Anaerobic Bacterium

P. modestum is an anaerobic bacterium that ferments succinate to propionate past a short reaction sequence:succinate→succinyl CoA→methylmalonyl CoA→propionyl CoA→propionate.

From: Bioenergetics 2 , 1992

Anaerobic Bacteria

Itzhak Brook , Sarah S. Long , in Principles and Practice of Pediatric Infectious Diseases (Fifth Edition), 2018

Classification

Anaerobic bacteria predominate on normal skin and amid the bacterial flora of mucous membranes. 1,2 Infections caused by anaerobic bacteria are common, ascend from the sites where they are normal flora (endogenous), and can be serious or life-threatening. Anaerobic bacteria are fastidious, hard to isolate, and ofttimes overlooked. Their recovery requires proper methods of collection, transportation, and cultivation. iii–seven Their ubiquity on mucocutaneous surfaces oft interferes with obtaining meaningful cultures. Although no universally accustomed or unproblematic and authentic way has been established to classify microorganisms according to conditions required for their replication, Tabular array 187.1 presents a useful framework for the clinician. Nevertheless, differences amidst strains exist within the aforementioned species.

Anaerobic bacteria do not replicate in the presence of oxygen; however, they showroom substantial differences in lethal effect of oxygen. In full general, anaerobic organisms plant exclusively as normal flora are strict anaerobes (i.e., die inside minutes in <0.5% oxygen), whereas those of clinical significance are somewhat aerotolerant (i.e., tolerate 2% to 8% oxygen). Strict anaerobes practice not grow in x% carbon dioxide in air; microaerophilic leaner can grow in 10% carbon dioxide in air or under aerobic or anaerobic conditions, and facultative organisms can grow in the presence or absence of air. The physiologic basis for oxygen sensitivity is not well understood. Common teaching is that negative oxidation-reduction potential (Eh) of the environment is the disquisitional factor. However, studies with Bacteroides fragilis reveal that oxygen has a direct toxic effect; chemic manipulation of oxidation-reduction potential has no upshot if oxygen is not introduced. Furthermore, aerotolerance and possibly virulence of anaerobic leaner correlate with the ability to induce the protective enzyme superoxide dismutase on exposure to oxygen. 4

The clinically important anaerobic genera are shown in Table 187.two. The taxonomy of anaerobic bacteria has changed because of improved characterization through the utilise of genetic studies. 3,5 Discriminating among strains enables better label of the source of infection and prediction of antimicrobial susceptibility. The genera and groups most frequently isolated from clinical infections, in descending frequency are: Bacteroides/Prevotella spp., Peptostreptococcus spp., Clostridium spp., Fusobacterium spp., gram-positive bacilli, and gram-negative cocci. 2,iii

The utilise of DNA technology (e.m., decision of Dna mole per centum guanine plus cytosine content, ribosomal RNA homology, gel electrophoresis sequencing) and chemotaxonomic analyses (e.1000., analysis of peptidoglycans, gas-liquid chromatography of whole cell fatty acids) has enlightened taxonomic relationships among anaerobic bacteria. Wide-ranging taxonomic changes have affected the family Bacteroidaceae and anaerobic gram-positive cocci. Bacteroides melaninogenicus, a unmarried species until 1977, now encompasses 2 genera (Prevotella and Porphyromonas) and >15 species. 8 Modest changes have been fabricated in the nomenclature of gram-positive bacilli, and the genus Eubacterium remains heterogeneous and inadequately examined.

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Etiologic Agents of Infectious Diseases

Itzhak Beck , Sarah S. Long , in Principles and Practice of Pediatric Infectious Diseases (Fourth Edition), 2012

Nomenclature

Anaerobic bacteria predominate in normal skin and the bacterial flora of mucous membranes. 1,ii Infections caused by anaerobic bacteria are mutual, arise from the sites where they are normal flora (endogenous) and can be serious or life-threatening. Anaerobic bacteria are captious, hard to isolate, and often overlooked. Their recovery requires proper methods of collection, transportation, and tillage. three–6 Their ubiquity on mucocutaneous surfaces often interferes with obtaining meaningful cultures. Although at that place is no universally accepted or simple and accurate style to classify microorganisms co-ordinate to weather condition required for their replication, Table 187-one presents a useful framework for the clinician. Nonetheless, differences between strains exist inside the aforementioned species.

