Sana’s Guidelines for Hospital Infection Control Mohd Samiullah Khan
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Microorganisms1

 
STRUCTURE OF TYPICAL BACTERIAL CELL
The outer layer or cell envelope consists of two components, one is a rigid cell wall and the second one is beneath it called cytoplasm or plasma membrane. The cell envelope encloses the protoplasm, comprising the cytoplasm, cytoplasm inclusions such as ribosomes and mesosomes, granules vacuoles and the nuclear body. The cell may be enclosed in a loose slime layer called as a capsule. Some bacterial carry filamentous appendages protruding form the cell surface – the flagella which are organs of locomotion and the fimbriae which appear to be organs for attachment.
 
The Cell Wall
The cell wall accounts for the shape of the bacterial cell and give it rigidity.
 
Cytoplasmic Membrane
The cytoplasmic (plasma) membrane is a thin layer lining the inner surface of the cell wall and separating it from the cytoplasm.
 
Cytoplasm
The bacterial cytoplasm is a colloidal system of a variety of organic and inorganic solutes in a viscous watery solution.
 
Ribosomes
Ribosomes are the centers of protein synthesis.
 
Mesosomes
Mesosomes are formed as invaginations of the plasma membrane into the cytoplasm. They are to the principal sites of respiratory enzymes in bacteria.
 
Intracytoplasmic Inclusions
Intracytoplasmic inclusions may be of various types, the chief of which are volutin, polysaccharide, lipid and crystals.2
 
Nucleus
Bacterial nuclei have no nuclear membrane and nucleolus. It consists of a single molecule of double stranded DNA arranged in the form of a circle.
 
CLASSIFICATION OF BACTERIA DEPENDING UPON THEIR MORPHOLOGY
 
Cocci
Round or oval bacteria
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Diplococci
Cocci in pairs e.g. Meningococci, Gonococci, Diplococcus pneumoniae
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Two round
 
Staphylococcus
Cocci in clusters
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Streptococci
Cocci in chains.
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Bacilli
Bacilli are rod or stick shaped bacteria.
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Streptobacilli
Bacilli in chains
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Diplobacilli
Bacilli in pairs
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Vibrios
Slightly curved rods
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Spirilla
Regularly coiled rigid organisms
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Spirochetes
Flexible, coiled organisms
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IMPORTANT PATHOGENS AND THE DISEASES THEY CAUSE
Gram-positive cocci
S.No
Organism
Morphology
Important disease
1.
Staphylococcus aureus
Cocci in groups
Boils, abscesses, bacteraemia, pneumonia, food poisoning.
2.
Streptococcus pyogenes
(Group A Streptococcus)
Cocci in chains
Sore throat, bacteraemia and rheumatic fever leading to heart disease.
3.
Streptococcus pneumoniae
(Diplococcus pneumoniae)
Capsulated diplococci
Meningitis pneumonia, otitis
Gram-positive Rods
S.No
Organism
Morphology
Important disease
1.
Bacillus anthracis
Large, spore – forming, capsulated, bacilli which tend to form chains
Anthrax
2.
Corynebacterium diphtheriae
Pleomorphic nonmotile rods
Diphtheria of the throat and skin
3.
Listeria monocytogenes
Small rods with tumbling motility at low temperatures
Meningitis, stillbirth, bacteraemia
4.
Clostridium botulinum
Nonmotile plemorphic rods, with oval subliminal spores.
Severe food-poisoning
5.
Clostridium tetani
Drumstick bacillus
Nonmotile, long thin rods with round terminals spores
Tetanus
4
Gram-negative rods
S.No
Organism
Morphology
Important disease
1.
Haemophilus influenza
Small, nonmotile cocco-bacilli (or) rods pleomor-phic
Acute respiratory infections, meningitis, ear infections
2.
Bordetella pertussis
Small, nonmotile cocco-bacilli
Whooping cough
3.
Brucella species
Small, nonmotile cocco-bacilli
Brucellosis (undulant fever)
4.
Yersinia pestis
(Pasteurella pestis)
Nonmotile, capsulated cocco-bacilli
Septicemia
5.
Francisella tularensis
Small, nonmotile, capsulated
Skin infections, eye infections, and respiratory infections.
6.
Bacteroides species
Nonmotile, small pleomorphic rods
Bedsores, abscesses, abdominal infections
7.
Escherichia coli
Motile (or) nonmotile rods
Urinary infections
8.
Klebsiella pneumonia
Nonmotile capsulated rods
Chest infections
9.
Proteus species
Motile rods
Urinary infections
10.
Pseudomonas aeruginosa
(Pseudomonas pyocyanea)
Motile rods
Urinary infections
11.
Shigella species
Nonmotile rods (or) Coccobacilli
Bacillary dysentery
12.
Salmonella species
Motile rods
Enteric fever (typhoid paratyphoid) food poisoning, septicemia, meningitis
13.
Vibrio cholera
Motile-slightly curved rods
Cholera
14.
Vibrio parahaemolyticus
Motile-slightly curved rods
Gastroenteritis
15.
Campylobacter jejuni, coli
Motile, curved spiral rods
Gastroenteritis
16.
Legionella pneumophila
Nonmotile rods
Severe pneumonia
Gram-negative Cocci
Neisseria meningitides
Intracellular diplococcic
Meningitis and septicemia
Neisseria gonorrhoeae
Intracellular diplococcic
Gonorrhoea, eye infection in newborns
Acid Fast Bacilli
Mycobacterium tuberculosis
Nonmotile bacilli
Tuberculosis
Mycobacterium leprae
Nonmotile bacilli after in ten in groups (globi)
Leprosy
5
 
