Clinical features and prognostic factors of anaerobic infections: a 7-year retrospective study

Polymicrobial Bacterial Meningitis in a Patient with Chronic Suppurative Otitis Media: Case Report and Literature Review

Polymicrobial meningitis is a rare entity in the adult population, especially in the antibiotic era. However, disorders such as chronic suppurative otitis media (CSOM) or even poor oral hygiene are considered risk factors for the development of such cerebral infection. We report a case of polymicrobial meningitis associated with oto-mastoiditis in a 64-year-old female patient known to have CSOM. The patient presented atypical symptoms for community-acquired meningitis, showing subacute evolution of headache, without fever or neck stiffness. The aerobe microorganisms Streptococcus anginosus and Corynebacterium spp., sensitive to beta-lactamines, and the anaerobe Prevotella spp., resistant to penicillin and metronidazole, were isolated from CSF specimens, while Proteus mirabilis and Enterococcus faecalis were identified from the ear drainage. The diversity of pathogens identified in our case led us to the hypothesis of two different sources of meningitis: otogenic and/or odontogenic. Favorable evolution was obtained after a multi-disciplinary approach, combining surgery and broad-spectrum antibiotics. In addition, we performed a literature review that highlights the low incidence of polymicrobial mixed aerobe-anaerobe meningitis.

A case report of severe Fusobacterium nucleatum sepsis secondary to nephrectomy

Background

Fusobacterium nucleatum (F. nucleatum) is a resident anaerobic bacterium, which in rare cases may invade blood from the head and neck or the digestive tract to cause bacteremia and induce venous thrombosis. F. nucleatum is closely related to abdominal tumors, but it has not been reported in relation to renal tumors. We report herein a possible case.

Case presentation

This patient had kidney cancer with thrombosis in the right renal vein but had no sign of infection. After radical nephrectomy, thrombi formed in his left renal vein, and when removed, severe sepsis occurred. He did not respond to treatment with antibiotics and died, but the blood culture done confirmed that he had F. nucleatum bacteremia.

Conclusion

F. nucleatum may also be associated with kidney cancer, and could cause post-operative renal vein thrombosis, and sepsis or septic shock after thrombectomy.

Anaerobic infections in patients admitted in various surgical units of a tertiary care hospital of north India: neglected but important

Background and Objectives:

Anaerobic infections are usually caused by the host’s endogenous flora due to a breach in the anatomical barriers and Bacteroides spp. are the most notorious organisms associated with anaerobic infections. The identification of anaerobes has been a challenge since times. MALDI-TOF-MS is a boon for aiding the rapid detection of anaerobic organisms and has helped us to enlist the distribution of various anaerobic pathogens.

Materials and Methods:

This retrospective analysis (January 2018 to December 2019) was carried out in a tertiary care hospital in North India, in which the anaerobic microbiological profile of all patients admitted to surgical wards, ICU, and OPD of various departments (Orthopedics, Surgery, Gynecology, and Obstetrics) was reviewed. Samples received were immediately processed aerobically (5% sheep blood agar and Mac Conkeyagar) as well as anaerobically (RCM and freshly prepared sheep blood agar) as per the laboratory protocols.

Results:

Bacteroides fragilis (19.12%) was the most common anaerobe whereas among aerobes Escherichia coli (30.2%) followed by Klebsiella pneumoniae (10.34%) were most commonly isolated. The majority of patients were males (56%) and the most common presentation was with abscesses (21.4%). Polymicrobial infections (69.51%) outnumbered monomicrobial ones (30.48%).

Conclusion:

There is a paucity of literature on anaerobe isolation from surgical infections from our country which motivated us to study anaerobic infections and the high sample size in our institute enabled us to study surgical infections from an anaerobic perspective. This will add to the knowledge of microbiologists and clinicians. MALDI-TOF MS helped in rapid and accurate identification and hence we could report a wider spectrum of organisms in our study.

