Experimental whole gut irrigation in the rat

Animal models of Klebsiella pneumoniae mucosal infections

Klebsiella pneumoniae is among the most relevant pathogens worldwide, causing high morbidity and mortality, which is worsened by the increasing rates of antibiotic resistance. It is a constituent of the host microbiota of different mucosa, that can invade and cause infections in many different sites. The development of new treatments and prophylaxis against this pathogen rely on animal models to identify potential targets and evaluate the efficacy and possible side effects of therapeutic agents or vaccines. However, the validity of data generated is highly dependable on choosing models that can adequately reproduce the hallmarks of human diseases. The present review summarizes the current knowledge on animal models used to investigate K. pneumoniae infections, with a focus on mucosal sites. The advantages and limitations of each model are discussed and compared; the applications, extrapolations to human subjects and future modifications that can improve the current techniques are also presented. While mice are the most widely used species in K. pneumoniae animal studies, they present limitations such as the natural resistance to the pathogen and difficulties in reproducing the main steps of human mucosal infections. Other models, such as Drosophila melanogaster (fruit fly), Caenorhabditis elegans, Galleria mellonella and Danio rerio (zebrafish), contribute to understanding specific aspects of the infection process, such as bacterial lethality and colonization and innate immune system response, however, they but do not present the immunological complexity of mammals. In conclusion, the choice of the animal model of K. pneumoniae infection will depend mainly on the questions being addressed by the study, while a better understanding of the interplay between bacterial virulence factors and animal host responses will provide a deeper comprehension of the disease process and aid in the development of effective preventive/therapeutic strategies.

A comparative histopathologic evaluation of the effects of three different solutions used for whole bowel irrigation: an experimental study

PURPOSE

Although whole bowel irrigation (WBI) is a widely used method of bowel preparation in daily surgical practice, almost nothing is known about the histopathologic alterations caused by WBI and whether these differences have any detrimental effect on the outcome of gastrointestinal surgical procedures. Therefore, an experimental study has been conducted to evaluate and compare the effects of WBI with various solutions on the histology of gastrointestinal tract.

METHODS

During the experimental procedures animals were divided into 4 groups consisting of 8 animals each as follows: group A, WBI performed by using isotonic saline solution; group B, WBI performed by using an isoosmolar solution containing polyethylene glycol (PEG); group C, WBI performed by using Lactated Ringer's solution; group D, Animals that were not irrigated but sham operations that were performed served as controls. Four hours after WBI the animals underwent laparotomy and a segment of transverse colon with intact vascular peduncle was prepared. After waiting for 30 minutes, specimens from duodenum, small intestine, large bowel, colonic segment, and liver were obtained from each animal. Histopathologically, all of the specimens were evaluated and graded by 3 parameters including congestion, edema, and inflammation.

RESULTS

Although varying degrees of congestion, edema, and inflammation were encountered from all of the specimens of group A, B, and C, only slight congestion was noted in all specimens of group D. The difference between group D and other groups was statistically very significant (P < .001). When the sections from duodenums of groups were evaluated, the degree of congestion, edema, and inflammation were found to be moderate in group B, mild-moderate in group A, and mild in group C. Histopathologic examinations of specimens of the small, large bowel, and isolated colonic segment showed severe congestion, edema, and inflammation in group A, moderate-mild in group B, and mild in group C. The difference between A and B, A and C, and A and D was statistically significant (P < .01). Although severe congestion was encountered in liver specimens of group A, only mild congestion was encountered in groups B and C (P= .0001). The matched durations of irrigations and total volume of irrigation solutions were found to be not related with the difference in histopathologic findings.

CONCLUSIONS

WBI has induced varying degrees of histopathologic alterations from mild to severe in the rat gastrointestinal tract. Lactated Ringer's solution and PEG solution have induced the least alterations. Therefore, WBI with Lactated Ringer's solution and PEG solution seem to be safe alternatives of mechanical bowel preparation before elective large bowel surgery. Because saline solution has caused detrimental alterations in distal gastrointestinal tract histology, WBI with saline solution seems to be unadvisable.

Escherichia coli K12 does not colonize the gastrointestinal tract of Fischer-344 rats

The colonizing potential of Escherichia coli K12 containing a vector coding for somidobove (bovine somatotropin) was determined. Treated male and female Fischer-344 rats were given a single oral gavage inoculum of sucrose with/without tetracycline (15 micrograms/ml). Untreated control animals received similar drinking water regimes. All animals survived until termination. There were no clinical signs of toxicity observed and no treatment-related effect upon body weight, food consumption, or efficiency of food utilization. Fresh fecal samples were collected from each rat every 24 h following inoculation and the population of the marked strain was quantitated until no bacterial colonies were observed for two consecutive days. While all inoculated rats were positive at 24 h, by 72 and 96 h all had become negative for the test (marked) strain, as were the corresponding control group throughout the test. The frozen stock of the marked strain used as the positive control demonstrated that the agar plates were selective for the test strain. Fourteen days following inoculation, all groups of rats were killed and the gastrointestinal tracts removed and treated to recover the marked strain. There was no evidence of the marked strain in the gastrointestinal tract of any from any group. Thus, the E. coli K12 host/vector system used in this experiment does not colonize the gastrointestinal tract of Fischer-344 rats.

Trimethoprim used for selective decontamination of the digestive tract in rats: possible route of excretion

Selective elimination of Enterobacteriaceae species from the digestive tract of rats has been accomplished by oral treatment with trimethoprim (235 mg/kg body weight/day) within 6 days. In the present study it was investigated whether this elimination was mainly due to antimicrobial activity of trimethoprim excreted with the gastrointestinal mucus or mainly by non-absorbed trimethoprim in the lumen contents. By means of whole gut irrigation (WGI) the lumen contents were washed out, followed by mucosa-associated flora. The concentration of the mucosa-associated Enterobacteriaceae remained at least 10(1)/ml as measured in the last samples of rectal effluent during WGI in untreated rats. During trimethoprim treatment, however, the amount of mucosa-associated Enterobacteriaceae had decreased significantly more (p less than 0.05) compared with the Enterobacteriaceae present in the lumen contents of the gastrointestinal tract (photospectrometrically measured by the color of the rectal effluent). No difference was observed in the concentration of mucosa-associated enterococci in the rectal effluent of trimethoprim treated and untreated rats. It is concluded that orally administered trimethoprim may be predominantly active against Enterobacteriaceae associated with the mucous blanket.