach 99 and 90%, respectively, after immersion in artificial seawater for 28 days. This research provides a facile and promising fabricating solution of an eco-friendly CNC-based coating having strong antifouling characteristics suitable for marine environments.

Microbially-derived cocktail of carbohydrases as an anti-biofouling agents: a 'green approach'

Enzymes, also known as biocatalysts, display vital properties like high substrate specificity, an eco-friendly nature, low energy inputs, and cost-effectiveness. Among their numerous known applications, enzymes that can target biofilms or their components are increasingly being investigated for their anti-biofouling action, particularly in healthcare, food manufacturing units and environmental applications. Enzymes can target biofilms at different levels like during the attachment of microorganisms, formation of exopolymeric substances (EPS), and their disruption thereafter. In this regard, a consortium of carbohydrases that can target heterogeneous polysaccharides present in the EPS matrix may provide an effective alternative to conventional chemical anti-biofouling methods. Further, for complete annihilation of biofilms, enzymes can be used alone or in conjunction with other antimicrobial agents. Enzymes hold the promise to replace the conventional methods with greener, more economical, and more efficient alternatives. The present article explores the potential and future perspectives of using carbohydrases as effective anti-biofilm agents.

Hurdle technology using encapsulated enzymes and essential oils to fight bacterial biofilms

Biofilm formation on abiotic surfaces has become a major public health concern because of the serious problems they can cause in various fields. Biofilm cells are extremely resistant to stressful conditions, because of their complex structure impedes antimicrobial penetration to deep-seated cells. The increased resistance of biofilm to currently applied control strategies underscores the urgent need for new alternative and/or supplemental eradication approaches. The combination of two or more methods, known as Hurdle technology, offers an excellent option for the highly effective control of biofilms. In this perspective, the use of functional enzymes combined with biosourced antimicrobial such as essential oil (EO) is a promising alternative anti-biofilm approach. However, these natural antibiofilm agents can be damaged by severe environmental conditions and lose their activity. The microencapsulation of enzymes and EOs is a promising new technology for enhancing their stability and improving their biological activity. This review article highlights the problems related to biofilm in various fields, and the use of encapsulated enzymes with essential oils as antibiofilm agents. KEY POINTS: • Problems associated with biofilms in the food and medical sectors and their subsequent risks on health and food quality. • Hurdle technology using enzymes and essential oils is a promising strategy for an efficient biofilms control. • The microencapsulation of enzymes and essential oils ensures their stability and improves their biological activities.

Impact of different enzymes on biofilm formation and mussel settlement

Enzymes have been known to impact the biofilm forming capacity. However, how the enzymes mediate the biofilm formation and macrofouling remains little known. Here, we investigated the effects of the three kinds of proteases, four kinds of glycosidases and one kind of lipase on the detachment of biofilms of Shewanella marisflavi ECSMB14101, identified biofilm total proteins response to enzyme treatments, and then tested the effects of biofilms treated with enzymes on the settlement of the mussel Mytilus coruscus plantigrades. The results showed that the cell density of bacteria in biofilms formed at different initial bacterial density were noticeably reduced after treating with all tested enzymes, and Neutrase and α-Amylase exhibited best removing efficiency of > 90%. Bacterial total proteins in S. marisflavi biofilm noticeably reduced or disappeared after treated by Alcalase. For the settlements of the mussel M. coruscus plantigrades, inducing capacities of S. marisflavi biofilm were noticeably suppressed and downregulation was > 75% at the initial density of 5 × 10⁶ cells/cm². Thus, the tested enzymes could effectively remove the adhered bacterial cell, inhibit the biofilm formation and finally suppress the mussel settlement. Our findings extend novel knowledge to developing eco-friendly approach to control micro- and macro-fouling.

Destruction of Staphylococcus aureus biofilms by combining an antibiotic with subtilisin A or calcium gluconate

In S. aureus biofilms, bacteria are embedded in a matrix of extracellular polymeric substances (EPS) and are highly tolerant to antimicrobial drugs. We thus sought to identify non-antibiotic substances with broad-spectrum activity able to destroy the EPS matrix and enhance the effect of antibiotics on embedded biofilm bacteria. Among eight substances tested, subtilisin A (0.01 U/mL) and calcium gluconate (CaG, Ca²⁺ 1.25 mmol/L) significantly reduced the biomass of biofilms formed by at least 21/24 S. aureus isolates. Confocal laser scanning microscopy confirmed that they both eliminated nearly all the proteins and PNAG from the matrix. By contrast, antibiotics alone had nearly no effect on biofilm biomass and the selected one (oxytetracycline-OTC) could only slightly reduce biofilm bacteria. The combination of OTC with CaG or subtilisin A led to an additive reduction (average of 2 log₁₀ CFU/mL) of embedded biofilm bacteria on the isolates susceptible to OTC (MBC < 10 μg/mL, 11/24). Moreover, these two combinations led to a reduction of the embedded biofilm bacteria higher than 3 log₁₀ CFU/mL for 20–25% of the isolates. Further studies are now required to better understand the factors that cause the biofilm produced by specific isolates (20–25%) to be susceptible to the combinations.

