chapter 9 air micro

Question 1

The atmosphere as a habitat is characterized by:

Answer 1

◦High light intensities,
◦Extreme temperature variation,
◦Low amount of organic matter
◦Insufficiency of available water

Question 2

Air is a non hospitable environment for microorganisms and generally an unsuitable habitat for their growth
However, considerable number of microorganisms are found in the lower regions of the atmosphere

Answer 2

Air is an unfavorable environment for microorganisms, in which they cannot grow or divide. It is merely a place which they temporarily occupy and use for movement.
Therefore, there are no metabolic connections occurring between different microorganisms in air (such as in soil or water). As a result they form only a random collection of microorganisms

Question 3

Microorganisms get into air as a consequence of

Answer 3

wind movement, which sweeps them away from various habitats and surroundings (soil, water, waste, plant surfaces, animals, and other), or they are introduced during the processes of sneezing, coughing, or sewage aeration.

Question 4

Microorganisms found in air

Answer 4

In addition to gases, dust, particles of water vapor, air also contains microorganisms
Bacteria (vegetative forms and spores), fungi , and viruses
The microflora of air : outdoor and indoor
◦In living and working indoor places, we usually find about 10 times higher concentrations than the outside atmosphere
◦Air microflora: Gram positive group: Bacillus, Corynebacterium

Question 5

I-Droplets:

Answer 5

They are usually formed by sneezing, coughing or talking, they consist of saliva and mucus
They may contain hundreds of microorganisms that may be pathogenic if discharged from diseased persons
Pathogens will be mostly of respiratory tract origin
The size of the droplet determines the time during which they can remain suspended
Most droplets are relatively large and they tend to settle rapidly in immobile air
-When inhaled these droplets are trapped on the moist surfaces of the respiratory tract, thus the droplets containing the microorganism may be a source of infectious diseases

Question 6

II-Infectious dust:

Answer 6

Large aerosol droplets settle out rapidly from air onto different surfaces and then dry out.
Nasal and throat discharges from a patient can also contaminate surfaces and become dry
So disturbance of this dried material by bed making, handling a handkerchief having dried secretion or sweeping floors in the patients’ room can generate dust particles that add microorganisms to the circulating air
However, microorganisms can survive for relatively longer period in dust, this create a significant hazard especially in hospital areas
Infective dust can also be produced during lab practices like opening the containers of freeze dried culture or withdrawal cotton plugs; these pose a threat to the people working in labs

Question 7

Distribution of microorganisms in air

Answer 7

No microbes are indigenous to the atmosphere
Microorganisms in air are originated from soil & water
Species vary greatly in their sensitivity to a given value of relative humidity RH , temperature and radiation exposures
Spores of fungi, especially Alternaria, Cladosporium, Peniclilliumand Aspergillusare more numerous than other forms
Below altitude of 500 feet in clear weather, air includes spores of Bacillus and Clostridium, yeasts, spores of molds, pollen, protozoan cyst, allergen

Question 8

Distribution of microorganisms in air (cont’d)

Answer 8

In the dust and air of schools and hospitals or the rooms of persons suffering from infectious diseases microbes like Tuberculosis, Streptococci and Staphylococci have been detected
Many plant pathogens are also transported from one field to another through air, the spread of many fungal diseases of plants have been also identified
Human bacterial pathogens that cause important airborne diseases: diphteria, pneumoniae, meningitis, TB , whooping cough,…

Question 9

Distribution of microorganisms in air (cont’d) 3

Answer 9

Microorganisms in water may also be released into the air in the form of water droplets and aerosols
Air currents may bring the microorganisms from plant or animal surfaces into air
These microorganisms may be either commensals or plant or animal pathogens
The main source of airborne microorganisms is human beings; commensal & pathogenic microflora of the upper respiratory tract and the mouth are discharged into the air

Question 10

Factors Affecting Air Microflora
A number of intrinsic and environmental factors influences the kind and distribution of the air microfloraA-Intrinsic factors

Answer 10

Include the nature and physiological state of microorganisms
Suspended spores are relatively more abundant than the vegetative bacterial cells: this is mainly due to the dormant nature of spores that enables them to tolerate unfavorable conditions like desiccation, lack of enough nutrients, and UV radiations
The size of microorganisms is another factor that determines the period of time for which they remain suspended in air
◦Generally, smaller microorganisms are easily liberated into the air and remain there for longer period of time
◦Droplets that are discharged into the air by coughing or sneezing are also suspended in air but for a short period of time
◦When their size decreases by evaporation they remain for a longer period in air

