Isolation of Actinomyces species and Eikenella corrodens from patients with chronic diffuse sclerosing osteomyelitis

Chronic Osteomyelitis of the Jaw: Pivotal Role of Microbiological Investigation and Multidisciplinary Management—A Case Report

A 15-year-old girl with a history of recurrent painful orofacial swelling was diagnosed on the basis of clinical findings, histopathological examination and imaging modalities as having primary chronic osteomyelitis of the jaw. Initial microbiological samples were performed but were inconclusive. She received multiple empirical antibiotic therapies and NSAIDs for 3 years without complete remission. Only MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization–Time Of Flight) analysis after additional multiple microbiological bone samples with adequate techniques yielded the final diagnosis of bacterial chronic osteomyelitis of the jaw. Its management requires a multidisciplinary approach, involving oral and maxillofacial surgeons, infectiologists and microbiologists, to limit treatment failure. Antibiotic therapy without surgery for 6 months achieved the complete radiographic resolution of the CBCT (Cone Beam Computed Tomography) and the normalization of laboratory tests. After 2 years of follow-up, no relapse had been reported. Modern microbiological investigation and sampling techniques are critical for the accurate diagnosis and management of osteomyelitis of the jaw, especially in unusual and clinically misleading forms of this infection.

Targeted histological evaluation shows high incidence of actinomyces infection in medication-related osteonecrosis of the jaws

Medication-Related Osteonecrosis of the Jaws (MRONJ) is a difficult-to-treat complication of the therapy of osteoporosis and some malignancies cured with bisphosphonates and antiresorptive drugs. The pathomechanism is unclear, but there is increasing observation that Actinomyces infection may play a role in its development and progression. The aim of our study was to demonstrate that histological examination using a validated triple staining procedure for Actinomyces bacteria strains can detect a high rate of Actinomyces infection in patient's samples with MRONJ. 112 previously hematoxylin-eosin (HE) stained samples submitted with the clinical diagnosis of MRONJ were re-evaluated histologically using an appropriate triple special staining validated for the identification of Actinomyces infection. During the first evaluation, when pathologists did not specifically look for Actinomyces, only 8.93% of the samples were reported as positive. In contrast, re-evaluation with triple staining provided a yield of 93.7% positive samples, therefore, we suggest the triple special staining to be standard in MRONJ histology evaluation. These results show that if the clinician suspects Actinomyces infection and brings this to the attention of the pathologist, it could significantly increase the number of correct diagnoses. It serves as an aid for clinicians in therapeutic success of MRONJ by selecting a long-term adequate antibiotic medication which is suitable for the elimination of actinomyces infection.

Head and neck infections in children due to Eikenella corrodens: Report of three cases and review of literature

INTRODUCTION

Eikenella corrodens is a small, nonmotile Gram-negative rod that is part of the normal flora in the mouth, upper respiratory, gastrointestinal, and genitourinary tracts. It is classically found in human bite (fist to mouth) infections but is also seen in respiratory tract and head and neck infections.

METHODS

We describe three cases of E. corrodens causing head and neck infections in children seen in our institution between 2013 and 2019. We also reviewed the available literature on pediatric head and neck infections caused by E. corrodens.

RESULTS

All 3 children recovered and fit the trends identified in the 58 patients published in the literature from 1976 to 2019.

CONCLUSIONS

E. corrodens is responsible for a range of head and neck infections in pediatric patients. It is a not infrequent cause of head and neck infections in children and should be considered when selecting presumptive antibiotic therapy.