Anaerobic bacteria practice non replicate in the presence of oxygen; notwithstanding, they showroom substantial differences in lethal outcome of oxygen. In general, anaerobic organisms establish exclusively as normal flora are strict anaerobes (i.due east., dice inside minutes in <0.5% oxygen), whereas those of clinical significance are somewhat aerotolerant (i.e., tolerate 2% to viii% oxygen). Strict anaerobes practice not grow in 10% COtwo in air; microaerophilic bacteria tin grow in 10% CO2 in air or under aerobic or anaerobic weather condition, and facultative organisms can grow in the presence or absence of air. The physiologic basis for oxygen sensitivity is not well understood. Mutual educational activity is that negative oxidation-reduction potential (Eh) of the environment is the disquisitional factor. However, studies with Bacteroides fragilis reveal that oxygen has a directly toxic effect; chemic manipulation of oxidation-reduction potential has no effect if oxygen is not introduced. Furthermore, aerotolerance, and possibly virulence, of anaerobic bacteria correlates with ability to induce the protective enzyme superoxide dismutase on exposure to oxygen. iv

Although Louis Pasteur is credited with discovery of the first truthful anaerobe, Clostridium butyricum in 1861, 4 and Altemeier 7 made landmark observations of their importance in intra-abdominal infections in the 1930s, major advances occurred in the 1960s with the increased ability to isolate and classify these bacteria and the potential to care for related infections.

The clinically important anaerobic genera are shown in Table 187-ii. The taxonomy of anaerobic leaner has changed because of improved characterization through the utilize of genetic studies. 3,5 The ability to differentiate betwixt similar strains enables improve label of the blazon of infection and prediction of antimicrobial susceptibility. The genera/groups nearly frequently isolated from clinical infections, in descending lodge of frequency, are: Bacteroides spp., Peptostreptococcus spp., Clostridium spp., Fusobacterium spp., gram-positive bacilli, and gram-negative cocci. 2,iii

The utilize of DNA technology (e.g., decision of DNA G+C mol%, ribosomal RNA homology, gel electrophoresis sequencing) and chemotaxonomic analyses (due east.g., assay of peptidoglycans, gas–liquid chromatography of whole-cell fatty acids) has enlightened taxonomic relationships amid anaerobic bacteria. Wide-ranging taxonomic changes have affected the family unit Bacteroidaceae and anaerobic gram-positive cocci. Bacteroides melaninogenicus, a single species until 1977, at present encompasses two genera (Prevotella and Porphyromonas) and >15 species. 8 Minor changes accept been made in the classification of gram-positive bacilli, and the genus Eubacterium remains heterogeneous and inadequately examined.

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Anaerobic Bacteria

Itzhak Brook , in Infectious Diseases (Fourth Edition), 2017

Introduction

Infections caused by anaerobic leaner are common and may be serious and life-threatening. Anaerobes are the predominant components of the bacterial flora of normal human pare and mucous membranes, 1 and are therefore a common cause of bacterial infections of endogenous origin. Considering of their fastidious nature, they are difficult to isolate and are oft overlooked. Delay in appropriate therapy often leads to clinical failures. Their isolation requires proper methods of drove, transportation and cultivation of specimens. 2–5 Treatment is complicated by the slow growth of these organisms, past the infection's polymicrobial nature and by the organisms' growing antimicrobial resistance.

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Infections Caused past Anaerobic Microorganisms

Fernando Cobo , in Reference Module in Biomedical Sciences, 2021

Abstruse

Anaerobic microorganisms are common pathogens in humans. Although most clinically significant anaerobes are involved in mixed infections alongside aerobic bacteria, they may be responsible for severe illness in sure circumstances, such as bloodstream infections. Anaerobes that commonly cause human infections are Bacteroides, Prevotella, Fusobacterium, Clostridium species and Gram-positive anaerobic cocci. Anaerobes are commensals in mucosal surfaces, such every bit the oral cavity and the gastrointestinal and female genital tracts. Infections involving anaerobes are unremarkably polymicrobial and often result from the disruption of mucosal surfaces mainly past surgery, trauma and the presence of tumors. Considering of their fastidious nature, anaerobic agents are hard to diagnose and are often disregarded. Their isolation requires appropriate methods for collection, ship and culture. Infections involving anaerobes include aspiration pneumonia and lung abscesses, brain abscesses, oral and dental processes, peritonitis, soft tissue and deep wounds post-surgical infections and bacteremia. Overall, successful treatment against anaerobic pathogens should include advisable antimicrobial agents and surgical management of infection. The antibiotics with the greatest activity against the bulk of anaerobic leaner include metronidazole, β-lactam/βlactamase inhibitor combinations and carbapenems. Antibiotic resistance among anaerobic microorganisms has increased significantly over the past years, merely resistance rates vary widely amongst different geographic regions.