Question 11

B-Environmental factors (cont’d)

Answer 11

Air current influences the time for which either the microorganism or the particles loaded with microorganisms remain suspended in air: a gentle air current can keep them in suspension for long time
Air current is also important in the dispersal of microorganisms as it carries them over a long distance

Question 12

Factors Affecting Air Microflora (cont’d) B-Environmental factors

Answer 12

Temperature, humidity, air current, the height the microorganisms are found…..
Temperature and RH are 2 important factors that determine the viability of microorganisms
◦Ex: viruses like influenza, poliomyelitis survive better at lower temperatures ( 7 C –24 C)
◦The optimum rate of RH for the survival of most microorganisms is between 40 –80 %
◦Very low and very high humidity cause the death of most microorganisms
◦Almost all viruses survive better at RH between 17 –25 %. An exception is the Poliomyelitis virus that survives better at 80 –81 % RH

Question 13

Air Microflora & Human Health

Answer 13

It relies on the fact that air acts as a medium for the transmission of infectious agents. An adult man inhale 5 m3air/ day.
The probability of a person to become infected will be greatest if he’s exposed to a high concentration of airborne pathogen
S. aureusis the most commonly found pathogen since the carriers are commonly present.
◦Their number may vary between 0-1 / m3and 50 / m3
Outdoor air doesn’t contain disease causing pathogen in a significant number to cause any infection

Question 14

Air Microflora & Human Health (cont’d)

Answer 14

In Indoor air: chance for the spread of infectious diseases is more especially in areas where people gather in large numbers like in schools, universities, hospitals, …
Allergic disorders by air microflora: airborne particles like pollen, fungal spores, insect debris, animal dander.
◦Allergic disorders such as bronchial asthma, allergic rhinitis and atopic dermatitis
Pollens and fungal spores are important causative agents of allergy

Question 15

Air Microflora & Human Health (cont’d) 3

Answer 15

Fungal allergens are found in moist walls, mattresses, window frames. Ex: Several molds (Aspergillus, Penicillium) and yeasts are shown to be implicated in allergy
Pollens are present between September and November (weeds + grasses) and in spring (March-May) for trees

Question 16

A-Bacteria1-Neisseria meningitidis

Answer 16

Gram negative diplococci with fastidious growth requirements
Grows best at 35Cto 37C in a humid atmosphere
Virulence: capsule, LPS (endotoxin), pili
Disease:
◦Meningococcal meningitis: fatal disease characterized by fever, intense headache, nausea and often vomiting, stiff neck frequently with rash, loss of mental alertness.
◦Meningoencephalitis
◦Bacteremia, pneumonia, arthritis, pharyngitis
Reservoir: Restricted to humans (5-10% are carriers)
Mode of transmission: person-to-person (close contact) via respiratory droplets and secretions in crowded institutions

Question 17

1-Neisseria meningitidis(cont’d)

Answer 17

Occurrence:
Meningococcal infections are ubiquitous, greatest incidence occurs during winter and spring
Primarily a disease of very small children
Occurs commonly in children and young adults
In crowded institutions
Incubation period: Varies from 2 to 10 days, commonly 3-4 days
Prevention: Immunization by vaccines

Question 18

2-Streptococcus pneumoniae

Answer 18

Gram positive, ovoid bacterium
Capsule, resistant to phagocytosis
Most human infections are caused by 23 variants.
Disease: pneumococcal pneumonia
◦Symptoms: high fever, breathing difficulty, and chest pain, sputum is often rust-colored from blood coughed up from the lungs.
Reservoir: man and many healthy carriers are present
Mode of transmission: person-to-person via respiratory droplets and secretions in crowded institutions

Question 19

3-Mycoplasma pneumoniae

Answer 19

The smallest free living bacterium, able to pass through 0.45μm pore filters
Absence of cell wall and a cell membrane containing sterols are unique among bacteria
Strict aerobe, slow rate of growth: generation time 1-6 hours
Cause of MycoplasmalPneumonia common in young adults and children (~20% of pneumonias)
Mode of transmission: not known exactly
◦Probably by droplet inhalation and direct contact with infected persons
Incubation period: 6 to 23 days
Preventive measures:
◦Avoid crowded living and sleeping quarters whenever possible especially in institutions
Occurrence:
◦Worldwide, sporadic, endemic and occasionally epidemic with no seasonal incidence

Question 20

3-Mycoplasma pneumoniae (cont’d)

