Consequently, the most likely agents to cover the vast majority of anaerobes encountered in mixed infections will be either a carbapenem or a BL-BLIC such as piperacillin-tazobactam. -Piperacillin/ tazobactam differs in spectrum with its ability to cover enterococcus and anaerobes. Surveillance studies performed in reference laboratories in the United States and worldwide most commonly use the CLSI method (see below). The data are then entered into a computer software program provided by the manufacturer, which determines the concentration of drug from the radius of growth and the molecular weight (i.e., diffusion characteristics) of the antimicrobial agent. The CLSI microdilution method is approved only for B. fragilis group organisms, because many other anaerobes will not consistently grow well in broth media. The standardization of testing methods by the CLSI allows comparisons of resistance trends among various laboratories. Clinical outcome was correlated with results of in vitro susceptibility testing of Bacteroides isolates recovered from blood and/or other sites and was determined by three endpoints: mortality at 30 days, clinical response (cure versus failure), and microbiological response (eradication versus persistence). The presence of the cfiA gene, as well as associated IS elements, can be determined by a PCR technique (57 Although several failures to eradicate anaerobic infections, including bacteremia, with chloramphenicol have been reported (114), this agent has been used for over 64 years for treatment of anaerobic infections. While 89% of B. fragilis strains are susceptible to ampicillin-sulbactam, 98% are susceptible to piperacillin-tazobactam (17), compared to 86% and 92%, respectively, of B. thetaiotaomicron isolates. Meropenem, sold under the brandname Merrem among others, is a broad-spectrum antibiotic used to treat a variety of bacterial infections. Many studies will acknowledge these differences and report results with both breakpoints. Quinolones with low activity against anaerobes include ciprofloxacin, ofloxacin, levofloxacin, fleroxacin, pefloxacin, enoxacin, and lomefloxacin. Aside from susceptibility patterns, other factors influencing the choice of antimicrobial therapy include the pharmacological characteristics of the various drugs, their toxicity, their effect on the normal flora, and their bactericidal activity (2, 3). If made in-house, trays can be tailored to the particular needs of the laboratory, using the drugs and concentration ranges needed. Xu X, Bai Z, Zhao Q, Li H, Shi Q, Deng J, Zhang J, Guo X, Qi X. J Transl Int Med. Meropenem is a carbapenem antibiotic that has a very broad spectrum of activity against aerobic and anaerobic bacteria, similar to that of imipenem. An 8-year study (1997 to 2004) revealed that 19.3% of 2,721 B. fragilis group, 29.6% of P. distasonis, 33.4% of B. ovatus, 33.3% of B. thetaiotaomicron, and 35.6% of B. vulgatus isolates were clindamycin resistant. Also, more strains exhibiting multidrug resistance (MDR) have been found (21, 23). describe atypical coverage by carbapenems. which 2nd gen cephalosporins have anaerobic coverage. This review describes the current methods for AST in research and reference laboratories. Resistance to this drug is rare, although it has been reported for some Bacteroides spp. Among the Gram-positive anaerobes, clinicians are also aware of Clostridium species, especially C. perfringens and Clostridium botulinum and, more recently, the great importance of C. difficile. at rates of 9%, 21%, and 6%, respectively. same as meropenem- gram +, gram -, anaerobes, p. aeruginosa A multiplex PCR test that could detect multiple resistance determinants in B. fragilis isolates was recently described by Pumbwe et al. Also, any tendency for spontaneously resistant mutants to develop (i.e., colonies that grow beyond the “endpoint”) can be easily determined (Fig. The question of whether these tests are FDA approved for diagnostic purposes is a bit confusing. Resistance to β-lactam antibiotics.Anaerobes manifest three major mechanisms of resistance to β-lactam antibiotics: inactivating enzymes, mainly beta-lactamases (BLAs), which include penicillinases and cephalosporinases; low-affinity penicillin-binding proteins (PBPs); and decreased permeability through alterations in the porin channel (35). Other side effects include the production of the potentially fatal “gray baby syndrome” when given to neonates, hemolytic anemia in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency, and optic neuritis in those who take the drug for a prolonged time. Resistance has also increased among other anaerobes, such as Clostridium spp., that were previously very susceptible. fragilis group species, and resistance to them is generally low, except that more than half of Prevotella species isolates may also produce BLAs. Resistance patterns have