Microbiology Examination
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Microbiology Examination Guo qinglian （ 郭清莲） Zhongnan Hospital of Wuhan University
The purpose of microbiology is to study the characteristics of microorganisms and how to examine them.
In previous lessons, the knowledge of bacteria was introduced. This lesson, we will discuss the contents about fungi and viruses, as well as that of hospital-acquired infections.
Fungi
Fungi are a diverse group of organisms ranging in size from some unicellular microscopic types called yeasts to some large multicellular branching forms such as mushrooms.
Yeast
mushroom
mushroo
Morphological and physiological characteristics are the major means of classification.
Environmental factors play a major role in determining fungal form and physiology ， so the classification has been difficult and frustrating.
Fungi were originally classified as plants, but because of their variability,diversity,and asorptive nutrition ,they have been placed in a separate kingdom:the Fungi, or Myceteae.
The thallus （菌体） is the basic vegetative （繁殖） unit of the fungi.
thallus
If the thallus is filamentous （丝状的） , it is called a mold. If the thallus is spherical ， it is called a yeast.
mould
yeast yeast
Individual filaments in the mold are called hyphae （菌丝） , which when organized into a dense mat are called a mycelium （菌丝体） .
hyphae
hyphae
mycelium
Hypae show variation in structure and function depending on the species involved.
Fungi are found primarily in the soil. They produce extracellular enzymes that digest organic debris,and therefore important in the recycling of elements and in maintaining the fertility of the soil.
Only a few species are infectious to animals or humans. Some of these infectious species are dimorphic and can exist in either a mold or yeastlike state, depending on environmental conditions.
Fungal reproduction may be sexual or asexual. Budding or binary fission occurs in some yeasts, but the spore is the major reproductive unit.
Budding
Budding
binary fission
Spores can be produced sexually or asexually. Asexual spores may arise directly from hyphae, or they may be produced on or in specialized structures arising from the hyphae.
Fungi diseases
Fungi diseases are called mycoses and are divided into the following types ： systemic, superficial, subcutaneous （皮下的） , cutaneous and opportunistic. Fungal diseases in the healthy person are rare.
Nearly all fungal diseases are acquired by contact with spores in the soil or by inhalation of spores dispersed in the air.
The ability of the spores to cause disease is related to the number of spores to which the host is exposed and the state of health of the individual.
Treatment of fungal diseases
Treatment of fungal diseases is divided between two types of agents:topical （表面的） and systemic. Topical agents include nystatin,tolnaftate and miconazole. Systemic agents include amphotericin B and flucytosine （氟胞嘧啶） .
Viruses
Viruses are submicroscope, obligate, intracellular parasites that rely on their host for energy and nutrients.
Viruses have plagued humans since their existence, but an understanding of their nature is only of recent origin. In 1886, the particles of smallpox was first seen, though it was thought to be spores of the bacterial .
Viruses are given independent status because they are the smallest of microbial agents and because they are obligate intercellular parasites.
The virus is totally dependent on a living host for its survival. Viruses are infectious agents that can parasize all forms of life.
HBV
Tobacco virus
bacteriophage
The absolute necessity of a virus for its host is emphasized by the fact that viruses cannot make their own ATP.
They lack the enzymatic capacity to totally replicate themselves.
Viruses range in size from 18nm to over 250nm. The largest virus is smallpox( 天花病 毒 ), and it is the only one which can be seen with compound microscope. The smallest virus is bacteriophage （噬菌体） .
smallp
bacteriophage
Structure of viruses
Chemically, viruses consist of a core of nucleic acid, either RNA and DNA, surrounded by a protein coat.
Some viruses also contain a lipid envelope called envelope.
Viruses are classified according to certain parameters:type of nucleic acid, capsid symmetry ,capsomere mumber, size of virus, and molecular weight of nucleic acid.
Viruses can be grown in tissue culture or embryonated egg. Growth often results in cellular degeneration, which can be detected as a cytopathic effect (CPE).
The CPE are visible with the naked eye or with a compound microscope.
Viral infection is usually associated with some cytopathic effect （ CPE ） .
The number of viruses in a suspension can be determined by applying certain tehniques: electron microscope, agglutination of red blood cells, or measurement of CPE
Nosocomial infection
Diseases acquired in the hospital are refered to as nosocomial.
Bacteria are the most frequent etiological agents of hospitalassociated diseases. Other microorganisms may also be involved.
The gram-negative aerobic bacilli, such as members of the Enterobacteriaceae, are the most common cause of bacterial deseases.
