TEST 3 MICROBIOLOGY THEORY Flashcards
prokaryote
no nucleus
classification of bacteria
based on shape, based on arrangement and based on oxygen requirement
shape classification for bacteria
spherical - coccus; rod-shaped - bacillus; spiral, cocco bacilli - looks like cocci and bacilli
arrangement classification for bacteria
diplo - arranged in pairs - diplococci/diplobacilli (e.g. neisseria)
strepto - arranged in chains - streptococci
staphylo - arranged in clusters - staphylococci
oxygen requirement classification for bacteria
obligate aerobes - organisms requiring oxygen to live (e.g. mycobacterium TB)
obligate anaerobes - organisms that does not require oxygen to live (e.g. clostridium tetani)
facultative anaerobes - able to grow in both aerobic and anaerobic conditions (e.g. escherichia, coli)
bacteria structure
Structures external to cell wall: Glycocalyx, Pili (attachment), flagella
(movement)
Cell Wall
* Stained by gram stain – divided to
- Gram positive -cell wall thick;
- Gram negative -cell wall thin
Endospores
When growing conditions become unfavourable - active bacteria becomes endospores in adverse conditions
(sporulation). Returns to vegetative state if conditions are favorable
Killed only by autoclave
E.g, Clostridium tetani
Pathogenesis / chain of infection
Pathogenesis is the process how pathogen causes diseases.
Includes:
1. Pathogen (infectious agent which causes disease) - bacteria, virus etc
2. Reservoir (Source of pathogens) – humans, animals, soil, water
3. Portal of exit (portals where the pathogen is released from the reservoir)- airway, parenteral etc
4. Methods of transmission (how pathogen transmitted from source to the host) – contact, airborne, waterborne,
5. Portal of entry (portals via which the pathogen enters host) - Mucous membrane, skin, parenteral, tranplacenta
6. Pathogenicity in the susceptible host (Ability of a pathogen to produce a disease in the host)
* Virulence: degree of pathogenicity. Adherence: Ability of the bacteria to attach to host cell (using pili)
medically important bacteria
gm positive cocci, gm negative cocci, gm positive bacilli, gm negative bacilli, others like mycobacterium tb, sphirochetes
Gram positive cocci
Staphylococcus aureus - clusters;
causes invasive disease (abscess) and toxigenic disease (Usage of tampons for longer periods)
Streptococcus - chains
S. pneumoniae - pneumonia
Gram negative cocci
Neisseria
- paired kidney beans- diplococci
- Neisseria meningitidis - causes meningitis; spread by airborne droplets
- Neisseria gonorrhoeae - causes gonorrhoea; spread by unprotected sexual contact
Gram positive bacilli
Clostridium tetani
- Tetani spores are widespread in soil- enters through wound
- causes Tetanus - exotoxin interferes with neurotransmitters –> uncontrollable muscle spasms eg. lockjaw
Corynebacterium diphtheriae
- Club shaped bacilli; airborne droplet transmission
- Causes diphtheria - exotoxin inhibits protein synthesis
Gram negative bacilli
Escherichia coli
- Commonly found in lower intestine; commensal – usually doesn’t cause disease
- Causes intestinal tract infection and urinary tract infection
Salmonella typhi
- Waterborne
- Causes enterocolitis – diarrhea;
typhoid fever - Fever, bacteremia and diarrhea and in extreme cases
Septicemia – Fever, bacteremia and diarrhea and shock
TB
- Aerobic bacilli; require special stain (Ziehl-Neelsen stain)
- droplet transmissionCauses tuberculosis
- Pathogenesis- bacilli enter lungs and phagocytosed by macrophages –> destroyed. If not destroyed, bacilli
multiply inside macrophage –> results in tubercle formation –> caseous necrosis –> ruptures, spreads to
bronchus, blood; later gets calcified (seen on X-ray) - cell-mediated immunity- diagnosed by tuberculin test (manteaux test)
- Prevention – BCG vaccine
syphilis
- Treponema Pallidum causes syphilis
- Transmitted by unprotected sexual contact and congenital syphilis (mother to fetus)
- Syphilis comes in three phases
Primary syphilis: chancre (painless ulcer) at site of infection - hallmark of syphilis
Secondary syphilis: rashes on skin, mucous membrane
Tertiary syphilis: (1- 10 years) - gummas (granuloma) palate, chest, organs – brain, heart
normal flora
- Permanent population of organisms; ONLY bacteria & fungi (not viruses & parasites)
- Found on linings of body surfaces, mucous membranes; NEVER found in internal organs
Functions:
- Protection -Resident bacteria prevent pathogens from invading. eg Lactobacillus
- Nutrition - Intestinal bacteria produce several B vitamins and vitamin K
opportunistic pathogen
Non-pathogenic microorganisms act as a pathogen in certain circumstances like immunocompromised and
debilitated patients
opportunistic infection
An infection caused by opportunistic pathogen.e.g., Candidiasis in AIDS patients
carrier
- Person who harbors a potential pathogen and is usually asymptomatic
- But is a potential source of infection
- eg Streptococcus pneumoniae (nose, throat) Salmonella typhi