MICROBIOLOGY - bacti, fungi, parasites (IAS46-49, 53) Flashcards
Rank: bacteria, prions, viruses, protozoa, parasites, fungi in terms of descending size
parasites > protozoa > fungi > bacteria > viruses > prions
Reservoir of pathogen meaning?
Habitat of a microorganism for their growth
Port of exit of pathogens in organisms?
Feces, secretions
Where do:
cytosolic
intravesicular
extracellular pathogens (and toxins) invade respectively
Any cell
Macrophages
B cells
Define microbial virulence - what are the characteristics of a virulent organism
Capacity of microbe to cause disease in host
characteristics: low infective dose, high attack rate, high fatality rate
Define virulence factors
facilitate microbial attachment, invasion, multiplication or host defence evasion
3 methods of pathogenic mechanisms? Elaborate on their mechanisms
Direct cytolysis - due to intracellular replication in bacteria or toxin secretion (no of bacteria plateaus eventually)
Immunopathological damage - immune system damages hosts themselves due to molecular mimicry or upregulated inflammation
oncogenesis - integration of viral genome into host chromosome (eg EBV, HBV) or due to chronic inflammation (H. pylori)
Koch’s postulate?
Microbe must be present in ALL disease cases
microbe must be isolated from diseased hosts and grown in culture
should cause disease when introduced to healthy organism
Microbe must be recovered from experimentally infected host
What is the bacterial cell wall made of? Its structure?
Outer wall in what kind of bacteria? What components does it have?
The LPS structure (ONLY IN GRAM NEGATIVE BACTI!!!!!) and its function?
Peptidoglycan - made of glucan chains of alternating NAG and NAM, glucan chains joined by short peptides on NAM
Gram-negative bacteria, outer wall increases antibiotic resistance
components: lipoproteins, lipids, proteins, polysaccharides, lipopolysaccharides
LPS structure: O-polysaccharide, core polysaccharide and lipid A
O-polysaccharide as the antigen
Lipid A responsible for endotoxin properties - CD14 triggers endocytosis, TLR4 responsible for triggering inflammation (Transcriptional response (cytokine expression & NLR-mediated canonical inflammasome activation)
What does the cytoplasm contain?
Plasmid function?
Cytoplasm - contains nucleoid + plasmids + ribosomes (30s and 50s subunits)
Plasmid may contain antibiotic resistant genes
Functions of capsule?
Functions of pili?
Structure of endospore? Its function and clinical implications?
Virulence factor for adhesion, antiphagocytic function
Virulence factor for adhesion, sex pili for exchange of plasmids
Outermost to innermost: exosporium > spore coat > spore cortex > inner membrane > spore cytoplasm containing nucleoid
Function: metabolically inert, dormant, highly resistant to heat/radiation/chemicals (so an issue with contamination/sterilization and disinfection/ infection control)
Bacteria phases of growth? Define generation time
1) lag phase - no change in bacti numbers as bacteria is adapting to new environment
2) log phase - bacteria numbers grow exponentially
3) stationary phase - bacteria numbers cannot increase because not enough nutrients/too much waste accumulated)
Generation time refers to the time needed for bacteria to double in amount in log phase, usually 30min
The 3 methods of genetic transformation of bacteria?
1) conjugation - exchange of plasmids between bacteria by sex pili’
2) transduction - bacteriophages infect bacteria, viral toxin gene incorporated into bacterial genome
3) Point mutation, changes antigenicity, virulence, transmissibility, antimicrobial susceptibility
Compare: intracellular bacteria and extracellular bacteria in terms of place of growth, growth opportunities, environmental conditions
Intracellular bacteria: grow within host cells, protected from host defense mechanisms
Extracellular bacteria: grow outside of host cells with more growth opportunities BUT harsher environmental conditions (eg have to face host immune system)
Gram stain process? Its principle? Appearance of gram +ve and gram -ve bacteria?
Crystal purple > iodine (forms complex with crystal violet) > alcohol (to decolorize Gram-negative bacteria) > safranin (counterstain to stain gram-negative bacteria)
Principle: the thin peptidoglycan wall of Gram-negative bacteria means these bacteria cannot retain the Gram stain well
+ve: purple, -ve: pink
How to classify bacti?
Check sid ppt for quick revision
Staphylococcus - catalase positive or negative? Oxygen requirement?
