Environmental Engineering Reference
In-Depth Information
Pathogens
Faecal indicator organisms
Microbial quality is usually assessed by measur-
ing 'faecal indicator bacteria' (also referred to as
faecal indicator organisms, or FIOs). Thermoto-
lerant coliforms (also termed faecal coliforms),
Escherichia coli and intestinal enterococci (pre-
viously termed faecal streptococci) are generally
harmless bacteria (although E. coli O157 is path-
ogenic) that are present in high numbers in
faecal material and are the most commonly
examined FIOs. Thus, their presence in water
samples is used to indicate the presence of faecal
pollution and the possibility that faecally asso-
ciated pathogens may also be present (see below).
Other, less frequently utilized, FIOs include
Clostridium perfringens and coliphage organ-
isms. The ecology and environmental survival
characteristics of bacterial, viral and protozoan
pathogens (see below) vary and so there is no
single ideal indicator organism (Savichtcheva
and Okabe 2006).
Pathogens are infectious microorganisms that can
cause infection and disease. They can be classified
as bacterial (e.g. Salmonella), protozoal (e.g. Cryp-
tosporidium), viral (e.g. enteroviruses), fungal (e.g.
Candida) or helminth (e.g. Trichobilharzia).
Pathogens may be introduced to the water as
a result of contamination (often from faecal
material) or may be naturally present in the
environment (i.e. autochthonous). The pathogens
identified in the literature review are outlined by
flood component in Table 21.1. Pathogens present
in the water as a result of contamination generally
do not grow in the environment, and thus con-
centrations decrease with time. Those naturally
present in the environment can increase in num-
bers in flood waters. The pathogens identified in
Table 21.1 reflect, to a large degree, those micro-
organisms for which routine tests are available.
Thus, the absence of a 'yes' for any entry may, in
many cases, mean that the pathogen has not been
Table 21.1
Pathogens by flood component
Flood component
UK
literature
Pathogen
Rivers
Sewage
CSO
Urban non-foul
Roofs
Rural diffuse
Bacteria
Aeromonas
yes
yes
Campylobacter
yes
yes
yes
yes
yes
Escherichia coli O157
yes
Helicobacter pylori
yes
yes
Legionella
yes
Listeria
yes
yes
yes
MAC
yes
yes
yes
Pseudomonas
yes
yes
yes
yes
yes
Salmonella
yes
yes
yes
yes
yes
yes
Staphylococcus
yes
Yersinia
yes
yes
Protozoa
Cryptosporidium
yes
yes
yes
yes
yes
yes
Giardia
yes
yes
yes
yes
yes
yes
Viruses
Adenoviruses
yes
yes
Astrovirus
yes
yes
Enterovirus
yes
yes
yes
Hepatitis A
yes
yes
Norovirus
yes
yes
Rotavirus
yes
yes
CSO, combined sewer over
ows; MAC, Mycobacterium avium complex.
