Hygiene in the home: good bugs, bad bugs and
superbugs
We often read about how some microbes are good or beneficial, whilst others are
bad or harmful. The reality is not quite so simple. This briefing document gives an
overview of microbes which are found in the home and their potential to benefit us, or
cause harm through infectious disease. This briefing material has been produced for
those who work in healthcare professions, the media and others who are looking for
background understanding and/or those who are responsible for informing the public
about infectious diseases in the home and their prevention through good hygiene
practice.
What are good and bad microbes?
Our world contains thousands of different types of micro-organisms which include
bacteria, fungi, viruses and protozoa. For each type, there are thousands of different
species, which vary significantly in their structure, how they function and what habitats
they prefer to live in. It would be useful to be able to divide them into those which are
good and those which are bad, but the reality is far more complex. At best we can
probably classify microbes into beneficial, harmless, potentially harmful and harmful,
but some species could be placed in more than one category depending on the
situation. One of the key properties of microbes, which underpins their survival is their
ability to adapt in order to survive, and evolve to take advantage of different and new
environments, which means that their behaviour is very unpredictable. Superbugs are
organisms which have evolved to become resistant to antibiotics.
Surveys of the home environment cause us alarm by reporting the presence of millions
of microbes on surfaces in the home, in the toilet or on the dishcloth. It is important to
be aware that virtually all the species found in these situations are harmless. However,
where there is a source of harmful (infectious) microbes in the home, (e.g. food
contaminated with harmful bacteria or a person infected with a virus) these harmful
organisms can spread via hands and surfaces, and even quite small numbers (10-100
bacterial cells or viral particles) can be enough to cause an infection. Good hygiene
practice is about focusing our activities on preventing the spread of harmful microbes.
What types of microbes are harmless?
We all carry millions of micro-organisms (bacteria, fungi, viruses, protozoa) on our
skin, in our mouths, in our intestines (there are more bacteria in just one person's
intestines than there are human beings in the world), and they play a variety of
important roles. Most of the microbial species found in our bodies and our environment
are mostly non-harmful to us.
Our environment (both indoor and outdoors) also contains millions of micro-organisms.
Every site and surface in our home will be contaminated with some micro-organisms.
Like humans, microbes need moisture and food to survive. This means that “wet”
places like sinks, drains, baths and toilets are the places where microbes like to breed,
but wet cleaning cloths and mops also contain sufficient moisture to support their
growth. Damp surfaces like bathroom tiles also have enough moisture to support the
growth of moulds and fungi which are more “drought tolerant” than bacteria and
viruses. Although microbes cannot grow on dry surfaces they can survive for periods
varying from an hour up to several days or months depending on the species. Given
the right conditions some bacteria can grow from a few cells to millions in the space of
a few hours.
What types of microbes are considered good or beneficial?
Bacteria can help the body to combat infection
We all carry millions of bacteria in our bodies, on the surface of our skin, and on the
mucous membranes which line our nose, mouth etc. Some are beneficial to the body
because they help to fend off harmful organisms. Some diseases, stress and
medicines, such as antibiotics, can wipe out the body's supply of friendly, or 'good',
bacteria. If these can't be replaced, then problems may develop.
One example of this is thrush. Antibiotics, taken for a bad throat or cystitis, kill not just
the harmful (bad) bacteria but also the beneficial ones that live in the vagina and keep
this delicate area healthy. Once these are gone, organisms such as the yeast Candida
can take over and increase in number, causing thrush.
Friendly bacteria in the gut
'Good' bacteria in the gastrointestinal tract are part of the body's immune system (the
gut contains more immune cells than anywhere else in the body). These good bacteria
help to prevent bad bacteria from growing in the bowel or entering the body through
the wall of the intestines to cause infection. When the gut bacteria are lost (e.g. after a
strong enema to clear out the intestines, or a course of antibiotics) the gut bacteria can
be lost and the risks of infection increases.
Good bacteria also play an important role in breaking down the food we eat to provide
a source of energy essential for the cells that line the intestines. If these friendly
bacteria are lost, the cells lining the intestines temporarily die off, which can cause
diarrhoea and difficulties absorbing food from the intestines.
