Multi-serotype outer membrane vesicles of Shigellae confer passive protection to the neonatal mice against shigellosis
Authors: Soma Mitra
Manoj K Chakrabarti
Hemanta Koley
Journal: Vaccine (2013)
Discipline: IMMUNOLOGY
Keywords: Immunization; Outer membrane vesicles; Shigella; Multi-serotype; Passive protection
Affiliations: Division of Bacteriology, National Institute of Cholera and Enteric Diseases, P-33, C.I.T. Road, Scheme XM, Beliaghata, Kolkata 700010, India.

Abstract:  Recently, we have demonstrated, immunization of adult female mice with outer membrane vesicles (OMVs) of Shigella boydii type 4 protected their offspring passively from shigellosis. In our present study, we have advanced our research by formulating multi-serotype outer membrane vesicles (MOMVs), mixing the OMVs of Shigella dysenteriae 1 Δstx, Shigella flexneri 2a, 3a and 6, S. boydii type 4 and Shigella sonnei to achieve a broad spectrum protection against shigellosis. Adult mice were immunized orally with 50 μg of MOMVs, four times at weekly intervals. Immunological parameters were observed at various time points, before, during and after immunization, in adult mice. Passive protection was examined in their offspring by measuring protective efficacy and studying intestinal colonization, after challenging with various Shigella strains. Immunized dams exhibited a consistent broad spectrum antibody response. 3-4 day-old offspring of immunized dams showed significant long term passive protection against wild type S. flexneri 2a, 3a, and 6, S. boydii type 2 and S. dysenteriae 1. Their stomach extracts, essentially containing mother's milk, have also exhibited significant levels of anti-MOMVs immunoglobulins. In conclusion, MOMVs formulation represents an easy, safe immunization strategy that was found suitable to provide complete passive protection to the neonatal mice against all four serogroups of Shigellae. It could be exploited for the development of a novel non-living vaccine against human shigellosis in near future. 

Retracted: No

PubPeer comments:
 This report presents impossible statistics. A Mann-Whitney test with a perfect separation between groups (U = 0) will result in a p value that is an order of magnitude larger than the authors present (checked with SPSS). It is impossible to get p = 0.002 in this test with n = 4. Moreover, the authors are working with paired data, which violates the basic assumption for the test. ![file] The authors claim in their abstract (and text) that the treatment changed a number of parameters. Yet, this is the only statistically significant difference found in the report. It seems the claims made by the authors are simply not supported by their data. , 
 Its paired data so the test should be Wilcoxon signed rank. In R for perfect separation between groups I get: wilcox.test(c(1:4), c(5:8), paired=F, exact=T, correct=F) tWilcoxon rank sum exact test data: c(1:4) and c(5:8) W = 0, p-value = 0.02857 wilcox.test(c(1:4), c(5:8), paired=F, exact=F, correct=F) tWilcoxon rank sum test data: c(1:4) and c(5:8) W = 0, p-value = 0.02092 wilcox.test(c(1:4), c(5:8), paired=T, exact=T, correct=F) tWilcoxon signed rank test data: c(1:4) and c(5:8) V = 0, p-value = 0.0455 wilcox.test(c(1:4), c(5:8), paired=T, exact=F, correct=F) tWilcoxon signed rank test data: c(1:4) and c(5:8) V = 0, p-value = 0.0455 So no combination of paired and unpaired or exact or approximate version gives a p value smaller than about .03. ,