Positive, facultatively anaerobic
S. aureus - coagulase +ve or -ve? Colony morphology?
Describe the 2 types of coagulase test
Positive, golden-yellow colonies, in clusters
slide coagulase test - Binding to fibrinogen; the fibrin deposited on the surface inhibits phagocytosis
Tube coagulase test - Activation of prothrombin to initiate clot formation in plasma
The 4 aims of virulence factors in S. aureus? For each aim list the virulence factors and their specific functions
Evasion of host defence mechanisms:
catalase, coagulase prevent clot formation,
protein A: helps avoid opsonization and induces B cell death (it acts as toxin to trigger B cell apoptosis)
Adherence to host cell: teichoic acid
Invasion into host cells: protease, lipases, DNAses, hyaluronidase (breakdown of hyaluronic acid)
Toxins: a-hemolysin damages blood cell, toxic shock syndrome toxin (TSS toxin causes TSS), enterotoxins cause food poisoning
Epidemiology of S. aureus (its reservoir) and mode of transmission?
Humans act as reservoir, transmitted by direct contact
2 categories of diseases that S. aureus can cause? Name examples for each category
Pyogenic (forms pus) -
skin, soft tissues (folliculitis, furuncles, carbuncles)
bone/joints: osteomyelitis, septic arthritis
heart: infective endocarditis
lungs: pneumonia (excess pus in lungs)
infection of wounds, surgical sites
toxin-mediated:
TSS (toxic shock syndrome), scalded skin syndrome
food poisoning
S. aureus antibiotic resistance types?
90% methicillin sensitive but MRSA (methicillin-resistant) occurs, VRSA also occurs, mostly penicillin resistant
S. epidermidis and S. saprophyticus - coagulase positive or negative, and what diseases they cause (1 example each)?
Coagulase negative
epidermidis: infections with prosthesis (triggering infective endocarditis, septic arthritis etc), boils common to staph infections etc
saprophyticus: acute cystitis in young women, urinary tract infection
Strep and enterococci - catalase positive or negative? Oxygen requirement?
Strep pneumoniae - hemolysis pattern and the pattern’s appearance?
Strep pyogenes, agalactiae - hemolysis pattern and its appearance? Lancefield group?
Enterococci hemolysis pattern and appearance? Lancefield group?
NEGATIVE, facultatively anaerobic
pneumoniae: a-hemolytic with greenish discoloration of blood agar
pyogenes/agalactiae: b-hemolytic, complete clearing of agar
pyogenes: Lancefield A, agalactiae: Lancefield B
enterococci: gamma-hemolytic, lancefield D
Diseases S. pneumoniae can cause? what antibiotic can it be resistant to? Does it have capsule?
Pneumonia, meningitis, acute otitis media, sinusitis, septicemia, penicillin
HAS CAPSULE, THICK POLYSACCHARIDE CAPSULE
Diseases S. pyogenes and agalactiae can cause?
Pyogenes: impetigo, cellulitis, PHARYNGITIS, necrotizing faciitis, SCARLET FEVER, RHEUMATIC FEVER, TSS
agalactiae: neonatal sepsis/meningitis, peripartum infections
Diseases enterococci can cause? Name 3
what antibiotic is enterococci especially resistant to?
Catheter-associated urinary tract infection, endocarditis, line sepsis, polymicrobial intra-abdominal/biliary infections
cephalosporins
Does Bacillus form spores? oxygen requirement?
diseases bacillus species can cause? 2 species + 1 disease each
Spore forming, aerobic
bacillus anthracis: anthrax
bacillus cereus: food poisoning
Listeria monocytogenes diseases? How is the disease transmitted? Form spores?
neonatal meningitis, invasive listeriosis in immunocompromised adults or elderly (>60), foodborne (esp milk, chicken)
No spores
Corynebacterium diphtheriae disease? Disease morphology?
Morphology of the bacteria? Any spores?
Diptheria, Sore throat with an adherent grey pseudo-membrane in the oropharynx (white throat)
V/L - shaped, “chinese character appearance” No spores
How to culture diphtheria:
Potassium tellurite agar
Selective agar, that inhibits growth of other bacteria
Nocardia morphology? Besides gram stain how can it be stained, and its stained appearance?
Disease it causes? Any spores?
Branched filaments, can be stained by modified Ziehl-Neelsen stain, pink color so acid fast
Nocardiosis (granulomatous infection) (pulmonary, CNS, cutaneous)
No spores
Mycobacterium: acid fast or not? Any spores?
Which disease can mycobacterium cause? and the species causing it?
What agar used to culture mycobacterium and Nocardia? What media is it?
Method of transmission?
Acid fast (pink stain), no spores
M. tuberculosis (tuberculosis)
Lowenstein-Jensen agar - selective media (has nutrients to promote growth of desired organism BUT antimicrobials to inhibit growth of others)
AIRBORNE
Clostridium oxygen requirement? Diseases some clostridium species can cause? Form spores?
