MicroscopesBlog: Expert's reviews, news, notes on Microscopes, Centrifuges, Lab Coats, Pipettes, Lab Safety, & more Lab Products!

The Nikon Small World competition is a microscopists opportunity for 15 minutes of fame. This competition is also for anyone who appreciates photography. This competition has been around since 1974 and is designed to recognize those involved in photography while using a light microscope. The competition is open to anyone with an interest in photography through a microscope and entries have been submitted from the U.S., Canada, Latin America, Europe and Africa. Both proffesional and hobbyists have won the competition. One may submit a photo of any specimen and can use microscopy techniques such as brightfield, phase contrast, polarized light, fluorescence, interference contrast, and darkfield, confocal and deconvolution. The entries are then judged by photomicrography and micrography experts who rate the entries based on things like originality and visual impact. First prize in this competition receives $3,000 towards the purchase of new Nikon equipment.

Stereomicroscopy is helpful in almost any endeavor requiring a long working distance and relatively modest magnification. Stereoscopic microscopes are commonly referred to as "dissecting microscopes" but their applications are much more diverse. Biology, botany and almost any other area of life science that you can think of has a need for a stereo microscope. But that is just the beginning. Geologists, gemologists, electronics assemblers (think circuit boards), minerologists, numismatists, philatelists, printers and archeologists are just a few of the non-life science professional and amateur observers who find stereos to be invaluable if not indispensable. One of the most common questions of new users is, how does a stereo work? The easy answer is "very well"! The scientific explanation is also straightforward and quite simple. A stereocopic microscope has dual optical paths, one for each eye, offset to one another at about the same angle as your eyes. This offset allows you to "see" in three dimensions through the microscope in exactly the same way as you see in three dimensions as you view the world around you. Stereoscopic vision works in much the same way as stereophonic sound (after all, your ears are offset too!). These microscopes come in two basic configurations. They either have fixed magnification(s) or a continuosly variable zoom configuration. Either way, the secret is in the offset optical paths that are the heart of stereoscopic vision. The next time you want to get up close and personal with a caterpillar, a leaf, a coin or a gemstone give a stereo microscope a try. You'll be amazed at what you will see...

The Kirby Bauer method is a laboratory technique used to determine the efficacy of a given antibiotic or antimicrobial agent. Paper disks containing specific concentrations of the antibiotic or antimicrobial agent are placed on the agar surface containing a lawn of bacteria. The chemotherapeutic agent then diffuses out, forming a concentration gradient. If the agent kills the test organism, there will be a zone around the disk where no growth occurs called the zone of inhibition. The zone of inhibition varies with the diffusability of the agent, the size of the inoculum, the type of medium, and many other factors. The recommended medium in this test is Mueller-Hinton II agar. Its pH should be between 7.2 and 7.4 and it is poured to a uniform thickness of 4mm in the petri plate. Innoculation of the medium is performed with a cotton swab from a broth culture. High potency disks are used that may be placed on the agar with a mechanical dispenser or sterile forceps. After 16-18 hours of incubation the discs are measured to the nearest millimeter and compared to each other.

Bacterial cells are surrounded by a cell wall that contains peptidoglycan, which is only found in prokaryotes. Peptidoglycan is a polymer held together by covalent bonds. A molecule made of four amino acids, a tetrapeptide, helps hold peptidoglycan together. Not all bacteria have the same tetrapeptide which accounts for the differences in shape. The cell wall of gram-positive bacteria is composed of 90% peptidoglycan in addition to teichoic acids. Teichoic acids are responsible for the net negative charge on gram positive cells. The cell walls of gram-negative bacteria are composed of a thin layer of peptidoglycan and an outer membrane that encloses the peptidoglycan. The outer membrane forms an additional permeability barrier in these organisms. Humans are born with non-immune factors that protect them from infection from bacteria. Lysozyme is one of these factors and is found in most bodily fluids like tears and saliva. Lysozyme can break down peptidoglycan which results in cell lysis and death.

Bottle top filters and sterile receivers aid the researcher in preparing sterile solutions for their work. For example cell culture media must be prepared sterile. Many different membrane materials are available including Nylon, Cellulose Acetate, Cellulose Nitrate, and Polyether Sulfone (PES). Pore sizes available range from 0.2um to 0.8um. Various receiver volumes are available from 115ml to 1L. These tools for sterile prep can be purchased separately or as complete units. If a lab has limited access to an autoclave or if a microbiology class only has a few lab classes requiring sterile media preparation, these filtration units are the answer to efficient sterile filtration. Nalge Nunc, Whatman, Pall, Greiner Bio-One, and VWR all offer sterile filtration units in various volumes, materials, and pore sizes.

It is important for microbiologists to understand the relationship between osmotic pressure and growth of bacteria. Osmotic pressure exists due to the concentration of solutes dissolved in water. During the process of osmosis water moves from an area of high concentration to an area of low concentration. Because there is normally a high concentration of nutrients in the cytoplasm relative to the outside of the cell, water will naturally diffuse into the cell. A medium where the concentrations of solutes outside of the cell is lower than inside the cell is called hypotonic. The cell wall of the bacteria protects it against this pressure. When the concentration of solutes outside of the cell is the same as inside this is called an isotonic environment. When the concentration of solute outside of the cell is higher than inside the cell, this is considered hypertonic. Water diffuses out of the cell in this environment. This type of environment is used to preserve food because there is no water available for the cells to grow. Some bacteria known as halophiles require high concentrations of salt between 15-30%. Some bacteria such as Staphylococcus aureus can tolerate sodium chloride solutions of up to 11%.

It is important to understand the relationship between pH and microbial growth. The pH or hydrogen ion concentration affects proteins and other charged molecules in the cell. Each organism has an optimal pH at which point they grow best. If the pH value exceeds the optimal pH the solubility of charged molecules can be adversely affected and molecules can precipitate out of solution. The pH can alter the charge on amino acids and result in denaturation of the protein. Like temperature, microorganisms can be subdivided into groups based on their ability to grow at different ph values. Bacteria that can grow at or near neutral pH are classified as neutrophiles. Most bacteria are neutrophiles although many can grow over a range of 2-3 pH units. Bacteria that grow at acidic pH values are acidophiles and bacteria that grow at alkaline pH values are termed alkaliphiles. Thiobacillus thiooxidans can grow at pH 1 and it derives its envergy needs from the oxidation of sulfide. They then produce sulfuric acid that lowers the pH of the environment. True alkalinophilic bacteria can be found growing in environments such as high carbonate soils where the ph is 10 or above.