Oxygen and Metabolism: Digesting Determinants of Antibiotic Susceptibility in the Gut

Microbial metabolism is a major determinant of antibiotic susceptibility. Environmental conditions that modify metabolism, notably oxygen availability and redox potential, can directly fine-tune susceptibility to antibiotics. Despite this, relatively few studies have discussed these modifications within the gastrointestinal tract and their implication on in vivo drug activity and the off-target effects of antibiotics in the gut. In this review, we discuss the environmental and biogeographical complexity of the gastrointestinal tract in regard to oxygen availability and redox potential, addressing how the heterogeneity of gut microhabitats may modify antibiotic activity in vivo. We contextualize the current literature surrounding oxygen availability and antibiotic efficacy and discuss empirical treatments. We end by discussing predicted patterns of antibiotic activity in prominent microbiome taxa, given gut heterogeneity, oxygen availability, and polymicrobial interactions. We also propose additional work required to fully elucidate the role of oxygen metabolism on antibiotic susceptibility in the context of the gut.

Fusobacterium bloodstream infections: A literature review and hospital-based case series

BACKGROUND

Infections with Fusobacterium, an anaerobic bacterium, have various clinical presentations, including bacteremia and Lemierre syndrome. Here, we report a case series of Fusobacterium bacteremia (FBB) from the largest academic center in Riyadh, Saudi Arabia, and provide a review of cases in the available literature.

METHOD

Records were retrospectively reviewed for all patients with at least one blood culture positive for Fusobacterium spp. admitted at King Khalid University Hospital, Riyadh, Saudi Arabia, between May 2015 to April 2019.

LITERATURE REVIEW

We conducted a MeSH Search on MedLine using the following terms: ("Bacteremia"[Mesh]) AND "Fusobacterium"[Mesh] for studies conducted from January 1, 1990, until March 30, 2019, excluding articles that lacked adequate clinical or microbiological details for individuals patients. Odds ratios and results of Chi-Square testing obtained in SPSS (Version 23.0, SPSS, Inc., Chicago, IL, USA) were considered statistically significant at p-values < 0.05.

RESULTS

Seven cases from our center and 205 cases from the literature were reviewed in this first reported case series for the region. Our patient series was similar to previous ones in terms of median age (45 vs. 45.5 years) and male predominance (85% vs. 65.9%). The species of Fusobacterium cultured from our cases were F. nucleatum (4 cases), F. varium (1 case), F. mortiferum (1 case), and one that could not be identified to the species level (1 case). We also report one case of FBB with renal vein thrombosis resembling that of atypical Lemierre syndrome. Analysis of literature cases revealed that bacteremia caused by the species most commonly associated with FBB, F. necrophorum, tended to be present in patients less than 40 years of age and be associated with head and neck infections and other complications, whereas F. nucleatum tended to affect people more than 40 years of age and be associated with mortality.

CONCLUSION

Although FBB is rarely reported in the literature, this case series and review of the literature suggests it is associated with morbidity and mortality. The type and duration of therapy used in these cases are underreported. Further research is needed to determine the most appropriate screening approach for FBB-associated complications and explore the relationship between FBB and specific malignancies, as well as optimal treatment type and duration.

Bacteroides fragilis requires the ferrous-iron transporter FeoAB and the CobN-like proteins BtuS1 and BtuS2 for assimilation of iron released from heme

The intestinal commensal and opportunistic anaerobic pathogen Bacteroides fragilis has an essential requirement for both heme and free iron to support growth in extraintestinal infections. In the absence of free iron, B. fragilis can utilize heme as the sole source of iron. However, the mechanisms to remove iron from heme are not completely understood. In this study, we show that the inner membrane ferrous iron transporter ∆feoAB mutant strain is no longer able to grow with heme as the sole source of iron. Genetic complementation with the feoAB gene operon completely restored growth. Our data indicate that iron is removed from heme in the periplasmic space, and the released iron is transported by the FeoAB system. Interestingly, when B. fragilis utilizes iron from heme, it releases heme-derived porphyrins by a dechelatase activity which is upregulated under low iron conditions. This is supported by the findings showing that formation of heme-derived porphyrins in the ∆feoAB mutant and the parent strain increased 30-fold and fivefold (respectively) under low iron conditions compared to iron replete conditions. Moreover, the btuS1 btuS2 double-mutant strain (lacking the predicted periplasmic, membrane anchored CobN-like proteins) also showed growth defect with heme as the sole source of iron, suggesting that BtuS1 and BtuS2 are involved in heme-iron assimilation. Though the dechelatase mechanism remains uncharacterized, assays performed in bacterial crude extracts show that BtuS1 and BtuS2 affect the regulation of the dechelatase-specific activities in an iron-dependent manner. These findings suggest that the mechanism to extract iron from heme in Bacteroides requires a group of proteins, which spans the periplasmic space to make iron available for cellular functions.

