microbiology (bacteria) Flashcards
Information regarding bacteria that may come up as part of microbiology.
bacterial shapes
cocci
bacilli
vibrio
spirochaete
ziehl-neelsen staining
used for Mycobacteria
acid-fast will stain pink/red
non acid-fast will stain blue
catalase test
staphylococci is catalase positive (will generate gas bubbles); streptococci is catalase negative (no reaction)
coagulase test
Staphylococcus aureus is coagulase positive (will clot when added to plasma); other Staphylococcus spp. are coagulase negative
oxidase test
bacteria that produce cytochrome oxidase are oxidase positive - e.g. Pseudomonas and Neisseria
positive result will turn black/purple in colour
optochin test
differentiates Strep. pneumonia from other alpha haemolytic Streptococci
Streptococci pneumonia + optochin will cause lysis
metronidazole
identifies sensitive anaerobes by inhibiting their growth on culture medium
MacConkey agar
isolates and identifies enteric bacteria
contains bile salts, lactose, and pH indicator
lactose fermenting bacteria will cause red/pink colony - Escherichia coli and Klebsiella
non-lactose fermenting bacteria will leave a clear colony - Salmonella, Shigella, and Pseudomonas
blood agar - haemolysis
alpha haemolysis - green - partial RBC and Hb breakdown - viridans
beta haemolytic - clear zones - complete erythrocyte lysis
non-haemolytic - no change
Lancefield grouping
differentiates between beta haemolytic Strep by detecting surface antigens
group A: Streptococcus pyogenes
group B: Stretococcus agalactiae
group D: Enterococcus
exotoxin
produced mostly by gram +ve bacteria
actively secreted toxins with a specific action (e.g. botulinum toxin)
endotoxin
a component of the cell wall that is released when bacteria are damaged
gram +ve: lipoteichoic acid
gram -ve: lipopolysaccharides
less specific actions include septic shock
gram positive bacterial groups
Streptococcus Staphylococcus Corynebacterium Listeria Bacillus Clostridium
Streptococcus
chains or diplococci gram +ve catalase negative alpha haemolytic: oralis, sanguis, mutans, mitis beta haemolytic: progenies, agalactiae non-haemolytic: Enterococcus faecalis Aerobic
Streptococcus pneumoniae
alpha haemolytic, diplococci, commensal of upper respiratory tract in 10-30%, droplet transmission
CAP, COPD exacerbation, sinusitis, otitis media
bacterial meningitis
treat with penicillin or erythromycin
Streptococcus Viridans (alpha haemolytic)
upper respiratory tract and GI tract commensal
bacterial endocarditis
dental caries
treat with penicillin/amoxicillin (erythromycin if allergic)
bacterial endocarditis treat with penicillin and gentomycin
Streptococcus pyogenes (group A ß-haemolytic)
upper respiratory tract commensal in 5%
transmission: airborne, respiratory secretions, hands
skin: cellulitis, necrotising fasciitis, impetigo, erysipelas, wound infections, scarlet fever
URTIs: pharyngitis (strep throat), tonsillitis, acute otitis media
invasive: sepsis
post-infective: rheumatic fever and glomerulonephritis
treat with penicillin/amoxicillin (erythromycin if allergic)
Streptococcus agalactiae (group B ß-haemolytic)
faecal commensal in 30-40% of population and vaginal in 10-30%
causes neonatal septicaemia and meningitis in children
causes UTIs, post-partum sepsis, bacterial endocarditis, and septicaemia in adults
Enterococcus (group D non-haemolytic, MacConkey growth)
GI tract commensal infective endocarditis UTI wound infections IV catheter infection treat with penicillin/vancomycin treat IE with penicillin/vancomycin + gentamicin
Staphylococcus
cocci in clumps
gram positive
catalase positive
S.aureus is coagulase positive; the others are coagulase negative
S.aureus has golden yellow colonies; S.epidermidis and S.saprophyticus have white colonies
aerobic
Staphylococcus aureus
coagulase positive
anterior nares in 20-30% of population
impetigo, paronychia, abscesses, cellulitis, wound/IV line infection
osteomyelitis and septic arthritis
septicaemia, conjunctivitis, IE, pneumonia
toxin mediated: toxic shock syndrome, scalded skin syndrome, and food poisoning
