Susceptibility of the Bacteroides fragilis group in the United States: analysis by site of isolation

Optimized extraction and characterization of antimicrobial phenolic compounds from mangosteen (Garcinia mangostana L.) cultivation and processing waste

BACKGROUND

Applications for antimicrobials derived from the mangosteen (Garcinia mangostana L.) plant are presently restricted by high production costs. Extraction from cultivation or processing waste streams using a solvent-free approach could lessen to permit commercial applications in food processing and preservation.

RESULTS

Phenolics were extracted from mangosteen bark, leaf and fruit pericarp in methanol and in water using response surface methodology to optimize recovery. Initial examination of antimicrobial effects revealed a lack of antimicrobial activity against fungi and weak activity against the Gram-negative bacteria Escherichia coli and Salmonella typhimurium. In contrast, extracts prepared from bark or fruit pericarp exhibited strong pH-dependent bacteriostatic and bactericidal effects against Listeria monocytogenes and Staphylococcus aureus. Activity was slightly weaker in aqueous extracts due to lower concentrations of tartaric acid esters and flavonols than in methanolic extracts. Measurement of propidium iodide uptake and ATP leakage indicated that the extracts induced damage to the membrane of Gram-positive bacteria.

CONCLUSION

Extracts of mangosteen bark and fruit pericarp contain mixtures of phenolic compounds with activity against Gram-positive bacteria, notably Listeria monocytogenes. Extraction of phenolics from mangosteen waste could yield fractions for potential applications in the formulation of low-cost processing aids or sanitizers for the food industry.

Susceptibility trends of Bacteroides fragilis group and characterisation of carbapenemase-producing strains by automated REP-PCR and MALDI TOF

Susceptibility testing of clinical isolates of anaerobic bacteria is not considered, often, mandatory in routine clinical practice and the treatments are empirically established. Thus, periodic monitoring of the susceptibility patterns of anaerobic bacteria is advisable. The aim of this study was to update on resistance of Bacteroides fragilis group in our Institution with special attention to carbapenems reporting metallo-beta-lactamase producing strains for the first time in Spain, and to compare fingerprinting analysis results obtained by using automated rep-PCR (DiversiLab System) and MALDI-TOF MS. A total of 830 non-duplicated clinical isolates of the B. fragilis group recovered from the years 2006 to 2010 were studied. B. fragilis was the most prevalent species (59.5%). The total susceptibility of B. fragilis group isolates were: penicillin, 13.3%; amoxicillin/clavulanic, 89.6%; piperacillin-tazobactam, 91.8%; cefoxitin, 65.8%; ertapenem, 95.9%; imipenem, 98.2%; clindamycin, 53.4% and metronidazole, 96.4%. The percentage of sensitive isolates did not change significantly over time for amoxicillin/clavulanic, cefoxitin, clindamycin and metronidazole. A slight increase in the rate of resistance to ertapenem and imipenem was observed. Imipenem resistance and carbapenemase production were detected for the first time in our laboratory in the year 2007. No other report of carbapenemase-producing B. fragilis in our country has been previously published. Six imipenem-resistant isolates were MBL-producing and PCR positive for cfiA gene. Four of them were PCR positive for IS-like immediately upstream cfiA gene and two of them were negative. Both, automated rep-PCR (DiversiLab) and MALDI-TOF MS, revealed a great genetic diversity among carbapenem-producing strains suggesting the acquisition of novel resistance genes more than clonal dissemination of them. Both methods seem to be useful tools for fast and accurate identification and strain typing of B. fragilis group in the daily laboratory routine. Because of the relevant increase observed in Bacteroides species isolated from blood cultures and the appearance of carbapenemase-producing strains in our Institution, we recommend to test the antimicrobial susceptibility of the isolates, at least in the most severe patients.

Prevalence of antimicrobial resistance among clinical isolates of Bacteroides fragilis group in Canada in 2010-2011: CANWARD surveillance study

Clinical isolates of the Bacteroides fragilis group (n = 387) were collected from patients attending nine Canadian hospitals in 2010-2011 and tested for susceptibility to 10 antimicrobial agents using the Clinical and Laboratory Standards Institute (CLSI) broth microdilution method. B. fragilis (59.9%), Bacteroides ovatus (16.3%), and Bacteroides thetaiotaomicron (12.7%) accounted for ~90% of isolates collected. Overall rates of percent susceptibility were as follows: 99.7%, metronidazole; 99.5%, piperacillin-tazobactam; 99.2%, imipenem; 97.7%, ertapenem; 92.0%, doripenem; 87.3%, amoxicillin-clavulanate; 80.9%, tigecycline; 65.9%, cefoxitin; 55.6%, moxifloxacin; and 52.2%, clindamycin. Percent susceptibility to cefoxitin, clindamycin, and moxifloxacin was lowest for B. thetaiotaomicron (n = 49, 24.5%), Parabacteroides distasonis/P. merdae (n = 11, 9.1%), and B. ovatus (n = 63, 31.8%), respectively. One isolate (B. thetaiotaomicron) was resistant to metronidazole, and two isolates (both B. fragilis) were resistant to both piperacillin-tazobactam and imipenem. Since the last published surveillance study describing Canadian isolates of B. fragilis group almost 20 years ago (A.-M. Bourgault et al., Antimicrob. Agents Chemother. 36:343-347, 1992), rates of resistance have increased for amoxicillin-clavulanate, from 0.8% (1992) to 6.2% (2010-2011), and for clindamycin, from 9% (1992) to 34.1% (2010-2011).

Diagnosis and management of complicated intra-abdominal infection in adults and children: guidelines by the Surgical Infection Society and the Infectious Diseases Society of America

Evidence-based guidelines for managing patients with intra-abdominal infection were prepared by an Expert Panel of the Surgical Infection Society and the Infectious Diseases Society of America. These updated guidelines replace those previously published in 2002 and 2003. The guidelines are intended for treating patients who either have these infections or may be at risk for them. New information, based on publications from the period 2003-2008, is incorporated into this guideline document. The panel has also added recommendations for managing intra-abdominal infection in children, particularly where such management differs from that of adults; for appendicitis in patients of all ages; and for necrotizing enterocolitis in neonates.

