In vivo protection of Fusobacterium necrophorum from penicillin by Bacteroides fragilis

Usage of antibiotics in aquaculture and the impact on coastal waters

For decades, coastal marine ecosystems have been threatened by a wide range of anthropogenic pollutants. Recently, there has been increasing concern about the accumulation and impacts of antibiotic compounds on marine ecosystems. However, information regarding the accumulation of antibiotics and the impacts they may have on microbial communities in coastal water bodies and on human health is sparse in literature. Antibiotics from aquacultures are constantly discharged into marine environments via rivers. Large rivers transport tons of antibiotics every year into coastal waters, e.g., 12 tons of sulfonamide by the river Mekong. Here, we discuss a potential influence of such imported antibiotics on bacterial communities in coastal waters. Potential accumulation of antibiotics in the uppermost surface layer of aquatic ecosystems, the so-called sea surface microlayer (SML), is of interest. Because of the ability of the SML to accumulate anthropogenic pollutants, it may serve as a pool for antibiotics and correspondingly also for resistant organisms. Also, due to its biofilm-like structure, the SML could serve as a hotspot for horizontal gene transfer, speeding up the spread of antibiotic resistant strains to encompassing marine environments. The emergence of antibiotic resistant bacteria is a global threat and scientists projected that it could pave the way for the next pandemic that could ravage the world in the next decades. For this reason, it is time to focus research on understanding and minimizing the impact of antibiotics on the sustainability of coastal waters and on the health of humans who depend on coastal resources for food and recreational purposes. Also, knowledge about antibiotics in the SML is necessary to understand the effects they are likely to have on bacterial abundance, diversity, and metabolic activities in coastal water bodies.

Antibiotics Drive Expansion of Rare Pathogens in a Chronic Infection Microbiome Model

Chronic (long-lasting) infections are globally a major and rising cause of morbidity and mortality. Unlike typical acute infections, chronic infections are ecologically diverse, characterized by the presence of a polymicrobial mix of opportunistic pathogens and human-associated commensals. To address the challenge of chronic infection microbiomes, we focus on a particularly well-characterized disease, cystic fibrosis (CF), where polymicrobial lung infections persist for decades despite frequent exposure to antibiotics. Epidemiological analyses point to conflicting results on the benefits of antibiotic treatment yet are confounded by the dependency of antibiotic exposures on prior pathogen presence, limiting their ability to draw causal inferences on the relationships between antibiotic exposure and pathogen dynamics. To address this limitation, we develop a synthetic infection microbiome model representing CF metacommunity diversity and benchmark on clinical data. We show that in the absence of antibiotics, replicate microbiome structures in a synthetic sputum medium are highly repeatable and dominated by oral commensals. In contrast, challenge with physiologically relevant antibiotic doses leads to substantial community perturbation characterized by multiple alternate pathogen-dominant states and enrichment of drug-resistant species. These results provide evidence that antibiotics can drive the expansion (via competitive release) of previously rare opportunistic pathogens and offer a path toward microbiome-informed conditional treatment strategies.

IMPORTANCE We develop and clinically benchmark an experimental model of the cystic fibrosis (CF) lung infection microbiome to investigate the impacts of antibiotic exposures on chronic, polymicrobial infections. We show that a single experimental model defined by metacommunity data can partially recapitulate the diversity of individual microbiome states observed across a population of people with CF. In the absence of antibiotics, we see highly repeatable community structures, dominated by oral microbes. Under clinically relevant antibiotic exposures, we see diverse and frequently pathogen-dominated communities, and a nonevolutionary enrichment of antimicrobial resistance on the community scale, mediated by competitive release. The results highlight the potential importance of nonevolutionary (community-ecological) processes in driving the growing global crisis of increasing antibiotic resistance.

