Objective: All characteristics of microorganisms colonized in host including their growth, virulence and antibiotic susceptibilities are controlled by host conditions. In our study, it has been aimed to determine the effects of estradiol, insulin, norepinephrine as host factors on the growth of various microorganisms (uropathogenic Escherichia coli C7, Candida albicans SC5314, Enterococcus faecalis ATCC 29212, Methicillin resistant Staphylococcus auerus (MRSA) ATCC 43300 and Pseudomonas aeruginosa ATCC 27853) in vitro setting.

Material and Methods: For this purpose, microorganisms were grown in different culture media (Tryptic Soy Broth and Sabouraud Dextrose Broth) supplemented with/without various concentrations of hormones. Growths of microorganisms were measured at 4^th, 6^th and 24^th hours using a spectrophotometer. Statistical analysis of growths were determined by using twoway ANOVA Bonferroni post-test.

Results: All hormone concentrations were shown to suppress the growth of E. faecalis significantly after 6 hours of incubation. The growth of C. albicans was found to be significantly altered (reduced in the presence of 200 μU/mL insulin and 20 pg/mL estradiol; increased in the presence of 150 pg/mL and 400 pg/ mL estradiol & 1700 pg/mL, 7500 pg/mL and 40000 pg/mL norepinephrine) in the presence of different hormones. However, hormones tested were shown to exert no effect on the growth of MRSA, P. aeruginosa and UPEC (p>0.05).

Conclusion: With demonstration of the effects of mammalian hormones also on the behaviour of microorganisms, it has been emphasized that they determine the pathogenicity of infectious diseases as an environmental factor. Our results have supported that, different concentrations of hormones have various effects on growth of microorganisms. All these, and similar studies have showed that, hormones determine the infectious process directly in human beings.