Novel Bacteriophage Shows Potential to Control Drug-Resistant Bacillus cereus in Milk, Rice, Pork
A new study published in Current Research in Food Science has identified a novel bacteriophage capable of significantly reducing or eliminating multidrug-resistant Bacillus cereus in milk, rice, and pork under both refrigerated and room-temperature conditions. The phage also demonstrated efficacy against B. cereus biofilms and inhibited the outgrowth of germinated spores, suggesting its potential as a biocontrol agent for food safety applications.
The study was conducted by researchers at South China Agricultural University in Guangzhou, China. The researchers isolated a novel lytic phage, named WAH2, from wastewater collected at a food factory, using a multidrug-resistant B. cereus strain previously isolated from Chinese sausages as the host.
Phage WAH2 Demonstrates Antibacterial and Antibiofilm Activity
The researchers characterized WAH2's biological properties, host range, genomic composition, and antibacterial efficacy. The phage was capable of infecting seven of 51 (13.7 percent) tested B. cereus strains, representing three sequence types. Although its host range was relatively narrow, all susceptible isolates were multidrug-resistant.
WAH2 remained stable at temperatures ranging from 4–45 °C, pH levels of 5–11, and salt concentrations of 2–10 percent. Genomic analysis identified no antibiotic resistance genes, virulence factors, or lysogeny-related elements, supporting its potential suitability for food biocontrol applications.
In laboratory experiments, WAH2 inhibited B. cereus growth for 36 hours without detectable bacterial regrowth. The phage also significantly reduced biofilm formation and disrupted mature biofilms on stainless steel surfaces. Treatment of established biofilms reduced viable bacterial counts by 3.68–3.84 log CFU/mL after 12 hours.
Additionally, WAH2 inhibited the outgrowth of germinated B. cereus spores under nutrient-rich conditions. However, the phage did not directly inactivate dormant spores or prevent spore germination, indicating that its activity depended on the presence of metabolically active bacterial cells.
Phage Treatment Reduces B. cereus in Food Matrices
To evaluate WAH2's potential for food biocontrol, the researchers inoculated milk, rice, and pork samples with B. cereus and treated them with different concentrations of the phage at 25 °C and 4 °C.
Looking for quick answers on food safety topics?
Try Ask FSM, our new smart AI search tool.
Ask FSM →
At 25 °C, the two highest phage concentrations reduced B. cereus in milk to below detectable levels within three hours. In rice, the highest concentration achieved the same result within three hours, while the lowest concentration required 24 hours.
In pork, the highest phage concentration reduced B. cereus to undetectable levels within 12 hours. Lower concentrations produced reductions of 1.66–6.68 log CFU/g after 72 hours.
WAH2 also demonstrated antibacterial activity under refrigerated conditions. At 4 °C, the highest phage concentration reduced B. cereus in milk to below detectable levels within 12 hours and in rice within 48 hours. In pork, the highest concentration achieved a 2.12-log CFU/g reduction after 72 hours.
No bacterial regrowth was observed in any of the treated food matrices during the 72-hour experimental period.
Additional experiments demonstrated that WAH2 remained infectious in milk and laboratory growth medium for at least 120 hours at both temperatures, with no detectable phage-resistant bacterial survivors.
Further Research Needed to Evaluate Practical Applications
The researchers concluded that WAH2 showed promise as a biocontrol agent against B. cereus contamination in food due to its sustained antibacterial activity, environmental stability, and efficacy against biofilms and germinated spores.
However, the study had several limitations. WAH2's narrow host range may restrict its effectiveness against genetically diverse B. cereus populations. Additionally, the food matrices were pretreated to minimize interference from background microorganisms, meaning the results may not fully represent performance in naturally contaminated foods.
The researchers suggested that future studies investigate phage cocktails to broaden the range of susceptible B. cereus strains, as well as improved phage delivery methods and validation under actual food processing and storage conditions.
