Structural change in GadD2 of Listeria monocytogenes field isolates supports nisin resistance

The Analysis of Field Strains Isolated From Food, Animal and Clinical Sources Uncovers Natural Mutations in Listeria monocytogenes Nisin Resistance Genes

“…Lineage differences also extended to serotype and CC level. Nisin tolerance trends of serotypes 1/2a and 1/2c > 1/2b > 4b were also observed in agreement with previous studies showing that serotype 1/2a and 4b strains were more tolerant and sensitive to nisin, respectively ( Buncic et al, 2001 ; Katla et al, 2003 ; Szendy et al, 2019 ). Comparing the strains at the MLST CC level we found that CC7 strains displayed highest nisin resistance whereas CC2 and CC3 strains showed the lowest nisin resistance levels similar to previous observations ( Malekmohammadi et al, 2017 ).…”

“…Based on the strain specific nisin inhibition induced percentage change in area growth curve (ΔPAUC) most (66%) of the examined strains were nisin resistant at 12.5 ppm. In this regard our observations were similar to a previous study showing that about a third of the 282 field strains tested were still capable of significant growth at 400 IU (10 ppm) nisin in liquid media ( Szendy et al, 2019 ). Ninety-nine percent of 381 field strains were also able to grow at 500 IU (12.5 ppm) nisin on solid media ( Mota-Meira et al, 2000 ).…”

“…Increased SigB regulon activation in the RsbU G77S mutant was supported by the higher mRNA levels for the SigB-dependent gene gadD3 detected in this mutant compared to a control strain from the same MLST CC without this RsbU amino acid substitution. gadD3 is positively regulated by SigB ( Raengpradub et al, 2008 ) and constitutes part of the GAD system, which is also involved in nisin response ( Begley et al, 2010 ; Szendy et al, 2019 ). In contrast, the nonsense mutation and in-frame deletions in rsbU gene could have resulted in the coding of a functionally impaired RsbU protein and the deletion of the five genes in the sigB operon may also have impaired the signal transduction, which is important for activation of SigB and its regulon.…”

“…Previously, various approaches have been used to identify specific nisin resistance mechanisms and interrelationship between various genes in L. monocytogenes including screening of transposon library mutants ( Collins et al, 2010a , b ) and transcriptome analysis ( Wu et al, 2018 ), but based on a few laboratory based strains. More recently, a combination of minimum inhibitory concentration and whole genome sequencing approach on six strains derived from the screening of 282 L. monocytogenes field isolates was used after which acquired nisin resistance was attributed to a gadD2 missense mutation ( Szendy et al, 2019 ). This makes it apparent that studies encompassing phenotypic and genotypic analyses of field isolates derived from different sources will lead to new understanding of the scope of molecular mechanisms and genes underlying nisin resistance in L. monocytogenes .…”

Nevertheless, She Resisted – Role of the Environment on Listeria monocytogenes Sensitivity to Nisin Treatment in a Laboratory Cheese Model

“…In contrast, Buncic et al, 2001, showed that serotype 1/2a isolates were more resistant to two antilisterial bacteriocins (Lb 265 and Lb706) than serotype 4b isolates (Buncic et al, 2001). More recently, a screen of 282 L. monocytogenes isolates from German RTE food products and food-processing environments revealed various degrees of nisin sensitivity between strains, however, isolates derived from milk/cheese and other dairy products (which were predominantly serotype 1/2a) showed significantly higher resistance to nisin concentrations than isolates from other sources (p < 0.002) (Szendy et al, 2019). It seems plausible that the overrepresentation of isolates from dairy products with higher resistance to bacteriocins could be explained by the intrinsic advantage these isolates would have in environments where bacteriocin-producing organisms are found.…”