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author:("Begley, mire")
1.  Structure-Activity Relationship of Synthetic Variants of the Milk-Derived Antimicrobial Peptide αs2-Casein f(183–207) 
Applied and Environmental Microbiology  2013;79(17):5179-5185.
Template-based studies on antimicrobial peptide (AMP) derivatives obtained through manipulation of the amino acid sequence are helpful to identify properties or residues that are important for biological activity. The present study sheds light on the importance of specific amino acids of the milk-derived αs2-casein f(183–207) peptide to its antibacterial activity against the food-borne pathogens Listeria monocytogenes and Cronobacter sakazakii. Trimming of the peptide revealed that residues at the C-terminal end of the peptide are important for activity. Removal of the last 5 amino acids at the C-terminal end and replacement of the Arg at position 23 of the peptide sequence by an Ala residue significantly decreased activity. These findings suggest that Arg23 is very important for optimal activity of the peptide. Substitution of the also positively charged Lys residues at positions 15 and 17 of the αs2-casein f(183–207) peptide also caused a significant reduction of the effectiveness against C. sakazakii, which points toward the importance of the positive charge of the peptide for its biological activity. Indeed, simultaneous replacement of various positively charged amino acids was linked to a loss of bactericidal activity. On the other hand, replacement of Pro residues at positions 14 and 20 resulted in a significantly increased antibacterial potency, and hydrophobic end tagging of αs2-casein f(193–203) and αs2-casein f(197–207) peptides with multiple Trp or Phe residues significantly increased their potency against L. monocytogenes. Finally, the effect of pH (4.5 to 7.4), temperature (4°C to 37°C), and addition of sodium and calcium salts (1% to 3%) on the activity of the 15-amino-acid αs2-casein f(193–207) peptide was also determined, and its biological activity was shown to be completely abolished in high-saline environments.
PMCID: PMC3753947  PMID: 23793637
2.  Selection for Loss of RpoS in Cronobacter sakazakii by Growth in the Presence of Acetate as a Carbon Source 
We demonstrate that growth of Cronobacter sakazakii in the presence of acetate as a carbon source promotes loss of RpoS, with a consequent reduction in stress tolerance. This suggests that C. sakazakii is capable of regulating cell fitness through mutation of the rpoS gene.
PMCID: PMC3592228  PMID: 23335773
3.  Polymorphisms in rpoS and Stress Tolerance Heterogeneity in Natural Isolates of Cronobacter sakazakii 
Applied and Environmental Microbiology  2012;78(11):3975-3984.
Significant phenotypic diversity was observed when we examined the abilities of a number of Cronobacter sakazakii natural isolates to cope with various sublethal stress conditions (acid, alkaline, osmotic, oxidative, or heat stress). Levels of catalase activity and use of acetate as a carbon source, phenotypes commonly used as indirect assays to predict RpoS function, revealed a high correlation between predicted RpoS activity and tolerance to acid, alkaline, osmotic, and oxidative treatments. The rpoS genes were sequenced and analyzed for polymorphisms. Loss-of-function mutations were found in two strains; C. sakazakii DPC 6523 and the genome-sequenced strain C. sakazakii ATCC BAA-894. The complementation of these strains with a functional rpoS gene resulted in an increase in bacterial tolerance to acid, osmotic, and oxidative stresses. The pigmentation status of strains was also assessed, and a high variability in carotenoid content was observed, with a functional rpoS gene being essential for the production of the characteristic yellow pigment. In conclusion, the evidence presented in this study demonstrates that rpoS is a highly polymorphic gene in C. sakazakii, and it supports the importance of RpoS for the tolerance under stress conditions that C. sakazakii may encounter in the food chain and in the host during infection.
PMCID: PMC3346413  PMID: 22447602
4.  Glutamate Decarboxylase-Mediated Nisin Resistance in Listeria monocytogenes▿  
Applied and Environmental Microbiology  2010;76(19):6541-6546.
Analysis of a complete set of glutamate decarboxylase (gad) mutants of Listeria monocytogenes strain LO28 (ΔgadD1, ΔgadDT1, ΔgadD2, ΔgadT2, and ΔgadD3 mutants) revealed that the ΔgadD1 mutant is impaired in its ability to tolerate exposure to both sublethal and lethal levels of the lantibiotic nisin. gadD1 is strain variable and is found only in approximately 50% of L. monocytogenes strains. Growth and survival experiments revealed that possession of gadD1 correlates with a higher degree of tolerance to nisin. Significantly, a similar finding using a gadB mutant of L. lactis IL1403 implies that this may be a general phenomenon in Gram-positive bacteria. Our findings thus suggest that the specific inhibition of GAD activity or a reduction in the levels of free glutamate may prevent the growth of otherwise resistant GAD+ bacteria in foods where low pH and/or nisin is used as a preservative.
