V. Microbiology of water
A. Waterborne microbial pathogens
B. Indicator bacteria for drinking water
C. Other indicators for drinking and
recreational water
A.Waterborne microbial pathogens
Microbiology review:
 Microbes
in water
include:
– Bacteria
– Virus
– Protozoa
 A few microbes (pathogens)
are capable of causing
disease, and may be
transmitted by water.
Waterborne pathogens:
 Some
common pathogens:
 Salmonella
typhi
 Escherichia coli
 Vibrio cholera
 Pseudomonas aeruginosa
 Shigella spp.
 Cryptosporidium
 Giardia lamblia
 Norwalkvirus
Cryptosporidum and
cryptosporidiosis
Cryptosporidium parvum
Crypto “Ooc
Giardia lamblia
(giardiasis)
Original image by Arturo Gonzalez, CINVESTAV, Mexico. Used with permission of Javier Ambrosio,
UNAM, Mexico
Giardia lamblia
 Giardia
lamblia
trophozoites live in the
small intestine of the
host.
 The trophozoites
average about 15 µm in
length, have a distinct
"tear-drop" shape and
two nuclei at the anterior
end
Giardia lamblia troph. The two nuclei are easy to see in this image. (Original image from a Japanese
language site tentatively titled "Internet Atlas of Human Parasitology."
B. Indicator bacteria for
Drinking Water:
 Indicator
microorganisms are used to
indicate an increased risk of pathogen
contamination due to fecal contamination.
 Indicator microbes should be:
– Always present when feces/sewage is present
– Always absent when feces/sewage is absent
– Survives longer in water than any of the
pathogenic species
– Easily isolated and identified.
Indicator bacteria:
 Coliform
bacteria (E. coli-like) are the
most often used indicator bacteria for
water quality assessment in the U.S.
Characteristics of coliforms:
 Aerobic
or facultative,
 Gram-negative,
 Non-spore forming,
 Bacilli,
which
ferment
lactose to form acid
and/or gas within
48 hours at 35 oC.
More specific coliforms:

Coliforms are often found naturally
in soil, water, plants, etc.

Fecal coliforms are a more specific
coliforms that usually come from
feces.
E.
coli is the most
specific indicator
Guidelines and methods for
enumerating coliforms:
 EPA guidelines
for coliforms in
drinking water are < 1 CFU/100
ml.
 Tests used to isolate and
enumerate coliforms in water
include:
– m-Endo media
– m-FC media
– MUG media
C. Other indicators for drinking and
recreational water
 Limitation
of Total coliform as
drinking water microbial
indicator
– Ubiquitous.
– Less resistant to traditional
disinfection.
– Proliferate in the biofilms of
water distribution systems
 Limitation
of Fecal coliforms
– Klebsiella pneumoniae
– Less resistant to traditional disinfection.
 Limitation
of E. coli
– Less resistant to traditional disinfection.
Microbial Indicators for
Recreational Water
Total
coliform?
Fecal coliform?
– Average 200 MPN/100 ml
E.
Coli (fresh water)?
– Average 126 MPN/100 ml.
Enterococci
(salt
water)
– Average 35 MPN/100 ml.