Chapter III - Med Biol Course Content to Ecology 2023-2024 PDF

Exercise 3 Topic. The aerosphere as a source of pathogenic agents for humans.Vectors of invasive diseases present in the aerosphere. Glossary Aerogenic diseases - infectious diseases transmitted through the air. Air pollution - gases, liquids and solids present in the air; they are components that d...

Exercise 3 Topic. The aerosphere as a source of pathogenic agents for humans.Vectors of invasive diseases present in the aerosphere. Glossary Aerogenic diseases - infectious diseases transmitted through the air. Air pollution - gases, liquids and solids present in the air; they are components that do not naturally occur in the air , or substances found in quantities significantly increased as compared to the natural composition of the air. Emission – the mass of substances released directly into the environment, both from natural (e.g. volcanic eruptions) and anthropogenic sources (e.g. fuel combustion); the amount of these substances is determined in units of weight over time, e.g. g/h, kg/year. Immission (concentration of pollutants) – is the amount of a dust or gas pollutants in a given volume of air unit; is determined in units of weight of the substance per unit volume, e.g. µ/m 3, g/m3. Infectious disease– a disease caused by pathogenic microorganisms, i.e. viruses, bacteria, rickettsiae, fungi. Invasive disease– a disease caused by pathogenic protozoa and macroorganisms: helminths or arthropods. Myiasis - occurrence and development of the fly larvae in a living human or animal body. Parasitemia - the presence of parasites in the blood. Reservoir - the host population in which the parasite persists without causing disease symptoms and which is a source of infection for other host species. Transmission – mode of spreading /transfering of patogenes from one individual to another; there are two modes of transmission: direct - direct human-to-human contact (touches, kisses), , droplet spread (coughs, sneezes), faecal-oral spread; indirect- airborne, by contaminated objects, transmission through food and water, vectorborne (mechanical or biologic) Vector (in epidemiological terms)–an organism, most often an arthropod being the carrier of pathogenic microorganisms: - biological vector (biological carrier)–an organism (most often a blood-feeding arthropod, e.g. a mosquitoAnopheles sp.), in which the parasite(virus, bacteria, protozoa, nematode) undergoes a part of the development cycle (usually the development stage changes and the population of the parasite increases); - mechanical vector (mechanical carrier)–an organism (usually arthropod, e.g. a housefly), mechanically carrying pathogens or dispersal forms of a parasite to another organism, but this is not related to the parasite's developmental cycle. Aerosphere The layer of gases surrounding the planet, held in place by gravity, is called the atmosphere. The lowest layer of the atmosphere above the Earth's surface, which includes the troposphere and part of the stratosphere up to the ozone layer, is called the aerosphere. It protects life on Earth from ultraviolet (UV) rays, keeps the planet warm through insulation, and prevents temperature extremes between day and night.Also, the aerosphere provides: - environment for the temporary and / or permanent presence of viruses and organisms of medical importance (e.g. bacteria, fungi, protozoa), - a way of the microorganismstransmission , - a habitat for microorganism vectors. Into the air are released a large amount of pollutants, which are considered to be one of the most harmful environmental threats to human health. Sources of the aerosphere pollution are divided into: - natural (volcanic eruptions, forest and steppe fires, airborne soil particles, sand, as well as organic dust coming from the lithosphere containing pathogens being the etiological agent of many human diseases); - anthropogenic (related to human activity). Air movements (wind) can transport contaminants in the aerospace at various distances. The air has a selfcleaning ability, the basic mechanism which is to settle the suspension of microorganisms under the influence of gravitational forces. The ultraviolet radiation is a factor that affects the natural purification of air. Anthropopression - physico-chemical pollution. The effects of anthropopressure are the ozone layer degradation, climate change (the greenhouse effect), acid rain and smog. The greenhouse effect consists in increasing the average global air temperature [the 2020 average surface temperature was 1.76° F (0.98° Celsius) warmer than the twentieth-century average and 2.14˚F (1.19˚C) warmer than the pre-industrial period (1880-1900)]. The warming of the earth's climate is caused by an increase in the concentration of the so-called