Antibiotics & Antivirals

Question 1

Summary of Lecture Outcomes

Answer 1

1) Explain how the introduction of the sulfonamides helped to pave the way for
the discovery and effective use of penicillin.
2) Identify the distinct roles Fleming and Florey played in the discovery of
penicillin.
3) Explain how breakthroughs in synthetic chemistry that allowed chemical
modification of the core penicillin structure led to the development of improved
penicillin derivatives
4) Identify in basic terms the key steps in the killing of sensitive bacteria by
penicillin.
5) Identify the problems raised by the emergence of drug-resistant organisms
(MDRO), the complex factors contributing to this global problem as well as the
“discovery void” afflicting this area of pharmaceutical innovation.

Question 2

Aim of Lecture

Answer 2

To explore major successes and
re-emerging threats in the use of
pharmaceuticals during the war
on microbial disease.

Question 3

How Sulfonamides Paved the Way

Answer 3

Proved that fatal infectious diseases
were “manageable” with drugs (e.g.,
pneumonia)
Fostered development of hospital
microbiology infrastructure:
 Well-equipped labs
 Handling lots of patient samples
 Sample analysis protocols
 Dosing guidelines
 Trained medical, nursing & scientific
staff

Question 3

Limitations of Salvarsan & “Sulfa Drugs”

Answer 3

Narrow “spectrum of action”
 i.e. didn’t kill a wide enough range of bacterial
species
Toxicity to patient with salvarsan (arsenic)
Skin stained with Prontosil (not a problem with
other sulfonamides)
Bacterial resistance a problem with sulfa drugs

Answer 3

Question 4

The Three “A” Drug Classes that Made Modern Surgery Possible

Answer 4

Anaesthetics
Antibiotics
Analgesics

Question 5

Alexander Fleming and the Discovery of Penicillin

Answer 5

 Born 1881 [Scotland] (d.1955)
 Watched soldiers die of infected wounds in Medical
Corps (WW-1)
 Noted failure of antiseptics to cure internal bacterial
infections
 1928, Director, Inoculation Lab, St Mary’s Hospital,
London
 Worked on anti-bacterial properties
of human nasal secretions
(lysozyme)

Question 5

“The Beginning of the Antibiotic Era”

Answer 5

2 Innovative Synthetic Drugs found via Animal
Testing of “Compound Libraries”

Salvarsan = (arsenic drug for treating
syphilis infections - 1911)

Prontosil = (azo drug for streptococcal
infections - 1935)

Question 6

The Penicillium Mould A Goldmine for Drugs?

Answer 6

Antiquity: Use of mouldy bread to treat infected wounds
(Greece, China, Egypt, etc)
 Anglo-Saxon recipe (1,000 yrs) recently shown to kill MRSA (methicillinresistant “Golden Staph”)
1870, Burdon-Sanderson, UK, attracted by Pasteur’s germ
theory
1871, reports ability of Penicillium mould (from fruit & jam) to
stop bacterial growth
 Joseph Lister [1827-1912] (found antiseptic properties of
phenol)
Observed curative properties of Penicillium-soaked
dressings on infected wounds

Answer 6

“An antibacterial with a broad
spectrum and high efficiency in
killing bacteria with minimal
toxic side-effects was badly
needed.”

Question 7

A Fluke Observation by Fleming

Answer 7

 July 1928, Fleming took 2-week
vacation
 Left used agar plates (Streptococcal
cultures) on lab bench
 Unusual cold snap (growth advantage
to Penicillium mould contaminant)
 Returned to work and noticed
inhibitory effect of mould on bacterial
growth

Question 8

Fleming’s “Half-Hearted” Follow-Up

Answer 8

 Fleming made bright yellow filtered broth from Penicillium
notatum mould
 Very active against growing Staph cultures as well as against other
bacterial species
 Non-irritating if applied directly to tissue
 Safe if injected into healthy mice (but
not tested in Staph-infected mice!)
 Couldn’t purify active chemical
(penicillin was unstable)
 “Forgot” drug for 13 years!

