A Simple Guide to Germs and Disease

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A Simple Guide toGerms and Disease
June 2005
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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
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Microbiology (2)

• What are Germs?
• Germs are microorganisms that are likely to cause
  disease
• Microorganisms are found throughout the
  environment. Onlya 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, brewingor cheese making
• Bacteria are just one type of micro-organism,
  alongside viruses, fungi and protozoa

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Germs - Family Tree
Germs
Bacteria
Viruses
Fungi
Protozoa
GramPositive
GramNegative
Enveloped
Non-Enveloped
Giardia Cryptosporidium
SporeFormers
Non-SporeFormers
Influenza HIv
Rotavirus Poliovirus SRSV
Moulds
Yeasts
Salmonella E.coli Campylobacter
Bacillus subtilis Bacillus cereus Clostridiumperf
ringens
Staphylococcus Listeria
Cladosporium Aspergillus Penicillium
Candida
Germs all potentially harmful micro-organisms
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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
Rod (bacilli) e.g Escherichia coli
Spiral/helical e.g. Treponema
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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

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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 byan outer membrane (made up of
  lipopolysaccharides and lipoprotein)

Lipoteichoicacids
Outermembrane
Cell wall (peptidoglycan)
lipoprotein
Cell membrane (lipid bilayer)
Gram-positive
Gram-negative
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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.

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Bacterial Growth (2)

• Typical Growth Curve for a Bacteria Population
• Lag Phasegrowth is slow whilst they become used
  to their new environment and nutrients
• Log Phaseonce the metabolic machinery is
  running, they start multiplying exponentially,
  doublingin number every few minutes
• Stationary Phaseas more and more bacteria are
  competing for nutrients which are decreasing,
  growth stops and the number of bacteria
  stabilises
• Death Phasetoxic waste products build up,
  nutrients have run out and thebacteria begin to
  die

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Bacterial Growth (3)
Bacteria divideby binary fission
Typical bacterial growth ratein optimum
conditions
Typical growth curvefor a bacteria population
8.0
6.0
Log10 viable organisms/ml
4.0
and so on ...
2.0
Stationary
Log
Lag
Death
0
Time
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Bacteria and Temperature
100
HIGH
Cl botulinum AB
Campylobacter
Bacteria die if heatedfor a sufficient time.
The longer the time, the greater the destruction
MinimumGrowthTemp.
Staph aureus E. coli Salmonella
Cl perfringens
Cl botulinum E Bacillus cereus
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Listeria
40
LOW
38
HIGH
LOW
Bacteria Grow at slower rate
Bacteria grow
Heat resistance
Bacteria grow quickly

• Pathogenic bacteria grow best at human body
  temperature 37ºC. However the majority will grow
  between 15-45ºC
• Non-sporing cells of bacteria are killed
  attemperatures above 60ºC. The length of
  timeranges depending on the organism
• Boiling kills living cells, but will not kill
  allbacterial spores
• Fridges should be set below 5ºC. Some
  bacteriasuch as Listeria monocytogenes can
  growat refrigeration temperatures

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15
7
Bacteria stop growing, but do not die
4
0
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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 poisoninginfections
  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 poisoningsome bacteria grow
  in food and produce a toxin within the foodwhich
  is then consumed e.g. Bacillus cereus and
  Staphylococcusaureus. When the food is consumed
  viable cells of the bacteriado not need to be
  present. Other microorganisms in food mayproduce
  harmful or deadly toxins while growing in the
  intestinaltract e.g. Clostridium perfringens,
  enterotoxigenic Escherichiacoli and
  enterohaemorrhagic E. coli

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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

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Bacterial Food Poisoning (3)

• Campylobacter jejunimost common cause of
  diarrhoea Sources raw and undercooked poultry
  and meat, raw milk and untreated water
• Listeria monocytogenescauses 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

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Bacterial Food Poisoning (4)

• Staphylococcus aureusproduces a toxin that
  causes vomiting shortly after ingestingSources
  cooked foods high in protein e.g. cooked meats,
  custard, cream cakes
• E. coli O157a bacterium that can produce a
  deadly toxinSources undercooked hamburger/
  minced beef, contaminated cooked meatand raw
  milk
• Shigella spp.poor hygiene causes this bacterium
  to be easily passed from person to
  personSources salads, milk and dairy products,
  and unclean water

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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 structuressuch 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 moderateto high
  humidity

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Fungi (2)

• Fungi responsible for human disease can be
  dividedinto 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

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Fungal Growth
Mother
Bud formation
Daughter
Yeasts - unicellularoval or spherical cells
which divide by budding and division
Spore
Mycelium
Branched hyphae
Hyphaldevelopment
Filamentous fungi - branched hyphal
structure often pigmented with age. Reproduce by
forming large amountsof spores
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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
• VOCs 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

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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 spreadto others
• e.g. Candida albicans (thrush and nappy rash)
• e.g. dermatophyte fungi Epidermophyton,
  Microsporum and Trichophyton (athletes 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 bodys defences are
  compromised in some way (e.g. Candida)

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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

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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

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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 insidea 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

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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
  virusEnveloped and Non-Enveloped

Non-enveloped
Enveloped
Protein/lipid coat
Envelope
Nucleicacid
Proteincoat



Polymerase
e.g. poliovirus adenovirus rotavirus
e.g. herpes simplex HIV Flu
e.g. hepatitis B
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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
  

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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

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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, childrens 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

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Viruses causing Respiratory Infections

• Viral respiratory infections are common in winter
  when people are crowded together indoors for
  longer periods of time, air in ill-ventilated
  rooms is more humid, favouring survival of
  suspended enveloped viruses
• Rhinoviruses and coronavirusestogether cause
  more than 50 of common colds can also cause
  acute bronchitis
• Influenza virusesmain cause of flu, can cause
  acute bronchitis
• Parainfluenza virusescause 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
• Adenoviruscommon cause of sore throats and acute
  bronchitis

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Virus Transmission (1)

• Presence or absence of an envelope is the major
  structural determinant for mode of transmission
• Non-enveloped virusesmost can withstand the
  acidic environment of the stomachor
  detergent-like bile of the intestines.
  Transmitted by respiratory and faecal-oral routes
  e.g. rotaviruses, SRSV
• Enveloped virusesmore 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

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Virus Transmission (2)

• Activities of the infected host may increasethe
  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

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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

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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 histolyticaan amoeba infecting the
  large intestine, causes diarrhoea/dysentery,
  spread via contaminated water or food
• Toxoplasma gondiicauses toxoplasmosis, a very
  severe disease that can produce central nervous
  system disorders

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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
• microorganisms - bacteria,viruses, protozoa
• toxins - bacterial, fungal

• Inhalation of
• toxins
• allergens/spores
• microorganisms

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Risk of health hazard from