Antibiotic Degradation by Commensal Microbes Shields Pathogens

The complex bacterial populations that constitute the gut microbiota can harbor antibiotic resistance genes (ARGs), including those encoding β-lactamase enzymes (BLA), which degrade commonly prescribed antibiotics such as ampicillin. The prevalence of such genes in commensal bacteria has been increased in recent years by the wide use of antibiotics in human populations and in livestock. While transfer of ARGs between bacterial species has well-established dramatic public health implications, these genes can also function in trans within bacterial consortia, where antibiotic-resistant bacteria can provide antibiotic-sensitive neighbors with leaky protection from drugs, as shown both in vitro and in vivo, in models of lung and subcutaneous coinfection. However, whether the expression of ARGs by harmless commensal bacterial species can destroy antibiotics in the intestinal lumen and shield antibiotic-sensitive pathogens is unknown. To address this question, we colonized germfree or wild-type mice with a model intestinal commensal strain of Escherichia coli that produces either functional or defective BLA. Mice were subsequently infected with Listeria monocytogenes or Clostridioides difficile, followed by treatment with oral ampicillin. The production of functional BLA by commensal E. coli markedly reduced clearance of these pathogens and enhanced systemic dissemination during ampicillin treatment. Pathogen resistance was independent of ARG acquisition via horizontal gene transfer but instead relied on antibiotic degradation in the intestinal lumen by BLA. We conclude that commensal bacteria that have acquired ARGs can mediate shielding of pathogens from the bactericidal effects of antibiotics.

Antibiotics for recurrent acute pharyngo-tonsillitis: systematic review

The purpose was to determine the current evidence for preferable antibiotic treatment in three common clinical situations with insufficient consensus: Q1: Can antibiotic treatment prevent future attacks of acute pharyngo-tonsillitis (APT) in patients with recurrent APT (RAPT)? Q2: Which antibiotic regimen is preferable in the treatment of APT in patients with RAPT? Q3: Which antibiotic regimen is preferable in the treatment of relapsing APT? Five databases were searched systematically for randomized clinical trials on patients with RAPT with or without current APT or with relapse of APT. Of the unique publications, 643 were found. Five studies addressing Q1 (n = 3) and Q2 (n = 2) met the eligibility criteria. No studies reporting on Q3 were included. Q1: Two studies found that clindamycin and cefpodoxime, respectively, were effective in preventing future APT episodes and in eradicating group A streptococci from the tonsils of RAPT patients. One study found that long-term azithromycin had no effect on the number of APT episodes. Q2: Two studies reported superior clinical and microbiological effects of clindamycin and amoxicillin with clavulanate, respectively, compared to penicillin. The four studies showing superior effects of clindamycin and amoxicillin with clavulanate were assessed to have high risk of bias. Hence, the level of evidence was moderate. There is considerable evidence to suggest that clindamycin and amoxicillin with clavulanate are superior to penicillin with preferable effects on the microbiological flora and the number of future attacks of APT in patients with RAPT. Antibiotic treatment is an option in patients with RAPT, who has contraindications for tonsillectomy.

Alloiococcus otitidis Forms Multispecies Biofilm with Haemophilus influenzae: Effects on Antibiotic Susceptibility and Growth in Adverse Conditions

Otitis media with effusion (OME) is a biofilm driven disease and commonly accepted otopathogens, such as Haemophilus influenzae, Streptococcus pneumonia, and Moraxella catarrhalis, have been demonstrated to form polymicrobial biofilms within the middle ear cleft. However, Alloiococcus otitidis (A. otitidis), which is one of the most commonly found bacteria within middle ear aspirates of children with OME, has not been described to form biofilms. The aim of this study was to investigate whether A. otitidis can form biofilms and investigate the impact on antibiotic susceptibility and survivability in polymicrobial biofilms with H. influenzae in vitro. The ability of A. otitidis to form single-species and polymicrobial biofilms with H. influenzae was explored. Clinical and commercial strains of A. otitidis and H. influenzae were incubated in brain heart infusion with and without supplementation. Biofilm was imaged using confocal laser scanning microscopy and scanning electron microscopy. Quantification of biofilm biomass and viable bacterial number was assessed using crystal violet assays and viable cell counting in both optimal growth conditions and in adverse growth conditions (depleted media and sub-optimal growth temperature). Antimicrobial susceptibility and changes in antibiotic resistance of single-species and multi-species co-culture were assessed using a microdilution method to assess minimal bactericidal concentration and E-test for amoxicillin and ciprofloxacin. A. otitidis formed single-species and polymicrobial biofilms with H. influenzae. Additionally, whilst strain dependent, combinations of polymicrobial biofilms decreased antimicrobial susceptibility, albeit a small magnitude, in both planktonic and polymicrobial biofilms. Moreover, A. otitidis promoted H. influenzae survival by increasing biofilm production in depleted media and at suboptimal growth temperature. Our findings suggest that A. otitidis may play an indirect pathogenic role in otitis media by altering H. influenzae antibiotic susceptibility and enhancing growth under adverse conditions.