Answer 20

Upper respiratory tract infection:
◦Low-grade fever, malaise, headache, and a dry, nonproductive cough develop after 2-3 weeks after exposure
◦The symptoms may persist for 3 weeks or longer.
Lower respiratory tract infectionsincluding tracheobronchitisand bronchopneumonia

Question 21

4-Bacillus anthracis

Answer 21

Spore-forming gram positive bacilli, Facultative anaerobe
Virulence factors: capsule, exotoxins, spores
Anthrax:
◦Cutaneous: most common form
◦Inhalation: most deadly form
◦Gastrointestinal: rare but commonly fatal disease
Cause of Pulmonary anthrax: a disease of herbivorous animals, and humans can be infected through exposure to contaminated animals or animal products (animal tissues, contaminated hair, wool,…)
Mode of transmission:
◦Contact with infected animals (tissues: cattle, sheep. Goats, horses, pigs) or contaminated soil
◦Infectious aerosols
◦Contaminated hair, wool, drums
The incubation period is between 2 and 7 days

Question 22

4-Bacillus anthracis 2

Answer 22

Reservoir:
◦Animals, including wildlife such as elephants; cattle, sheep, goats
Occurrence:
◦Infrequent and sporadic human infection in most industrial countries
Prevention:
◦Immunization necessary for high risk people
◦Education and training of employees handling potentially contaminated articles
◦Control dust and proper ventilation
◦Animal vaccination is effective
Treatment: Antibiotics

Question 23

5-Corynebacterium diphtheriae

Answer 23

Gram positive bacilli with an irregular shape, facultative anaerobes, non-spore forming.
Cause of diphtheria:
◦It’s a disease of colder months in temperate zones involving unimmunized children under 15 years
◦Respiratory illness which is primarily a disease of children and can be fatal if not treated
◦Acute disease of tonsils, pharynx, larynx, nose, occasionally of other mucous membranes or skin, and sometimes the conjunctiva or genitalia
Symptoms: sore throat,low grade fever, malaise, loss of appetite, swelling of the neck
Highly virulent toxin (0.01mg can be fatal): interferes with protein synthesis. Ex: if the heart and kidneys are affected the disease can rapidly be fatal, the nerves may be involved, and partial paralysis may result.
Reservoir: man

Question 24

5-Corynebacterium diphtheriae 2

Answer 24

Mode of transmission:
◦By droplets or skin contact
◦By Contact with patient or carrier (cutaneous diphtheria)
Occurrence:
◦Worldwide distribution among the “urban poor area”
◦Disease of colder months in temperate zones involving unimmunized children under 15 years
◦No seasonal incidence
Incubation period:2-5 days, occasionally longer
Prevention:
◦Educational measures
◦Active immunization with diphtheria toxoid, DTaPvaccine

Question 25

6-Legionella pneumophila

Answer 25

Slender, pleomorphic, aerobic gram negative rod, stains poorly with common reagents, nutritionally fastidious
Capable of replication within macrophages
Resistant to chlorine
It occurs in natural water, at times it enters and proliferates in cooling tower, air coolers, shower baths. It may inhabit the water lines of hospitals, hotels.
Spraying and splashing of water containing pathogen may produce aerosols (outbreaks have been traced to spas, humidifiers, showers, decorative fountains..)

Question 26

6-Legionella pneumophila(cont’d)

Answer 26

Disease:
◦Asymptomatic infections are common
◦Legionnaire’s disease (Legionellosis): severe form of pneumonia bronchopneumonia severe fatal if not well treated;
Characteristics symptoms : high fever (40.5ᵒC), chills, dry cough, vomiting, diarrhea, headache, multi-organ disease is common (gastrointestinal tract, CNS, liver, and kidneys)
Incubation period 2-10 days, fever, chills, dry cough,
Men over 50 are the most susceptible especially heavy smokers, alcohol abusers, or chronically ill.
◦Pontiac fever: (Influenza like illness) non fatal disease , self limited febrile illness: chills, dry cough , myalgias, malaise and headache.

Question 27

6-Legionella pneumophila(cont’d) 3

Answer 27

Occurrence:
◦Most states of USA, Africa, Australia, Canada, S America and Europe
Reservoir:
◦Probably primarily aqueous
◦Hot water systems, air conditioning cooling towers and evaporative condensers
Patients at high risk:
◦Patients with compromised pulmonary function
◦Patients with decreased cellular immunity (transplant patients)
Mode of transmission:
◦Airborne transmission
◦Person to person transmission has not been demonstrated
Preventive measures:
◦For environmental sources associated with disease, treat with ionization, hyperchlorination, and superheating

