classification of pathogenic bacteria, pathogens & host

Question 1

gram’s stain

Answer 1

• 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)

Question 2

cells wall differences in gram +ve vs -ve bacteria

Answer 2

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

Question 3

classification of gram +ve bacteria

Answer 3

stain purple2 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

Question 4

coagulase +ve gram +ve bacteria

Answer 4

staphylococcus aureus

Question 5

staphylococcus aureus

Answer 5

○ 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

Question 6

coagulase -ve gram +ve bacteria

Answer 6

• 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

Question 7

alpha haemolytic streptococci

Answer 7

partial haemolysis - Turn blood agar green Streptococcus pneumoniae (pneumococcus) Viridans streptococci

Question 8

Streptococcus pneumoniae

Answer 8

alpha haemolytic pneumonia, meningitis, septicaemia Produces capsule to protect S. pneumoniae from the host so it cant be recognised as foreign

Question 9

Viridans streptococci

Answer 9

○alpha haemolytic ○ Normal oral flora, cause infection in other areasCause of infective endocarditis

Question 10

beta haemolytic streptococci

Answer 10

(complete haemolysis)Turn blood agar clearFurther identified by carbohydrate surface antigens: groups A-G), A,B,D,F clinically most important A. streptococcus pyogenesb. streptococcus agalactiaeD. Enterocossu faecalis, Enterococcus faecium

Question 11

streptococcus pyogenes

Answer 11

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)

Question 12

streptococcus agalactiae,

Answer 12

group B beta haemolytic neonatal sepsis (meningitis, bacteraemia), genital tract carriage commoninvasive infections in adults often older and underlying factors e.g. diabetes, liver disease/alcohol abuse, CVD, malignancy )

Question 13

enterococcus

Answer 13

group D beta haemolytic often non-haemolytic, enterococcus faecalis found in the gut as normal commensal, cause of UTI and infective endocarditis

Question 14

classification of gram +ve bacilli

Answer 14

• Aerobic Anaerobic (grow only in the absence of oxygen)spore forming/non-spore forming

Question 15

classification of gram +ve cocci

Answer 15

coagulase test blood agar culture - haemolysis

Question 16

CLOSTRIDIUM DIFFICILE

Answer 16

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

Question 17

CLOSTRIDIUM PERFRINGENS

Answer 17

• 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

Question 18

CLOSTRIDIUM TETANI

Answer 18

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

Question 19

colonisation

Answer 19

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

Question 20

infection

Answer 20

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

Question 21

gram -ve cocci

Answer 21

Neisseria meningitidis Neisseria gonorrhoeaeMoraxella catarrhalis

Question 22

Neisseria meningitidis

Answer 22

gram -ve coccus meningitis and septicaemiaimportant 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

Question 23

Neisseria gonorrhoeae

Answer 23

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)

Question 24

Moraxella catarrhalis

Answer 24

gram -ve coccus causative agent of respiratory tract infections, especially in those with underlying lung pathology

Question 25

what are coliforms

Answer 25

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)

Question 26

ESCHERICHIA COLI

Answer 26

-gram -ve bacilli Human and animal reservoirs160 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 enterohaemorrhagicDon’t treat with antiobiotics - these could lead to more toxins being produced

Question 27

SALMONELLA SPP.

Answer 27

-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

Question 28

SALMONELLA TYPHI

Answer 28

- gram -ve bacilli Distinct from Salmonella enterica- Cause of typhoid fever - Fever, constipation early stagesfatal if untreated- Organism can be isolated from blood cultures as well as faecesRisk during foreign travel but vaccine available

Question 29

curved gram -ve bacilli

Answer 29

Campylobacter sppHelicobacter pylorivibrio spp

Question 30

Campylobacter spp.

