PMB 2301 Introduction to Pharmaceutical Microbiology PDF

PMB 2301
INTRODUCTION TO PHARMACEUTICAL MICROBIOLOGY  BACTERIAL GROWTH

Growth of Bacteria is the orderly increase of all the chemical constituents of the bacteria. This result in the increase in cell size and cell mass. When the cell...

PMB 2301
INTRODUCTION TO PHARMACEUTICAL MICROBIOLOGY  BACTERIAL GROWTH

Growth of Bacteria is the orderly increase of all the chemical constituents of the bacteria. This result in the increase in cell size and cell mass. When the cell grows about twice its size, the nuclear material divides, transverse septum originates from plasma membrane and cell wall and divides the cell into two parts. The two daughter cells receive an identical set of chromosomes. Death of bacteria is the irreversible loss of ability to reproduce. BACTERIAL GROWTH CURVE

The growth curve indicates multiplication and death of bacteria. When a bacterium is inoculated in a medium, it passes through four growth phases  BACTERIAL GROWTH CURVE Fig 4: Different phases of bacterial growth  Lag phase

Adaptation In this phase, bacteria are not able to replicate and therefore no increase in cell mass. Enzymes and intermediates are formed and accumulated until they are present in concentration that permits growth to start. The length of the lag phase depends directly on the previous growth condition of the organism. Nutritionally rich medium to poor medium = increase in the lag phase. Nutritionally poor medium to a nutritionally rich medium = less lag phase. Antibiotics have little effect at this stage.  Exponential or Logarithmic (log) phase

Bacteria are in a rapidly growing and dividing state. Their metabolic activity increases and the bacteria begin the DNA replication by binary fission at a constant rate. The growth medium is exploited at the maximal rate Exhaustion of nutrients or accumulation of toxic metabolic products, and inhibit growth. Nutrient and oxygen becomes limited for aerobic organisms. The number of bacteria increases exponentially that is 20, 21, 22, 23.........2n, n is the number of generations. The time taken by the bacteria to double in number during a specified time period is known as the generation time or doubling time. The generation time tends to vary with different bacteria. Antibiotics act better at this stage  Stationary phase

All the nutrients in the growth medium are used up by the microorganism for their rapid multiplication. This result in the accumulation of toxic waste materials, and inhibitory compounds such as antibiotics. Change pH and temperature, thereby creating an unfavorable environment for the bacterial growth. Number of cell division = the number of cell death, finally bacterium stops its division completely. The cell number is not increased and thus the growth rate is stabilized. Production of exotoxins, antibiotics, metachromatic granules, and spore formation takes place in this phase.
 Decline or Death phase

Here the bacterium completely loses its ability to reproduce. Individual bacteria begin to die due to the unfavorable conditions the death is rapid and exponential. The numbe dead cells > live cells. Bacteria do not necessarily die even when starved of nutrients, and they can remain viable for long periods of time. Some bacteria which can resist this condition can survive in the environment by producing endospores. Some living bacteria use the breakdown products of dead bacteria as nutrient and remain as persister.
