Transcript IFH guide on germs in the home

A Simple Guide to
Germs and Disease
June 2005
Microbiology (1)
Microbiology is the study of organisms not visible to the naked
eye, thus requiring the use of a microscope to see them
(i.e. microscopic organisms or sometimes called microbes)
Smallest
Prions
Viruses
Bacteria
Fungi
Protozoa
Largest
Microbiology (2)
What are Germs?
• Germs are microorganisms that are likely to cause disease
• Microorganisms are found throughout the environment. Only
a very small number are pathogenic, i.e. capable of causing
disease, and not all diseases are caused by microorganisms
• Some bacteria live in our gut and help to digest food.
Some yeasts and bacteria are used in baking, brewing
or cheese making
• Bacteria are just one type of micro-organism, alongside viruses,
fungi and protozoa
Germs* - Family Tree
Germs
Bacteria
Gram
Positive
Spore
Formers
Viruses
Gram
Negative
Non-Spore
Formers
Fungi
Enveloped
NonEnveloped
Influenza
HIv
Rotavirus
Poliovirus
SRSV
Protozoa
Giardia
Cryptosporidium
Moulds
Yeasts
Salmonella
E.coli
Campylobacter
Bacillus subtilis
Bacillus cereus Staphylococcus
Listeria
Clostridium
perfringens
*Germs = all potentially harmful micro-organisms
Cladosporium
Aspergillus
Penicillium
Candida
Bacteria (1)
Bacteria are prokaryotes and have a characteristic cellular
organisation. They are simple, small, unicellular organisms, varying
in size between 1-20 um long
Bacteria can be classified by shape:
Spherical (coccus)
e.g. Staphylococcus aureus
Spiral/helical
e.g. Treponema
Rod (bacilli)
e.g Escherichia coli
Bacteria (2)
• Not all bacteria cause disease. Most bacterial species cannot
cause disease. Many even play beneficial roles e.g. producing
antibiotics. Our bodies are covered with commensal bacteria (the
normal flora)
• Even among bacteria that can cause disease, only a few species
are always pathogenic. Many free-living bacteria or members of
the normal flora are potentially pathogenic in certain types of
individual (particularly the immuno-compromised), but are most
of the time harmless
• Consumers tend to be very aware of pathogenic bacteria such as
Salmonella, Listeria and E.coli that have made headlines in
recent years in connection with outbreaks of food poisoning.
They often regard bacteria as modern problems that are more
hazardous than traditional “germs”
Bacterial Classification
The nature of the cell wall determines the classification of bacteria
as either Gram-positive or Gram-negative, as determined by the
Gram stain
• Gram-positive bacteria: cell wall is a thick multi-layer of
peptidoglycan (a mixture of sugars and amino acids)
• Gram-negative bacteria: cell wall is thin and surrounded by
an outer membrane (made up of lipopolysaccharides and lipoprotein)
Lipoteichoic
acids
Outer
membrane
Cell wall
(peptidoglycan)
lipoprotein
Cell membrane
(lipid bilayer)
Gram-positive
Gram-negative
Bacterial Growth (1)
Given good growing conditions, a bacterium grows slightly in
size or length, new cell wall grows through the centre, and
the mother cell splits into two daughter cells.
If the environment is optimum, the two daughter cells may
split into four in 15-30 minutes.
This will continue for some time until the nutrients start to
run out or conditions become unstable.
Conditions are rarely optimum all of the time.
Bacterial Growth (2)
Typical Growth Curve for a Bacteria Population
• Lag Phase
growth is slow whilst they become used to their new environment and
nutrients
• Log Phase
once the metabolic machinery is running, they start multiplying
exponentially, doublingin number every few minutes
• Stationary Phase
as more and more bacteria are competing for nutrients which are
decreasing, growth stops and the number of bacteria stabilises
• Death Phase
toxic waste products build up, nutrients have run out and thebacteria
begin to die
Bacterial Growth (3)
Typical bacterial growth rate
in optimum conditions
Time
N° of bacteria
0
1
20 mins
2
2 hours
64
6 hours
262,144
8 hours
16,777,216
Bacteria divide
by binary fission
Log10 viable organisms/ml
Typical growth curve
for a bacteria population
8.0
6.0
4.0
2.0
and so on ...
Lag
Log
Stationary
0
Time
Death
Bacteria and Temperature
100
HIGH
Minimum
Growth
Temp.
Campylobacter
Cl botulinum A&B
Staph aureus
E. coli
Salmonella
Cl perfringens
Listeria
Cl botulinum E
Bacillus cereus
LOW
LOW
HIGH
Bacteria die if heated
for a sufficient time.
