The growth limits of a large number of Listeria monocytogenes strains at combinations of stresses show serotype--and niche-specific traits.
OBJECTIVE
The aim of this study was to associate the growth limits of Listeria monocytogenes during exposure to combined stresses with specific serotypes or origins of isolation, and identify potential genetic markers.


RESULTS
The growth of 138 strains was assessed at different temperatures using combinations of low pH, sodium lactate, and high salt concentrations in brain heart infusion broth. None of the strains was able to grow at pH < or = 4.4, a(w) < or = 0.92, or pH < or = 5.0 combined with a(w) < or = 0.94. In addition, none of the strains grew at pH < or = 5.2 and NaLac > or = 2%. At 30 degrees C, the serotype 4b strains showed the highest tolerance to low pH and high NaCl concentrations at both pH neutral (pH 7.4) and mild acidic conditions (pH 5.5). At 7 degrees C, the serotype 1/2b strains showed the highest tolerance to high NaCl concentrations at both pH 7.4 and 5.5. Serotype 1/2b meat isolates showed the highest tolerance to low pH in the presence of 2% sodium lactate at 7 degrees C. ORF2110 and gadD1T1 were identified as potential biomarkers for phenotypic differences.


CONCLUSIONS
Differences in growth limits were identified between specific L. monocytogenes strains and serotypes, which could in some cases be associated with specific genetic markers.


CONCLUSIONS
Our data confirm the growth limits of L. monocytogenes as set out by the European Union for ready-to-eat foods and provides an additional criterion. The association of L. monocytogenes serotypes with certain stress responses might explain the abundance of certain serotypes in retail foods while others are common in clinical cases.
van der Veen
S
S
Top Institute Food and Nutrition (TIFN), Nieuwe Kanaal, Wageningen, the Netherlands. Stijn.vanderVeen@wur.nl
Moezelaar
R
R
Abee
T
T
Wells-Bennik
M H J
MH
D000222:Adaptation, Physiological / Q000235:genetics; D015169:Colony Count, Microbial; D003470:Culture Media / Q000737:chemistry*; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D005819:Genetic Markers; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D008089:Listeria monocytogenes / Q000235:genetics / Q000254:growth & development* / Q000502:physiology; D016133:Polymerase Chain Reaction; D012703:Serotyping; D012965:Sodium Chloride
D003470:Culture Media; D005819:Genetic Markers; D012965:Sodium Chloride