Medically Important Bacteria Flashcards
Staphylococcus aureus properties
- Gram + cocci that occur in clusters
- Golden yellow colonies on agar
- Catalase and coagulase positive
- Anaerobe
- Normal flora of humans found in nasal passages, skin and mucous membranes
Staphylococcus aureus diseases
- skin infections, such as pimples, impetigo, boils, cellulitis, folliculitis, scalded skin syndrome and abscesses
- life threatening diseases like pneumonia, meningitis, osteomyelitis, endocarditis, TSS, septicaemia, food poisoning
- Post surgical wound infections
Staphylococcus aureus virulence factors
- Coagulase: causes clots
- Invasins: promote bacterial spread in tissues (eg. Hyaluronidase, leucocidin, kinases)
- Haemolysins
- Exotoxins: exfoliative toxin, toxic shock syndrome toxin, entrotoxin
Streptococcus pyogenes properties
- Gram + cocci that occurs in chains
* Produces large zones of beta haemolysis on blood agar
Streptococcus pyogenes infections
- Sore throats, tonsillitis
- Cellulitis, impetigo
- Bactremia
- Endocarditis
- Toxin mediated scarlet fever and toxic shock syndrome
- Immune mediated/post streptococcal disease - rheumatic fever, rheumatic heart disease, glomerulonephritis
- Sinusitis
- Necrotising fasciitis
- Poststreptococcal glomerulonephritis
Streptococcus pyogenes virulence factors
- Hyaluronidase: breaks down hyaluronic acid, enabling bacterial spread
- Cell wall antigens: capsular polysaccharide, peptidoglycan, lipoteichoic acid
- Streptokinase: digests clots
- Streptolysins: cause beta hemolysis
- DNAses: liquefaction of pus, generate substrate for growth
- M protein (in fimbriae) : facilitate attachment to various host cells
- Erythrogenic toxin: scarlet fever
- Pyrogenic toxin: STSS (streptococcal toxic shock syndrome)
Streptococcus pneumoniae properties
- Gram + cocci that occurs in pairs
- Often capsulate
- Aerobic, anaerobic respiration
- Alpha haemolytic on blood agar
- Produce draughtsman colonies
- Catalase negative
- Bile soluble
- Susceptible to optochin
Streptococcus pneumoniae infections
- Bronchopneumonia
- Lobar pneumoniae
- Meningitis
- Bacteraemia
Streptococcus pneumoniae virulence factors
- Capsule
- Pili: colonisation of upper respiratory tract
- PspA surface protein: inhibits complement activation, binds lactoferrin, inhibits uptake to phagocytes
- LytA, B, C: autolysins
- CbpA: adhesin, which is choline-binding protein
Gram positive bacilli (aerobes) examples
- Bacillus anthracis
* Bacillus cereus
Bacillus anthracis properties
- Spore forming
- Causative form of anthrax (infection affecting skin, lungs, intestines, injection)
- Soil organisms
- Humans acquire infection when spores enter skin or when inhaled
Bacillus cereus properties
- Spore forming
- Causes food poisoning (reheated rice, pulses)
- Cause Bacteraemia in immunocompromised
Gram positive bacilli (anaerobes) examples
- Clostridium tetani (tetanus)
- Clostridium botulinum (botulism)
- Clostridium difficile (colitis)
- Clostridium perfringes (gas gangrene)
Clostridium tetani properties
- Spore forming with terminal spore (drumstick)
- Humans acquire infection by contaminated soil entering wound
- Grows on blood agar under anaerobic conditions, giving ground glass appearance
- Causes tetanus, convulsive contractions of voluntary muscles
Clostridium perfringes properties
- Gas gangrene resulting from dirty wounds
* Food poisoning following ingestion of food contaminated with enterotoxin producing strains
Clostridium perfringes virulence factors
- Toxins
* Tissue destroying enzymes
Clostridium difficile properties
- Component of gut flora
- Flourishes under selective pressure of antibiotics
- Pseudomembranous colitis or antibiotic associated diarrhoea
- Fatal in the immunocompromised
Corynebacterium diphtheriae properties
- Gram + bacilli
- Non spore forming
- Cells arranged as Chinese letters or pallisades
- Causes diphtheria
- Caused by toxigenic strains only
- Infects throat and skin
Corynebacterium diphtheriae virulence factors
- Diphtheria toxin: inhibits protein synthesis by inactivating elongation factor
- Pili
Diphtheria condition properties
- Upper respiratory tract illness
- Sore throat, Low fever
- Adherent membrane (pseudomembrane on tonsils, pharynx)
- Diphtheria toxin: myocarditis, polyneuritis
Lab diagnosis for diphtheria
- Gram staining
- Blood tellurite medium
- ELEK test
