Can the Disinfection Period(Exposure Time) Be Arbitrarily Increased?

Learning Objectives

• Describe why the phenol coefficient is used
• Compare and contrast the disk-diffusion, use-dilution, and in-use methods for testing the effectiveness of antiseptics, disinfectants, and sterilants

The effectiveness of various chemical disinfectants is reflected in the terms used to depict them. Chemic disinfectants are grouped by the power of their activity, with each category reflecting the types of microbes and viruses its component disinfectants are effective against. High-level germicides have the ability to kill vegetative cells, fungi, viruses, and endospores, leading to sterilization, with extended utilize. Intermediate-level germicides, as their name suggests, are less effective confronting endospores and certain viruses, and low-level germicides kill only vegetative cells and certain enveloped viruses, and are ineffective confronting endospores.

Even so, several environmental atmospheric condition influence the dominance of an antimicrobial agent and its effectiveness. For example, length of exposure is peculiarly important, with longer exposure increasing efficacy. Similarly, the concentration of the chemical agent is likewise important, with higher concentrations existence more than effective than lower ones. Temperature, pH, and other factors can besides affect the say-so of a disinfecting agent.

One method to determine the effectiveness of a chemical agent includes swabbing surfaces before and after use to ostend whether a sterile field was maintained during utilise. Boosted tests are described in the sections that follow. These tests allow for the maintenance of advisable disinfection protocols in clinical settings, controlling microbial growth to protect patients, wellness-care workers, and the community.

Phenol Coefficient

The effectiveness of a disinfectant or antiseptic can be determined in a number of means. Historically, a chemical amanuensis'due south effectiveness was often compared with that of phenol, the first chemical amanuensis used by Joseph Lister. In 1903, British chemists Samuel Rideal (1863–1929) and J. T. Ainslie Walker (1868–1930) established a protocol to compare the effectiveness of a variety of chemicals with that of phenol, using as their test organisms Staphylococcus aureus (a gram-positive bacterium) and Salmonella enterica serovar Typhi (a gram-negative bacterium). They exposed the test leaner to the antimicrobial chemic solutions diluted in water for 7.5 minutes. They then calculated a phenol coefficient for each chemical for each of the two bacteria tested. A phenol coefficient of i.0 means that the chemical agent has about the same level of effectiveness equally phenol. A chemical agent with a phenol coefficient of less than ane.0 is less effective than phenol. An example is formalin, with phenol coefficients of 0.3 (S. aureus) and 0.7 (S. enterica serovar Typhi). A chemic agent with a phenol coefficient greater than 1.0 is more effective than phenol, such every bit chloramine, with phenol coefficients of 133 and 100, respectively. Although the phenol coefficient was in one case a useful mensurate of effectiveness, information technology is no longer commonly used because the conditions and organisms used were arbitrarily called.

Call back About Information technology

• What are the differences between the three levels of disinfectant effectiveness?

Disk-Improvidence Method

The disk-diffusion method involves applying dissimilar chemicals to separate, sterile filter paper disks. The disks are then placed on an agar plate that has been inoculated with the targeted bacterium and the chemicals diffuse out of the disks into the agar where the leaner have been inoculated. As the "backyard" of bacteria grows, zones of inhibition of microbial growth are observed as clear areas effectually the disks. Although at that place are other factors that contribute to the sizes of zones of inhibition (e.g., whether the agent is water soluble and able to diffuse in the agar), larger zones typically correlate to increased inhibition effectiveness of the chemic amanuensis. The diameter beyond each zone is measured in millimeters.

A disk-diffusion assay is used to make up one's mind the effectiveness of chemical agents against a detail microbe. (a) A plate is inoculated with diverse antimicrobial discs. The zone of inhibition around each disc indicates how effective that antimicrobial is against the item species beingness tested. (b) On these plates, 4 antimicrobial agents are tested for efficacy in killing Pseudomonas aeruginosa (left) and Staphylococcus aureus (right). These antimicrobials are much more effective at killing S. aureus, as indicated by the size of the zones of inhibition. (credit b: modification of work by American Society for Microbiology)

Call up About It

• When comparing the activities of ii disinfectants confronting the same microbe, using the deejay-improvidence analysis, and bold both are h2o soluble and can easily diffuse in the agar, would a more than constructive disinfectant have a larger zone of inhibition or a smaller one?

Use-Dilution Test

Other methods are also used for measuring the effectiveness of a chemic agent in clinical settings. The utilize-dilution examination is unremarkably used to determine a chemic's disinfection effectiveness on an inanimate surface. For this test, a cylinder of stainless steel is dipped in a culture of the targeted microorganism and then dried. The cylinder is then dipped in solutions of disinfectant at diverse concentrations for a specified amount of time. Finally, the cylinder is transferred to a new examination tube containing fresh sterile medium that does not contain disinfectant, and this exam tube is incubated. Bacterial survival is demonstrated by the presence of turbidity in the medium, whereas killing of the target organism on the cylinder by the disinfectant will produce no turbidity.

