Anaerobic infection

Anaerobic infections are caused by anaerobic bacteria. Obligately anaerobic bacteria do not grow on solid media in room air (0.04% carbon dioxide and 21% oxygen); facultatively anaerobic bacteria can grow in the presence or absence of air. Microaerophilic bacteria do not grow at all aerobically or grow poorly, but grow better under 10% carbon dioxide or anaerobically. Anaerobic bacteria can be divided into strict anaerobes that can not grow in the presence of more than 0.5% oxygen and moderate anaerobic bacteria that are able of growing between 2 and 8% oxygen. Anaerobic bacteria usually do not possess catalase, but some can generate superoxide dismutase which protects them from oxygen. Anaerobic infections are caused by anaerobic bacteria. Obligately anaerobic bacteria do not grow on solid media in room air (0.04% carbon dioxide and 21% oxygen); facultatively anaerobic bacteria can grow in the presence or absence of air. Microaerophilic bacteria do not grow at all aerobically or grow poorly, but grow better under 10% carbon dioxide or anaerobically. Anaerobic bacteria can be divided into strict anaerobes that can not grow in the presence of more than 0.5% oxygen and moderate anaerobic bacteria that are able of growing between 2 and 8% oxygen. Anaerobic bacteria usually do not possess catalase, but some can generate superoxide dismutase which protects them from oxygen. The clinically important anaerobes in decreasing frequency are: 1. Six genera of Gram-negative rods (Bacteroides, Prevotella, Porphyromonas, Fusobacterium, Bilophila and Sutterella spp.);2. Gram-positive cocci (primarily Peptostreptococcus spp.);3. Gram-positive spore-forming (Clostridium spp.) and non-spore-forming bacilli (Actinomyces, Propionibacterium, Eubacterium, Lactobacillus and Bifidobacterium spp.); and 4. Gram-negative cocci (mainly Veillonella spp.) . The frequency of isolation of anaerobic bacterial strains varies in different infectious sites. Mixed infections caused by numerous aerobic and anaerobic bacteria are often observed in clinical situations. Anaerobic bacteria are a common cause of infections, some of which can be serious and life-threatening. Because anaerobes are the predominant components of the normal flora of the skin and mucous membranes, they are a common cause of infections of endogenous origin. Because of their fastidious nature, anaerobes are hard to culture and isolate and are often not recovered from infected sites. The administration of delayed or inappropriate therapy against these organisms may lead to failures in eradication of these infections. The isolation of anaerobic bacteria requires adequate methods for collection, transportation and cultivation of clinical specimens. The management of anaerobic infection is often difficult because of the slow growth of anaerobic organisms, which can delay their identification by the frequent polymicrobial nature of these infections and by the increasing resistance of anaerobic bacteria to antimicrobials. Anaerobes have been found in infections throughout the human body. The frequency of the host or patient's recovery depends on the employment of proper methods of collection of specimen, their transportation to the microbiology laboratory and cultivation. The recovery of organisms depends on the site of infection and is related to the adjacent mucous membranes microbial flora. Anaerobes are able to cause all types of intracranial infections. These often cause subdural empyema, and brain abscess, and rarely cause epidural abscess and meningitis. The origin of brain abscess is generally an adjacent chronic ear, mastoid, or sinus infection oropharynx, teeth or lungs. Mastoid and ear or infections generally progress to the temporal lobe or cerebellum, while facial sinusitis commonly causes frontal lobe abscess. Hematogenous spread of the infection into the CNS often occurs after oropharyngeal, dental, or pulmonary infection. Infrequently bacteremia originating of another location or endocarditis can also cause intracranial infection. Meningitis due to anaerobic bacteria is infrequent and may follow respiratory tract infection or complicate a cerebrospinal fluid shunt. Neurological shunt infections are often caused by skin bacteria such as Cutibacterium acnes, or in instances of ventriculoperitoneal shunts that perforate the gut, by anaerobes of enteric origin (i.e. Bacteroides fragilis).Clostridium perfringens can cause of brain abscesses and meningitis following intracranial surgery or head trauma. The anaerobes often isolated from brain abscesses complicating respiratory and dental infections are anaerobic Gram-negative bacilli (AGNB, including Prevotella, Porphyromonas, Bacteroides), Fusobacterium and Peptostreptococcus spp. Microaerophilic and other streptococci are also often isolated. Actinomyces are rarely isolated. At the stage of encephalitis, antimicrobial therapy and utilization of measures to lower the increase in the intracranial pressure can prevent the formation of an intracranial abscess However, after an abscess has emerged, surgical removal or drainage may be necessary, along with an extended course of antimicrobial therapy (4–8 weeks). Some advocate complete drainage of intracranial abscess, while others use repeated aspirations of the abscess., Repeated aspirations of an abscess are preferable in those with multiple abscesses or when the abscess is located in a predominate brain site. Administration of antimicrobials in a high-dose for an extended period of time can offer an alternative treatment strategy in this type of patients and may substitute for surgical evacuation of an abscess.