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principles of disease > classification of pathogenic bacteria, pathogens and host > Flashcards

classification of pathogenic bacteria, pathogens and host Flashcards

1
Q

gram’s stain

A
  • Quick, simple, inexpensive way to classify clinically important organisms
    • Provides an early indication of the genus of bacteria that may be causing infection
      ○ Combine knowledge from gram stain with morphology
    • Different species have varying capacity to cause disease (pathogenicity)
      Different classes of antibiotics are effective against gram +ve and -ve bacteria (targeted treatment)
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2
Q

cells wall differences in gram +ve vs -ve bacteria

A

Thick peptidoglycan layer in gram +ve

Thin peptidoglycan layer, more complex cell wall, thick lipopolysaccharide layer in gram -ve

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3
Q

classification of gram +ve bacteria

A

stain purple
2 major types of classification are aerobic/anaerobic or their morphology (cocci/bacilli)
Chains - streptococcus
Clusters - staphylococci
Streptococcus - how do they grow on blood agar
Partial/complete/no haemolysis

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4
Q

coagulase +ve gram +ve bacteria

A

staphylococcus aureus

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5
Q

staphylococcus aureus

A

○ Commensal organism carried in nose, axilla and perineum
○ Major human pathogen causing a wide range of disease
boils/abscesses and soft tissue infections to septicaemia and osteomyelitis

  • Commonly penicillin resistant due to production of penicillinase
  • By a different mechanism, some strains are methicillin resistant
    MRSA poses major problems for infection prevention and control in hospitals
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6
Q

coagulase -ve gram +ve bacteria

A
  • many different species (staphylococcus
    S. epidermis, S. haemolyticus, S. saprophyticus., S. lugdunensis - has many of the virulence factors of S. aureus)
  • Mainly skin commensals
  • can be pathogenic in the presence of foreign bodies or immunocompromised
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7
Q

alpha haemolytic streptococci

A

partial haemolysis - Turn blood agar green

Streptococcus pneumoniae (pneumococcus)

Viridans streptococci

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8
Q

Streptococcus pneumoniae

A

alpha haemolytic

pneumonia, meningitis, septicaemia

Produces capsule to protect S. pneumoniae from the host so it cant be recognised as foreign

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9
Q

Viridans streptococci

A

○alpha haemolytic

○ Normal oral flora, cause infection in other areas
Cause of infective endocarditis

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10
Q

beta haemolytic streptococci

A

(complete haemolysis)
Turn blood agar clear
Further identified by carbohydrate surface antigens: groups A-G),
A,B,D,F clinically most important
A. streptococcus pyogenes
b. streptococcus agalactiae
D. Enterocossu faecalis, Enterococcus faecium

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11
Q

streptococcus pyogenes

A

group A beta haemolytic
major pathogen -

pharyngitis, cellulitis, necrotising fasciitis

(skin and soft tissue infections, bone and joint infections and can lyse human muscle and connective tissue, can lead to sepsis)

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12
Q

streptococcus agalactiae,

A 
group B beta haemolytic 
neonatal sepsis (meningitis, bacteraemia), genital tract carriage common

invasive infections in adults often older and underlying factors e.g. diabetes, liver disease/alcohol abuse, CVD, malignancy )

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13
Q

enterococcus

A

group D beta haemolytic
often non-haemolytic,

enterococcus faecalis

found in the gut as normal commensal, cause of UTI and infective endocarditis

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14
Q

classification of gram +ve bacilli

A
  • Aerobic
    Anaerobic (grow only in the absence of oxygen)

spore forming/non-spore forming

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15
Q

classification of gram +ve cocci

A

coagulase test

blood agar culture - haemolysis

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16
Q

CLOSTRIDIUM DIFFICILE

A

gram +ve bacilli

  • Asymptomatic gut carriage in healthy people
  • Important cause of diarrhoea, associated with toxin production and potentially fatal (toxins found in stool sample)
  • Increased risk with antibiotic use and anything else that disrupts the normal gut flora
  • Pseudomembranous colitis - inflammation of the large intestine
  • Spread/transmitted via spores
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17
Q

CLOSTRIDIUM PERFRINGENS

A
  • gram +ve bacilli
    Found in soil and normal commensal in human and animal gut/faeces
  • Spread by spores
  • Can contaminate food and cause gastroenteritis (enterotoxin producing strains)
    Infects wounds and can cause gas gangrene
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18
Q

CLOSTRIDIUM TETANI

A
  • gram +ve bacilli
  • Spread by spores
  • Toxin produced by C. tetani can produce tetanus
    ○ Uncontrolled muscle spasm
    Antigenically modified toxin (toxoid) used for immunisation
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19
Q

colonisation

A

bacteria grow on body sites exposed to the environment, without causing any infection. This is a normal process.