Question 9

Florey & Chain – The Penicillin
Extraction Problem Solved

Answer 9

Howard Florey, University of Adelaide-trained
clinical pathologist
Professor of Pathology, Oxford
1937, hired Ernst Chain (talented biochemist)
 Fled Nazi Germany with the rise of anti-Semitism
Chain overcame penicillin instability & extraction
problems
Made penicillin as a stable lyophilised salt at pH 5-8

“The abrasive Australian who had more effect
upon the world than any other.”
Australian PM Robert Menzies

Question 10

Feb 1941 - The First Human Tests

Answer 10

 43 y.o. policeman with invasive Strep & Staph infections
 200 mg penicillin (i.v. drip) + 100 mg every 3 hrs
 24 hr, strong recovery but drug ran-out after 3 days
Administered recycled penicillin (from urine)
Good response but death after drug ran out
Heroic effort to scale-up penicillin production in the
hospital (War-time Britain – limited resources)
Grew the penicillium mould in bedpans!
Subsequent patient also died (girl) before success
with 2 patients

Question 10

The Semi-Synthetic Penicillins

Answer 10

Question 11

Nov 1942 – An Unplanned Human Trial (USA)

Answer 11

Over 500 deaths in tragic night club fire (Boston)
220 survivors secretly treated with penicillin
US Military amazed by drug’s effectiveness
By 1944, monthly US production > 130 billion units
Sufficient for Allied troops at Normandy invasion
(i.e., D-Day, June 6, 1944)
Allayed fears regarding gangrene from gunshot wounds

Question 11

March 1940 – Florey has Stunning Success in First Animal Tests

Answer 11

Question 12

1941 – Uncle Sam to the Rescue

Answer 12

 1940 &1941 – two papers published in The Lancet
 British drug companies unable to help (war pressures)
US$5000 grant from Rockefeller Foundation allowed travel to US
Links with US Dept Agriculture researchers
Isolated high yield Penicillium strain (i.e., produced more penicillin than Oxford
strains)
Collected from the skin of a rock melon or “cantaloupe”
Consortium with US companies (e.g. Pfizer, Squibb, Eli Lilly, Abbott, Merck, etc)
Perfected large scale deep vat growth of Penicillium mould

Question 13

A Remaining Mystery: How Does Pencillin Work?

Answer 13

Jack Strominger, Professor of Pharmacology, Uni of Wisconsin
(USA)
Studied bacterial cell wall + around 30 enzymes needed to
make it
Identified peptidoglycan– chains of aminosugars cross-linked
by small peptides
1965 – famous paper on inhibitory effect of penicillin on cell
wall synthesis in bacteria
Penicillin = CWSI – cell wall synthesis inhibitor
Cell wall = semi-rigid but dynamic structure which helps
bacteria maintain their shape
 Identified transpeptidase as key target for many CWSIs

Question 13

The Race to Make Penicillin

Answer 13

1943, both US and UK teams made drug
crystals but found they were working with
different “penicillins” (wrong structures)
Many penicillin variants soon isolated from
Penicillium broths
WW2: >1000 scientists, 39 unis & companies
tried to make drug synthetically (most gave
up!)
1945, Dorothy Hodgkin (UK) solved unusual
β–lactam structure (X-ray crystallography)
1957, John Sheehan (USA) – first “total
synthesis” of penicillin

Question 14

The “Golden Age” of Antibiotic Discovery

Answer 14

 After WW-2, need for secrecy concerning
penicillin ended
 Allowed commercial development of many
new drug classes
 Widespread, global screening of microbes for
new drugs (e.g., derived from soil samples)
 Of all antibiotics discovered from 1945 to 1978,
55% came from the genus Streptomyces (soil)
 Many lethal diseases receded (pneumonia,
syphilis, gonorrhoea, diphtheria, scarlet fever,
childbirth infections, etc
)

Question 15

Penicillin Blocks A Key “Crosslinking” Step in Bacterial Peptidoglycan
Production for Cell Wall

Answer 15

Question 16

Microbial Origins of Some Classic Antibiotics

Answer 16

Question 17

Antibiotics: The Big Picture

Answer 17

“It has been suggested that during
the 20th century, antibiotics have
been responsible for a ten-year
increase in lifespan because of their
ability to diminish the threat of
premature death through bacterial
infection; this is compared to a twoyear increase in lifespan if all
cancers were curable.”