CLASSIFICATION OF THE MEDICALLY IMPORTANT VIRUS GROUPS
RNA VIRUSES
S.No
Virus group
Shape
Envelope
1.
Toga virus
Spherical
Yes
2.
Reovirus
Spherical
No
3.
Bunya virus
Spherical
Yes
4.
Arenavirus
Spherical
Yes
5.
Rhabdovirus
Elongated (Bullet-shaped)
Yes
6.
Paramyxovirus
Spherical filamentous
Yes
7.
Picornavirus
Spherical
No
8.
Orthomyxovirus
Spherical filamentous
Yes
9.
Coronavirus
Spherical pleomorphic
Yes
10.
Retrovirus
Spherical
Yes
DNA VIRUSES
S.No
Virus group
Shape
Envelope
1.
Herpesvirus
Spherical
Yes
2.
Adenovirus
Spherical
No
3.
Papovavirus
Spherical
No
UNCLASSIFIED VIRUSES
S.No
Virus group
Shape
Envelope
1.
Marburg – Ebola
Virus group (RNA)
Filamentous, U – shaped
Ring shaped
No
2.
Hantaan Virus
(Probably RNA)
Spherical
No
3.
Hepatitis A Virus (RNA)
Spherical
No
4.
Hepatitis B Virus (DNA)
Spherical
No
 
VIRUSES
 
Introduction
Unicellular microorganisms may be classified in the descending order of complexity as the eukaryotes, such as protozoa and fungi and the prokaryotes, such as bacteria, mycoplasma, rickettsiae, and chlamydiae.
Viruses do not fall strictly into the category of unicellular microorganisms, as they do not posses a cellular organization. They contain only one type of nucleic acid, either DNA or RNA but never both.
They are obligates intracellular parasites. They lack the enzyme necessary for proteins and nucleic acid synthesis and are dependent for replication on the synthetic 6machinery of host cells. They multiply by a complex process and not by binary fission. They are unaffected by antibacterial antibodies.
 
Morphology of Viruses
The extracellular infectious virus practice is called the virion.
 
Structure and Shape
The virion consists essentially of a nucleic acid and core surrounded by a protein coat, called the capsid. The capsid with the enclosed nucleic acid is known as the nucleocapsid.
The function of the capsid is to protect the nucleic acid from activation by nucleases and other deleterious agents in the environment. The capsid is composed of a large number of capsomere, which form its morphological units.
Chemical capsid is composed of polypeptide molecules, which form a shell around the nucleic acid core. One of the major functions of the capsid is to introduce viral genome into host cell by adsorbing readily to cell surfaces.
Two kinds of symmetry is there within the capsid. One is octahedral (cubical) and other is helical. Virion may be enveloped or nonenveloped (naked) the envelopes or outer covering of viruses is divided from host cell membrane when the progeny virus is released by budding.
The envelope is lipoprotein in nature. Proteins subunits may be seen as projecting spikes on the surface of the envelope called peptonieres.
 