- PCR to detect DNA seq encoding toxin
ELEK test
- Production of diphtheria toxin detected within 18 to 48 hours
- Formation of toxin-antitoxin precipitin band on agar
Gram negative diplococci examples
- Neisseria gonorrhoea (gonorrhoea)
* Neisseria meningitidis (meningitis)
Neisseria gonorrhoea properties
- Kidney shaped, diplococci
- Causes gonorrhoea
- In females: pelvic inflammatory disease, salpingitis
- In infants: ophthalmia neonaturm (neonatal conjunctivitis)
- Can be carried in anus, nasopharyngeal tract, genital tract
Gonorrhoea treatment
- Beta-lactamase stable cephalosporin
- Amoxycillin
- Ampicillin
Gonorrhoea prevention
- Condoms
- Education
- Contact tracing
- Treatment
Gram negative bacilli main examples
- Salmonella typhi (typhoid fever)
- Salmonella paratyphi A, B, C (paratyphoid fever)
- Shigella dysentriae, Shigella sonnei, Shigella flexneri, Shigella boyii (bacillary dysentery)
Gram negative bacilli other examples
- Eschericha coli
- Klebsiella pneumoniae
- Proteus sp
- Pseudomonas aeruginosa
Escherichia coli properties
- Gram negative rod
- Motile
- Most strains are harmless
- Live in gut of man and animals
- Spread by fecal oral route
- Grows on MacConkey agar, produce pink colonies indicating that it is lactose fermenter
Escherichia coli virulence factors
- Adhesins: P fimbriae, S fimbriae, Type 1 fimbriae
- Invasins: haemolysins, shigella like Invasins
- Toxins: endotoxins (LPS), shigella like toxins, cytotoxins, ST toxin, LT toxin
- Antiphagocytic and defence against immune responses: capsules, K-antigen, LPS
Salmonella properties
- Predominantly motile
- Can survive for weeks outside the body
- May cause bacteraemia
Salmonella transmission
- Humans to animals and vice versa
- Encountered in food chain
- Acquired by ingestion of contaminated food via fecal oral route
Gram negative comma shaped bacteria examples
- Vibrio cholerae (cholera)
- Vibrio parahaemolyticus (haemolyses RBCs)
- Vibrio vulnificus (wound infections, bacteraemia)
Vibrio cholerae properties
- Highly motile using single flagellum
* Virulence factors: mucinase, adhesins, enterotoxin
Gram negative curved or spiral shaped bacteria examples
- Campylobacter foetus: bacteraemia
* Helicobacter pylori: gastritis, gastric ulcer, gastric carcinoma
Helicobacter pylori virulence factors
- Protease which affects stomach mucosa
* Urease which produces ammonia, buffers stomach acid
Gram negative bacilli examples (2)
- Bordetella pertussis (whooping cough)
- Haemophilus influenza (meningitis, sinusitis, upper respiratory infections)
- Yersinia pestis (plague)
- Legionella pneumophila (pneumonia)
Mycoplasma properties
- Lacks a cell wall
* Cannot be acted on by beta lactam antibiotics
Mycoplasma examples
- Mycoplasma pneumoniae (pneumonia)
- Mycoplasma genitalum (pelvic inflammatory disease)
- Mycoplasma hominis (pelvic inflammatory disease)
Mycoplasma hominis properties
• Growth of “fried egg” colonies on glucose agar medium within 24-48 hours
Mycoplasma pneumoniae virulence factors
- Produce Community Acquired Respiratory Distress Syndrome (CARDS) toxin
- Aids in colonisation and pathogenic pathways leading to inflammation and airway dysfunction
Mycobacterium properties
- Gram stain with difficulty because of mycolic acids
* Ziehl-Neelsen stain
Mycobacteria examples
- Mycobacterium tuberculosis (tuberculosis)
- Mycobacterium leprae (leprosy)
- Mycobacterium other than tuberculosis MOTT: range of illnesses in the immunocompromised (M. Avium)
Mycobacterium tuberculosis properties
- Infects lung
- Causes lesion in lung called Ghon’s complex
- Transmission: droplet infection
Mycobacterium tuberculosis virulence factors
- Grow intracellularly
- Antigen 85 complex: bind fibronectin, aid in walling bacteria off from immune system and facilitate tubercle formation
- Mycolic acids: prevent Attack of mycobacterium by phagocytes
- High lipid conc in cell wall: resistance to antibiotics
- Cord factor (glycolipid found in cell walls of mycobacteria): toxic to mammalian cells
Treponema pallidum properties
- Spirochaete (spiral-shaped bacteria)
- Viewed by dark ground microscopy or immunoflourescence microscopy
- Causative agent of syphilis
Leptospira interrogans properties
- Finely coiled spirochetes with hooked ends
- Causes leptospirosis, kidney disease
- Viewed by dark ground microscopy, immunoflourescence, light microscope