Impact of microbiota in colorectal carcinogenesis: lessons from experimental models

A role of gut microbiota in colorectal cancer (CRC) growth was first suggested in germ-free rats almost 50 years ago, and the existence of disease-associated bacteria (termed pathobionts) had becoming increasingly evident from experimental data of fecal transplantation, and microbial gavage or monoassociation. Altered bacterial compositions in fecal and mucosal specimens were observed in CRC patients compared to healthy subjects. Microbial fluctuations were found at various cancer stages; an increase of bacterial diversity was noted in the adenoma specimens, while a reduction of bacterial richness was documented in CRC samples. The bacterial species enriched in the human cancerous tissues included Escherichia coli, Fusobacterium nucleatum, and enterotoxigenic Bacteroides fragilis. The causal relationship of gut bacteria in tumorigenesis was established by introducing particular bacterial strains in in situ mouse CRC models. Detailed experimental protocols of bacterial gavage and the advantages and caveats of different experimental models are summarized in this review. The microbial genotoxins, enterotoxins, and virulence factors implicated in the mechanisms of bacteria-driven tumorigenesis are described. In conclusion, intestinal microbiota is involved in colon tumorigenesis. Bacteria-targeting intervention would be the next challenge for CRC.

Odontogenic orbital abscess with intracranial and pulmonary involvement

A 58-year-old woman presented to the emergency department with left ptosis and complete ophthalmoplegia. Imaging demonstrated a left orbital abscess. Her past medical history included cavitatory lung disease and "aseptic" meningitis 2 months previously. An anaerobic organism and commensal of the oral flora, Peptostreptococcus sp., was cultured from the orbital abscess. The patient was found to have a carious upper molar with chronic buccal abscess, which was extracted. This case presents an uncommon pathogen arising from an odontogenic infection as the etiology for orbital abscess, cavitatory lung disease, and meningitis in one patient.

Anaerobic bacteria growth in the presence of cathelicidin LL-37 and selected ceragenins delivered as magnetic nanoparticles cargo

BACKGROUND

Cationic antibacterial peptides (CAPs) and synthetic molecules mimicking the amphiphilic structure of CAPs, such as ceragenins, are promising compounds for the development of new antimicrobials.

RESULTS

We tested the in vitro activity of ceragenins CSA-13 and CSA-131 against several anaerobic bacteria including Bacteroides spp. and Clostridium difficile. We compared results to the activity of cathelicidin LL-37, metronidazole and nanosystems developed by attachment of CSA-13 and CSA-131 to magnetic nanoparticles (MNPs). The antibacterial effect was tested using killing assay and modified CLSI broth microdilution assay. Ceragenins CSA-13 and CSA-131 displayed stronger bactericidal activity than LL-37 or metronidazole against all of the tested bacterial strains. Additionally CSA-131 revealed an enhanced ability to prevent the formation of Bacteroides fragilis and Propionibacterium acnes biofilms.

CONCLUSIONS

These data confirmed that ceragenins display antimicrobial activity against a broad range of microorganisms including anaerobic bacteria and deserve further investigations as compounds serving to develop new treatment against anaerobic and mixed infections.

Clostridium baratii: a rare case of pneumonia associated with an Alzheimer patient in Rio de Janeiro, Brazil

Introduction:

Clostridium baratii is rarely associated with human diseases. Infection is usuallcaused by ingestion of contaminated food, and infant botulism is the most common clinical presentation.