been monitored through national and local surveys, but susceptibility testing of anaerobic bacteria at individual hospitals is rarely done (20). Linezolid is active against Fusobacterium nucleatum, other Fusobacterium spp., Porphyromonas spp., Prevotella spp., and Peptostreptococcus spp. In our personal experience, clinicians are generally aware of the importance of anaerobic bacteria in a wide variety of infections. Most studies conform to CLSI breakpoints, but certain EUCAST breakpoints are different. In B. fragilis, 16 homologs of tripartite efflux pumps of the resistance nodulation division (RND) family have been described ( In addition, clinicians may be less aware of the variability between laboratories in their capabilities and interest in anaerobic bacteriology and the specific level of performance and capability of their own clinical microbiology laboratories to both isolate anaerobes and perform susceptibility testing (20, 36, 37). Metronidazole can be used but in combination with another agent. The Clinical and Laboratory Standards Institute (CLSI) has standardized many laboratory procedures, including anaerobic susceptibility testing (AST), and has published documents for AST. The addition of penicillin, cefoxitin, and cefotetan may be ordered for testing of Clostridium. Active against gram negative organisms, no anaerobe coverage, little to no strep coverage . Levels exceeding 25 μg/ml are commonly considered potentially toxic in terms of reversible bone marrow suppression, and levels of 40 to 200 μg/ml have been associated with gray syndrome in neonates or encephalitis in adults (115). It is used for dental infections, especially in patients who are allergic to penicillin, and for aspiration pneumonia. Moderate-severe ... Putrid discharge is diagnostic for the presence of anaerobes. The antibiograms of anaerobic bacteria have become increasingly unpredictable, and multiresistant clinical isolates are appearing, confounding the concept of foolproof anaerobic therapy (21, 23, 147). Cefoxitin is relatively inactive against most species of Clostridium, including C. difficile, with the exception of Clostridium perfringens (6, 7, 79). Isolates from patients likely to undergo long-term therapy should be tested so that any development of resistance can be recognized. Microaerophilic streptococci, P. acnes, and Actinomyces spp. Imipenem, a thienamycin, is a beta-lactam antibiotic that is effective against a wide variety of aerobic and anaerobic Gram-positive and Gram-negative organisms, including normally multiresistant species such as Pseudomonas aeruginosa, Serratia spp., Enterobacter spp., Acinetobacter spp., and enterococci (93, 94). 17). Preliminary findings also indicate efficacy in the treatment of respiratory tract infections in patients with cystic fibrosis. 17). (33) observed that 90% of B. fragilis isolates recovered from nosocomial infections and bacteremias in Taiwan were susceptible to moxifloxacin. However, meropenem and doripenem are less active against E. faecalis than imipenem. However, species-to-species variations in susceptibility occur, and many non-BLA-producing P. distasonis strains have elevated MICs at or approaching the susceptible breakpoint (112). and other Gram-negative organisms as anaerobic pathogens. Bacteroides fragilis has high rates of resistance to Cefotetan (Cefoxitin is a bit better) – for serious intrabdominal infections, should use other agents. (Right) Detail of the endpoint and observation of resistant colonies past the endpoint. All Rights Reserved. what type of organism is clostridium. It is indicated for complicated intra-abdominal and skin structure infections, including diabetic foot infections without osteomyelitis, and acute pelvic infections, including postpartum endomyometritis, septic abortion, and postsurgical gynecological infections. The side effect of most concern is C. difficile-associated colitis (125, 126). Some broad-spectrum antibacterial agents possess such qualities, while for some organisms, additional agents should be added to the therapeutic regimen. Table 1 illustrates the antimicrobials effective against anaerobic bacteria and their efficacy against both aerobic and anaerobic bacteria. Some studies refer to other method documents; a recent German multicenter study referred to a specific German document for testing methodology (24). The antimicrobials potentially effective against anaerobic bacteria include beta-lactams, combinations of beta-lactams and beta-lactamase inhibitors, metronidazole, chloramphenicol, clindamycin, macrolides, tetracyclines, and fluoroquinolones. – – reliably predicts outcome (specificity of 97% and positive predictive value of 82%). Large reference laboratories may use CLSI-approved methods (described briefly below), which are more laborious and require more in-house preparation than commercially available methods.