Lemierre's Syndrome Associated with Mechanical Ventilation and Profound Deafness

Lemierre's syndrome is a rare disorder that is characterized by anaerobic organisms inducing a thrombophlebitis of the internal jugular vein (IJV) following a course of oropharyngeal infection. It often occurs in young and healthy patients. Clinicians continuously misinterpret early symptoms until infection disseminates systematically and life-threatening sepsis transpires. We report the case of a 58-year-old female developing Lemierre's syndrome accompanied by invasive ventilation support and a profound deafness requiring the implementation of a cochlear implant. This is one of two reported cases of Lemierre's syndrome associated with mechanical ventilation support and the only case associated with a cochlear implant.

Oscillatory dynamics in a bacterial cross-protection mutualism

Cooperation between microbes can enable microbial communities to survive in harsh environments. Enzymatic deactivation of antibiotics, a common mechanism of antibiotic resistance in bacteria, is a cooperative behavior that can allow resistant cells to protect sensitive cells from antibiotics. Understanding how bacterial populations survive antibiotic exposure is important both clinically and ecologically, yet the implications of cooperative antibiotic deactivation on the population and evolutionary dynamics remain poorly understood, particularly in the presence of more than one antibiotic. Here, we show that two Escherichia coli strains can form an effective cross-protection mutualism, protecting each other in the presence of two antibiotics (ampicillin and chloramphenicol) so that the coculture can survive in antibiotic concentrations that inhibit growth of either strain alone. Moreover, we find that daily dilutions of the coculture lead to large oscillations in the relative abundance of the two strains, with the ratio of abundances varying by nearly four orders of magnitude over the course of the 3-day period of the oscillation. At modest antibiotic concentrations, the mutualistic behavior enables long-term survival of the oscillating populations; however, at higher antibiotic concentrations, the oscillations destabilize the population, eventually leading to collapse. The two strains form a successful cross-protection mutualism without a period of coevolution, suggesting that similar mutualisms may arise during antibiotic treatment and in natural environments such as the soil.

Live to cheat another day: bacterial dormancy facilitates the social exploitation of β-lactamases

The breakdown of antibiotics by β-lactamases may be cooperative, since resistant cells can detoxify their environment and facilitate the growth of susceptible neighbours. However, previous studies of this phenomenon have used artificial bacterial vectors or engineered bacteria to increase the secretion of β-lactamases from cells. Here, we investigated whether a broad-spectrum β-lactamase gene carried by a naturally occurring plasmid (pCT) is cooperative under a range of conditions. In ordinary batch culture on solid media, there was little or no evidence that resistant bacteria could protect susceptible cells from ampicillin, although resistant colonies could locally detoxify this growth medium. However, when susceptible cells were inoculated at high densities, late-appearing phenotypically susceptible bacteria grew in the vicinity of resistant colonies. We infer that persisters, cells that have survived antibiotics by undergoing a period of dormancy, founded these satellite colonies. The number of persister colonies was positively correlated with the density of resistant colonies and increased as antibiotic concentrations decreased. We argue that detoxification can be cooperative under a limited range of conditions: if the toxins are bacteriostatic rather than bacteridical; or if susceptible cells invade communities after resistant bacteria; or if dormancy allows susceptible cells to avoid bactericides. Resistance and tolerance were previously thought to be independent solutions for surviving antibiotics. Here, we show that these are interacting strategies: the presence of bacteria adopting one solution can have substantial effects on the fitness of their neighbours.