Surgical Management of Primary Chronic Osteomyelitis of the Jaws: The Use of Computer-Aided-Design/Computer-Aided Manufacturing Technology for Segmental Mandibular Resection

The term osteomyelitis of the jaws identifies different pathological patterns characterized by the involvement of the cortical bone and bone marrow in osteoarticular infections.At the head and neck level, the segment most affected by osteomyelitis is the mandible and in most of the cases the cause of the infection is bacterial, as a result of pulp or periodontal infections, post-extraction alveolitis, foreign bodies and fractures. The mandibular PCO often presents with an insidious onset, without a striking acute phase, and it is characterized by recurrent episodes of pain, swelling, lockjaw, latero-cervical lymphadenopathy, without signs of suppuration.Three patients have been collected and recorded for the study.The authors believe that in the more advanced cases of PCO in adult patients, in which the mandibular bone appears almost entirely sclerotic and deformed, and that are not responsive to pharmacological therapy or to conservative surgical therapies such as decortication, it is necessary to perform a complete removal of the portion affected by osteomyelitis, with lower alveolar nerve preservation and contextual reconstruction with free microvascular bone flap.Our review aims to describe the clinico-pathological features of a rare pathological entity, propose a surgical treatment algorithm using computer-aided-design/computer-aided manufacturing technology and review the existing literature.

"Holes" in the Jaw-A Report of Two Cases of Periapical Actinomycosis

Periapical actinomycosis is a relatively rare form of cervicofacial actinomycosis, which typically involves the periapical region with subsequent potential spread to the jaw bones. We hereby present two cases of periapical actinomycosis. Both patients presented with jaw pain and "holes" in their gum and lacked the characteristic clinical features commonly seen in cervicofacial actinomycosis such as jaw mass, draining ulcers, sinuses and fistulae. The first patient was an immunocompetent host with chronic stable medical conditions but with a rather bad dentition requiring multiple recent teeth extractions. The second patient was edentulous, had refractory multiple myeloma, was on low-dose chronic steroids and pomalidomide therapy and therefore relatively immunocompromised. Both cases of actinomycosis were diagnosed by jaw bone histopathology, which showed characteristic sulfur granules and embedded Actinomyces-like organisms. The two patients had excellent clinical response to six months of penicillin therapy without any need for surgical intervention. The cases remind clinicians of including actinomycosis in the differential diagnosis of periapical lesions and illustrates the possibility of achieving cure with non-surgical treatment.

Microbiology of Acute and Chronic Osteomyelitis and Antibiotic Treatment

Osteomyelitis is an inflammation of bone marrow with a tendency for progression, involving the cortical plates and often periosteal tissues, with most cases occurring after trauma to bone or bone surgery or secondary to vascular insufficiency. Antimicrobial therapy and surgical débridement are the primary modalities of osteomyelitis treatment, although often it is associated with a prolonged course, requiring a large commitment between patient and clinician as well as sizable health care costs. Despite surgical and chemotherapeutic advancements, osteomyelitis remains difficult to treat, and no universally accepted protocol for treatment exists.

Subcutaneous Eikenella corrodens, Actinomyces sp., and α-Hemolytic Streptococcus Abscess of the Thigh following a Vitamin B12 Injection

This case report describes a 38-year-old female presenting with a thigh abscess caused by Eikenella corrodens, Actinomyces sp., and α-hemolytic Streptococcus following an intramuscular vitamin B12 injection administered at an outpatient clinic. After failure to improve clinically with intravenous daptomycin and after visualization of the abscess with gas bubbles on CT scan, she was taken to the operating room for three separate surgical irrigation and debridement procedures. Treatment also included intravenous ampicillin/sulbactam followed by oral amoxicillin/clavulanic acid therapy. She remained symptom free and without infection at nine months following hospitalization. It was suspected that poor hygiene played a role in the infection, but a definitive cause was not identified.

Juvenile Mandibular Chronic Osteomyelitis: Role of Surgical Debridement and Antibiotics

PURPOSE

To document outcomes of management of juvenile mandibular chronic osteomyelitis (JMCO) using a standardized treatment protocol including open biopsy, decortication, microbial culture, and long-term antibiotic therapy.

