Acid stress management by Cronobacter sakazakii

Area of Science:

• Food Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• Cronobacter sakazakii is a foodborne pathogen linked to severe infant illnesses, often through contaminated powdered infant formula (PIF).
• Understanding its survival mechanisms in acidic environments, like the infant stomach, is crucial for food safety.
• This study focuses on a specific, stress-tolerant clinical isolate, C. sakazakii DPC6529.

Purpose of the Study:

• To investigate the growth of C. sakazakii DPC6529 in acidified laboratory media and PIF.
• To explore the potential for a stationary-phase acid tolerance response (ATR) in this strain.
• To elucidate the molecular mechanisms underlying C. sakazakii's acid resistance.

Main Methods:

• Culturing C. sakazakii DPC6529 in acidified LB broth and PIF at varying pH levels.
• Inducing and assessing stationary-phase ATR using glucose supplementation and subsequent acid challenge.
• Employing transposon mutagenesis to identify genes involved in acid stress response.
• Analyzing specific mutants, including those affecting CpxR and OmpR regulators.

Main Results:

• C. sakazakii DPC6529 demonstrated growth in LB broth at pH 4.2 and PIF at pH 5.0.
• A stationary-phase ATR was induced in glucose-supplemented broth, enhancing survival at pH 3.0.
• Key survival mechanisms include DNA/protein repair, tRNA modification, and maintaining cell envelope integrity.
• Mutants with insertions in CpxR and OmpR genes showed increased acid sensitivity, with OmpR being a significant factor in acid stress response.

Conclusions:

• C. sakazakii can proliferate in acidic conditions relevant to infant digestion.
• The development of an adaptive stationary-phase ATR contributes to its survival in the infant gut.
• Molecular mechanisms involving envelope stress regulators like OmpR are vital for acid resistance.
• These findings highlight potential vulnerabilities for controlling C. sakazakii contamination in infant products.