Case Report:

Here we report a case of pneumonia by a non-toxigenic strain of C. baratii in an Alzheimer 70-year-old male with sepsis in Rio de Janeiro, Brazil. The micro-organism was identified by phenotypical tests, mass spectrometry (MALDI-TOF), DNA amplification (PCR) and sequencing of the 16S rRNA gene. Testing for the presence of botulinum F toxin was made using multiplex PCR. Bioassay for a large number of colonies was performed in mice to evaluate the production of any lethal toxin, but the results were negative.

Conclusion:

To our knowledge, there are no cases of C. baratii infection reported in Brazil and we highlight the importance of anaerobic lab tests in the standard routine of diagnosis.

Epidemiology and antimicrobial susceptibilities of wound isolates of obligate anaerobes from combat casualties

Data from recent conflicts related to war wounds and obligate anaerobes are limited. We define the epidemiology and antimicrobial susceptibility of obligate anaerobes from Iraq and Afghanistan casualties (6/2009-12/2013), as well as their association with clinical outcomes. Susceptibility against eleven antibiotics (7 classes) was tested. Overall, 59 patients had 119 obligate anaerobes identified (83 were first isolates). Obligate anaerobes were isolated 7-13 days post-injury, primarily from lower extremity wounds (43%), and were largely Bacteroides spp. (42%) and Clostridium spp. (19%). Patients with pelvic wounds were more likely to have Bacteroides spp. and concomitant resistant gram-negative aerobes. Seventy-three percent of isolates were resistant to ≥1 antimicrobials. Bacteroides spp. demonstrated the most resistance (16% of first isolates). Patients with resistant isolates had similar outcomes to those with susceptible strains. Serial recovery of isolates occurred in 15% of patients and was significantly associated with isolation of Bacteroides spp., along with resistant gram-negative aerobes.

Ferritin-like family proteins in the anaerobe Bacteroides fragilis: when an oxygen storm is coming, take your iron to the shelter

Bacteroides are gram-negative anaerobes and one of the most abundant members the lower GI tract microflora where they play an important role in normal intestinal physiology. Disruption of this commensal relationship has a great impact on human health and disease. Bacteroides spp. are significant opportunistic pathogens causing infections when the mucosal barrier integrity is disrupted following predisposing conditions such as GI surgery, perforated or gangrenous appendicitis, perforated ulcer, diverticulitis, trauma and inflammatory bowel diseases. B. fragilis accounts for 60-90 % of all anaerobic infections despite being a minor component of the genus (<1 % of the flora). Clinical strains of B. fragilis are among the most aerotolerant anaerobes. When shifted from anaerobic to aerobic conditions B. fragilis responds to oxidative stress by inducing the expression of an extensive set of genes involved in protection against oxygen derived radicals and iron homeostasis. In Bacteroides, little is known about the metal/oxidative stress interactions and the mobilization of intra-cellular non-heme iron during the oxidative stress response has been largely overlooked. Here we present an overview of the work carried out to demonstrate that both oxygen-detoxifying enzymes and iron-storage proteins are essential for B. fragilis to survive an adverse oxygen-rich environment. Some species of Bacteroides have acquired multiple homologues of the iron storage and detoxifying ferritin-like proteins but some species contain none. The proteins found in Bacteroides are classical mammalian H-type non-heme ferritin (FtnA), non-specific DNA binding and starvation protein (Dps) and the newly characterized bacterial Dps-Like miniferritin protein. The full contribution of ferritin-like proteins to pathophysiology of commensal and opportunistic pathogen Bacteroides spp. still remains to be elucidated.

[Anaerobic bacteria 150 years after their discovery by Pasteur]

