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Relationship between antibody susceptibility and lipopolysaccharide O-antigen characteristics of invasive and gastrointestinal nontyphoidal Salmonellae isolates from Kenya.

Onsare RS, Micoli F, Lanzilao L, Alfini R, Okoro CK, Muigai AW, Revathi G, Saul A, Kariuki S, MacLennan CA, Rondini S - PLoS Negl Trop Dis (2015)

Bottom Line: Typhimurium, but not Enteritidis, O-antigen expression correlated with reduced sensitivity to killing (r = 0.29, 95% CI = 0.10-0.45, p = 0.002).Typhimurium.Genome studies are required to understand whether invasive and gastrointestinal isolates differ at the genotypic level.

View Article: PubMed Central - PubMed

Affiliation: Centre for Microbiology Research (CMR), Kenya Medical Research Institute (KEMRI), Nairobi, Kenya; Jomo Kenyatta University of Agriculture and Technology (JKUAT), Nairobi, Kenya.

ABSTRACT

Background: Nontyphoidal Salmonellae (NTS) cause a large burden of invasive and gastrointestinal disease among young children in sub-Saharan Africa. No vaccine is currently available. Previous reports indicate the importance of the O-antigen of Salmonella lipopolysaccharide for virulence and resistance to antibody-mediated killing. We hypothesised that isolates with more O-antigen have increased resistance to antibody-mediated killing and are more likely to be invasive than gastrointestinal.

Methodology/principal findings: We studied 192 NTS isolates (114 Typhimurium, 78 Enteritidis) from blood and stools, mostly from paediatric admissions in Kenya 2000-2011. Isolates were tested for susceptibility to antibody-mediated killing, using whole adult serum. O-antigen structural characteristics, including O-acetylation and glucosylation, were investigated. Overall, isolates were susceptible to antibody-mediated killing, but S. Enteritidis were less susceptible and expressed more O-antigen than Typhimurium (p<0.0001 for both comparisons). For S. Typhimurium, but not Enteritidis, O-antigen expression correlated with reduced sensitivity to killing (r = 0.29, 95% CI = 0.10-0.45, p = 0.002). Both serovars expressed O-antigen populations ranging 21-33 kDa average molecular weight. O-antigen from most Typhimurium were O-acetylated on rhamnose and abequose residues, while Enteritidis O-antigen had low or no O-acetylation. Both Typhimurium and Enteritidis O-antigen were approximately 20%-50% glucosylated. Amount of S. Typhimurium O-antigen and O-antigen glucosylation level were inversely related. There was no clear association between clinical presentation and antibody susceptibility, O-antigen level or other O-antigen features.

Conclusion/significance: Kenyan S. Typhimurium and Enteritidis clinical isolates are susceptible to antibody-mediated killing, with degree of susceptibility varying with level of O-antigen for S. Typhimurium. This supports the development of an antibody-inducing vaccine against NTS for Africa. No clear differences were found in the phenotype of isolates from blood and stool, suggesting that the same isolates can cause invasive disease and gastroenteritis. Genome studies are required to understand whether invasive and gastrointestinal isolates differ at the genotypic level.

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Related in: MedlinePlus

OAg production of S. Typhimurium (STm) and S. Enteritidis (SEn) isolates after growth and normalization to the same final OD: 35.Dashed/continuous line indicates median OAg production of S. Typhimurium (STm) (14.4 μg/ml/OD) and S. Enteritidis (SEn) (16.8 μg/ml/OD) isolates, respectively.
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pntd.0003573.g002: OAg production of S. Typhimurium (STm) and S. Enteritidis (SEn) isolates after growth and normalization to the same final OD: 35.Dashed/continuous line indicates median OAg production of S. Typhimurium (STm) (14.4 μg/ml/OD) and S. Enteritidis (SEn) (16.8 μg/ml/OD) isolates, respectively.

Mentions: OAg was extracted from all 192 NTS study isolates normalized to the same final OD and total amount was quantified by phenol sulphuric acid assay [34]. NTS isolates produced a range of OAg amounts, with low (<10 μg/ml/OD) and high producers (>25 μg/ml/OD). On average, S. Enteritidis isolates expressed more OAg than S. Typhimurium, with 70.9% of the isolates producing more than 15 μg/ml/OD OAg compared to only 42.1% S. Typhimurium. Median OAg production for S. Enteritidis isolates was 16.8 μg/ml/OD compared to 14.4 μg/ml/OD of S. Typhimurium (p<0.0001 by Mann Whitney test) (Fig. 2). All study isolates contained one single main OAg population with average MW of 21–33 kDa (Fig. 3a); <5% isolates contained OAg population with average MW < 6 kDa.


