Antimicrobial susceptibility of anaerobic bacteria in New Zealand: 1999-2003

OBJECTIVES: Routine susceptibility testing of all anaerobic organisms is not advocated, but it is useful for laboratories to test periodically for anaerobic organisms and provide local susceptibility data to guide therapy. This study reports the national trend of antibiotic susceptibility of clinically significant anaerobes in New Zealand. METHODS: Clinical isolates were tested using standardized methods against a range of antibiotics commonly used to treat anaerobic infections. Susceptibility was determined using NCCLS criteria. The change in susceptibility trends between this study and earlier studies was measured by comparing the geometric mean of the MIC. RESULTS: A total of 364 anaerobes were tested. Penicillin had poor activity against Bacteroides spp., Prevotella spp., Eubacterium spp., Clostridium tertium and Veillonella spp. In general, Fusobacterium spp., Bacteroides ureolyticus, Propionibacterium spp., Clostridium perfringens and anaerobic streptococci isolates, with the exception of Peptostreptococcus anaerobius, were penicillin susceptible. Amoxicillin/clavulanate showed good activity against most anaerobes, but resistance was seen with Bacteroides fragilis group and P. anaerobius isolates. Cefoxitin was more active than cefotetan, particularly against non-B. fragilis species, Eubacterium spp. and P. anaerobius. Meropenem and imipenem showed good activity against all anaerobes, with only 2 and 4% of Bacteroides spp., respectively, showing resistance. With the exception of Propionibacterium acnes isolates, which are predictably resistant, metronidazole was active against all anaerobes tested. There has been little change in susceptibility since 1997. CONCLUSIONS: Metronidazole, cefoxitin, piperacillin/tazobactam and amoxicillin/clavulanate remain good empirical choices when anaerobes are expected in our setting. No clinically relevant changes in susceptibility over time were found.     

Comparative in vitro susceptibilities of anaerobic bacteria to cefmenoxime, cefotetan, and N-formimidoyl thienamycin.

The in vitro activities of cefmenoxime, cefotetan, and N-formimidoyl thienamycin were compared with those of other antimicrobial agents (metronidazole, clindamycin, cefoxitin, and moxalactam) against anaerobic bacteria. The data obtained indicate that N-formimidoyl thienamycin exhibits excellent activity against anaerobic bacteria; cefotetan and cefmenoxime, though less active, should be of value in treating selected anaerobic infections.     

Anaerobic bacteremia: the yield of positive anaerobic blood cultures: patient characteristics and potential risk factors.

The anaerobic blood culture (AN) bottle is routinely used in Japan with little discussion as to its justification or validity. We retrospectively studied the AN bottle yield of obligate anaerobes and the characteristics of, and potential risk factors in, patients with anaerobic bacteremia during a 2-year period (1999-2000) at four university hospitals and one community hospital. Thirty-four of 18,310 aerobic and anaerobic blood culture sets from 6,215 patients taken at the university hospitals, and 35 of 2,464 samples taken from 838 patients at the community hospital, yielded obligate anaerobes. Bacteroides species and Clostridium species accounted for 60% of the isolates. Fifty-seven patients from 69 blood culture sets containing anaerobes had clinically significant anaerobic bacteremia. Among these 57 patients, 24 (49%) were oncology patients, 40 (70%) had an obvious source of anaerobic infection, 15 (26%) had recent surgery and/or were in an immunosuppressed state. We concluded that the recovery rate of obligate anaerobes isolated from AN bottles was low, and the patients with anaerobic bacteremia had limited number of underlying diseases or potential risk factors for anaerobic infections. Therefore, anaerobic blood cultures may be selectively used according to the potential risk for anaerobic infections.     

