Tài liệu Nature and Properties of Micro-organisms doc

 Shell of protein capsid surrounding nucleic acid  Classification on basis of nucleic acid DNA viruses: eg Herpes simplex virus HSV RNA viruses: eg influenza virus... Obligate intra

Nature and Properties

of Micro-organisms

Laura JV Piddock

tissue and tonsils

 Shell of protein (capsid) surrounding nucleic acid

 Classification on basis of nucleic acid

DNA viruses: eg Herpes simplex virus (HSV)

RNA viruses: eg influenza virus

DNA viruses: herpes simplex virus (HSV)

RNA viruses: Influenza

Obligate intracellular parasites

Use host cell for nucleic acid and protein synthesis

Cell attachment: target for blocking antibody vaccines

Intracellular replication: target for antiviral drugs

n.b retroviruses (RNA) e.g HIV

RNA  DNA

Viral effects on host cells

 Degeneration (cytopathic effect): CMV

 Cell lysis

 Cell fusion, syncytia formation: RSV

 Cell proliferation

 Transformation: malignancy (parvoviruses)

 Latent infection - no sign of infection until reactivation

 ‘cold sores’ (HSV)

 chickenpox  shingles (VZV)

CMV hepatitis

owl eye effect inclusion body

Varicella zoster virus (VZV)

 Classified according to:

 size & shape

 cell wall (Gram stain)

Wound swab: S aureus

Neisseria gonorrhoeae

Gram stained urethral discharge The image shows many polymorphonuclear leukocytes (PMNs) and

Pneumococci in sputum

Other important bacteria

 Strict anaerobes: e.g Bacteroides fragilis

M tuberculosis causes TB

 M leprae causes leprosy

complex cell wall

(acid-alcohol fast bacilli; AFB)

Treponema pallidum

Unusual bacteria

 Mycoplasma

 E.g Mycoplasma pneumoniae (pneumonia)

 lack peptidoglycan - resistant to penicillins

 E.g Chlamydia trachomatis (trachoma; NSU)

 obligate intracellular parasite

 needs host ATP

Chlamydia trachomatis

Important bacterial cell components 1: (endo)spores.

usually Bacillus spp and Clostridium e.g

Clostridium tetani (tetanus)

spore is a resting cell, highly resistant to

desiccation, heat and chemical agents

produced in response to environmental

conditions e.g nutritional depletion, usually

reduction in nitrogen or carbon sources

Gram positive, bacillus,

anaerobic, spores

Clostridium spp

Important bacterial cell components 2: Flagella

Flagellum can be removed but is rapidly

replaced

 Involved in motility and impart spinning

movement and usually requires proton

motive force

 Chemotaxis: flagella move bacteria

towards or away from chemical

attractant/repellent e.g Vibrio cholerae

Flagellae

Important bacterial cell components 3: Pili (Fimbrae)

 Found on Gram negative

bacteria, shorter and finer than

flagella

 Two classes:

 ordinary pili ‘colonisation

antigens’ Protein, attachment to host cells

Can be involved in host

cell invasion e.g Neisseria

meningitidis

 sex pili, role in conjugation

(transfer of plasmid DNA)

Important bacterial products 1:

extracellular polysaccharide

 CAPSULE condensed, well defined layer closely

surrounding the cell contributes to invasiveness of

pathogenic bacteria by reducing opsonisation and

protecting from phagocytosis

 E.g Streptococcus pneumoniae in RTI

 vaccination: pneumococcal; meningococcal A and C

 GLYCOCALYX loose meshwork of fibrils

extending outward from the cell plays a major role in

bacterial adherence to surfaces

Capsule

Important bacterial products 2:

 Exotoxins: secreted by Gram positive

bacteria E.g C tetani

active immunity - toxoid

passive immunity - antitoxin

Bacterial cell walls

Lipid bilayer with proteins

Lipoteichoic acid

Important cell wall components 1

Important cell wall components 2

LPS, Endotoxin

 Firmly bound to cell and only released upon lysis

 Only Lipid A is toxic

 Polysaccharide is a major surface antigen,

O-antigen

 Antigenic specificity conferred by the terminal repeat units, and many types possible, e.g Salmonella >1000

Fungi

Moulds

Yeasts