STRUCTURE OF A TYPICAL FUNGI
 
MYCOLOGY: Study of Fungus
 
Introduction
Fungi (singular, fungus) are a group of eukaryotic organisms. Fungi comprise the molds and yeast, fungi are spore bearing protist that lack chlorophyll. They divide asexually, sexually or by both process. The thallus (Plural thalli) or body of a fungus essentially consists of two parts, the mycelium (Plural mycelia) and the spore.
The mycelium is a complex of several filaments called hyphae (singular hypha). New hyphae generally arise from a spore which on germination puts out a germ tube or tubes. These germ tubes elongate and branch to form hyphae. Hyphae are composed of an outer tube like surrounding a cavity, the lumen which is filled by protoplasm. Between the protoplasm, and the wall is plasmalemma, a double layered membrane which surrounds the protoplasm.
Fungus posses rigid cell wall containing chitin, mannan and other polysaccharides. Hyphae are normally divided into cells by cross wall referred to as septa. And hyphae, which do not have septa, are called as nonseptate unlike bacterial colonies, fungal colonies spread readily by the hyphae, producing branching growth.
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The rate of growth texture, color and form of the colonies is distinct for each species and these characteristics are therefore important in identification.
Depending on cell morphology, fungi can be divided into 4 classes.
 
Yeast
Yeasts are unicellular fungi which occur as spherical or oval cells and reproduce by simple budding on culture, they form smooth, creamy colonies the only pathogenic yeast is Cryptococcus neoformans.
 
Yeast-like Fungi
Grow partly as yeast and partly as elongated cells resembling hyphae. The latter form a pseudomycelium. Candida albicans is a pathogenic yeast-like fungus.
 
Moulds or Filamentous Fungi
Form true mycelia and reproduce by the formation of different type of spore. Dermatophytes are example of pathogenic moulds.
 
Dimorphic Fungi
Can occur as filaments or as yeast depending upon the condition of growth. In host tissue culture at 37°C they occur as yeasts, which in the soild and in culture at 22ºC. They appear as mould, most fungi causing systemic infection are dimorphic fungi.
 
MODE OF TRANSMISSION OF VARIOUS DISEASES
 
Airborne Infections
By inhaling aerosols (airborne droplets) containing pathogens secreted by an infected person, sneezing, coughing, laughing and spitting bacterial respiratory diseases such as tuberculosis, whooping cough, pneumonia.
Viral. e.g. Measles, influenza virus, adenovirus and rhinovirus.
 
Water or Foodborne Infections
By ingesting pathogens in water or food contaminated with urine or feces from sick persons or disease carries.
Bacterial diseases, e.g. Cholera, typhoid and bacillary dysentery.
Viral diseases, e.g. Enteroviruses, rotaviruses, HAV.
 
Sexually Transmitted Diseases
Bacterial: syphilis and gonorrhea.
Viral: HIV, HSV, HBV8
 
Transfer of Pathogens from Mother to Fetus During Pregnancy
Bacterial-Syphilis, N. gonorrhoeae, Chlamydiae and group B Streptococcus.
Viral: Cytomegalovirus, rubellavirus, HIV.
Pathogens entering wound, cuts or burns by way of contaminated hands, or unsterile instruments. Infections of the skin and tissues, such as boils and abscesses are transmitted in this way.
 
FUNGAL INFECTIONS
 
Superficial Mycosis
Fungus infecting the skin, hair and needs.
Ex: Tinea, Candida, dermatophytes like Trichophyton, Microsporum and epidermophyton.
 
Deep or Systemic Mycosis
Fungus infecting the subcutaneous tissues and/or internal organs.
Subcutaneous – Ex: Cladosporium, Mad hrella spp. Sporottrix, Candida
Systemic – Ex: - Candida, Cryptococcus, Histoplasma, Blastomyces etc.
 
Opportunistic Infections
Fatal infections in persons who are otherwise debilitated or immunocompromised. Ex: Candida, Aspergillus, Penicillium, Mucor and Rhizopus, etc.