Antibiofilm Activity of α-Amylase from Bacillus subtilis and Prediction of the Optimized Conditions for Biofilm Removal by Response Surface Methodology (RSM) and Artificial Neural Network (ANN)

α-amylase is known to have antibiofilm activity against biofilms of both Gram positive and Gram-negative bacterial strains. Partially purified α-amylase from Bacillus subtilis was found to have inhibit biofilm formed by P. aeruginosa and S. aureus. The spectrophotometric and microscopic studies revealed that the antibiofilm efficacy of the working strain is greater than commercially purchased α-amylase. Response surface methodology (RSM) and artificial neural network (ANN) help to predict the optimum conditions [pH 8, treatment time 6 h and enzyme concentration (200 µg/mL)] for maximum biofilm eradication. This was confirmed by several in vitro experiments. Molecular docking interactions of α-amylase with the extracellular polymeric substances (EPS) of both P. aeruginosa and S. aureus indicate towards the existence of an efficient energy driven spontaneous process. Thus, this study highlights a combination of experimental and computational approach showing the naturally extracted α-amylase from B. subtilis having the potency of removing the biofilms of harmful bacterial strains involved in causing various nosocomial infections.

Co-delivery of antibiotic and baicalein by using different polymeric nanoparticle cargos with enhanced synergistic antibacterial activity

To evaluate the effect of polymer structures on their unique characteristics and antibacterial activity, this study focused on developing amphiphilic copolymers by using three different molecules through RAFT polymerization. Three amphiphilic copolymers, namely, PBMA-b-(PDMAEMA-r-PPEGMA) (BbDrE), (PBMA-r-PDMAEMA)-b-PPEGMA (BrDbE), and PBMA-r-PDMAEMA-r-PPEGMA (BrDrE), are successfully self-assembled into spherical or oval shaped nanoparticles in aqueous solution and remain stable in PBS, LB, and 10% FBS solutions for at least 3 days. The critical micelle concentrations are 0.012, 0.025, and 0.041 mg/mL for BbDrE, BrDbE, and BrDrE, respectively. The zeta potential values under pH 5.5 and pH 7.4 conditions are 3.18/0.19, 8.57/0.046, and 2.54/-0.69 mV for BbDrE, BrDbE, and BrDrE nanoparticles, respectively. The three copolymers with similar monomer compositions show similar molecular weight and thermostability. Baicalein (BA) and ciprofloxacin (CPX) are encapsulated into the three nanoparticles to obtain BbDrE@BA/CPX, BrDbE@BA/CPX, and BrDrE@BA/CPX nanocomposites, with LC values of 63.9/78.3, 63.9/74.7, and 55.3/64.8, respectively. The two drugs are released from the three drug-loaded nanocomposites with 60%-95% release in pH 5.5 over 24 h and 15%-30% release in pH 7.4. The drug-loaded nanocomposites show synergistic antibacterial activity than the naked drug (2-8 fold reduction for CPX) or single drug-loaded nanocomposites (4-8 fold reduction for CPX) against Pseudomonas aeruginosa and Staphylococcus aureus. The drug-loaded nanocomposites inhibit the formation of bacterial biofilms above their MIC values and eliminate bacterial biofilms observed by fluorescent microscope. Finally, the nanocomposites improve the healing of infection induced by P. aeruginosa and S. aureus on rat dermal wounds. These results indicate that antimicrobial agents with different structures could be an alternative treatment strategy for bacteria-induced infection.

Deciphering Streptococcal Biofilms

Streptococci are a diverse group of bacteria, which are mostly commensals but also cause a considerable proportion of life-threatening infections. They colonize many different host niches such as the oral cavity, the respiratory, gastrointestinal, and urogenital tract. While these host compartments impose different environmental conditions, many streptococci form biofilms on mucosal membranes facilitating their prolonged survival. In response to environmental conditions or stimuli, bacteria experience profound physiologic and metabolic changes during biofilm formation. While investigating bacterial cells under planktonic and biofilm conditions, various genes have been identified that are important for the initial step of biofilm formation. Expression patterns of these genes during the transition from planktonic to biofilm growth suggest a highly regulated and complex process. Biofilms as a bacterial survival strategy allow evasion of host immunity and protection against antibiotic therapy. However, the exact mechanisms by which biofilm-associated bacteria cause disease are poorly understood. Therefore, advanced molecular techniques are employed to identify gene(s) or protein(s) as targets for the development of antibiofilm therapeutic approaches. We review our current understanding of biofilm formation in different streptococci and how biofilm production may alter virulence-associated characteristics of these species. In addition, we have summarized the role of surface proteins especially pili proteins in biofilm formation. This review will provide an overview of strategies which may be exploited for developing novel approaches against biofilm-related streptococcal infections.

Non-antibiotic antimicrobial agents to combat biofilm-forming bacteria

Biofilms can be produced by multiple species or by a single strain of bacteria. The biofilm state enhances the resistance of the resident microorganisms to antimicrobial agents by producing extracellular polymeric substances. Typically, antibiotics are used to stop the growth of bacteria, but emerging resistance has limited their effectiveness. Bacteria in biofilms are less susceptible to antibiotics compared with their free-floating state, as biofilms impair antibiotic penetration. To obviate this challenge, non-antibiotic antimicrobial agents are needed. This review describes two classes of these agents, namely antimicrobial nanoparticles and antimicrobial peptides. Applications of these antimicrobials in the food industry and medical applications are discussed, and the directions for future research are highlighted.

