Becky Wright - bacteria Flashcards

Question

Shigella vs Salmonella

Answer 1

Both gram-negative bacilli Both non-lactose fermenters (unlike E.coli) Shigella doesn't produce H₂S like Salmonella

Answer 2

Travel associated, and paediatric, transmitted by faeco-oral route, unwashed hands on food? Pathogenesis: **Infects M cells of intestine**, spreads to surround epithelial cells, **causes abscesses** as cells killed Can cause HUS with Stx. Dysentery = Blood mucus stools, abdo pain --\> Abx if severe/extreme ages

Answer 3

Gram negative bacilli but comma-shaped Vibrio = Monotrichous flagellum Like Enterotoxic ETEC, cholera toxin increases cAMP, like heat-labile toxin, LT Cholera reservoirs = water and people

Answer 4

Animal faeces source e.g. poultry Symptoms like gastroenteritis or dysentery

Answer 5

Lower UTI, cystitis or urethritis (dysuria, lower abdo pain, increased frequency) Upper UTI, **Pyelonephritis **or urethritis (pyelonephritis kidney damage, sepsis, fever chills and rigor, flank pain, nausea vomiting)

Answer 6

Gram negative cell wall contains **LPS (lipopolysaccharide) endotoxin** LPS released upon lysis, bound to **LPS-binding-protein. LBP** **LBP** binds PRRs **CD14 and TLR-4** receptor complex on **macrophages.** Binding causes intracellular activation of **nuclear factor kappa beta** Causes release of cytokines --\> shock

Answer 7

Urine flow _Antibacterial properties of urine:_ High osmolarity High urea content Sphincters Epithelial barrier

Answer 8

Diphtheroids Streptococci Lactobacilli and Gram negative bacilli in women

Answer 9

_Adhesins:_ **(Type1 and P-) Fimbriae** adhere to urinary epithelial cell receptors: Type-1 fimbriae to **Mannosides in bladder** and P-fimbriae to **Glycosphingolipids in kidneys** respectively _Toxin:_ **a-Haemolysin** lyses RBCs (helps spread) Gram neg capsule prevents phagocytosis **Siderophores** such as **Aerobactin** collect **iron**

Answer 10

In renal tubule epithelial cells: UPEC bacteria bind using their **P-fimbriae to glycosphingolipids** Sensed by **TLR-4**, a PRR, which causes release of **chemokine IL-8** Binds **CXCR1** (chemokine receptor 1) on **neutrophils** and on renal **epithelial cells**! **Recruits neutrophils** and causes their **migration across epithelium.**

Answer 11

Escherichia *coli* (causes up to 90%) Proteus mirabilis Klebsiella pneumoniae

Answer 12

Strong **urease** activity (as seen on blood agar) Cleaves urea to ammonia --\> alkaline urine **Alkaline urine --\> KIDNEY STONES**

Answer 13

Gram positive cocci, catalase negative Acquired typically from hospital equiment like cystoscopes.

Answer 14

Gram negative bacilli, [oxidase positive unlike UPEC]. **Makes blue green fluorescent colonies**. Opportunistic typically nosocomial pathogen infects immunocompromised patients, patients with catheters or vesicoureteral reflux. Often contaminates hospital water supply!

Answer 15

Staphylococcus *aureus*

Answer 16

E.coli UTI --\> Mostly young women after sexual activity. Also in children (perhaps vesicoureteral reflux or poor hygiene) Elderly men (prostatic enlargment) Uncommon in young men.

Answer 17

Pus cells (neutrophils) suggest infection Epithelial cells suggest contamination Casts suggest kidney pathology Crystals suggest underlying abnormality (maybe fragments of a kidney stone?)

