Waterborne Pathogens: Bacteria

February 9th-11th, 2010

Bacterial pathogens in water

• Important causes of waterborne disease• We don’t always know the distribution of

causes of diarrheal disease, but bacteria are major contributors

• Can be endemic or epidemic• Epidemic disease is often found where

people are crowded, hygiene and sanitation are poor– Disaster situations– Displaced populations

Categories of waterborne disease

• Diseases contracted by ingestion of contaminated water

• Most are diarrheal diseases, but not all

• The largest burden of these diseases is in countries that lack water infrastructure

• But they are NOT gone even in countries that have infrastructure

Categories of waterborne disease

• Diseases contracted by ingestion of contaminated water– Escherichia coli– Shigella spp.– Vibrio cholerae– Salmonella typhi

Categories of waterborne disease

• Diseases spread by contact with contaminated water– Bathing, wading– Contact with floodwaters– Pathogen lives naturally in the water– Leptospira

• Diseases spread by inhalation of contaminated water– Aerosols– Legionella

Escherichia coli

• Are both commensal (harmless) and pathogenic types

• There are several distinct types of pathogenic E. coli

• Pathogenic process differs between them

• Some have toxins, some other virulence factors

• Fecal-oral and person-to-person transmission

Escherichia coli

• Gram negative rods• Identified by O and H antigens• O157:H7 strains are identified by

their inability to break down sorbitol

Escherichia coli

• Example: O157:H7• Belongs to the enterohemorrhagic group• Cattle are the major reservoir

– Found in their intestinal tracts

• Toxin producer– Shiga and Vero toxins

• Occurs as both a foodborne and waterborne pathogen

• Major risk group is children: hemolytic uremic syndrome

Shigella

• Bacterial dysentery• Four species in the genus

– dystenteriae– flexneri– boydii– sonnei

• Estimated 600,000 deaths per year

Shigella

• Gram negative rods• Distinguished from E. coli by their

inability to ferment lactose

Shigella

• Profuse diarrhea and dehydration• Humans are the reservoir• Fecal-oral and person-to-person

transmission• A disease of crowded conditions and

poor hygiene• Lack of sufficient clean water for

adequate hygiene• Handwashing is a crucial control

measure

Vibrio cholerae

• Cholera• There are other species that are

causes of foodborne disease• Cause of epidemic diarrheal disease• Crowding, poor sanitation, lack of

water treatment• Currently: Zimbabwe• Reservoir: marine environments

Vibrio cholerae

• Gram negative curved rods• Distinguished by their salt tolerance

and ability to ferment sucrose• Divided into biotypes; epidemic

causes are O1 and O139

Vibrio cholerae

• Fecal-oral and person-to-person transmission

• There are asymptomatic carriers who can transmit disease

• Bacteria produces a toxin that causes severe fluid and electrolyte loss from the intestine

• Can kill by severe dehydration• Characteristic “rice water” stool• Treatment: Oral rehydration therapy

Salmonella typhi

• Typhoid fever• Other species cause foodborne

disease• Typhoid can be food or water borne• Mostly in developing world• 200,000 deaths per year

Salmonella typhi

• Gram negative rods• Distinguished by their inability to

ferment lactose

Salmonella typhi

• Fecal-oral and person-to-person transmission

• Humans are the reservoir• Asymptomatic people in a chronic

carrier state can spread disease• Vaccination is only done for travelers• Again, a disease of inadequate water

treatment and sanitation

Leptospira

• Leptospirosis• Systemic bacterial infection; can be

fatal• Zoonotic disease• Several pathogenic species• Infection enters through broken skin

– Often from contact with contaminated natural water sources

– Contact with floodwaters after disasters also a common transmission route

• Very rarely person-to-person

Leptospira

• Spirochete• Fastidious (difficult to culture)

Leptospira

• Endemic in tropical areas– Both urban and rural

• Occupational hazard for rice and sugarcane field workers

• Animals are reservoirs– Often dogs and rats– Shed organism into water in their urine

Legionnaire’s Disease

• Legionella pneumophila• Respiratory and systemic disease• Bacterium lives in water• Inhalation of water droplets leads to

disease

Legionnaire’s Disease

• Gram negative bacilli• Need cysteine in the agar to support

their growth

Legionnaire’s Disease

• Reservoirs: potable water systems– Cooling towers– Water distribution systems– Fountains – Humidifiers

• Like warm, stagnant water (up to 42°C)• Significant hospital-acquired pathogen

– Can live in hospital distribution systems– Aersolized by showers– Immunocompromised patients are susceptible

• Control by superchlorination and high temp (>50°C)

Control of waterborne bacteria

• Drinking water:• Prevention of water contamination

– ADEQUATE SANITATION

• Barrier methods– Treatment trains– Filtration– disinfection