Download Chapter 7: The Control of Microbial Growth

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Sepsis refers to microbial contamination
Asepsis is the absence of significant
contamination
Aseptic surgery techniques prevent
microbial contamination of wounds
Sterilization: Removing all microbial life
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Disinfection: Removing pathogens from
surfaces
Antisepsis: Removing pathogens from living
tissues
Sanitization: Lowering microbial counts to
acceptable (public health) standards
Biocide/germicide: Kills microbes
Bacteriostasis: Inhibiting, not killing,
bacteria
A. the microbe’s characteristics
ex. Mycobacterium tuberculosis vs. HIV
B. environmental conditions
ex. blood present
C. concentration of agent
ex. 70% alcohol
D. time of exposure
E. number of microbes to begin with
A. physical removal – ex. soaps
B. disruption of p.m. – ex. alcohols
C. denaturing proteins – ex. phenols
D. damage to DNA – ex. UV light
E. damage to many molecules – ex. H2O2
I. Physical Methods of Control:
A. Heat
1. dry – oven, 160o C for several hours
2. moist – autoclave/
pressure cooker 121o C for
15 minutes at 15 psi
3. pasteurization – 63o C for
30 min, 72o C for 15 seconds,
~ 140o C for 1 second
4. flaming/incineration
B. Cold(?)
1. refrigeration – 4o C/40o F ;doesn’t kill;
slows down growth
2. freezer – minus 20o C; ice crystals in cells may
kill them
C. Removal of water
1. dessication
2. adding solutes, ex. salts, sugars
http://www.takarafood.com/images/dried-fruits.jpg
http://www.mnpork.com/consumers/images/curedHam1.jpg
D. Filtration
HEPA (High Efficiency Particulate Air) filters
Membrane filters
Used to sterilize things that can’t be heated, etc.
Ex. Antibiotics, vaccines, enzymes, some
media, vitamins, etc.
Blue colonies grown on agar are fecal coliform bacteria (left). A close-up,
colorized view of fecal coliform (right).
http://www.oberlin.edu/ajlc/images/education/fecal_coliform.jpg
E. Radiation
1. Ionizing radiation – X-rays, gamma
irradiation
2. Ultraviolet light
F. Soaps and detergents
http://i.bnet.com/blogs/tide.jpg
II. Chemical Methods of Control
A. phenol compounds – ex. phenol, Cresol,
pHisoHex, Lysol
i. Denaturation of proteins
ii. Effective against TB
http://bkimrey1.files.wordpress.com/2008/09/lysol.jpg
B. chlorhexidine – in hand scrubs
i. Hibiclens (brand name)
ii. Low toxicity
iii. Effective against spores, TB, cysts
of parasites, etc.
http://www.prestoimages.net/graphics08/648_pd204969_1.jpg
C. halogens – iodine, bleach, Betadine (with
alcohol)
Iodines for skin;
bleach for surfaces and water
http://www.clorox.com/img/product_shots/marquee/clb.jpg
D. alcohols – rubbing alcohol, ethanol
i. Work best with some water;
ii. 70% concentration most effective
iii. Low toxicity
http://www.chemistryland.com/CHM107Lab/Exp10_pHindicator/Lab/RubbingAlcohol.jpg
E. heavy metals – mercury, lead, silver, etc.
Mercury in vaccines -- thimerosal
Lead in paints
Silver nitrate for newborn eyes
Copper for algae
Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children.
Wakefield AJ, Murch SH, Anthony A, Linnell J, Casson DM, Malik M, Berelowitz M, Dhillon AP, Thomson MA, Harvey P, Valentine
A, Davies SE, Walker-Smith JA.
Inflammatory Bowel Disease Study Group, University Department of Medicine, Royal Free Hospital and School of Medicine, London,
UK.
BACKGROUND: We investigated a consecutive series of children with chronic enterocolitis and regressive developmental disorder.
METHODS: 12 children (mean age 6 years [range 3-10], 11 boys) were referred to a paediatric gastroenterology unit with a history of
normal development followed by loss of acquired skills, including language, together with diarrhoea and abdominal pain. Children
underwent gastroenterological, neurological, and developmental assessment and review of developmental records. Ileocolonoscopy
and biopsy sampling, magnetic-resonance imaging (MRI), electroencephalography (EEG), and lumbar puncture were done under
sedation. Barium follow-through radiography was done where possible. Biochemical, haematological, and immunological profiles
were examined. FINDINGS: Onset of behavioural symptoms was associated, by the parents, with measles, mumps, and rubella
vaccination in eight of the 12 children, with measles infection in one child, and otitis media in another. All 12 children had intestinal
abnormalities, ranging from lymphoid nodular hyperplasia to aphthoid ulceration. Histology showed patchy chronic inflammation in
the colon in 11 children and reactive ileal lymphoid hyperplasia in seven, but no granulomas. Behavioural disorders included autism
(nine), disintegrative psychosis (one), and possible postviral or vaccinal encephalitis (two). There were no focal neurological
abnormalities and MRI and EEG tests were normal. Abnormal laboratory results were significantly raised urinary methylmalonic acid
compared with age-matched controls (p=0.003), low haemoglobin in four children, and a low serum IgA in four children.
INTERPRETATION: We identified associated gastrointestinal disease and developmental regression in a group of previously normal
children, which was generally associated in time with possible environmental triggers.
PMID: 9500320 [PubMed - indexed for MEDLINE]
Retraction of an interpretation.
Murch SH, Anthony A, Casson DH, Malik M, Berelowitz M, Dhillon AP, Thomson MA, Valentine A, Davies
SE, Walker-Smith JA.
Centre for Paediatric Gastronenterology, Royal Free and University College Medical School, Royal Free
Campus, London NW3 2PF, UK. [email protected]
PMID: 15016483
F. ammonia compounds
NH3
Pseudomonas spp. can GROW in some
ammonia compounds
G. preservatives
Sulfites in wine and many other foods
Nitrates/nitrites in meats
H. aldehydes
Formaldehyde – embalming, preservation
of specimens
Glutaraldehyde – preserving eukaryotic
cells
I. gases
Ethylene oxide – high toxicity, not wet,
even mattresses can be treated
J. peroxides – highly reactive with many
molecules
Hydrogen peroxide – most effective
against anaerobes
The End