ANAEROBIC, FORMS SPORES
C. botulinum: botulism
C. tetani: tetanus
C. perfringens: gas gangrene, intra-abdominal/pelvic sepsis, food poisoning
C. difficile: pseudomembranous colitis
Neisseria morphology and oxygen requirement? Oxidase + or -?
Diplococci, AEROBIC (most are aerobic unless specified), oxidase positive
Neisseria gonorrhoeae epidemiology? Reservoir and mode of transmission?
Humans as reservoir, transmission by sexual and mucosal contact
N. gonorrhoeae diseases? How to diagnose N. gonorrhoeae
What type of media (supportive/selective/enrichment/differential) is the agar used to test
GONORRHEA!
Urethritis in men (PUS FORMED)!!!!!!!
urogenital infection in women (endocervicitis, pelvic inflammatory disease)
extragenital infection (pharyngitis, rectum proctitis)
disseminated infection (infective endocarditis, septic arthritis, meningitis)
GONOCOCCAL OPTHALMIA NEONATORUM (infection of newborn baby)
Thayer-Martin agar (selective media)
N. meningitidis epidemiology?
Human reservoir, transmission by respiratory droplets, direct mucosal contact
Virulence factors of N. meningitidis?
Polysaccharide capsule (for attachment & antiphagocytic) - ONLY IN N. meningitidis
Pili/fimbriae (attachment)
lipooligosaccharide - for endotoxin (trigger immune response) - CD14 for endocytosis, TLR4 for triggering transcriptional response (cytokine expression & NLR-mediated canonical inflammasome activation)
Diseases N. meningitidis can cause?
MENINGITIS, septicemia
◆ purulent conjunctivitis
◆ meningococcal pneumonia
◆ purpura fulminans
Vaccine types against N. meningitidis?
polysaccharide vaccine; quadrivalent conjugate vaccine; serogroup B protein-based vaccine
Know that: all enterobacterales are glucose fermenters and lactose fermenters (EXCEPT SALMONELLA AND SHIGELLA)
Enterobacterales aerobic requirement? Normal habitat?
Facultatively anaerobic, human and animal large bowel
Enterobacterales antigen?
KOH -
K antigen: capsule antigen
O antigen: somatic LPS (the O polysaccharide)
H antigen: flagellar antigen
General diseases Enterobacterales can cause?
GI infections: gastroenteritis, dysentery
extra-intestinal infections: UTI, respiratory tract infections, bacteremia, meningitis, intra-abdominal sepsis
Diseases E. coli can cause?
ETEC (enterotoxigenic E. coli): Traveller’s diarrhea,
STEC: (shiga toxin-producing E. coli) hemorrhagic colitis, hemolytic uraemic syndrome
What color are E. coli colonies on CHROMID agar
Red
Klebsiella morphology on agar (reasons for this look?) and diseases it can cause (name 2) and risk factors
Is it a lactose fermenter (if yes specifically which type)
Mucus look because of capsule formation
Diseases: community pneumonia, abcess formation
Risk factor: elderly, alcoholics, those with underlying diseases
Yes - mucoid lactose fermenter
What diseases does Salmonella cause? (there are 2 types of salmonella- classify by this categorization)
What disease does Shigella cause? Function of shiga toxin?
How to determine whether a person may have salmonella/shigella (what agar)
Salmonella typhi: eg S. enterica - typhoid fever, paratyphoid fever
Non-typhi salmonella: gastroenteritis
Shigella: dysentery,
Shiga toxin: Inhibits eukaryotic protein synthesis, eventually leading to host cell death
MacConkey agar - clear colonies then XLD agar: black colonies (if E. coli gold colonies)
Vibrionaceae: Morphology, oxidase + or -, reservoir?
Curved bacilli, oxidase +ve, found in water bodies (freshwater and seawater)
General diseases Vibrios can cause?
GI tract infection, Severe systemic infections, e.g., skin and soft tissue infections (rare)
Vibrio cholerae disease - symptom as well? Is it fatal and why
Cholera - rice water stool, rapidly fatal because of rapid dehydration
How does cholera toxin work
increases intracellular cAMP at intestinal epithelium -> inhibits sodium and chloride absorption -> increases chloride and water secretion
What diseases do V. parahaemolyticus and V. vulnificus cause
how to differentiate V. cholerae and non-cholera vibrios
parahaemolyticus: gastroenteritis
vulnificus: skin infection
TCBS agar - for V. cholerae only, agar turns yellow
Non-fermenters: oxygen requirement? Are they antibiotic resistant? (name 3)
STRICTLY aerobic, VERY antibiotic resistant
pseudomonas aeruginosa, acinetobacter, burkholderia pseudomallei
P. aeruginosa morphology? Oxidase + or -?
Metallic green appearance, fruity smell, oxidase positive
P. aeruginosa disease?
Hospital-acquired infections, fatal in neutropenic septicemia, pneumonia
Acinetobacter and Burkholderia diseases?
