Successful surgeries and animal welfare depend on informed decisions regarding aseptic technique.Successful surgeries and animal welfare depend on informed decisions regarding aseptic technique.

The use of aseptic technique in rodent surgery is particularly challenging. Rodent surgeries are often performed in batches (several sequential operations within one day) and the expense of surgical instruments make it challenging to provide an individual surgical pack for each rodent surgery. Limitations in rodent body size and the relatively limited size of the surgical field are impediments to the application of aseptic technique. Personnel performing rodent surgeries often lack adequate surgical training and experience, and frequently do not have access to a trained surgeon.1 Additionally, mouse and rat aseptic technique is not well defined by the laws and regulations within the laboratory animal science field, and therefore leaves room for interpretation. A misconception that needs to be addressed assumes that mice and rats are not susceptible or are less susceptible to infections than other mammalian species.2,3 Studies have shown that their risk of post operative infections is real when asepsis is ignored.4 Even when infection is not clinically evident, subclinical infections affect the animal’s homeostasis,2,5-7 which may in turn have profound effects on the animal’s physiology and eventually data yield.8 Furthermore, subclinical infection can develop into clinical presentations under stressful conditions or co-infections.4,9The misconception that mice and rats are not susceptible or less susceptible to infections is a major factor in the lack of progress being made towards developing an aseptic technique protocol for rodents. The information in this article will provide guidance to rodent surgeons to formulate informed decisions regarding aseptic technique to facilitate successful surgeries and ensure animal welfare.

Regulations and Guidelines
Prior to 1985, the guidelines for rodent surgery only required clean but not aseptic technique, where clean was then defined as a surgically created wound produced under aseptic technique with no introduction of infection without entering the respiratory, alimentary, genital, or uninfected urinary tract. Currently the Animal Welfare Act,10 which applies to all institutions that utilize animals covered by the United States Department of Agriculture (USDA), requires aseptic technique to be utilized during surgical procedures and it stipulates that personnel involved in surgical procedures must undergo aseptic technique training.

The Guide for the Care and Use of Laboratory Animals (the Guide) applies to all institutions that utilize federal funding for animal research (and those that elect to be AAALAC accredited regardless of funding), and its guidelines are similar to the AWA.10,11 The Guide includes all vertebrates,which applies to mice and rats not covered by the AWA, and allows for the modification of standard aseptic techniques depending on certain characteristics such as the length of the procedure, the number of surgical procedures performed and the species on which the procedures are performed.7,12

Rodents and Infection Susceptibility
Bacteria and bacterial products retard normal wound healing processes and prevent wound closure.13 The skin has rich microbial flora, which can not be fully removed prior to surgical procedures. It is therefore important to decrease the overall microbial burden to levels that will minimize postsurgical complications or infections.14 Not doing so leads to post operative infection, whether clinical or subclinical,15 which can affect surgical outcome and introduce research variables. It should be remembered that subclinical infections have an effect on surgical outcome and data yield.2,5-7

As few as 105 to 108 infectious particles per gram of tissue can lead to postsurgical infection.16-26 However, bacterial load is not the only factor leading to post-operative infection. Elek demonstrated that the number of bacteria required for infection is decreased by 10 fold when silk suture is introduced.27 The presence of foreign material such as medical devices and other biomaterials commonly used in research significantly enhance the ability of bacteria to grow in tissue.14,15,19,24,25,28-30 Additional factors affecting postsurgical infection are the type of surgical procedure being performed, the length of the procedure, age, and immune status.31-34

Aseptic Technique Overview
Aseptic technique is defined as “a set of specific practices and procedures performed under carefully controlled conditions with the goal of minimizing contamination by pathogens.”35 The purpose of aseptic technique is to protect the animal from infection (clinical and subclinical) by maximizing and maintaining asepsis, and minimizing the presence of pathogenic microorganisms in the surgical setting.7

Surgeons should understand that the risk of wound infection depends on 1) the characteristics of microorganisms such as their pathogenicity and assumed level of contamination, 2) the characteristics of the patient such as its immune status, 3) surgical characteristics such as the type of surgery being performed, 36,37 4) the surgeon’s experience, 5) surgical technique, 6) length of procedure, and 7) the patient’s homeostasis (blood loss, temperature).38 This information will allow the surgical personnel to make knowledgeable decisions regarding aseptic technique.

There is a tremendous amount of training, planning, and consideration that must be adopted when aseptic technique is utilized. Every aspect of the surgery, from instrumentation, surgeon and patient preparation to the judicious use of antibiotics,must be considered. In order to evaluate the effectiveness of aseptic technique, competency assessments can be instituted.

Assessment of Aseptic Technique Competency
Assessment of competency in the Laboratory Animal Science (LAS) field has received much attention with the goal of making assessments more objective. Competency assessment is challenging because often time it is limited and large numbers of trainees must be assessed. Competency assessment scoring sheets allow for efficient formative and summative feedback of multiple participants in a short time. The authors have developed a score sheet which is being implemented or considered at their institutions.

Post operative surgical infections are a major concern in both human and veterinary surgery. Within the LAS community, surgical infections can have a significant impact on data and animal welfare. The impact can be minimized by the appropriate use of aseptic technique to reduce microbial burden to the lowest possible practical level.7 Aseptic technique involves several aspects including pre-surgical planning, preparation of the patient,39 preparation of the surgeon,43,48,49 sterilization of instruments, 40 operative techniques,12,41-44 and pre- and post-operative care. The contribution and importance of each portion varies with the surgical procedure being performed, animal status, surgeon’s training and experience, etc. All of these factors can be assessed using a competency assessment score sheet.


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Szczepan W. Baran, Veterinary Bioscience Institute, Harleysville, PA 19438

Elizabeth J. Johnson, Putney Inc, Portland, ME, 04101

Vince Mendenhall, Preclinical Surgical Services, Piedmont Triad Research Park, Winston-Salem, NC 27101

Marcel Perret-Gentil, Laboratory Animal Resources Center, The University of Texas at San Antonio, San Antonio, TX 78249