Lemierre's Syndrome: Recognising a Typical Presentation of a Rare Condition

Lemierre's syndrome is a rare complication following an acute oropharyngeal infection. The aetiological agent is typically anaerobic bacteria of the genus Fusobacterium. The syndrome is characterised by a primary oropharyngeal infection followed by metastatic spread and suppurative thrombophlebitis of the internal jugular vein. If left untreated, Lemierre's syndrome carries a mortality rate of over 90%. Whilst relatively common in the preantibiotic era, the number of cases of Lemierre's syndrome subsequently declined with the introduction of antibiotics. With the increase of antibiotic resistance and a greater reluctance to prescribe antibiotics for minor conditions such as tonsillitis, there are now concerns developing about the reemergence of the condition. This increasing prevalence in the face of an unfamiliarity of clinicians with the classical features of this “forgotten disease” may result in the misdiagnosis or delay in diagnosis of this potentially fatal illness. This case report illustrates the delay in diagnosis of probable Lemierre's syndrome in a 17-year-old female, its diagnosis, and successful treatment which included the use of anticoagulation therapy. Whilst there was a positive outcome, the case highlights the need for a suspicion of this rare condition when presented with distinctive signs and symptoms.

Bacterial cheating drives the population dynamics of cooperative antibiotic resistance plasmids

Inactivation of β-lactam antibiotics by resistant bacteria is a 'cooperative' behavior that may allow sensitive bacteria to survive antibiotic treatment. However, the factors that determine the fraction of resistant cells in the bacterial population remain unclear, indicating a fundamental gap in our understanding of how antibiotic resistance evolves. Here, we experimentally track the spread of a plasmid that encodes a β-lactamase enzyme through the bacterial population. We find that independent of the initial fraction of resistant cells, the population settles to an equilibrium fraction proportional to the antibiotic concentration divided by the cell density. A simple model explains this behavior, successfully predicting a data collapse over two orders of magnitude in antibiotic concentration. This model also successfully predicts that adding a commonly used β-lactamase inhibitor will lead to the spread of resistance, highlighting the need to incorporate social dynamics into the study of antibiotic resistance.

The role of beta-lactamase-producing-bacteria in mixed infections

Beta-lactamase-producing bacteria (BLPB) can play an important role in polymicrobial infections. They can have a direct pathogenic impact in causing the infection as well as an indirect effect through their ability to produce the enzyme beta-lactamase. BLPB may not only survive penicillin therapy but can also, as was demonstrated in in vitro and in vivo studies, protect other penicillin-susceptible bacteria from penicillin by releasing the free enzyme into their environment. This phenomenon occurs in upper respiratory tract, skin, soft tissue, surgical and other infections. The clinical, in vitro, and in vivo evidence supporting the role of these organisms in the increased failure rate of penicillin in eradication of these infections and the implication of that increased rate on the management of infections is discussed.

Beta-lactamase-producing nontypeable Haemophilus influenzae fails to protect Streptococcus pneumoniae from amoxicillin during experimental acute otitis media