Third Belgian multicentre survey of antibiotic susceptibility of anaerobic bacteria

OBJECTIVES: To collect recent data on the susceptibility of anaerobes and to compare them with results from previous studies. METHODS: Four hundred and forty-three anaerobic clinical isolates from various body sites were prospectively collected from October 2003 to February 2005 in nine Belgian hospitals. MICs were determined for nine anti-anaerobic and three recently developed antibiotics. RESULTS: Most gram-negative bacilli except Fusobacterium spp. were resistant to penicillin. Piperacillin/tazobactam, metronidazole, chloramphenicol, meropenem and amoxicillin/clavulanic acid were very active against all groups, but only 86% of Bacteroides fragilis group strains were susceptible to the latter. Cefoxitin, cefotetan and clindamycin were less active. In particular, only 62%, 52% and 48% of B. fragilis group strains were susceptible, respectively. Clindamycin shows a continuing decrease in activity, as 83% were still susceptible in 1987 and 66% in 1993-94. Anti-anaerobic activity of the new antibiotics is interesting, with MIC50 and MIC90 of 1 and >32 mg/L for moxifloxacin, 2 and 4 mg/L for linezolid and 0.5 and 8 mg/L for tigecycline. CONCLUSIONS: The susceptibility of anaerobic bacteria remains stable in Belgium, except for clindamycin, which shows a continuous decrease in activity. However, for each of the tested antibiotics, at least a few resistant organisms were detected. Consequently, for severe infections involving anaerobic bacteria, it could be advisable to perform microbiological testing instead of relying on known susceptibility profiles. Periodically monitoring background susceptibility remains necessary to guide empirical therapy.     

Intra-abdominal infections: review of the bacteriology, antimicrobial susceptibility and the role of ertapenem in their therapy

Complicated intra-abdominal infections require a combination of surgery/drainage and antimicrobial therapy that is active against both the aerobic and the anaerobic bacteria that comprise the intestinal flora. Ertapenem, a parenteral carbapenem, is highly resistant to a wide variety of beta-lactamase enzymes, and has a broad spectrum of activity against bacteria associated with community-acquired infections including those of complicated intra-abdominal conditions. This article reviews the bacteriology of complicated intra-abdominal infections, their antimicrobial susceptibility, especially to anaerobes, the utility of animal models in these mixed infections, and the supportive clinical trials and in vitro susceptibility data that show ertapenem to be generally well tolerated and as effective as either piperacillin-tazobactam or ceftriaxone plus metronidazole in the therapy of complicated intra-abdominal infections.     

Comparative in vitro antimicrobial activity of a novel quinolone, garenoxacin, against aerobic and anaerobic microbial isolates recovered from general, vascular, cardiothoracic and otolaryngologic surgical patients

OBJECTIVES: The aim of the study was to analyse the susceptibility of unique and non-duplicate aerobic and anaerobic isolates from surgical patients to a novel des-F(6)-quinolone (garenoxacin) and other selected antimicrobial agents. METHODS: Eleven hundred and eighty-five aerobic and anaerobic isolates from general, vascular, cardiothoracic and otolaryngologic surgical patients were tested for susceptibility to garenoxacin and seven other antibiotics (ciprofloxacin, moxifloxacin, levofloxacin, piperacillin/tazobactam, imipenem, clindamycin and metronidazole) using the referenced microbroth and agar-dilution method. RESULTS: Garenoxacin exhibited greater antimicrobial activity than comparator quinolones such as ciprofloxacin, levofloxacin and other antimicrobials when tested against selected gram-positive organisms. The in vitro aerobic and anaerobic activity of garenoxacin was similar to that of moxifloxacin. All fluoroquinolones tested were effective against most gram-negative facultative anaerobes including Escherichia coli. Garenoxacin and moxifloxacin demonstrated similar in vitro antimicrobial activity against selected anaerobic gram-positive and gram-negative anaerobic bacteria such as members of the Bacteroides fragilis group. Overall, the in vitro activity of the advanced spectrum quinolones against anaerobic surgical isolates compared favourably with selected comparator agents, metronidazole, imipenem and piperacillin/tazobactam. CONCLUSIONS: These findings suggest that 82.4% of aerobic surgical isolates were susceptible to a concentration of garenoxacin < or = 1.0 mg/L, whereas 84.5% of the anaerobic isolates were susceptible to a garenoxacin concentration < or = 1.0 mg/L. Garenoxacin may be a valuable surgical anti-infective for treatment of serious head and neck, soft tissue, intra-abdominal and diabetic foot infections.     

