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
virus structure
- Nucleic acids - Consists of either DNA or RNA
- Capsid - Surrounds nucleic acid core, Made up of capsomere
- Envelope - outside capsid, consists of lipoprotein membrane
- Viral proteins
- Replication – virus has to invade host cell to replicate
pathogenesis
- Viruses can cause disease in several ways.
- They are classified based on the onset of signs and symptoms (incubation period)
Acute infection – influenza, zika, rabies, SARS, COVID
Slow infection - HIV
Latent infection – herpes labialis
Oncogenic infection – HIV, HPV, HBV
influenza virus
2 surface glycoproteins - Hemagglutinin (HA) Neuraminidase (NA)
zika
- Caused by a virus transmitted by mosquitoes.
- Symptoms - fever, skin rash, conjunctivitis, muscle and joint pain, malaise or headache.
- During pregnancy, virus affects foetus cause microcephaly and severe foetal brain defects
rabies
- Rabies is caused by a virus, transmitted to humans from animals.
- After animal bite, virus reaches the nerve and reaches brain
- Symptoms - headache, fever, confusion, pain or tingling at the site of the bite, hydrophobia (fear of water),
paralysis and coma and death
SARS
- Caused by SARS-associated coronavirus
- Originated from horseshoe bats- started as zoonotic disease
- Transmission via respiratory droplet- direct / indirect
- Causes respiratory symptoms –> deteriorates fast –> causes respiratory arrest
COVID
- Caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
- Likely a zoonotic (from bats/ pangolins)
- Transmitted from one person to another via respiratory droplets
- Affects respiratory system–> pneumonia –> acute respiratory distress syndrome
HIV
- HIV spreads through four body fluids: semen, vaginal fluid, blood, breast milk.
- HIV infection causes gradual deterioration of immune function.
Three stages:
- Acute infection – flu like symptoms
- Chronic infection- asymptomatic, virus slowly reproduces
- Acquired Immuno Deficiency syndrome (AIDS) -CD4+ T cell count < 200 cells per μL; prone for opportunistic infections
Herpes labialis (cold sores)
- Caused by herpes simplex virus (HSV) causes initial infection of skin around lips
- Virus enters the nerve cells, stays until activated by stresslatent infections causes painful blisters.
Herpes zoster or “shingles”
- Caused by varicella zoster virus.
- Initial infection (chicken pox) characterised by fever and generalized vesicular rash.
- Virus is remains in ganglions of sensory nerves.
- Stress / less immunity –> virus reactivated, travels along the sensory nerve causes painful vesicular rash
(shingles).
oncogenic infection
- Causes malignant changes in host cells by activating oncogenes
- They integrate their own genetic material into the host cell’s DNA
Human papilloma Virus (HPV)
- Mainly sexually transmitted
- Causes warts in both female and male and cervix cancer
- Vaccines available for strains causing cancer cervix and anal cancer - Gardasil and cervarix
Human Immunodeficiency Virus (HIV)
- Cause numerous cancer (commonest is Kaposi sarcoma) & opportunistic infections
Hepatitis B Virus(HBV)
- Diseases caused hepatitis – jaundice
- Cause hepatocellular carcinoma
prion disease - kuru
- Caused by prions (proteinaceous infectious particle)– lacks nucleic acids
- Incubation period: 10 – 50yrs and above
- Affected only the primitive tribesmen in New Guinea who eat the brains of their dead relatives.
- Disease that severely damages the nervous system (prions)- irreversible damage. The affected people
gradually become insane and die.
fungus
ringworm (tinea infections), tinea versicolor, candidiasis
ringworm (tinea infections)
- caused by dermatophytes Infects superficial keratinized structures
- Spread by direct contact
- Cause chronic skin infection characterized by severe pruritus
- aggravated by heat, humidity
tinea versicolor
- Superficial skin infection caused by Malassezia furfur (yeast)
- Hypo-pigmented areas, especially on tanned skin
- usually asymptomatic
- Occurs more frequently in hot, humid weather
candidiasis
- Caused by candida albicans.
- Part of normal flora, infection occurs when host defences are impaired (opportunistic infection)
Causes:
- White patches in mouth (oral thrush)*
- Vulvo-vaginitis with itching & vaginal discharge
- Chronic finger nail infections
parasite: protozoa
trichomonas vaginalis, entamoeba histolytica, malaria
trichomonas vaginalis
- spindle shaped with 4 anterior flagella
- Sexual mode of transmission
- site of infection -vagina, prostate
- Symptoms -watery foul-smelling greenish vaginal discharge, itching,
entamoeba histolytica
- an anaerobic protozoa
- food or water contamination
- It invades the colon causing acute dysentery
- loose stools mixed with blood and mucus
malaria
- Caused by plasmodium -obligate intracellular parasite
- Transmitted by bite of female Anopheles mosquito
- Characterized by fever, chills at 2-3 day intervals
- Often associated with vomiting, headaches
parasite: helminths
tapeworm, pinworm, round worm, hook worm
tapeworm
- Flattened segmented worms living in intestines; Spread by faeco - oral route
- Lifecycle - Adult worm in colon release egg which comes out via faeces. Eggs contaminated in food swallowed by intermediate host (cow / pig). They hatch to larva which enters muscle of the intermediate host (cysticercosis). When human consumes this infected uncooked muscle –> eggs hatches –> adult worm
pinworm
- Adult worms live in the intestine; children are usually affected; Spread by faeco - oral route
- Lifecycle - Female pinworm leaves anus at night and lays egg in anus (causes itching) - pruritis ani: most prominent feature. Itching causes human to scratch anus and eggs soiled hands. When they handle food, eggs
enter another host and hatches to adult worm
roundworm
- Adult worms live in intestine; Spread by faecal - oral route
- Lifecycle: Adult worm in colon releases egg –> comes out via faeces. Eggs contaminated in food enter another human and hatches in intestine to form larva. Larvae penetrate intestine wall and migrate to lungs. Later enter
the alveoli and pass through the trachea where they are swallowed. Larva reaching intestine again becomes adult worms and releases eggs.
hookworm
- Adult worms live in the intestine
- Spread by faeco - oral route
- Lifecycle - adult worm lives in colon and releases egg in faeces. Eggs in soil hatches to form larva. Larvae penetrate intact skin and reaches lungs and enter the alveoli to pass up the trachea. In trachea, larva are swallowed and reaches intestine and become adult worms which releases eggs
nosocomial infection
- Infections acquired as a result of stay in hospital, nursing home and health-related facility
- Transmitted by direct and indirect contact
- Common Nosocomial infections: UTI (50%), surgical wound infection, lower resp tract infection and bacteremia.
sterilisation and disinfection
- Sterilization - Killing/removal of all microbes (including endospores)
- Disinfection - killing of many but not all micro-organism
chemical agents
- Phenol
- Chlorhexidine
- Alcohol
- Surface active agents
- Soaps
- Quaternary ammonium compounds
- Halogens – chlorine & iodine
- Aldehydes
- formaldehydes
- glutaraldehyde
physical agents
- Heat
- Moist heat
- Dry heat
- Pasteurization
- Filtration
- Radiation