Enhanced Clearing of Wound-Related Pathogenic Bacterial Biofilms Using Protease-Functionalized Antibiotic Nanocarriers

Biofilms are prevalent in chronic wounds and once formed are very hard to remove, which is associated with poor outcomes and high mortality rates. Biofilms are comprised of surface-attached bacteria embedded in an extracellular polymeric substance (EPS) matrix, which confers increased antibiotic resistance and host immune evasion. Therefore, disruption of this matrix is essential to tackle the biofilm-embedded bacteria. Here, we propose a novel nanotechnology to do this, based on protease-functionalized nanogel carriers of antibiotics. Such active antibiotic nanocarriers, surface coated with the protease Alcalase 2.4 L FG, "digest" their way through the biofilm EPS matrix, reach the buried bacteria, and deliver a high dose of antibiotic directly on their cell walls, which overwhelms their defenses. We demonstrated their effectiveness against six wound biofilm-forming bacteria, Staphylococcus aureus, Pseudomonas aeruginosa, Staphylococcus epidermidis, Klebsiella pneumoniae, Escherichia coli, and Enterococcus faecalis. We confirmed a 6-fold decrease in the biofilm mass and a substantial reduction in bacterial cell density using fluorescence, atomic force, and scanning electron microscopy. Additionally, we showed that co-treatments of ciprofloxacin and Alcalase-coated Carbopol nanogels led to a 3-log reduction in viable biofilm-forming cells when compared to ciprofloxacin treatments alone. Encapsulating an equivalent concentration of ciprofloxacin into the Alcalase-coated nanogel particles boosted their antibacterial effect much further, reducing the bacterial cell viability to below detectable amounts after 6 h of treatment. The Alcalase-coated nanogel particles were noncytotoxic to human adult keratinocyte cells (HaCaT), inducing a very low apoptotic response in these cells. Overall, we demonstrated that the Alcalase-coated nanogels loaded with a cationic antibiotic elicit very strong biofilm-clearing effects against wound-associated biofilm-forming pathogenic bacteria. This nanotechnology approach has the potential to become a very powerful treatment of chronically infected wounds with biofilm-forming bacteria.

Enzymatic Inactivation of Pathogenic and Nonpathogenic Bacteria in Biofilms in Combination with Chlorine

This study investigated the effects of enzyme application on biofilms of bacterial isolates from a cafeteria kitchen and foodborne pathogens and the susceptibility of Salmonella biofilms to proteinase K combined with chlorine treatment. For four isolates from a cafeteria kitchen ( Acinetobacter, Enterobacter, and Kocuria) and six strains of foodborne pathogens ( Salmonella enterica, Staphylococcus aureus, and Vibrio parahaemolyticus), the inhibitory effect of enzymes on biofilm formation at 25°C for 24 h or the degradative efficacy of enzymes on 24-h mature biofilm at 37°C for 1 h in tryptic soy broth (TSB) was examined in a polystyrene microtiter plate. The effect of enzymes was also evaluated on a subset of these strains in 20 times diluted TSB (1/20 TSB) at 25°C. The working concentrations of five enzymes were 1 U/100 μL for α-amylase, amyloglucosidase, cellulase, and DNase and 1 milli-Anson unit/100 μL for proteinase K. In addition, 24-h mature Salmonella Typhimurium biofilm on a stainless steel coupon was treated with proteinase K for 1 h at 25°C followed by 20 ppm of chlorine for 1 min at 25°C. The results showed that certain enzymes inhibited biofilm formation by the kitchen-originated bacteria; however, the enzymatic effect was diminished on the mature biofilms. Biofilm formation of V. parahaemolyticus was suppressed by all tested enzymes, whereas the mature biofilm was degraded by α-amylase, DNase I, and proteinase K. Proteinase K was effective in controlling Salmonella biofilms, whereas a strain-dependent variation was observed in S. aureus biofilms. In 1/20 TSB, Enterobacter cancerogenus and Kocuria varians were more susceptible to certain enzymes during biofilm formation than those in TSB, whereas the enzymatic effect was much decreased on 24-h mature biofilms, regardless of nutrient conditions. Furthermore, synergistic inactivation of Salmonella Typhimurium in biofilms was observed in the combined treatment of proteinase K followed by chlorine. Live/Dead assays also revealed a decrease in density and loss of membrane integrity in Salmonella Typhimurium biofilms exposed to the combined treatment. Therefore, certain enzymes can control biofilms of isolates residing in a cafeteria kitchen and foodborne pathogens. This study demonstrates the potential of enzymes for the sanitation of food processing environments and of proteinase K combined with chlorine to control Salmonella biofilms on food contact surfaces.

Actinobacteria-a promising natural source of anti-biofilm agents

A biofilm is a community of microorganisms attached to a surface and embedded in a matrix of extracellular polymeric substances. Biofilms confer resistance towards conventional antibiotic treatments; thus, there is an urgent need for newer and more effective antimicrobial agents that can act against these biofilms. Due to this situation, various studies have been done to investigate the anti-biofilm effects of natural products including bioactive compounds extracted from microorganisms such as Actinobacteria. This review provides an insight into the anti-biofilm potential of Actinobacteria against various pathogenic bacteria, which hopefully provides useful information, guidance, and improvements for future antimicrobial studies. Nevertheless, further research on the anti-biofilm mechanisms and compound modifications to produce more potent anti-biofilm effects are required.

