Control of Bacteria and Pathogens
Chapter 9 –Chemical and physical agents
(also see Chapter 25 about food preservation )
Chapters 10 – Chemotherapeutic agents
Who and Why?
1) Food industry
2) Public welfare
3) Manufacturing Industry
4) Individual/ population
Combating spread through
1) antimicrobial agents
2) aseptic techniques
3) epidemiological strategies
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How are Physical and Chemical agents
antimicrobial?
-- damage to membranes
-- denaturation of proteins
-- DNA damage
How do different agents control growth
“- cidals” (e.g., heating)
vs
“- statics” (e.g., chilling)
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Physical & Chemical Agents – in Chapter 9
Read about physical gents
-- Heat-related methods
-- Filtration
-- osmotic pressure
-- Ionizing and nonionizing radiation
Chemical agents can be
Antiseptics or disenfectants or chemotherapeutics
-- how are these different?
Read about non-chemotherapeutic chemical agents
-- alcohols
-- acidification
-- sulfactants
-- heavy metals
-- gaseous agents
Some of these agents are important for Food preservation
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“Noah carried the slabs of
meat into the kitchen and
cut it into small salting
blocks, and Ma patted the
coarse salt in, laid it piece
by piece in the kegs, careful
that no two pieces touched
each other. She laid the
slabs like bricks, and
pounded salt in the spaces.”
John Steinbeck, The Grapes
of Wrath
Food preservation
see Chapter 25
What does “spoilage” mean”
‘Shelf life’
prevent microbial growth
maintain food quality
‘commercial sterilization’
Methods
1) Food modifications
drying
acidification
salting
2) Temperature
heating
Pasteurization
cooling
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Food preservation, con’t.
3) Reduce O2content
canning, jarring, etc
4) Chemical preservatives
Benzoates, sorbates, sulfites, nitrites
[BHT and BHA are antioxidants]
Concerns
FDA and the GRAS list
Na Nitrite & ‘nitrosamines’
5) Ionizing radiation
cobalt-60
Food approved by FDA for irradiation
spices & grains (to kill insects)
imported fruits (to control insects)
potatoes & onions (to inhibit sprouting)
poultry and red meats (to control pathogens)
Other countries irradiate much more food
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Chemotherapeutic agents (Chapter 11)
Some Ideal attributes:
1) selective toxicity
2) stability
… in body ‘biotransformation’
… on shelf
… with other substances
Acyclovir:
a synthetic antiviral agent
3) limited solubility
Two categories
1) Synthetic drugs
2) Antibiotics
“Chemicals produced by one organism
that are effective at low concentration in
inhibiting growth of another organism.”
semi-synthetic Abs
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Synthetic drugs
Discovery
Paul Ehrlich’s ‘Magic Bullet’
Syphilis
Salvarsan-606: 1909
1930s: Age of the Sulfa-Drugs
Sulfanilamide
an “antimetabolite” or
“metabolite analog”
only ‘bacteriostatic’
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Antibiotics
Discovery
Alexander Fleming
Penicillium notatum
‘bacteriocidal’
Development
WWII
Oxford University
Howard Florey and
Norman Heatley
U.S. mass production
Major sources of antibiotics
Bacteria (Streptomyces, Bacillus)
Fungi (Penicillium, Cephalosporium)
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Major families of Antibiotics
β-Lactam
-- penicillin, cephalosporins, etc
Streptomycin
Aminoglycosides
-- steptomycin, neomycin, etc
Tetracyclines
Quinolones
Macrolides – e.g., erythomycin
Tetracyclin
Polymyxins – polymycin-B
Polymyxin-B
Rifamycins – e.g., rifampin
Erythomycin
Fluoroquinolone
Rifamycin
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Properties of Antibiotics
Spectrum of activity
narrow
broad
Mechanisms of action
-- of antibiotics
(Anti-virals in Virology ppt)
Neomycin
Bacitracin
Polymixin
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Dr Spilatro’s Big Adventure
The antibiotics
The bacterium
ESBL E. coli
Extended Spectrum β-lactamase
-- carried on plasmid
Multiple Ab resistance
1. Ciprofloxacin - Fluoroqinolone
2. Levafloxin - Fluoroqinolone
3. Ceftriaxone - β-lactam
(cephalosporin derivative)
4. Tobramycin - Aminoglycoside
(from Streptomyces)
5. Piperamycin - β-lactam
(“Zocyn”)
(penicillin derivative)
+ Tazobactam - β-lactamase inhibitor
6. Doripenem – carbepenem
(modified β-lactam)
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Properties of Antibiotics, con’t.
Examples of Adverse reactions
1) Toxicity: “therapeutic dose” vs “toxic dose” levels
Tissue damage (e.g., kidney)
bacitracin, polymyxin, amyloglycosides
-- Tobramycin
Congenital defects
tetracycline
Digestive disorders
many
2) Allergic reactions
penicillin & cephalosporins
3) Kill indigenous bacteria
-- growth of Clostridium difficile
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Resistance to Antibiotics
Intrisic vs Acquired resistance
Mechanisms
1) Enzymatic inactivation
β-lactamase
2) Alteration of site of action
streptomycin, erythromycin
3) change in cell membrane or
cell wall permeability
4) membrane pumps (efflux)
somewhat indescriminate
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Resistance to Antibiotics
Ab resistance in 75 VRE isolates
Epidemiological aspects
Moritz & Hergenrother 2007 PNAS 104:311-316
Current serious problems
MRSA
VRE
CRE
My ESBL E. coli
Resistant
Ampicillin
– β-lactam
Aztreonam – monobactam
Cefazolin
– β-lactam
Cefuroxime – β-lactam
Ceftriaxone – β-lactam
Ceftazidme – β-lactam
Ciprofloxacim – fluoroqinolone
Levaquin
– fluoroqinolone
Gentamicin – aminoglycoside
Tmp/Smx
– sulfonamides
Sensitive
(I) Ticarcillin (β-lactam) + clavulanate (inhibitor)
Tobramycin – aminoglycoside
Amikacin – aminoglycoside
Pip/Tazo – β-lactam + inhibitor
Imipenem – monobactam
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Resistance to Antibiotics
Epidemiological aspects
Controlling spread
1) complete prescription
2) optimize dosage
` 3) double prescribe
4) avoid indescriminate use
5) reduce agricultural uses
fluoroquinolones and
Campylobacter jejuni
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