Which of the following is not a human use of microorganisms

Microbial Complications

The initial cases of the acquired immunodeficiency syndrome (AIDS) were identified when unusual infectious diseases occurred in patients who had no prior diagnosis of an immunodeficiency.Pneumocystis pneumonia (PCP), toxoplasma encephalitis, cytomegalovirus (CMV) retinitis, andMycobacterium avium complex (MAC) bacteremia, as well as Kaposi sarcoma and central nervous system (CNS) lymphoma were so unusual in previously healthy patients that suspicion was quickly raised that the patients must have had some new form of immune deficit, especially when individual patients manifested several such infections either serially or concurrently, and when the number of such patients rapidly increased. The specific infectious syndromes were so characteristic of this new syndrome that their occurrence in previously healthy patients was soon considered as “AIDS defining” until the retroviral etiology of the syndrome was discovered and diagnostic tests for human immunodeficiency virus (HIV) became available for widespread clinical testing.

The first few years of the AIDS epidemic were devoted to learning how to recognize and treat these opportunistic infectious diseases and tumors. At the onset of the epidemic, clinicians were hampered by a dearth of available and accurate diagnostic tools for many of these opportunistic pathogens. There was also a dearth of therapeutic and preventive therapies for some of the common causative organisms. As better diagnostic techniques were developed and effective drug therapies were discovered and tested, patients survived their opportunistic infections with increasing frequency. The demonstration that specific chemoprophylaxis could prevent many of these infectious diseases also improved modestly the quality and duration of patient survival. However, patient survival did not improve dramatically until antiretroviral regimens were developed that provided durable HIV suppression and immunologic reconstitution, which thus substantially reduced or eliminated the occurrence of subsequent opportunistic infections.

Despite the widespread availability of effective antiretroviral regimens in the United States since the late 1990s, AIDS-related opportunistic infections are still seen frequently at many health care facilities, especially those serving populations with poor access to health care.

Approximately 10% of HIV-infected patients in the United States are unaware of their retroviral infection. This group often presents to health care facilities with opportunistic infections as their initial clue that they have HIV infection.

In addition, a substantial number of patients are aware of their HIV infection but are not in care as a result of economic, behavioral, or social factors. These patients also present with initial or serial opportunistic infections because they are not benefitting from stable and effective antiretroviral therapy (ART).

Even for patients who initiate ART and adhere carefully to their regimens, opportunistic infections can occur. Within the first few weeks or months after ART is started, opportunistic infections may develop due to immune reconstitution or unmasking (immune reconstitution inflammatory syndrome), that is, infectious syndromes can occur due to enhanced immunologic response to latent organisms or to residual antigen (seeChapter 367). In addition, even for the many patients who have sustained viral suppression and CD4 rise due to ART, such patients continue to be at enhanced risk lifelong for certain infections such as pneumococcal disease and tuberculosis, although the magnitude of the enhanced risk declines as the CD4 count rises. Finally, some opportunistic infections occur rarely at unexpectedly high CD4 counts.

Abstract

Microorganisms differ considerably in their ability to oxidize various carbohydrates. Some microorganisms can utilize one or more carbohydrates and produce acid and gas; others are able to produce acid but not gas; still others fail to ferment any carbohydrate. These characteristics of microorganisms are considerable value in the identification and classification of microorganisms. The chemical reactions that occur in the living microorganisms by enzymes are called metabolism. Bacteria use oxidation or fermentation to produce energy in their metabolic systems. Oxidative microorganisms carry the electron among organic compounds in metabolic pathways and use oxygen as the final electron (as hydrogen) accepter and produce carbon dioxide (CO2) and water as the final products. Fermentative microorganisms produce lower amount of energy, organic substances from organic compounds. Indication of oxidative fermentation characteristics of microorganisms are explained in this practice.

Microbiota and Microbial Pathogens

Microbial pathogens (e.g., bacteria, viruses, fungi) can alter electrolyte transport, increase intestinal permeability, and trigger inflammation, all of which can lead to diarrhea. They do this by a variety of mechanisms, including attaching to epithelial cells to insert their own products and alter host cell machinery, and by elaborating enterotoxins, which may be cytotoxic or can capture cell-signaling mechanisms to elicit secretion or disrupt TJs (seeTable 101.3 andChapter 110).186-190 In addition, the intestinal microbiota has been shown to influence host susceptibility to infectious colitis.191,192 A few pertinent examples are provided here.

The archetypal enterotoxin-mediated diarrhea is cholera. There are recent developments that demonstrate a role for biofilms inV. cholera survival193 and type VI secretion systems in delivery of toxin/proteins to commensal bacteria or to the host.194Vibrio cholerae carries a virulence cassette that produces at least 3 different molecules: an enterotoxin (CT) that stimulates CFTR, a zonula occludens toxin that disrupts TJ permeability, and an accessorycholera toxin (ACE) that stimulates TMEM-16F (ANO6, anoctamin 6) Cl− channel.195 The response to CT enterotoxin is not rapid, but is an unregulated, sustained increase in cAMP, which activates CFTR, and inhibits NHE3, resulting in copious fluid secretion (seeFig. 101.10 legend for details). Mice lacking CFTR do not respond to cholera toxin. Recently, in-vivo studies in mice have elegantly demonstrated that ACE stimulated TMEM-16F Cl− channel, is independent of rise in [Ca2+]i, and involves a PIP2/RhoA/ROCK/PIP5 kinase pathway. It rapidly initiates secretion and precedes the slow-acting CT enterotoxin-induced copious fluid loss.195 Bacteria such asSalmonella species,Campylobacter jejuni, andE. coli elaborate enterotoxins similar to CT, and likewise use the cAMP machinery to elicit fluid secretion.