Matrix metalloprotease-1 inhibits and disrupts Enterococcus faecalis biofilms

Enterococcus faecalis is a major opportunistic pathogen that readily forms protective biofilms leading to chronic infections. Biofilms protect bacteria from detergent solutions, antimicrobial agents, environmental stress, and effectively make bacteria 10 to 1000-fold more resistant to antibiotic treatment. Extracellular proteins and polysaccharides are primary components of biofilms and play a key role in cell survival, microbial persistence, cellular interaction, and maturation of E. faecalis biofilms. Degradation of biofilm components by mammalian proteases is an effective antibiofilm strategy because proteases are known to degrade bacterial proteins leading to bacterial cell lysis and growth inhibition. Here, we show that human matrix metalloprotease-1 inhibits and disrupts E. faecalis biofilms. MMPs are cell-secreted zinc- and calcium-dependent proteases that degrade and regulate various structural components of the extracellular matrix. Human MMP1 is known to degrade type-1 collagen and can also cleave a wide range of substrates. We found that recombinant human MMP1 significantly inhibited and disrupted biofilms of vancomycin sensitive and vancomycin resistant E. faecalis strains. The mechanism of antibiofilm activity is speculated to be linked with bacterial growth inhibition and degradation of biofilm matrix proteins by MMP1. These findings suggest that human MMP1 can potentially be used as a potent antibiofilm agent against E. faecalis biofilms.

α-Chymotrypsin Immobilized on a Low-Density Polyethylene Surface Successfully Weakens Escherichia coli Biofilm Formation

The protease α-chymotrypsin (α-CT) was covalently immobilized on a low-density polyethylene (LDPE) surface, providing a new non-leaching material (LDPE-α-CT) able to preserve surfaces from biofilm growth over a long working timescale. The immobilized enzyme showed a transesterification activity of 1.24 nmol/h, confirming that the immobilization protocol did not negatively affect α-CT activity. Plate count viability assays, as well as confocal laser scanner microscopy (CLSM) analysis, showed that LDPE-α-CT significantly impacts Escherichia coli biofilm formation by (i) reducing the number of adhered cells (-70.7 ± 5.0%); (ii) significantly affecting biofilm thickness (-81.8 ± 16.7%), roughness (-13.8 ± 2.8%), substratum coverage (-63.1 ± 1.8%), and surface to bio-volume ratio (+7.1 ± 0.2-fold); and (iii) decreasing the matrix polysaccharide bio-volume (80.2 ± 23.2%). Additionally, CLSM images showed a destabilized biofilm with many cells dispersing from it. Notably, biofilm stained for live and dead cells confirmed that the reduction in the biomass was achieved by a mechanism that did not affect bacterial viability, reducing the chances for the evolution of resistant strains.

Enzyme treatment improves the performance of laboratory-scale vertical flow constructed wetland

An enzyme treatment was developed and evaluated for its effectiveness in alleviating bioclogging through a laboratory-scale vertical-flow constructed wetland (VFCW) experiment in this study. The enzyme preparation was a combination of α-glucoamylase and β-glucanase. The results show that the enzyme treatment greatly reduced bioclogging, and the peak hydraulic conductivity after treatment increased by a factor of 16, mainly because polysaccharides in the clogging matter were decomposed and the gelatinous clogging matter was dissolved and dispersed. The results also show that the abundance of Proteobacteria microbes increased by 89.4% after the enzyme treatment, although the diversity of the microbial community within the substrate decreased slightly. These microbes can increase the capability of the constructed wetland to purify influent water, and thus the rate of reduction of COD improved. It offers a solution to the problem of bioclogging in constructed wetlands.

Thermostable xylanase inhibits and disassembles Pseudomonas aeruginosa biofilms

Pseudomonas aeruginosa biofilms are problematic and play a critical role in the persistence of chronic infections because of their ability to tolerate antimicrobial agents. In this study, various cell-wall degrading enzymes were investigated for their ability to inhibit biofilm formation of two P. aeruginosa strains, PAO1 and PA14. Xylanase markedly inhibited and detached P. aeruginosa biofilms without affecting planktonic growth. Xylanase treatment broke down extracellular polymeric substances and decreased the viscosity of P. aeruginosa strains. However, xylanase treatment did not change the production of pyochelin, pyocyanin, pyoverdine, the Pseudomonas quinolone signal, or rhamnolipid. In addition, the anti-biofilm activity of xylanase was thermally stable for > 100 days at 45°C. Also, xylanase showed anti-biofilm activity against one methicillin-resistance Staphylococcus aureus and two Escherichia coli strains.

Therapeutic Potential of Biofilm-Dispersing Enzymes

Surface-attached colonies of bacteria known as biofilms play a major role in the pathogenesis of medical device infections. Biofilm colonies are notorious for their resistance to antibiotics and host defenses, which makes most device infections difficult or impossible to eradicate. Bacterial cells in a biofilm are held together by an extracellular polymeric matrix that is synthesized by the bacteria themselves. Enzymes that degrade biofilm matrix polymers have been shown to inhibit bio film formation, detach established bio film colonies, and render biofilm cells sensitive to killing by antimicrobial agents. This review discusses the potential use of biofilm matrix-degrading enzymes as anti-biofilm agents for the treatment and prevention of device infections. Two enzymes, deoxyribonuclease I and the glycoside hydrolase dispersin B, will be reviewed in detail. In vitro and in vivo studies demonstrating the anti-biofilm activities of these two enzymes will be summarized, and the therapeutic potential and possible drawbacks of using these enzymes as clinical agents will be discussed.