Answer 30

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

Question 31

Helicobacter pylori:

Answer 31

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

Question 32

Haemophilus influenzae

Answer 32

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

Question 33

Pseudomonas SPP - P. aeruginosa

Answer 33

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

Question 34

anaerobes

Answer 34

- 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

Question 35

oral anaerobes

Answer 35

- 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

Question 36

miscellaneous bacteria

Answer 36

- Not all bacteria can be stained w/ Gram's method - Not all bacteria can be cultured by standard methodsMycobacterium spp, spirochaetes, chlamydia/chlamydophila

Question 37

acid and alcohol fast bacteria

Answer 37

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

Question 38

lab identification of mycobacteria

Answer 38

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

Question 39

tuberculosis

Answer 39

• 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

Question 40

Mycobacterium leprae

Answer 40

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

Question 41

SPIROCHAETES

Answer 41

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)

Question 42

SYPHILIS

Answer 42

spirochaete treponema pallidum 1y - non-painful skin lesion2y - generalised systemic illness and rash, latent phase - symptomatic episodes may occur3y -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

Question 43

lyme disease

Answer 43

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)

Question 44

leptospirosis

Answer 44

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)

Question 45

chlamydia

Answer 45

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 infectionChlamydia 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

Question 46

define commensal

Answer 46

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

Question 47

define pathogen

Answer 47

organism which can cause disease

Question 48

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

Answer 48

infectivity and virulence

Question 49

infectivity

Answer 49

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)

Question 50

virulence

Answer 50

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

Question 51

exotoxins

Answer 51

released extracellularly by the microorganism

Question 52

enterotoxins

Answer 52

exotoxins which act on the GI tract

Question 53

example of an exotoxin

Answer 53

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

Question 54

examples of enterotoxins

Answer 54

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

Question 55

endotoxins

Answer 55

structurally part of the gram -ve cell wall

Question 56

examples of endotoxins

Answer 56

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

Question 57

superantigens

Answer 57

- 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

Question 58

influenza A

Answer 58

- 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

Question 59

antigenic drift in influenza A

Answer 59

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

Question 60

antigenic shift in influenza A

Answer 60

(abrupt major changes in antigenic structure)leads to generation of novel influenza viruses

Question 61

enterovirus infections (5)

Answer 61

- Poliomyelitis (poliovirus)- Aseptic meningitis (many enteroviruses)- Myocarditis (coxsackie B viruses)- Pancreatitis (coxsackie B viruses)Respiratory infections (many enteroviruses)

Question 62

example of a latent virus infection

Answer 62

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

Question 63

virus induced tumours

Answer 63

- E.g. papillomaviruses - cervical carcinoma, Retroviruses - lymphomas and leukaemiasHuman 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

Question 64

active immunisation

Answer 64

natural/artificialantigen stimulates immune responselong term immunity immunological memory no immediate effect but faster and better response to next antigenic encounter

Question 65

live attenuated vaccine

Answer 65

attenuation of a pathogenic organism by repeated passage in cell culture or non-human hostusually promote a full, long-lasting antibody response after one or two dosesreversion to wild-type organism may occur contraindicated in some individualsrequire refrigeration until administration

Question 66

killed vaccine

Answer 66

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

Question 67

adjuvants

Answer 67

substances that enhance the antibody response

Question 68

examples of attenuated vaccine

Answer 68

MMR, BCG, polio, varicella zosterm, yellow fever

Question 69

examples of killed vaccines

Answer 69

polio, hep A, rabies

Question 70

toxoid vaccine

Answer 70

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

Question 71

examples of toxoid vaccine

Answer 71

tetanus, diphtheria

Question 72

define latent infection

Answer 72

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

Question 73

define asymptomatic infection

Answer 73

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

Question 74

host defence mechanisms

Answer 74

innate and acquired immunity phagocytosis antibodies and complement cell mediated immunity

Question 75

innate immunity

Answer 75

physical defencesphagocytic cells

Question 76

acquired immunity

Answer 76

specific response to antigen leads to immunological memory humoral and cellular

Question 77

phagocytosis

Answer 77

polymorphs (neutrophils, eosinophils, basophils) and monocytes in bloodmononuclear phagocytic system: spleen, liver and regional lymph nodesother white cells

Question 78

antibody and complement

Answer 78

involves immunoglobulinsneutralised toxin, neutralised virus, prevents adherence of microorganisms, opsonises capsulate organisms, useful in diagnosis humoral immunity: mostly bacterial infection, extra-cellular, acute inflammation, neutrophilia

Question 79

cell mediated immunity

Answer 79

combat intracellular infectionmacrophages present antigen and stimulate T cells, cytokines produced and control the response

Question 80

enterotoxogeic E coli

Answer 80

commonest cause of traveller's diarrhoea (contaminated water)

Question 81

- Enterohaemorrhagic E. coli

Answer 81

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

Question 82

shigella

Answer 82

not lactose fermenting low infective dosefaecal-oral spreadbacillary dysentery some strains produce toxin4 species