According to my knowledge, if you want to check the pathogenicity you have either to check at molecular level (by looking for virulent genes sequence or their expression products) or by in-vivo model.........I don't know if there is media for that purpose, some additives to media make them selective for drug-resistance property of the organism ... for example CCCP is added to investigate for carpabenem resistance, in addition to other media for VRE and others

You could test adhesivity and  invasivity properties of your microorganisms by infecting cell lines. Cytotoxicity properties can be verified by extracting toxins from microbial suspensions (by centrifugation followed by surnatant filtration) and inoculating toxin dilutions in wells containing cells; then cell viability can be checked by MTS assay.

At a molecular level you should verify the presence of virulence genes in the microorganism genome and the expression of these genes by reverse transcription Real Time PCR for example. You could look for the presence of virulence proteins by western blotting too, but it's harder when you don't have commercially available antibodies.

Hi Kunal,

First you should know that from where this sample is collected. Then you should check the literature about the source of specimen to check whether it is pathogen or not. Finally based on the commercial media that are available do your culture. so if you have an unknown sample the best way to check  is to do a gram stain to determine the type of bacteria whether it is cocci or bacillus then make a culture on appropriate media like as general on, blood agar, or selective one EMB or MacConkey Agar for gram negative bacteria. Also you can use Thio for fastidious bacteria then use a gram stain. 

For fungi as they can grow on Blood agar you can get another wet or gram stain from them and check them using microscope then use an appropriate fungi media. 

Fungi are no motile and there is a distinct shape and character on blood agar like as shape and colour.  

However, if you want to discover a new bacteria or fungi and share it with us :),  the best way is to use Molecular assay like as PCR.

Good Luck

Dear Kunal, please see the link below:

http://www.sciencedirect.com/science/article/pii/S1075996405000028

Dear Kunal

To test if this isolate is pathogenic  or not you need deferential varieties obtained from the breeders and the pathologists, degree of the resistance of those differentials should be known, and their reaction against the identified pathogenic strains are determined. always the susceptible plant genotype is required to check if the isolate is pathogenic and made disease symptoms or not

Cell cultures, natural / laboratory host inoculation, and molecular tools revealing virulence markers and sequencing can be tried for

if you must know, you should only do Koch's postulates.... and Ruchi Tiwari,  she has the reason....

Pathogenicity is not the same as  virulence....¡¡¡¡¡¡

Please check this reference:

Pak J Biol Sci. 2013 Oct 15;16(20):1204-7.

Pathogenicity test of bacterial and fungal fish pathogens in Cirrihinus mrigala infected with EUS disease.

Abstract

The study was conducted for 8 weeks to determine pathogenic effect of different fish pathogens in Cirrihinus mrigal (C. mrigala) which was infected with EUS disease. The pathogenic organisms (bacteria and fungi) collected from the infected part of the disease fish. Isolation and screening of microbes were carried out with the help of a number of biochemical tests. A total of eight bacterial isolates were obtained from the diseased fish. Out of eight, six bacteria viz., Streptococcus grp Q1, Aeromonas hydrophilla, Shigella spp., Streptococcus faecalis, Cellobiosococcus sciuri, Micrococcus luteus were found to be pathogenic. The fungus, Aphanomyces invadens was also isolated from the diseased fishes. The pathogenicity of disease causing organisms was tested through in vitro and in vivo experiments in different treatments. The result of experiment was found to be significant at level of p < or = 0.05.

In vitro and In vivo pathogenicity tests both can be used for pathogenicity indexing / testing,

Koch Postulate is ok, but nowadays if you know that major determinant of pathogenicity and virulence genes are available then these are also markers of pathogenicity.If we remove these - apathogenic / avirulent pathogen can be made - or of lesser pathogenicity

Pathogenicity tests of fungi or bacteria are done by arficial inoculation of the pathogen inoculum applied on the host surface. Depending on the penetration mechanism  of the pathogen one has to make wounds on the host surface but others that penetrate through natural openings or directly through the epidermis, the inoculum can be applied directly wthout wound. After inoculation, the inoculated plants have to be incubated under favorable conditions for infection (moist chamber, controlled temperature and some times in the dark)

to check the pathogenicity of test isolate of bacteria or fungi you should done artifical inoculation of pathogen inoculun on the host through mechanical injury. its Also depend on what kind of bacterial and fungal sp. there are so many mehod its depend on what king of fungal and bacterial spp.

Pathogenicity tests of fungi or bacteria are done by arficial inoculation of the pathogen inoculum applied on the host surface. Depending on the penetration mechanism  of the pathogen one has to make wounds on the host surface but others that penetrate through natural openings or directly through the epidermis, the inoculum can be applied directly wthout wound. After inoculation, the inoculated plants have to be incubated under favorable conditions for infection (moist chamber, controlled temperature and some times in the dark)

Thanks Kunal for posting this question, which I myself had been trying to get more light on. I am also grateful to all those who made efforts at providing the above answers.

To my understanding the suspected pathogen has to be injected or administered to a susceptible host system and then look for the abnormal symptoms in the form of behavioural, physiological or any other serum biochemical changes. If sacrifice of the host system is possible, the spleen, kidney or liver could be checked for the presence of the pathogen through spread plating on a suitable medium.