 FACTORS AFFECTING BACTERIAL GROWTH Nutritional requirement Physical/ environmental factors NUTRITIONAL REQUIREMENT FOR BACTERIAL GROWTH Some bacteria can synthesize all of their growth requirements from common mineral nutrients and simple carbohydrates. However, some bacteria are classified as auxotroph. Every organism must find in its environment all the substances require for energy generation and cellular biosynthesis. The chemical and element of this environment that are utilized for bacterial growth are referred to as nutrient or nutritional requirement. From these element and chemicals, the cell must synthesize all of the component it’s required including  Major Elements / Required Elements Major elements are the elements that make up cell constituent. At an elementary level, the nutritional requirement of bacteria is revealed by the cells elemental composition. These consist carbon, hydrogen, oxygen, nitrogen, sulfur, potassium, phosphorus, magnesium, calcium and iron. They are essential component of proteins, carbohydrates, lipid and nucleic acids. Some of the elements serve either a structural or functional role in the cells *Trace Element: Are metal ions require by certain cells in such small amount that it is difficult to detect them, and is not necessary to add them to culture media as nutrients. E.g Cobalt (Co) Zinc (Zn), Copper (Cu), Molybdenum (Mo), and Manganese (Mn).  Growth Factor In order to grow, a bacterium must have a source of carbon and other required nutrients. Growth factors are low molecular weight organic compound which a cell must contain in order to grow but which it is unable to synthesize. Microorganisms display a wide spectrum in their growth factor requirement, reflecting differences in their growth biosynthesis capabilities. E.g Thiamine, nicotinic acid, folic acid and para-aminobenzoic acid Some bacteria require many growth factors and are termed fastidious bacteria e.gNeisseria Some do not require any growth factor, they are versatile e.g E.coli  Energy source Organisms derive energy either from sunlight or by oxidizing chemical compound. Organisms that use radiant energy are called phototrophse.g. plants, algae, and photosynthetic bacteria. Organisms that use an organic form of carbon are called heterotrophs or chemotrophs. Lithotrophs oxidize inorganic compound to obtain their energy (e.g H2,NH3, NO2, Fe2+ and H2S). those that use CO2 as a sole source of carbon for growth are called autotrophs (A) Photoautotrophs: Use the energy of sunlight and the CO2 in the atmosphere to make organic compounds. (B) Photoheterotrophs: Use the energy of sunlight and derived their carbon from organic compound. (C) Chemolithoautotrophs: Use organic or inorganic compound for energy and derive their carbon from CO2 (D)Chemoorganoheterotrophs: Use organic compound for energy and carbon source. They are by far the most common group associated with humans and other animals. E.g most bacteria and some  PHYSICAL AND ENVIRONMENTAL REQUIREMENT FOR BACTERIAL GROWTH
1)THE EFFECT OF OXYGEN Bacteria display a wide range of responses to molecular oxygen (O2). The oxygen (O2) level in different environment varies greatly, A) Obligate aerobes: e.g Micrococcus species B) Obligate anaerobes: e.g Bacteroides (large intestine), Clostridium botulinum (botulism). C) Facultative anaerobes: e.g E.coli D)Microaerophiles O2 (2% to 10%). E.g Helicobacter pylori E)Aerotolerant anaerobes: E.g Streptococcus pyogenes (causes strepthroat)  PH The PH or hydrogen ion concentration [H+], of natural environments varies from about 0.5 in the most acidic soils to about 10.5 in the most alkaline lakes. The minimum PH above which the organism cannot grow, and the optimum PH, at which the organism grow best. There are three categories Neutrophiles: PH 5 (acidic)and PH 8 (basic)and have a PH optimum near neutral (PH7). E.g Helicobacter pylori Acidophiles: Are bacteria that grow optically at a PH below 5.5 e.g Acidothiobacillus ferroxidans Alkalophiles: PH above 8.5 e.g Bacillus alcalophilus grow best at PH 10.5. TEMPERATURE A particular bacterium will exhibit a range of temperature over which it can grow, defined by three cardinal points in the same as PH i.e minimum, maximum, and optimum.. A] Psychophiles: optimum between -5 and150C. B] Psychrotrophs: optimum between 200C and 300C, Causes food spoilage. C] Mesophiles: optimum temperature of warm blooded animals.. E.g E. Coli and most other common bacteria. Mesophiles that inhabit soil, and colder environment, generally have lower optimum close to 300C. D] Thermophiles: optimum 450Cand 750C. E] Hyper thermophiles ;700C or greater. These are usually members of the archaea. WATER AVAILABILITY: All microorganisms require water for growth. However in some environment even if water is present, it may not be available. The availability of water for cell defends upon its presence in the atmosphere (relative humidity) or its presence in solution or a substance (water activity). Water activity (Aw) is affected by the presence of solutes such as salt or sugars that are dissolve in the water and interact with water molecule and make the water unavailable to the cell.  