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20
Q

infection

A

presence of microorganisms causing damage to body tissues, usually in the presence of acute inflammation

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21
Q

gram -ve cocci

A

Neisseria meningitidis
Neisseria gonorrhoeae
Moraxella catarrhalis

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22
Q

Neisseria meningitidis

A

gram -ve coccus
meningitis and septicaemia
important when isolated from a sterile site (e.g. blood cultures or CSF, gram staining is very important to identify the bacteria here), PCR available on EDTA blood for N. meningitidis, often life threatening

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23
Q

Neisseria gonorrhoeae

A

gram -ve coccus
causes urethritis in men and pelvic inflammatory disease in women, spread by sexual contact, causes gonorrhoea, identical appearance to Neisseria meningitidis on gram stain (differentiate by clinical findings)

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24
Q

Moraxella catarrhalis

A

gram -ve coccus

causative agent of respiratory tract infections, especially in those with underlying lung pathology

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25
Q

what are coliforms

A

organisma which are in the family Enterobacteriaceae
• Mainly commensals of the human large intestine (gut commensals)
• Key example is E. coli
Lactose fermentation is a useful preliminary test in classifying gram -ve bacilli (can use selective agar)

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26
Q

ESCHERICHIA COLI

A

-gram -ve bacilli
Human and animal reservoirs
160 serotypes, strains vary in terms of disease potential
- Sexual virulence mechanisms: pili, capsule endotoxin and exotoxins
- Major form of food borne infection
- Ferments lactose

  • Important cause of UTI and septicaemia, also neonatal sepsis
  • enterotoxogenic and enterohaemorrhagic
    Don’t treat with antiobiotics - these could lead to more toxins being produced
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27
Q

SALMONELLA SPP.

A

-gram -ve bacilli
- Major form of food borne infection
- DOES NOT ferment lactose
- Salmonella enterica:
Self-limiting enterocolitis with or without bloody diarrhoea

  • 2nd commonest cause of bacterial diarrhoae in the UK
  • Can be invasive i.e. enters bloodstream
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28
Q

SALMONELLA TYPHI

A
  • gram -ve bacilli
    Distinct from Salmonella enterica
  • Cause of typhoid fever
  • Fever, constipation early stages
    fatal if untreated
  • Organism can be isolated from blood cultures as well as faeces
    Risk during foreign travel but vaccine available
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29
Q

curved gram -ve bacilli

A

Campylobacter spp
Helicobacter pylori
vibrio spp

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30
Q

Campylobacter spp.

A

curved gram -ve bacilli
microaerophilic (likes low oxygen), source is domestic animals and chickens, spread via faecal-oral route, foul smelling –> bloody diarrhoea (incubation period 2-5 days), commonest cause of bacterial diarrhoea in UK , no vaccine currently, often seen in springtime, can enter the bloodstream, not treated with antibiotics unless very severe

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31
Q

Helicobacter pylori:

A

curved gram -ve bacilli
natural habitat is human stomach, damages mucosa and causes ulcers, strong risk factor for gastric adenocarcinoma (oncogenic organism), treat to avoid future cancer risk

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32
Q

Haemophilus influenzae

A

gram -ve cocco-bacilli (mixed appearance), causes respiratory tract infection (2y to S, pneumoniae), capsulate for (type b) was formerly an important cause of meningitis in children, other no-typable forms of H. influenzae still able to cause meningitis

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33
Q

Pseudomonas SPP - P. aeruginosa

A 
anaerobic gram -ve bacilli-
Water and soil coloniser - drains, sinks, mops
- May contaminate medical equipment 
- Can colonise upper resp tract 
- Hospital acquired cause of sepsis e.g. UTI, bacteraemia, pneumonia (rare)
- Feared respiratory pathogen in CF
- Multi drug resistance mechanisms 
Limited treatment options
34
Q

anaerobes

A
  • Often part of polymicrobial infection e.g. liver/brain abscess
  • Increasing importance and recognition
  • Bacteroides spp, Prevotella, Porphyromonas
  • Difficult to grow in the lab due to their sensitivity to oxygen

Bacteroides fragilis
• Part of normal colonic flora
• Causes intra-abdominal abscess
• May spread to other sites e.g. blood

35
Q

oral anaerobes

A
  • Prevotella
  • Porphyromonas e.g. P. gingivalis
  • Pasteurella spp
  • Capnocytophyga spp
  • Important in aetiology of periodontal disease and may be part of polymicrobial dental abscesses
  • Role in aspiration pneumonia
  • Human and animal bit infections
36
Q

miscellaneous bacteria

A
  • Not all bacteria can be stained w/ Gram’s method
  • Not all bacteria can be cultured by standard methods
    Mycobacterium spp, spirochaetes, chlamydia/chlamydophila
37
Q

acid and alcohol fast bacteria

A

• Resistant to decolourisation by acid or alcohol after staining with carbol fuchsin
Mycobacterium species are visualised with special stains e.g. ZN or auramine