MATERIALS AND METHODS

This was a retrospective case study of pediatric patients with JMCO treated at Massachusetts General Hospital for Children from 1996 through 2014. Inclusion criteria included age younger than 18 years, diagnosis of JMCO, management by the protocol, adequate clinical and radiographic data in the record, and follow-up of at least 1 year after initial treatment. Inpatient and outpatient records were reviewed for demographics, clinical and radiographic findings, and histologic and laboratory evaluations. The predictor variable was the standardized treatment protocol and the primary outcome variables were disease status at end of treatment and complications of treatment.

RESULTS

Twenty patients (mean age at onset, 10.7 yr; range, 3 to 14 yr) were treated, 12 (11 girls) of whom met the inclusion criteria. Management of all patients consisted of biopsy (extraoral when feasible, n = 9; intraoral, n = 3), decortication, cultures, and long-term antibiotic therapy. Nonsteroidal anti-inflammatory drugs (NSAIDs) were administered only as needed for pain control. There was complete resolution of osteomyelitis with no recurrence in 7 of 12 patients (mean follow-up, 4.3 yr; range, 1 to 11 yr). Five patients had partial responses, with decreased frequency and severity of disease recurrence. These were well controlled with short courses of antibiotics (4 to 12 weeks) with NSAIDs only as needed for pain control (mean follow-up, 1.4 yr; range, 1 to 3 yr). There were no major complications related to antibiotic therapy. Minor complications included rash (n = 2), nausea and vomiting (n = 1), and vaginal candidiasis (n = 1).

CONCLUSION

The results of this study indicate that 58.3% of patients were cured and had no recurrent symptoms (mean follow-up, 4.3 yr). The remaining patients continue on intermittent treatment with antibiotics for recurrent episodes of swelling and pain. Favorable responses to antibiotic therapy support the hypothesis that JMCO is an infectious disease and that negative cultures might represent a failure of standard culture techniques to isolate the responsible organisms.

Actinomycotic Osteomyelitis of Maxilla Presenting as Oroantral Fistula: A Rare Case Report

Actinomycosis is a chronic granulomatous infection caused by Actinomyces species which may involve only soft tissue or bone or the two together. Actinomycotic osteomyelitis of maxilla is relatively rare when compared to mandible. These are normal commensals and become pathogens when they gain entry into tissue layers and bone where they establish and maintain an anaerobic environment with extensive sclerosis and fibrosis. This infection spreads contiguously, frequently ignoring tissue planes and surrounding tissues or organ. The portal of entry may be pulpal, periodontal infection, and so forth which may lead to involvement of adjacent structures as pharynx, larynx, tonsils, and paranasal sinuses and has the propensity to damage extensively. Diagnosis is often delayed and is usually based on histopathology as they are cultured in fewer cases. The chronic clinical course without regional lymphadenopathy may be essential in diagnosis. The management of actinomycotic osteomyelitis is surgical debridement of necrotic tissue combined with antibiotics for 3-6 months. The primary actinomycosis arising within the maxilla with contiguous involvement of paranasal sinus with formation of oroantral fistula is rare. Hence, we present a 50-year-old female patient with chronic sclerosing osteomyelitis of maxilla which presented as oroantral fistula with suppurative and sclerotic features.

Surgical management of primary chronic osteomyelitis of the jaws in children: a prospective analysis of five cases and review of the literature

INTRODUCTION

Primary chronic osteomyelitis (PCO) of the jaws is an uncommon non-suppurative inflammatory disease of unknown origin. Although the disease is not age-specific, only sparse cases with onset during childhood or adolescence have been reported in the literature.

PURPOSE

This study seeks to present five cases of maxillofacial PCO in children and to evaluate the effectiveness of the applied therapeutic protocol. A review of the literature concerning diagnosis and treatment of PCO with special emphasis on surgical therapy is also performed.

PATIENTS AND METHODS

Demographic data, clinical, radiographic and histopathologic findings, blood tests results, and the treatment protocol applied to five young patients suffering from PCO and referred to the Department of Oral and Maxillofacial Surgery at "A. & P. Kyriakou Children's Hospital" over the past 5 years are presented. Decortication and contouring of the affected bone were performed; antibiotics were administered for a short period of time and the patients remained under follow-up evaluation.