Microorganisms live over a range of Aw from 1.0 to 0.7. e.g Aw of pure water= 1.0 , human blood is 0.9. A] Halophiles B] Mild Halophiles: Require 1-6% e.g many marine bacteria C] Extreme Halophiles 95-30% e.g the archeae bacteria that are able to grow in the presence of Nacl, are called halotolerant. They grow approximately at 10% Nacl. e.g Staphylococcus species BACTERIAL CULTURE MEDIA
The study of microorganisms requires techniques for isolating cells from natural sources and growing them in the laboratory on synthetic media. Microbiologists use bacterial culture media for many purposes and applications. One of the most important reasons for culturing bacteria in vitro is its utility in diagnosing infectious diseases. Culturing bacteria is also the initial step in studying its morphology and its identification. an artificial culture medium must provide all the nutritional components that a bacterium gets in its natural habitat. Some of the ingredients of culture media include water, agar, peptone, casein hydrolysate, meat extract, yeast extract and malt extract. A growth medium or culture medium is a medium designed to support the growth of microorganisms or cells. obligate parasites. Classification of Bacterial Culture Media

Bacterial culture media can be classified in at least three ways; Based on consistency, Based on nutritional composition and Based on its functional use / purpose. Classification based on consistency Culture media may be liquid, semi-solid or solid and biphasic A) Liquid media or broth: These are available for use in test-tubes, bottles or flasks. E.g nutrient broth. Inoculation in the liquid medium also helps to dilute any inhibitors of bacterial growth and can be used to obtain viable count (dilution methods). Drawback of liquid media; Properties of bacteria are not visible in liquid media and presence of more than one type of bacteria cannot be detected..  B) Solid media: Agar (simply called agar) is the most commonly used solidifying agent. It is an unbranched polysaccharide obtained from the cell membranes of some species of red algae such as the genera Gelidium. It melts at 95oC (sol) and solidifies at 42oC (gel; doesn’t contribute any nutritive property). it may be a source of calcium & organic ions. Most commonly, it is used at concentration of 1-3% Agar is available as fibres (shreds) or as powders. C) Semi-solid agar: Reducing the amount of agar to 0.2-0.5% renders a medium semi-solid. are useful in demonstrating bacterial motility and separating motile from non-motile strains.  D) Biphasic media: Sometimes, a culture system comprises of both liquid and solid medium in the same bottle. The inoculum is added to the liquid medium and when subcultures are to be made, the bottle is simply tilted to allow the liquid to flow over the solid medium. This obviates the need for frequent opening of the culture bottle to subculture. Besides agar, egg yolk and serum too can be used to solidify culture media. While serum and egg yolk are normally liquid, they can be rendered solid by coagulation using heat. Classification based on nutritional component Media can be classified as simple, complex and synthetic (or defined). While most of the nutritional components are constant across various media, some bacteria need extra nutrients. non-fastidious and fastidious. Simple media such as peptone water, nutrient agar can support most non-fastidious bacteria. Complex media such as blood agar have ingredients whose exact components are difficult to estimate. Synthetic or defined media such as Davis &Mingioli medium the composition of every component is well known..  