Diagnosis and Management of Complicated Intra-abdominal Infection in Adults and Children: Guidelines by the Surgical Infection Society and the Infectious Diseases Society of America

Evidence-based guidelines for managing patients with intra-abdominal infection were prepared by an Expert Panel of the Surgical Infection Society and the Infectious Diseases Society of America. These updated guidelines replace those previously published in 2002 and 2003. The guidelines are intended for treating patients who either have these infections or may be at risk for them. New information, based on publications from the period 2003–2008, is incorporated into this guideline document. The panel has also added recommendations for managing intra-abdominal infection in children, particularly where such management differs from that of adults; for appendicitis in patients of all ages; and for necrotizing enterocolitis in neonates.

Susceptibility trending of blood isolates of the Bacteroides fragilis group over a 12-year period to clindamycin, ampicillin-sulbactam, cefoxitin, imipenem, and metronidazole

Numerous reports have described a steady overall increase in resistance among clinical isolates of the Bacteroides fragilis group to several antimicrobial agents, particularly clindamycin. Determination of resistance rates is significantly influenced by the number of isolates of each species within the B. fragilis group tested. Historically, the B. fragilis species has remained the most susceptible to most antimicrobials when compared to non-B. fragilis species. This study compares the effect of a gradually changing ratio of blood isolates of B. fragilis to non-B. fragilis species tested by broth micro-dilution over a 12-year period on selected antimicrobial agents. In 1987, the ratio of blood isolates of B. fragilis to non-B. fragilis was 68% to 32%; in 1991 it was 59% to 41%; and in 1999 it was 51% to 49%. Both metronidazole and imipenem showed the least changes because of their inherent high activity against all species. For clindamycin, decreases in susceptibility ranged from 84% to 64% for B. fragilis compared to 58% to 67% for non-B. fragilis species. Ampicillin-sulbactam showed a decrease in susceptibility in B. fragilis and non-B. fragilis species, but was highest in 1999 when the ratio of non-B. fragilis species was the highest. Overall resistance rates to cefoxitin varied from 8% to 25% during the testing years and was consistently higher among the non-B. fragilis species. These comparisons indicate that the ratio of B. fragilis group species isolated from the blood has changed over the last 12 years and has appreciably affected the resistance rates to some commonly used anti-anaerobic agents. Whether the noted changes in species isolation rates are a result of selective antibiotic pressure or other factors is yet to be determined.

Anaerobic pulmonary infections in children

Pulmonary infections due to anaerobic bacteria usually occur in children prone to aspiration. The source of the anaerobic bacteria is the oropharyngeal bacterial flora, where these organisms outnumber aerobic and facultative organisms in a 10:1 ratio. The most common lower respiratory tract infections where anaerobic bacteria are recovered mixed with aerobic organisms are aspiration pneumonia, lung abscess, and empyema. The predominant isolated anaerobic bacteria are Peptostreptococcus, Fusobacterium, pigmented Prevotella, and Porphyromonas spp. and Bacteroides fragilis group. Management of these infections includes the administration of antimicrobials effective against the anaerobic as well as the aerobic pathogens.

Bacteremia due to Bacteroides fragilis group: distribution of species, beta-lactamase production, and antimicrobial susceptibility patterns

A retrospective analysis of susceptibility data on 542 blood isolates of the Bacteroides fragilis group tested from 1987 to 1999 by the same NCCLS-recommended broth microdilution method throughout is presented. Metronidazole, beta-lactam-beta-lactamase inhibitor combinations, carbapenems, and trovafloxacin were the most active agents (susceptibility of >or=93%). Among the cephalosporin-cephamycins, the order of activity was cefoxitin > ceftizoxime > cefotetan = cefotaxime = cefmetazole > ceftriaxone. All isolates were resistant to penicillin G, and 22% were resistant to clindamycin. The susceptibility rates to piperacillin-tazobactam, imipenem, and meropenem were affected least among isolates resistant to cefoxitin or clindamycin. Except for piperacillin-tazobactam, imipenem, and meropenem, the B. fragilis species was more susceptible than were the non-B. fragilis species. These data underscore the importance of susceptibility testing of the B. fragilis group and can serve as a guide in the choice of empirical antimicrobial therapy.

In vitro susceptibilities of the Bacteroides fragilis group species: change in isolation rates significantly affects overall susceptibility data

A comparison of antimicrobial susceptibility data of species of the Bacteroides fragilis group for 1989-1990 and 1998-1999 studies showed statistically significant increases or decreases in in vitro activity. Overall significant increases in resistance were noted for ampicillin-sulbactam and clindamycin, while significant decreases in resistance were noted for ertapenem and cefoxitin. Susceptibilities to piperacillin-tazobactam, imipenem, meropenem, and trovafloxacin remained virtually the same for the two studies. Importantly, a change in the rates of isolation of the various species showed the B. fragilis species comprised 58% of the isolates in 1989 to 1990 and 45% of the isolates in 1998 to 1999. This change in rates of isolation of B. fragilis versus non-B. fragilis species had an overall effect on susceptibility data.

Evolution of anaerobe susceptibility testing in the United States

Susceptibility testing of anaerobes has been described for approximately 45 years, some 15 years fewer than descriptions for aerobic organisms. During that time period, >16 methods, >16 media, and a host of other variables have been described in the United States literature, culminating in the most recent standards published by the National Committee for Clinical Laboratory Standards (NCCLS) in 2001. These new guidelines include a single agar dilution reference method as well as an alternative minimal inhibitory concentration method validated by extensive multilaboratory collaborative trials. In addition, the Food and Drug Administration-approved E-test has proved valuable as a user-friendly alternative to NCCLS methods. Highlights of the "evolution" of various methods, their variations and their failures, factors that affected the development of the current standards, and the rationale for susceptibility testing of anaerobes are discussed herein.