greenhouse gases - carbon dioxide, nitrogen oxides, methane and other hydrocarbons and their derivatives, as well as water vapour in the air. These gases remain in the atmosphere and make it difficult to emit heat outside the earth. Global warming causes the melting of glaciers, which may result in floods, but also may contribute to the drying of arable soils, which in turn reduces the size of crops and may cause famine. Climate change also creates a risk of hurricanes, long-term heat, and it may also lead to species extinction. "Ozone hole"- the ozone layer depletion is the second global threat to atmospheric pollution, next to the greenhouse effect. The ozone layer is located in the stratosphere at an altitude of 15-55 km, with a maximum gas concentration between 25 and 30 km. The degradation of the ozone layer is mainly caused by chlorofluorocarbons and halons, which are commonly used, among others, in aerosols, refrigeration systems for refrigerators and freezers, in cleaning liquids and as a blowing agent in the production of plastics. Destruction of the ozone layer is conducive to the exposure of living organisms to the ultraviolet radiation, which can lead to disturbance of the balance of entire ecosystems (including the diminishing of UV-sensitive crop and industrial species), and may increase the risk of skin diseases (including skin cancers) ) and eye conditions (cataracts) in humans and animals. Acid rain contains acids formed in the reaction of water with gases absorbed from the air, such as sulphur dioxide, nitrogen oxides, hydrogen sulphide, hydrogen chloride, fuels emitted to the atmosphere during the combustion process and various types of industrial production. These gases dissolve with great ease in atmospheric waters (rainfall, snow), causing their acidification and precipitation in the form of diluted sulphuric and nitric acids. Acid rain exerts direct and indirect effects not only on the natural environment (e.g. damage to the protective layer of plant leaf wax, soil acidification), but also in the infrastructure (e.g.it increases the corrosion potential of anthropogenic structures). It poses a direct threat to plants and animals, as well as humans; it can, among others, increase the frequency of respiratory, eye and skin diseases. Smog can be defined as fog saturated with gases and dust contaminants. It occurs in the areas with significant emissions of pollution spreading slowly and in favorable meteorological conditions and it leads to enormous condensation of pollutants in the air. There are two types of smog. Acid smog of London type (sulphuric) develops as a result ofsignificant emissions of SO2 (sulphur dioxide) in high humidity; SO2 is oxidised to sulphuric acid; it occurs in cities in the moderate climatic zone. Oxidative smog of Los Angeles type (photochemical) develops as a result of significant emissions of cars’ exhaust in high volume of solar radiation; nitrogen compounds are oxidised by hydrocarbons; strong oxidising compounds with ozone are produced; it occurs in big cities in the tropical climatic zone. Air pollution significantly affects human health by triggering many ailments mainly of the respiratory and circulatory systems. WHO estimates that the percentage rate of deaths related to air pollution is 5-6% per year. WHO data shows that 9 out of 10 people breathe air that exceeds WHO guideline limits containing high levels of pollutants, with low- and middle-income countries suffering from the highest exposures. The greatest impact of air pollution on human health is observed in industrial and urban areas. Types of pollutants can be divided in terms of their source, mode of release and composition (Figure 1). Figure 1. Types of air pollutants. The Air Quality Index (AQI) is a numerical indicator used to determine the degree of air pollution (Table 1). The higher the AQI index, the higher the percentage rate of the population exposed to negative health effects. Individual countries have their own air quality indicators, corresponding to different state air quality standards. The air quality index is calculated solely on the basis of 1-hour unverified data from air monitoring stations on the following substances: NO2, SO2, PM10, PM2.5, O3, benzene (C6H6) and carbon monoxide (CO) (Table 1). Table 1. Air quality index values (acc. Chief Inspectorate of Environmental Protection, Poland). Classes of air quality index Very Good (1) Good (2) Satisfactory (3) Sufficient (4) Bad (5) Very bad (6) PM10 [µg/m3] 0-20 21-60 61-100 101-140 141-200 >200 PM2,5 [µg/m3] 0-12 13-36 37-60 61-84 85-120 >120 O3 [µg/m3] 0-30 31-70 71-120 121-160 161-240 >240 NO2 [µg/m3] 0-40 41-100 101-150 151-200 201-400 >400 SO2 [µg/m3] 0-50 51-100 101-200 201-350 351-500 >500 C6H6 [µg/m3] 0-5 6-10 11-15 16-20 21-50 >50 CO [mg/m3] 0-2 