chapter 9 air micro Flashcards
The atmosphere as a habitat is characterized by:
◦High light intensities,
◦Extreme temperature variation,
◦Low amount of organic matter
◦Insufficiency of available water
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
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
Microorganisms get into air as a consequence of
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.
Microorganisms found in air
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
I-Droplets:
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
II-Infectious dust:
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
Distribution of microorganisms in air
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
Distribution of microorganisms in air (cont’d)
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,…
Distribution of microorganisms in air (cont’d) 3
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
Factors Affecting Air Microflora
A number of intrinsic and environmental factors influences the kind and distribution of the air microfloraA-Intrinsic factors
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
B-Environmental factors (cont’d)
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
Factors Affecting Air Microflora (cont’d) B-Environmental factors
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
Air Microflora & Human Health
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
Air Microflora & Human Health (cont’d)
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
Air Microflora & Human Health (cont’d) 3
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
A-Bacteria1-Neisseria meningitidis
Gram negative diplococci with fastidious growth requirements
Grows best at 35Cto 37C 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
1-Neisseria meningitidis(cont’d)
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
2-Streptococcus pneumoniae
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
3-Mycoplasma pneumoniae
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
3-Mycoplasma pneumoniae (cont’d)
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
4-Bacillus anthracis
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
4-Bacillus anthracis 2
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
5-Corynebacterium diphtheriae
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
5-Corynebacterium diphtheriae 2
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
6-Legionella pneumophila
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..)
6-Legionella pneumophila(cont’d)
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.
6-Legionella pneumophila(cont’d) 3
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
7-Mycobacterium tuberculosis
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
7-Mycobacterium tuberculosis 2
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
8-Bordetella
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
8-Bordetella pertussis:
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
8-Bordetella pertussis (cont’d):
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
9-Haemophilusinfluenzae
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
9-Haemophilusinfluenzae(cont’d)
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
Viruses1-Influenza viruses
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
1-Influenza viruses (cont’d)
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
2-Rhinoviruses (Picornaviruses)
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
3-Paramixoviridae
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)
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4-Rubella virus
Infects only humans Virus causes asymptomatic disease German measles Transmission: respiratory route Control: ◦MMR Vaccine
5-Respiratory Syncytial Virus (RSV)
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
6-Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
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.
C-Fungi1-Blastomycosis dermatitidis
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
1-Blastomycosisdermatitidis(cont’d)
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
2-Aspergillusfumigatus
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.
3-Pneumocystis jirovercii
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
Control of Airborne Microorganisms
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