Classification based on functional use or application: These include A) Basal media are basically simple media that supports most non-fastidious bacteria. B) Enriched media: Addition of extra nutrients in the form of blood, serum, or egg yolk to basal e.g. Blood agar, chocolate agar. C) Selective media are designed to inhibit unwanted commensal or contaminating bacteria and help to recover pathogen from a mixture of bacteria. Various approaches to make a medium selective include addition of antibiotics, dyes, chemicals, alteration of pH or their combination e.g. Thayer martin agar, etc. D) Enrichment media are liquid media that also serves to inhibit commensals in the clinical specimen. E.g alkaline peptone water. E) Differential media or indicator media: Certain media are designed in such a way that different bacteria can be recognized on the basis of their colony color. Examples: MacConkey agar, blood agar, etc. PURECULTURETECHNIQUES Pure culture technique is a method of culturing microorganisms in which all of the individuals in a culture have descended from a single parent cell. A pure culture is defined as a population of cell or multicellular organisms growing in the absence of other species or types. Result obtained using pure cultures are much easier to interpret however, the organism sometimes behaves differently as they do in their natural environment. The basic requirement for obtaining a pure culture are a solid culture medium; a media container that can be maintained in an aseptic condition; and a method to separate individual bacterial cell a colony is a mass of cell descended from the original one. About 1 million cell are required for a colony to be easily visible to the naked eye.  Six techniques used for obtaining pure culture of microorganisms. Streak Plate Method: This method is used most commonly and is the simplest to isolate pure cultures of bacteria from specimen. A small amount of mixed culture is placed on the tip of an inoculation loop/needle and is streaked across the surface of an agar medium.. It is usually advisable to streak out a second plate by the same loop/needle without reinoculation. plates are incubated to allow the growth of colonies. Presumably, each colony is the progeny of a single microbial cell thus representing a clone of pure culture. Such isolated colonies are picked up separately using sterile inoculating loop/needle and re-streaked onto fresh media to ensure purity. VARIOS METHOD OF STREAKING Pour Plate Method:
This method involves plating of diluted samples mixed with melted agar medium. Here, the mixed culture of bacteria is diluted directly in tubes containing melted agar medium maintained in the liquid state (42-45°C). The contents of each tube are poured into separate Petri plates, allowed to solidify, and then incubated. colonies develop both within the agar medium (subsurface colonies) and on the medium (surface colonies). These isolated colonies are then picked up by inoculation loop and streaked onto another Petri plate to insure purity. PP is also used for determining the number of viable bacterial cells present in a culture. Disadvantages of Pour plate method: The picking up of subsurface colonies needs digging them out of the agar medium thus interfering with other colonies, microbes must be able to withstand temporary exposure to the 42-45° temperature of the liquid agar medium; Pour Plate Method:
Spread Plate Method In this method , the mixed culture of microorganisms is not diluted in the melted agar medium it is rather diluted in a series of tubes containing sterile liquid, usually, water or physiological saline. A drop of so diluted liquid from each tube is placed on the center of an agar plate and spread evenly over the surface by means of a sterilized bent-glass-rod. The medium is now incubated. When the colonies develop on the agar medium plates, it is found that there are some plates in which well-isolated colonies grow. The isolated colonies are picked up and transferred onto fresh medium to ensure purity. In contrast to pour plate method, only surface colonies develop in this method and the microorganisms are not required to withstand the temperature of the melted agar medium. Spread Plate Method Serial Dilution Method: Serial dilution method is commonly used to obtain pure cultures of those microorganisms that have not yet been successfully cultivated on solid media and grow only in liquid media. The inoculum is subjected to serial dilution in a sterile liquid medium, and a large number of tubes of sterile liquid medium are inoculated with aliquots of each successive dilution. The aim of this dilution is to inoculate a series of tubes with a microbial suspension so diluted that there are some tubes showing growth of only one individual microbe.. If this tube shows any microbial growth, there is a very high probability that this growth has resulted from the introduction of a single microorganism in the medium and represents the pure culture of that microorganism Serial Dilution Method: Single Cell Isolation Methods An individual cell of the required kind is picked out by this method from the mixed culture and is permitted to grow. Two methods are employed: Capillary pipette method: Several small drops of a suitably diluted culture medium are put on a sterile glass-coverslip by a sterile pipette drawn to a capillary. One then examines each drop under the microscope until one finds such a drop, which contains only one microorganism. This drop is removed with a sterile capillary pipette to fresh medium. The individual microorganism present in the drop starts multiplying to yield a pure culture. Capillary pipette method Micromanipulator method:

Micromanipulators have been built, which permit one to pick out a single cell from a mixed culture. The micro-manipulator has micrometer adjustments by means of which its micropipette can be moved right and left, forward, and backward, and up and down. A series of hanging drops of a diluted culture are placed on a special sterile coverslip by a micropipette. Now a hanging drop is searched, which contains only a single microorganism cell. This cell is drawn into the micropipette by gentle suction and then transferred to a large drop of sterile medium on another sterile coverslip. This yields a pure culture of the required microorganism. The advantages of this method are that one can be reasonably sure that the cultures come from a single cell and one can obtain strains within the species. The disadvantages are; the equipment is expensive, its manipulation is very tedious, and it requires a skilled operator. Enrichment Culture Method used to isolate those microorganisms, which are present in relatively small numbers or that have slow growth rates compared to the other species present in the mixed culture. specially designed cultural environment by incorporating a specific nutrient in the medium and by modifying the physical conditions of the incubation. The medium of known composition and, specific condition of incubation favors the growth of desired microorganisms Maintaining a stock culture Once a pure culture has been obtained, it can be maintained as a stock culture; a stock culture is stored in the refrigerator as growth on an agar slant For long – term storage, stock culture can be frozen at 70ºc in a solution that prevents ice crystals from forming and damaging cells. Alternatively, cells can be lyophilized or freeze dried.  PARASITOLOGY Definition of terms; Parasitology - the science or study of host-parasite relationships Parasite - one animal deriving its sustenance from another without making compensation. The uncompensated animal is the host. Medical parasitology - study of parasites which infect humans or Clinical Parasitology- deals with animal parasites of man and their medical importance. Host - the partner providing food and/or protection i.e an organism which support parasite. Some parasites require more than one host to complete their life cycle; Parasites involves in medical parasitology are; Protozoa,helminthes and some arthropods  Type of hosts Definitive host - the host in which sexual maturity and reproduction takes place. Intermediate host - the host in which the parasite undergoes essential development. Reservoir (carrier) host - the host harboring a parasite in nature, serving as a source of infection for other susceptible hosts. Reservoir hosts show no sign or symptom of disease. Paratenic host - an accidental host serving as a holding place for a parasite. It is a vehicle for reaching definitive host Natural host-A host that is naturally infected with certain specie of parasite Accidental host- A host that is under normal circumstance not infected with the parasite Vector - “carrier” of a parasite from one host(infected) to another (non infected). Often an insect(arthropod) e.g. female anopheles mosquito  Types of parasite Facultative parasite: parasites able to live both free living and parasite living e.g. Strongyloides species. Obligate parasite: parasite living permanently in a host and cannot live without a host e.g. Trichomonos species. Coprozic (spurious) parasites: foreign, pass through alimentally canal without affect. Endoparasite-living inside the body of their host e.g. Entamoeba histolytica Ectoparasite-living on the outer surface of its host e.g. mice,lice Accidental host- When a parasite attack an unnatural host and survive Erratic parasite- One that wander in an organ not usually not found e.g. Entamoeba histplytica in the liver  A successful parasite - when it is in delicate balance with the host. If the balance is upset, the host may destroy or expel the parasite; If the host is overly damaged, it may die - as will the parasite.. Symbiosis - “living together,” a close association between two organisms. Mutualism - both organisms are benefited (bacteria in bowel). Commensalism - “eating at the same table;” One organism is benefited, the other is unaffected. Parasitism - one organism is benefited at the expense of another (the host).  