Good bacteria can also help to make the vitamins needed by the body, and keep the
digestive system working as it should.
Probiotics restore healthy bacteria
Probiotics are foods or other supplements which contain "live micro-organisms” which,
when administered or eaten in adequate amounts, can confer a health benefit.
Probiotics work to repopulate the gut with healthy bacteria. There is a difference of
opinion about which types of bacteria are the best. Lactobacilli plantarum, are good
bacteria which are found on many fresh foods, such as the surfaces of unwashed
vegetables. To get enough probiotics requires us to consume a large amount of
vegetables daily. An alternative is to eat 'live' yoghurts or similar dairy products which
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contain a variety of types of Lactobacilli or bacteria called Bifidobacteria. Some experts
believe that Bifidobacteria are more important for our health than Lactobacilli, but
Lactobacilli are more easy to use in manufactured foods. Whatever probiotics are
chosen, they need to be eaten regularly to get the benefit.
Research shows that probiotics may have widespread health benefits including the
treatment and prevention of acute diarrhoea and antibiotic-induced diarrhoea,
Clostridium difficile colitis, urinary tract infections, respiratory infections in children,
dental caries, irritable bowel syndrome, inflammatory bowel disease, allergic disease,
rheumatoid arthritis and, possibly, the prevention of bowel cancer.
Good bacteria used in production of food and beverages
Yeasts are widely used in cookery to produce bread and pastries. Other types of
yeasts are fundamental to the production of wines, beers and other alcoholic drinks
A summary of recent data and thinking on use of probiotics can be found at:
http://en.wikipedia.org/wiki/Probiotic
The Hygiene Hypothesis
How, and to what extent, parents should protect infants and children from infectious
illness has been the subject of much debate in recent years. In the last 30 years we
have seen an epidemic of chronic inflammatory diseases in the industrialized world.
For young children the major concern is asthma, hayfever, food and other allergies,
but, in reality, the problem extends to a broader range of diseases including Type 2
diabetes, inflammatory bowel disease, and autoimmune diseases like multiple
sclerosis. The concept of a link between reduced “infection” exposure and increasing
levels of allergic diseases, as first proposed in the 1990s, was named the hygiene
hypothesis. This fuelled the idea that we have become too clean for our own good,
and still persists, despite the fact that the hypothesis has been substantially revised.
A more rational explanation, the ‘Old Friends’ hypothesis, is now becoming more
widely accepted and argues that the vital exposures are not colds, influenza, measles
and other common childhood infections which have evolved relatively recently over
the last 10,000 years, but the microbes already present over 2 million years ago in
hunter-gatherer times when our immune system was developing.
Although we cannot be sure precisely what microbes are involved, current thinking is
that the Old Friends organisms include harmless commensal microbes found on the
human and animal body and in the gut, and organisms from the natural environment.
It also includes some infections such as parasitic worm infections that can persist as
relatively harmless carrier states.
This suggests that, whereas on one hand it is important to maintain good hygiene
practices on the other it is advisable not to become cleanliness/hygiene-obsessed,.
Babies are inevitably exposed to some micro-organisms in their environment which, in
addition to some germs, will also include some of the Old Friends which need to
become established as their normal gut flora, on their skin etc. Gradual exposure to
small numbers of a wide range of microbes is also important for priming the immune
system. Hygiene practices are important because they focus on protecting against
exposure to “infectious doses” of harmful organisms which our immune systems are
not equipped to deal with. The latest findings on this issue can be found in a 2012
IFH review.1
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What are bad or harmful micro-organisms?
Bad microbes are those which are pathogenic i.e. they infect the body and cause
disease. Infectious diseases which commonly circulate in the home include respiratory
infections (colds, flu) gut infections (food poisoning, norovirus/winter vomiting) skin and
eye infections (MRSA, conjunctivitis, athletes foot) and are caused by bacteria, fungi or
viruses etc. The spread of these diseases can be reduced or prevented by good
hygiene practice.
