Streptococcus pneumoniae strain:Spn1 Genome sequencing and assembly. Streptococcus pneumoniae strain:Spn1

Pneumococcal diseases caused by Streptococcus pneumoniae are a major public health concern worldwide due to antibiotic resistance. Here, we report that a clinical isolate of S. pneumoniae Spn1 can kill the larvae of silk moth, Bombyx mori within 24 h and dead larvae turned black due to melanization. The phenoloxidase (PO) activity was increased within 6 h of infection. The bacterial load started to increase within 9 h post-infection along with a reduction of viable hemocytes after 6 h p.i. Ampicillin, ceftriaxone, tetracycline, imipenem, and erythromycin showed therapeutic effect in infected larvae, although the bacterial strain showed resistance towards erythromycin in vitro. The antimicrobial peptide (AMP) genes, Bmdefensin-A and Bmdefensin-B were significantly upregulated in fat body after bacterial infection. Mammalian Toll-like receptors, TLR2 and TLR4 are upregulated during S. pneumoniae infection in mammals and we found that their Bombyx homologs, BmToll-2 and BmToll-9, respectively, were upregulated in both fat body and trachea either after direct injection of bacteria into hemolymph or after topical application of bacteria. Our study showed that the larvae of Bombyx can be a useful infection model not only to study S. pneumoniae pathogenicity but also to screen for compounds with antimicrobial properties against this important human pathogen.