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Laboratory equipment. Lab 2. Laboratory Equipment in A Modern Laboratory. • Antimicrobial susceptibility test instruments • Disc dispensers • pH meters • Plate pouring and other culture preparation systems • Inoculating loops, wires and spreaders • Pipetting devices and pipette tips
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Laboratory equipment Lab 2
Laboratory Equipment in A Modern Laboratory • Antimicrobial susceptibility test instruments • Disc dispensers • pH meters • Plate pouring and other culture preparation systems • Inoculating loops, wires and spreaders • Pipetting devices and pipette tips • Racks and baskets for tubes and bottles • Disposable plastic items, including Petri dishes, pipette tips • Specimen and sample containers of glass or plastic • Microscopes of different types • Centrifuges of different types • Incubators of different types • Water baths and heating blocks • Refrigerators and freezers • Autoclaves • Microbiological safety cabinets • Colony counters • Shakers and mixers • Multi-point inoculators • Micro-organism detection and identification systems • Automatic pipettors
Microscope • An instrument to see objects too small for the naked eye. • The small size of bacteria means that individual organisms can only be observed directly using the microscope, although large numbers may be visible to the naked eye as colonies on solid media
Incubators • Incubators provide automatic control of temperature, CO2 and humidity. • In medical and veterinary laboratories, bacteriology incubators are usually operated at 35–37°C, while fungi which are kept at 25-26°C. • Carbon dioxide incubators are used for growing bacteria which require 5% carbon dioxide, a microaerobic incubator which operates at 4% oxygen and the anaerobic incubator is used to provide anaerobic atmospheres.
Centrifuges Instructions for using the centrifuge: 1. Select two centrifuge tubes of identical lengths and thickness. Place liquid to be centrifuged in one tube and water in the other to within about 2 cm of the top. 2. Place the tubes in paired centrifuge buckets and place the buckets on the pans of the centrifuge balance. 3. Place the paired buckets and tubes in diametrically opposite positions in the centrifuge head. 4. Close the centrifuge lid and make sure that the speed control is at zero before switching on the current. 5. Move the speed control slowly until the speed indicator shows the required number of revolutions per minute.
Water baths • Used for short-term incubation • Raise the required temperature much more rapidly than in an incubator • Water-baths should be fitted with lids in order to prevent heat loss and evaporation
Refrigerators and freezers • Media and perishable test kits are stored at +4°C in fridges or cold rooms. • Sera and tissues and cultures are stored in freezers at -20°C. • Delicate tissues (cell cultures) and some bacterial strains are stored at -70°C. • Monoclonal cell lines and some other infectious agents are stored in liquid nitrogen flasks at -196°C. • Finally, cultures may be maintained on slopes or in broth
Microbiological safety cabinets • Are intended to capture and retain infected airborne particles released in the course of certain manipulations, and to protect the laboratory worker from infection that may arise from inhaling them. • There are three kinds: Classes I, II and III. • Class I and Class II cabinets are used in Level 2 Containment, and Level 3 laboratories for work with Hazard Group 3 organisms. • Class III cabinets are used for Hazard Group 4 viruses.
Class I • The operator sits at the cabinet, works with the hands inside, and sees what he or she is doing through the glass screen. Any aerosols released from the cultures are retained because a current of air passes in at the front of the cabinet. This sweeps the aerosols up through the filters, which remove all or most of the organisms. The clean air then passes through the fan, which maintains the airflow, and is exhausted to atmosphere.
Class II • In the Class II cabinet most the air is re-circulated through filters, so that the working area is bathed in clean (almost sterile) air. This entrains any aerosols produced in the course of the work, which are removed by the filters. Some of the air is exhausted to atmosphere and is replaced by room air. This prevents the escape of any particles or aerosols released in the cabinet.
Class III • Class III cabinets are totally enclosed and are tested under pressure to ensure that no particles can leak from them into the room. The operator works with gloves that are an integral part of the cabinet. Air enters through a filter and is exhausted to atmosphere through one or two more filters.
Autoclaves • Also known as Steam under pressure. • Temperature increases with pressure, e.g. at 1 bar (about 15 lb/in2) until reaches 121°C. Bacteria are killed by autoclaving at this temperature for 20 min. • There are two varieties of laboratory autoclave: • Pressure cooker types • Gravity displacement models.
Blenders and shakers • Blenders are instruments suitable for grinding and emulsifying large samples, e.g. for homogenizing small pieces of tissue. • They should be used inside a microbiological safety cabinet and be held in the gloved hand • They suffer from the disadvantage of requiring a fresh, sterile cup for each sample. These cups are expensive and it takes time to clean and re-sterilise them. • Shakers are useful for mixing and shaking cultures, but should be fitted with racks which hold the bottles or tubes firmly.
Bunsen burner • Used for bacterial decontamination as well as in bacterial staining. • A loop or inoculating wire is inserted into the flame about 6 seconds organic material is incinerated and sterilised at a high temperature.
Inoculating loops and spreaders • Growing cultures are transferred by mean of sterile wire loops. • These are flamed (sterilised a flame by dry heat) before use and allowed to cool. As all the colonies produced on a plate are descendants of single bacteria cells. • Many workers prefer spreaders to loops for inoculating Petri dishes with more than one loopful of material.
Microscope slides and cover glasses • Used to visualise bacteria under the microscope, either using wet mounts or after staining. • Slides are also used to carry out other tests such as catalase test, motility test and slide agglutination test.
Pipettes • A. Two micropipettes • B. Filling bulb for standard pipette • C. Two plastic Pasteur pipettes • D. Rechargeable battery-operated pipettor • E. Manually operated pipettor • F. Plastic pipette
Petri dishes • Disposable plastic Petri dishes of variable sizes are now widely used in most laboratories. • They are supplied already sterilised and packed in batches in polythene bags. • They can be stored indefinitely. • Petri dishes are used to prepare solid media.
Test tubes and flasks • Culture media may be distributed in either test tubes or small bottles. • Test tubes are easier to handle and take up less space in storage. • Media in test tubes may dry up during storage. Screw-capped test tubes are available. • Flasks are used to grow bacteria in bulk in liquid media.
Media storage bottles • Used to store liquid media for the latter use. • These are usually available with screw caps are made in sizes from 60 ml upwards. • The most convenient sizes are 110 ml, holding 50–100 ml of medium, and 560 ml, for storing 250–500 ml. • Available in flat or round bottoms. The flat bottles are easiest to handle and store but the round ones are more robust
Specimen containers • There are too many different containers, many of plastic: some are satisfactory, others not • Specimen containers should not leak.
Racks and baskets • Used to stand test tubes and to store flasks and bottles.
Colony counters • Composed of a source of light and a magnifier to visualise and count bacterial colonies.