The longer the time, the
greater the destruction
63
40
38
Heat resistance
• Pathogenic bacteria grow best at human body
temperature 37ºC. However the majority will grow
between 15-45ºC
• Non-sporing cells of bacteria are killed at
temperatures above 60ºC. The length of time
ranges depending on the organism
• Boiling kills living cells, but will not kill all
bacterial spores
• Fridges should be set below 5ºC. Some bacteria
such as Listeria monocytogenes can grow
at refrigeration temperatures
Bacteria
grow
quickly
Bacteria
grow
36
15
7
4
0
Bacteria stop growing,
but do not die
Bacteria
Grow
at slower
rate
Bacterial Food Poisoning (1)
Because harmful microorganisms are present everywhere in
the environment, any food can become contaminated if not
properly handled before consumption. There are several
causes of food poisoning (bacteria, viruses, parasites,
chemicals)
• Infective bacterial food poisoning
infections occur when pathogens are ingested via contaminated food and
the bacteria is established in the body, usually growing inside the intestinal
tract and irritating intestines e.g. Salmonella spp. and Campylobacter jejuni.
The infection may involve subsequent growth in other tissues
• Toxic bacterial food poisoning
some bacteria grow in food and produce a toxin within the food
which is then consumed e.g. Bacillus cereus and Staphylococcus
aureus. When the food is consumed viable cells of the bacteria
do not need to be present. Other microorganisms in food may
produce harmful or deadly toxins while growing in the intestinal
tract e.g. Clostridium perfringens, enterotoxigenic Escherichia
coli and enterohaemorrhagic E. coli
Bacterial Food Poisoning (2)
The main causes of food poisoning are:
• preparing foods too far in advance
• not cooking foods properly
• storing foods wrongly; so bacteria grow rapidly
• cross contamination of foods after cooking
• infection from people handling foods due to poor hygiene
Bacterial Food Poisoning (3)
• Campylobacter jejuni
most common cause of diarrhoea
Sources: raw and undercooked poultry and meat, raw milk and untreated water
• Listeria monocytogenes
causes listeriosis, a serious disease for pregnant women,
babies, elderly and immunocompromised individuals
Sources: dairy products, soft cheeses, raw and undercooked meat, poultry and
meat patés
• Salmonella spp.
second most common cause of foodborne illness
Sources: raw and undercooked eggs,undercooked poultry and meat, dairy
products, fruits and vegetables
Bacterial Food Poisoning (4)
• Staphylococcus aureus
produces a toxin that causes vomiting shortly after ingesting
Sources: cooked foods high in protein e.g. cooked meats, custard, cream cakes
• E. coli O157
a bacterium that can produce a deadly toxin
Sources: undercooked hamburger/ minced beef, contaminated cooked meat
and raw milk
• Shigella spp.
poor hygiene causes this bacterium to be easily passed from
person to person
Sources: salads, milk and dairy products, and unclean water
Fungi (1)
• Fungi are eukaryotic and exist in different growth forms in
different environments. They range from small single cells such
as yeasts (~5um) to large complex structures
such as mushrooms (~5cm)
• The high humidity and temperatures often found in bathrooms
and kitchens are conducive to fungal growth. Mould, or mildew
as it is sometimes referred, likes warmth and moderate
to high humidity
Fungi (2)
Fungi responsible for human disease can be divided
into two distinct morphological forms
• Yeasts
which grow as oval or spherical single cells like bacteria and multiply by
budding and division
• Filamentous fungi
more commonly known as moulds, consist of long, branching hyphae
forming a mycelium. Asexual reproduction results in formation of spores
Fungal Growth
Bud formation
Mother
Daughter
Yeasts - unicellular
oval or spherical cells which divide by budding and division
Spore
Hyphal
development
Branched
hyphae
Filamentous fungi - branched hyphal structure
Mycelium
often pigmented with age. Reproduce by forming large amounts
of spores
Why are fungi a problem?
• They can be responsible for infections
• They can cause an allergic response
• Fungi cause discolouration and deterioration of household surfaces
giving the characteristic blackening of walls, tile grouting, plaster and
around window frames
• Can cause unpleasant odours which are difficult to disguise. Fungi
such as Aspergillus, Penicillium, and Alternata have been found to
produce volatile organic compounds
• Numerous fungi have been found to produce volatile organic
compounds (VOC) and it has been suggested that these affect the
health of persons living in mouldy houses. Symptoms include headache,
eye, nose and throat irritation and fatigue
• VOC’s have been implicated in health issues relating to sick building
syndrome
• Spores of toxigenic fungi contain mycotoxins (toxic secondary
metabolites). Many fungal spores are small enough to reach the alveoli
in the lungs. The mycotoxins may be transported via the blood from the
lung to other body sites, possibly causing other effects e.g. skin lesions
What infections do fungi cause?