Antimicrobial resistance and clinical outcome of Bacteroides bacteremia: findings of a multicenter prospective observational trial

There is debate regarding the correlation between in vitro susceptibility testing and clinical response to therapy for Bacteroides bacteremia. We conducted a prospective multicenter observational study of 128 patients with bacteroides bacteremia. Outcome was correlated with results of in vitro susceptibility testing of Bacteroides isolates recovered from blood and/or nonblood sites, determined with use of 3 end points: mortality at 30 days, clinical response (cure vs. failure), and microbiological response (eradication vs. persistence). The mortality rate among patients who received inactive therapy (45%) was higher than among patients who received active therapy (16%; P=.04). Clinical failure (82%) and microbiological persistence (42%) were higher for patients who received inactive therapy than for patients who received active therapy (22% and 12%, respectively; P=.0002 and.06, respectively). In vitro activity of agents directed at Bacteroides species reliably predicts outcome: the specificity was 97%, and positive predictive value was 82%. Antimicrobial susceptibility testing may be indicated for patients whose blood specimens yield Bacteroides species.

Susceptibility of clinical isolates of Bacteroides fragilis group strains to cefoxitin, cefoperazone and ticarcillin/clavulanate

A total of 40 strains of the B. fragilis group was isolated from clinical specimens in two hospital centers in Fortaleza from 1993 to 1997. The most frequently isolated species was Bacteroides fragilis (19 strains) and most isolates came from intra-abdominal and wound infections. The susceptibility profile was traced for cefoxitin, cefoperazone and ticarcillin-clavulanate by using the agar dilution reference method. All isolates were susceptible to ticarcillin-clavulanate (128/2 microg/ml). Resistance rates of 15 and 70% were detected to cefoxitin (64 microg/ml) and cefoperazone (64 microg/ml), respectively. Such regional results permit a better orientation in choosing this group of antibiotics for prophylaxis and therapy especially in relation to cefoxitin, which is frequently used in the hospital centers studied.

Distribution of the cfiA gene among Bacteroides fragilis strains in Japan and relatedness of cfiA to imipenem resistance

The cfiA gene, encoding an imipenem-hydrolyzing metallo-beta-lactamase produced by Bacteroides fragilis, and insertion-like elements were detected by PCR amplification with B. fragilis strains isolated in Japan. The cfiA gene was found in 1.9 and 4.1% of the imipenem-susceptible B. fragilis isolates collected from 1987 to 1988 and from 1992 to 1994, respectively. Insertion-like elements adjacent to the cfiA gene were found in all nine metallo-beta-lactamase-producing imipenem-resistant strains tested but not in nine cfiA-positive strains with no detectable metallo-beta-lactamase activity.

Multicenter study of in vitro susceptibility of the Bacteroides fragilis group, 1995 to 1996, with comparison of resistance trends from 1990 to 1996

Antimicrobial resistance, including plasmid-mediated resistance, among the species of the Bacteroides fragilis group is well documented. An analysis of the in vitro susceptibility of B. fragilis group species referred between 1995 and 1996 as well as during a 7-year (1990 to 1996), prospective, multicenter survey of over 4,000 clinical isolates of B. fragilis group species was undertaken to review trends in the percent resistance to and geometric mean MICs of the antibiotics tested. There was a trend toward a decrease in the geometric mean MICs of most beta-lactam antibiotics, while the percent resistance to most agents was less affected. Within the species B. fragilis, the geometric mean MICs showed significant (P < 0.05) decreases for piperacillin-tazobactam, ticarcillin-clavulanate, piperacillin, ticarcillin, ceftizoxime, cefotetan, and cefmetazole; a significant increase was observed for clindamycin and cefoxitin. For the non-B. fragilis species, a significant decrease in the geometric mean MICs was observed for meropenem, ampicillin-sulbactam, ticarcillin-clavulanate, piperacillin, ticarcillin, ceftizoxime, and cefmetazole; a significant increase was observed for cefoxitin. Significant increases in percent resistance were observed within the B. fragilis strains for ticarcillin and ceftizoxime and within the non-B. fragilis isolates for cefotetan. Significant increases in percent resistance among all B. fragilis group species were observed for clindamycin, while imipenem showed no significant change in resistance trends. The trend analysis for trovafloxacin was limited to 3 years, since the quinolone was tested only in 1994, 1995, and 1996. During the 7 years analyzed, there was no resistance to metronidazole or chloramphenicol observed. The data demonstrate that resistance among the B. fragilis group species has decreased in the past several years, the major exception being clindamycin. The majority of the resistance decrease has been for the beta-lactams in B. fragilis, compared to other species. The reasons for these changes are not readily apparent.

Clindamycin, metronidazole, and chloramphenicol

Clindamycin, metronidazole, and chloramphenicol are three antimicrobial agents useful in the treatment of anaerobic infections. Clindamycin is effective in the treatment of most infections involving anaerobes and gram-positive cocci, but emerging resistance has become a problem in some clinical settings. Metronidazole is effective in the treatment of infections involving gram-negative anaerobes, but it is unreliable in the treatment of gram-positive anaerobic infections and is ineffective in treating aerobic infections. Additionally, metronidazole is often the drug of choice in treating infections in which Bacteroides fragilis is a serious concern. Chloramphenicol is effective in the treatment of a wide variety of bacterial infections, including serious anaerobic infections, but is rarely used in Western countries because of concerns about toxicity, including aplastic anemia and gray baby syndrome.