PMCID: PMC2950483  PMID: 20693450
5.  Identification of a Novel Two-Peptide Lantibiotic, Lichenicidin, following Rational Genome Mining for LanM Proteins▿  
Applied and Environmental Microbiology  2009;75(17):5451-5460.
Lantibiotics are ribosomally synthesized peptide antimicrobials which contain considerable posttranslational modifications. Given their usually broad host range and their highly stable structures, there have been renewed attempts to identify and characterize novel members of the lantibiotic family in recent years. The increasing availability of bacterial genome sequences means that in addition to traditional microbiological approaches, in silico screening strategies may now be employed to the same end. Taking advantage of the highly conserved nature of lantibiotic biosynthetic enzymes, we screened publicly available microbial genome sequences for genes encoding LanM proteins, which are required for the posttranslational modification of type 2 lantibiotics. By using this approach, 89 LanM homologs, including 61 in strains not known to be lantibiotic producers, were identified. Of these strains, five (Streptococcus pneumoniae SP23-BS72, Bacillus licheniformis ATCC 14580, Anabaena variabilis ATCC 29413, Geobacillus thermodenitrificans NG80-2, and Herpetosiphon aurantiacus ATCC 23779) were subjected to a more detailed bioinformatic analysis. Four of the strains possessed genes potentially encoding a structural peptide in close proximity to the lanM determinants, while two, S. pneumoniae SP23-BS72 and B. licheniformis ATCC 14580, possess two potential structural genes. The B. licheniformis strain was selected for a proof-of-concept exercise, which established that a two-peptide lantibiotic, lichenicidin, which exhibits antimicrobial activity against all Listeria monocytogenes, methicillin-resistant Staphylococcus aureus, and vancomycin-resistant enterococcus strains tested, was indeed produced, thereby confirming the benefits of such a bioinformatic approach when screening for novel lantibiotic producers.
PMCID: PMC2737927  PMID: 19561184
6.  Exposure to bile influences biofilm formation by Listeria monocytogenes 
Gut Pathogens  2009;1:11.
In the present study we demonstrate that the initial attachment of Listeria monocytogenes cells to plastic surfaces was significantly increased by growth in the presence of bile. Improved biofilm formation was confirmed by crystal violet staining, microscopy and bioluminescence detection of a luciferase-tagged strain. Enhanced biofilm formation in response to bile may influence the ability of L. monocytogenes to form biofilms in vivo during infection and may contribute to survival of this important pathogen in the human gastrointestinal tract and gallbladder.
PMCID: PMC2693109  PMID: 19476630
7.  Analysis of the Isoprenoid Biosynthesis Pathways in Listeria monocytogenes Reveals a Role for the Alternative 2-C-Methyl-d-Erythritol 4-Phosphate Pathway in Murine Infection▿  
Infection and Immunity  2008;76(11):5392-5401.
Most bacteria synthesize isoprenoids through one of two essential pathways which provide the basic building block, isopentyl diphosphate (IPP): either the classical mevalonate pathway or the alternative non-mevalonate 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway. However, postgenomic analyses of the Listeria monocytogenes genome revealed that this pathogen possesses the genetic capacity to produce the complete set of enzymes involved in both pathways. The nonpathogenic species Listeria innocua naturally lacks the last two genes (gcpE and lytB) of the MEP pathway, and bioinformatic analyses strongly suggest that the genes have been lost through evolution. In the present study we show that heterologous expression of gcpE and lytB in L. innocua can functionally restore the MEP pathway in this organism and confer on it the ability to induce Vγ9Vδ2 T cells. We have previously confirmed that both pathways are functional in L. monocytogenes and can provide sufficient IPP for normal growth in laboratory media (M. Begley, C. G. Gahan, A. K. Kollas, M. Hintz, C. Hill, H. Jomaa, and M. Eberl, FEBS Lett. 561:99-104, 2004). Here we describe a targeted mutagenesis strategy to create a double pathway mutant in L. monocytogenes which cannot grow in the absence of exogenously provided mevalonate, confirming the requirement for at least one intact pathway for growth. In addition, murine studies revealed that mutants lacking the MEP pathway were impaired in virulence relative to the parent strain during intraperitoneal infection, while mutants lacking the classical mevalonate pathway were not impaired in virulence potential. In vivo bioluminescence imaging also confirmed in vivo expression of the gcpE gene (MEP pathway) during murine infection.
