Rggs are a group of transcriptional regulators with diverse roles in metabolism and virulence. Here, we present work on the Rgg1518/SHP1518 quorum sensing system of Streptococcus pneumoniae. The activity of Rgg1518 is induced by its cognate peptide, SHP1518. In vitro analysis showed that the Rgg1518 system is active in conditions rich in galactose and mannose, key nutrients during nasopharyngeal colonization. Rgg1518 expression is highly induced in the presence of these sugars and its isogenic mutant is attenuated in growth on galactose and mannose. When compared with other Rgg systems, Rgg1518 has the largest regulon on galactose. On galactose it controls up‐ or downregulation of a functionally diverse set of genes involved in galactose metabolism, capsule biosynthesis, iron metabolism, protein translation, as well as other metabolic functions, acting mainly as a repressor of gene expression. Rgg1518 is a repressor of capsule biosynthesis, and binds directly to the capsule regulatory region. Comparison with other Rggs revealed inter‐regulatory interactions among Rggs. Finally, the rgg1518 mutant is attenuated in colonization and virulence in a mouse model of colonization and pneumonia. We conclude that Rgg1518 is a virulence determinant that contributes to a regulatory network composed of multiple Rgg systems.

Microbes acquire unique lifestyles under different environmental conditions. Although this is a widespread occurrence, our knowledge of the importance of various host signals and their impact on microbial behavior is not clear despite the therapeutic value of this knowledge.

Salmonella typhi is one of the most common causes of typhoid fever in Iraq. The aim of this study was to test the synergistic between different tests for the diagnosis of S. typhi . It was found, there are ability for preparing local Media which can be used instead of Blood agar for diagnosing typhoid fever by using dates, alfalfa and fish extractors. Both fish and dates extractors were used to prepare a local medium as well as alfalfa and fish. The results showed that dates -fish medium are more efficient than blood agar and alfalfa -fish medium to isolate S. typhi. When contrasting culture results with Widal test data of laboratories , it had shown differences in these results because only (57)% from Widal test was confirmed by culture. When Widal test results were evaluated which is done in different health analysing laboratories in Nineveh Governorate by using Widal test (dilution method) the results showed great differences of results whether result type (positive or negative) or kind of antigens which showed positive results. Leukocyte count was done as a test to enhance the diagnosis of this microbe, it was clear that there is a relation between typhoid fever and decreasing white blood cell count.