Question 18

Consequences of MDRO Emergence for Humanity

Answer 18

 The Golden Age is over
 More antibiotics are losing effectiveness
 ADR: Antibiotic
Drug
Resistance
 O’Neill Report (UK, 2016) – predicted 10 million deaths p.a. due to
ADR by 2050
 ↑↑ Cost of treaTng paTents with resistant strains
 Resorting to nastier drugs
 MDRO are a growing problem in hospitals
 Especially in low- and middle-income countries (LMICs)
 Need to be smarter with existing drugs

“antibiotic stewardship

Question 18

Drug Resistance: The Bugs Fight Back!

Answer 18

• Loss of effectiveness common for
  most if not all antibiotics
  *Bacteria can develop resistance
  spontaneously
  *Or acquire via plasmids
  *Often share multiple resistance
  mechanisms via plasmids –“superbugs” [i.e., bacteria that are
  resistant to many antibiotics from
  different classes] –Much harder to treat (increase cost
  and duration of treatment)

Answer 19

Answer 20

Question 21

The Visible Impact of Multiple Drug Resistance Organisms (MDRO)

Question 22

The Economic Dimension of the Problem

Answer 22

 Drug companies need to receive adequate
returns on their antibiotic investments
 Recover huge discovery and development costs
 Can’t do this if drugs quickly lose effectiveness
due to emergence of drug resistance
 i.e., the “lifespan” of clinical use of many
antibiotics is shorter than for many other
medicines
 We need cheaper ways of discovering and
testing antibiotics in humans

Question 22

Complexities of Antibiotic Drug Resistance in LMICs

Answer 22

Question 23

Lecture Conclusions

Answer 23

• Penicillin effected one of the most dramatic revolutions
  in human health standards ever
• Fleming, Florey, Chain - primary discoverers
• Hodgkin, Sheehan, Strominger - crucial follow-up discoveries
• Confidence from the Penicillin Revolution inspired
  discovery of many other valuable antibiotics in
  subsequent 30 years
• But today, we are struggling with the impact of overuse - multidrug resistance & drug discovery void
• “The more you use them, the more you lose them.”
• Thankfully, the news is not all bleak
• Good antibiotic stewardship can reverse MRDO prevalence
• Genetic engineering of organisms is leading to promising new
  anTbioTcs (switch on dormant genes in bugs → make novel
  antibiotic drugs)

Question 24

Further Reading

Answer 24

 Amyes, SGB (2013) Bacteria: A Very Short Introduction, Chapter 7, OUP.
 Bud, R (2007) Penicillin: Triumph and Tragedy, OUP.
 Goldsworthy, PD (2002) Howard Florey, Alexander Fleming and the Fairy Tale of Penicillin, Med J Aust, 176,
178-180.
 Henderson, JW (1997) The Yellow Brick Road to Penicillin, Mayo Clinic Proc. 72, 683-687
 Hutchings, M et al (2019) Antibiotics: past, present & future. Current Opinion in Microbiology, 51, 72-80
 Joklik, WK (1996) The Story of Penicillin, FASEB Journal, 10, 525-528.
 Li, JJ (2006) Laughing Gas, Viagra & Lipitor, Chapter 2, OUP.
 Siulis, et al (2021) Antimicrobial resistance in low- & middle-income countries: current status and future
directions. Expert Rev Anti Infect Ther, 19;1-14.
 Van den Brink, R (2021) The End of an Antibiotic Era: Bacteria’s Triumph Over a Universal Remedy, Springer
(available as e-book from UWA library).
 Zaffiri, L et al (2012) History of Antibiotics, J Invest Surg, 25, 67-77