The organisms causing disease in the hospital may be derived from the host (endogenous) or from sources, outside the host (exogenous). So nosocomial infection can be divided as endogenous infecton and exogenous one.
The infectious agents can be transmitted in the hospital in the same way as in the community.
Many factors contribute to the acquisition of hospital-associated diseases and may be associated with the patient or with the hospital.
The host’s susceptibillity to infection is influenced by the type of microorganism invoved, the dose of the microorganism, the site of infection, and the efficiency of the specific and nonspecific immune mechanism.
Most diseases develop in patients who have some underlying disease or condition that impairs the normal immunological response.
Hospital procedures, both diagnostic and therapeutic, have increased in recent years, and with their increase has been an increase in hospotal-associated diseases.
Catheterization （导管插入） and the use of intravenous infusion devices have contributed to the majority of diseases, but other sourses such as respiratory therapy and anesthetic （麻 醉） devices also play an important role.
The improper use of drugs, primarily antimicrobials, has led to the development of resistant species of microorganisms, toxic reactions, and allergic responses in the hospitalized patient.
Some antimicrobials destroy members of the indigenous microflora and create sites for infection by resistant species.
Other drugs, particularly those used during leukemia, cancer therapy, or transplantation, susppress the immunological response and also make the patient susceptible to infection by his own microorganisms.
The hospitalized patient is also subject to cross-infection from other patients and from hospital staff who may be carriers of infectious microorganisms. Nurses and physicians are the most frequent carriers of infectious agents.
The principal sites of infection and the microorganisms involved
The urinary tract – E.coli and other G- bacilli The respiratory tract - G- bacilli and staphylococci Surgical wounds – staphylococci Skin and eyes – staphylococci and G- bacilli Burn wounds – pseudomonas aerugiosa and Staphylococcus aureus Bacteremia –E.coli and other G- bacilli
Preventing methods
The most important method for preventing hospital-associated diseases is handwashing by hospital staff.
Disinfection of the site of injection is also an important means of preventing infection, since many hospitalized patients are subjected to hypodermic injections.
In most hospitals an infectioncontrol committee is in charge of surveying the number, types and sites of infection in the hospitalized patients and promulgating this information to hospital personnel.
It is also the purpose of the committee to suggest methods for reducing hospital-associated disease. Such proposals may include reducing the use of certain antimicrobials for treatment or suggesting the use of new disinfectants.
The purpose of microbiology is to study the characteristics of microorganisms and how to examine them.
In previous lessons, the knowledge of bacteria was introduced. This lesson, we will discuss the contents about fungi and viruses, as well as that of hospital-acquired infections.
Fungi
Fungi are a diverse group of organisms ranging in size from some unicellular microscopic types called yeasts to some large multicellular branching forms such as mushrooms.
Yeast
mushroom
mushroo
Morphological and physiological characteristics are the major means of classification.
Environmental factors play a major role in determining fungal form and physiology ， so the classification has been difficult and frustrating.
Fungi were originally classified as plants, but because of their variability,diversity,and asorptive nutrition ,they have been placed in a separate kingdom:the Fungi, or Myceteae.
The thallus （菌体） is the basic vegetative （繁殖） unit of the fungi.
thallus
If the thallus is filamentous （丝状的） , it is called a mold. If the thallus is spherical ， it is called a yeast.
mould
yeast yeast
Individual filaments in the mold are called hyphae （菌丝） , which when organized into a dense mat are called a mycelium （菌丝体） .
hyphae
hyphae
mycelium
Hypae show variation in structure and function depending on the species involved.
Fungi are found primarily in the soil. They produce extracellular enzymes that digest organic debris,and therefore important in the recycling of elements and in maintaining the fertility of the soil.
Only a few species are infectious to animals or humans. Some of these infectious species are dimorphic and can exist in either a mold or yeastlike state, depending on environmental conditions.
Fungal reproduction may be sexual or asexual. Budding or binary fission occurs in some yeasts, but the spore is the major reproductive unit.
Budding
Budding
binary fission
Spores can be produced sexually or asexually. Asexual spores may arise directly from hyphae, or they may be produced on or in specialized structures arising from the hyphae.
Fungi diseases
Fungi diseases are called mycoses and are divided into the following types ： systemic, superficial, subcutaneous （皮下的） , cutaneous and opportunistic. Fungal diseases in the healthy person are rare.
Nearly all fungal diseases are acquired by contact with spores in the soil or by inhalation of spores dispersed in the air.
The ability of the spores to cause disease is related to the number of spores to which the host is exposed and the state of health of the individual.