Despite voluminous secretion, specific intestinal Na+-coupled nutrient absorptive (Na+/glucose, Na+/amino acids) pathways are unaltered by the toxin, forming the physiologic basis for ORT. As also discussed under “Nutrient Coupled Na+ Transport,” this is because SGLT transport is not affected by cAMP or cGMP. In the past 2 decades, the formulations of ORS have been refined based on several scientific observations. First, based on traditional remedies,160 is the addition of amylase-resistant starch, which can be converted to SCFAs such as butyrate in the colon. As mentioned above, butyrate increases Na+ absorption via a cAMP-independent mechanism and promotes fluid absorption.123 Second, zinc stimulates Na+ absorption by reversing the cAMP-induced inhibition of NHE3 and increasing NHE3 activity; zinc also inhibits Cl− secretion. Supplementation of zinc in ORS was observed to decrease the number of diarrheal episodes and stool volume. Therefore, current formulations of ORS from the World Health Organization include amylase-resistant starches and zinc supplementation.

3 NUTRITIONAL TYPES OF MICROBES

Microbes can be grouped nutritionally on the basis of how they satisfy their requirements for carbon, energy, and electrons or hydrogen. Indeed, the specific nutritional requirements of microorganisms are used to distinguish one microbe from another for taxonomic purposes.

Microorganisms may be grouped on the basis of their energy sources. Two sources of energy are available to microorganisms. Microbes that oxidize chemical compounds (either organic or inorganic) for energy are called chemotrophs; those that use light as their energy sources are called phototrophs. A combination of these terms with those employed in describing carbon utilization results in the following nutritional types:

Chemoautotrophs: microbes that oxidize inorganic chemical substances as sources of energy and carbon dioxide as the main source of carbon.

Chemoheterotrophs: microbes that use organic chemical substances as sources of energy and organic compounds as the main source of carbon.

Photoautotrophs: microbes that use light as a source of energy and carbon dioxide as the main source of carbon.

Photoheterotrophs: microbes that use light as a source of energy and organic compounds as the main source of carbon.

Microorganisms also have only two sources of hydrogen atoms or electrons. Those that use reduced inorganic substances as their electron source are called lithotrophs. Those microbes that obtain electrons or hydrogen atoms (each hydrogen atom has one electron) from organic compounds are called organotrophs.

A combination of the above terms describes four nutritional types of microorganisms:

Photolithotrophic autotrophy

Photo-organotrophic heterotrophy

Chemolithotrophic autotrophy

Chemo-organotrophic heterotrophy.

The characteristics of these types with representative microoganisms as well as other organisms are shown in Table 1.2.

TABLE 1.2. Nutritional types of microbes and other organisms

Nutritional TypeEnergy sourceElectron or hydrogen sourceCarbon sourceExamples of organismsPhotolithotrophic autotrophyLightInorganic compounds, waterCarbon dioxidePurple and green sulphur bacteria; algae; plants; cyanobacteriaPhoto-organotrophic heterotrophyLightOrganic compoundsOrganic compoundsPurple and green non-sulphur bacteriaChemolithotrophic autotrophyInorganic compoundsInorganic compoundsCarbon dioxideNitrifying, hydrogen, iron, and sulphur bacteriaChemo-organotrophic heterotrophyOrganic compoundsOrganic compoundsOrganic compoundsMost bacteria, fungi, protozoa, and animals

Photolithotrophic autotrophs are also called photoautotrophs. The cyanobacteria, algae and green plants use light energy and carbon dioxide as their carbon source but they employ water as the electron donor and release oxygen in the process. The purple and green sulphur bacteria use inorganic compounds as electron donors (e.g., H2S, S0) and do not produce oxygen in the process. Thus they are described as anoxygenic. Chemo-organotrophic heterotrophs are also called chemoheterotrophs. They use organic compounds for energy, carbon and electrons/hydrogen. The same organic nutrient compound often satisfies all these requirements. Animals, most bacteria, fungi, and protozoa are chemoheterotrophs. Photo-organotrophic heterotrophs are also called in short photoheterotrophs. The purple and green non-sulphur bacteria are photoheterotrophs and use radiant energy and organic compounds as their electron/hydrogen and carbon donors. These common microorganisms, found in polluted lakes and streams, can also grow as photoautotrophs with molecular hydrogen as electron donor. The chemolithotrophic autotrophs are also called chemoautotrophs in brief. They include the nitrifying, hydrogen, iron and sulphur bacteria. They oxidize reduced inorganic compounds, such as nitrogen, iron or sulphur molecules, to derive both energy and electrons/hydrogen. They use carbon dioxide as their carbon source. A few of them, however, can make use of carbon from organic sources and thus become heterotrophic. Such bacteria that use inorganic energy sources and carbon dioxide, or sometimes organic compounds, as carbon sources can be called mixotrophic, because they combine autotrophic and heterotrophic processes. Chemotrophs are important in the transformations of the elements, such as the conversion of ammonia to nitrate and sulphur to sulphate, that continually occur in nature.

Even though a particular species of microorganism usually belongs to only one of the four nutritional types, some show great metabolic flexibility and can alter their nutritional type in response to environmental change. For example, many purple non-sulphur bacteria are photoheterotrophs in the absence of oxygen but become chemoheterotrophs in the presence of oxygen. When oxygen is low, photosynthesis and oxidative metabolism can function simultaneously. This affords a survival advantage to the bacteria when there is a change in environmental conditions.

The specific nutritional requirements of bacteria are used extensively for taxonomic purposes. Specific identification tests have been designed for particular groups of bacteria, such as the Gram-negative intestinal bacilli, to determine the nature of water pollution.

Which of the following is not a use of microorganisms?

What are the human uses of microorganisms?

Which of the following is not true of microorganisms?

What are the four uses of microorganisms?