## 2 History of Discovery and Definitions of Probiotics  
Experiments for studying effects of bacteria on treating health problems and promoting good health have been performed for a long time. Theodor Escherich has been credited as the first pediatric infectious disease physician and described _Bacterium coli commune_ (now referred to as _Escherichia coli_) in 1886 [9]. While working under Theodor Escherich, Dr. Jozef Brudzinski treated infants for acute infectious diarrhea by using a _Bacillus lactis arogenes_ suspension described in publications from 1899 [10; 11]. Although Elie Metchnikoff [12] believed that intestinal putrefraction can shorten life, he noted the work of Dr. Brudzinski and similar work by Dr. Henry Tissier and recommended people \"to absorb large quantities of microbes\". He believed that lactic bacteria can fight against intestinal putrefraction. He also wrote that Stamen Grigoroff observed many centenarians in Bulgaria, which is a region where yahourth (yogurt) was commonly consumed [12]. The fact that diet affects the types of bacteria that develops within the intestinal tract was first clearly established by Herter and Kendall in 1910, but suggested as early as 1886 by Escherich and Hirschler [13].  
Many of the starter cultures and probiotics now used in yogurt making were first described in the late 1800s or early 1900s. The name \"_Streptococcus_\" was first used in 1874 by Albert Theodor Billroth [14]. _Streptococcus thermophilus_ (later reclassified as _Streptococcus salivarius_ subsp. _thermophilus_ by Farrow and Collins in 1984 [15] but revived back to _Streptococcus thermophilus_ by Schleifer et al. in 1991 [16]) was described by S. Orla-Jensen in 1919 [17]. In 1901, Martinus Beijerinck proposed the genus _Lactobacillus_ to include Gram-positive, fermentative, facultatively anaerobic, non-sporeforming bacteria [18]. Stamen Grigoroff discovered Bulgarian bacillus (now _Lactobacillus delbrueckii_ ssp. _bulgariacus_) in 1905 [19]. _Lactobacillus acidophilus_ (originally called _Bacillus acidophilus_) was described by Ernst Moro in 1900 [20]. In 1899 and 1900, Henry Tissier first described _Bacillus bifidus communis_, later referred to as _Lactobacillus bifidus_ and now referred to as _Bifobacterium_[21]. He found that _Bifidobacteria_ was the main type of bacteria comprising the gut microflora of breast-fed babies and _Bifidobacteria_ could treat acute gastroenteritis [19].  
Dr. Isaac Carosso recommended to his patients who suffered from gastrointestinal problems to consume yogurt. Afterwards, he started producing yogurt and founded the Danone Company in 1919 [19].  
The term \"probiotic\" (meaning \"for life\") originated in 1953 from Werner Kollath to mean \"active substances that are essential for a healthy development of life\" [22]. Lilly and Stillwell [23] used the term probiotic as \"substances secreted by one organism which stimulate the growth of another\" in 1965. Parker [24] described probiotics as \"organisms and substances which contribute to intestinal microbial balance\" in 1974. Fuller [25] defined probiotics as \"A live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance\" in 1989. A panel from the International Scientific Association for Probiotics and Prebiotics defined probiotic as \"live microorganisms that, when administered in adequate amounts, confer a health benefit on the host\" in 2014 [26].