Microbiology Lecture No. 4 Notes
Dilutions; viable count, total count, percent viability, valid plates, plating factors...
http://pls.atu.edu/biology/biology/people/bisk/bisk.htm click Microbiology; Dilution
probs/solutions
Mycobacteria: Acid fast stain, epidemiological considerations, antibiotic resistance
Risks posed to the general population by indiscriminate use of antibiotics
Organelles of eucaryotes; Endosymbiont Hypothesis
Cell walls of Gram positives and Gram negatives. Mycoplasma, L-forms,etc.
Capsules; their ubiquitous nature and varied functions
Variable porin syntheses in E. coli
Shapes and arrangements of bacteria
Membrane structure and function
Extracellular structures; pili, fimbriae, and flagella.
Chemo-; photo-; aero-; taxes
PHB, glycogen, volutin (poly-P), etc. and rationale for storage granules
Bacterial endospores
Archaebacteria and some of their distinguishing features
Procaryotic and eukaryotic cells
Diffusion, osmosis, facilitated diffusion, and active transport
Endocytosis and exocytosis
The war against invasive bacteria that stick to surfaces
http://res2.agr.gc.ca/crda/pubs/art4_e.htm
by Mafu Akier Assanta
For the food industry, the world of microbes might be compared to a
minuscule battlefield, where its allies and its enemies are engaged in a deadly struggle on a
microscopic scale. Pathogens and micro-organisms that cause spoilage are particularly formidable
adversaries, as they give rise to many economic problems and threats to human health. One major
source of contamination is surfaces. Bacteria tend to stick tightly to surfaces, even surfaces that
have been meticulously disinfected. Any food, regardless of
whether it is fresh or processed, or of plant or animal origin,
inevitably harbours various micro-organisms, such as bacteria,
viruses, yeasts, parasites and moulds, which may either be
vegetating passively or multiplying. In the latter case, if the micro-organisms in question happen to be harmful ones, they may
become a major source of contamination.
Food that has been contaminated with pathogens such as
Aeromonas hydrophila, Clostridium botulinum, Eschericha coli,
Listeria monocytogenes, Salmonella, Staphylococcus aureus and
Yersinia enterocolitica may cause illnesses of various kinds, and
this situation is a source of concern both for the food industry
and for public health officials. Many epidemiological reports
have pointed to the fact that the potential sources of food
contamination are many and complex, and that they include, in
particular, the surfaces with which the product comes into
contact: processing equipment, tanks, counters and so on. Even cleaning with disinfectants does
not always eliminate these lurking microscopic intruders.
Microcolonies, effectively protected by the glycocalyx, form on the surface. As these grow and
run together, they form a coating which is thin and superficial at first, but becomes progressively
thicker as the bacteria grow, ultimately attaining a thickness of several millimetres. This is what is
known as a biofilm.The most familiar type of biofilm, of course, is the plaque that forms on teeth.
It is a hazard to dental health, and can be removed only by meticulous brushing. Once a biofilm
has formed, it constitutes a microniche that provides bacteria with an environment which is highly
conducive to their survival while also protecting them from various types of aggression from
outside, such as flows of liquids, changes in pH or temperature, and chemical cleansers or
disinfectants expressly designed to exterminate them! In food processing, the charged surface of
a biofilm constitutes a continuing source of contamination for any food product that comes into
contact with it.