Question 28

7-Mycobacterium tuberculosis

Answer 28

Slender rod, acid fast, obligate aerobe
Slow grower (20 hour or longer Generation time), form filaments and tend to grow in clumps. On the media their growth appear moldlike.
Lipid rich cell wall, making the organism resistant to disinfectants, detergents, drying, common antibacterial antibiotics, and traditional stains
Diseases:
◦Primary infection is pulmonary
◦Dissemination to any body site occurs most commonly in immunocompromised patients and untreated patients
Reservoir: primarily man

Question 29

7-Mycobacterium tuberculosis 2

Answer 29

Mode of transmission: Person-to-person spread by infectious aerosols, droplets
Occurrence:
◦Worldwide
◦Most common in Southeast Asia, sub-Saharan Africa, and Eastern Europe
◦Populations at greatest risk are immunocompromised patients (HIV), drug or alcohol abusers, homeless, and people exposed to diseased patients
Prevention and control
◦Immunoprophylaxis
◦Education
◦Make available medical, laboratory and X-ray facilities
◦Improvement of social conditions

Question 30

8-Bordetella

Answer 30

Extremely small (0.2 to 0.5 x 1μm), strictly aerobic, non-fermentative, gram negative coccobacilli
Three species are responsible for human disease:
◦Bordetellapertussis: Whooping cough
◦Bordetellaparapertussis: milder form of pertussis
◦Bordetellabronchiseptica: respiratory disease in dogs, swine, laboratory animals, and occasionally pertussis-like symptoms in humans

Question 31

8-Bordetella pertussis:

Answer 31

Very difficult to identify in laboratories
It produces several toxins: tracheal cytotoxinand pertussis toxin.
Virulent strains are capsulated
Disease:whooping cough
◦Very difficult to diagnose and to treat
◦First stage: sore throat like any viral infection, resembles common cold
◦Second stage: dry cough, non stop, uncontrolled (violence of coughing in children may result in broken ribs): 1-6 weeks
◦Third stage: may last for months, irreversible damage to the brain may occur in children
Reservoir:
◦Man is the only host
Mode of transmission:
Person to person by infected aerosols

Question 32

8-Bordetella pertussis (cont’d):

Answer 32

Occurrence:
◦Worldwide distribution
◦Children younger than 1 year
◦Prevalence of disease is increasing in older children and adults
◦Non-vaccinated individuals
◦Incubation period: commonly 7 to 10 days and rarely exceeding 14 days
Treatment, prevention and control:
◦Antibiotics
◦Vaccination: DTP (Diphtheria, Tetanus, Pertussis)
◦Tdap, DTaP: new vaccines
◦Prevention: educate the public, active immunization, protection of health workers in case of outbreaks

Question 33

9-Haemophilusinfluenzae

Answer 33

Small, pleomorphic, gram negative coccobacilli, facultative anaerobes, fermentative, very fastidious organism
Virulence factors: capsule, fimbriae, LPS
Reservoir: man
Mode of transmission:
◦By droplet infection and discharges from nose and throat during the infectious period
Infections:
◦Meningitis, bronchitis, arthritis, pneumonia, otitis, sinusitis, lower respiratory tract disease, conjunctivitis

Question 34

9-Haemophilusinfluenzae(cont’d)

Answer 34

Occurrence:
◦Worldwide, most prevalent in the 2-months to 3 year age group, unusual over the age of 5 years
◦Susceptible population: alcoholics, poor nutrition, cancer patients, diabetes patients
Incubation period:
◦Unknown, probably short 2-4 days
Preventive measures:
◦Several protein-polysaccharide vaccines have shown to prevent meningitis in children
◦Educate parents regarding the risk of secondary cases in siblings
◦Rifampin prophylaxis is used to eliminate carriage in children at high risk

Question 35

Viruses1-Influenza viruses

Answer 35

Only influenza A and B viruses (RNA viruses) cause human disease
Enveloped viruses
Inactivated by detergents
Transmission:
◦Inhalation of small aerosol droplets expelled during talking, breathing, and coughing
Worldwide occurrence, more common in winter

Question 36

1-Influenza viruses (cont’d)

Answer 36

Disease: Flu
◦Characterized by chills, fever, headache, and muscular aches.
◦Recovery normally occurs in a few days, and cold like symptoms appear as the fever subsides
Children: asymptomatic to severe infection
Adults: classic flu syndrome, Common cold
High risk population:
◦Elderly, immunocompromised patients, people with cardiac or respiratory problems

Question 37

2-Rhinoviruses (Picornaviruses)

