Week 06 - Microbiology

• Staphylococcus aureus
• CoNS
• Group A strep [scarlet fever]
• B-haemolytic strep
• Strep Pneumoniae
• Enterococci
• Strep Viridans

• Neisseria Meningitidis; mild sore throat → meningitis
• Neisseria Gonoccocus
• Moraxella Catarrhalis

• Listeria → bacteraemia & meningitis [v young & old]
• Clostridia species → C. Diff, C perfingens, C tetani

• E.Coli
• Klebsiella
• Salmonella
• H. Influenzae

Virulence = ability of organism to cause disease [ability to invade host tissue

Microbial organism that can produce symptomatic disease

• when a Pt grows up in a disease endemic area
• initial infection → symptoms
• subsequent infections have a decreasing severity of symptoms [asymptomatic]
• but pathogen still in blood
• e.g. malaria

• Mycobacterium Tuberculosis
• [inhaled droplet spread]

• Inhaled droplets
• 95% individuals → dromant lesions
• replicate in macrophages
• Reactivation of MTB [HIV, immunosuppression, smoking]
• disease progresses to cavitating MTB
• cavities open onto bronchi facilitating spread via coughing
• 5% get full blown TB after 1st infection

• Miliary TB
• Lots in both lung feilds
• looks like millet seed [CXR]

• CNS TB
• Tuberculomata across brain
• epileptic fits & space occupying lesions

Renal TB

Formed when pathogen cannot be digested

• Central necrosis
• epitheliod cells [macrophages]
• Giant cells
• Lymphocytes [outermost, mainly T cells]

• Imaging
• CXR → apical destruction & cavity formation

• B/C
• ZN stain for acid fast bacilli

• Mantoux RXN/ Heaf test
• inject MTB cell walll extract into dermis
• ?prev infection → area of inflammation
• no RXN? → no previous exposure
• not perfect, some cross reactin w BCG

MTB is RIPE for Tx

• Rifampicin → red urine, CYP450 inducer
• Isoniazid
• Pyrazinamide
• Ethambutol

• 6m R & I
• Drop P & E if sensitive to RI after 2m

Most common → Strep Pneumoniae

• Typicals
• Haemophilus influenzae
• Mraxella Catarrhalis

• ^ alcohol intake
• Smoking
• Immunosuppression
• Existing airway disease [COPD/ Asthma]
• Influenza infection

• S&S
• Productive cough
• Fever
• Pleuritic chest pain

• O/E
• Lobar consolidation
• Coarse creps
• ^vocal resonance
• Dull percussion

Amoxicillan [beware resisitance, check travel Hx]

• Unsuccessful?
• Co-amoxiclav
• Clarithromycin
• Doxicyclin

Mycoplasma Pneumoniae → flu symptoms, insiduous onset, Tx = Macrolides [clarithromycin]

Legionella Pneumonia → contaminated water supply, headache & fever, Tx = macrolides

Chlamydia Pneumonia

Chlamydia Psittaci

Coxiella Burnetti

CURB65

• Confusion
• Urea >7mmol/l
• RR >30
• BP → sys >90, dia <60
• Age >65

Scor >3 = admission, ^^mortality

• Beta-Lactams
• Glycopeptides

• Flouroquinolones
• Rifampicin
• Nitrofurantoin

• Aminoglycosides
• Tetracyclines
• Macrolides
• Loncosamides
• Fusidic Acid
• Mupirocin
• Chloramphenicol
• Metronidazole

Trimethoprim

• Penicillins → pen/ amoxicillin etc
• Cephalosporins → cephtriaxone
• Carbopenems → meropenem

• MoA
• inhibit bacterial cell wall synthesis

• Sensitivities
• most gram +ve
• MSSA = resistant to pen & amox
• Enterococci = resistant to all cephalosporins
• P aeruginosa = resistant to all [except → tazocin, meropenem & cephtazidime]

e.g. Vancomycin/ Teicoplanin

• MoA
• Inhibit cell wall synthesis
• bactericidal

• Sensitivities
• Only gram +ves

e.g. Gentamicin/ Streptomicin

• MoA
• Inhibit protein sythesis → irreversibly bind to 30S ribosomal unit
• bactericidal

• Sensitivities
• mostly gram neg
• esp sepsis

e.g. tetracycline, doxycycline

• MoA
• Inhibit protein synthesis → reversibly bind to 30S ribosomal unit
• bacteristatic

• Sensitivities
• Staph & strep
• some gram -ve [NO e. coli]
• active against intracellular organisms [chlamydia, coxiella burnetti, plasmodium]

e.g. Erythromycin, Clarithromycin

• MoA
• reversibly bind to 30S ribosomal unit → inhibit protein synthesis
• Bacteristatic

• Sensitivities
• ~mycobacteria [not MTB]
• Erythromycin → CAP, Campylobacter gastroenteritis
• Calrithromycin → CAP, H. Pylori, mycobacter

• Orthomyxoviridae
• Segmented virus

• 3 subtypes [A, B & C]
• A = Pandemic Flu
• A & B = 8 RNA segments, cause epidemics
• C = 7 RNA, milder

• Classification of type a
• Haemagluttinin → cell entry [16 types], antigenic drift
• Neurominidase → exit cells [9 types]
• e.g. H5N1

• Incubation ~1-4d
• 'flu like symptoms' → fever, malaise, sore throat, joint pain

• Complications
• pneumonia [secondary bacterial infections]
• Bronchitis
• otitis media etc

Usually suportive

• Oseltamivir [tamiflu]
• Neurominidase blocker
• pre-exposure prophylaxis in at risk groups [pregnant]

• Amantidine
• soon after Pc
• A/E → CNS & GI

• Vaccine
• Inactivated/subunit
• trivalent [2 A strains & 1 B]

• ssRNA retrovirus
• reverse transcribed into host DNA → latent infection
• mainly in T4 [also DC & macrophages]
• antiretrovirals only target circulating virus.

Seroconversion = development of detectable antibodies [i.e. finding out your HIV+]

• Fever
• Sore throat
• Rash
• Also → headache, lymphadenopathy, myalgia

• Palatal Kaposis Sarcoma [purple macules, herpes virus]
• Oesophageal Candida
• Oral KS
• Gingivitis
• Apthous Ulcers
• Cerebral Toxoplasmosis
• CMV retinits → Late stage
• MTB

Reverse Transcriptase inhibitors → nucleoside analogoues or allostearic inhibitors

Protease inhibitors → e.g. Atazanivir

Integrase inhibitors

Fusion inhibitors

Co-receptor binding inhibitors → maraviroc [block CCR5 receptor]

Aim of therapy is to decrease viral load.

• Spotaneous Mt in selective environment
• confers advantage
• rapid proliferation → resisitant

Alter drug target → block antibiotic/ create new target

Alter access to drug → decrease cellular permeability

Enzymatic inactivation → destroy/alter anti-b

New metabolic pathway → bypass inhibited RXN

• Plasmids
• Transposons
• Integrons