In vitro activity against anaerobes of retapamulin, a new topical antibiotic for treatment of skin infections

OBJECTIVES: Retapamulin is the first agent of the pleuromutilin class formulated as a topical antibacterial for treating skin infections. The aim of this study was to determine the antimicrobial activity of retapamulin by determining the minimal inhibitory concentration (MIC) values of this new drug and comparators against a wide range of anaerobic bacteria of human origin. METHODS: The in vitro activity of retapamulin and six comparators (amoxicillin, amoxicillin/clavulanic acid, ceftriaxone, imipenem, clindamycin and metronidazole) was evaluated against 232 anaerobic clinical isolates. MICs were determined by the CLSI reference agar dilution method (M11-A6). RESULTS: Ceftriaxone, clindamycin and amoxicillin/clavulanic acid resistance rates were 54%, 42% and 9.6%, respectively, within the Bacteroides fragilis group. Despite high resistance rates to various antibiotics, retapamulin inhibited 37/52 (71%) strains of the B. fragilis group and 85/87 (98%) of the other Gram-negative bacilli at a concentration of 2 mg/L or less. All the investigated strains of Clostridium perfringens were inhibited by 1 mg/L retapamulin. Three strains of C. difficile and one strain of C. clostridioforme demonstrated decreased susceptibility to retapamulin. Based on inhibitory concentrations, retapamulin was more active than clindamycin, metronidazole and ceftriaxone against Propionibacterium acnes and anaerobic Gram-positive cocci, as all isolates were inhibited by 相似文献   

Comparative in vitro activities of trovafloxacin (CP 99,219) and other antimicrobials against clinically significant anaerobes.

A total of 590 strains of clinically important anaerobes were tested to determine their susceptibility to trovafloxacin. Overall, trovafloxacin had a mode MIC of 0.25 micrograms/ml and a MIC at which 90% of the isolates were inhibited of 1 micrograms/ml and had activity comparable to that of metronidazole. Trovafloxacin was 8-, 8-, 16-, 32-, and 64-fold more active than ampicillin-sulbactam, clindamycin, ciprofloxacin, cefoxitin, and cefotetan, respectively. Of the Bacteroides fragilis group, 97% of the isolates were inhibited by trovafloxacin at 21 micrograms/ml, and trovafloxacin was more active than ciprofloxacin, cefoxitin, cefotetan, ampicillin-sulbactam, and clindamycin against Clostridium, Fusobacterium, Porphyromonas, and Prevotella strains.     

Use of cephalosporins for prophylaxis and therapy of polymicrobial infection in mice.

Cefoxitin, cefotetan, and cefmetazole were compared in 10-day therapy of intra-abdominal and subcutaneous infections caused by three organisms: Bacteroides fragilis and Bacteroides thetaiotaomicron combined with either Escherichia coli or Staphylococcus aureus. Intra-abdominal infection was caused by B. fragilis plus B. thetaiotaomicron plus E. coli. Therapy was initiated immediately before inoculation or was delayed for 8 h. Mortality was 14 of 30 (47%) for saline-treated mice, and all survivors developed abscesses. Immediate therapy reduced mortality and the percentage of mice with abscesses (in survivors), respectively, to 17 and 20% with cefoxitin, 0 and 13% with cefotetan, and 0 and 17% with cefmetazole, and the numbers of all bacteria were reduced by all the cephalosporins. Delayed therapy reduced mortality and abscess formation, respectively, to 20 and 8% of mice with cefoxitin, 10 and 93% with cefotetan, and 7 and 96% with cefmetazole. B. thetaiotaomicron survived in all abscesses treated with cefotetan and cefmetazole. Subcutaneous abscesses were caused by each organism alone or in combinations of one aerobe (S. aureus or E. coli) and one or two Bacteroides species. Early therapy reduced the numbers of all bacteria independent of their in vitro susceptibility. All agents reduced the number of each Bacteroides species with either E. coli or S. aureus. However, when therapy was delayed, cefotetan and cefmetazole were less effective than cefoxitin against B. thetaiotaomicron. Cefotetan was the most active agent against E. coli, and cefmetazole was the most effective against S. aureus. These data illustrate the efficacy of all tested cephalosporins in the prophylaxis of polymicrobial infections.     

