This work proposes a novel and highly-sensitive optical device to sense the presence of different pathogenic bacteria in drinking water. The initial sensing structure consists of a decladded multimode fiber with a higher order Bessel-Gauss beam shining on it. It relies on the notion of intermodal interference, where the transmitted output power varies with changeable cladding refractive index because of different pathogenic bacteria as present in the water sample. For the designing of bacteria sensor, such coalescence of higher order Bessel-Gauss beam along with a decladded multimode fiber has never been mentioned in any of the existing literatures. The device’s sensing behavior was substantiated using a finite difference Eigenmode analysis in Mode solution software (commercially available from Lumerical Inc., Canada). By selecting the sensing length as 7 cm, the obtained spectral sensitivity of 1179 dB/RII is 3.78 times superior to the typical Gaussian sensor. Therefore such an emerging beam known as higher-order beam Bessel-Gauss offers new prospects in the biosensing field.