Conclusions
After 30 years, the classification of B. thuringiensis strains
based on H serotyping remains an effective method for distinguishing
strains. This classification is based on stable and distinctive
features. Therefore, H serotyping of B. thuringiensis isolates
secluded from feces of 20 animal species was performed in laboratory
conditions. Of the 190 isolates, 166 represented 14 mammalian species,
20 were obtained from 5 species of reptiles, as well as from 4 species
of birds. The obtained bacterial populations were assigned to 8 H
serotypes: H31, H6, H3abc, H7, H4ab/43, H5ab/21, H8ab, and H9. The
studied populations consisted of 3 atypical, as well as 65 non-verified
isolates. Among the 8 serotypes studied, the most common was H3abc
(82.0% of cases) out of 122 serotyped samples, less common was H6
(8.5%), the remaining 6 serotypes accounted for no more than 1.5%.
Parasporal inclusions in true fecal isolates can be divided into 4
different groups in terms of morphology. These included bipyramidal,
spherical, or irregularly shaped. Of the 190 isolates tested, 125
(65.8%) formed bipyramidal inclusions, and 63 (33.2%) were spherical.
All H3abc isolates demonstrated bipyramidal inclusions. The same was
true for H8ab and H7 isolates. Fecal isolates of B. thuringiensiscontaining sporulated cultures have been analyzed for oral toxicity
against insect larvae to elucidate the properties of the obtained
serotypes. Of the 190 isolates tested, 133 (70.1%) showed insecticidal
activity, 128 killed B. mori and Aedes sp. Other 3
isolates showed effects only on B. mori , and 2 showed effects
only on Aedes sp., proving their biological selectivity against
laboratory test objects. All H3abc isolates with bipyramid inclusions
were double-toxic to silkworms and mosquitoes. In addition, all H5ab/21
isolates exhibited dual toxicity. Monotoxic B. thuringiensisagainst Aedes sp. were recorded only in cultures of the spherical
group. These samples belonged to the H4ab/43 serotype.
Funding. This research did not receive any specific grant from
funding agencies in the public, commercial, or not-for-profit sectors.
Declarations of interest. None.
Data Accessibility. All data generated or analysed during this
study are included in this published article.
Acknowledgments. Not applicable.
Ethics approval . The authors declare that the work is written
with due consideration of ethical standards. The study wasconducted in
accordance with the ethical principles approved by the Ethics Committee
of Federal State Budgetary Educational Establishment of Higher Education
“Sechenov First Moscow State Medical University” (Protocol №13 of
13.09.2022).
Consent to participate . Informed consent was signed by
participants.
Consent for publication . Not applicable
Authors’ contributions . Both authors contributed to the study
conception and design. Material preparation, data collection and
analysis were performed by ES and AA. The first draft of the manuscript
was written by ES and AA. All authors read and approved the final
manuscript.