Comparison and evaluation of experimental mediastinitis models: precolonized foreign body implants and bacterial suspension inoculation seems promising

Adjunctive Hyperbaric Oxygen Therapy or Alone Antibiotherapy? Methicillin Resistant Staphylococcus aureus Mediastinitis in a Rat Model

OBJECTIVE

In the post-sternotomy mediastinitis patients, Staphylococcus aureus is the pathogenic microorganism encountered most often. In our study, we aimed to determine the efficacy of antibiotic treatment with vancomycin and tigecycline, alone or in combination with hyperbaric oxygen treatment, on bacterial elimination in experimental S. aureus mediastinitis.

METHODS

Forty-nine adult female Wistar rats were used. They were randomly divided into seven groups, as follows: non-contaminated, contaminated control, vancomycin, tigecycline, hyperbaric oxygen, hyperbaric oxygen + vancomycin and hyperbaric oxygen + tigecycline. The vancomycin rat group received 10 mg/kg/day of vancomycin twice a day through intramuscular injection. The tigecycline group rats received 7 mg/kg/day of tigecycline twice a day through intraperitoneal injection. The hyperbaric oxygen group underwent 90 min sessions of 100% oxygen at 2.5 atm pressure. Treatment continued for 7 days. Twelve hours after the end of treatment, tissue samples were obtained from the upper part of the sternum for bacterial count assessment.

RESULTS

When the quantitative bacterial counts of the untreated contaminated group were compared with those of the treated groups, a significant decrease was observed. However, comparing the antibiotic groups with the same antibiotic combined with hyperbaric oxygen, there was a significant reduction in microorganisms identified (P<0.05). Comparing hyperbaric oxygen used alone with the vancomycin and tigecycline groups, it was seen that the effect was not significant (P<0.05).

CONCLUSION

We believe that the combination of hyperbaric oxygen with antibiotics had a significant effect on mediastinitis resulting from methicillin-resistant Staphylococcus aureus. Methicillin-resistant Staphylococcus aureus mediastinitis can be treated without requiring a multidrug combination, thereby reducing the medication dose and concomitantly decreasing the side effects.

Linking neuron and skin: matrix metalloproteinases in amyotrophic lateral sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) mainly affects the motor neurons but may also include other organs such as the skin. We aimed to determine whether matrix metalloproteinases could provide a link between neuronal degeneration and skin alterations in ALS. We measured CSF, serum and skin tissue MMP-2 and MMP-9 using ELISA and malondialdehyde (MDA), a marker of lipid peroxidation, using High Performance Liquid Chromatography (HPLC) in 54 ALS patients and 36 controls. We found CSF and skin MMP-9 to be elevated in ALS as compared to controls (p<0.001, p=0.03, respectively). We observed CSF MMP-9 to be highest in patients with a rapid progressive course of disease (p=0.008). In contrast, we found no significant differences of CSF, serum or skin concentrations of MMP-2 as compared to controls. CSF MMP-2 concentrations decreased with duration of disease (p=0.04, R=-0.31). MDA was elevated in serum of ALS (p<0.001), though no correlation with MMP-2 or MMP-9 was observed. Our findings indicate a general upregulation of MMP-9 in ALS. MMP-9 seems to play a role in both neurodegeneration and skin changes in ALS and could thus be a common factor linking otherwise distant aspects of disease pathology.

Staphylococcus aureus mediastinitis and sternal osteomyelitis following median sternotomy in a rat model

OBJECTIVES

Median sternotomy (MS) wound infections are severe complications causing high morbidity and mortality after cardiac surgery. We aimed to develop a new Staphylococcus aureus mediastinitis and sternal osteomyelitis model in rats that can be used to evaluate the efficacy of new antimicrobial treatments.

METHODS AND RESULTS

A complete MS wound was induced in anaesthetized rats. S. aureus was injected into the sternum. Kinetics of bacterial growth in the sternum (10(7) cfu/sternum) was assessed for histopathology and bacterial counts. A non-infected MS group served as a control. To evaluate antibiotic efficacy, 5 days of intraperitoneal vancomycin therapy (50 mg/kg, twice a day) was initiated 24 h following bacterial challenge. Macroscopic and histological examination confirmed that infection resulted in sternitis and mediastinitis. S. aureus bacterial counts in the sternum were inoculum-dependent, and it was proven that infecting rats with an inoculum of 10(7) cfu/sternum induced mediastinitis and sternal osteomyelitis. At this inoculum, bacterial counts in the infected sternum increased with time, reaching a maximum level of 2 +/- 1 x 10(7) cfu/g of sternum 8-12 days post-infection and then decreased with time to 2 x 10(4) cfu/g of sternum 20 days after infection. Histological changes paralleled bacterial counts. Vancomycin administration showed a protective effect against induction of sternal osteomyelitis; sternums from vancomycin-treated rats showed a significant decrease in S. aureus counts by 0.72 +/- 0.35 log cfu/g compared with untreated controls (P = 0.0162).

CONCLUSIONS

This new rat model of S. aureus sternal osteomyelitis and mediastinitis allows quantitative measurement of bacterial counts in the sternum. This model is reproducible and simple and thus suitable for the evaluation of new antimicrobials and new treatment modalities in MS infections.