Acinetobacter: For A. baumannii nosocomial infections
B. pseudomallei: melioidosis
Haemophilus influenzae factors that require blood or blood components for its growth?
X factor, V factor (XAVI)
X factor: haemin
V factor: NAD or NADP
Diseases caused by H. influenzae? (rod or cocci?)
Epiglottitis, Meningitis, pneumonia, sinusitis, acute otitis media (basically same as S. pneumoniae). gram -ve rod
Does H. influenzae have capsule? If yes, how many types of capsules and which type causes most invasive diseases in children and infants?
Yes - 6 capsule types, type b
What vaccine is available against H. influenzae
Polysaccharide conjugate vaccine (against capsular polysaccharide type B)
Legionella disease and Bordetella disease?
Which agar to culture Bordetella
Legionella pneumophila: Legionnaire’s disease
Bordetella pertussis: pertussis (whooping cough)
Bordet-Gengou agar or Regan-Lowe medium (RL is charcoal + antibiotics)
2 types of strict anaerobes, gram-negative bacilli?
What diseases are these 2 associated to
Oral flora (Fusobacterium)
Gut flora (Bacteroides)
■ diseases caused usually when out of normal habitat
■ mixed infections (with other bacteria); abscess formation; intra-abdominal infections; genital tract infections; head and neck infections
Spirochaetes: name 2, which diseases do they cause
Treponema pallidum: causes syphilis (STD)
H. pylori (stomach ulcer), related to gastritis, adenocarcinoma of stomach
Syphilis symptoms? Name 2
Can Treponema pallidum be cultured in vitro
Congenital infections, notched abnormal teeth
NO
Methods of transmission of bacteria? (name the bacti that is transmitted by droplet and a bacti that is airborne)
Most by contact - direct contact on mucosal surfaces or indirect contact on contaminated surfaces
N. meningitidis: droplet transmission
Mycobacterium TB: airborne
Infection-based question:
Name bacti that can cause acute community acquired pneumonia
Strep pneumoniae (NUMBER 1),
H. influenzae (NUMBER 2)
Staph aureus/strep pyogenes (NUMBER 3)
Klebsiella pneumoniae
Pseudomonas aeruginosa
Burkholderia pseudomallei
Myco tuberculosis
Infection-based question: Name bacti causing ATYPICAL pneumonia syndrome
Legionella pneumophila
Mycoplasma pneumoniae
Chlamydia trachomatis
Chamydophila pneumoniae/psittaci
name bacti causing nosocomial pneumonia
MRSA,
non-glucose fermenters (p. aeruginosa/acinetobacter etc)
Legionella pneumophila
Infection-based question: Name bacti that can cause diphtheria and the bacti that can cause pertussis
Diphtheria: Corynebacterium diphtheriae
Pertussis: Bordetella pertussis
Infection-based question: name the type of bacti causing bacillary dysentery
Shigella
Infection-based question: name the bacti that can cause cholera
Vibrio cholerae
Infection-based question: name bacteria causing tuberculosis
Mycobacterium tuberculosis
Infection-based question:
Name bacti that can cause infective endocarditis
Staph aureus/epidermidis
Viridans Strep, enterococci
N. gonorrhoeae
Infection-based question:
Name bacti that can cause meningitis (as much as you can, ideally 3)
S. pneumoniae/agalactiae (neonatal meningitis)/suis
Listeria
N. gonorrheae/meningitidis
E. coli (neonatal)
salmonella (non-typhi)
Infection-based question:
Name bacti that can cause skin/soft tissue infections
S. aureus
S. pyogenes/agalactiae/dysgalactiae/suis
V. vulnificus
Infection-based question:
name bacti that can cause UTI (urinary tract infection)
Enterococcus, S. agalactiae, E. coli,
Infection-based question: name bacti that can cause food poisoning
S. aureus, B. cereus, C. perfringens, salmonella
Infection-based question: name bacti that can cause gastroenteritis
E. coli, Listeria, V. parahaemolyticus
Infection-based question: name bacti that can form abcesses
S. anginosus, Nocardia (brain abcess)