Carbapenems and monobactams: imipenem, meropenem, and aztreonam

Imipenem and meropenem, members of the carbapenem class of beta-lactam antibiotics, are among the most broadly active antibiotics available for systemic use in humans. They are active against streptococci, methicillin-sensitive staphylococci, Neisseria, Haemophilus, anaerobes, and the common aerobic gram-negative nosocomial pathogens including Pseudomonas. Resistance to imipenem and meropenem may emerge during treatment of P. aeruginosa infections, as has occurred with other beta-lactam agents; Stenotrophomonas maltophilia is typically resistant to both imipenem and meropenem. Like the penicillins, the carbapenems have inhibitory activity against enterococci. In general, the in vitro activity of imipenem against aerobic gram-positive cocci is somewhat greater than that of meropenem, whereas the in vitro activity of meropenem against aerobic gram-negative bacilli is somewhat greater than that of imipenem. Daily dosages may range from 0.5 to 1 g every 6 to 8 hours in patients with normal renal function; the daily dose of meropenem, however, can be safely increased to 6 g. Infusion-related nausea and vomiting, as well as seizures, which have been the main toxic effects of imipenem, occur no more frequently during treatment with meropenem than during treatment with other beta-lactam antibiotics. The carbapenems should be considered for treatment of mixed bacterial infections and aerobic gram-negative bacteria that are not susceptible to other beta-lactam agents. Indiscriminate use of these drugs will promote resistance to them. Aztreonam, the first marketed monobactam, has activity against most aerobic gram-negative bacilli including P. aeruginosa. The drug is not nephrotoxic, is weakly immunogenic, and has not been associated with disorders of coagulation. Aztreonam may be administered intramuscularly or intravenously; the primary route of elimination is urinary excretion. In patients with normal renal function, the recommended dosing interval is every 8 hours. Patients with renal impairment require dosage adjustment. Aztreonam is used primarily as an alternative to aminoglycosides and for the treatment of aerobic gram-negative infections. It is often used in combination therapy for mixed aerobic and anaerobic infections. Approved indications for its use include infections of the urinary tract or lower respiratory tract, intra-abdominal and gynecologic infections, septicemia, and cutaneous infections caused by susceptible organisms. Concurrent initial therapy with other antimicrobial agents is recommended before the causative organism has been determined in patients who are seriously ill or at risk for gram-positive or anaerobic infection.

Epidemiology and antimicrobial resistance of B. fragilis group organisms isolated from clinical specimen and human intestinal microbiota

Epidemiological aspects and the antimicrobial susceptibility profile of the Bacteroides fragilis group isolated from clinical and human intestinal specimens were examined in this study. B. fragilis group strains were isolated from 46 (37%) of 124 clinical specimens and the source of the samples was: Blood culture (3), intraabdominal infection (27), brain abscess (2), soft tissue infection (17), respiratory sinus (3), pleural aspirate (9), breast abscess (3), surgical infected wound (22), pelvic inflammatory disease (22), chronic otitis media (9) and miscellaneous (7). Intraabdominal and soft tissue infections were responsible for more than half of the clinical isolates. Susceptibility to penicillin, cefoxitin, tetracycline, metronidazole, chloramphenicol and clindamycin was examined. All isolates were susceptible to metronidazole and chloramphenicol. For clindamycin and cefoxitin the resistance rates observed were 21.7% and 10.9% respectively. Susceptibility profiles varied among the different species tested. A total of 37 species of B. fragilis group isolated from intestinal microbiota of individuals who had no antimicrobial therapy for at least 1 month before the sampling was also examined. All strains were also susceptible to chloramphenicol and metronidazole and the resistance rates to clindamycin and cefoxitin were 19.4% and 5.4% respectively. A few institutions, in Brazil, have monitored the antimicrobial susceptibility of B. fragilis group strains isolated from anaerobic infections. The resistance rates to cefoxitin and clindamycin and the variation in susceptibility patterns among the species isolated in this study emphasize the need for monitoring of susceptibility patterns of B. fragilis group organisms isolated, especially at our University Hospitals.

Antibiotic use in the emergency department. III. The quinolones, new beta lactams, beta lactam combination agents, and miscellaneous antibiotics

This article reviews several new, relatively broad-spectrum antibiotics that have utility in the emergency department (ED). The quinolones have excellent activity against gram-negative organisms, including gonococcus, and are characterized by very high bioavailability after oral administration. The new beta-lactams aztreonam and imipenem have broad spectra but limited usefulness to the emergency physician, and should be reserved for judicious use in severe infections, particularly those involving Pseudomonas. Clavulanate, sulbactam, and tazobactam are themselves antimicrobials that have been combined with beta-lactams such as ampicillin and ticarcillin to produce agents with significant potential utility in the ED; these are typically not first-line agents, however, and their use should be governed by both clinical and cost concerns. Finally, three older antibiotics--vancomycin, metronidazole, and clindamycin--are reviewed with respect to updated indications for their use in the ED.

beta-Lactamases in laboratory and clinical resistance

beta-Lactamases are the commonest single cause of bacterial resistance to beta-lactam antibiotics. Numerous chromosomal and plasmid-mediated types are known and may be classified by their sequences or phenotypic properties. The ability of a beta-lactamase to cause resistance varies with its activity, quantity, and cellular location and, for gram-negative organisms, the permeability of the producer strain. beta-Lactamases sometimes cause obvious resistance to substrate drugs in routine tests; often, however, these enzymes reduce susceptibility without causing resistance at current, pharmacologically chosen breakpoints. This review considers the ability of the prevalent beta-lactamases to cause resistance to widely used beta-lactams, whether resistance is accurately reflected in routine tests, and the extent to which the antibiogram for an organism can be used to predict the type of beta-lactamase that it produces.

Detection of Bacteroides fragilis in clinical specimens by polymerase chain reaction amplification of the neuraminidase gene

The polymerase chain reaction (PCR) was used in an attempt to detect Bacteroides fragilis by amplifying a segment of the gene encoding B. fragilis neuraminidase. Forty-five reference strains representing 45 species and 113 clinical isolates were tested. Only B. fragilis was PCR positive, except for Bacteroides merdae ATCC 43184, which gave a band by ethidium bromide staining that showed no signal by Southern hybridization. Using a protocol that employed DNA extraction by Sepa Gene kit and a highly sensitive digoxigenin-chemiluminescence detection system, detection of B. fragilis by PCR was in complete agreement with culture results for 44 clinical specimens from which a wide range of aerobic and anaerobic organisms and fungi were recovered.

