New way to perform serial dilutions

The preparation of serial dilutions has been used for decades for bacterial cell counting without any significant innovations. Inlabtec has set itself the task of modernising this traditional method in compliance with the relevant ISO standards. The outcome is an ingenious solution that simplifies laboratory processes, is helping to save time and money while improving the quality of results and reducing the laboratory’s ecological footprint.

Serial dilution in microbiological testing

The purpose of serial dilutions in microbiology is to reduce the concentration of microorganism in the original sample to the extent that the determination of the total number of viable microorganisms such bacteria, yeast or mould species becomes possible. Total viable count (TVC) is a key indicator for routine hygiene control which is essential for healthy food supply as well as for other products of daily use like personal care products, cosmetics, etc. TVC determination is also used to quantify bacterial cultures like probiotic strains.

For the traditional serial dilution method capped glass test tubes filled with 9 ml of sterile diluent are used. 1 ml of the sample to be diluted is pipetted into a first test tube, mixed and 1 ml of this is pipetted into the next tube. In this way, a decimal dilution series is obtained.

Performing a serial dilution is simple in theory, but manipulation of the capped test tubes, accurate pipetting, and homogeneous mixing place high demands on the manual skills and concentration. Not surprising, that laboratory workers complain about the high stress levels and pain felt due to repetitive movements and overuse associated with high workload.

Furthermore, the preparation of the filled test tubes including cleaning, filling and sterilization is time-consuming as well as the quality control for release for use. Therefore, many labs purchase prefilled containers for single use. The convenience due to instant use is high but the costs are high too as well as the environmental impact. In addition, carrying out serial dilutions is not necessarily simplified.

Inlabtec serial dilution process

Compared to the standard method, serial dilution with Inlabtec is performed just simply by pipetting into Serial Dilution Bags and moving a lever. The preparation of filled test tubes and the manipulations for the addition and removal of samples are eliminated, as is manual mixing, which is automated and thus standardised.

Method comparison

Working StepTraditional MethodInlabtec Method
Preparations for a serial dilutionHave filled test tubes ready at the workplace. Place the test tubes required for a dilution series clearly arranged in a separate rack.Connect diluent to the Serial Diluter, insert bags and fill the first one.
Transfer 1 ml sample into 9 ml diluentTake a test tube, remove the cap, pipette the sample into the test tube and close the test tube again.Pipette the sample into the bag.
Mix sample and diluentPress the test tube with the sample onto the Vortexer for totally > 5 seconds. Alternate between pressing and releasing to create turbulence in the test tube for a homogenous mixture.Move the dosing lever to the right.
Transfer 1 ml diluted sample into Petri dish and/ or perform next dilution stepUncap the test tube again and pipette from the dilution into the Petri dishes and/or into a next test tube to perform a further dilution. Store used test tubes separately from unused test tubes to prevent errors due to mix-ups.Pipette from the dilution into Petri dishes and/or into next bag to perform a further dilution.

Advantages of the Inlabtec Solution

Cost savings through simplification
  • Simple bags instead of elaborately prepared test tubes or expensive disposable containers
  • Intuitive use – no extensive user training or specialists necessary
  • Several times lower costs for purchasing, transport, storage and disposal compared to conventional consumables

Productivity gain through acceleration
  • Fast commissioning with connection of diluent and pipette
  • Simplified pipetting – no handling of test tubes and caps for pipetting and mixing
  • Automatic mixing and diluting while changing the pipette tip for the next dilution
  • Decommissioning and cleaning after work in no time

Constant reliability and quality through semi automation
  • Constantly precise dilution volume
  • Homogeneous sample dilutions through standardised mixing
  • Clearly defined work steps for high process reliability
  • High purity bags for unrestricted cell growth od sensitive microorganisms
  • No differences in the results due to individual working techniques of the laboratory technicians
  • Easy use of any type of diluent from any type of container
  • Minimum space requirement for the system and consumables
Efficiency through user-friendly technologies
  • Working with less hand movements for reduced risk of stress-realateed complaints from employees
  • Easy, intuitive commissioning and use
  • Can be used in any existing work process
  • Low operating costs – no regular external maintenance required
Sustainability through sensible use of resources
  • Reduces energy, water and laboratory space requirements compared to using test tubes
  • 90 % less plastic waste and disposal costs than for conventional consumables
  • 90% less energy required for transport, storage and disposal than with conventional consumables

Savings Calculator

For equipment, the related cost savings and the payback period are of interest. The savings calculator provides initial answers to these questions. For a precise profitability analysis, however, the distributor must be contacted. There are country-specific price differences as well as the price of Serial Dilution Bags is lower, the greater the demand. Because of simplicity and internationality, calculations are based on US Dollars [USD].

The following entries must be made for the savings calculations: Number of dilutions per day, number of laboratory working days per year and current cost per dilution in cents (1 USD = 100 cents). If consumables such as pre-filled dilution blanks, dilution vials or cups are used, the purchase price must be entered. If the test tubes for the dilutions are prepared in the laboratory itself, the current cost per test tube should be determined as accurately as possible based on the cost of labor and materials.