Bezold's abscess.

Intra-abdominal infections (IAI) continue to be a serious clinical problem. Bacterial synergism is an important factor that influences the shift from contamination to IAI, leading to the development of lesions and abscess formation. Escherichia coli and Bacteroides fragilis are particularly abundant in IAI. The underlying molecular mechanisms of this pathogenic synergy are still unclear. The role of the hemoglobin protease (Hbp) autotransporter protein from E. coli in the synergy of IAI was investigated. Hbp is identical to Tsh, a temperature-sensitive hemagglutinin associated with avian pathogenic E. coli. Clinical isolates from miscellaneous extraintestinal infections were phenotypically and genotypically screened for Hbp. The presence of Hbp was significantly associated with E. coli isolated from IAI and other extraintestinal infections. In a murine infection model, Hbp was shown to contribute to the pathogenic synergy of abscess development. Mice immunized with Hbp were protected against mixed infections and did not develop abscess lesions. Furthermore, an E. coli wild-type strain that did not induce abscess formation in the synergy model was transformed with a plasmid encoding the hbp gene, and mixed infections with this strain lead to increased growth of B. fragilis and induction of abscess lesions. Growth-promoting studies showed that purified Hbp is able to deliver heme to B. fragilis strain BE1. In conclusion, results suggest the synergy of abscess formation by E. coli and B. fragilis can be partly explained by the capacity of B. fragilis to intercept Hbp and iron from heme to overcome the iron restrictions imposed by the host.

Abscess↗

PubMed2002

Nonenhancing tissue on MR imaging of pedal infection: characterization of necrotic tissue and associated limitations for diagnosis of osteomyelitis and abscess.

OBJECTIVE: We studied the frequency, location, extent, and signal characteristics of nonenhancing tissue in pedal infections and correlated those areas with surgical and histologic findings. MATERIALS AND METHODS: One hundred ten contrast-enhanced 1.5-T MR imaging foot examinations in 102 patients (28 women, 74 men; mean age, 59 years), 82% of whom had diabetes mellitus, were reviewed by two musculoskeletal radiologists for the presence of areas without recognizable enhancement. The number, size, location, signal characteristics, and enhancement ratio of nonenhancing regions were noted. MR imaging findings were compared with surgical and histology reports. RESULTS: Nonenhancing regions were found in 27 feet (24.5%, 96.3% in diabetic patients, p = 0.032) at the forefoot (n = 16), toes (n = 8), and heel (n = 3). The mean size of the nonenhancing regions was 4.1 x 2.7 x 1.4 cm. Signal characteristics on T1-weighted images were isointense to muscle (n = 21, 77.8%), hypointense to muscle (n = 3, 11.1%), heterogeneous (n = 2, 7.4%), and isointense to fat (n = 1, 3.7%). On T2-weighted images, the signal was hyperintense to muscle (n = 12, 44.4%), heterogeneous to muscle (n = 9, 33.3%), equal to fluid (n = 3, 11.1%), and hypointense to muscle (n = 3, 11.1%). The mean signal increase after contrast administration was 3.57% for observer 1 and 2.68% for observer 2. Necrotic tissue was surgically confirmed in the nonenhancing areas in 26 feet (96.3%). Five abscesses and three cases of osteomyelitis were misdiagnosed on MR images because of lack of enhancement. CONCLUSION: Nonenhancing areas are seen in one fourth of pedal infections, occur almost exclusively in diabetic patients, and represent necrotic tissue. Only contrast-enhanced images allow reliable recognition of these regions. Lack of enhancement in these areas can mask the presence of abscess and osteomyelitis.

Abscess↗