Answer 18

Semi-quantitative culturing: 100,000 colony forming units per ml is cut off (100/µl) CLED (cystine, lactose, electrolyte deficient) agar is common medium to differentiate between organisms Bromothymol Blue indicator Yellow = lactose fermenting (like E.coli) Electrolyte deficiency prevents Proteus 'swarming'

Answer 19

**Neisseria meningitidis** (gram -ve cocci, oxidase +ve) AKA "meningococcus" (capsule serogroups A,B,C (B most common as vaccine only recently created) **Streptococcus pneumoniae** (gram +ve cocci) **Haemophilus influenzae** (gram -ve bacilli) type B (HIB vaccine) **Listeria monocytogenes**

Answer 20

**Human nasopharynx** only reservoir of N.meningitidis. Spread through close contact, overcrowding. Enters blood stream (septicaemia --\> non-blanching rash) --\> CSF Or straight to CSF through cribiform plate/olfactory nerve (meningitis: stiff neck, photophobia, severe headaches)

Answer 21

**(Type IV) Pili twitch** --\> move through **mucus** **Capsule** (makes C3b opsonin inaccessible to WBCs) **LOS** (small version of LPS, endotoxin --\>haemolysis, DIC (activates coagulation) and sepsis via TLR4) Coats self in **non-immunogenic** host **Sialic acid** **Ig A protease** digests IgA! Complement inhibitor (fHbp) **Survives ROS attack inside neutrophils** --\> hides in them

Answer 22

**_Mucociliary escalator_**: Mucus (trap bacteria) Cilia (beat in coordinated waves) + Mucous membranes + Lysozyme (attacks peptidoglycans, esp. in Gram pos cell wall)

Answer 23

Extremes of **age** (2 or under or 65+) Chronic lung disease (**asthma, COPD**) **Smoking** **Hospitalisation** (nosocomial infection) **Immunosuppression** (HIV, steroids etc)

Answer 24

**Viruses** like RSV (children) **Strepococcus pneumoniae** (commonest bacterial) Atypical (**Legionella pneumophila, Mycoplasma pneumoniae**)

Answer 25

Cough (productive) and Dyspnoea High Fever, Fatigue, Myalgia

Answer 26

**Colonises nasopharynx**, aspirated into lungs, requires weak immune response or structural problem to survive **Capsule** poorly immunogenic and resists phagocytosis, but is basis for pneumococcal vaccine. Can lead to **septicaemia** in immunocompromised persons Can lead to **meningitis in children**

Answer 27

Symptoms important. Sputum culture is problematic as Strep. pneumoniae are normal commensals of pharynx, **contamination**. **Alpha haemolytic** gram pos cocci, **optochin sensitivity** differentiates from harmless Strep.viridans. (see pic)

Answer 28

Non-specific symptoms (headache, malaise, myalgia, nausea), typically don't seem severe (walking pneumonia) Legionella pneumophila (caught from water or soil) Mycoplasma pneumoniae (no peptidoglycan --\> Resists Abx, intracellular) **Recquire different ABx, and hard to culture** (fastidious)

Answer 29

Contaminated water supplies cause local outbreaks Evades lysosome fusion after phagocytosis, creates its own ER-like vesicle Replicates to high numbers and lyses cell.

Answer 30

**Lowest concentration of antimicrobial that inhibits visible growth of a microorganism after incubation** (gives a guide on whether resistant and how much needed, MIC in tubes is cumbersome --\> use disk diffusion testing)

Answer 31

Cut-off points published by **BSAC** defining at what diameter **zone of inhibition** or MIC a bacteria is considered resistant or susceptible (or indeterminate). Depends on type of bacteria, type of antibiotic and even sometimes type of infection (location etc)

Answer 32

A method for **internal quality control** in antimicrobial susceptibility testing. Standard suspensions representing **opacity** of different concentration bacterial suspensions, used for **comparison to standardise innoculum density for MIC.**

Answer 33

Used for **disk diffusion antimicrobial susceptibility testing.** (loose agar --\> better ABx diffusion) (contains starch, which neutralises toxins that could otherwise interfere with Abx)

Answer 34

**National external quality assessment service.** **External quality control** for microbial laboratories, for example antimicrobial susceptibility testing. Samples and results sent for assessment regularly.