Iodine-infused aeration for hull fouling prevention: a vessel-scale study

Biofouling is a significant economic and ecological problem, causing reduced vessel performance and increases in fuel consumption and emissions. Previous research has shown iodine vapor (I₂)-infused aeration to be an environmentally friendly method for deterring the settlement of fouling organisms. An aeration system was deployed on a vessel with hull sections coated with two types of antifoulant coatings, Intersleek^® 1100 (fouling-release) and Interspeed^® BRA-640 (ablative copper biocide), as well as an inert epoxy barrier coating, to assess the effectiveness of aeration in conjunction with common marine coatings. I₂-infused aeration resulted in consistent reductions of 80-90% in hard fouling across all three coatings. Additionally, aeration reduced the soft fouling rate by 45-70% when used in conjunction with both Intersleek^® and Interspeed^® BRA versus those coatings alone. The results of this study highlight the contribution of I₂-infused aeration as a standalone mechanism for fouling prevention or as a complement to traditional antifouling coatings.

Antibiofilm agents: A new perspective for antimicrobial strategy

Biofilms are complex microbial architectures that attach to surfaces and encase microorganisms in a matrix composed of self-produced hydrated extracellular polymeric substances (EPSs). In biofilms, microorganisms become much more resistant to antimicrobial treatments, harsh environmental conditions, and host immunity. Biofilm formation by microbial pathogens greatly enhances survival in hosts and causes chronic infections that result in persistent inflammation and tissue damages. Currently, it is believed over 80% of chronic infectious diseases are mediated by biofilms, and it is known that conventional antibiotic medications are inadequate at eradicating these biofilm-mediated infections. This situation demands new strategies for biofilm-associated infections, and currently, researchers focus on the development of antibiofilm agents that are specific to biofilms, but are nontoxic, because it is believed that this prevents the development of drug resistance. Here, we review the most promising antibiofilm agents undergoing intensive research and development.

Mini-Review: Antifouling Natural Products from Marine Microorganisms and Their Synthetic Analogs

Biofouling causes huge economic loss and generates serious ecological issues worldwide. Marine coatings incorporated with antifouling (AF) compounds are the most common practices to prevent biofouling. With a ban of organotins and an increase in the restrictions regarding the use of other AF alternatives, exploring effective and environmentally friendly AF compounds has become an urgent demand for marine coating industries. Marine microorganisms, which have the largest biodiversity, represent a rich and important source of bioactive compounds and have many medical and industrial applications. This review summarizes 89 natural products from marine microorganisms and 13 of their synthetic analogs with AF EC50 values ≤ 25 μg/mL from 1995 (the first report about marine microorganism-derived AF compounds) to April 2017. Some compounds with the EC50 values < 5 μg/mL and LC50/EC50 ratios > 50 are highlighted as potential AF compounds, and the preliminary analysis of structure-relationship (SAR) of these compounds is also discussed briefly. In the last part, current challenges and future research perspectives are proposed based on opinions from many previous reviews. To provide clear guidance for the readers, the AF compounds from microorganisms and their synthetic analogs in this review are categorized into ten types, including fatty acids, lactones, terpenes, steroids, benzenoids, phenyl ethers, polyketides, alkaloids, nucleosides and peptides. In addition to the major AF compounds which targets macro-foulers, this review also includes compounds with antibiofilm activity since micro-foulers also contribute significantly to the biofouling communities.

Exploiting extracellular polymeric substances (EPS) controlling strategies for performance enhancement of biological wastewater treatments: An overview

Extracellular polymeric substances (EPS) are present both outside of the cells and in the interior of microbial aggregates, and account for a main component in microbial aggregates. EPS can influence the properties and functions of microbial aggregates in biological wastewater treatment systems, and specifically EPS are involved in biofilm formation and stability, sludge behaviors as well as sequencing batch reactors (SBRs) granulation whereas they are also responsible for membrane fouling in membrane bioreactors (MBRs). EPS exhibit dual roles in biological wastewater treatments, and hence the control of available EPS can be expected to lead to changes in microbial aggregate properties, thereby improving system performance. In this review, current updated knowledge with regard to EPS basics including their formation mechanisms, important properties, key component functions as well as sub-fraction differentiation is given. EPS roles in biological wastewater treatments are also briefly summarized. Special emphasis is laid on EPS controlling strategies which would have the great potential in promoting microbial aggregates performance and in alleviating membrane fouling, including limitation strategies (inhibition of quorum sensing (QS) systems, regulation of environmental conditions, enzymatic degradation of key components, energy uncoupling etc.) and elevation strategies (enhancement of QS systems, addition of exogenous agents etc.). Those strategies have been confirmed to be feasible and promising to enhance system performance, and they would be a research niche that deserves further study.

In situ analysis of Bacillus licheniformis biofilms: amyloid-like polymers and eDNA are involved in the adherence and aggregation of the extracellular matrix

AIMS

This study attempts to determine which of the exopolymeric substances are involved in the adherence and aggregation of a Bacillus licheniformis biofilm.