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Infections in the Immunocompromised Host

J. Peter Donnelly , ... Walter J.F.Chiliad. van der Velden , in Mandell, Douglas, and Bennett'due south Principles and Exercise of Infectious Diseases (8th Edition), 2015

Microbial Microbiota

Anaerobic bacteria predominate among the resident microbiota of the oral crenel and large intestine population and play a crucial role in maintaining a healthy commensal microbiota by providing the facility to withstand the institution of exogenous organisms, which is known as colonization resistance. 34 However, the microbial microbiota is non the but participant in the establishment and maintenance of colonization resistance. Recently, in that location has been renewed interest in the human commensal microbiota, which can be divided into microbiomes that are associated with health and disease. The diverse species as well participate in training and shaping the immune response, maintaining information technology and keeping information technology healthy. In fact, the host-microbial interaction is far more than complex than hitherto imagined, involving host pattern recognition receptors, bacteriocins, and lactic acrid, to name but a few, likewise as competitors for bachelor nutrients and the release of host antimicrobial peptides. 35-37

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Cellulases

Joana L.A. Brás , ... Carlos Yard.Thousand.A. Fontes , in Methods in Enzymology, 2012

half-dozen Summary

Anaerobic microbes produce a remarkably efficient nanomachine to deconstruct institute cell wall polysaccharides, which was termed, when discovered more than 20 years ago, equally the cellulosome. Cellulases and hemicellulases are assembled into multienzyme complexes through a high analogousness interaction established betwixt type I dockerin domains of the modular enzymes and type I cohesin modules of a noncatalytic scaffoldin (Fig. 21.4). Information technology is believed that integration of the microbial biocatalysts into cellulosomes potentiates catalysis through the maximization of enzyme synergism afforded past enzyme proximity and efficient substrate targeting. Substantial structural and functional prove exists, suggesting that cellulosomal dockerins display a dual cohesin binding interface. The dual binding manner expressed by cohesin–dockerin complexes may innovate enhanced flexibility in the fourth organization of the multienzyme complex thus potentiating the hydrolysis of a predominantly insoluble substrate. Recently, information technology has get apparent that the cohesin–dockerin interaction is quite widespread in nature and may fulfill a large range of, mostly currently unknown, functions which remain to be described.

Effigy 21.four. The dual binding mode of cohesin–dockerin complexes. Ribbon representation of the superposition of the dockerin modules of type I cohesin–dockerin native complex (light gray) with the S45A–T46A mutant complex (night gray) in C. thermocellum. For simplification, only ane cohesin module is represented. The inset shows a more than detailed view of the cohesin–dockerin contacts and of the almost perfect superposition of helices 1 and iii of both complexes. In the mutant complex, helix-1 (containing Ser-11 and Thr-12) dominates binding whereas, in the native complex, helix-3 (containing Ser-45 and Thr-46) plays a central office in ligand recognition. Ser-11, Thr-12, Ser-45, and Thr-46, which interact with the cohesin module, are depicted as ball-and-stick models.

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Osteomyelitis

David K. Hong , Kathleen Gutierrez , in Principles and Practice of Pediatric Infectious Diseases (5th Edition), 2018

Anaerobic Bacterial Osteomyelitis

Anaerobic leaner are associated with chronic and nonhematogenously acquired osteomyelitis. 161–163 Run a risk factors include surgery, trauma, diabetes mellitus, homo bites, chronic otitis media or sinusitis, dental infection, gristly dysplasia of bone, a prosthesis, and decubitus ulcers (Fig. 76.vi). Children are more than likely than adults to experience anaerobic osteomyelitis of the skull and facial bones. 161 Osteomyelitis of ribs follows contiguous spread from aspiration lung infection; Actinomyces spp. are the primary pathogens. Soft tissue swelling or abscess can be the presenting abnormality. Similarly, Actinomyces spp. can cause osteomyelitis of the maxilla or mandible, frequently without dental pathology.

Infection normally is polymicrobial. Gram-positive cocci, Bacteroides spp., Prevotella spp., and Fusobacterium spp. are the most common anaerobes, and S. aureus is the most commonly associated aerobic isolate. 162

Therapy consists of treatment of underlying conditions, surgical debridement of necrotic bone, and appropriate antibiotic therapy. Examples of effective antibiotics are clindamycin, metronidazole, imipenem, and amoxicillin-clavulanate. Many anaerobic isolates, including Actinomyces, are susceptible to penicillin. The choice of antibiotic depends on the specific organisms isolated and their potential for β-lactamase production. Therapy is protracted, frequently exceeding 1 year of oral penicillin or amoxicillin plus probenecid for actinomycosis.