Meta-analysis of parenteral clindamycin dosing regimens

OBJECTIVE

We used meta-analysis to compare clinical cure and success rates for parenteral clindamycin 600 mg q8h or 900 mg q8h therapy to treat adult intraabdominal or female pelvic infections.

DATA SOURCES

We located English-language articles describing clindamycin use in humans using MEDLINE, International Pharmaceutical Abstracts, and Embase and from personal and drug information center files, plus all article references.

STUDY SELECTION

Eligible studies used parenteral clindamycin 600 mg q8h or 900 mg q8h to treat intraabdominal or pelvic infection in at least 1 arm of a study and provided a definition of clinical outcome. Accepted were comparative trials in adults who were not critically ill or expected to die.

DATA SYNTHESIS

The DerSimonian and Laird method was used to calculate weighted overall success rates for cure and success (cure plus improved) rates along with 95% confidence intervals for each dosage in intraabdominal and pelvic infections. Regimens were compared with respect to both cure and success rates using the Mann-Whitney U test.

MAIN RESULTS

Twenty-three articles were eligible for inclusion. Abdominal cure rates were 75.6% and 90.5% for clindamycin 600 mg q8h and 900 mg q8h, respectively (p = 0.03): success rates were 89.8% and 92.5%, respectively (p = 0.29). Pelvic cure rates were 82.8% and 89.4%, respectively (p = 0.51): success rates were 87.2% and 89.9%, respectively (p = 0.51).

CONCLUSIONS

In pelvic infections, a dosage of clindamycin 600 mg q8h appears to be clinically acceptable for all patients. Although clinical outcomes for intraabdominal infections are generally similar for both regimens, the significantly higher cure rate with a dosage of clindamycin 900 mg q8h suggests that dosage recommendations should be patient specific.

Genotypic identification of two groups within the species Bacteroides fragilis by ribotyping and by analysis of PCR-generated fragment patterns and insertion sequence content

Molecular typing allowed the separation of the species Bacteroides fragilis into two genotypically distinct groups. A unique set of 50 strains of B. fragilis carrying the chromosomal metallo-beta-lactamase gene cfiA was subjected to a comparative analysis with respect to sets of up to 250 randomly collected strains devoid of this gene. The two groups were found to be distinct on the basis of the following results: (i) ribotyping, after DNA digestion with AvaI, revealed a practically homogeneous DNA fragment pattern for the cfiA-positive strains and distinct multiple patterns for the cfiA-negative strains; (ii) PCR, arbitrarily primed with an experimentally selected decamer, generated fragment patterns typical for the strains of each group; (iii) the three insertion sequences described to date in the species B. fragilis, i.e., IS4351, IS942, and IS1186, were all but confined to the cfiA-positive group, in which they were capable of providing promoter sequences for the transcription of cfiA; and (iv) the cepA gene, encoding the so-called endogenous cephalosporinase of B. fragilis, was found exclusively in the cfiA-negative group, in which it was present in ca. 70% of the strains. The cfiA-, cepA-negative fraction was not characterized further. In a natural population of 500 randomly selected strains of B. fragilis, the cfiA-positive and cfiA-negative groups represented ca. 3 and 97% of the strains, respectively. Analysis of 82 metabolic traits revealed no difference between the two groups.

Clindamycin and metronidazole

Metronidazole is a bactericidal antibiotic with strong activity against most anaerobes and certain parasites. The drug has excellent bioavailability and good penetration in most tissues, including the cerebrospinal fluid and brain abscess contents. It is usually well tolerated with few side effects. With a few exceptions, the percentage of anaerobes, including B. fragilis group, that are resistant to metronidazole remains low. Metronidazole has been used extensively in clinical practice for years, and its uses have expanded. Its exact role in the management of Crohn's disease and entities related to H. pylori is evolving.

The role of cefotaxime in the treatment of surgical infections

This study examines the role of cefotaxime in the treatment of both Gram-negative and Gram-positive surgical infections. A dose of 2 g of cefotaxime will sustain peripheral compartment concentrations of 2.6, 3.9, 1.6, and 0.7 micrograms/ml for 6, 8, 10 and 12 h, respectively. Therefore, the proportion of pathogens with a minimal inhibitory concentration (MIC) below the peripheral compartment cefotaxime concentrations was assessed as a measure of therapeutic potential. It was observed that bacterial elimination in infections correlates well with such pharmacodynamic predictions. Therefore, treatment recommendations for surgical infections are based on the following pharmacodynamics. The times above the MIC in the tissue compartment for various pathogens (1988-1994) known to cause surgical infections were: Escherichia coli, 12 h; all pyogenic streptococci, 12 h; pneumococci, 12 h; Haemophilus spp., 12 h; Proteus mirabilis, 12 h; Klebsiella spp., 10.9 h; viridans streptococci, 10.6 h; oxacillin-susceptible, coagulase-negative staphylococci, 9.7 h; Providencia spp., 9.2 h; Clostridium perfringens, 8.6 h; Peptostreptococcus spp., 8 h; oxacillin-susceptible Staphylococcus aureus, 7.3 h; and all S. aureus, 6.8 h. From the examination of pharmacodynamic parameters, cefotaxime appears to be a viable choice for the therapy of surgical infections other than the Gram-negative anaerobes. For those infections, metronidazole with cefotaxime would be preferred.

