Visualization of Murine Intranasal Dosing Efficiency Using Luminescent Francisella tularensis: Effect of Instillation Volume and Form of Anesthesia

Abstract

Intranasal instillation is a widely used procedure for pneumonic delivery of drugs, vaccine candidates, or infectious agents into the respiratory tract of research mice. However, there is a paucity of published literature describing the efficiency of this delivery technique. In this report we have used the murine model of tularemia, with Francisella tularensis live vaccine strain (FTLVS) infection, to evaluate the efficiency of pneumonic delivery via intranasal dosing performed either with differing instillation volumes or different types of anesthesia. FTLVS was rendered luminescent via transformation with a reporter plasmid that constitutively expressed the Photorhabdus luminescens lux operon from a Francisella promoter. We then used an IVIS Spectrum whole animal imaging system to visualize FT dissemination at various time points following intranasal instillation. We found that instillation of FT in a dose volume of 10 µl routinely resulted in infection of the upper airways but failed to initiate infection of the pulmonary compartment. Efficient delivery of FT into the lungs via intranasal instillation required a dose volume of 50 µl or more. These studies also demonstrated that intranasal instillation was significantly more efficient for pneumonic delivery of FTLVS in mice that had been anesthetized with inhaled (isoflurane) vs. parenteral (ketamine/xylazine) anesthesia. The collective results underscore the need for researchers to consider both the dose volume and the anesthesia type when either performing pneumonic delivery via intranasal instillation, or when comparing studies that employed this technique.

Animal models of hospital-acquired pneumonia: current practices and future perspectives

“…Less invasive methods include intranasal administration, whereby bacterial dose is administered in droplets through the nostrils followed by aspiration by the animal (52), or aerosol administration, that can be performed in unrestrained animals (53). However, the exact dose that reaches the lower respiratory tract in both methods is uncontrolled and animals frequently develop upper respiratory tract infections (52) or infections other than pneumonia (53). One method to control dose delivery with aerosolization is to immediately sacrifice a few (sentinel) animals after aerosolization for quantitative colony counts performed on bronchoalveolar lavage fluid or lung tissue lysates (53).…”

Intubation-mediated Intratracheal (IMIT) Instillation: A Noninvasive, Lung-specific Delivery System

“…While relatively simple, caveats such as instillation volume and type of anesthesia used can impact the efficiency of instillation into the LRT via intranasal inoculation [3][4][5] . Specifically, Miller et al have shown that intranasal instillation of Francisella tularensis in volumes less than 50 µl did not result in instillation of the bacteria into the LRT 6 . They further observed better LRT instillation when using inhaled isoflurane as opposed to injected ketamine/xylazine for anesthesia.…”

Noninvasive Intratracheal Intubation to Study the Pathology and Physiology of Mouse Lung

“…Various methods have been used by a number of investigators in different settings to deliver materials of interest to mouse lungs, including inhalation, intranasal instillation, intratracheal instillation, and intratracheal intubation [1][2][3][4] . The latter procedure has not been routinely used because it is considered rather difficult to perform.…”