A RAT MODEL OF POLYPROPYLENE GRAFT INFECTION CAUSED BY STAPHYLOCOCCUS EPIDERMIDIS

The effect of different types of honey on healing infected wounds

OBJECTIVE:

To investigate the effects of treatments of 'mad honey', blossom honey and nitrofurazone on infected wound healing.

METHOD:

Male albino Wistar rats were randomly divided into four groups: 'mad honey' (MH), blossom honey (BH), nitrofurazone (N) and control (C). All rats were anaesthetised intraperitoneally. A circular skin incision was made to the back regions. Grafts containing slime-producing Staphylococcus epidermidis were placed on the incision area and then sutured to the skin. Infection in the wound area was confirmed after 48 hours. Wounds were dressed twice daily with the various treatment materials. Rats were randomly euthanised on days 7 or 14, and tissue samples taken. Tissue samples were assessed for hydroxyproline (HP), tensile strength (TS) and macroscopic measurement (area and intensity).

RESULTS:

HP levels were higher in the treatment groups (MH, BH, N) at days 7 and 14 compared with the control group. 'Group x day' interaction was found in the HP levels (p=0.015). Increases in HP levels in the MH and N groups between days 7 and 14 were significantly higher than those in the other groups (p<0.05). Intensity was significantly lower in the control group and significantly higher in group MH compared with the other groups. Significant 'group x day' interaction was observed in intensity (p=0.006). TS was significantly lower on day 7 than on day 14 (p=0.022). No marked difference was observed between the groups, nor any 'group x day' interaction, in terms of TS.

CONCLUSION:

Honey administration successfully healed infected wounds. However, there was no significant difference between the effect of MH and that of N in terms of wound healing.

Do Nano-crystalline Silver-Coated Hernia Grafts Reduce Infection?

PURPOSE

Inguinal hernia repairs are the most common interventions in adults in general surgery clinics. Depending on the type of mesh and repair, the incidence of mesh-related infection ranges from 0.6 to 8%. Methicillin-resistant Staphylococcus aureus is the most common microorganism causing graft infection. The aim of this study was to investigate the efficacy of nano-crystalline silver-coated polypropylene grafts against graft infection created with MRSA in rats.

METHODS

A total of 60 female, Wistar albino rats were used in the study. Polypropylene grafts 1 × 1 cm in size were coated in silver ion-doped, calcium phosphate-based, antibacterial ceramic powder (NS-coated graft) to provide an antimicrobial effect. The MRSA seeding procedure was applied at the same time as surgery. In Group 1, normal graft was applied without MRSA seeding, in Group 2, normal graft with MRSA seeding, in Group 3, NS-coated graft without MRSA seeding, and in Group 4, NS-coated graft with MRSA seeding. For the groups which were to be infected, the bacteria were seeded in the surgical area during the operation. On the 7th day postoperatively, all the animals were killed. The grafts were removed and one from each group was examined under electron microscope and the others were implanted in culture medium and the number of colonies was counted after 24 h.

RESULTS

In Groups 1 and 3, the incision site was seen to have healed on day 3, no clinical surgical area infection was seen during follow-up, and in the exploration made on the 7th day, no findings of infection were observed. In Group 2, hyperemia and collection were seen to have formed on day 3, abscess had started to form in all the rats of this group on day 4, a purulent discharge in the wound site had started in 12 animals on day 5, separation of the wound site was observed in 6 on day 6, and in the exploration on day 7, there was seen to be a fibrin and pus-rich collection around the graft in all cases. In Group 4, there were hyperemia and collection in 6 animals on day 4, and in 3 of these, abscess was seen to have formed on the 5th day. No purulent discharge or wound separation was observed. In the exploration on the 7th day, it was seen that in the animals with abscess development, the formation was of a localized abscess. The results of the cultures of the grafts removed from Groups 1 and 3 showed no production, whereas production was seen in all the grafts removed from Groups 2 and 4. Clinical surgical area infection was seen to have developed in 100% of Group 2 and in 40% of Group 4. In the comparison of the number of colonies, a statistically significantly lower number of bacteria were determined in Group 4 compared to Group 2 (p < 0.05). In the SEM images taken of Group 2, bacteria clusters were seen attached to the graft.

CONCLUSION

Consistent with previous findings in the literature, the NS-coated polypropylene graft was seen to have a significantly better bactericidal effect than the normal polypropylene graft. Development of NS-coated grafts seems to be a reliable and applicable method to reduce the incidence of postoperative graft infection.

Use of an experimental model to evaluate infection resistance of meshes in abdominal wall surgery

BACKGROUND

Staphylococcal species are the most common organisms causing prosthetic mesh infections, however, infections due to rapidly growing mycobacteria are increasing. This study evaluates the resistance of biomaterial for abdominal wall prostheses against the development of postoperative infection in a rat model.

MATERIAL AND METHODS

In 75 rats, we intramuscularly implanted three different types of prostheses: (1) low-density polypropylene monofilament mesh (PMM), (2) high-density PMM, and (3) a composite prosthesis composed of low-density PMM and a nonporous hydrophilic film. Meshes were inoculated with a suspension containing 10⁸ colony-forming units of Staphylococcus aureus, Staphylococcus epidermidis, Mycobacterium fortuitum, or Mycobacterium abscessus before wound closure. Animals were sacrificed on the eighth day postoperatively for clinical evaluation, and the implants were removed for bacteriologic analyses.

