Microbiology research has been and continues to be, central to meeting many of the current global aspirations and challenges, such as maintaining food, water and energy security for a healthy population on habitable earth.
The epidemiological history of waterborne diseases after the 1970s is marked by the emergence of enteric viruses and protozoans. Many of them are resistant to conventional chlorination and have thus been involved in waterborne outbreaks. Other new pathogens include environmental bacteria capable of growing in water supply networks, such as Legionella spp., Aeromonas spp., Mycobacterium spp. and Pseudomonas aeruginosa. These new epidemiological data have questioned the ability of conventional treatment to provide a safe water supply and the use of marker organisms such as coliforms to monitor the efficiency of water treatment.
It is estimated that there are 1407 species of pathogens infecting humans, and 177 of the species are considered emerging or reemerging pathogens. These pathogens include bacteria (538 species), viruses (208 types), fungi (317 species), parasitic protozoa (57 species), and helminths (287 species) (Woolhouse, 2006). Infection of susceptible hosts may sometimes lead to overt disease. The development of the disease depends on various factors, including infectious dose, pathogenicity, host susceptibility, and environmental factors. One important factor is the minimal infective dose (MID) which varies widely (a few viruses or oocysts to 107 bacterial cells) with the type of pathogen or parasite (Table 1.3; Bitton, 2011). Some organisms, however, are opportunistic pathogens that cause disease, mostly in immunocompromised individuals (e.g., infants, the elderly, patients on antimicrobial chemotherapy, HIV, or cancer patients.
Several pathogenic microorganisms and parasites and indigenous microorganisms are commonly found in water supplies and may end up in drinking water.
The three categories of pathogens generally encountered in aquatic environments are
1.Bacterial Pathogens: Some of these pathogens (e.g., Salmonella, Shigella, Vibrio cholerae) are enteric bacteria. Others (e.g., Legionella, Mycobacteriumavium, Aeromonas) are indigenous aquatic bacteria.
2. Viral Pathogens: They are also released into aquatic environments but are unable to multiply outside their host cells. Their MIDs are generally lower than for bacterial pathogens.
3. Protozoan Parasites: They are released into aquatic environments as cysts oroocysts which are quite resistant to environmental stress and to disinfection inwater and wastewater treatment plants.