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Bacteroides and Prevotella Species and Other Anaerobic Gram-Negative Bacilli

Itzhak Brook , in Principles and Practice of Pediatric Infectious Diseases (Fifth Edition), 2018

Primal Nervous System Infections

Anaerobic leaner, including AGNB, tin can cause a variety of intracranial infections: brain abscess, subdural empyema, epidural abscess, and meningitis. 11,12 Infection by and large is polymicrobial, mixed with microaerophilic streptococci. The main source of brain abscess is an next, generally chronic infection in the center ear, mastoid, sinus, oropharynx, teeth, or lungs. Middle ear or mastoid infections tend to spread to the temporal lobe or cerebellum, whereas sinusitis often causes abscess of the frontal lobe. Hematogenous spread ofttimes occurs after dental, oropharyngeal, or pulmonary infection. 13,14 Rarely, bloodstream infection (BSI) has another origin, or endocarditis can lead to central nervous system infection. Meningitis is rare and tin can follow respiratory tract infection, or information technology can occur every bit a complication of a cerebrospinal fluid shunt. Ventriculoperitoneal shunt infection with the B. fragilis group can have an enteric origin after perforation of the gut. 15

At the stage of encephalitis, antimicrobial therapy tin prevent the formation of abscesses. In one case an abscess has formed, excision or drainage by and large are needed, combined with four to eight weeks of antibiotics. Administration of antibiotics for an extended period is an alternative arroyo that can replace surgical drainage in selected patients. Depending on the organism or organisms isolated and β-lactamase production, metronidazole, penicillins, and chloramphenicol often are called considering of their spectrum and favorable pharmacodynamic profile.

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Nitric Oxide and Other Pocket-size Signalling Molecules

Jeffrey A. Cole , in Advances in Microbial Physiology, 2018

2.1 Chemic and Biochemical Sources of NO

Anaerobic bacteria encounter NO from substantially 3 main sources—but there are also other pocket-sized sources. Oxygen is severely express in the lower regions of the alimentary canal, where a wide variety of anaerobic leaner live by fermentation of the arable supply of carbon compounds. Many of the bacteria are in biofilms fastened to the epithelial jail cell layer. Notwithstanding, NO generated from arginine in the claret stream diffuses rapidly across membranes and through tissues. Bacteria in closest contact with the epithelium are therefore exposed to this source of NO and must exist able to protect themselves appropriately.

A second source is NO released by denitrifying bacteria, which, although scarce in the gastrointestinal tract, are arable in anaerobic soils, sediments and h2o treatment plants. For many years whether NO is an obligate intermediate in denitrification was itself controversial (Averill & Tiedje, 1982; Payne, Riley, & Cox, 1971). The controversy was resolved when Braun and Zumft (1991) demonstrated that a Pseudomonas stutzeri mutant defective in NO reductase could non survive exposure to nitrate or nitrite unless there was a secondary mutation in the genes required for nitrite reduction to NO, which in this organism is the factor nirK encoding a copper-containing nitrite reductase. Denitrifying bacteria differ widely in their ability to minimise NO accumulation, reflecting their different abilities to tolerate or detoxify NO (Mania, Heylen, van Spanning, & Frostegård, 2015; and references therein).

Finally, NO is generated during the anaerobic reduction of nitrite to ammonia when the supply of electron donors is abundant, just the concentrations of nitrate or nitrite are low (see Department 2.3).

Among the pocket-sized sources of NO in an anaerobic environment is the chemical reduction of nitrite by ferrous ions or the reduced forms of cytochromes and atomic number 26–sulphur centres. This has not been quantified.

Other sources include NO generated from atmospheric North2 and O2 at high temperatures such every bit those generated during a lightning strike (Levine, Augustsson, Anderson, Hoell, & Brewer, 1984). Worldwide this could account for the generation of eight.6 1000000 tonnes of nitric oxide and nitrogen dioxide annually (Ott et al., 2010). In comparison, information technology has been estimated that emissions of nitrogen oxides, NO and North2O, resulting from fossil fuel combustion are well-nigh thirty million tonnes (Schumann & Huntrieser, 2007). Although NO is a reactive-free radical gas, its reaction with O2 is highly concentration dependent, increasing with the square of the NO concentration. At low concentrations, NO is relatively stable even in the presence of oxygen. For example, the half-life of oxidation of 10 parts per one thousand thousand of atmospheric NO to NO2 is well-nigh 6   h, just less than 1   min at ten,000   ppm. At depression concentrations, the half-life is sufficiently long for some NO to be washed into oxygen-express layers of soil by rain.

