Medical Microbiology And Immunology PDF

SEMESTER-III MB-201-MJ - Medical Microbiology and Immunology Credits – 2 (30 Hours) Ms. Vedanti Prakash Satonkar Assistant Professor MES Abasaheb Garware College,Pune-05 ...

SEMESTER-III MB-201-MJ - Medical Microbiology and Immunology Credits – 2 (30 Hours) Ms. Vedanti Prakash Satonkar Assistant Professor MES Abasaheb Garware College,Pune-05  Pathogens Of the thousands of species of viruses, bacteria, fungi, and parasites, only a tiny portion are involved in disease of any kind. These are called pathogens. Among pathogens, there are degrees of potency called virulence, which sometimes makes the dividing line between benign and virulent microorganisms  Infection It is process in which a pathogenic organism enters , establishes itself , multiplies and invades the normal anatomical barrier of the host resulting in disease. When infection becomes apparent results in clinical manifestation and it is referred as “infectious disease”  Incubation period : The incubation period is the interval between the initial infection and the first appearance of any signs or symptoms. In some diseases, the incubation period is always the same; in others, it is quite variable. The time of incubation depends on the specific microorganism involved, its virulence (degree of pathogenicity), the number of infecting microorganisms, and the resistance of the host  Viability Traditionally, the operational definition of the capacity of a cell to form a colony on an appropriate agar medium (the colony or cfu count) has been almost universally accepted. Viability is also often expressed as the proportion of cells within a population that are capable of forming colonies. This has been used extensively in recognizing the cidal (lethal) and static (growth inhibitory) activities of antibiotics. In the former case, cfu counts decline, and in the latter they remain constant. However, it must be emphasized that viability is not a clearly measurable property  Susceptibility Lack of ability to resist some extraneous agent (such as a pathogen or drug) This information can be used to optimize treatment for the individual patient, while, in the aggregate, data of this type can be used to form a picture of the degree of resistance to each drug in the population at large. According to the new ISO 20776-1 standard, which is valid all over the world, these terms are defined as follows: Susceptible (s): A bacterial strain is said to be susceptible to a given antibiotic when it is inhibited in vitro by a concentration of this drug that is associated with a high likelihood of therapeutic success  Intermediate (i): The sensitivity of a bacterial strain to a given antibiotic is said to be intermediate when it is inhibited in vitro by a concentration of this drug that is associated with an uncertain therapeutic effect. Resistant (r): A bacterial strain is said to be resistant to a given antibiotic when it is inhibited in vitro by a concentration of this drug that is associated with a high likelihood of therapeutic failure  Pathogenicity Is the ability to produce disease in a host organisms Characteristics of pathogenic bacteria transmissibility , adherence to host cells, persistence, invasion of host cells and tissues , toxigenicity and ability to evade host’s immune system. Pathogenicity is expressed in means of virulence , referring to the degree of pathogenicity of the microbe.  Virulence Sum of the disease-causing properties of a strain of a pathogenic species Most bacteria have the ability to grow and survive under harsh conditions. Yet of the many thousands of bacterial species, only a small percentage are associated with humans as part of the natural flora or as causative agents of disease. This fact generates the question central to medical microbiology from the very start: What makes a bacterium pathogenic? The answer is not simple, because it turns out that many properties are necessary for a bacterial cell to gain entrance to a human, evade its defense systems, and establish an infection.  They include: Adherence to and penetration of host cell surfaces Evasion of phagocytic and immunologic attack Secretion of toxic proteins to weaken the host and promote spread of the pathogen Acquisition of nutrients, including iron, to permit growth within the host Survival under adverse conditions both within and outside the host and its macrophages  Pathogenesis Pathogenesis is the study of bacterial infection including the initiation of the infectious process and the mechanisms leading to the development of the signs and symptoms of disease. The variations are many, but the mechanisms used by many pathogens are now being dissected at the molecular level. The first step for any pathogen is to attach and persist at whatever site it gains access. This usually involves specialized surface molecules or structures that correspond to receptors on human cells. Because human cells were not designed to receive the microorganisms, they are usually exploiting some molecule important for essential functions of the cell.  