RESULTS

The posterior mandible was affected in four cases and the maxilla-zygomatic bone in one case. All patients showed remission of signs and symptoms after surgical treatment. The postsurgical clinical course was uneventful in all cases. However, recurrences have been noted, as reported in the literature.

CONCLUSION

PCO of the jaws is a complex clinical entity, presenting both a diagnostic and therapeutic challenge, especially in young patients. Surgical treatment in conjunction with antibiotics and non-steroid anti-inflammatory drugs proved to be beneficial and to improve considerably the patients' quality of life. Nevertheless, exacerbation of the disease may appear and regular follow-up of the patients is required.

SAPHO syndrome with TMJ involvement: review of the literature and case presentation

Synovitis, acne, pustulosis, hyperostosis, osteitis (SAPHO) syndrome is a rare group of sterile, inflammatory osteoarticular disorders classically associated with skin manifestations. The etiology is unknown but probably involves genetic, infectious, and immunological components. The characteristic feature of the disease is found in the bone lesions, which typically involve the anterior chest wall and axial skeleton. In the literature review, six case reports discussed involvement of the TMJ. Treatment of SAPHO is geared toward symptom management as there is no cure. Surgery for mandibular lesions is usually a last resort as results are reported to be temporary with symptoms recurring within a year. Surgery appears to be performed early after diagnosis of TMJ related pathology; probably because lesions affecting the TMJ involve some limitation in mouth opening with varying degrees of ankylosis. The authors provide a literature review and describe a case of SAPHO syndrome with ankylosis of the left TMJ. The patient was treated with joint reconstruction using a patient-fitted total joint prosthesis (TMJ Concepts Inc., Ventura CA) in single stage surgery. This paper is the first to report maxillary involvement in SAPHO syndrome.

Diagnosis and classification of mandibular osteomyelitis

To establish a unified classification system for mandibular osteomyelitis, various diagnostic terms were critically assessed and clinicopathologic findings of the lesions were carefully reviewed. We recommend classifying mandibular osteomyelitis into bacterial osteomyelitis and osteomyelitis associated with the synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO) syndrome. Other diagnostic terms were excluded because they were not appropriate for classification. Diagnostic criteria for bacterial osteomyelitis are suppuration and osteolytic change. The lesions are easily cured by antibiotic treatments. Mandibular osteomyelitis in SAPHO syndrome is characterized by nonsuppuration and a mixed pattern on radiography, with solid type periosteal reaction, external bone resorption, and bone enlargement. The presence of osteomyelitis in other bones, arthritis, or skin diseases (palmoplantar pustulosis, pustular psoriasis, and acne) strongly suggests this syndrome. Antibiotic therapy is usually ineffective and the symptoms of SAPHO syndrome are often persistent.

Scanning and transmission electron microscopy demonstrates bacteria in osteoradionecrosis

According to the current concept of osteoradionecrosis such tissue has become hypoxic, hypovascular and hypocellular and it has previously failed to show any bacterial growth. By using a molecular method, i.e., DNA-DNA hybridization, the presence of microorganisms in radionecrotic bone has formerly been demonstrated by us. The aim of the present study was to visualise bacteria in such bone by using scanning and transmission electron microscopy. Fourteen deep medullar specimens from resected radionecrotic mandibles were studied. Microorganisms were detected in 9 of the 14 samples (64%). The bacteria seen included rods, spirochetes and cocci, with rods being the predominant cells. One sample also contained yeasts (blastoconida and pseudohyphae). The data from this study strongly suggest an association between microorganisms and osteoradionecrosis. This may call for a revision of its presumed pathophysiology, including the possibility of an infectious etiology.