METHODS AND RESULTS

The involvement of extracellular proteins and eDNA were particularly investigated using DNase and proteinase K treatment. The permeability of the biofilms increased fivefold after DNase I treatment. The quantification of the matrix components showed that, irrespective to the enzyme tested, eDNA and amyloid-like polymers were removed simultaneously. Size-exclusion chromatography analyses supported these observations and revealed the presence of associated nucleic acid and protein complexes in the biofilm lysates. These data suggest that some extracellular DNA and amyloid-like proteins were closely interlaced within the matrix. Finally, confocal laser scanning microscopy imaging gave supplementary clues about the 3D organization of the biofilms, confirming that eDNA and exoproteins were essentially layered under and around the bacterial cells, whereas the amyloid-like fractions were homogeneously distributed within the matrix.

CONCLUSION

These results confirm that some DNA-amyloid complexes play a key role in the modulation of the mechanical resistance of B. licheniformis biofilms.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study highlights the need to consider the whole structure of biofilms and to target the interactions between matrix components. A better understanding of B. licheniformis biofilm physiology and the structural organization of the matrix will strengthen strategies of biofilm control.

Targeting microbial biofilms using Ficin, a nonspecific plant protease

Biofilms, the communities of surface-attached bacteria embedded into extracellular matrix, are ubiquitous microbial consortia securing the effective resistance of constituent cells to environmental impacts and host immune responses. Biofilm-embedded bacteria are generally inaccessible for antimicrobials, therefore the disruption of biofilm matrix is the potent approach to eradicate microbial biofilms. We demonstrate here the destruction of Staphylococcus aureus and Staphylococcus epidermidis biofilms with Ficin, a nonspecific plant protease. The biofilm thickness decreased two-fold after 24 hours treatment with Ficin at 10 μg/ml and six-fold at 1000 μg/ml concentration. We confirmed the successful destruction of biofilm structures and the significant decrease of non-specific bacterial adhesion to the surfaces after Ficin treatment using confocal laser scanning and atomic force microscopy. Importantly, Ficin treatment enhanced the effects of antibiotics on biofilms-embedded cells via disruption of biofilm matrices. Pre-treatment with Ficin (1000 μg/ml) considerably reduced the concentrations of ciprofloxacin and bezalkonium chloride required to suppress the viable Staphylococci by 3 orders of magnitude. We also demonstrated that Ficin is not cytotoxic towards human breast adenocarcinoma cells (MCF7) and dog adipose derived stem cells. Overall, Ficin is a potent tool for staphylococcal biofilm treatment and fabrication of novel antimicrobial therapeutics for medical and veterinary applications.

Effect of deflocculation on the efficiency of sludge reduction by Fenton process

A novel approach to improve the efficiency of Fenton treatment for sludge reduction through the implication of a deflocculating agent citric acid, for the exclusion of extracellular polymeric substances (EPS) from waste-activated sludge (WAS), was investigated. Deflocculation was achieved with 0.06 g/g suspended solids (SS) of citric acid dosage. Fenton optimization studies using response surface methodology (RSM) revealed that 0.5 and 0.0055 g/g SS were the optimal dosages of H2O2 and Fe(2+). The addition of a cation-binding agent set the pH value of sludge to 5 which did not affect the Fenton efficiency. The results presented in this study shows the advantage of deflocculating the sludge as SS and volatile suspended solids (VSS) reductions were found to be higher in the deflocculated (53 and 63 %, respectively) than in the flocculated (22 and 34 %, respectively) sludges. Kinetic investigation of the treatment showed that the rate of the reaction was four times higher in the deflocculated sludge than control. The methodology reported in this manuscript was successfully applied to a real case were the deflocculated mediated Fenton process reduced the sludge disposal cost from 297.8 to 61.9 US dollars/ton of sludge.

Effects of surface-active block copolymers with oxyethylene and fluoroalkyl side chains on the antifouling performance of silicone-based films

Block copolymers made from a poly(dimethyl siloxane) (Si) and a poly(meth)acrylate carrying oxyethylene (EG) or fluoroalkyl (AF) side chains were synthesized and incorporated as surface-active components into a silicone matrix to produce cross-linked films with different surface hydrophilicity/phobicity. Near-edge X-ray absorption fine structure (NEXAFS) studies showed that film surfaces containing Si-EG were largely populated by the siloxane, with the oxyethylene chains present only to a minor extent. In contrast, the fluorinated block was selectively segregated to the polymer-air interface in films containing Si-AF as probed by NEXAFS and X-ray photoelectron spectroscopy (XPS) analyses. Such differences in surface composition were reflected in the biological performance of the coatings. While the films with Si-EG showed a higher removal of both Ulva linza sporelings and Balanus amphitrite juveniles than the silicone control, those with Si-AF exhibited excellent antifouling properties, preventing the settlement of cyprids of B. amphitrite.