Acute otitis media (AOM) is the most common reason for outpatient antimicrobial therapy. Mixed infections pose a potential problem, since the first-line drug used for the treatment of AOM, amoxicillin, can be neutralized by beta-lactamase-producing pathogens of the upper respiratory tract. To study the effects of a 5-day course of amoxicillin on a mixed middle ear infection, rats were challenged with Streptococcus pneumoniae alone or in combination with beta-lactamase-producing nontypeable Haemophilus influenzae. Amoxicillin was introduced at the clinical peak of the infection. Local and systemic changes were monitored by otomicroscopy, bacterial culture, and analysis of histological changes and the expression of the transforming growth factor beta (TGF-beta) gene. beta-Lactamase-producing H. influenzae did not demonstrate an ability to protect S. pneumoniae. Amoxicillin eradicated the pneumococci in all treated animals but increased to some degree the ability of H. influenzae to persist at the site of infection. Thus, only an insignificant acceleration of the resolution of the AOM caused by a mixture of pathogens was observed during treatment. Moderate to major morphological changes could not be avoided by treatment of the mixed infections, but a slight downregulation of TGF-beta expression was observed. In contrast to infections caused by a single pathogen, the mixed infections induced white plaques in the tympanic membrane at a remarkably high frequency independent of treatment. These experimental findings constitute support for further studies of antimicrobial drugs and AOM caused by bacteria with and without mechanisms of antibiotic resistance.

β-Lactamase-producing bacteria in mixed infections

Beta-lactamase-producing bacteria (BLPB) can play an important role in polymicrobial infections. They can have a direct pathogenic impact in causing infections, as well as an indirect effect through their ability to produce the beta-lactamase. BLPB may not only survive penicillin therapy themselves, but can also protect other penicillin-susceptible bacteria from penicillin by releasing free beta-lactamase into their immediate environment. This phenomenon occurs in upper respiratory tract, skin, soft tissue, surgical and other infections. The in-vitro and in-vivo clinical evidence supporting the role of BLPB in the increasing failure of penicillin to resolve such infections, and the implications of this phenomenon for the management of infections, are discussed.

Tonsil surface and core cultures in recurrent tonsillitis: prevalence of anaerobes and beta-lactamase producing organisms

The bacterial flora of the tonsil surface and core was compared in patients suffering from recurrent tonsillitis. Surface swabs and tonsil core tissues were received as paired samples from 50 patients admitted for elective tonsillectomy. Analysis of paired samples from individual patients revealed differences in the bacterial flora of the tonsil core and the tonsil surface. Of 366 aerobic isolates, 30% grew from the surface alone, 26% from the core only and 44% from both sites. Of 290 anaerobic isolates, 35% grew from the surface alone, 33% from the core only and 31% from both sites. The total number of isolates from surface and core samples was similar (average 9.2 and 8.8, respectively). The range of species isolated was also similar for both surface and core samples, as was the proportion of organisms producing beta-lactamase from each site (10.7% and 9.5%, respectively). Eighty-two percent of patients carried beta-lactamase-producing organisms on either the tonsil surface or in the core tissue. A surface swab does not reliably reflect the types of organisms present in the tonsil core in individual patients. Anaerobes are a major component of tonsil surface and core bacterial flora in patients with recurrent tonsillitis. The high carriage rate of beta-lactamase-producing organisms in the tonsils should be considered when selecting antimicrobial therapy for persistent or recurrent tonsillitis.

Evaluation of bacterial interference and beta-lactamase production in management of experimental infection with group A beta-hemolytic streptococci

The in vivo effects of penicillin and cefprozil therapy on the interaction between organisms commonly recovered from inflamed tonsils were studied by using a subcutaneous abscess model in mice. These organisms were group A beta-hemolytic streptococci (GABHS), Streptococcus salivarius (which is capable of interfering with GABHS), and Staphylococcus aureus. In mice infected with GABHS and S. salivarius alone or in combination, penicillin eliminated both organisms and cefprozil eliminated GABHS and S. aureus but not S. salivarius. Penicillin did not, however, reduce the number of GABHS or S. salivarius in the presence of S. aureus. The present study demonstrated the ability of beta-lactamase-producing S. aureus to protect GABHS from penicillin. However, no such protection was present following the administration of cefprozil. Furthermore, the preservation of S. salivarius that interferes with GABHS growth may provide protection from reinfection with GABHS. This study supports and provides an explanation for the increased efficacies of cephalosporins administered orally over that of penicillin when treating patients with acute GABHS pharyngitis or tonsillitis.