Relationship between antibody susceptibility and lipopolysaccharide O-antigen characteristics of invasive and gastrointestinal nontyphoidal Salmonellae isolates from Kenya.

Onsare RS, Micoli F, Lanzilao L, Alfini R, Okoro CK, Muigai AW, Revathi G, Saul A, Kariuki S, MacLennan CA, Rondini S - PLoS Negl Trop Dis (2015)

OAg production of S. Typhimurium (STm) and S. Enteritidis (SEn) isolates after growth and normalization to the same final OD: 35.Dashed/continuous line indicates median OAg production of S. Typhimurium (STm) (14.4 μg/ml/OD) and S. Enteritidis (SEn) (16.8 μg/ml/OD) isolates, respectively.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4352093&req=5

pntd.0003573.g002: OAg production of S. Typhimurium (STm) and S. Enteritidis (SEn) isolates after growth and normalization to the same final OD: 35.Dashed/continuous line indicates median OAg production of S. Typhimurium (STm) (14.4 μg/ml/OD) and S. Enteritidis (SEn) (16.8 μg/ml/OD) isolates, respectively.
Mentions: OAg was extracted from all 192 NTS study isolates normalized to the same final OD and total amount was quantified by phenol sulphuric acid assay [34]. NTS isolates produced a range of OAg amounts, with low (<10 μg/ml/OD) and high producers (>25 μg/ml/OD). On average, S. Enteritidis isolates expressed more OAg than S. Typhimurium, with 70.9% of the isolates producing more than 15 μg/ml/OD OAg compared to only 42.1% S. Typhimurium. Median OAg production for S. Enteritidis isolates was 16.8 μg/ml/OD compared to 14.4 μg/ml/OD of S. Typhimurium (p<0.0001 by Mann Whitney test) (Fig. 2). All study isolates contained one single main OAg population with average MW of 21–33 kDa (Fig. 3a); <5% isolates contained OAg population with average MW < 6 kDa.

Bottom Line: Typhimurium, but not Enteritidis, O-antigen expression correlated with reduced sensitivity to killing (r = 0.29, 95% CI = 0.10-0.45, p = 0.002).Typhimurium.Genome studies are required to understand whether invasive and gastrointestinal isolates differ at the genotypic level.

View Article: PubMed Central - PubMed

Affiliation: Centre for Microbiology Research (CMR), Kenya Medical Research Institute (KEMRI), Nairobi, Kenya; Jomo Kenyatta University of Agriculture and Technology (JKUAT), Nairobi, Kenya.

ABSTRACT

Background: Nontyphoidal Salmonellae (NTS) cause a large burden of invasive and gastrointestinal disease among young children in sub-Saharan Africa. No vaccine is currently available. Previous reports indicate the importance of the O-antigen of Salmonella lipopolysaccharide for virulence and resistance to antibody-mediated killing. We hypothesised that isolates with more O-antigen have increased resistance to antibody-mediated killing and are more likely to be invasive than gastrointestinal.

Methodology/principal findings: We studied 192 NTS isolates (114 Typhimurium, 78 Enteritidis) from blood and stools, mostly from paediatric admissions in Kenya 2000-2011. Isolates were tested for susceptibility to antibody-mediated killing, using whole adult serum. O-antigen structural characteristics, including O-acetylation and glucosylation, were investigated. Overall, isolates were susceptible to antibody-mediated killing, but S. Enteritidis were less susceptible and expressed more O-antigen than Typhimurium (p<0.0001 for both comparisons). For S. Typhimurium, but not Enteritidis, O-antigen expression correlated with reduced sensitivity to killing (r = 0.29, 95% CI = 0.10-0.45, p = 0.002). Both serovars expressed O-antigen populations ranging 21-33 kDa average molecular weight. O-antigen from most Typhimurium were O-acetylated on rhamnose and abequose residues, while Enteritidis O-antigen had low or no O-acetylation. Both Typhimurium and Enteritidis O-antigen were approximately 20%-50% glucosylated. Amount of S. Typhimurium O-antigen and O-antigen glucosylation level were inversely related. There was no clear association between clinical presentation and antibody susceptibility, O-antigen level or other O-antigen features.

Conclusion/significance: Kenyan S. Typhimurium and Enteritidis clinical isolates are susceptible to antibody-mediated killing, with degree of susceptibility varying with level of O-antigen for S. Typhimurium. This supports the development of an antibody-inducing vaccine against NTS for Africa. No clear differences were found in the phenotype of isolates from blood and stool, suggesting that the same isolates can cause invasive disease and gastroenteritis. Genome studies are required to understand whether invasive and gastrointestinal isolates differ at the genotypic level.

Show MeSH
Related in: MedlinePlus