control of bacteria and pathogens1 chapter 9 –chemical and physical agents (also see chapter 25...
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Control of Bacteria and Pathogens 1
Control of Bacteria and PathogensChapter 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 through1) antimicrobial agents
2) aseptic techniques
3) epidemiological strategies
Control of Bacteria and Pathogens 2
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)
Control of Bacteria and Pathogens 3
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
Control of Bacteria and Pathogens 4
Food preservationsee Chapter 25
What does “spoilage” mean”
‘Shelf life’ prevent microbial growthmaintain food quality ‘commercial sterilization’
Methods
1) Food modificationsdrying
acidification
salting
2) Temperatureheating
Pasteurization
cooling
“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
Control of Bacteria and Pathogens 5
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 radiationcobalt-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
Control of Bacteria and Pathogens 6
Chemotherapeutic agents (Chapter 11)
Some Ideal attributes:1) selective toxicity
2) stability… in body ‘biotransformation’… on shelf… with other substances
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
Acyclovir: a synthetic antiviral agent
Control of Bacteria and Pathogens 7
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’
Control of Bacteria and Pathogens 8
Antibiotics
Discovery
Alexander Fleming
Penicillium notatum
‘bacteriocidal’
Development WWII
Oxford UniversityHoward Florey andNorman Heatley
U.S. mass production
Major sources of antibioticsBacteria (Streptomyces, Bacillus)Fungi (Penicillium, Cephalosporium)
Control of Bacteria and Pathogens 9
Major families of Antibiotics
β-Lactam
-- penicillin, cephalosporins, etc
Aminoglycosides
-- steptomycin, neomycin, etc
Tetracyclines
Quinolones
Macrolides – e.g., erythomycin
Polymyxins – polymycin-B
Rifamycins – e.g., rifampin
Streptomycin
Tetracyclin
FluoroquinoloneErythomycin
Polymyxin-B
Rifamycin
Control of Bacteria and Pathogens 10
Properties of Antibiotics
Spectrum of activity
narrow
broad
Mechanisms of action -- of antibiotics
(Anti-virals in Virology ppt)
NeomycinBacitracinPolymixin
Control of Bacteria and Pathogens 11
Dr Spilatro’s Big Adventure
The antibiotics1. Ciprofloxacin - Fluoroqinolone2. 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)
The bacterium
ESBL E. coli
Extended Spectrum β-lactamase -- carried on plasmid
Multiple Ab resistance
Control of Bacteria and Pathogens 12
Properties of Antibiotics, con’t.
Examples of Adverse reactions1) Toxicity: “therapeutic dose” vs “toxic dose” levels
Tissue damage (e.g., kidney)bacitracin, polymyxin, amyloglycosides
-- TobramycinCongenital defects
tetracyclineDigestive disorders
many2) Allergic reactions
penicillin & cephalosporins3) Kill indigenous bacteria
-- growth of Clostridium difficile
Control of Bacteria and Pathogens 13
Resistance to Antibiotics
Intrisic vs Acquired resistance
Mechanisms
1) Enzymatic inactivationβ-lactamase
2) Alteration of site of actionstreptomycin, erythromycin
3) change in cell membrane orcell wall permeability
4) membrane pumps (efflux)somewhat indescriminate
Control of Bacteria and Pathogens 14
Resistance to AntibioticsEpidemiological aspects
Current serious problems
MRSA
VRE
CRE
My ESBL E. coli
ResistantAmpicillin – β-lactamAztreonam – monobactamCefazolin – β-lactamCefuroxime – β-lactamCeftriaxone – β-lactamCeftazidme – β-lactamCiprofloxacim – fluoroqinoloneLevaquin – fluoroqinoloneGentamicin – aminoglycosideTmp/Smx – sulfonamides
Ab resistance in 75 VRE isolatesMoritz & Hergenrother 2007 PNAS 104:311-316
Sensitive (I) Ticarcillin (β-lactam) + clavulanate (inhibitor)Tobramycin – aminoglycosideAmikacin – aminoglycosidePip/Tazo – β-lactam + inhibitorImipenem – monobactam
Control of Bacteria and Pathogens 15
Resistance to AntibioticsEpidemiological aspects
Controlling spread1) complete prescription
2) optimize dosage
` 3) double prescribe
4) avoid indescriminate use
5) reduce agricultural usesfluoroquinolones andCampylobacter jejuni
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