38
Q

lab identification of mycobacteria

A 
• ZN or auramine phenol screening 
	• Doesn’t identify species
	• Culture required for ID 
		○ New automated liquid culture
		○ Growth in 2-4 wks
Molecules detection and identification of MTB possible
39
Q

tuberculosis

A

• Caused by mycobacterium tuberculosis
• Linked with HIV
• Recommended rapid diagnostic nucleic acid amplification tests for diagnosing pulmonary (including laryngeal) TB in adults if there is:
Clinical suspicion of TB disease and the person has HIV
In circumstances in which rapid info about mycobacterial species would alter the person’s care
In a situation where a large contact tracing initiative is being exploited

40
Q

Mycobacterium leprae

A

cant be cultured, mainly India, Nepal, Brazil, parts of Africa, attacks peripheral nerves

41
Q

SPIROCHAETES

A

mycobacteria
long, spiral shaped bacteria; not easily visualised by light microscopy, very difficult to culture (never Treponema pallidum), dark ground microscopy or immunofluorescence, often diagnosed by serology
Common spirochaete diseases: Treponema pallidum (syphilis), Borrelia burgdoferi (lyme disease), Leptospira interrogans (Leptospirosis)

42
Q

SYPHILIS

A

spirochaete
treponema pallidum
1y - non-painful skin lesion
2y - generalised systemic illness and rash, latent phase - symptomatic episodes may occur
3y -CNS, congenital syphilis: stillbirth, neonatal death or disease
diagnosis - serology, nucleic acid amplification tests (NAAT), part of antenatal screening, management - antibiotics, contact tracing and screening

43
Q

lyme disease

A

mycobacteria
transmitted by ticks, stage 1: skin rash (erythema chronicum migrans) appears at the site of the tick bite, stage 2: systemic illness occurs in some patients, wks/mths later when patients suffer cardiac or neurological and muscoloskeletal symptoms, stage 3: chronic disease, occuring yrs later when patients present with chronic skin, nervous system or joint abnormalities. Diagnosed by clinical assessment and serology (antibody detection)

44
Q

leptospirosis

A

mycobacteria
infects animals and concentrates in the kidneys, spread is via urine and other body fluids and tissues (zoonosis), at risk groups (sewage workers, water sports), range of clinical presentations (Weil’s disease: febrile illness with systemic upset, liver and renal failure, aseptic meningitis, 10% mortality)

45
Q

chlamydia

A

obligate intracellular bacteria, cultured only in cell lines, can be diagnosed by serology, respiratory infection (chlamydophila pneumoniae, Chlamydophila psittaci (psittacosis) - contact with birds), ophtalmic and genital tract infection
Chlamydia trachomatis: trachoma (tropical eye infections), genital and neonatal infection, diagosis: NAAT on 1st void urine or vulval/vaginal swabs, often asymptomatic in women, can lead to pelvic inflammatory disease and infertility

46
Q

define commensal

A

organism which is part of the normal flora e.g. E. coli in the gut, S. aureus in the nose

47
Q

define pathogen

A

organism which can cause disease

48
Q

what are the requirements for a micro-organism to cause infection

A

infectivity and virulence

49
Q

infectivity

A

ability to become established on or within a host
○ Attachment: E. coli (P-fimbriae, receptor on uroepithelial cells)
Acid resistance: Helicobacter pylori - lives in the stomach and causes gastritis and gastric ulcers (urease, makes ammonia from urea)

50
Q

virulence

A

capacity to cause harmful effects (disease) once established
○ Conferred by virulence factors: genetically determined microbial components
§ Invasiveness, toxin production, evasion of immune system
□ INVASIVENESS: Streptococcus pyogenes (Group A streptococci), necrotising fasciitis, cellulitis, connective tissue breakdown (hyaluronidase, collagenase), fibrinolysis (streptokinase)
Specific to strains, not species

51
Q

exotoxins

A

released extracellularly by the microorganism

52
Q

enterotoxins

A

exotoxins which act on the GI tract

53
Q

example of an exotoxin

A

e.g. SUPERANTIGENS: Certain exotoxins of S. pyogenes and S. aureus. Able to stimulate division of T cells in the absence of specific antigen. Overwhelming cytokine production causes toxic shock

54
Q

examples of enterotoxins

A

CHOLERA: Vibrio cholera, colonises S intestine, enterotoxin production (increases cAMP levels, inhibits uptake of Na+ and Cl- ions, stimulates secretion of Cl- and HCO3- ions. Passive (massive) outflow of water, causes death by dehydration, treated by rehydration