Is primary chronic osteomyelitis a uniform disease? Proposal of a classification based on a retrospective analysis of patients treated in the past 30 years

INTRODUCTION

Primary chronic osteomyelitis of the jaw is a rare, non-suppurative, chronic inflammatory disease of unknown aetiology. To date, classification is confusing due to a non-uniform terminology. The aim of this study was to establish a simple (clinical) classification based on patient data from our clinic.

METHODS

Retrospective analysis revealed 30 cases of which clinical course, radiology, pathology, therapy and outcome were analysed.

RESULTS

Both sexes were equally represented. The mean age at onset of disease was 35 years (range 5-76 years). Onset of disease revealed two peaks of incidence, one in adolescence and one after age 50 years. While clinical symptoms were similar in all cases, an increased intensity of these symptoms was noted in younger individuals as well as in the early stages of the disease. Five adults and one adolescent presented with additional non facial bone, joint and skin manifestations consistent with the diagnosis of SAPHO (synovitis, acne, pustulosis, hyperostosis, osteitis) syndrome, or chronic recurrent multifocal osteomyelitis. Radiology demonstrated sclerosis, osteolysis and periosteal reaction in variable stages in all cases. However, findings were more extensive in younger patients. Histology revealed different stages of chronic inflammation in all cases. Microabscess formation was noted in 11 cases, six of which were children/adolescents. Therapy consisted mainly of surgery, antibiotics and hyperbaric oxygen therapy. At the end of the follow up period, 11 patients demonstrated complete remission, while in 14 cases amelioration and in 5 no significant improvement was noted.

CONCLUSION

Based on differences in age at presentation, clinical appearance and course, radiology and histology, a subclassification into early and adult onset primary chronic osteomyelitis has been established. Cases with purely mandibular involvement should further be distinguished from cases associated with other syndromes.

Osteomyelitis of the mandible

Before application of any cross-sectional imaging modality, the orthopanoramic view is indispensable in assessing the status of dentition, in recognizing direct radiographic signs of osteomyelitis, or in determining the presence of predisposing conditions such as a fracture or systemic bone disease. The orthopanoramic view is the procedure of choice in follow-up examinations in patients who have osteomyelitis. In acute osteomyelitis, the higher sensitivity of MR imaging for detection of intramedullary inflammation advocates this imaging modality for confirmation of the clinical diagnosis. If surgical treatment is planned, high-resolution CT is required to specify the degree of cortical destruction, the presence of sequestra in particular, and to define the extent of osseous removal required. In chronic osteomyelitis, the higher sensitivity of MR imaging to detect periosteal inflammation and soft tissue involvement advocates this modality to reveal the presence, location, and extent of chronic inflammation. The assessment of persistence or recurrence of chronic inflammation after surgical treatment is by high-resolution CT for the first 6 months following surgery. Finally, scintigraphy is recommended when multi-focal systemic disease is suspected, such as in CRMO and SAPHO syndrome.

In vitro activities of tigecycline (GAR-936) and 12 other antimicrobial agents against 90 Eikenella corrodens clinical isolates

The activity of tigecycline was compared with those of other antimicrobials against 90 isolates of Eikenella corrodens. The MIC at which 90% of the isolates were inhibited was 2 micro g/ml for tigecycline and 1, </=0.5/0.25, 0.5, </=0.12, </=2, and 0.5 micro g/ml for ampicillin, amoxicillin-clavulanate, cefotaxime, imipenem, chloramphenicol, and ciprofloxacin, respectively.

In vitro activities of a new des-fluoroquinolone, BMS 284756, and seven other antimicrobial agents against 151 isolates of Eikenella corrodens

The des-fluoroquinolone BMS 284756 was active in vitro against all 151 clinical strains of Eikenella corrodens at a MIC of < or = 0.25 microg/ml and was comparable in activity to moxifloxacin and levofloxacin. The MIC at which 90% of the isolates were inhibited by penicillin G was 2 microg/ml; MICs for 8.6% of the strains (13 of 151) were > or = 4 microg/ml, including for two beta-lactamase-producing isolates. Amoxicillin-clavulanate and ampicillin-sulbactam inhibited all strains at a MIC of < or = 1 microg/ml.