Answer 35

**Anaerobic, gram positive bacilli!** **Spore forming **(survival under harsh conditions) Vegetative cells produce various **exotoxins**

Answer 36

Found in **soil, dust, and intestinal tracts** of animals and humans. Infects **wounds** directly, needs **anaerobic environment** e.g. deep wounds. Produces **tetanospasmin** and tetanolysin toxins.

Answer 37

2 heavy chains: Heavy chain binds to **gangliosides** on peripheral neuron terminal and **endocytosed** **Retrograde axonal transport to CNS** Enters **inhibitory** neurons in CNS Light chain released and **cleaves synaptobrevin,** a SNARE protein (involved in neurotransmitter release) Therefore BLOCKS INHIBITORY SIGNALS!

Answer 38

**Wound infection** in unimmunised person. **Neonatal tetanus** from umbilical stump infection. (unimmunised mother and unsanitised conditions) **Maternal tetanus** following childbirth Symptoms: muscle spasm (lock jaw, respiratory muscle spasm leads to death)

Answer 39

A **toxoid**: toxin extracted from culture and inactivated by formaldehyde. Toxoid triggers primary immune response --\> memory cells. Immunity.

Answer 40

**Soil, contaminated food** (ingestion of toxin), **wound infection** (e.g. IV drug users), **Infant botulism** most common, normal gut flora not well established and bile acids low. Botulism: Blurred vision, drooping eyelids, paralysis of various muscles (potentially fatal)

Answer 41

Enters blood stream to spread throughout body. **Blocks ACh release at NMJ -**-\> paralysis. **Blocks** **SNARE protein SNAP 25** (so vesicles cannot fuse) Antitoxin (antibodies against toxin given)

Answer 42

* **Diarrhoea upon toxin production,** abdo pain, fever, raised WBC, blood in stools? * **Resides in human gut, **asymptomatic carriage without toxin, associated with **ABx treatment** reducing competing flora (opportunistic) _Complications_ include **Pseudomembranous colitis** in severe cases and **recurrence** due to persistant spores.

Answer 43

Toxin A, TcdA, enterotoxin binds apical side. Endocytosed, cytotoxic, cells lose structure because reduces F-actin --\> opens tight junctions between cells. Recruits neutrophils Toxin B, TcdB, cytotoxin binds basolateral side (through opened tight junction?) Recruits neutrophils.

Answer 44

_Diagnosis: _**Stool sample,** **detect toxins A and B with ELISA. Or PCR for toxin genes.** Culture and testing for cytopathic (toxin) effects on cell lines is slow but gold standard for confirmation. _Treatment:_ Stop original Abx, start anti Cdiff ABx. Infection spread control (isolation, decontamination, handwashing), faecal transplants?

Answer 45

**They are acid fast,** (when stained with Carbol fuschin, appear **red, not-decolourised by acid**, methylene blue counterstain background) _Further classified_ into '**fast**' and '**slow**' growing, fast are typically harmless environmental, slow include M.tuberculosis and M.bovis, **culture takes weeks**!!

Answer 46

**Waxy coat** present in the cell wall of mycobacteria. It enhances the hardiness and pathogenicity of the mycobacteria, by resisting common Abx and digestion within macrophages. Also accounts for poor staining with gram's. (hence acid fast staining used)

Answer 47

**Acid fast staining of samples (e.g. sputum) has high false negative rate.** (low sensitivity) Symptoms non-specific **Culture is SLOW.** Risk to lab tech, need level 3 containment.

Answer 48

When TB bacilli present they are never normal flora, always pathogenic. Therefore it is a latent infection. However it is different from active TB disease, which requires symptoms and signs. Chronic disease associated with chronic inflammation.

Answer 49

1/3rd of worlds pop infected. 5-10% of those infected will develop active disease. Often associated with HIV, more likely to develop disease

Answer 50

I**nfected humans are main reservoir** (rarely cattle) **Positive smear** (for acid-fast bacilli) means **more infectious**. Mode of transmission is inhalation, increased by crowding, close contact. Possible genetic susceptibility?