The Clan of Official Agricultural Chemists International (AOAC), a nonprofit group that establishes many protocol standards, has determined that a minimum of 59 of sixty replicates must show no growth in such a exam to achieve a passing effect, and the results must be repeatable from different batches of disinfectant and when performed on different days. Disinfectant manufacturers perform use-dilution tests to validate the efficacy claims for their products, as designated past the EPA.

Think Almost It

• Is the use-dilution test performed in a clinical setting? Why?

In-Use Test

An in-use examination can determine whether an actively used solution of disinfectant in a clinical setting is microbially contaminated. A one-mL sample of the used disinfectant is diluted into 9 mL of sterile broth medium that also contains a compound to inactivate the disinfectant. X drops, totaling approximately 0.2 mL of this mixture, are so inoculated onto each of two agar plates. Ane plate is incubated at 37 °C for three days and the other is incubated at room temperature for 7 days. The plates are monitored for growth of microbial colonies. Growth of five or more colonies on either plate suggests that feasible microbial cells existed in the disinfectant solution and that it is contaminated. Such in-utilize tests monitor the effectiveness of disinfectants in the clinical setting.

Figure 2. Used disinfectant solutions in a clinical setting can be checked with the in-use exam for contamination with microbes.

Call back About It

• What does a positive in-use test indicate?

Clinical Focus: Jenny, Resolution

This instance concludes Jenny's story that started in Controlling Microbial Growth.

Despite antibiotic treatment, Jenny's symptoms worsened. She developed pyelonephritis, a severe kidney infection, and was rehospitalized in the intensive care unit (ICU). Her condition continued to deteriorate, and she developed symptoms of septic shock. At this point, her physician ordered a culture from her urine to determine the exact cause of her infection, besides as a drug sensitivity test to determine what antibiotics would be effective confronting the causative bacterium. The results of this exam indicated resistance to a broad range of antibiotics, including the carbapenems, a class of antibiotics that are used every bit the final resort for many types of bacterial infections. This was an alarming outcome, suggesting that Jenny's infection was caused by a then-called superbug: a bacterial strain that has developed resistance to the bulk of commonly used antibiotics. In this case, the causative agent belonged to the carbapenem-resistant Enterobacteriaceae (CRE), a drug-resistant family of leaner normally found in the digestive organisation. When CRE is introduced to other body systems, as might occur through improperly cleaned surgical instruments, catheters, or endoscopes, aggressive infections can occur.

CRE infections are notoriously hard to treat, with a forty%–50% fatality rate. To care for her kidney infection and septic shock, Jenny was treated with dialysis, intravenous fluids, and medications to maintain blood pressure and foreclose blood clotting. She was likewise started on aggressive handling with intravenous administration of a new drug called tigecycline, which has been successful in treating infections caused by drug-resistant bacteria.

Afterward several weeks in the ICU, Jenny recovered from her CRE infection. Yet, public wellness officials presently noticed that Jenny's instance was not isolated. Several patients who underwent like procedures at the same infirmary also adult CRE infections, some dying equally a result. Ultimately, the source of the infection was traced to the duodenoscopes used in the procedures. Despite the infirmary staff meticulously following manufacturer protocols for disinfection, bacteria, including CRE, remained within the instruments and were introduced to patients during procedures.

Effigy three. CRE is an extremely drug-resistant strain of bacteria that is typically associated with nosocomial infections. (credit: Centers for Illness Command and Prevention)

Who Is Responsible?

Carbapenem-resistant Enterobacteriaceae infections due to contaminated endoscopes take go a high-profile problem in contempo years. Several CRE outbreaks have been traced to endoscopes, including a case at Ronald Reagan UCLA Medical Center in early 2022 in which 179 patients may accept been exposed to a contaminated endoscope. 7 of the patients developed infections, and two later died. Several lawsuits have been filed against Olympus, the manufacturer of the endoscopes. Some claim that Olympus did not obtain FDA approval for pattern changes that may have led to contagion, and others merits that the manufacturer knowingly withheld data from hospitals concerning defects in the endoscopes.

Lawsuits like these enhance difficult-to-answer questions about liability. Invasive procedures are inherently risky, but negative outcomes tin be minimized by strict adherence to established protocols. Who is responsible, however, when negative outcomes occur due to flawed protocols or faulty equipment? Can hospitals or wellness-care workers exist held liable if they have strictly followed a flawed procedure? Should manufacturers be held liable—and perhaps exist driven out of concern—if their lifesaving equipment fails or is found defective? What is the government's role in ensuring that use and maintenance of medical equipment and protocols are fail-safe?