flucloxacillin
vancomycin for MRSA
Staphylococcus epidermidis
coagulase negative
skin and mucous membranes
foreign body infection or native valve endocarditis
treat with flucloxacillin (or vancomycin if resistant)
Staphylococcus saprophyticus
coagulase negative
UTIs in sexual active young women
treat with trimethoprim or flucloxacillin
Corynebacterium
bacilli
gram positive
aerobic
e.g. C.diptheriae
Corynebacterium diphtheriae
nasopharyngeal carriers
droplet spread
diphtheria toxin –> epithelial cell destruction and myocardial/neural cell damage –> bull neck lymphadenopathy and pseudomembrane covering tonsils
treat with erythromycin, diphtheria antitoxin and vaccination
less than 5 cases per year in UK (due to vaccination)
Listeria
bacilli
gram positive
aerobic
e.g. Listeria monocytogenes
Listeria monocytogenes
domestic animal faeces and food
transmission: contact with animals, ingestions, transplacentally, perinatally
miscarriage and stillbirth
can cause meningitis, pneumonia, encephalitis, and sepsis in neonates, the elderly, or the immunocompromised
treat with ampicillin/erythromycin and gentamicin
Bacillus
bacilli gram positive spore forming aeorbic e.g. Bacillus anthracis, B. cereus
Bacillus anthracis
infected herbivore carcasses
transmission from handling infected materials (not from eating)
cutaneous lesions
anthrax may also be pulmonary or gastrointestinal
treat with ciprofloxacin or doxycycline
Bacillus cereus
foods (e.g. rice)
ingestion of infected foods
self-limiting
Clostridium
bacilli gram positive anaerobic Clostridium tetani has terminal spores C. perfringens is brick-shaped
Clostridium perfringens
human gut commensal, skin, soil
gas gangrene, intra-abdominal sepsis, anaerobic cellulitis, food poisoning, septicaemia, post-abortion infection
treat with penicillin and clindamycin, and antitoxin
Clostridium tetani
human and animal gut commensal, soil
spores entering open wounds
causes tetanus
treat with human tetanus immunoglobulin and benzodiazepines
Clostridium difficile
faecal commensal in neonates and young children
spores via faecal oral route
causes pseudomembranous colitis (diarrhoea following abc therapy)
treat with vancomycin
Clostridium botulinum
human and animal GI tracts, soil and plants
transmission from food ingestion and wound contamination
causes botulism - descending paralysis secondary to botulinum toxin
treat with vancomycin or metronidazole
gram negative bacterial groups
Neisseria Coliforms (also Enterobacteriaceae) Parvobacteria Helicobacter Vibrio Pseudomonas
Neisseria
gram negative diplococci
oxidase positive
aerobic
e.g. Neisseria meningitidis
Neisseria meningitidis
nasopharynx in 5-20% or general population
transmission: droplets or direction mucosal contact
meningitis
septicaemia with purpuric skin rash
treat with benzylpenicillin or cefotaxime
treat close contacts with rifampicin, ciprofloxacin, or ceftriaxone
vaccine available for some strains
Neisseria gonorrhoeae
transmission by direct mucosal contact
gonorrhoea, ophthalmia neonatorum, Reiter’s syndrome (urethritis, conjunctivitis, arthritis)
treat with ciprofloxacin or cefixime
Coliforms (enterobacteriaceae)
gram negative bacilli
E.coli and Klebsiella pneumonia pink colonies on MacConkey agar
Salmonella type, paratyphoid, and enteritis clear colony on MacConkey
aerobic
Escherichia coli
colonic commensal
faecal-oral route
diarrhoea, UTIs, pneumonia (HAP or neonatal), neonatal meningitis, haemolytic uraemia syndrome (anaemia, thrombocytopenia, oliguria, and renal failure)
treatment depends on site of infection - give trimethoprim for UTI and cephalosporins for pneumonia
Klebsiella pneumoniae
HAP, UTI, neonatal meningitis (rare)
treat with cephalosporins
Proteus mirabilis
faecal commensal
UTIs in young females
wound and IV catheter infection
treat with trimethoprim
Salmonella typhi and paratyphi (A, B, and C)
faecal-oral route
typhoid and paratyphoid (enteric fever)
treat with ciprofloxacin
Salmonella enteritidis
commensal of animal GI tracts - infection from inadequately cooked food contaminated with animal faeces