Question 25

Learning outcomes

Answer 25

After completing this lecture, you should be able to
* describe the current trends in HIV prevalence and incidence in Australia and the key
contributing factors
* list the two clinical markers for AIDS
* describe the origin and structure of HIV and list key HIV proteins as drug targets
* list key steps of the HIV life cycle and the relevant anti-HIV drug class(es)
* describe the scientific events surrounding the development and action of zidovudine as the
first approved anti-HIV drug
* describe anti-HIV drug development and HIV treatment
* relate HIV prevention strategies to the mode of HIV transmission
* distinguish between pre-exposure prophylaxis (PrEP) and post-exposure prophylaxis (PEP)

Question 26

First official reporting of AIDS

Answer 26

1981
a cluster of cases of pneumocystis carinii
pneumonia in five young, previously healthy
gay men in LA
* fungal infection
a cluster of cases of Kaposi’s Sarcoma among
gay men in New York and California
* cancer affecting the skin and mucous
membranes; caused by viral infection

Answer 26

Question 27

AIDS - clinical markers

Answer 27

epidemiological investigations → low CD4+ T cell counts and acquired immune deficiency
* CD4+ T cell count
* HIV RNA copies

Answer 28

Question 29

The structure of a HIV virion

Answer 29

Question 29

The origin of HIV

Answer 29

originated from simian immunodeficiency virus (SIV)
* from primates to humans - preparation and consumption of bushmeat?
earliest known case of HIV-1 infection
* a 1959 plasma sample (Democratic Republic of Congo)

Answer 30

Question 30

The HIV life cycle and anti-HIV drug classes

Answer 30

BFRIM

Question 31

HIV1 and HIV2

Answer 31

HIV-1: first isolated in 1983 (Barré-Sinoussi et al., 1983)
* Françoise Barré-Sinoussi (shared the 2008 Nobel Prize in Physiology or Medicine)
HIV-2: first isolated in 1986 (Clavel et al., 1986) and is mostly limited to West Africa

Question 31

Anti-HIV drug development - challenges

Answer 31

• few antiviral drugs available when AIDS epidemic broke in 1981
• existing antiviral drugs ineffective against HIV
• HIV has a small number of genes → few drug targets
• HIV hijacks human cells
• integration of HIV DNA into genome of host cells

treat complications from opportunistic infections

Question 32

Important anti-HIV drug classes

Answer 32

Reverse transcriptase inhibitors (RTIs)
* nucleoside reverse transcriptase inhibitors (NRTIs)
* non-nucleoside reverse transcriptase inhibitors (NNRTIs)
Protease inhibitors (PIs)
Integrase strand transfer inhibitors (INSTIs)

Question 32

HIV-host cell interaction

Answer 32

Question 33

Antimetabolites to block DNA synthesis

Answer 33

Question 34

Zidovudine - the first anti-HIV drug

Answer 34

Question 35

Anti-HIV drug development

Answer 35

Answer 35

Question 36

HIV treatment

Answer 36

HIV/AIDS is now a manageable chronic disease - life-long ART
* viral suppression (< 200 copies/ml)
* undetectable viral load (< 20 copies/ml) = untransmissible (U=U)
Treatment initiation
* CD4
+ cell count (< 350) in decision-making has changed
* immediately following HIV diagnosis
Antiretroviral regimens
* INSTI-based (e.g., Stribild®)
* NNRTI-based (e.g., Atripla®)
* PI-based
Mutations and (multi)drug resistance

Question 37

From treatment to prevention

Answer 37

unprotected sexual contact

• Use condoms: highly effective in preventing HIV transmission and certain STIs
• Treatment as prevention (TasP): initiate ART in seropositive individuals
• PrEP (pre-exposure prophylaxis)
• PEP (post-exposure prophylaxis)

blood-borne exposure

• needle and syringe programs

perinatal transmission

• PrEP / HIV screening and initiation of ART
• CDC: avoid breastfeeding completely

Question 37

HIV prevention - PrEP and PEP

Answer 37

Question 38

Summary - what you have learned

Answer 38

• HIV: global and local perspective
• HIV: clinical markers, origin, structure
• HIV: life cycle and relevant drug classes
• HIV: drug development and treatment
• HIV: prevention, with a focus on comparing PrEP and PEP