Influence of clavulanic acid on the activity of amoxicillin against an experimental Streptococcus pneumoniae-Staphylococcus aureus mixed respiratory infection

An experimental respiratory infection caused by Streptococcus pneumoniae was established in weanling rats by intrabronchial instillation. Treatment of this infection with amoxicillin rapidly eliminated the pneumococci from the lung tissue. A beta-lactamase-producing strain of Staphylococcus aureus, when inoculated in a similar manner, did not persist adequately in the lungs long enough to permit a reasonable assessment of the therapy, but staphylococcal survival was extended in the lungs of rats infected 24 h previously with S. pneumoniae. Amoxicillin therapy was relatively ineffective against the pneumococci in this polymicrobial infection and had no effect on the growth of S. aureus. In contrast, amoxicillin-clavulanic acid eliminated the pneumococci from the lung tissue and brought about a reduction in the numbers of staphylococci. The data illustrate the utility of this model for the study of polymicrobial lung infections and demonstrate the role of amoxicillin-clavulanic acid in the treatment of polymicrobial infections involving beta-lactamase-producing bacteria.

Direct and indirect pathogenicity of beta-lactamase-producing bacteria in mixed infections in children

The recent emergence of numerous aerobic and anaerobic beta-lactamase-producing bacterial strains has been associated with an increase in the failure rate of penicillins in the therapy of infection caused by these organisms. These include respiratory tract, skin of soft tissue, female genital tract, intra-abdominal, and other miscellaneous infections. The important aerobic beta-lactamase-producing bacteria (BLPB) include Staphylococcus aureus, Branhamella catarrhalis, Haemophilus sp., Neisseria gonorrhoeae, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Legionella sp. The anaerobic BLPB are all Bacteroidiaceae and include Bacteroides fragilis group, B. melaninogenicus group, B. oralis, B. oris-buccae, and Fusobacterium sp. Laboratory, animal, and clinical studies that support the indirect pathogenicity of these organisms and the distribution of these BLPB in various infections are reviewed. BLPB may not only have a direct pathogenic role in causing the infection, but also an indirect pathogenic role. The indirect pathogenicity of these organisms is apparent through their ability not only to survive penicillin therapy, but also to protect penicillin-susceptible pathogens from that drug. These direct and indirect virulence characteristics of aerobic and anaerobic BLPB require the administration of appropriate antimicrobial therapy directed against all pathogens in mixed infections.

Direct and indirect pathogenicity of Branhamella catarrhalis

Branhamella catarrhalis has been recovered from various sites of infection in the respiratory tract. These include chronic otitis media, tonsillitis, adenoiditis and pneumonia. This organism was recovered in many of these infections mixed with other aerobic, facultative anaerobic and anaerobic bacteria. Increasing numbers of isolates of this organism have been noted to produce beta-lactamase. This may contribute to the high failure rate of penicillins in eradicating polymicrobial respiratory infections.

Treatment of patients with a history of recurrent tonsillitis due to group A beta-hemolytic streptococci. A prospective randomized study comparing penicillin, erythromycin, and clindamycin

Forty-five patients with a history of recurrent tonsillitis associated with Group A beta-hemolytic streptococcal (GABHS) infection participated in a prospective, randomized study comparing penicillin, erythromycin, or clindamycin therapy. Surface tonsillar cultures were obtained before therapy, 10 days after termination of therapy, and once a month for a period of 12 to 18 months. The specimens were processed for aerobic and anaerobic bacteria. Beta lactamase-producing aerobic and anaerobic bacteria were present in 43 of the 45 (96%) tonsillar cultures. GABHS colonization was eradicated in two of 15 patients treated with penicillin, in six of 15 treated with erythromycin, and in 14 of the 15 treated with clindamycin. In long-term follow-up, 12 of 14 patients treated with penicillin, eight of 14 treated with erythromycin, and one of 15 treated with clindamycin (p less than 0.0001 when compared to penicillin and p = 0.002 when compared to erythromycin) continued to suffer from recurrent tonsillitis.