Immobilized Hydrolytic Enzymes Exhibit Antibiofilm Activity Against Escherichia coli at Sub-Lethal Concentrations

The effects of two commercially available immobilized enzymes (namely the glycosidase pectinase and the protease subtilisin A) at sub-lethal concentrations were investigated in terms of their influence on biofilm genesis, on the composition of the biofilm matrix, and their antibiotic synergy against Escherichia coli biofilm, used as a model system of bacterial biofilms. The best antibiofilm performance of solid-supported hydrolases was obtained at the surface concentration of 0.022 and 0.095 U/cm(2) with a reduction of 1.2 and 2.3 log CFU/biofilm for pectinase and subtilisin, respectively. At these enzyme surface concentrations, the biocatalysts affected the structural composition of the biofilm matrix, impacting biofilm thickness. Finally, the immobilized hydrolases enhanced biofilm sensitivity to a clinically relevant concentration of the antibiotic ampicillin. At the final antibiotic concentration of 0.1 mg/ml, a reduction of 2 and 3.5 log10 units in presence of 0.022 Upectinase/cm(2) and 0.095 Usubtilisin/cm(2) was obtained, respectively, in comparison the antibiotic alone. Immobilized pectinase and subtilisin at sub-lethal concentrations demonstrated a great potential for antibiofilm applications.

The Control of Microbiological Problems∗∗Some excerpts taken from Bajpai P (2012). Biotechnology for Pulp and Paper Processing with kind permission from Springer Science1Business Media

Methods used to control microbiological problems are discussed. Good housekeeping and regular inspection of all areas, effective boilouts, and regularly scheduled washups reduce slime development. Conventional slime control methods generally employ combinations of biocides. Alternative control measures use enzymes, biodispersants, bacteriophages, competing organisms, and biological complex formers. Using enzymes for slime control is expected to bring important benefits to the pulp and paper industry. Enzymes represent a clean and sustainable technology: they are nontoxic, readily biodegradable, and are produced using renewable raw materials. Use of enzymes in combination with biodispersants appears to be a promising method for slime control.

A novel bioassay for evaluating the efficacy of biocides to inhibit settling and early establishment of marine biofilms

This paper presents a novel assay that allows a quick and robust assessment of the effects of biocides on the initial settling and establishment of marine photoautotrophic biofilms including the multitude of indigenous fouling organisms. Briefly, biofilms are established in the field, sampled, comminuted and re-settled on clean surfaces, after 72h chlorophyll a is measured as an integrating endpoint to reflect both settling and growth. Eight antifoulants were used to evaluate the assay. Efficacy ranking, based on EC98 values from most to least efficacious compound is: copper pyrithione>TPBP>DCOIT>tolylfluanid>zinc pyrithione>medetomidine>copper (Cu(2+)), while ecotoxicological ranking (based on EC10 values) is irgarol, copper pyrithione>zinc pyrithione>TPBP>tolylfluanid>DCOIT>copper (Cu(2+))>medetomidine. The algaecide irgarol did not cause full inhibition. Instead the inhibition leveled out at 95% effect at 30 nmoll(-)(1), a concentration that was clearly lower than for any other of the tested biocides.

The effects of the natural enzyme, Pectinex Ultra SP-L, on human cell cultures and bacterial biofilms in vitro

Background

Pectinex Ultra SP-L (Pectinex) is a microbial-derived enzyme that is used in the food industry and that has been shown to inhibit bacterial biofilms. It has been suggested that Pectinex may be useful in the management of biofilm-related bacterial infections and therefore warrants further investigation in this regard. The aim of this study was to investigate the cytotoxicity of Pectinex on cervical adenocarcinoma cells (HeLa), lymphocytes and neutrophils. Cell viability and morphology were assessed using an in vitro spectrophotometric MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide) assay and polarization-optical transmitted light differential interference contrast microscopy. This study also investigated the antibacterial and antibiofilm actions of Pectinex, alone and in combination with antibiotics, on standard and clinical cultures of Staphylococcus aureus and Pseudomonas aeruginosa. Minimum inhibitory (MIC) and bactericidal (MBC) concentrations were determined using p-iodo-nitrotetrazolium violet staining of bacterial cultures and regrowth of subcultures. Biofilm biomass and cell viability were quantified spectrophotometrically after staining with crystal violet and MTT.

Results

The IC₅₀ (±SEM) of Pectinex was 193.9 (±22.2) PGU/ml for HeLa cells, 383.4 (±81.5) and 629.6 (±62.8) PGU/ml for fMLP-stimulated and non-stimulated lymphocytes respectively, and 245.9 (±9.4) and 529.7 (±40.7) PGU/ml for fMLP-stimulated and non-stimulated neutrophils, respectively. Induced morphological features characteristic of apoptosis and necrosis included cell membrane blebs and vacuolization in HeLa cells, clumping in lymphocytes, as well as shrunken rounded cells, apoptotic bodies and debris in all cultures. Pectinex (7.42 – 950 PGU/ml⁻¹) was not bactericidal. In clinical cultures of Staphylococcus aureus, co-administration of Pectinex was associated with a 28.0% increase in both the MIC and MBC of amoxicillin-clavulanate. In clinical cultures of P. aeruginosa, there was an 89.0% and 92.8% increase in the MIC and MBC of ciprofloxacin, respectively. Pectinex ≤ 118.75 PGU/ml⁻¹ and incubation periods ≥ 6 h were associated with increased biomass and cell viability in S. aureus or P. aeruginosa biofilms.

Conclusions

Pectinex appeared to antagonize the antibacterial effects of amoxicillin-clavulanate and ciprofloxacin and furthermore demonstrated significant cytotoxicity. It was therefore deemed unsuitable for the management of either planktonic or biofilm phenotypes of S. aureus or P. aeruginosa.