Answer 37

Most important cause of the common cold and upper respiratory tract infections
Resistant to drying and to detergents
Transmission
◦Direct contact via infected hands and fomites
◦Inhalation of infectious droplets from coughing, sneezing
People of all ages are at risk
Worldwide occurrence:
◦disease is more common in early autumn and late spring
Control:
◦Washing hands and disinfecting contaminating objects

Question 38

3-Paramixoviridae

Answer 38

Enveloped viruses
Transmission: inhalation of large-droplets aerosols
Include
◦Morbillivirus: measles virus
Affect children
Symptoms: fever, cough cold red blotchy skin, rash
◦Paramyxoviruses: parainfluenza and mumps
◦Mumps:
Communicable disease
Common childhood disease characterized by painful, swelling of parotid glands and salivary gland
Transmission: Droplets containing saliva are the main source of the disease
◦Pnemoviruses: respiratory syncitial virus (RSV)
4/13/2021 40

Question 39

4-Rubella virus

Answer 39

Infects only humans
Virus causes asymptomatic disease
German measles
Transmission: respiratory route
Control:
◦MMR Vaccine

Question 40

5-Respiratory Syncytial Virus (RSV)

Answer 40

Most common cause of viral respiratory disease in infants
It can cause a life threatening pneumonia in older adults
Epidemics usually occur during winter and early spring
Symptoms:
◦Coughing and wheezing that last for more than one week
◦Fever only occurs in the presence of bacterial complications

Question 41

6-Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)

Answer 41

Coronavirus disease (COVID-19)
◦spreads primarily through droplets of saliva or discharge from the nose when an infected person coughs or sneezes Symptoms: COVID-19 affects different people in different ways. Most infected people will develop mild to moderate illness and recover without hospitalization.
Most common symptoms:
fever.
dry cough.
tiredness.
Less common symptoms:
aches and pains.
sore throat.
diarrhea.
conjunctivitis.
headache.
loss of taste or smell.
a rash on skin, or discoloration444/13/2021 of fingers or toes.
Serious symptoms:
difficulty breathing or shortness of breath.
chest pain or pressure.
loss of speech or movement.
On average it takes 5–6 days from when someone is infected with the virus for symptoms to show, however it can take up to 14 days.

Question 42

C-Fungi1-Blastomycosis dermatitidis

Answer 42

Incubation period: ranges from weeks to months.
Mode of transmission: The fungus is probably inhaled by people whose work or recreation brings them in close contact with the soil.
Blastomycosis: a fungal infection that usually affects the lungs and produces bronchopneumonia.
◦During the chronic stage of illness, the disease may circulate through the blood and cause skin disorders (most commonly), osteomyelitis, genitourinary (GU) disorders, and central nervous system (CNS) disorders (rarely).
Untreated blastomycosis is slowly progressive and usually fatal, although spontaneous decrease may occur.
Although most infections are asymptomatic, the mortality rate is 15% in appropriately treated cases

Question 43

1-Blastomycosisdermatitidis(cont’d)

Answer 43

Signs and Symptoms
◦Cough (the sputum may be brown or bloody)
◦Shortness of breath
◦Sweating
◦Fever
◦Rash
◦Skin lesions
◦Chest pain
◦General discomfort, ( malaise )
Treatment
◦Antibiotics like Amphotericin B; Alternative treatment is advised like consuming anti fungal herbs like garlic, green tea, and others

Question 44

2-Aspergillusfumigatus

Answer 44

Aspergillosis
Occurrence:worldwide, uncommon and sporadic
Opportunistic infections
Mode of transmission:
◦Inhalation of airborne conidia
◦Compost piles are ideal sites for growth and farmers and gardeners are most often exposed to infective amounts of these conidia.

Question 45

3-Pneumocystis jirovercii

Answer 45

Yeast-like fungus
Pneumocystis pneumonia
Symptoms:
◦Immunocompetent adults: few or no symptoms
◦Newly infected infants: show symptoms occasionally of a lung infection
The pathogen may be found in human health lungs
Susceptible groups: immunosuppressed individuals (cancer, HIV, transplant,…)
◦The most common opportunistic infection in persons withHIV infection
Mode of transmission: probably by inhalation

Question 46

Control of Airborne Microorganisms

Answer 46

Suppression of dust in room cleaning operation is important
Use of vacuum pick up + application of appropriate disinfectant, detergent has been recommended for dust removal
The UV radiation UV light wave is microbicidal (length 254 nm)
Bactericidal vapors: vapors of propylene glycol, triethylene glycol are strongly germicidal and are colorless , tasteless, , non toxic, non irritating, and non explosive.
Filtration + ventilation