Intra-abdominal sepsis

This article addresses controversial issues in the field of intra-abdominal sepsis with particular attention to major changes in management that have evolved during the past decade. In the area of diagnostics, scanning techniques have revolutionized the ability to detect loculated collections, although many of these techniques are of limited value in the early stages of inflammation. The greatest debate concerns the relative merits of scanning techniques; the author's choice is CT scans with contrast, although ultrasonography is preferred in patients who cannot be transported and is probably preferred for pelvic infections. In the area of therapeutics, virtually all studies seem to show that single-drug treatment is as effective as dual combinations or triple-combination therapy that has been standard practice in the past with the proviso that the drug used has activity versus Enterobacteriaceae and B. fragilis. The role of enterococcus remains enigmatic; this organism was readily discounted as an important pathogen in the great majority of cases 10 years ago, but it has subsequently become a major nosocomial pathogen that now commands newfound respect. P. aeruginosa is also controversial, but most studies show that antipseudomonad treatment is not necessary in the empiric selection of drugs and may not be necessary even when P. aeruginosa is found at infected sites; the corollary to this is that aminoglycosides may no longer be required in the dual drug treatment regimens. There is increasing resistance by B. fragilis and some other species of Bacteroides to some of the drugs considered "standard" in the past, including clindamycin, cefoxitin, and cefotetan; nevertheless, it has been difficult to demonstrate that resistance of these organisms correlates with antibiotic failure. It was demonstrated 20 years ago that elective colon surgery must be accompanied by preoperative antibiotics, and erythromycin plus neomycin has evolved as the regimen of choice according to recommendations of authoritative sources for the past 20 years. Nevertheless, surveys of practicing surgeons indicate that most actually combine this oral preparation with parenteral agents as well. The final controversy concerns percutaneous drainage, which has now become a standard technique for dealing with intra-abdominal abscesses in 50% to 90% of cases. This controversy has sometimes been seen as a territorial battle between surgeons and radiologists, and most cases are clearly the prerogative of one discipline or the other, but many are in a gray zone in which clearly defined indications are not readily available.

Longitudinal study of susceptibilities of species of the Bacteroides fragilis group to five antimicrobial agents in three medical centers

A total of 579 clinical isolates of the Bacteroides fragilis group collected from three Canadian hospitals were tested for susceptibility to five antimicrobial agents by using an agar dilution method. During the 4-year survey, isolates from intra-abdominal infections were collected from the following sites: abdominal abscesses (48%), peritoneal fluid (39%), blood (10%), and bile (3%). B. fragilis was the most prevalent species (35.4%), followed by B. thetaiotaomicron (19.2%), B. ovatus (15.9%), and B. vulgatus (11%). No metronidazole- or imipenem-resistant strains were found during the survey. Resistance profiles varied among the different species tested: 7.8, 2.9, and 7.3% of B. fragilis strains (n = 205) and 68.1, 17.2, and 9.4% of non-B. fragilis strains (n = 373) were resistant to cefotetan, cefoxitin, and clindamycin, respectively. B. fragilis and B. vulgatus demonstrated lower resistance rates than B. thetaiotaomicron, B. ovatus, B. distasonis, and B. caccae. During the study, rates of resistance to cefotetan and clindamycin fluctuated but rates of resistance to cefoxitin increased, particularly at one center. These data indicate a need to determine the susceptibility patterns of the B. fragilis group periodically at each hospital.

Cefotetan: a second-generation cephalosporin active against anaerobic bacteria. Committee on Antimicrobial Agents, Canadian Infectious Disease Society

OBJECTIVE

To offer guidelines for the use of cefotetan, a cephamycin antibiotic, in order to minimize its overprescription.

OPTIONS

Clinical practice options considered were treatment of infections with the use of second- and third-generation cephalosporins, carbapenems such as imipenem as well as combination regimens of agents active against anaerobic bacteria, such as metronidazole or clindamycin with an aminoglycoside.

OUTCOMES

In order of importance: efficacy, side effects and cost.

EVIDENCE

A MEDLINE search of articles published between January 1982 and December 1993. In-vitro and pharmacokinetic studies published in recognized peer-reviewed journals that used recognized standard methods with appropriate controls were reviewed. For results of clinical trials, the reviewers emphasized randomized double-blind trials with appropriate controls.

VALUES

The Antimicrobial Agents Committee of the Canadian Infectious Disease Society (CIDS) and a recognized expert (M.J.G.) recommended use of cefotetan to prevent and treat infections against which it has proved effective in randomized controlled trials.

BENEFITS, HARMS AND COSTS

These guidelines should lead to less inappropriate prescribing of cefotetan, with its attendant costs and risk of development of resistant bacteria.

RECOMMENDATIONS

Cefotetan could be considered an alternative single agent for prophylaxis of infection in patients undergoing elective bowel surgery. It may be used to treat patients with acute pelvic inflammatory disease and endometritis.

VALIDATION

This article was prepared, reviewed and revised by the Committee on Antimicrobial Agents of the CIDS. It was then reviewed by the Council of the CIDS, and any further necessary revisions were made by the chairman of the committee.

In vitro activities of metronidazole and its hydroxy metabolite against Bacteroides spp

Metronidazole is metabolized to two major oxidative products: an acid metabolite and a hydroxy metabolite. While the activity of the acid metabolite is negligible, the activity of the hydroxy metabolite is approximately 65% of the activity of the parent drug. Pharmacokinetic studies of metronidazole and its hydroxy metabolite have shown that the MICs of both compounds remain above the MICs for most anaerobic organisms over an 8-h dosing interval. By a checkerboard assay, the combined activities of metronidazole and the hydroxy metabolite were examined against 4 quality control strains of Bacteroides species. Macrobroth tube dilutions were set up with Wilkins-Chalgren broth. Serial twofold dilutions of each agent were performed to achieve final concentrations ranging from 0.06 to 4.0 micrograms/ml. The MICs for Bacteroides fragilis and B. distasonis were 1.0 microgram/ml for both parent drug and metabolite. For B. thetaiotamicron and B. ovatus, the MICs of metronidazole and the hydroxy metabolite were 1.0 and 2.0 micrograms/ml, respectively. Synergy was determined by calculating the fractional inhibitory concentration (FIC) index. The interpretative criteria for the FIC index were as follows: synergy, FIC < or = 0.5; partial synergy, 0.51 to 0.75; indifference, FIC 0.76 to 4.0; and antagonism, FIC > 4.0. Partial synergy was observed for the four anaerobes tested, with FIC indices ranging from 0.63 to 0.75. On the basis of this data, in vitro susceptibilities to agents such as metronidazole may ultimately require reevaluation to account for active metabolites.