3-6 7-10 11-14 15-20 >20 The classification of air quality allows the assessment of risks to human health (Table 2). Table 2. Air quality categories and health information for the public. AQI values 0-50 (0-54 ppb) 51-100 (55-70 ppb) 101-150 (71-85 ppb) Air quality good moderate unhealthy for sensitive groups 151-200 (86-105 ppb) unhealthy 201-300 (106-200 ppb) very unhealthy Recommendation no health impacts sensitive people should consider limiting outdoor exertion active children and adults, as well as persons with respiratory tract diseases should limit outdoor exertion all people should limit outdoor exertion; active children and adults, as well as persons with respiratory tract diseases should avoid outdoor activities all people should limit outdoor exertion; active children and adults, as well as persons with respiratory tract diseases should avoid outdoor activities Worldwide ambient air pollution accounts for: - 29% of all deaths and disease from lung cancer; - 17% of all deaths and disease from acute lower respiratory infection; - 24% of all deaths from stroke; - 25% of all deaths and disease from ischaemic heart disease; - 43% of all deaths and disease from chronic obstructive pulmonary disease. Particulate matter (PM) are inhalable and respirable particles composed of sulphate, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water. Depending on their size particles are divided into PM10 with a diameter of less than 10 microns and PM2.5with diameter of less than 2.5 microns. PM10 and PM2.5 pose the greatest risks to health, as they are capable of penetrating human lungs, reachingthe alveoli and further entering the bloodstream. Sources of PM include combustion engines, solid-fuel (coal, lignite, heavy oil etc.) combustion for energy production in households and industry, as well as other industrial activities (building, mining, manufacture of cement, ceramic and bricks, smelting). Diseases of the respiratory system caused by inorganic dusts - occupational diseases The accumulation of dust in the lungs and the occurrence of lung reactions to its presence leads to the development of pneumoconiosis. It is a chronic respiratory disease caused by long-term inhalation of dust. It is characterized by the occurrence of chronic bronchitis and progressive pulmonary emphysema, accompanied by pulmonary heart (hypertrophy and failure of the right ventricle) and circulatory insufficiency. Types of dust diseases: - collagen dust disease – a permanent damage of the structure of pulmonary alveoli and collagenic fibrosis: silicosis (silica dust), asbestosis, talc and aluminium pneumoconiosis; - non-collagen dust disease – a marginal growth of collagen fibres or cellular infiltration without any alteration in the alveoli structure in the lungs: barytosis (BaSO4), siderosis (ferric oxide), tin-oxide pneumoconiosis (SnO). Silicosis is a respiratory disease caused by breathing in (inhaling) silica dust (a common, naturally-occurring crystalfound in most rock beds; it forms during mining, quarrying, tunnelling, and working with certain metal ores). The following symptom types of silicosis may be distinguished: - simple chronic silicosis – results from long-term exposure (lasting longer than 20 years) to low amounts of silica dust; swelling in the lungs and chest lymph nodes (mainly exposure lasting longer than 15 years); - accelerated silicosis – occurs after exposure to larger amounts of silica over a shorter period of time (lasting from 5 to 15 years); swelling in the lungs; - acute silicosis – results from short-term exposure to very large amounts of silica; lung inflammation. Coal Worker’s Pneumoconiosis /Anthracosis/black lung/Caplan syndromeis a chronic lung disease characterized by deposits of coal dust in the lungs and formation of black nodules in the bronchioles, which results in focal emphysema. After long time of exposure develops pulmonary massive fibrosis. It affects in coal miners and it is aggravated by cigarette smoking. Asbestosis is an inflammation and fibrosis of the lung and it is caused by inhaling asbestos dust. With the development of asbestosis, about four times increases the risk of cancer diseases (lung cancer, bronchial cancer)and in the case of pleural mesothelioma the risk increases almost a thousandfold. Biological dust diseases  byssinosis– an occupational disease of the lungs caused by inhalation of cotton dust or dusts from other vegetable fibres such as flax, hemp, or sisal with Gram (-)bacteria.  