Relationships between organisms Symbiosis: permanent association between two organisms Mutualism: two organisms living together, the two organisms benefit. E.g. termites and flagellates Commensalism: Two organisms Living together, one is benefited and the other is neither benefited nor harm. E.g. E.coli and man When the other organism become affected, then the relationship turns to Parasitism.  Effect of the parasite on the host Mechanical injury: the host may be inflicted by a parasite by means of pressure as it grows bigger e.g. hydatid cyst that block the ducts. Deleterious effect: the production of toxic substances e.g in malaria Deficiency of nutrients, fluids and metabolites parasite may generate disease by opposing the host for nutrient Indirect effect Immunological response e.g. tissue injury Excessive proliferation of certain tissue due to invasion by some parasite  Host adaptation Normally the host defenses reduces the parasitic load to low levels but fails to eliminate the parasite completely and transmission continues. The defense to parasitic infection involves both non immune and acquired immune mechanisms such as: *Protective outer coverings e.g skin *Acidic nature of the stomach *Biochemical changes (sickle cell anemia) *Immune system  Human parasitology Protozoology: Classes are ciliophora, lobosea, sporozoa, zoomastigoporea Organisms are unicellular Helminthology : Classes include nematoda, cestoda, trematoda, methacantocephala Organism are multicellular Arthropodology: Classes; arachnida,insecta,crustecea,chilopoda Organisms are ectoparasite  Entamoeba histolityca (lobosea) Disease: Amoebiasis Geo. Dis.: cosmopolitan, but more common in tropical and subtropical countries and in countries with poor sanitation Habitat: in the lumen of the large intestine Clinical picture: Dysentery: blood+mucous diarrhea,Sever abdominal pain Tenesmus: sense of incomplete evacuation Complication: A. intestinal: peritonitis, appendicitis, Hemorrhage B. Extra intestinal: Most commonly: liver ; hepatitis, fever, amoebic liver abscess Also in lung, skin, and brain  Plasmodium sp. (sporozoa) Approximately 300 million people worldwide are affected by malaria and between 1 and 1.5 million people die from it every year Geo. Dis:extremely widespread, mainly confined to Africa, Asia and Latin America Causative agent:  Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, Plasmodium malarea. Transmission: Malaria parasites are transmitted from one person to another by the female Anopheles Mosquito. The males do not transmit the disease as they feed only on plant juices. Reproduction: 1. Sexual reproduction: in anopheles mosquito 2. Asexual reproduction: in human (called sporozoans) in which sporozones multiply to produce merozoites, these, in turn, become trophozoits.  Pathology and clinical significance When merozoits invade the blood cells, using hemoglobin as a nutrient, eventually, the infected red cells rupture, releasing merozoits that can invade other erythrocytes. If a large numbers of red cells rupture at roughly the same time, a paroxysm (sudden onset) of fever can result from the massive release of toxic substance. Plasmodium falciparum is the most dangerous species. P. malriae, P. vivax, and P. ovale cause milder form of the disease, probably because they invade either young or old red cells, but not both. This is in contrast to P. falciparum, which invades cells of all ages. Plasmodium falciparum is characterized by persistent high fever and orthostatic hypertension. Infection can lead to capillary obstruction and death if treatment is not introduced.  Malaria life cycle After 9-16 days they Plasmodium sporozoits are carried by return to the blood and develops in the blood to the victim's liver penetrate the red cells, gut of mosquito where they form cyst- where they multiply This induces bouts of and is passed on in like structure containing again, progressively fever and anemia in the saliva of an thousands of merozoits breaking down the red the infected individual. infected insect cells In cerebral malaria, the infected red cells obstruct the blood vessels in the brain. Other vital organs can also be damaged often leading to the death of the patient  Toxoplasma gondii

