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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

SBA results of STm and SEn isolates with Malawi serum pool.Bacterial colony forming units (CFU) were counted at time 0 (T0) and after 3 h (T180) incubation of bacteria in 45 μL undiluted serum (final bacterial concentration 1×106 CFU/ml). Killing/growth was determined by Log10 (CFU at T180)-Log10 (CFU at T0). Strains that could grow (Log10 change >0) were considered “resistant”, strains that were killed (Log10 change <0) were considered susceptible. Dashed/continuous line indicates median Log10 change of STm (-2.9) and SEn (-1.2) isolates, respectively.
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pntd.0003573.g001: SBA results of STm and SEn isolates with Malawi serum pool.Bacterial colony forming units (CFU) were counted at time 0 (T0) and after 3 h (T180) incubation of bacteria in 45 μL undiluted serum (final bacterial concentration 1×106 CFU/ml). Killing/growth was determined by Log10 (CFU at T180)-Log10 (CFU at T0). Strains that could grow (Log10 change >0) were considered “resistant”, strains that were killed (Log10 change <0) were considered susceptible. Dashed/continuous line indicates median Log10 change of STm (-2.9) and SEn (-1.2) isolates, respectively.

Mentions: SBA results using the serum pool demonstrated a marked difference in susceptibility to antibody-mediated killing among individual isolates and a clear difference in susceptibility between S. Typhimurium and S. Enteritidis isolates (Fig. 1, and see S2a and S2b Table for supporting information).). We have previously demonstrated that this killing is through the antibody-dependent complement-mediated mechanism and requires the presence of specific antibodies and intact complement function [26]. We have also demonstrated that the control sera used in this assay from healthy Malawian adults contains abundant antibody levels to NTS [32]. All except one S. Typhimurium isolate (0.9%, 1/114) underwent a reduction in viable bacterial counts over the 180 minute time course of the assay, and so were designated ‘sensitive’ to antibody-mediated killing. Overall median Log10 reduction in viable bacteria after 180 minutes was 2.9 for S. Typhimurium. Indeed 50% (57/114) S. Typhimurium were highly susceptible to killing, undergoing a 3.0 Log10 reduction. In contrast S. Enteritidis as a group were less susceptible to antibody-mediated killing than S. Typhimurium, being killed by a median of 1.2 Log10 (p<0.0001, Mann Whitney test). However, all S. Enteritidis were sensitive to killing. A small proportion (10.3%, 6/78) was killed by a full 3.0 Log10.


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)

SBA results of STm and SEn isolates with Malawi serum pool.Bacterial colony forming units (CFU) were counted at time 0 (T0) and after 3 h (T180) incubation of bacteria in 45 μL undiluted serum (final bacterial concentration 1×106 CFU/ml). Killing/growth was determined by Log10 (CFU at T180)-Log10 (CFU at T0). Strains that could grow (Log10 change >0) were considered “resistant”, strains that were killed (Log10 change <0) were considered susceptible. Dashed/continuous line indicates median Log10 change of STm (-2.9) and SEn (-1.2) isolates, respectively.
© Copyright Policy
Related In: Results  -  Collection

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

pntd.0003573.g001: SBA results of STm and SEn isolates with Malawi serum pool.Bacterial colony forming units (CFU) were counted at time 0 (T0) and after 3 h (T180) incubation of bacteria in 45 μL undiluted serum (final bacterial concentration 1×106 CFU/ml). Killing/growth was determined by Log10 (CFU at T180)-Log10 (CFU at T0). Strains that could grow (Log10 change >0) were considered “resistant”, strains that were killed (Log10 change <0) were considered susceptible. Dashed/continuous line indicates median Log10 change of STm (-2.9) and SEn (-1.2) isolates, respectively.
Mentions: SBA results using the serum pool demonstrated a marked difference in susceptibility to antibody-mediated killing among individual isolates and a clear difference in susceptibility between S. Typhimurium and S. Enteritidis isolates (Fig. 1, and see S2a and S2b Table for supporting information).). We have previously demonstrated that this killing is through the antibody-dependent complement-mediated mechanism and requires the presence of specific antibodies and intact complement function [26]. We have also demonstrated that the control sera used in this assay from healthy Malawian adults contains abundant antibody levels to NTS [32]. All except one S. Typhimurium isolate (0.9%, 1/114) underwent a reduction in viable bacterial counts over the 180 minute time course of the assay, and so were designated ‘sensitive’ to antibody-mediated killing. Overall median Log10 reduction in viable bacteria after 180 minutes was 2.9 for S. Typhimurium. Indeed 50% (57/114) S. Typhimurium were highly susceptible to killing, undergoing a 3.0 Log10 reduction. In contrast S. Enteritidis as a group were less susceptible to antibody-mediated killing than S. Typhimurium, being killed by a median of 1.2 Log10 (p<0.0001, Mann Whitney test). However, all S. Enteritidis were sensitive to killing. A small proportion (10.3%, 6/78) was killed by a full 3.0 Log10.

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