In promoting home hygiene, it is important to know which are the infections which are
transmitted via food, water, hands, surfaces etc. These are the infections, as listed
below, for which hygiene is a contributory factor (although it may not be the only factor)
in preventing their spread. Other infections are transmitted from person-to-person only
by close or direct personal contact, which means that home hygiene practices are not
relevant to their prevention.
It is important to bear in mind that, for any given microbial species, the pathogenicity
(ability to cause an infection) can vary considerably from one strain to another. An
example of this is E.coli. Most strains of E. coli form part of the normal gut microflora in
humans and warm-blooded animals. However, some strains have the ability to cause
disease in humans through the presence of specific virulence factors. These diseases
include food poisoning, e.g. E. coli O157, or infections outside the intestinal tract such
as urinary tract infections, and bacteraemia.
Bacteria
viruses
Infectious illnesses associated with poor hygiene include:
Gastrointestinal
Salmonella spp.
rotavirus
Campylobacter spp
norovirus
E.coli (including O157 and O104) adenovirus
Listeria monocytogenes
hepatitis
Shigella spp
adenovirus
Cholera
astrovirus
Typhoid, paratyphoid
Helicobacter pylori,
Clostridium difficile
Clostridium perfringens,
Bacillus spp.
Respiratory infections (colds, flu)
Legionella pneumophila
rhinovirus
influenza
respiratory syncitial
virus
(RSV)
parainfluenza
adenovirus
SARS
Skin and eye infections (including impetigo)
Staphylococcus aureus (including adenovirus
MRSA)
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fungi and
protozoa
Apergillus,
Cryptosporidium,
Entamoeba
histolytica,
Giardia
Trichophton rubrs
(athletes foot)
Others
Acinetobacter
hepatitis A
Candida
Citrobacter spp.
Toxoplasma
Klebsiella spp.
Aspergillus
Enterobacter spp.
Pseudomonas aeruginosa
Infectious illnesses not thought to be associated with poor hygiene* include:
Anthrax
HIV
Bordetella pertusis (whooping
mumps
cough)
measles
Diptheria
german measles
Clostridium botulinum
herpes,
Gonorrheoa
chickenpox
Streptococcus spp.
hepatitis B &C
Tuberculosis
human papillomavirus (HPV)
Chlamydia
polio
whooping cough
*Note: although “home hygiene” practices such as handwashing do not prevent the
spread of these diseases, other forms of “hygiene” may be important e.g. sexual
“hygiene” is key to preventing the spread of HIV and other sexually transmitted
diseases.
In addition to microbes that cause diseases, some microbes are considered “bad”,
because they cause spoilage of foods, degradation of materials, discolouring of
bathroom tiles etc, bad odours etc.
What are “potentially harmful” organisms?
Some microbial species are “normally” harmless – but can cause infection under
certain specific conditions. These are referred to as “opportunist or potential
pathogens”. Some examples include:
 S. aureus can live harmlessly in the nostrils, throat, and on the skin (particularly in
areas such as the armpits and groin). About one third of the general population
constantly carry S. aureus, and one third carry it on a transient basis. Usually the
individual is quite unharmed by colonisation. S. aureus can also rapidly colonise
broken or abnormal skin such as superficial wounds, ulcers, psoriasis and eczema,
often without any symptoms, but on occasion it may produce boils or, more
seriously, it can enter the bladder or blood stream causing bacteraemia.
 E. coli is carried harmlessly as part of the gut flora in up to 90% of the population.
Under certain conditions E. coli can be transferred to and infect the urinary tract
causing cystitis.
 Legionella pneumophila is an organism which lives harmlessly in our environment
(e.g. in stagnant water), but can cause respiratory infections if inhaled into the
lungs. If the water reservoir of an air conditioning system becomes contaminated
with Legionella, the conditioned air can carry infected water droplets which are
then inhaled. Legionella is normally only pathogenic to people with lowered general
resistance to infection such as the elderly.
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So - what are germs?