Protocols for cleaning or sterilizing medical equipment are ofttimes adult by government agencies similar the FDA, and other groups, similar the AOAC, a nonprofit scientific organization that establishes many protocols for standard use globally. These procedures and protocols are and so adopted by medical device and equipment manufacturers. Ultimately, the stop-users (hospitals and their staff) are responsible for following these procedures and can be held liable if a breach occurs and patients become sick from improperly cleaned equipment.

Unfortunately, protocols are non infallible, and sometimes it takes negative outcomes to reveal their flaws. In 2008, the FDA had approved a disinfection protocol for endoscopes, using glutaraldehyde (at a lower concentration when mixed with phenol), o-phthalaldehyde, hydrogen peroxide, peracetic acid, and a mix of hydrogen peroxide with peracetic acid. Nonetheless, subsequent CRE outbreaks from endoscope employ showed that this protocol lonely was inadequate.

As a result of CRE outbreaks, hospitals, manufacturers, and the FDA are investigating solutions. Many hospitals are instituting more rigorous cleaning procedures than those mandated by the FDA. Manufacturers are looking for means to redesign duodenoscopes to minimize hard-to-attain crevices where bacteria can escape disinfectants, and the FDA is updating its protocols. In February 2015, the FDA added new recommendations for conscientious hand cleaning of the duodenoscope elevator mechanism (the location where microbes are virtually probable to escape disinfection), and issued more conscientious documentation about quality control of disinfection protocols.

In that location is no guarantee that new procedures, protocols, or equipment will completely eliminate the run a risk for infection associated with endoscopes. However these devices are used successfully in 500,000–650,000 procedures annually in the United States, many of them lifesaving. At what point do the risks outweigh the benefits of these devices, and who should exist held responsible when negative outcomes occur?

Effigy 4. The elevator mechanism in a duodenoscope contains crevices that are difficult to disinfect. Pathogens that survive disinfection protocols can exist passed from ane patient to another, causing serious infections. (credit "photos": modification of work by Centers for Disease Control and Prevention)

Key Concepts and Summary

• Chemical disinfectants are grouped by the types of microbes and infectious agents they are effective against. High-level germicides kill vegetative cells, fungi, viruses, and endospores, and can ultimately pb to sterilization. Intermediate-level germicides cannot kill all viruses and are less effective against endospores. Low-level germicides kill vegetative cells and some enveloped viruses, but are ineffective confronting endospores.
• The effectiveness of a disinfectant is influenced by several factors, including length of exposure, concentration of disinfectant, temperature, and pH.
• Historically, the effectiveness of a chemical disinfectant was compared with that of phenol at killing Staphylococcus aureus and Salmonella enterica serovar Typhi, and a phenol coefficient was calculated.
• The disk-improvidence method is used to test the effectiveness of a chemical disinfectant against a particular microbe.
• The apply-dilution test determines the effectiveness of a disinfectant on a surface. In-use tests can determine whether disinfectant solutions are being used correctly in clinical settings.

Multiple Choice

Which type of test is used to determine whether disinfectant solutions actively used in a clinical setting are beingness used correctly?

1. disk-diffusion assay
2. phenol coefficient test
3. in-use examination
4. apply-dilution exam

Show Respond

c. An in-use exam is used to determine whether disinfectant solutions actively used in a clinical setting are beingness used correctly.

The effectiveness of chemical disinfectants has historically been compared to that of which of the following?

1. phenol
2. ethyl alcohol
3. bleach
4. formaldehyde

Prove Answer

a. The effectiveness of chemical disinfectants has historically been compared to phenol.

Which of the following refers to a germicide that can kill vegetative cells and sure enveloped viruses but not endospores?

1. high-level germicide
2. intermediate-level germicide
3. low-level germicide
4. sterilant

Show Answer

c. Low-level germicide tin can kill vegetative cells and sure enveloped viruses but not endospores.

Fill in the Blank

If a chemical disinfectant is more effective than phenol, then its phenol coefficient would be ________ than i.0.

Show Answer

If a chemic disinfectant is more effective than phenol, then its phenol coefficient would be greater than 1.0.

If used for extended periods of time, ________ germicides may atomic number 82 to sterility.

Prove Answer

If used for extended periods of time, high-level germicides may lead to sterility.

In the disk-improvidence analysis, a large zone of inhibition around a deejay to which a chemic disinfectant has been practical indicates ________ of the examination microbe to the chemical disinfectant.

Show Answer

In the deejay-diffusion assay, a big zone of inhibition around a disk to which a chemical disinfectant has been applied indicates susceptibility or sensitivity of the test microbe to the chemic disinfectant.

Think Virtually It

1. Why were chemical disinfectants once commonly compared with phenol?
2. Why is length of exposure to a chemical disinfectant important for its activity?
3. What are some advantages of employ-dilution and in-use tests compared with the disk-improvidence assay?

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Source: https://courses.lumenlearning.com/microbiology/chapter/testing-the-effectiveness-of-antiseptics-and-disinfectants/

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