Antimicrobial susceptibility of anaerobic bacteria in Australia.

The susceptibilities of 900 clinical isolates of anaerobic bacteria to 14 antimicrobial agents were determined by an agar dilution technique. Chloramphenicol, imipenem and metronidazole were found to be active against virtually all of the strains; only a single Bacteroides fragilis isolate was resistant to both imipenem and metronidazole. The addition of clavulanic acid to amoxycillin and ticarcillin potentiated the activities of these agents against all anaerobes including members of the B. fragilis group. Ampicillin/sulbactam and clindamycin were the next most active agents, 91 and 89% of isolates respectively being susceptible. Seventy-three per cent of the bacteria tested were susceptible to cefoxitin and 65% to cefotetan, with the MICs of almost 50% of the isolates clustering between 16 and 32 mg/L. There was also clustering around the breakpoint (64 mg/L) of piperacillin. Azithromycin exhibited poor activity against the B. fragilis group; only 18% of isolates were susceptible to < or = 4 mg/L. However, 92% of non-B. fragilis Bacteroides group strains were susceptible to this agent. We conclude that imipenem, metronidazole, chloramphenicol, ticarcillin/clavulanate, co-amoxiclav and, to a lesser extent, ampicillin/sulbactam are suitable as empirical therapy for infections caused by anaerobic bacteria.     

Carbenicillin in the Treatment of Infections Involving Anaerobic Bacteria

Twenty-one patients with serious infections involving anaerobic bacteria were treated with carbenicillin. Multiple anaerobes were involved in 8 cases, and in 10 cases, facultative anaerobes were also isolated. Bacteroides fragilis was isolated in 10 cases. Results were judged excellent in 7 cases, good in 8 cases, and fair in 5 cases. These data suggest that carbenicillin may be an effective antibiotic for the therapy of infections due to anaerobic bacteria, particularly those involving B. fragilis.     

The comparative in-vitro activity of cefotetan against anaerobic bacteria

The in-vitro activity of cefotetan, a new cephamycin, was assessed against a total of 336 strains of anaerobic bacteria by means of an agar dilution procedure and compared with that of cefoxitin, mezlocillin, piperacillin, clindamycin and metronidazole. Overall clindamycin and metronidazole were the most active of the test compounds. Cefotetan showed good activity against anaerobic cocci and clostridia, except for Clostridium difficile (MIC90 = 16 mg/l), although it was comparatively less active than the other beta-lactams against anaerobic cocci. In the case of the Gram-negative anaerobes, cefotetan showed moderate activity comparable to that of cefoxitin; against the 120 test strains of Bacteroides fragilis both cefotetan and cefoxitin were markedly more active than the penicillins. In studies with antibiotic combinations, cefotetan + cefsulodin showed marked synergy (FIC index less than 0.3) against the majority of strains of Bact. fragilis tested.     