Pamidronate in the treatment of diffuse sclerosing osteomyelitis of the mandible

Diffuse sclerosing osteomyelitis of the mandible is characterized by bouts of intense pain, sometimes associated with trismus and paresthesia, and leads to progressive deformity. It is of unknown etiopathology, but it is suggested to be one manifestation of the synovitis, acne, pustulosis, hyperostosis, osteomyelitis syndrome, the other features of which may have been overlooked. Treatment results are disappointing, and decortication may be necessary to achieve an acceptable outcome. We report a case restricted to the mandible that responded favorably to treatment with pamidronate. Further trials of pamidronate in patients with diffuse sclerosing osteomyelitis of the mandible, even in those with the aforementioned syndrome, are needed to assess its effectiveness.

Eikenella corrodens infections in children and adolescents: case reports and review of the literature

Eikenella corrodens is a slow-growing, gram-negative, nonmotile, facultative rod that can cause infection in humans. Although the clinical characteristics of Eikenella infections in adults are well described, the literature regarding Eikenella infections in children is lacking. Thirteen cases of Eikenella infection in children and adolescents reported from a hospital and an additional 41 cases from the literature were reviewed. Eikenella species can be serious pediatric pathogens, particularly when there is an exposure to human oral secretions. Empirical therapy used to manage most oropharyngeal flora may be ineffective against Eikenella species. The treatment of choice for children and adolescents who are infected with Eikenella species includes a combination of surgical management and antibiotics.

Benign fibro-osseous lesions: a review of current concepts

The benign fibro-osseous lesions (BFOL) represent a clinically diverse group of disorders of bone that share similar histopathologic features. As a group, they are relatively common in the craniofacial complex, especially the jaws. Although the general concept of BFOL is relatively well known, specific diagnostic interpretation of individual cases is often challenging. New concepts and controversies have arisen over the past 10 to 15 years regarding classification and diagnostic criteria. However, among the new theories and contentions, there is now essential agreement that the osseous dysplasias represent a single disease process, while the so-called "juvenile active ossifying fibroma" and other "aggressive," "active," "psammomatoid" ossifying/cementifying fibromas remain controversial. This review is presented to update the surgical pathologist on the various entities comprising the spectrum of BFOL and to examine the criteria for their diagnosis.

Primary chronic osteomyelitis associated with synovitis, acne, pustulosis, hyperostosis and osteitis (SAPHO syndrome)

Diffuse sclerosing osteomyelitis may indicate the mandibular localisation of the SAPHO syndrome. Twelve patients with diffuse sclerosis of the mandible were examined for symptoms of the SAPHO syndrome. Nine patients were found to have primary chronic osteomyelitis and eight of these represented a SAPHO syndrome. Results in this series support the hypothesis of an association between primary chronic osteomyelitis and the SAPHO syndrome.

A modified protocol for early treatment of osteomyelitis and osteoradionecrosis of the mandible

BACKGROUND

The treatment of osteoradionecrosis (ORN) and early chronic osteomyelitis (COM) of the mandible and maxilla is controversial. Hyperbaric oxygen (HBO) at two to three times the atmospheric pressure at sea level can result in tissue oxygen tension of almost 400 mmHg. Herewith HBO increases oxygen supply in hypoxic tissue, thus inducing fibroblastic proliferation and capillary formation.

METHODS

From 1981 to 1991, we used a monoplace chamber and since 1992, we have also had a multiplace chamber for HBO treatment. Hyperbaric oxygen was given at 2.5-2.8 atmosphere absolute pressure (ATA) for 90-120 minutes, once per day. The patients had five to 10 preoperative and five to seven postoperative sessions. Surgical therapy consisted of decortication of the affected bone, subsequently covered with a free periosteal transplant from the tibia.