RESULTS

Prostheses infected with S aureus showed a higher bacterial viability, worse integration, and clinical outcome compared with infection by other bacteria. Composite prostheses showed a higher number of viable colonies of both M fortuitum and Staphylococcus spp., with poorer integration in host tissue. However, when the composite prosthesis was infected with M abscessus, a lower number of viable bacteria were isolated and a better integration was observed compared with infection by other bacteria.

CONCLUSIONS

Considering M abscessus, a smaller collagen-free contact surface shows better resistance to infection, however, depending on the type of bacteria, prostheses with a large surface, and covered with collagen shows reduced resistance to infection, worse integration, and worse clinical outcome.

Modeling Staphylococcus epidermidis-Induced Non-Unions: Subclinical and Clinical Evidence in Rats

S. epidermidis is one of the leading causes of orthopaedic infections associated with biofilm formation on implant devices. Open fractures are at risk of S. epidermidis transcutaneous contamination leading to higher non-union development compared to closed fractures. Although the role of infection in delaying fracture healing is well recognized, no in vivo models investigated the impact of subclinical low-grade infections on bone repair and non-union. We hypothesized that the non-union rate is directly related to the load of this commonly retrieved pathogen and that a low-grade contamination delays the fracture healing without clinically detectable infection. Rat femurs were osteotomized and stabilized with plates. Fractures were infected with a characterized clinical-derived methicillin-resistant S. epidermidis (10³, 10⁵, 10⁸ colony forming units) and compared to uninfected controls. After 56 days, bone healing and osteomyelitis were clinically assessed and further evaluated by micro-CT, microbiological and histological analyses. The biofilm formation was visualized by scanning electron microscopy. The control group showed no signs of infection and a complete bone healing. The 10³ group displayed variable response to infection with a 67% of altered bone healing and positive bacterial cultures, despite no clinical signs of infection present. The 10⁵ and 10⁸ groups showed severe signs of osteomyelitis and a non-union rate of 83–100%, respectively. The cortical bone reaction related to the periosteal elevation in the control group and the metal scattering detected by micro-CT represented limitations of this study. Our model showed that an intra-operative low-grade S. epidermidis contamination might prevent the bone healing, even in the absence of infectious signs. Our findings also pointed out a dose-dependent effect between the S. epidermidis inoculum and non-union rate. This pilot study identifies a relevant preclinical model to assess the role of subclinical infections in orthopaedic and trauma surgery and to test specifically designed diagnostic, prevention and therapeutic strategies.

Bacterial adherence to different meshes used in abdominal surgery

BACKGROUND

We studied the influence of morphology and type of material of abdominal wall prostheses in the avoidance of bacterial adhesion in acute and chronic mesh infections.

METHODS

Three different types of prostheses were compared: 1) High-density polypropylene monofilament mesh (PMM); 2) low-density PMM; and 3) prostheses composed of low-density polypropylene and a non-porous hydrophilic film (composite prostheses). Microbial adhesion tests were performed using reference strains of Staphylococcus aureus 15981, Staphylococcus epidermidis ATCC 35984, Mycobacterium abscessus DSM 44196, and Mycobacterium fortuitum ATCC 13756 using a protocol described previously.

RESULTS

Both Staphylococcus spp. and M. fortuitum strains showed lower adherence to PMM. Mycobacterium abscessus also exhibited lower adherence to composite prostheses. Both Mycobacterium spp. strains had lower adherence than Staphylococcus spp. strains for all materials except for low-density PMM. Mycobacterium fortuitum showed higher adherence to composite prostheses than M. abscessus, whereas the latter species had higher adherence to high-density PMM than M. fortuitum.

CONCLUSION

Depending on the type of bacteria, collagen-coated hydrophilic prostheses with a large surface increased bacterial adherence significantly. These differences should be taken into consideration when choosing a mesh graft, which limits infection in abdominal wall reconstruction.

Comparison of the adherence of E.Coli and S. Aureus to ten different prosthetic mesh grafts: In vitro experimental study

BACKGROUND

The prosthetic mesh grafts used to repair the abdominal wall may become infected, primarily by S. aureus and E. coli. This study sought to provide a rational basis for the choice of mesh used to repair a hernia when there is a likelihood of infection or contamination.

METHODS

S. aureus and E. coli were incubated with ten types of prosthetic mesh graft (Table 1) in liquid growth medium. After sequential dilution of samples from the prosthetic mesh grafts, the colony forming units of adherent S. aureus and E. coli were counted.

RESULTS

There was no significant difference in the numbers of E. coli and S. aureus adherent to simple polypropylene mesh grafts. Significantly more of both species were adherent to the polyester, expanded polytetrafluoroethylene (ePTFE), and composite prosthetic mesh grafts, except for E. coli on graft 5. Significantly fewer E. coli were adherent to composite mesh grafts 5, 8, and 10 than S. aureus.

CONCLUSION

S. aureus and E. coli adhere to polypropylene similarly. In vitro, fewer S. aureus and E. coli adhere to simple polypropylene mesh grafts than to polyester, ePTFE, or composite prosthetic mesh grafts.