In vitro susceptibility of anaerobic flora of the female genital tract to ampicillin compared to spectinomycin

Pelvic inflammatory disease (PID) may be caused by anaerobic bacteria and or gonococcus and therefore the efficacy of two antibiotics, ampicillin (AMP) and spectinomycin (SPM) commonly used in this setting was examined against 370 isolates of anaerobic bacteria. At the highest therapeutically achievable serum levels, AMP (16 micrograms/ml) inhibited 83% of all anaerobes and 70% of Bacterioides fragilis, and SPM (128 micrograms/ml) inhibited 98% of all anaerobes and 95% of B. fragilis strains tested. It therefore appears that both AMP and SPM may have a place in the treatment of PID. In our study, greater percentage of anaerobes were susceptible to SPM than previously reported. We used the 'glove box' technique used for testing the susceptibility of anaerobes.     

Treatment of Anaerobic Bacterial Infections with Clindamycin-2-Phosphate

Thirty-five patients with a variety of serious infections caused by anaerobic bacteria responded to clindamycin. Cure was achieved in 27 of the 32 patients with pleuropulmonary and intra-abdominal infections. Mean serum concentrations of clindamycin for the 8 h after intramuscular administration of clindamycin in these patients were at least 2.5 times the minimal inhibitory concentration of clindamycin for more than 90% of anaerobes. This experience suggests that clindamycin is an excellent and relatively safe antibiotic for treatment of infection caused by anaerobes when combined with surgery (when indicated) or other antibiotics active against aerobic gram-negative bacilli, if present.     

Colonization of lower respiratory tract with anaerobic bacteria in mechanically ventilated patients

Objective To study lower respiratory tract colonization by anaerobic bacteria in ICU patients on prolonged mechanical ventilation using two types of protected tracheal sampling methods.Design and setting Prospective clinical investigation in the intensive care unit of a university hospital.Patients Twenty-six consecutive patients mechanically ventilated within 24 h after their admission in ICU and with expected duration of mechanical ventilation longer than 7 days.Measurements and results Two types of protected tracheal sampling methods were obtained without the use of bronchoscopic guidance on the day following intubation and twice a week until extubation: protected tracheal aspiration and protected tracheal specimen brush. Specific methods for anaerobic isolation were used. Early colonization was defined if colonization occurred within the first 5 days after intubation. Of the 26 patients studied 22 were colonized by at least one bacterial strain. Twenty-one patients were colonized by aerobic and 15 by anaerobic bacteria. Twenty-eight anaerobic strains were identified, with bacterial counts higher than 10³ cfu/ml in 11 cases. Of the 15 patients colonized by anaerobes 14 were also colonized by aerobic bacteria. The use of protected specimens ruled out oropharyngeal contamination. Early onset colonization occurred in 16 of 22 patients colonized by aerobes and in 8 of 15 patients colonized by anaerobes. Five patients developed ventilatory-acquired pneumonia following colonization (by anaerobic bacteria in two cases). In eight patients colonization by anaerobic bacteria occurred despite antimicrobial therapy.Conclusions These results show that anaerobic bacteria frequently colonize the lower respiratory tract of mechanically ventilated patients and underline the potential importance of the anaerobic bacteria in ventilatory acquired pneumonia.An editorial regarding this article can be found in the same issue ()An erratum to this article can be found at     

Anaerobic infection in cancer patients: comparative evaluation of clindamycin and cefoxitin.

Clindamycin and cefoxitin with or without gentamicin were administered to cancer patients having localized infections presumably caused by anaerobic pathogens. The rates of favorable response were 89% in patients receiving clindamycine alone and 78% in patients receiving cefoxitin alone. When the total experience is considered (clindamycin or cefoxitin with and without gentamicin), 20 of 24 patients (83%) responded to clindamycin and 18 of 22 (82%) responded to cefoxitin. Both therapies were well tolerated. Clindamycin was found to be more effective than cefoxitin in eradicating the offending anaerobic pathogens from the site of infection. Aerobic pathogens were frequently isolated along with anaerobes from the infectious sites in this series; their susceptibility or resistance to clindamycin or cefoxitin did not influence the therapeutic response.     