The presence of beta-lactamase-producing bacteria as a guideline in the management of children with recurrent tonsillitis

Thirty-eight children who had recurrent tonsillitis and who were chronic carriers of group A beta-hemolytic streptococci (GABHS) were treated with oral clindamycin. Surface tonsillar cultures, obtained prior to therapy and two weeks after the termination of therapy, were processed for aerobic and anaerobic microorganisms. Mixed aerobic and anaerobic flora were obtained from all cultures. Prior to therapy, the average yield was 9.3 isolates (5.2 aerobes and 4.1 anaerobes) per specimen; after the completion of therapy, the average yield was 5.5 isolates (3.0 aerobes and 2.5 anaerobes). The GABHS were completely eliminated after clindamycin therapy, and the numbers of isolates of Bacteroides spp and Staphylococcus aureus were reduced. Beta-lactamase production was detected prior to therapy in 57 isolates recovered from all tonsillar surfaces. This group included all isolates of S. aureus (15) and Bacteroides fragilis (eight), 19 of 34 Bacteroides melaninogenicus isolates (56 per cent), and seven of 12 Bacteroides oralis isolates (58 per cent). Only four isolates of beta-lactamase-producing bacterial strains were recovered after the conclusion of therapy. Follow-up study of 33 children for eight to 16 months (average, 13 months) showed no recurrence of GABHS in 31.

Experimental anaerobic brain abscess. Computerized tomographic and neuropathological correlations

The neuropathological progression of brain abscess formation induced by a mixed anaerobic culture of Bacteroides fragilis and Staphylococcus epidermidis was studied experimentally in dogs. Histological findings were correlated with computerized tomographic (CT) brain scans. The evolution of brain abscess formation could be divided into three stages based on histological criteria: early cerebritis (Days 1 to 3); late cerebritis (Days 4 to 9); and capsule formation (Day 10 and later). Capsule formation could not be divided into early and late stages because encapsulation was delayed compared with a previously reported model of alpha-Streptococcus brain abscess. Histologically, there was evidence for a very virulent infection. Leptomeningitis was significant even in the late stages. Early ventricular rupture occurred in 25% of the animals. A pattern of extensive purulent encephalitis was seen in 25% of the animals. In the early cerebritis stage, blood vessels near the necrotic center were engorged and were surrounded by hemorrhage and/or protein-rich fluid. Cerebral edema was extensive. Although fibroblasts appeared in late cerebritis, there was marked delay of capsule formation. Three-week-old lesions still had areas of incomplete capsule formation and foci of uncontrolled infection. In the cerebritis stages, CT scans showed an area of ring enhancement which was incomplete on early scans (at 5 minutes after injection of contrast material) but partially filled in and thickened on delayed scans (at 20 to 45 minutes). On even later delayed scans there was no decrease in intensity of ring enhancement. Lesions in which capsule formation occurred also showed ring enhancement, but delayed scans showed a decrease in the intensity of enhancement. The lesions that ruptured into the ventricular system showed atypical CT findings, with either lack of contrast enhancement (histologically there was minimal cerebritis adjacent to the abscess cavity) or a marked delay in contrast enhancement (cerebritis was more extensive and corresponded to the width of ring of enhancement). This study suggests that Bacteroides fragilis is a virulent organism in the brain. The developing abscesses enlarged quickly, were prone to early ventricular rupture, and showed incomplete and delayed encapsulation.