A five-year multicenter study of the susceptibility of the Bacteroides fragilis group isolates to cephalosporins, cephamins, penicillins, clindamycin, and metronidazole in the United States

Over 2800 clinical strains of the Bacteroides fragilis group were collected during a 5-year period from ten geographically separate sites and tested for their susceptibility to various antimicrobial agents using a broth microdilution method. Among the cephalosporins, ceftizoxime was the most active (13% resistance) and importantly exhibited relatively equal activity against both B. fragilis species and non-B. fragilis species. Cefotaxime exhibited similar activity with an overall resistance rate of 18%. Both ceftriaxone and cefoperazone were appreciably less active cephalosporins especially against non-B. fragilis species. With regard to cephamycins, cefoxitin (MIC90, 32 micrograms/ml) was more active than cefotetan (MIC90, > or = 256 micrograms/ml) and cefmetazole (MIC90, 64 micrograms/ml). Non-B. fragilis species were highly resistant to cefotetan and cefmetazole. Imipenem was highly active against all strains with the exception of four strains of B. fragilis. Ampicillin-sulbactam, amoxicillin-clavulanate, piperacillin-tazobactam, and cefoperazone-sulbactam were all highly active with resistance rates < 2%. No resistance was detected to metronidazole, whereas 14% of isolates were resistant to clindamycin. When compared with other studies, these findings underscore the wide variability in susceptibility patterns reported nationwide and the need to continue monitoring these patterns to aid in choosing the most active compounds for therapy.

Activity of fleroxacin alone and in combination with clindamycin or metronidazole in experimental intra-abdominal abscesses

To assess the potential efficacy of fleroxacin in combination with clindamycin or metronidazole in mixed aerobic and anaerobic infections, we used a rat model of intra-abdominal abscesses in which the inoculum consisted of pooled rat feces mixed with BaSO4. Two hours after bacterial challenge, antimicrobial therapy was begun intravenously with regimens designed to stimulate human pharmacokinetics. A combination of clindamycin and gentamicin was included as an established treatment regimen. After 8.5 days of therapy, final bacterial counts in abscesses showed that fleroxacin alone or combined with metronidazole or clindamycin effectively eradicated Escherichia coli, with bacterial densities of < or = 2.84 +/- 0.1, < or = 2.9 +/- 0.1, and < or = 2.9 +/- 0.1 (mean +/- standard error of the mean) log10 CFU/g, respectively. The addition of either clindamycin or metronidazole to fleroxacin substantially enhanced the effectiveness of the regimens against Bacteroides fragilis, with bacterial counts of < or = 3.0 +/- 0.1 or < or = 2.9 +/- 0.1 log10 CFU/g, respectively, versus 9.2 +/- 0.2 log10 CFU/g for fleroxacin alone. The combination of metronidazole and fleroxacin also resulted in a significantly greater reduction of peptostreptococci and Bacteroides thetaiotaomicron than fleroxacin alone (< or = 2.9 +/- 0.1 versus 6.1 +/- 0.9 log10 CFU/g and 3.3 +/- 0.4 versus 8.3 +/- 0.1 log10 CFU/g, respectively). Except for those of B. fragilis, counts of other anaerobes were reduced to a greater extent by metronidazole plus fleroxacin than by clindamycin plus fleroxacin, although differences were not always significant. Metronidazole plus fleroxacin was at least as active a clindamycin plus gentamicin against all species and was significantly more active against Clostridium spp. No regimen effectively eradicated enterococci from the abscesses. These results suggest that the addition of either metronidazole or clindamycin would effectively enhance the spectrum of fleroxacin for treatment of mixed aerobic and anaerobic infections.

A new tetracycline resistance determinant, Tet H, from Pasteurella multocida specifying active efflux of tetracycline

The tetracycline resistance determinant on plasmid pVM111 from an avian strain of Pasteurella multocida mediates tetracycline resistance by a regulated active efflux mechanism. DNA coding for the determinant did not hybridize at high stringency with DNA representing a group of common tetracycline resistance determinants. The DNA sequence, however; revealed a structural gene and a repressor gene which had significant (37 to 64%) sequence similarities with previously described classes of efflux-type tetracycline resistance genes from members of the family Enterobacteriaceae. The new determinant has been assigned to class H.

Cloning and characterization of the endogenous cephalosporinase gene, cepA, from Bacteroides fragilis reveals a new subgroup of Ambler class A beta-lactamases

Bacteroides fragilis CS30 is a clinical isolate resistant to high concentrations of benzylpenicillin and cephaloridine but not to cephamycin or penem antibiotics. beta-Lactam resistance is mediated by a chromosomally encoded cephalosporinase produced at a high level. The gene encoding this beta-lactamase was cloned from genomic libraries constructed in Escherichia coli and then mated with B. fragilis 638 for identification of ampicillin-resistant (Apr) strains. Apr transconjugants contained a nitrocefin-reactive protein with the physical and enzymatic properties of the original CS30 isolate. The beta-lactamase gene (cepA) was localized by deletion analysis and subcloned, and its nucleotide sequence was determined. The 903-bp cepA open reading frame encoded a 300-amino-acid precursor protein (predicted molecular mass, 34,070 Da). A beta-lactamase-deficient mutant strain of B. fragilis 638 was constructed by insertional inactivation with the cepA gene of CS30, demonstrating strict functional homology between these chromosomal beta-lactamase genes. An extensive comparison of the CepA protein sequence by alignment with other beta-lactamases revealed the strict conservation of at least four elements common to Ambler class A. A further comparison of the CepA protein sequence with protein sequences of beta-lactamases from two other Bacteroides species indicated that they constitute their own distinct subgroup of class A beta-lactamases.