Tigecycline: a novel glycylcycline antibiotic

Tigecycline, the first-in-class glycylcycline, was developed to recapture the broad spectrum of activity of the tetracycline class and to treat patients with difficult-to-treat bacterial infections. Tigecycline's in vitro spectrum of activity encompasses aerobic, facultative and anaerobic Gram-positive and -negative bacteria, including antimicrobial-resistant bacteria such as methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis and Enterococcus faecium, and extended-spectrum beta-lactamase-producing Enterobacteriaceae. Clinical trials involving patients with complicated skin and skin-structure infections and complicated intra-abdominal infections, including patients infected with methicillin-resistant S. aureus, demonstrated that tigecycline was bacteriologically and clinically effective with mild-to-moderate gastrointestinal adverse events (i.e., nausea, vomiting and diarrhea) the most commonly reported. Tigecycline is a promising new broad-spectrum parenteral monotherapy for the treatment of patients with Gram-positive and -negative bacterial infections.     

Combating bacterial resistance in skin and skin-structure infection: importance of beta-lactamase inhibition.

Serious skin and skin-structure infections may require parenteral antibiotic therapy. Such infections are generally polymicrobial, and they often involve both gram-positive and gram-negative aerobes as well as anaerobic bacteria. Effective treatment thus requires the use of a broad-spectrum antibiotic or combination therapy. The development of antibiotic resistance by clinically important pathogens has significantly increased the difficulty of treating skin and skin-structure infections. One of the major mechanisms of resistance observed in organisms likely to be associated with such infections is the development of beta-lactamases that inactivate beta-lactam antibiotics. Two approaches have been taken to combat this problem: the use of beta-lactam/beta-lactamase inhibitor combinations and the development of beta-lactamase-stable drugs. Both strategies have resulted in treatments that are clinically and bacteriologically effective in patients with skin and skin-structure infections. The use of one beta-lactam/beta-lactamase inhibitor combination, ampicillin/sulbactam, has been demonstrated to be more cost-effective than treatment with beta-lactamase-stable antibiotics, such as cefoxitin and imipenem/cilastatin, for this indication.     

Activity of cefotetan against anaerobic bacteria

The in vitro activity of cefotetan, a new cephamycin, was compared with that of cefoxitin, cefotaxime, moxalactam, and piperacillin against 368 strains of anaerobic bacteria. Cefotetan was similar to cefoxitin, moxalactam, and piperacillin in its activity against B. fragilis, B. vulgatus, Bacteroides species, anaerobic gram-positive cocci, Fusobacterium and Clostridium species. High resistance rates for cefotetan, however, were demonstrated among B. thetaiotaomicron-ovatus group and B. distasonis. Increasing inoculum concentrations had little effect on the activity of cefotetan.     

Activity of Spectinomycin Against Anaerobes

The in vitro inhibitory activity of spectinomycin was tested against various anaerobic bacteria. Different results were obtained with different media and with different initial pH's of the media. The highest minimum inhibitory concentrations for Bacteroides fragilis ([Formula: see text] 128 mug/ml) were obtained with the use of Wilkins-Chalgren agar (pH 7.2) and Brucella blood agar (pH 7.0). Brucella blood agar at higher pH's (7.4 and 8.0) and Mueller-Hinton and Diagnostic Sensitivity Test agars produced lower minimum inhibitory concentrations (32 and 64 mug/ml). This same relationship between spectinomycin activity and pH of the medium was, in general, observed with these media and other anaerobes, including isolates of B. melaninogenicus, Fusobacterium, gram-positive cocci, Clostridium perfringens, and C. ramosum. The variable results observed in this study and in two others make it difficult to predict the clinical usefulness of spectinomycin in the treatment of anaerobic infections. It is probably most appropriate to be guided by results obtained with Wilkins-Chalgren agar and the method proposed as a reference to the National Committee for Clinical Laboratory Standards. These results indicate that spectinomycin is not a potent inhibitor of B. fragilis or other clinically significant anaerobes.