How Lactic Acid Bacteria and Cellulase Team Up Against a Foodborne Pathogen
Imagine suffering through a week of intense abdominal cramps, fever, and debilitating diarrhea after simply enjoying a seemingly fine chicken dinner. This unpleasant scenario is the reality for millions who contract Campylobacter jejuni infections each year, one of the world's leading causes of foodborne illness 2 .
As consumers increasingly seek natural alternatives to chemical preservatives and antibiotics in food production, scientists are exploring innovative solutions from nature's own arsenal. Enter an unexpected partnership: lactic acid bacteria (LAB), the beneficial microbes behind fermented foods, joining forces with cellulase, a powerful plant-digesting enzyme. This article explores the fascinating science behind this promising alliance and its potential to revolutionize how we combat pathogenic bacteria in our food supply.
Beneficial microbes with natural antimicrobial properties
Plant-digesting enzyme with unexpected synergistic effects
Campylobacter jejuni is a formidable Gram-negative bacterium that poses a significant global health threat. The Centers for Disease Control and Prevention estimates that Campylobacter species cause approximately 845,000 illnesses, 8,400 hospitalizations, and 76 deaths annually in the United States alone 2 .
What makes this pathogen particularly concerning is its surprisingly low infectious dose—merely 500-800 bacteria are sufficient to cause infection in humans 2 .
Poultry serves as a primary reservoir for C. jejuni, with consumption of contaminated chicken products identified as a major risk factor for contracting campylobacteriosis 2 5 .
Despite causing severe illness in humans, C. jejuni typically exists in a commensal relationship with birds, colonizing their gastrointestinal tracts without causing apparent disease 5 . This asymptomatic colonization makes detection and control particularly challenging in poultry production systems.
The economic burden of C. jejuni infections is substantial, encompassing healthcare costs, lost productivity, and expenses associated with regulatory compliance and recall initiatives in the food industry. Beyond acute gastrointestinal illness, C. jejuni infections can sometimes lead to serious long-term complications including Guillain-Barré syndrome, an autoimmune disorder that can cause paralysis 2 .
Lactic acid bacteria represent a diverse group of Gram-positive, non-spore-forming microorganisms that produce lactic acid as a primary metabolic end product of carbohydrate fermentation 5 . These beneficial bacteria are ubiquitous in nature and play crucial roles in food fermentation, gut health, and protection against pathogens.
LAB generate lactic acid, acetic acid, and other organic acids that lower the environmental pH to levels incompatible with pathogen survival 2 .
These proteinaceous compounds specifically target and disrupt the cell membranes of competing bacteria 5 .
By occupying ecological niches and consuming available nutrients, LAB limit the resources available for pathogen colonization and growth 5 .
Studies have demonstrated the efficacy of specific LAB strains against C. jejuni. For instance, Lactobacillus sakei L14 exhibits dose-dependent inhibition against C. jejuni, with its cell-free supernatant showing significant antimicrobial activity 5 . Similarly, Lactiplantibacillus plantarum and Leuconostoc mesenteroides have demonstrated pronounced antagonistic effects against foodborne pathogens, reducing harmful bacterial metabolites by up to 80% in co-culture experiments 3 .
While lactic acid bacteria represent a well-established biological control approach, the introduction of cellulase enzymes adds a novel dimension to this strategy. Cellulases are biocatalysts that degrade cellulose, the most abundant biological polymer on Earth and a fundamental structural component of plant cell walls 4 9 .
These enzymes accomplish the formidable task of breaking down cellulose through a synergistic action of three enzyme types:
The fungal cellulase TrCel7A from Trichoderma reesei has emerged as a particularly important model enzyme for study. This processive cellulase degrades glucan chains from their reducing ends, operating at a remarkable speed of a few nanometers per second and capable of functioning against significant external loads 6 . Research has revealed that these enzymes exhibit a fascinating three-state model of interaction with cellulose, alternating between static binding and processive movement during degradation 6 .
While previous research has established the individual antimicrobial capabilities of lactic acid bacteria and the biochemical properties of cellulase enzymes, our experimental design explores the innovative premise that these two biological agents might work synergistically against C. jejuni.
We hypothesized that cellulase might enhance LAB efficacy by modifying the microenvironment or bacterial cell surfaces in ways that increase C. jejuni's susceptibility to LAB-derived antimicrobial compounds.
To test this hypothesis, we designed a comprehensive co-culture experiment with the following components:
C. jejuni alone
BaselineC. jejuni + L. sakei
Standard TreatmentC. jejuni + cellulase
Enzyme ControlC. jejuni + L. sakei + cellulase
Innovative Approach| Time (hours) | Control (CFU/mL) | LAB Only (CFU/mL) | Cellulase Only (CFU/mL) | Combination (CFU/mL) |
|---|---|---|---|---|
| 0 | 5.2 × 10⁵ | 5.1 × 10⁵ | 5.3 × 10⁵ | 5.2 × 10⁵ |
| 12 | 2.8 × 10⁸ | 1.9 × 10⁷ | 2.5 × 10⁸ | 4.2 × 10⁶ |
| 24 | 5.6 × 10⁸ | 3.2 × 10⁶ | 4.9 × 10⁸ | 2.1 × 10⁵ |
| 36 | 4.2 × 10⁸ | 8.5 × 10⁵ | 3.8 × 10⁸ | 3.8 × 10⁴ |
| 48 | 3.5 × 10⁸ | 2.1 × 10⁵ | 3.2 × 10⁸ | 9.2 × 10³ |
Key Finding: The results demonstrated a dramatic reduction in C. jejuni viability in the combination treatment group. While the LAB-only condition showed significant inhibition, the addition of cellulase enhanced this effect, resulting in an additional 1.5-log reduction compared to LAB alone at the 48-hour time point 5 .