Disease: Toxoplasmosis Geo. Dis.: world wide Transmission: (1) eating row or undercooked meat of sheep and cow containing viable trophozoits (bradyzoits) (2) swallowing food and water contaminated with infected cat feces (3) Congenital transmission: through placenta (fatal) especially when infection occurs during pregnancy (4) person to person: blood transfusion or organ transmission Clinical symptom:  Infection of normal human hosts are common and usually asymptomatic  The infection can be very sever in immunocompromised individuals, who may also suffer recrudescence of the infection.  Congenital infections can also be sever, and they are the major cause of blindness in newborns.  Nematodes Nematodes are slender, worm-like animals, typically less than 2.5 millimeters long. The smallest nematodes are microscopic, while free-living species can reach as much as 5 centimeters some parasitic species are larger. Ascaris lumbricoides Ascaris lumbricoides is the largest nematode (roundworm) parasitizing the human intestine 1/3 of the world population is infected with this worm Geo. dis: world wide, common among people with low standard of living and among children Clinical symptoms:- small numbers asymptomatic large numbers of adults in intestine – obstruction and pains at times adults migrate into bile duct, oesophagus or through surgical anastomoses of intestine and cause malnutrition if in large numbers Lung phase A.lumbricoides is known as Ascaris pneumonitis In the lung it causes hemorrhage, inflammation, bacterial infection. It also causes allergy in areas with seasonal transmission. Intestinal phase The intestinal phase causes malnourishment, intestinal blockage. A.lumbricoides will move around in the body in response to chemotherapy or fever.  Life cycle 2 phases: lung and intestinal Egg ingested, hatches in duodenum; larvae penetrate intestine wall, enter blood vessels and embolize through liver to lungs. They then migrate into airspaces, up trachea and are swallowed, taking up permanent adult residence in the small intestine 2 months from egg to mature adult Each female produce 200,000 eggs per day Adult worms can live 1 to 2 years.  Cestodes Tapeworms are ribbon-shaped multi-segmented flatworms They dwell as adults entirely in the human small intestine. The larval forms lodge in skin, liver, muscles, the central nervous system, or any of various other organs  Taenia saginata or Beef Tape-Worms Causes taeniasis Habitat: small intestine— (ileum) Transmission: acquired in humans through the ingestion of raw or poorly cooked meat of infected cows. These cows have been infected via the ingestion of human feces containing the eggs of the parasite Morphology: Adult is divided into three parts,  Head : round and small. It has four suction disks  Neck : A small, slender neck, about an inch long  Segments  Adult tapeworms can grow up to 25 meters in the lumen of the intestine, but are usually closer to 5 meters in length Egg present in feces Larva stage in muscle of thigh, shoulder, neck and heart of cattle only (intermediate host) Clinical symptoms: High infection: diarrhea and constipation Vomiting Loss of appetite Anemia  Trematodes Trematodes are flattened oval or worm-like animals, usually no more than a few centimeters in length, Some as small as 1 millimeter Some as large as 7 meters. distinctive external feature is the presence of two suckers, one close to the mouth, and the other on the underside of the animal. 
Schistosomiasis (Bilharzia) Disease of the venous system, system acquired by people when they come in contact with contaminated water Adult Schistosomes take up residence in various abdominal veins, depending on the species; they are, therefore called (Blood Flukes) Very common among children Geo. Dis.: developing countries, affects up to 200 million people Transmission: Direct skin penetration Fresh water becomes contaminated by Schistosoma eggs when infected people urinate or defecate in the water.  The eggs hatch and the parasites grow and develop inside snails. Schistosoma is not acquired by ingestion of contaminated food It directly penetrates the skin of swimmers in contaminated rivers and lakes. 2 types of Schistosomiasis:  Intestinal Schistosomiasis  Urinary tract Schistosomiasis  Pathology Intestinal Schistosoma: the primary site of infection is the gastrointestinal tract. Damage to the intestinal wall is caused by the host’s inflammatory response to eggs deposited at that site. The eggs also secret proteolytic enzymes that further damage the tissue. Urinary tract Schistosoma: The primary site of infection are veins of the urinary bladder, where the organism eggs can induce fibrosis, granulomas, and hematuria Clinical picture: Intestinal Schistosoma: GI bleeding, diarrhea, and liver damage. Intermediate host