Environmental Health Microbiology
ENVR 421
Lecture 1
Mark D. Sobsey
Microbes and the Environment
• Microbes are fundamental and essential to life on earth
• Most microbes in the environment are harmless or beneficial
• A small proportion of microbes are capable of causing
disease in humans and/or other hosts
– Some are “frank” pathogens and almost always have the potential to
cause illness
– Others are “opportunistic” pathogens and only cause illness in
compromised hosts or unusual conditions of exposure
– Yet others are capable of causing illness when they get into parts of
the body by unusual circumstances that are normally unavailable to
microbes (e.g., into deep tissues via wounds)
• Microbes are almost everywhere on the planet and the more
we look the more places we find them
Routes or Pathways of Exposure for
Environmentally Transmitted Infectious Diseases
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Water
Wastes
Food
Fomites
Vectors
– many human pathogens have animal reservoirs;
zoonoses
• Air
• Soil
• Sediment
Pathogen-Human/AnimalEnvironmental Relationships
• Many human pathogens are potentially
transmitted by multiple environmental routes
• Some pathogens exist in the environment
independent from human hosts
– their existence and perpetuation is not dependent
on human or (for some) even animal hosts
• Other pathogens depend exclusively on
human for their existence and perpetuation
– Viruses: smallpox (Variola) virus (eradicated);
poliovirus
– Bacteria: Shigella spp.; Salmonella typhi
– Parasites: Ascaris lumbricoides (round worm)
History of Microbiology and Infectious Diseases:
Role of Water in Cholera Transmission - London
• Water, wastes and microbes are traditional/historical concerns
• Sir John Snow: cholera in London and the Broad Street pump
– A key historical event in environmental health, epidemiology,
infectious disease, water hygiene, environmental engineering
and GIS: he did it all!
– Developed a population-based approach to track the spread of
cholera in individual London boroughs; source was unknown
– Plotted the distribution of reported cases on a map
– In one London borough the source was water polluted by
sewage, which entered the Thames above the water intake.
– In another it was one water pump
• Snow ordered the handle to be removed from the "Broad Street
Pump“; locally the epidemic subsided.
• Explained the etiology of cholera and the mechanism of its
transmission via contaminated water.
Sir John Snow and his Maps of the
Water Plants of London
http://www.ph.ucla.edu/epi/snow.html#BROAD
Sir John Snow’s 1854 Map of the
Broad Street Pump Outbreak
Cholera cases, each marked by a hash,
were clustered around the Broad Street
Pump and were associated with drinking
water from this pump
Microbiology and Infectious Diseases
• Infectious disease risks from water, poor sanitation and
hygiene, food and air are still with us in the developed and
developing world
• Global Water Supply and Sanitation Assessment 2000
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2.4 billion people have inadequate sanitation
1.1 billion people have inadequate/unsafe water
4 billion cases of diarrhea every year
2.2 million deaths from diarrheal disease every year
Most illness and death in children <5 years old
Less services in rural than in urban areas
Urban settlement/slums remain a problem
In the developing world wastewater treatment is rare
Water losses in large urban systems is typically 40%
• Millennium Development Goals call for halving by 2015 the
number of people lacking sustained access to safe water
– a key goal for reducing World poverty
Global Burden of Infectious Diarrheal
Disease and the Role of Water
• Burden of infectious diarrhea is higher in developing than in
developed countries
– Developed: 1 illness per person per year
– Undeveloped: about 5 illnesses per person per year
• The attributable fraction of diarrheal illness for different
exposure routes or sources may not be very different in
developed versus developing countries:
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1/4th contact
¼ water
¼ food
1/4 other
• Most waterborne disease is caused by microbes – not chemicals
Classes or Categories of Pathogenic Microorganisms:
The Microbial World
Viruses: smallest (0.02-0.3 µm diameter); simplest:
nucleic acid + protein coat (+ lipoprotein envelope)
Bacteria: 0.5-2.0 µm diameter; prokaryotes; cellular;
simple internal organization; binary fission.
Protozoa: most >2 µm- 2 mm; eucaryotic; uni-cellular;
non-photosynthetic; flexible cell membrane; no cell
wall; wide range of sizes and shapes; hardy cysts
Groups: flagellates, amoebae, ciliates, sporozoans
(complex life cycle) and microsporidia.
Helminths (Worms): multicellular animals; some are
parasites; eggs are small enough (25-150 µm) to pose
health risks from human and animal wastes in water.
THE MICROBIAL WORLD:
SIZES OF MICROBES
Viruses
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smallest (0.02-0.3 micrometers diameter
simplest (nucleic acid + protein coat (+ lipoprotein envelope)
spherical (icosahedral) or rod-shaped (helical)
no biological activity outside of host cells/or host organisms
– obligate intracellular parasites; recruit host cell to make new
viruses, often destroying the cell
• non-enveloped viruses are most persistent in the environment
– protein coat confers stability
• enteric viruses are most important for environmental health
– transmitted by direct and indirect contact, fecally contaminated
water, food, fomites and air.