Fungi cause 2 types of infection:
• Superficial mycoses
– fungus grows at the body surface in skin, hair and nails
– spread by direct contact, highly contagious and easily spread
to others
• e.g. Candida albicans (thrush and nappy rash)
• e.g. dermatophyte fungi: Epidermophyton, Microsporum and
Trichophyton (athlete’s foot)
• Deep mycoses
– involve internal organs, usually life-threatening
– rare except in immunocompromised people
– caused by opportunistic fungi (e.g. Aspergillus)
– acquired by inhalation of spores or by entry through wounds
– some part of the normal body flora and are harmless unless the
body’s defences are compromised in some way (e.g. Candida)
Fungi are also a source of allergens
• Allergic rhinitis (hayfever)
• Bronchitis
• Asthma
• Extrinsic allergic alveolitis
Almost all microbial allergens are fungal in origin, with the major
ones being Penicillium, Aspergillus, Cladosporium and Alternaria
Asthma can be initiated and provoked by allergens commonly
encountered in the general environment, for example pollens
(trees, grass), house dust mites and moulds, e.g. Alternaria
alternata, Cladosporium herbatum and Aspergillus fumigatus
Fungi in the Home
What evidence is there for occurrence of fungal
contamination in the home?
There have been a number of studies investigating fungi in the
home. Fungi isolated include:
• Penicillium spp.
• Cladosporium spp.
• Aspergillus spp.
• Mycelia sterilia
• Rhodotorula (pink yeasts)
• Sporobolomyces (yeasts)
Fungi isolated from the air was similar in homes surveyed in
Scotland, Germany, Finland, North America, Taiwan, Canada and
Australia
Viruses
What is a virus?
• It is not a bacterium
• It is very small, typically 0.1um
• It is not a true cell
• It is not an independently living organism. It must be inside
a living cell to replicate
• They have genetic material but lack cell membranes, cytoplasm and
machinery
• The virus uses the infected cell's machinery and enzymes to generate
virus parts which are later assembled into new virus particles which
leave the cell to infect other cells
• It can infect bacteria, fungi, plants, animals and man
• It may remain viable for long time, even in dry conditions
• It can survive but does not grow in food
Structure of Viruses
Classification based on characteristics such as genetic material present (RNA
or DNA), symmetry of virus particle and presence or absence of an envelope
Structurally there are 2 distinct types of virus:
Enveloped and Non-Enveloped
Non-enveloped
Enveloped
Protein/lipid coat
Protein
coat
Envelope
Nucleic
acid
Polymerase
e.g. poliovirus
adenovirus
rotavirus
e.g. hepatitis B
e.g. herpes simplex
HIV
Flu
What infections do viruses cause? (1)
Nearly 1000 different types of viruses are known to infect
humans and it has been estimated that they account for
approx. 60% of human infections. The young, elderly and
immuno-compromised are particularly at risk from virus
infections
Many viral diseases are well known and easily
identified:
• from colds and flu to chicken pox and measles
• from mumps and herpes to polio, hepatitis and HIV
What infections do viruses cause? (2)
From the ‘Home Hygiene’ point of view, we are mainly concerned
with virus infections relating to poor personal or surface hygiene,
and are thus preventable
• Gastrointestinal infections
– Gastroenteritis
– Diarrhoea
– Infectious intestinal disease
• Respiratory infections
– Flu
– Common cold
– Bronchitis
Viruses causing Gastrointestinal Infections
• Rotavirus
– Most important viral cause of diarrhoea in children worldwide
– Infects virtually all children 3-5 years old in developed and developing
countries
– Can be asymptomatic excreter
• Small Round Structured Virus (SRSV)
– Play a predominant part in epidemic viral gastroenteritis
– Main symptom is projectile vomiting generating aerosols and virus can be
transmitted via aerosols, can contaminate work surfaces with potential for
subsequent transfer to food
• Astroviruses and Adenoviruses
– Have been associated with gastroenteritis outbreaks in schools, nursing
homes, day-care centres, children’s hospital wards
• Hepatitis A
– Viral hepatitis is most common of the food associated virus diseases,
most common vehicle is shellfish
– Easily spread in areas where good personal hygiene is not observed.