Cross-resistance to beta-lactam-beta-lactamase inhibitor combinations and clindamycin among cefoxitin-resistant and cefoxitin-susceptible strains of the Bacteroides fragilis group

In the present study the cross-resistance rates of cefoxitin-resistant and cefoxitin-susceptible strains of the Bacteroides fragilis group were compared with regard to beta-lactam-beta-lactamase inhibitor combinations and clindamycin. Piperacillin-tazobactam was the most active agent tested with an overall resistance rate of 0.2% and no resistance among cefoxitin-resistant strains. Ticarcillin-clavulanate was the least active combination with an overall resistance rate of 1.6% but a resistance rate of 13.1% among cefoxitin-resistant strains. For ampicillin-sulbactam, amoxicillin-clavulanate, and clindamycin resistance, rates of cefoxitin-resistant versus cefoxitin-susceptible strains were 9.1% and 0.4%, 8.3% and 0.9%, and 28% and 12.9%, respectively.

Rationale for selective use of anaerobic blood cultures

Because of the declining frequency of anaerobic bacteremia, routinely using half the collected blood volume for anaerobic culture has been challenged. There is no data indicating whether more clinically relevant isolates would be recovered if all or most of the given blood sample were cultured aerobically. In this two-part study, we reviewed cases of anaerobic bacteremia to determine what proportion occurred in situations when anaerobes would be expected and then estimated the yield of different culture approaches by reanalyzing the data from a large prospective clinical blood culture study. The records of 61 patients who had an anaerobic isolate (excluding Propionibacterium species) recovered only from an anaerobic bottle were examined to define clinical settings in which such isolates occur. Fifty-six (92%) patients had clinically important isolates, and the source of infection was obvious at the time of culture in 47 of the 56 (84%). Of 56 patients, 36 (64%) had abdominal signs and symptoms, including 12 with recent abdominal surgery. Of nine patients without an obvious source of infection, six were on high-dose steroids. Relative yields were compared for (i) one aerobic bottle and one anaerobic bottle (5 ml to each) for all blood cultures, (ii) two aerobic bottles (5 ml to each), or (iii) two aerobic bottles plus an extra anaerobic bottle (only for clinically suspected anaerobic sepsis) (5 ml to each). The third approach had the highest yield (475 isolates), because the routine use of two aerobic bottles recovered more Candida spp., members of the family Enterobacteriaceae, and nonfermenters than did the first approach (448 isolates) (P < 0.02), and clinically directed culturing for anaerobes would recover anaerobes missed with the second approach (458 isolates). Our data suggest that the use of two aerobic bottles with selective culturing for anaerobes could increase the number of clinically relevant isolates by at least 6% compared with the current practice of inoculating an aerobic bottle and an anaerobic bottle with equal volumes of blood.

In vitro and in vivo activities of the nitroimidazole CGI 17341 against Mycobacterium tuberculosis

CGI 17341 (2-ethyl-5-nitro-2,3-dihydro[2-1b]imidazo-oxazole) is a novel orally active representative of the 5-nitroimidazole series of antimicrobial agents. At concentrations ranging from 0.1 to 0.3 micrograms/ml, CGI 17341 inhibited the drug-susceptible and multi-drug-resistant strains of Mycobacterium tuberculosis. CGI 17341 had no cross-resistance with isoniazid, rifampin, streptomycin, or ethambutol. While the in vitro activity of CGI 17341 against M. tuberculosis was comparable to those of isoniazid and rifampin, it was superior to those of streptomycin, ciprofloxacin or norfloxacin, and oxazolidinone DuP 721. The MIC of CGI 17341 was not affected when the pH of the medium was decreased from 6.8 to 5.6, while four- to sixfold increases in the MICs of ciprofloxacin and isoniazid were observed. In mice infected with M. tuberculosis, the 50% effective dose for CGI 17341 was 7.7 mg/kg of body weight (95% confidence limits, 3.5 and 10.27) when administered on days 11 and 12 postinfection. CGI 17341 gave a dose-dependent (r = 0.995) and significant increase in the survival time. Our data indicate that the 5-nitroimidazole CGI 17341 is a promising and novel antituberculosis compound with potent in vitro and in vivo activities. Further investigations on this compound are warranted.

Survey of the susceptibility patterns of Bacteroides fragilis group strains in France from 1977 to 1992

Rates of antibiotic resistance within the Bacteroides fragilis group were monitored over a 15-year period in France by examining studies that employed the same methodology to test susceptibility of anaerobic bacteria. Chloramphenicol, metronidazole, beta-lactam/beta-lactamase inhibitor combinations and imipenem remained very active against Bacteroides fragilis. There was little or no change in rates of resistance to these antibiotics. Resistance to clindamycin increased from 1% in 1977 to a peak of 19% in 1987, and since then has remained at 8 to 12%. There was some evidence that resistance to most beta-lactam agents increased during the same period. These results emphasize the need for periodic surveys of resistance patterns of the Bacteroides fragilis group in each country.

A reassessment of the activity of the third-generation cephalosporins against anaerobes and Staphylococcus aureus

The in vitro activity of cefotaxime (CTX) alone and in combination with its metabolite desacetylcefotaxime (dCTX) was evaluated against 106 isolates of Bacteroides species. and 32 strains of Staphylococcus aureus. All strains were recovered from infected tissues of diabetic patients. Addition of dCTX to the parent compound markedly increased the inhibitory activity against Bacteroides species in general and Bacteroides fragilis and Bacteroides vulgatus in particular. No effect of the combination of both agents on Bacteroides thetaiotaomicron or Bacteroides ovatus was observed; 50% of B. fragilis infections were susceptible to CTX alone and 81% became susceptible to CTX plus dCTX. In addition, a partial synergistic interaction against 20 strains of B. fragilis resulted in a four- to nine-fold reduction in the minimal inhibitory concentration (MIC) after dCTX was added to CTX. Interestingly, 10 of 20 strains that exhibited an MIC of 64-128 micrograms/mL with CTX alone became very susceptible after the combination of parent and metabolite. This favorable positive interaction of both agents was also observed with S. aureus; a two- to four-fold reduction in MIC values was observed when dCTX was added.