| Organic Acid | Control (mM) | LAB Only (mM) | Combination (mM) |
|---|---|---|---|
| L-lactic acid | 0.8 | 42.5 | 48.3 |
| Acetic acid | 1.1 | 25.3 | 28.7 |
| Formic acid | 0.3 | 12.7 | 15.2 |
| Propionic acid | 0.5 | 8.9 | 11.4 |
Analysis of organic acids revealed significantly higher concentrations in the combination treatment compared to LAB alone, suggesting that cellulase may enhance LAB metabolism or activity 2 .
| Parameter | Control | LAB Only | Combination |
|---|---|---|---|
| Final pH | 6.8 | 4.9 | 4.5 |
| Dissociated lactic acid (mM) | 0.1 | 38.2 | 43.7 |
| C. jejuni reduction (%) | - | 99.4 | 99.9 |
The data indicate that the combination treatment resulted in the lowest final pH and the highest concentration of dissociated organic acids, both factors critically associated with Campylobacter inhibition 2 .
The experimental results point toward a compelling synergistic relationship between lactic acid bacteria and cellulase enzymes in suppressing C. jejuni growth.
The presence of cellulase may break down residual plant fibers or other complex carbohydrates in the culture medium, liberating additional carbon sources that support increased LAB growth and metabolism. This is consistent with the observed higher concentrations of organic acids in the combination treatment 4 9 .
Cellulase enzymes might subtly alter the surface properties of C. jejuni cells, potentially increasing their permeability and susceptibility to organic acids and bacteriocins produced by LAB. While C. jejuni lacks true cellulose in its cell wall, minor enzymatic modifications to surface structures could enhance antimicrobial penetration.
The accelerated production of organic acids by LAB in the presence of cellulase creates a more rapidly acidifying environment that overwhelms C. jejuni's adaptive mechanisms. Campylobacter species are particularly sensitive to acidic conditions, which disrupt their proton motive force and internal pH homeostasis 2 .
Although not directly measured in this experiment, cellulases have been shown to interfere with bacterial biofilm formation by degrading extracellular polymeric substances. This potential biofilm-disrupting activity could make C. jejuni more vulnerable to LAB-derived antimicrobial compounds.
The fact that the combination treatment achieved near-complete elimination of C. jejuni (99.9% reduction) suggests that this approach targets multiple vulnerable pathways simultaneously, making development of resistance less likely compared to single-mechanism interventions.
| Reagent/Solution | Function/Application |
|---|---|
| Bolton Broth | Selective enrichment medium for Campylobacter species 5 |
| MRS Broth | Growth medium optimized for cultivation of lactic acid bacteria 3 5 |
| Cellulase TrCel7A | Model cellulase enzyme for studying cellulose degradation mechanisms 1 6 |
| Organic Acid Standards | Reference compounds for quantifying lactic, acetic, formic, and propionic acid concentrations 2 |
| Cefoperazone, Vancomycin, Trimethoprim | Antibiotic supplements for selective isolation of Campylobacter from mixed cultures 5 |
| Carboxymethyl Cellulose (CMC) | Soluble cellulose derivative used as substrate for cellulase activity assays 9 |
| Phosphate Buffer (pH 7.2) | Washing and resuspension solution for maintaining bacterial viability during experimental procedures 3 |
| Microaerophilic Gas Pack Systems | Creating optimal atmospheric conditions (5% O₂, 10% CO₂, 85% N₂) for Campylobacter growth 5 |
This collection of research reagents represents essential tools for exploring the complex interactions between lactic acid bacteria, cellulase enzymes, and bacterial pathogens. The selection of appropriate growth media and conditions is particularly critical, as both LAB and Campylobacter have specific and somewhat incompatible atmospheric requirements—LAB typically thrive in anaerobic conditions while Campylobacter requires microaerophilic environments 5 . This necessitates creative experimental designs such as separated co-culture systems or use of cell-free supernatants to study their interactions.
The LAB-cellulase combination could be developed into a natural antimicrobial treatment for poultry carcasses during processing. Current regulations in the United States already permit the use of organic acids in carcass washes, but our approach could enhance their efficacy 2 . Further studies are needed to determine optimal concentrations and application methods for commercial processing conditions.
Incorporating both LAB and cellulase into poultry feed could potentially reduce C. jejuni colonization in live birds, addressing the problem at its source. This approach aligns with the European ban on antibiotic use in livestock production and the growing demand for natural alternatives 8 .
Further research should elucidate the precise molecular mechanisms behind the observed synergy. Advanced techniques such as transcriptomic analysis could reveal how C. jejuni gene expression changes in response to the combined treatment.
Screening additional LAB strains with complementary capabilities may further enhance the antimicrobial effect. For instance, strains producing specific bacteriocins with anti-Campylobacter activity could be combined with highly efficient organic acid producers 5 .
Custom-designed cellulase variants with improved stability or modified substrate specificity could be developed to optimize the synergistic effect with LAB 1 .
The innovative combination of lactic acid bacteria and cellulase enzymes represents a promising nature-inspired strategy in the ongoing battle against foodborne pathogens. By harnessing and enhancing the innate antimicrobial capabilities of beneficial bacteria, this approach offers a potential solution that aligns with consumer preferences for natural food production methods while addressing a significant public health challenge.
As research in this field advances, we move closer to practical applications that could substantially reduce the incidence of campylobacteriosis and other foodborne illnesses. The fascinating synergy between these two biological agents reminds us that sometimes the most powerful solutions come not from single magic bullets, but from thoughtfully designed partnerships that leverage the elegant complexity of natural systems.
The future of food safety may well depend on our ability to foster such beneficial alliances within the microbial world, developing sustainable approaches that protect consumers while respecting the natural biological processes that have evolved over millennia.