• respiratory viruses also important
– transmitted by direct and indirect contact, air and fomites (some
by water and food, too).
ENTERIC VIRUSES: ~25-100 nm diameter
Nucleic acid + protein coat (+envelope)
Nucleic acid:
•DNA or RNA
•single or doublestranded
•1 or several segments
•Capsid (protein coat):
• multiple copies of 1 or
more proteins in an array
Envelope:
•lipid bilayer membrane
+ glycoproteins)
•typically acquired from
host cell membranes
Enteroviruses:
~27-30 nm diameter; singlestranded RNA; icosahedral protein coat (capsid)
Human Rotavirus: ~75 nm diameter;
double-layered capsid; double-stranded, segmented RNA
ADENOVIRUSES: ~80 nm diameter; double-stranded
DNA; protein coat with attachment fibers
Procaryotes: Bacteria and Others
Cellular organisms
Simple internal organization
Multiply by binary fission
Diameter ~0.5-1.0 micrometer
Envelope: cytoplasmic membrane, cell wall & capsule
(polysaccharide)
Some have appendages:
flagella: for locomotion
pili:
• attachment to other cells for genetic transfer;
• virus receptor site
Pathogenic Bacteria
Pathogenic bacteria possess virulence properties in the form of
structures or chemical constituents that contribute to
pathophysiology
– Outer cell membrane of Gram negative bacteria:
endotoxin (fever producer)
– Exotoxins
Pili: for attachment and effacement to cells and tissues
Invasins: to invade cells
Some bacteria make spores:
– highly to physical and chemical agents and
– very persistent in the environment
Enteric and respiratory bacteria are important in environmental
health
Escherichia coli cells: ~0.5 x 1.0 micrometers
Typical rod-shaped bacteria:
fecal indicator and pathogenic strains
Procaryotic Cell (left) and Eucaryotic Cell (right)
Unicellular Eucaryotes: The Protists
• Complex internal organization:
– organelles: nucleus, mitochondria, etc.
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Wide range of sizes; 2 micrometers and larger
Protozoa
• Important group of protists for environmental health
• Uni-cellular; non-photosynthetic; flexible cell
membrane; no cell wall
• Wide range of sizes and shapes; 2 micrometers to 2
mm
– flagellates
– amoeba
– ciliates
– sporozoans (complex life cycle)
– microsporidia
Cryptosporidium parvum oocysts: ~5 m diameter
Acid fast stain of fecal preparation
Giardia lamblia: flagellate protozoan parasite
Giardia lamblia cyst: ~10 x 8 micrometers
More Protists: Fungi
Fungi (yeasts and molds):
•non-photosynthetic
• immotile;
•rigid cell wall
Molds:
•grow as branched, interlacing
chains or filaments (hyphae)
called mycelia
•Yeasts:
• do not form mycelia
•grow as single cells that bud
•sexual reproduction possible
Mitospores (conidia) of
Penicillium, one of the
asexual Ascomycota
Yeasts
More Protists: Algae
• Photosynthetic
• Rigid cell wall
• Wide range of
sizes and shapes
Nostoc
– 2 micrometers and
larger
Anabaena and Aphanocapsa
Helminths (Worms)
• Multicellular animals
• Some are human and/or animal parasites
• Eggs are small enough to pose environmental
health problems from human and animal excreta in
water, food, soil, etc.
• Several major groups:
– Nematodes (roundworms): ex. Ascaris
– Trematodes (flukes; flatworms): ex.
Schistosomes
– Cestodes (tapeworms): pork and beef
tapeworms
• Most helminthic disease is not waterborne, but it is
associated with water contact, food, and exposure
to fecal wastes and fecally contaminated soil.
Roundworm:
Ascaris lumbricoides
Roundworms: Hookworms
Recommended Readings
• Relevant material in any microbiology text
• Indicators for Waterborne Pathogens, National Research
Council, National Academy of Sciences, National Academy
Press, Washington, DC, 2004.
– Chapters 1, 3 and 4
• Water Quality: Guidelines, Standards and Health. 2001. L.
Fewtrell and J. Bartram, eds., IWA Publishing, London, for WHO,
Geneva.
– Chapter 4, 5 and 13
• Assessing microbial safety of drinking water: Improving
approaches and methods, 2003. A. Dufour, M. Snozzi, W. Koster,
J. Bartram, E. Ronchi and L. Fewtrell, eds., IWA Publishing,
London for WHO, Geneva.
– Chapters 1, 2 and 8