suberosis – caused by inhalation of cork dust containing spores of Penicillium glabrum  farmer’s lung– an occupational disease caused by inhalation of organic dust from moldy hay containing spores of Actinomycetes and certain fungi  hay fever– an allergic reaction to airborne substances such as pollen that get into the upper respiratory passages - the nose, sinus, throat or the eyes Bioaerosol Bioaerosols are airborne particles comprising of or derived from living organisms. According to Hirst (1995) “a bioaerosol is an aerosol comprising particles of biological origin or activity which may affect living things through infectivity, allergenicity, toxicity, pharmacological or other processes.Bioaerosols include fungi, bacteria, viruses, and pollen and constitute from 5 to even 34% of indoor air pollution. Particles smaller than 5.0 μm usually remain suspended in the air for a long time, while large particles ones usually undergo sedimentation. Bioaerosols are derived from have a range of both natural and anthropogenic sources and that may lead to unique or complex assemblages at a given time and space (Figure 2). Health effects of bioaerosol exposure in occupational settings, for example agricultural environments, have been long established and there is growing evidence that these can range in infectivity, toxicity and allergenicity depending on various process-specific factors related to the size of particles and site of their depositionHealth effects of bioaerosol exposure is related to related to the size of particles and site of their deposition (Table 3). intensive agriculture: animal breeding, plant farming and storing waste management: sewage, comp osting, etc. natural disasters and terrorism: earthquakes, fl oods, accident al and deliberate dissemination natural: living organisms, nat ural environments Sources of bioaerosols industrial: food processing, ind ustries, laborat ories building technologies: air conditioning systems, water supplies Figure 2. Sources of bioaerosols. Table 3. Size of bioaerosol particles and site of their deposition. Particles size 9-30μm 5.5-9μm 3.3-5.5μm 2-3.3μm 1-2μm 0.1-1 Site of deposition eyeball nose and throat main air passages smallerair passages bronchi bronchioles and alveoli Biological aerosol can contain microorganisms which can cause infectious diseases. Examples of diseases whose etiological factors are transmitted by air are the following: - viral: chickenpox, flu, mononucleosis, rubella, mumps, meningitis; - bacterial: bronchitis and pulmonary disease, pulmonary tuberculosis, diphtheria, pertussis, scarlet fever, actinomycosis; - fungal: pulmonary aspergillosis, pulmonary mucormycosis, cryptococcosis, lung geotrichosis, tracheal and bronchial mycosis, fungal pneumonitis, pleural mycosis and others Examples of potential pathogenic fungi in bioaerosol are presented in table 4. Table 4. Example of microorganisms fungi present in bioaerosol Species Penicillium spp. (Penicillium chrysogenum /P. notatum) Aspergillus niger - growth on Czapek-Dox medium – compact white or - growth on Czapek-Dox medium – blue-green yellow basal felt covered by a dense layer of dark- velvety colonies; Morphology brown to black conidial heads; - conidiophores – smooth-walled, hyaline, multiple - conidiophores – smooth-walled, hyaline; branches; - conidial heads – biseriate with the phialides borne - conidia – globose to ellipsoidal (3-3.5μm), blueon brown, often septate metulae; green and smooth-walled; produced on phialides - conidia – globose to subglobose (3.5-5.0μm), dark borne on septate metulae. brown to black and rough-walled. Pathogenicicty opportunistic infections (invasive pulmonary opportunistic infections (pulmonary penicilliosis, aspergillosis, otomycosis – ear infection, cerebral ear infection, cornea infection, cutaneous aspergillosis, endophthalmitis, cutaneous infection), often allergic reaction, toxicosis and aspergillosis, hepatosplenic aspergillosis, fungemia), Sick Building Syndrome. allergic reaction and toxicosis. Primary pathogenic to humans is P. marneffei. Aerosol particles are exposed to ultraviolet and ionizing radiation in the air.The radiation and the loss of water as well as meteorological factors, especially atmospheric pressure, temperature and humidity, determine the instability of a biological aerosol. The quantitative and qualitative composition of microorganisms in the air depends on: - season of the year - the highest number of microorganisms occurs in the summer (June-August), the lowest in winter (December-January); - climatic conditions (e.g. air before raining contains more microbial cells than after raining); - location (the least polluted air is over mountains, seas, oceans and forests); - land development (in urban streets there are from several to several hundred thousand microbial cells in 1dm 3 of air, the number of microorganisms in rooms, especially those with high density of people and equipment, is many times higher than in the air in outdoor areas). The concentration of pollutants in indoor air (the air surrounding human areas) is much higher than in outdoor