PMCID: PMC2573353  PMID: 18765739
8.  Bile Salt Hydrolase Activity in Probiotics 
PMCID: PMC1393245  PMID: 16517616
9.  Tolerance of Listeria monocytogenes to Cell Envelope-Acting Antimicrobial Agents Is Dependent on SigB 
Mutation of sigB impairs the ability of Listeria monocytogenes to grow in sublethal levels, and to survive in lethal concentrations, of the bacteriocins nisin and lacticin 3147 and the antibiotics ampicillin and penicillin G. SigB may therefore represent an attractive target for the development of new control and treatment strategies for this important pathogen.
PMCID: PMC1393204  PMID: 16517678
10.  Contribution of Three Bile-Associated Loci, bsh, pva, and btlB, to Gastrointestinal Persistence and Bile Tolerance of Listeria monocytogenes  
Infection and Immunity  2005;73(2):894-904.
Listeria monocytogenes must resist the deleterious actions of bile in order to infect and subsequently colonize the human gastrointestinal tract. The molecular mechanisms used by the bacterium to resist bile and the influence of bile on pathogenesis are as yet largely unexplored. This study describes the analysis of three genes—bsh, pva, and btlB—previously annotated as bile-associated loci in the sequenced L. monocytogenes EGDe genome (lmo2067, lmo0446, and lmo0754, respectively). Analysis of deletion mutants revealed a role for all three genes in resisting the acute toxicity of bile and bile salts, particularly glycoconjugated bile salts at low pH. Mutants were unaffected in the other stress responses examined (acid, salt, and detergents). Bile hydrolysis assays demonstrate that L. monocytogenes possesses only one bile salt hydrolase gene, namely, bsh. Transcriptional analyses and activity assays revealed that, although it is regulated by both PrfA and σB, the latter appears to play the greater role in modulating bsh expression. In addition to being incapable of bile hydrolysis, a sigB mutant was shown to be exquisitely sensitive to bile salts. Furthermore, increased expression of sigB was detected under anaerobic conditions and during murine infection. A gene previously annotated as a possible penicillin V amidase (pva) or bile salt hydrolase was shown to be required for resistance to penicillin V but not penicillin G but did not demonstrate a role in bile hydrolysis. Finally, animal (murine) studies revealed an important role for both bsh and btlB in the intestinal persistence of L. monocytogenes.
PMCID: PMC546953  PMID: 15664931
11.  Bile Stress Response in Listeria monocytogenes LO28: Adaptation, Cross-Protection, and Identification of Genetic Loci Involved in Bile Resistance 
Applied and Environmental Microbiology  2002;68(12):6005-6012.
Bile is one of many barriers that Listeria monocytogenes must overcome in the human gastrointestinal tract in order to infect and cause disease. We demonstrated that stationary-phase cultures of L. monocytogenes LO28 were able to tolerate concentrations of bovine, porcine, and human bile and bile acids well in excess of those encountered in vivo. Strain LO28 was relatively bile resistant compared with other clinical isolates of L. monocytogenes, as well as with Listeria innocua, Salmonella enterica serovar Typhimurium LT2, and Lactobacillus sakei. While exponential-phase L. monocytogenes LO28 cells were exquisitely sensitive to unconjugated bile acids, prior adaptation to sublethal levels of bile acids or heterologous stresses, such as acid, heat, salt, or sodium dodecyl sulfate (SDS), significantly enhanced bile resistance. This adaptive response was independent of protein synthesis, and in the cases of bile and SDS adaptation, occurred in seconds. In order to identify genetic loci involved in the bile tolerance phenotype of L. monocytogenes LO28, transposon (Tn917) and plasmid (pORI19) integration banks were screened for bile-sensitive mutants. The disrupted genes included a homologue of the capA locus required for capsule formation in Bacillus anthracis; a gene encoding the transcriptional regulator ZurR; a homologue of an Escherichia coli gene, lytB, involved in isoprenoid biosynthesis; a gene encoding a homologue of the Bacillus subtilis membrane protein YxiO; and a gene encoding an amino acid transporter with a putative role in pH homeostasis, gadE. Interestingly, all of the identified loci play putative roles in maintenance of the cell envelope or in stress responses.
PMCID: PMC134417  PMID: 12450822

Results 1-11 (11)