– Outbreaks occur in day-care centres, hospitals, nurseries and schools
– Outbreaks may lead to secondary cases in the general community
Viruses causing Respiratory Infections
Viral respiratory infections are common in winter when people are
crowded together indoors for longer periods of time, air in illventilated rooms is more humid, favouring survival of suspended
enveloped viruses
• Rhinoviruses and coronaviruses
together cause more than 50% of common colds can also cause acute
bronchitis
• Influenza viruses
main cause of flu, can cause acute bronchitis
• Parainfluenza viruses
cause of pneumonia in children
• Respiratory Syncytial Virus (RSV)
most important cause of bronchiolitis and pneumonia in infants major cause
of hospital-acquired illness on neonatal wards
• Adenovirus
common cause of sore throats and acute bronchitis
Virus Transmission (1)
Presence or absence of an envelope is the major
structural determinant for mode of transmission
• Non-enveloped viruses
most can withstand the acidic environment of the stomach
or detergent-like bile of the intestines. Transmitted by respiratory and
faecal-oral routes e.g. rotaviruses, SRSV
• Enveloped viruses
more fragile, require an intact envelope for infectivity, sensitive
to acids and detergents, so not spread via faecal-oral route; spread in
respiratory droplets, blood, saliva. e.g. influenza
Virus Transmission (2)
Activities of the infected host may increase
the efficiency of transmission
• Coughing and sneezing
viruses that are better at increasing fluid secretions or irritating
respiratory lining will induce more coughing and sneezing increasing
efficiency of shedding and transmission
• Diarrhoea
eliminates infection more rapidly but is great for contamination of the
environment and therefore will spread the microbes
• Projectile vomiting
generates aerosols, virus can be transmitted via aerosols, can
contaminate work surfaces with potential for subsequent transfer to
food
Protozoa (1)
• Protozoa are single-celled eukaryotes
• Live in water or moist places or other
organisms as parasites
• Have a resistant transmissable cyst
stage
• Transmission to humans via insect bite
or accidental ingestion of infective
stages
Protozoa (2)
• Cryptosporidium spp.
infects the intestines causing Cryptosporidiosis. Large outbreaks are
associated with contaminated water or treatment deficiency of water
supplies
• Giardia lamblia
causes giardiasis, an infection of the small intestine, spread via
contaminated food and water and by direct person-to-person contact.
Ingestion of one or more cysts may cause disease
• Entamoeba histolytica
an amoeba infecting the large intestine, causes diarrhoea/dysentery,
spread via contaminated water or food
• Toxoplasma gondii
causes toxoplasmosis, a very severe disease that can produce central
nervous system disorders
Hygiene Hazards In The Home
• Micro-organisms are introduced continually into the home via: people,
food, pets, water, insects, air. Wet sites such as sinks, toilets, dishcloths
and facecloths can also support microbial growth and themselves
become reservoirs of potentially hazardous microorganisms
• Many organisms occurring in the home are of little consequence.
Some organisms have the potential to cause infectious disease
• Some people carry highly pathogenic organisms without themselves
being affected - other family members unaware of hazard
• Hands, and a whole range of food and hand contact surfaces,
combine to provide transfer routes that can move pathogens around the
home and ultimately into the body producing infection
Ingestion of:
Inhalation of:
• microorganisms - bacteria,
viruses, protozoa
• toxins
• toxins - bacterial, fungal
• microorganisms
• allergens/spores
Risk of health hazard from
Primary sources
Skin
Infection
Air
Moulds
Water
Parasites
Direct
Ingestion
G-bacteria,
Protozoa, viruses
Food
Positioning
Inhalation
Mycotoxins
Moulds, viruses,
Legionella,
G+bacteria
G-bacteria,
viruses
Legionella
Walls/Ceiling
Environment
Moulds
Shower/bath/sink
Dermatophytes,
G-bacteria
Toilet
?
Kitchen
Surface/sink
Furnishing/fabrics
Cleaning aids
Pets
Insect
G-bacteria, viruses G-/G+bacteria
G-/G+bacteria,
Listeria
G-/G+bacteria,
Listeria
Derm atophytes,
viruses
Dustmites,
Moulds
G-/G+bacteria
Utensils and
equipment
People
G-bacteria
G-bacteria
Dermatophytes,
viruses
Dermatophytes,
Parasites,
viruses
Parasites,
viruses,
G-bacteria
G-bacteria,
viruses?
G-/G+bacteria,
Listeria
G-/G+bacteria,
Listeria
G-bacteria,
Staphylococcus
G+bacteria,
viruses
G-bacteria
Hairfur, viruses?
G-bacteria