In 2011 we celebrated the 150th anniversary of the discovery of anaerobic bacteria by Louis Pasteur. The interest of the biomedical community on such bacteria is still maintained, and is particularly focused on Clostridium difficile. In the past few years important advances in taxonomy have been made due to the genetic, technological and computing developments. Thus, a significant number of new species related to human infections have been characterised, and some already known have been reclassified. At pathogenic level some specimens of anaerobic microflora, that had not been isolated from human infections, have been now isolated in some clinical conditions. There was emergence (or re-emergence) of some species and clinical conditions. Certain anaerobic bacteria have been associated with established infectious syndromes. The virulence of certain strains has increased, and some hypotheses on their participation in certain diseases have been given. In terms of diagnosis, the routine use of MALDI-TOF has led to a shortening of time and a cost reduction in the identification, with an improvement directly related to the improvement of data bases. The application of real-time PCR has been another major progress, and the sequencing of 16srRNA gene and others is currently a reality for several laboratories. Anaerobes have increased their resistance to antimicrobial agents, and the emergence of resistance to carbapenems and metronidazole, and multi-resistance is a current reality. In this situation, linezolid could be an effective alternative for Bacteroides. Fidaxomicin is the only anti-anaerobic agent introduced in the recent years, specifically for the diarrhoea caused by C.difficile. Moreover, some mathematical models have also been proposed in relation with this species.

Expression of Bacteroides fragilis hemolysins in vivo and role of HlyBA in an intra-abdominal infection model

Bacteroides fragilis is the most frequent opportunistic pathogen isolated from anaerobic infections. However, there is a paucity of information regarding the genetic and molecular aspects of gene expression of its virulence factors during extra-intestinal infections. A potential virulence factor that has received little attention is the ability of B. fragilis to produce hemolysins. In this study, an implanted perforated table tennis "ping-pong" ball was used as an intra-abdominal artificial abscess model in the rat. This procedure provided sufficient infected exudate for gene expression studies in vivo. Real-time reverse transcription polymerase chain reaction (RT-PCR) was used to quantify the relative expression of hlyA, hlyB, hlyC, hlyD, hlyE, hlyF, hlyG, and hlyIII mRNAs. The hlyA mRNA was induced approximately sixfold after 4 days postinfection compared with the mRNA levels in the inoculum culture prior to infection. The hlyB mRNA increased approximately sixfold after 4 days and 12-fold after 8 days postinfection. Expression of hlyC mRNA increased sixfold after 1 day, 45-fold after 4 days, and 16-fold after 8 days postinfection, respectively. The hlyD and hlyE mRNAs were induced approximately 40-fold and 30-fold, respectively, after 4-days postinfection. The hlyF expression increased approximately threefold after 4-days postinfection. hlyG was induced approximately fivefold after 4 and 8 days postinfection. The hlyIII mRNA levels had a steady increase of approximately four-, eight-, and 12-fold following 1, 4, and 8 days postinfection, respectively. These findings suggest that B. fragilis hemolysins are induced and differentially regulated in vivo. Both parent and hlyBA mutant strains reached levels of approximately 3-8 × 10(9) cfu/mL after 1 day postinfection. However, the hlyBA mutant strain lost 2 logs in viable cell counts compared with the parent strain after 8 days postinfection. This is the first study showing HlyBA is a virulence factor which plays a role in B. fragilis survival in an intra-abdominal abscess model.

Oxygen tolerance in anaerobic pathogenic bacteria

A prerequisite for successful identification of anaerobic pathogenic bacteria from samples of clinical material is the method of cultivation. Currently, several methods of cultivation in anaerobic environment are used: cultivation in anaerobic box, anaerobic jar, and in nonrecurring cultivation system. Here, we determined the suitability of the above methods of cultivation using the estimation of the growth (diameters of colony size) of commonly isolated anaerobic pathogens (Bacteroides fragilis, Clostridium difficile, and Clostridium perfringens). The tested bacterial strains were exposed to atmospheric oxygen for various time periods and then they were cultivated using different anaerobic cultivation systems. Maximum growth differed, depending on the type of cultivation and the strain used. Thus, largest zone diameters, in the majority of measurements, were achieved in the anaerobic box. However, nonrecurring cultivation system seemed better in several cases; this applied to the cultivation of C. perfringens after 15, 30, and 60 min exposure to atmospheric oxygen as well as the cultivation of B. fragilis after 30 and 60 min of oxygen exposure. The cultivation in anaerobic box was the most convenient method for growth of C. difficile. In almost all cases, higher growth was observed in nonrecurring cultivation system than in the system of anaerobic jar. On the other hand, no significant differences were observed among these anaerobic cultivation systems which confirmed their applicability (taking into account some individual features concerning the optimization of cultivations) for identification of pathogenic anaerobes.