gastroenteritis ± bacteraemia
self-limiting
Shigella dysenteriae
faecal-oral
bacillary dysentery
ciprofloxacin
Parvobacteria
gram negative bacilli
aerobic
e.g. Haemophilus influensa, Bordatella pertussis, Campylobacter, Legionella pneumophila
Haemophilus influenzae
type B (Hib) is most pathogenic but is now rare due to vaccine
upper respiratory tract commensal
acute epiglottis, meningitis, osteomyelitis, cellulitis, otitis media, septic arthritis, pneumonia
treat with cefotaxime or ceftriaxone
Bordatella pertussis
non-commensal
inhalation of airborne droplet
whooping cough
treat with erythromycin
Legionella pneumophila
warm water
inhalation or aerosolised droplet
Legionnaire’s disease: severe pneumonia and high fever
Pontiac fever: flu-like illness
treat with erythromycin, in severe cases give rifampicin or ciprofloxacin
Campylobacter jejune and coli
contaminated poultry or pork or unpasteurised milk gastroenteritis ±dysentery reactive arthritis Guillain-Barré syndrome self-limiting if severe, treat with ciprofloxacin
Helicobacter
curved/spiral bacilli
gram negative
aerobic
e.g. H.pylori
Helicobacter pylori
faecal oral route chronic gastritis duodenal and gastric ulcers increased gastric cancer risk treat with clarithromycin and amoxicillin or metronidazole - also with PPI (omeprazole)
Vibrio
vibrio shaped, gram negative
aerobic
e.g. Vibrio cholerae
Vibrio cholerae
water, seafood, faecal-oral
cholera: rice water diarrhoea (up to 25 litres of fluid lost per day)
treat with rehydration and ciprofloxacin for severe cases
Pseudomonas
gram negative bacilli
oxidase positive
aerobic
e.g. P. aeruginosa
Pseudomonas aeruginosa
moist environments, fruit and veg, faeces hand borne and direct contact pneumonia (esp. in CF pts) wound, burn, and IV catheter infections external otitis folliculitis UTIs (esp. with catheters) treat with gentamicin or IV ceftazidime treat with ciprofloxacin for children with CF and adults with bronchiectasis
Chlamydia
no distinct bacterial shape
gram negative
intracellular
e.g. Chlamydia trachomatis, C.psittaci
Chlamydia trachomatis
mucosal contact chlamydia Trachoma: chronic follicular keratoconjunctivitis Reiter's syndrome pelvic inflammatory disease treat with doxycycline or azithromycin
Chlamydia psittaci
pigeon fancier’s lung, atypical pneumonia
treat with tetracycline
Coxiella
no staining - diagnosis by serology
intracellular
e.g. Coxiella burnetti
Coxiella burnetti
cattle and sheep, inhaled in dust, unpasteurised milk, infected carcasses, droplet spread
Q-fever: flu-like illness, hepatitis ±splenomegaly
treat with tetracycline or doxycycline
Rickettsia
no staining
intracellular
e.g. R.prowazeki, rickettsii, conorii, typhi, akari
transmission via arthropods (e.g. ticks)
causes typhus
treat with doxycycline, chloramphenicol, or tetracycline
mycobacteria
acid fast bacilli
ziehl-neelson staining pink/red
Lowenstein-Jensen culture medium (up to 12 weeks)
e.g. M. tuberculosis, M. leprae
Mycobacterium tuberculosis/africanum/bovis
aerosol droplets
tuberculosis
treatment: rifampicin and isoniazid for 6 months, ethambutol and pyrizinamide for first 2 months
Mycobacterium leprae
aerosol droplet spread
leprosy
treat with rifampicin and dapsone
Treponema
spirochaete
no staining
e.g. T. pallidum
Treponema pallidum
sites of broken mucosa during sexual contact, congenital, blood transfusion
syphilis
treat with penicillin or doxycycline
Borrelia
spirochaete
no staining
e.g. B. burdorferi
Borrelia burdorferi
tick bites
Lyme disease
treat with doxycycline
Leptospira
spirochaete
no staining
e.g. L. interrogans
Leptospira interrogans
water and animals
open wounds, mucous membranes, conjunctivae
Leptospirosis ranges from fever to Weil’s disease
treat with doxycycline, benzylpenicillin, or amoxicillin
Mycoplasma
no staining
very small organism without a cell wall
aerobic or facultative anaerobe
e.g. M. pneumoniae
Mycoplasma pneumoniae
droplet tranmission atypical pneumonia (commonly in young adults) treat with erythromycin or doxycycline