For some toxin-producing pathogens, this attachment is all they need to produce disease. For most pathogens, it just allows them to persist long enough to proceed to the next stage, invasion into or beyond the mucosal cells. For viruses, invasion of cells is essential, because they cannot replicate on their own. Invading pathogens must also be able to adapt to a new milieu. For example, the nutrients and ionic environment of the cell surface differs from that inside the cell or in the submucosa  MANIFESTATIONS Fever, pain, and swelling are the universal signs of infection. Beyond this, the particular organs involved and the speed of the process dominate the signs and symptoms of disease. Cough, diarrhea, and mental confusion represent disruption of three different body systems. On the basis of clinical experience, physicians have become familiar with the range of behavior of the major pathogens. However, signs and symptoms overlap considerably. Skilled physicians use this knowledge to begin a deductive process leading to a list of suspected pathogens and a strategy to make a specific diagnosis and provide patient care. Through the probability assessment, an understanding of how the diseases work is a distinct advantage in making the correct decisions  Lab diagnosis Laboratory confirmation may include the study of different clinical samples, such as blood, urine, throat washings, and post-mortem tissue specimens. Laboratory diagnosis is based on isolation of pathogens by cell culture, electron microscopy, serological assay, and nucleic acid detection based techniques (RT-PCR). With regard to serological tests, ELISA, antigen-detection assays and serum neutralization tests can be used.  Most microorganisms can be isolated from the patient, grown in artificial culture, and identified. Others can be seen microscopically or detected by measuring the host specific immune response. Preferred modalities for diagnosis of each agent have been developed and are available in clinic, hospital, and public health laboratories all over the world. Empiric diagnosis made on the basis of clinical findings can be confirmed and the treatment plan modified accordingly. The new molecular methods, which detect molecular structures or genes of the agent, are not yet practical for most infectious diseases  Epidemiology Epidemiology is the “who, what, when, and where” of infectious diseases. The power of the science of epidemiology was first demonstrated by Semmelweis, who by careful data analysis alone determined how streptococcal puerperal fever was transmitted. He even devised a means to prevent it decades before the organism itself was discovered  Since then each organism has built its own profile of vital statistics. Some agents are transmitted by the air, others by food, others by insects, and some spread by the person-to-person route. Some agents occur worldwide, and others only in certain geographic locations or ecologic circumstances. Knowing how an organism gains access to its victim and spreads are crucial to understanding the disease. It is also essential to discovering the emergence of “new” diseases, whether they are truly new (AIDS) or just undiscovered (Legionnaires’ disease). Solving mysterious outbreaks or recognizing new epidemiologic patterns have usually pointed the way to the isolation of new agents. Epidemic spread and disease are facilitated by malnutrition, poor socioeconomic conditions, natural disasters, and hygienic inadequacy.  In previous centuries, epidemics, sometimes caused by the introduction of new organisms of unusual virulence, often resulted in high morbidity and mortality. The possibility of recurrence of old pandemic infections remains, and, in the case of AIDS, we are currently witnessing a new and extended pandemic infection. Modern times and technology have introduced new wrinkles to epidemiologic spread. Intercontinental air travel has allowed diseases to leap continents even when they have very short incubation periods (cholera).  The efficiency of the food industry has sometimes backfired when the distributed products are contaminated with infectious agents. The well-publicized outbreaks of hamburger associated Escherichia coli O157:H7 infection are an example. The nature of massive meatpacking facilities allowed organisms from infected cattle on isolated farms to be mixed with other meat and distributed rapidly and widely. By the time outbreaks are recognized, cases of disease are widespread, and tons of meat must be recalled. In simpler times, local outbreaks from the same source would have been detected and contained more quickly