55
Q

endotoxins

A

structurally part of the gram -ve cell wall

56
Q

examples of endotoxins

A

Lipopolysaccharide (Lipid A, oligosaccharide core, specific polysaccharide chain), E. coli and other gram -ve bacilli, Neisseria meningitidis, induces severe uncontrolled host response (cytokine production, fever, rigors, hypotension, tachycardia, collapse

57
Q

superantigens

A
  • Certain exotoxins of S. pyogenes and S. aureus
  • Able to stimulate division of T cells in the absence of specific antigen
  • Overwhelming cytokine production causes toxic shock
58
Q

influenza A

A
  • Virus infects cells of the respiratory tract
  • Destruction of respiratory epithelium which can lead to secondary bacterial infections
  • Altered cytokine expression leading to fever
    • Non-human host for influenza a play a key role in generating new virus types through antigenic shift
59
Q

antigenic drift in influenza A

A

minor changes, in the genes of flu viruses, occurs gradually over time to generate antigenic variants
leads to a generation of novel influenza viruses

60
Q

antigenic shift in influenza A

A

(abrupt major changes in antigenic structure)

leads to generation of novel influenza viruses

61
Q

enterovirus infections (5)

A
  • Poliomyelitis (poliovirus)
  • Aseptic meningitis (many enteroviruses)
  • Myocarditis (coxsackie B viruses)
  • Pancreatitis (coxsackie B viruses)
    Respiratory infections (many enteroviruses)
62
Q

example of a latent virus infection

A

herpes simplex virus - cold sores (type 1) and genital lesions (type 2)

63
Q

virus induced tumours

A
  • E.g. papillomaviruses - cervical carcinoma, Retroviruses - lymphomas and leukaemias
    Human T - lymphotropic virus 1 (HTLV-1): transmission by blood and mother to child, infects T cells, modifies host cell gene expression using a transactivating protein, variety of diseases including leukaemia (adult T cell lymphoma-leukaemia), directly responsible for the tumour
64
Q

active immunisation

A 
natural/artificial
antigen stimulates immune response
long term immunity 
immunological memory 
no immediate effect but faster and better response to next antigenic encounter
65
Q

live attenuated vaccine

A

attenuation of a pathogenic organism by repeated passage in cell culture or non-human host
usually promote a full, long-lasting antibody response after one or two doses
reversion to wild-type organism may occur
contraindicated in some individuals
require refrigeration until administration

66
Q

killed vaccine

A

inactivated pathogenic organism
reversion to wild type organism doesnt occur
promote weaker immune responses in comparison to live vaccines - multiple doses may be required
some inactivated vaccines contain adjuvants
possible side effects of producing inflammatory responses

67
Q

adjuvants

A

substances that enhance the antibody response

68
Q

examples of attenuated vaccine

A

MMR, BCG, polio, varicella zosterm, yellow fever

69
Q

examples of killed vaccines

A

polio, hep A, rabies

70
Q

toxoid vaccine

A

toxin treated with formalin
toxin retains antigenicity but has no toxic activity
only induces immunity against the toxin and not the organism that produced it

71
Q

examples of toxoid vaccine

A

tetanus, diphtheria

72
Q

define latent infection

A

type of infection that may occur after an acute episode; the organism is present but symptoms are not; after time the disease can reappear

73
Q

define asymptomatic infection

A

patient is a carrier for a disease or infection but experiences no symptoms

74
Q

host defence mechanisms

A

innate and acquired immunity
phagocytosis
antibodies and complement
cell mediated immunity

75
Q

innate immunity

A

physical defences

phagocytic cells

76
Q

acquired immunity

A

specific response to antigen
leads to immunological memory
humoral and cellular

77
Q

phagocytosis

A

polymorphs (neutrophils, eosinophils, basophils)
and monocytes in blood
mononuclear phagocytic system: spleen, liver and regional lymph nodes
other white cells

78
Q

antibody and complement

A

involves immunoglobulins
neutralised toxin, neutralised virus, prevents adherence of microorganisms, opsonises capsulate organisms, useful in diagnosis

humoral immunity: mostly bacterial infection, extra-cellular, acute inflammation, neutrophilia

79
Q

cell mediated immunity

A

combat intracellular infection

macrophages present antigen and stimulate T cells, cytokines produced and control the response

80
Q

enterotoxogeic E coli

A

commonest cause of traveller’s diarrhoea (contaminated water)

81
Q
  • Enterohaemorrhagic E. coli
A

more severe form, bloody diarrhoea, haemolytic uraemic syndrome (HUS) associated w/ E. coli O157

82
Q

shigella

A 
not lactose fermenting 
low infective dose
faecal-oral spread
bacillary dysentery 
some strains produce toxin
4 species

principles of disease (40 decks)

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