Antimicrobial drugs used in the management of anaerobic infections in children

Optimum antimicrobial therapy effective against anaerobes is required to rapidly resolve infections due to these organisms and to prevent serious complications. Selection of antimicrobial therapy should be based on clinical experience and presumptive evidence until culture and sensitivity tests are available. If an abscess should develop, surgical drainage (when possible) is of paramount importance. Antimicrobial therapy for anaerobic infections should usually be given for prolonged periods because of the tendency for relapse, and should include coverage for aerobic bacteria whenever they are present. Penicillin G remains the drug of choice for most anaerobic infections except those caused by beta-lactamase-producing Bacteroides spp. such as B. fragilis and B. melaninogenicus, and some strains of Fusobacterium varium, which can be resistant. Other antimicrobials which are available for treatment of anaerobic infections in paediatric patients, and are generally active against B. fragilis, are carbenicillin, ticarcillin, chloramphenicol, clindamycin and cefoxitin. Experience in the use of metronidazole suggests that it could be a very valuable antimicrobial agent in the treatment of anaerobic infections. Experience with synergistic antimicrobial combinations in the treatment of anaerobic infections is limited; only experimental data are available suggesting synergism between penicillin and aminoglycosides against some Bacteroides spp. beta-Lactamase-producing anaerobic bacteria may protect other penicillin-susceptible bacteria in mixed infections. This phenomenon may explain penicillin failure in eradicating mixed infections.

New medium for selection and presumptive identification of the Bacteroides fragilis group

A medium, Bacteroides fragilis bile-esculin (BBE) agar, was designed for the selection and, presumptive identification of the B. fragilis group. BBE agar contains bile, esculin, ferric ammonium citrate, hemin, and gentamicin in a Trypticase soy agar base. Growth in the presence of 20% bile and esculin hydrolysis, detected by blackening of the medium, provide presumptive evidence for the identification of the B. fragilis group. In addition to stimulating the growth of many strains of the B. fragilis group, hemin provides the option of testing isolates for catalase production. Gentamicin and bile prevent the growth of most organisms other than the esculin-positive bacteroides that can tolerate bile. Of 160 clinical isolates of the B. fragilis group tested on BBE agar, 159 grew well on the medium and 157 blackened it. Other anaerobes, Enterobacteriaceae, and enterococci either failed to grow on BBE agar or did not produce the characteristic morphology and blackening associated with isolates of the B. fragilis group. In a clinical laboratory trial, 687 specimens from patients were inoculated onto BBE agar plates. The B. fragilis group was recovered from 81 (11.8%) of these specimens in 24 to 48 h. Use of BBE agar in the clinical laboratory enables earlier recovery and identification of this important pathogen.

Anaerobic bacteria in otitis media

Anaerobic bacteria, Peptostrepotococcus intermedius and Propionibacterium acnes, were found in mixed culture specimens from four to ten tested cases of chronic secretory otitis media. These anaerobic bacteria were in a mixed infection flora with aerobic bacteria most often Staphylococcus epidermidis and Cornybacterium sp. which do not fit any established species. The findings of anaerobic bacteria in otitis media is consistent with the sporadic report of the involvement of anaerobic bacteria in otitis media in the literature since 1898.

Chemotherapy of an experimental Bacteroides fragilis infection in mice

The efficacies of five common antimicrobial agents were determined for a pure Bacteroides fragilis infection in mice. Therapy was begun 4 h after bacterial injection and given every 8 h thereafter for 5 days. Blood levels were determined over an 8-h period for each concentration of antibiotic tested. Clindamycin and tetracycline were the most effective in preventing the formation of abscesses. Chloramphenicol, penicillin G, and cephalothin were not effective in protecting the mice from infection.

Use of semisolid agar from initiation of pure Bacteroides fragilis infection in mice

The development of a pure Bacteroides fragilis infection in mice is described. The infection produces large subcutaneous abscesses at the site of injection which can be observed grossly within 7 days after injection. The infection was initiated by infection of pure cultures grown in semisolid agar medium. Similar infections were also produced with pure cultures of B. distasonis, B. ovatus, B. thetaiotaomicron, and B. vulgatus. However, a distinct deoxyribonucleic acid homology group, formerly classified as B. thetaiotaomicron, did not produce abscesses in any of the mice tested.

Comparison of cefoxitin and cephalothin therapy of a mixed Bacteroides fragilis and Fusobacterius necrophorum infection in mice

Cefoxitin, a beta-lactamase-resistant cephalosporin, was found to be more effective than cephalothin against an experimental mixed infection containing Bacteroides fragilis and Fusobacterium necrophorum.