Necrotizing Mediastinitis With Lactobacillus plantarum
The origin of the abscess in our patient was difficult to identify, but we suspect the most likely source to have been his oropharyngeal flora. Mediastinal abscess formation is known to be closely related to cervical abscess development and in this case appeared to be comprised of polymicrobial infectious organisms resembling isolates from the neck abscess. It was reasonable to consider the infectious source in this case to most likely have been the oropharyngeal lumen in the view of both the neck abscess and DNM. If so, in this case, the mediastinal abscess was due not only to L. plantarum but also to F. necrophorum, P. melanogenica, and Str. anginosus/milleri groups, cultured from the neck abscess before the diagnosis of DNM. However, only L. plantarum was obtained from the mediastinal abscess. No L. plantarum was isolated from the neck abscess. It was unclear why only L. plantarum was isolated from the mediastinal abscess by direct puncture via thoracic surgery.
We suspected that the phenomenon observed in this patient was attributable to the pharmacodynamics of antibiotics. We initially treated the neck abscess with meropenem, which effectively eradicated all of these isolates. Though we did not measure the MICs of neck isolates, according to previous records, the susceptibilities of organisms from the neck cultures to meropenem were (MIC90, μg/ml): F. necrophorum 0.25,P. melanogenica 0.25, and Str. anginosus/milleri groups 0.12. The MIC90 and MIC of L.plantarum obtained from thoracic surgery (0.5) did not differ significantly. If there was no difference in antibiotic shift into tissue between the neck and mediastinal abscesses, L. plantarum would also be eradicated, along with the other organisms isolated, by meropenem. However, only L. plantarum was isolated from the surgical specimen, despite using the same culture method as that employed for the neck abscess. Though the majority of DNM cases are attributed to polymicrobial infection and we obtained other isolates which may have been involved in DNM from the neck site, we concluded that L. plantarum alone may have been responsible for the present mediastinal abscess.
On the other hand, lactate production and the resulting pH decreasing are powerful antimicrobial activities of Lactobacillus spp. against other microorganisms. Among these secies, L. plantarum can produce not only lactate but also hydrogen peroxide, providing protection from manganese catalase but not hem catalase. We thus speculated that a high concentration of hydrogen peroxide produced by L. plantarum inhibited the growth of other microorganisms in mediastinal lymph nodes.
Discussion
The origin of the abscess in our patient was difficult to identify, but we suspect the most likely source to have been his oropharyngeal flora. Mediastinal abscess formation is known to be closely related to cervical abscess development and in this case appeared to be comprised of polymicrobial infectious organisms resembling isolates from the neck abscess. It was reasonable to consider the infectious source in this case to most likely have been the oropharyngeal lumen in the view of both the neck abscess and DNM. If so, in this case, the mediastinal abscess was due not only to L. plantarum but also to F. necrophorum, P. melanogenica, and Str. anginosus/milleri groups, cultured from the neck abscess before the diagnosis of DNM. However, only L. plantarum was obtained from the mediastinal abscess. No L. plantarum was isolated from the neck abscess. It was unclear why only L. plantarum was isolated from the mediastinal abscess by direct puncture via thoracic surgery.
We suspected that the phenomenon observed in this patient was attributable to the pharmacodynamics of antibiotics. We initially treated the neck abscess with meropenem, which effectively eradicated all of these isolates. Though we did not measure the MICs of neck isolates, according to previous records, the susceptibilities of organisms from the neck cultures to meropenem were (MIC90, μg/ml): F. necrophorum 0.25,P. melanogenica 0.25, and Str. anginosus/milleri groups 0.12. The MIC90 and MIC of L.plantarum obtained from thoracic surgery (0.5) did not differ significantly. If there was no difference in antibiotic shift into tissue between the neck and mediastinal abscesses, L. plantarum would also be eradicated, along with the other organisms isolated, by meropenem. However, only L. plantarum was isolated from the surgical specimen, despite using the same culture method as that employed for the neck abscess. Though the majority of DNM cases are attributed to polymicrobial infection and we obtained other isolates which may have been involved in DNM from the neck site, we concluded that L. plantarum alone may have been responsible for the present mediastinal abscess.
On the other hand, lactate production and the resulting pH decreasing are powerful antimicrobial activities of Lactobacillus spp. against other microorganisms. Among these secies, L. plantarum can produce not only lactate but also hydrogen peroxide, providing protection from manganese catalase but not hem catalase. We thus speculated that a high concentration of hydrogen peroxide produced by L. plantarum inhibited the growth of other microorganisms in mediastinal lymph nodes.
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