My Assistant

Gram staining

[17 Dec 2017] (i thought i’d posted but it’s not appearing? ):) so sorry for the lack of original posts all these months! school has been so tough & i’ve just completed my mid-sem assessments & it’s finally my break! can’t wait to unwind and catch up on my sleep ;-;

CAMP test for the identification of Streptococcus agalactiae (group B). 

(A) Streptococcus (group B) shows a positive CAMP reaction arrow-shaped zone of enhanced hemolysis .

(B) Streptococcus pyogenes (group A) shows a negative reaction when inoculated at a right angle to

© Staphylococcus aureus.

ANTIBIOTICS CHEAT SHEET :)

Also, REMEMBER!!!!

* Sulfonamides compete for albumin with:

Bilirrubin: given in 2°,3°T, high risk or indirect hyperBb and kernicterus in premies

Warfarin: increases toxicity: bleeding

* Beta-lactamase (penicinillase) Suceptible:

Natural Penicillins (G, V, F, K)

Aminopenicillins (Amoxicillin, Ampicillin)

Antipseudomonal Penicillins (Ticarcillin, Piperacillin)

* Beta-lactamase (penicinillase) Resistant:

Oxacillin, Nafcillin, Dicloxacillin

3°G, 4°G Cephalosporins

Carbapenems 

Monobactams

Beta-lactamase inhibitors

* Penicillins enhanced with:

Clavulanic acid & Sulbactam (both are suicide inhibitors, they inhibit beta-lactamase)

Aminoglycosides (against enterococcus and psedomonas)

* Aminoglycosides enhanced with Aztreonam

* Penicillins: renal clearance EXCEPT Oxacillin & Nafcillin (bile)

* Cephalosporines: renal clearance EXCEPT Cefoperazone & Cefrtriaxone (bile)

* Both inhibited by Probenecid during tubular secretion.

* 2°G Cephalosporines: none cross BBB except Cefuroxime

* 3°G Cephalosporines: all cross BBB except Cefoperazone bc is highly highly lipid soluble, so is protein bound in plasma, therefore it doesn’t cross BBB.

* Cephalosporines are "LAME“ bc they  do not cover this organisms 

L  isteria monocytogenes

A  typicals (Mycoplasma, Chlamydia)

M RSA (except Ceftaroline, 5°G)

E  nterococci

* Disulfiram-like effect: Cefotetan & Cefoperazone (mnemonic)

* Cefoperanzone: all the exceptions!!!

All 3°G cephalosporins cross the BBB except Cefoperazone.

All cephalosporins are renal cleared, except Cefoperazone.

Disulfiram-like effect

* Against Pseudomonas:

3°G Cef taz idime (taz taz taz taz)

4°G Cefepime, Cefpirome (not available in the USA)

Antipseudomonal penicillins

Aminoglycosides (synergy with beta-lactams)

Aztreonam (pseudomonal sepsis)

* Covers MRSA: Ceftaroline (rhymes w/ Caroline, Caroline the 5°G Ceph), Vancomycin, Daptomycin, Linezolid, Tigecycline.

* Covers VRSA: Linezolid, Dalfopristin/Quinupristin

* Aminoglycosides: decrease release of ACh in synapse and act as a Neuromuscular blocker, this is why it enhances effects of muscle relaxants.

* DEMECLOCYCLINE: tetracycline that’s not used as an AB, it is used as tx of SIADH to cause Nephrogenic Diabetes Insipidus (inhibits the V2 receptor in collecting ducts)

* Phototoxicity: Q ue S T  ion?

Q uinolones

Sulfonamides

T etracyclines

* p450 inhibitors: Cloramphenicol, Macrolides (except Azithromycin), Sulfonamides

* Macrolides SE: Motilin stimulation, QT prolongation, reversible deafness, eosinophilia, cholestatic hepatitis

* Bactericidal: beta-lactams (penicillins, cephalosporins, monobactams, carbapenems), aminoglycosides, fluorquinolones, metronidazole.

* Baceriostatic: tetracyclins, streptogramins, chloramphenicol, lincosamides, oxazolidonones, macrolides, sulfonamides, DHFR inhibitors.

* Pseudomembranous colitis: Ampicillin, Amoxicillin, Clindamycin, Lincomycin.

* QT prolongation: macrolides, sometimes fluoroquinolones

Penicillin

Penicillin is a widely used antibiotic prescribed to treat staphylococci and streptococci bacterial infections. 

beta-lactam family 

Gram-positive bacteria = thick cell walls containing high levels of peptidoglycan

gram-negative bacteria = thinner cell walls with low levels of peptidoglycan and surrounded by a lipopolysaccharide (LPS) layer that prevents antibiotic entry 

penicillin is most effective against gram-positive bacteria where DD-transpeptidase activity is highest.

Examples of penicillins include:

amoxicillin

ampicillin

bacampicillin

oxacillin

penicillin

Mechanism(s)

Penicillin inhibits the bacterial enzyme transpeptidase, responsible for catalysing the final peptidoglycan crosslinking stage of bacterial cell wall synthesis.

Cells wall is weakened and cells swell as water enters and then burst (lysis)

Becomes permanently covalently bonded to the enzymes’s active site (irreversible)

Alternative theory: penicillin mimics D-Ala D-Ala

Or may act as an umbrella inhibitor

Resistance

production of beta-lactamase - destroys the beta-lactam ring of penicillin and makes it ineffective (eg Staphylococcus aureus - most are now resistant)

In response, synthetic penicillin that is resistant to beta-lactamase is in use including egdicloxacillin, oxacillin, nafcillin, and methicillin. 