Treatment of fungal diseases
Treatment of fungal diseases is divided between two types of agents:topical （表面的） and systemic. Topical agents include nystatin,tolnaftate and miconazole. Systemic agents include amphotericin B and flucytosine （氟胞嘧啶） .
Viruses
Viruses are submicroscope, obligate, intracellular parasites that rely on their host for energy and nutrients.
Viruses have plagued humans since their existence, but an understanding of their nature is only of recent origin. In 1886, the particles of smallpox was first seen, though it was thought to be spores of the bacterial .
Viruses are given independent status because they are the smallest of microbial agents and because they are obligate intercellular parasites.
The virus is totally dependent on a living host for its survival. Viruses are infectious agents that can parasize all forms of life.
HBV
Tobacco virus
bacteriophage
The absolute necessity of a virus for its host is emphasized by the fact that viruses cannot make their own ATP.
They lack the enzymatic capacity to totally replicate themselves.
Viruses range in size from 18nm to over 250nm. The largest virus is smallpox( 天花病 毒 ), and it is the only one which can be seen with compound microscope. The smallest virus is bacteriophage （噬菌体） .
smallp
bacteriophage
Structure of viruses
Chemically, viruses consist of a core of nucleic acid, either RNA and DNA, surrounded by a protein coat.
Some viruses also contain a lipid envelope called envelope.
Viruses are classified according to certain parameters:type of nucleic acid, capsid symmetry ,capsomere mumber, size of virus, and molecular weight of nucleic acid.
Viruses can be grown in tissue culture or embryonated egg. Growth often results in cellular degeneration, which can be detected as a cytopathic effect (CPE).
The CPE are visible with the naked eye or with a compound microscope.
Viral infection is usually associated with some cytopathic effect （ CPE ） .
The number of viruses in a suspension can be determined by applying certain tehniques: electron microscope, agglutination of red blood cells, or measurement of CPE
Nosocomial infection
Diseases acquired in the hospital are refered to as nosocomial.
Bacteria are the most frequent etiological agents of hospitalassociated diseases. Other microorganisms may also be involved.
The gram-negative aerobic bacilli, such as members of the Enterobacteriaceae, are the most common cause of bacterial deseases.
The organisms causing disease in the hospital may be derived from the host (endogenous) or from sources, outside the host (exogenous). So nosocomial infection can be divided as endogenous infecton and exogenous one.
The infectious agents can be transmitted in the hospital in the same way as in the community.
Many factors contribute to the acquisition of hospital-associated diseases and may be associated with the patient or with the hospital.
The host’s susceptibillity to infection is influenced by the type of microorganism invoved, the dose of the microorganism, the site of infection, and the efficiency of the specific and nonspecific immune mechanism.
Most diseases develop in patients who have some underlying disease or condition that impairs the normal immunological response.
Hospital procedures, both diagnostic and therapeutic, have increased in recent years, and with their increase has been an increase in hospotal-associated diseases.
Catheterization （导管插入） and the use of intravenous infusion devices have contributed to the majority of diseases, but other sourses such as respiratory therapy and anesthetic （麻 醉） devices also play an important role.
The improper use of drugs, primarily antimicrobials, has led to the development of resistant species of microorganisms, toxic reactions, and allergic responses in the hospitalized patient.
Some antimicrobials destroy members of the indigenous microflora and create sites for infection by resistant species.
Other drugs, particularly those used during leukemia, cancer therapy, or transplantation, susppress the immunological response and also make the patient susceptible to infection by his own microorganisms.
The hospitalized patient is also subject to cross-infection from other patients and from hospital staff who may be carriers of infectious microorganisms. Nurses and physicians are the most frequent carriers of infectious agents.
The principal sites of infection and the microorganisms involved
The urinary tract – E.coli and other G- bacilli The respiratory tract - G- bacilli and staphylococci Surgical wounds – staphylococci Skin and eyes – staphylococci and G- bacilli Burn wounds – pseudomonas aerugiosa and Staphylococcus aureus Bacteremia –E.coli and other G- bacilli
Preventing methods
The most important method for preventing hospital-associated diseases is handwashing by hospital staff.
Disinfection of the site of injection is also an important means of preventing infection, since many hospitalized patients are subjected to hypodermic injections.
In most hospitals an infectioncontrol committee is in charge of surveying the number, types and sites of infection in the hospitalized patients and promulgating this information to hospital personnel.
It is also the purpose of the committee to suggest methods for reducing hospital-associated disease. Such proposals may include reducing the use of certain antimicrobials for treatment or suggesting the use of new disinfectants.
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