RESULTS

Thirty-six patients with ORN and 33 with COM of the mandible and maxilla was treated with this protocol. The median follow-up time in this material is 34 months, with a minimum of 10 months. Thirty-six ORN patients (92%) and 26 COM patients (79%) have remained symptom-free after the first treatment period. Three failed ORN patients were successfully treated with a free microvascular flap. The seven failed COM patients have been retreated, and five of them have occasional clinical symptoms.

CONCLUSIONS

Hyperbaric oxygen is a promising adjunct to surgery in the treatment of mandibular and maxillary ORN and COM. Using this protocol, the necessary HBO treatment sessions have been reduced from earlier protocols, without adverse effect on the outcome.

Radiographic evaluation of possible etiology of diffuse sclerosing osteomyelitis of the mandible

To examine the cause and site of origin of diffuse sclerosing osteomyelitis of the mandible, we compared various radiographic findings for the mandibular lesions in 20 patients with diffuse sclerosing osteomyelitis with those in 48 patients with osteomyelitis caused by bacterial infection. In osteomyelitis of infectious origin, a typical radiographic feature was a radiolucent lesion spreading in the cancellous bone, with cortical bone perforation and lamellated periosteal reaction. In diffuse sclerosing osteomyelitis, intermingled sclerotic and osteolytic lesions with solid periosteal reaction or external bone resorption were a common finding, and in some patients the cortical bone was initially affected by the fresh or recurrent lesion. Based on these distinct differences, we suggest that the cause of diffuse sclerosing osteomyelitis is not bacterial infection and that the site of origin is not in the bone but in the periosteum.

Protein degradation by Prevotella intermedia and Actinomyces meyeri supports the growth of non-protein-cleaving oral bacteria in serum

The proteolytic activities of oral bacteria are thought to play an important role in the aetiology of dental abscesses. Bacteria-derived proteases may contribute to tissue destruction, and are likely to impair host defence by degrading immunoglobulins and complement. Degraded periodontal tissue and tissue fluid are likely to constitute essential sources of nutrients in the abscess. Tissue fluid, which is derived from serum, is rich in protein and poor in carbohydrate, suggesting that breakdown of protein and fermentation of amino acids is a crucial step to generate energy for growth of the microflora. The number of oral bacterial species that perform hydrolytic cleavage of protein into polypeptides, the first step in protein degradation, is relatively small compared to the large majority of peptidase-producing species. In this study, we therefore investigated the growth-promoting effect of proteinase-producing species like Prevotella intermedia and Actinomyces meyeri on the growth of some non-proteinase producing bacteria in mixed cultures. We used serum as a substitute for the supposed natural substrate of the abscess microflora. The breakdown of serum proteins was investigated using capillary electrophoresis. Poor growth was found in mono- and mixed cultures of non-proteinase producing species Eubacterium lentum, Fusobacterium nucleatum. Peptostreptococcus micros, and Streptococcus intermedius. The presence of P. intermedia in mixed cultures strongly enhanced growth of these 4 species, according to the hypothesis that the growth of the mixed cultures was peptide-limited. The enhanced growth of P. intermedia in pronase-digested serum indicated peptide-limited growth of this organism in serum, despite its production of proteinase. We found that growth of monocultures of Actinomyces meyeri was poor. In contrast, A. meyeri grew well in mixed cultures and its presence stimulated growth of F. nucleatum and P. micros, suggesting a synergistic relationship. The growth of mono- and mixed cultures was investigated using one representative strain of each species. Thus, there is a small risk of having selected unique strains. Proteinase inhibitors reduced the growth of Porphyromonas gingivalis, Prevotella nigrescens, and P. intermedia in trypticase peptone-yeast extract medium with, and without, IgG. Our study indicated that proteinase-producing organisms play a key role in mixed cultures of oral bacteria in human serum by providing polypeptides for growth. This may explain their association with dental abscesses.