Answer 51

1. Engulfed by macrophages, but survive due to waxy coat (mycolic acid) and **serine protease** that helps maintain a normal pH, 2. Macrophages and activated T-cells keep infection localised to **primary lesion** in lung. Consisting of activated giant epitheloid macrophage cells. 3. Primary complex = lesion and enlarged hilar lymph nodes. Lesion sometimes becomes necrotic, caseous. 4. In latent stage lesion is sealed off by fibroblasts. Sometimes becomes calcified. 5. Occassionally dissemination could lead to miliary TB, or more commonly reactivation in immunosuppressed (e.g. older) patients

Answer 52

From reactivation of dormant bacteria, increasing cavitation occurs, this is common in patients with lowered immunity. If this cavity communicates with an airway sputum is contaminated and the person is infectious. In rare cases of severe immunocompromise (e.g. in HIV) spread can occur by bloodstream (miliary TB)

Answer 53

Tuberculin skin test, against TB antigen (Mantoux test) (won't be acid-fast bacilli in sputum until reactivation) or PCR, new test, can also diagnose Rifampicin resistant

Answer 54

_Discharge and infertility_: Chlamydia trachomatis Neisseria Gonorrhoea _Ulcerating_: Herpes Syphilis (Treponema pallidum Pallidum)

Answer 55

Oligate human parasite, transmission either by **sexual contact** (through mucous membranes, intact or abraded) Or **mother to child** in labour or in utero.

Answer 56

Primary stage = **chancre** after 3 wk incubation (single painless ulcer, on genitals, mouth, anus) INFECTIOUS (promotes HIV transmission too) Secondary stage = **bloodstream** (2-12 weeks later) --\> **Fever**, **rash** (not itchy, palms, soles, elsewhere, widespread) myalgia etc. V.INFECTIOUS Latent stage: less infectious, asymptomatic (years), typically final stage **Tertiary syphilis is rare with treatment: Neurosyphilis,** skin/bone/liver/other **lesions**, cardiovascular syphilis (**aortitis**), can be fatal.

Answer 57

Infected mother to foetus, or during birth. (therefore **screen all pregnant women**!) Many foetuses infected early will be **stillborn**. Can cause: Developmental delay, seizures, deformities, hepatosplenomegaly etc. death? Characteristic symptoms, like syphilitic rhinitis, deafness etc..

Answer 58

Syphilis is delicate, obligate human parasite: cannot be cultured! **Dark field microscopy** (with silver stain) or **DFA** (direct fluorescent antibody) testing involves visualising Treponema pallidum Pallidum within 10 minutes of sample collection and such **specialist equipment is rarely available** (test not sensitive, but very specific) **Antibody testing doesn't work in lag period** before antibodies have been generated.

Answer 59

Cheap, sensitive, non-specific screen: Tests for antibodies against common bacterial lipid, **Cardiolipin.** **Antigen bound to carbon particles, to visualise _agglutination_ reaction if antibody present.**

Answer 60

**Expensive Specific test for antibodies** against specific treponemal antigen. Antigen in kits **bound to RBCs!** --\> Visible **diffuse clumping** if antibody present in patient serum. (negative is small dark button)

Answer 61

1) Abx (Benzathine Penicillin) 2) Treat partners too! 3) Prevention with safe sex.

Answer 62

**Gram** **negative**, **obligate intracellular** bacterium (either shape!) 2 forms: **Elementary** (spore-like) form, infects cells. [infective, metabolically inactive] **Reticular** (vegetative form) intracellular (replicate in inclusion bodies) [non-infective, metabolically active]

Answer 63

Often silent, asymptomatic (50% men, 75% women) Or urethritis, discharge. Women: can lead to PID: pelvic inflammatory disease can lead to infertility. Men: Epididymo-orchitis: pain, swelling etc

Answer 64

**NAAT** nucleic acid amplification tests (e.g. **PCR**) **detect chlamydial DNA from cervical swabs or urine.** Screening offered to all young people from 2003, as chlamydia common, silent, treatable with ABx.

Becky Wright - bacteria Flashcards

(88 cards)