Effect of proteases against biofilms of Staphylococcus aureus and Staphylococcus epidermidis

Biofilms play a key role in bacterial resistance against antibacterial agents-an issue that causes multiple problems in medical fields, particularly with Staphylococcus biofilms that colonize medical indwelling devices. The literature reports several anti-biofilm strategies that have been applied in medicine. Disrupting the biofilm formation process creates new sites open to colonization by treatment-generated planktonic bacteria, so efforts have turned to focus on strategies to prevent and control the initial Staphylococci adhesion. Here, we investigated the preventive activities of three commercial proteases (Flavourzyme, Neutrase and Alcalase) against biofilm formation by two Staphylococcus strains. Some proteolytic extracts revealed interesting results with Staphylococcus epidermidis and Staphylococcus aureus aureus biofilms.

SIGNIFICANCE AND IMPACT OF THE STUDY

Three proteases were tested against Staphylococcus aureus and Staphylococcus epidermidis biofilms in standard conditions. The Flavourzyme containing a mix of Aspergillus orizae endo- and exoproteases demonstrated significant efficacy against Staph. epidermidis biofilm formation. These results could prove valuable in the effort to develop simple anti-biofilm methods.

A novel sulfate-reducing bacteria detection method based on inhibition of cysteine protease activity

Sulfate-reducing bacteria (SRB) have been extensively studied in corrosion and environmental science. However, fast enumeration of SRB population is still a difficult task. This work presents a novel specific SRB detection method based on inhibition of cysteine protease activity. The hydrolytic activity of cysteine protease was inhibited by taking advantage of sulfide, the characteristic metabolic product of SRB, to attack active cysteine thiol group in cysteine protease catalytic sites. The active thiol S-sulfhydration process could be used for SRB detection, since the amount of sulfide accumulated in culture medium was highly related with initial bacterial concentration. The working conditions of cysteine protease have been optimized to obtain better detection capability, and the SRB detection performances have been evaluated in this work. The proposed SRB detection method based on inhibition of cysteine protease activity avoided the use of biological recognition elements. In addition, compared with the widely used most probable number (MPN) method which would take up to at least 15days to accomplish whole detection process, the method based on inhibition of papain activity could detect SRB in 2 days, with a detection limit of 5.21×10(2) cfu mL(-1). The detection time for SRB population quantitative analysis was greatly shortened.

Mini-review: Antimicrobial peptides and enzymes as promising candidates to functionalize biomaterial surfaces

Biomaterial-associated infections remain a serious concern in modern healthcare. The development of materials that can resist or prevent bacterial attachment constitutes a promising approach to dealing with this problem. Antimicrobial peptides (AMPs) and enzymes have been recognized as promising candidates for the new generation of antimicrobial surfaces. AMPs have been the focus of great interest in recent years owing to a low propensity for developing bacterial resistance, broad-spectrum activity, high efficacy at very low concentrations, target specificity, and synergistic action with classical antibiotics. Biofilm-dispersing enzymes have been shown to inhibit biofilm formation, detach established biofilm, and increase biofilm susceptibility to other antimicrobials. This review critically examines the potential of these protein-like compounds for developing antibacterial coatings by reporting their immobilization into different substrata using different immobilization strategies.

Aging biofilm from a full-scale moving bed biofilm reactor: characterization and enzymatic treatment study

Effective removal of aging biofilm deserves to receive more attention. This study aimed to characterized aging biofilm from a full-scale moving bed biofilm reactor treating pharmaceutical wastewater and evaluate the hydrolysis effects of biofilm by different enzymatic treatments. Results from FTIR and biochemical composition analyses showed that it was a predominately organic-based biofilm with the ratio of total protein (PN) to polysaccharide (PS) of 20.17. A reticular structure of extracellular polymeric matrix (EPM) with filamentous bacteria as the skeleton was observed on the basal layer through SEM-EDS test. Among the four commercial proteases and amylases from Genencor®, proteases were shown to have better performances than amylases either on the removal of MLSS and PN/MLSS or on DOC (i.e., dissolved organic carbon)/MLSS raising of biofilm pellets. Difference of dynamic fluorescence characteristics of dissolved organic matters after treated by the two proteases indicated distinguishing mechanisms of the treating process.

Enhancing aerobic digestion potential of municipal waste-activated sludge through removal of extracellular polymeric substance

A protease-secreting bacteria was used to pretreat municipal sewage sludge to enhance aerobic digestion. To enhance the accessibility of the sludge to the enzyme, extracellular polymeric substances were removed using citric acid thereby removing the flocs in the sludge. The conditions for the bacterial pretreatment were optimized using response surface methodology. The results of the bacterial pretreatment indicated that the suspended solids reduction was 18% in sludge treated with citric acid and 10% in sludge not treated with citric acid whereas in raw sludge, suspended solids reduction was 5.3%. Solubilization was 10.9% in the sludge with extracellular polymeric substances removed in contrast to that of the sludge with extracellular polymeric substances, which was 7.2%, and that of the raw sludge, which was just 4.8%. The suspended solids reduction in the aerobic reactor containing pretreated sludge was 52.4% whereas that in the control reactor was 15.3%. Thus, pretreatment with the protease-secreting bacteria after the removal of extracellular polymeric substances is a cost-effective and environmentally friendly method.