This is a common term, not used scientifically. Most experts use it to define
collectively those bacterial, viral, fungal and protozoal strains which are harmful or
potentially harmful i.e. cause infectious disease – as opposed to those which are not.1
The term is often misused however to refer to ALL microbes – both those which are
harmful as well as those which are not. Reports which talk about “millions of germs”
found on surfaces such as the toilet seat should therefore be interpreted with care.
Closer inspection may reveal that these organisms are species that are non-harmful
or only harmful in rare situations. Since some bacteria can multiply very rapidly,
finding “millions of germs” in the toilet is quite “normal” and should not be seen as a
risk, unless it is established that they are species which are potentially harmful.
A common misconception is that whereas we have always had to guard against
germs, we now have even worse things like bacteria such as Salmonella and E. coli to
deal with. In reality Salmonella, E. coli, norovirus and rotavirus are all types of germs.
It’s just that the media now often refer to these different types of germs by their
names.
and - what are superbugs?
The term superbug was originally coined to describe microbial strains which have
developed resistance to one or more antibiotics. The best known examples are the
strains of S. aureus known as methicillin resistant Staphylococcus aureus or MRSA.
Other examples are the microbial strains which have developed resistance to beta
lactamase antibiotics such as penicillin and ampicillin. The best known of these strains
are the extended-spectrum beta-lactamases (ESBL) producing strains of E. coli. There
is a tendency to assume that because these strains are “strong” enough to resist the
action of antibiotics they are also more virulent i.e. they are more aggressive in
causing infections. This is not the case. MRSA and other antibiotic resistant strains are
no more infectious than the parent strains of E. coli and S. aureus from which they
evolved. For healthcare-associated strains of MRSA, it is thought that these strains are
actually less virulent than the parent strains, hence the reason they mainly infect
individuals, such as hospital patients, whose immunity is compromised, and rarely
infect normal healthy individuals in the community. Of concern are the communityacquired strains of MRSA. Some of these strains have also acquired a gene which
enables them to produce the Panton Valentine Leucocidin (PVL) toxin which is thought
to increase their pathogenicity. Clostridium difficile is often incorrectly referred to as a
superbug, but the current strains are sensitive to antibiotics. C. difficile can occur in its
dormant spore state in the human gut without causing any problems. It is thought
however that antibiotics can trigger it to germinate into its active disease-causing state.
In this fact sheet the term “germs” is being used to define those microbes (bacteria,
fungi viruses etc) which can cause infectious diseases, and distinguish them from
other microbes which are considered non- harmful.
1
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Are there disinfectants we can use which will kill bad bugs and superbugs, but
not the good bugs?
Unfortunately not. Different disinfectants do have different properties, for example,
some are active against the full spectrum of microbes including bacteria, viruses and
protozoa, whilst others are active against bacteria, but have relatively limited activity
against viruses (see IFH information sheet “Cleaning and disinfection: Chemical
Disinfectants Explained” for more details2). However, developing disinfectants which
are active e.g. against those bacterial strains which are harmful, but inactive against
bacterial strains which are non-harmful, is not feasible.
Superbugs are so-called because of their ability to resist the action of antibiotics.
Development of resistance to antibiotics is not accompanied by development of
resistance to disinfectants. This is because the mechanisms by which disinfectants kill
microbes are generally different. Although there are some data to show that in some
cases, antibiotic resistant strains show some reduced sensitivity to sublethal
concentrations of disinfectants, disinfectants used at recommended use concentration,
are equally effective against antibiotic resistant strains as against the parent strains
from which the superbug evolved.
How can we demonstrate the presence of harmful microbes in the home and
how they spread?
Demonstrating the presence of harmful microbes in the home, and the ways in which
they are spread, is difficult because they are invisible to the naked eye. The approach
which is most often used is to take samples from a range of sites and surfaces in the
home and identify and count them using standard microbiological techniques.