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LUNG ABSCESS

H. Koziel , in Encyclopedia of Respiratory Medicine, 2006

Etiology

Anaerobic bacteria are considered the well-nigh common pathogens in community-caused lung abscess, reflecting both pathogenic potential and representing the predominant component of normal flora of the upper airways (although any pathogen can create a lung abscess under the appropriate circumstances). Prior studies using transtracheal aspirates or transthoracic needle aspirates reported recovery rates of anaerobic bacteria from 85% to 93% of lung abscess cases. Anaerobes were the only isolates in up to 46% of cases, whereas 43% of cases had a mixture of aerobes and anaerobes (Table ane). Although anaerobic abscesses generally comprise multiple anaerobic isolates, occasionally lung abscesses may consequence from a single anaerobic organism recognized as highly virulent, such equally Fusobacterium nucleatum or Peptopstreptococcus species. Anaerobes may besides exist in combination with aerobic or facultative anaerobic species such as microaerophilic streptococci.

Table 1. Reported microbiology of lung abscess

Anaerobic organisms (common) a
Fusobacterium nucleatum
Peptopstreptococcus species
Prevotella melaninogenica
Bacteroides species
Clostridium species
Eubacterium species
Lactobacillus
Propionibacteria
Aeorobic organisms (common)
Staphylococcus aureus
Streptococcus pyogenes
Klebsiella pneumoniae
Pseudomonas aeruginosa
Aeorobic organisms (uncommon)
Escherichia coli
Haemophilus influenzae type B
Other pathogens (rare)
Nocardia asteroids
Paragonimus westermani
Legionella species
Burkholdaria pseudomallei
Burkholdaria mallei (glanders)
Mycobacterium tuberculosis
Mucoraceae species
Aspergillus species
Entameoba histolytica
Organisms associated with lung abscess in immunocompromised hosts (including HIV)
Pseudomonas aeruginosa
Streptococcus pneumonia
Pneumocystis jiroveci
Klebsiella pneunmoniae
Staphylococcus aureus
Haemophilus influenzae
Stenotrophomonoas maltophilia
Legionella species (nonpneumophilia)
Enterobacter species
Streptococcus milleri
Proteus mirabilis
Cryptococcus neoformans
Aspergillus species
Mycobacteria (nontuberculous)
Nocardia
Rhodococcus
Zygomycetes
a
Mouth flora.

In contrast to community-acquired lung abscess, aerobic leaner may exist a more important etiological amanuensis in hospital-caused lung abscess. Nosocomial aspiration is often associated with Gram-negative bacteria and Staphylococcus aureus, including organisms with hospital-caused antibody resistance patterns. Furthermore, the spectrum of microbiological agents responsible for lung abscess in immunocompromised hosts may exist quite unlike and singled-out from that of immunocompetent patients. This is evident in the study of the Beth Israel Deaconess Medical Center'south experience during 1984–96 in 34 cases of lung abscesses in adults. Aerobic bacteria were the most common isolates in both immunocompromised and non-immunocompromised patients. However, immunocompromised patients more often had multiple pathogens, and certain pathogens were exclusively isolated from the lung abscess of immunocompromised patients, including Pseudomonas aeruginosa, and Hemophilus spp. (non-influenzae), Stenotrophomonas maltophilia, Haemophilus influenza, Enterobacter spp., Klebsiella oxytoca, nonpneumophilia Legionella spp., Mycobacterium avium complex and Candida spp. Anaerobes were isolated in only xx% of the cases of non-immunocompromised patients, and non isolated in any specimens from immunocompromised patients. Other reports of lung abscess in HIV+ patients demonstrate bacteria in 65% of isolates, followed past fungi (9%), and mixed infections (16%), although despite constructive treatment, high relapse (36%) and mortality (nineteen%) rates were experienced.

More recent data advise that the microbiology of lung abscess may exist evolving, perhaps in part in response to external pressures induced by the indiscriminate use of wide-spectrum antimicrobials, development of bacterial resistance, presence of multiple or complex medical comorbidities in patients, and the expanding population of immuosuppressed individuals. Every bit the microbiology of customs-acquired pneumonia changes (e.1000., the expanding role of methicillin-resistant Staphylococcus aureus), the agents responsible for community-caused lung abscess are likely to change.

Although certain genetic diseases that result in chronic lung affliction (e.chiliad., cystic fibrosis, Kartangener's syndrome) or chronic infection (e.g., Mycobacterium tuberculosis) may predispose to lung abscess formation, in that location are no known specific genetic markers that identify persons at adventure for the evolution of lung abscess.

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