air, while the composition of both quantitative and qualitative indoor air is more stable. We spend more time indoors and therefore the quality of indoor air is significant in terms of human health. It is estimated that people stay in closed buildings from 80 to 95% of the time. An adult man takes approximately 20-22 thousand breaths per day – inhaling,during that time, more than 10 m3 of air (up to 20 m3) including all pollutants suspended in it. Standards of microbiological air quality WHO sets recommended limits for health-harmful concentrations of key air pollutants both outdoors and inside buildings and homes, based on a global synthesis of scientific evidence: - WHO Air Quality Guidelines for particulate matter, ozone, nitrogen dioxide and sulphur dioxide - Global update 2005; - WHO Guidelines for Indoor Air Quality - Dampness and Mould (2009) – the only standard regarding microbiological quality; - WHO Guidelines for Indoor Air Quality - selected pollutants (2010); - WHO Guidelines for Indoor Air Quality - household fuel combustion (2014). In the countries of the European Union there are also no relevant legal acts regulating / determining the permissible content of microorganisms in the atmospheric air. As a result of the adaptation of Polish law to EU law, the standards for atmospheric air pollution that were earlier in force under Polish law (Table 5) were repealed in August 2015, however, they were not replaced by new ones. Table 5. Former Polish Standards of atmospheric air quality. Air quality unpolluted moderately polluted heavily polluted Total number of microorganisms in 1m3 (in CFU/m3) Bacteria Fungi 3000 >10000 Methods for assessing the degree of air pollution The following bacteria shall be included in the assessment of the aerobic composition of aerosols: - actinomycetes –an indicator of air pollution with soil particles; - Pseudomonas fluorescens–an indicator of contamination by biological aerosols from surface water; - hemolytic bacteria β - aerosol indicators originating from the respiratory tract of humans and animals. So far, there has been no specific, effective method that enables continuous monitoring of microbial air pollution (such methods exist in the case of determination of dust and gas pollution). Current techniques only allow for determininga momentary state of air pollution. The simplest method used to determine the number of microorganisms (bacteria and fungi) in the air is the Koch method - sedimentation method. It is a low-cost technique that does not require any specialist equipment, however, it provides only low-accuracy data; it cannot detect small particles of bioaerosol that do not sediment or settle very slowly, and the volume of air being tested is only an estimate. Much more accurate results of air microbial contamination assessment are obtained when using volumetric samplers (aspirators, aerosols, impactors) that enable collection and testing of a precisely defined volume of air. Depending on the device used, the following methods can be distinguished: collision, filtration, scrubbing, electroprecipitation, centrifugal and flow cytometry. The use of volumetric methods allows for selection of the assessment of the number of microorganisms in a given volume of the air to be tested using breeding or non-culture methods, including microscopic (phase-contrast microscopy), biochemical (determination of microbial metabolism products such as enzymes, ergosterol, toxins), luminescent (determination ATP), and even genetic tests (PCR method) and flow cytometry. Koch sedimentation method The most commonly used test method for assessing the degree of microbial air pollution is the sedimentation method. It is based on free settling under the influence of gravity, pollen and dust particles that carry microorganisms. The sampling consists in opening and leaving a Petri dish with sterile microbiological mediumfor a specific time. An empirical conversion formula (Omelianski formula) is used to calculate the biological index of air pollutants (A) based on the assumption that within 5 minutes, the microorganism cells located in 10 dm 3 of air fall down onto the surface of 100 cm2. ā – the average number of colonies r – radius of the Petri dish t – time of the plate exposure Vectors transmitting infectious and invasive diseases Numerous adult insects (imago), for which air is the basic living environment, are mechanical or biological carriers of microorganisms and parasites. The biological carriers (biological vectors) of human parasites are: - ticks (Babesia microti - babesiosis); - common bugs (genus: Rhodnius, Triatoma and Panstrongylus for Trypanosma cruzi - Chagas disease); - mosquitoes (female Anopheles maculipennis and Anopheles gambiae( and species) for Plasmodium vivax and Plasmodium falciparum - malaria); - mosquitoes (Phlebothomus sp. for Leishmania tropica - leishmaniasis / abscess ulcer); - tse-tse flies (Glossina palpalis for Trypanosoma brucei gambiense - African sleeping sickness). Cosmopolitan insects: domestic fly, greenbottle fly and flesh fly participate in passive transmission (transfer) of protozoa (eg: Entamoeba histolytica, E. coli, Giardia intestinalis) and helminths (eggs) parasitizing in the human digestive tract, as well as numerous fungi and bacteria. Table 6. Characteristics of vectors transmitting infectious and invasive diseases. Characteristics Geographical occurrence Anopheles maculipennisgroup (genus Anopheles – about 70 species have the capacity to transmit human malaria parasites) Mosquito in Europe and the Mediterranean Culex pipiens complex Calliphora vicina Sarcophaga haemorrhoidalis Northern mosquito cosmopolitan Bluebottle fly Cosmopolitan Flesh fly cosmopolitan Stages in the life cycle egg larvae pupa imago adult female egg larvae pupa imago adult female egg larvae pupa imago larvae taking blood taking blood Stages involved in pathogen transmission Transmitted pathogens adult female adult female development human tissue imago Plasmodium spp. ornithoses neurotropic viruses Pathogenicity - - Stage invasive humans Parasitisms type for egg larvae pupa imago larvae in typhoid and pseudotyphoid bacilli, cholera bacilli, tuberculosis bacilli, dysentery bacilli, anthrax and tetanus bacilli myiasis development human tissue imago in typhoid and pseudotyphoid bacilli, cholera bacilli, tuberculosis bacilli, dysentery bacilli, anthrax and tetanus bacilli myiasis Myiasis is a disease caused by penetration and wandering larvae of flies in a living human or animal tissue. Parasitism may be necessary (obligatory) for the development cycle (eg. Dermatobia hominisin Central and South America), accidental (optional) or casual (e.g. Lucilia). Different forms of myiasis are distinguished: dermal (localized, moving), nasal, anterior and ocular, as well as the gastrointestinal tract and genital tract. Among the flies occurring in Poland(also widespread almost all over the world), parasitic larval stages (wounds and natural body orifices) occur in species - housefly - Musca domestica, - greenbottle fly - Lucillia sericata, - red-tailed flesh fly - Sarcophaga haemorrhoidalis, - bluebottle fly - Calliphora vicina. Etiological factors of human parasitosis, whose vectors are in the aerosphere Human blood is a permanent habitat for some protozoan and helminths.The parasitic trypomastigota Trypanosoma brucei gambiense or Loa loa microfilariae may be present in plasma, and forms of Plasmodium spp (rings, trophozites, schizonts, merozoites, gametocytes) may develop in red blood cells.The presence of parasites in the blood is referred to as parasitemia. Table 7. Characteristics of pathogenes transmitted by vectors in aerosphere. Characteristics Types of organisms Geographical occurrence Stages in the life cycle Stages invasive for humans Localization in the human body Trypanosoma brucei gambiense protozoa West Africa: Democratic Republic of Congo, Angola, Sudan, Central African Republic, Chad, northern Uganda trypomastigotes epimastigotes – in vector trypomastigotes bloodstream Loa loa roundworm West and Central Africa microfilariae L1-L3 larvae – in vector adult filariae L3 larvae adults – the subcutaneous tissue (often the eyeball) Vector Route of invasion Pathogenicity Symptoms in man Glossina palpalis (tse-tse fly) tse-tse fly bite African sleeping sickness - the first phase (the presence of trypanosomes in the blood and lymph) - feverish conditions appear irregularly (temperature up to 40°C), chills, night sweats, headaches, later there is damage to the heart muscle, kidneys, enlargement of the lymph nodes and liver - the second phase occurs several weeks or months after infection and is associated with the invasion of trypanosomes into the central nervous system - become apparent mental disorders occurring with alternating periods of stimulation and apathy, followed by coma. microfilariae – the bloodstream (10am-2pm), sputum, urine, spinal fluid Chrysops spp. (deer fly) repeated deer fly bites loasis - usually asymptomatic in endemic areas - short-term itchy eczema and erythematous lesions - periodic, painful infiltrates appear, usually in the area of large joints (Calabrian swelling), which disappear after a few days and may appear elsewhere - mature forms and microfilariae migrating to the eyeball cause pain, itching, tearing and photosensitivity References: 1. Buczek A. „Parasitology for medical students”, Koliber, Lublin 2007 2. Murray PR., Rosenthal KS., Pfaller MA. “Medical microbiology”, Elsevier, 2016 3. Meder S., Windelspecht M.: Human Biology. McGraw-Hill Science/Engineering/Math, Twelfth Edition 2011