Experience has shown however, that although such studies usually show the presence
of a whole variety of different microbial species in the home, often in very large
numbers, the majority of these organisms are non-harmful species. Although, harmful
or potentially harmful organisms are constantly present in the home, their presence is
difficult to demonstrate unless very large numbers of samples are taken, and a large
number of homes are sampled. The alternative approach which is now adopted is to
carry out studies in situations where there is a known source of infection:
 Following preparation of Salmonella and Campylobacter-contaminated chickens in
domestic kitchens, these species were isolated from 17.3% of hands, and hand
and food contact surfaces. Isolation rates were highest for hands, chopping boards
and cleaning cloths (25, 35 and 60%, respectively, of surfaces sampled).
 In 6% of 200 UK homes, where cases of salmonellosis occurred, Salmonella was
isolated from the dishcloth
 In four out of six homes where there was a Salmonella case, the causative species
was isolated from faecal soiling under the flushing rim, and scale material in the
toilet bowl, for up to 3 weeks after notification of infection.
 In homes containing an infant recently vaccinated for polio (during which time
shedding occurs in faeces), virus was isolated from 13% of bathroom, living room
and kitchen surfaces. Most frequently contaminated were hand contact sites such
as bathroom taps, door handles, toilet flushes, soap dispensers, nappy changing
equipment and potties.
 In homes of infants with recurrent C. difficile infection, 12% of environmental
surfaces were positive for C. difficile. In a control home with no household carriers,
none of 84 environment samples were positive for C. difficile.
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
In a study of US domestic homes, whilst no influenza was detected on home
surfaces during the summer, influenza was detected on 59% of surfaces sampled
during March in five homes where there was an influenza-infected child. No virus
was recovered from three other homes where household members were healthy.
Influenza virus was recovered most frequently from telephone receivers, computer
keyboards, refrigerators, kitchen faucets, light switches, microwaves, TV remote
controls, door knobs, bath and faucet and toilet handles.
One exception to this is the organism S. aureus which is quite often isolated from sites
and surfaces in the home. For example:
 A sampling study was carried out in 35 US homes of healthcare and non–
healthcare workers, each with a child in diapers and either a cat or dog in the
home. S aureus was found on a variety of household surfaces in 34 of the homes
(97%) and MRSA was isolated from 9 homes (26%). A positive correlation was
indicated for the presence of a cat and the isolation of MRSA from surfaces.
Because it is difficult to demonstrate the presence of pathogens such as Salmonella or
norovirus in the home environment, unless we investigate homes where there is a
known infected person, we often use “faecal coliforms” or “faecal
streptococci/enterococci” as indicators of infection transmission risks. All of us carry
these organisms in our gut. This means that, if we find these organisms on
environmental surfaces, it is an indicator of e.g. poor “toilet hygiene”, that is, it
indicates that if a family member was carrying a pathogen in the gut, there is a risk that
this organism would be found in the home environment.
A technique which has proved very useful to help people visualise the spread of
invisible germs in the home involves the use of a preparation which is invisible in
normal light, but glows under UV light. The preparation can be applied to the hands or
a door handle – or the surface of a chicken. People are then invited to touch the
surface, shake hands, or handle and prepare the chicken etc. in their normal way. The
UV light is then passed over the object and its environment in order to demonstrate
how extensively the “invisible” material has spread. A frequent problem is persuading
people that, when it comes to preventing transmission of infection, what is ‘visibly
clean’ is not necessarily ‘hygienically clean’. An exercise to help this, involves coating
peoples hands or a surface or object with the same preparation and asking them to
wash their hands or clean the surface in their normal way. The UV light can be used to
see how well the hands or surface was cleaned. “Mini-kits for doing this are obtainable
from “Wash and Glow” for a cost of around £40 at http://www.wash-andglow.com/wash-and-glow-buy-now.htm.
References
1
2
Bloomfield SF, Stanwell-Smith R, Rook GA. The hygiene hypothesis and its
implications for home hygiene, lifestyle and public health: summary. International
Scientific Forum on Home Hygiene. http://www.ifh-homehygiene.org/best-practicereview/hygiene-hypothesis-and-its-implications-home-hygiene-lifestyle-and-public
Cleaning and disinfection: Chemical Disinfectants Explained http://www.ifhhomehygiene.org/factsheet/cleaning-and-disinfection-chemical-disinfectantsexplained
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