Some is resistant to methicillin - methicillin-resistant Staphylococcus aureus (MRSA).  

Demonstrating blanket resistance to all beta-lactam antibiotics -extremely serious health risk.

Stuff in my Office

From 1930. This well-dressed young scientist is experimenting with The Air. Exactly what he is doing is a mystery.

July 25 …. I finally get it!  He’s holding an eye dropper with a bulb on the end. I thought it was a pair of chopsticks! He’s picking up pieces of paper using the vacuum from squeezing the bulb! Still very formal, though …

Medically Important Fungi

Influenza

Happy flu season! I’ve just been stuck inside for 5 days with a mild case, so this is a bit bitter

There are 3–5 million cases of flu per year, and ~375,000 deaths, usually in older, younger, and immunocompromised individuals.

Enveloped, Single-stranded RNA virus

First identified in 1933, but existed long before

Generally considered an infection of the bronchi

so effectively a form of bronchitis – i.e. it causes inflammation of the bronchi 

There are 3 types - A, B and C

B & C appear restricted to humans 

C is less common

A is found in wide range of species including pigs and poultry as well as man

Type A appears to be responsible for more severe disease

Basics

Transmission by aerosols

Incubation ~2 days

Contagious during first 3-5days of illness

Symptoms – fever, myalgia, headache, dry cough, sore throat, aches, fatigue

Recovery ~7-10 days for most

Complications – most frequent = secondary bacterial pneumonia, rarely = viral pneumonia, myocarditis, encephalitis

No specific treatment

Vaccination for high risk groups including the elderly, health care workers, those with underlying respiratory conditions.

Avian

The main reservoir is wildfowl that are resistant to the disease

doesn’t usually affect animals other than poultry and pigs

However some transfer events occur

Seasonal

Incidence highest in winter

Strains vary from year to year -  hard to predict and vaccinate (this year’s vaccine has been pretty rubbish)

Pandemic

Can be caused by any strain that has not been seen in the human population for many years

New strains evade the herd immunity that exists to previously encountered strains

1918 /19 –( Spanish) estimated 40-50 million deaths worldwide

1957 – Influenza A/H1N1 (Asian)

1968 – Influenza A/H3N2 (Hong Kong)

Eventually the virus runs out of susceptible hosts and the epidemic fizzles out

Experts generally agree another pandemic is inevitable, and may be imminent – maybe we have had some minor pandemics 

16000 confirmed H1N1 deaths in 2009 affecting over 200 countries

Consensus is that the prompt action of the Hong Kong authorities probably prevented a pandemic in 1997

The prediction is scary - for industrialised countries they predic 1.0 – 2.3 million hospitalisations

280,000-650,000 deaths 

in two years

A network of 112 centres monitor flu isolates to identify unusual strains that can then be examined further

The WHO has a Pandemic Preparedness Plan in place http://www.who.int/influenza/preparedness/pandemic/en/

Diagnosis

Generally based on GP diagnosis

Virus isolation / virus demonstration from nasopharyngeal secretions during acute phase

Demonstration of viral antigen in secretions

Antibody rise using paired sera ( 1st sample taken between days 1-3 of illness, 2nd taken around day 12 of illness) by haemagglutination inhibition or complement fixation test

Molecular methods evolving rapidly – in particular in response to the recent epidemic/pandemic strains emerging

A range of respiratory illnesses have the same symptoms, only laboratory testing can confirm the aetiological agent

Treatment/Vaccination 

In the UK NICE argue that immunisation against predicted strains is the best form of defence – traditionally focused on the elderly and those with underlying lung problems, but recently started rolling out a childhood vaccine (nasal spray)

Vaccines generally based on the H & N surface structures which mutate, however hopes of an M protein based vaccine which will give longer lasting protection raised recently

Antivirals

Antivirals not recommended in otherwise healthy people (amantadine should not be used at all) - should ride it out

However when incidence reaches a certain level zanamivir and oseltamivir should be used in those considered high risk for the development of complications – PROVIDED THAT TREATMENT IS STARTED WITHIN 48 HOURS OF ONSET OF SYMPTOMS

Resistance is becoming an issue

Normal Flora

Blood, Spinal Fluid, Urine: sterile

Cutaneous surfaces (urethra, outer ear included): Staph epidermidis, Staph aureus, Corynobacteria (dyphteroids),Streptocci, Candida spp

Nose: Staph aureus, Staph epidermidis, dyphteroids, assorted streptococci

Gingival crevices: anaerobes = Bacterioides/Prevotella, Fusobacterium, Streotococci, Actinomyces

Oropharynx: Viridans group (alpha hemolytic strep), Neisseria (non pathogenic), H. influenzae (non typeable, meaning, w/o capsule), Candida albicans

Stomach: none

Breast-fed babies colon: microaerophilic/anaerobic = Bifidobacterium, Lactobacillus, streptococci.

Adult Colon: microaerophilic/anaerobic = Bacteroides/Prevotella, E.coli, Bifidobacterium, Eubacterium, Fusobacterium, Gram- anaerobic rods, Lactobacillus, E.faecalis, streptococci

Vagina: Lactobacillus, streptococci, diphteroids, yeasts, Veillonella, Gram- rods