In vitro activities of MK-826 (L-749,345) against 363 strains of anaerobic bacteria

The activity of MK-826 was compared to the activities of cefoxitin, ceftriaxone, imipenem, and meropenem against 363 gram-negative and gram-positive anaerobes by using NCCLS procedures. At least 98% of the strains were susceptible to the carbapenems. All strains of Clostridium perfringens, Fusobacterium nucleatum, Peptostreptococcus, and Sutterella wadsworthensis were susceptible to all agents tested.

Ampicillin/sulbactam and cefoxitin in the treatment of cutaneous and other soft-tissue abscesses in patients with or without histories of injection drug abuse

A randomized, double-blind trial compared the clinical and bacteriologic efficacy of ampicillin/sulbactam (2 g/1 g) and cefoxitin (2 g) administered intravenously every 6 h to patients with (n=49) or without (n=47) histories of injection drug abuse who presented with cutaneous or other soft-tissue infections. Cure or improvement occurred in 89.8% of ampicillin/sulbactam-treated patients, compared with 93.6% of cefoxitin-treated patients. The median time to resolution of all symptoms was 10.5 days with ampicillin/sulbactam treatment and 15.5 days with cefoxitin treatment. Mixed aerobic-anaerobic infection was encountered frequently in both treatment groups. A significantly higher percentage of Streptococcus species was found in the major abscesses of the patients with histories of injection drug abuse, compared with those without such histories (37% vs. 19%, respectively; P=.0009). Overall, ampicillin/sulbactam eradicated pathogens from the major abscesses in 100% of patients, whereas the eradication rate with cefoxitin was 97.9%. The 2 drugs were well tolerated. Ampicillin/sulbactam and cefoxitin were equally effective for the empirical treatment of cutaneous or other soft-tissue infections in injection drug abusers and patients who did not inject drugs.

Short-term benefit from oral vancomycin treatment of regressive-onset autism

In most cases symptoms of autism begin in early infancy. However, a subset of children appears to develop normally until a clear deterioration is observed. Many parents of children with "regressive"-onset autism have noted antecedent antibiotic exposure followed by chronic diarrhea. We speculated that, in a subgroup of children, disruption of indigenous gut flora might promote colonization by one or more neurotoxin-producing bacteria, contributing, at least in part, to their autistic symptomatology. To help test this hypothesis, 11 children with regressive-onset autism were recruited for an intervention trial using a minimally absorbed oral antibiotic. Entry criteria included antecedent broad-spectrum antimicrobial exposure followed by chronic persistent diarrhea, deterioration of previously acquired skills, and then autistic features. Short-term improvement was noted using multiple pre- and post-therapy evaluations. These included coded, paired videotapes scored by a clinical psychologist blinded to treatment status; these noted improvement in 8 of 10 children studied. Unfortunately, these gains had largely waned at follow-up. Although the protocol used is not suggested as useful therapy, these results indicate that a possible gut flora-brain connection warrants further investigation, as it might lead to greater pathophysiologic insight and meaningful prevention or treatment in a subset of children with autism.

Beta-lactamase production in Prevotella intermedia, Prevotella nigrescens, and Prevotella pallens genotypes and in vitro susceptibilities to selected antimicrobial agents

The present study investigated the beta-lactamase production of 73 Prevotella intermedia, 84 Prevotella nigrescens, and 14 Prevotella pallens isolates and their in vitro susceptibilities to six antimicrobial agents. The P. intermedia and P. nigrescens isolates were recovered from oral and extraoral samples obtained from subjects in two geographic locations from 1985 to 1995. The clonality of the beta-lactamase-positive and beta-lactamase-negative isolates and the clustering of the genotypes were studied by arbitrarily primed-PCR fingerprinting. beta-Lactamase production was detected in 29% of P. intermedia isolates, 29% of P. nigrescens isolates, and 57% of P. pallens isolates. No difference in the frequencies of beta-lactamase production by P. intermedia and P. nigrescens between isolates from oral and extraoral sites, between isolates obtained at different time periods, or between P. intermedia isolates from different geographic locations was observed. However, the P. nigrescens isolates from the United States were significantly more frequently (P = 0.015) beta-lactamase positive than those from Finland. No association between the genotypes and beta-lactamase production or between the genotypes and the sources of the isolates was found. The penicillin G MICs at which 90% of the isolates were inhibited were 8 microg/ml for P. intermedia, 8 microg/ml for P. nigrescens, and 16 microg/ml for P. pallens. For the beta-lactamase-negative isolates, the corresponding values were 0.031, 0.031, and 0.125 microg/ml, and for the beta-lactamase-positive isolates, the corresponding values were 16, 8, and 32 microg/ml. All isolates were susceptible to amoxicillin-clavulanate, cefoxitin, metronidazole, azithromycin, and trovafloxacin. The MICs of amoxicillin-clavulanate and cefoxitin were relatively higher for the beta-lactamase-positive population than for the beta-lactamase-negative population.

In vitro efficacy of beta-lactam/beta-lactamase inhibitor combinations against bacteria involved in mixed infections

Mixed infections are usually caused by a relatively limited range of bacteria, with the anaerobes and opportunistic pathogens contributing to their severity. In order to make the best therapeutic choice for a patient with a life-threatening infection, which is probably of mixed etiology, clinicians must be aware of the organisms that are likely to be involved, and the fact that most of them will produce beta-lactamase. Of the options available for empiric therapy, the beta-lactam/beta-lactamase inhibitor combinations represent a good choice. Their antibacterial spectra include both aerobic and anaerobic pathogens. Five combinations are available in clinical practice: ampicillin-sulbactam, piperacillin-tazobactam, ticarcillin-clavulanic acid, amoxicillin-clavulanic acid, and cefoperazone-sulbactam. More strains of clinically important anaerobic bacteria are susceptible to ampicillin-sulbactam than to either piperacillin-tazobactam or ticarcillin-clavulanic acid, which are also available widely and suitable for more life-threatening infections. In addition, sulbactam itself has the highest intrinsic activity of the beta-lactamase inhibitors against the opportunistic pathogen, Acinetobacter baumannii. Thus, ampicillin-sulbactam could be considered a drug of choice for the empirical treatment of mixed infections where there is a reasonable possibility of the presence of A. baumannii.

Ticarcillin/clavulanate versus imipenem/cilistatin for the treatment of infections associated with gangrenous and perforated appendicitis

The objective of this study was to compare ticarcillin/clavulanate given at 3.1 g every 6 hours with imipenem/cilistatin given at 500 mg every 6 hours for the treatment of infections associated with gangrenous or perforated appendicitis. One hundred thirty-seven patients were found to have gangrenous or perforated appendicitis and received the study medication for 3 to 5 days in a double-blinded, randomized manner. Clinical success was similar for the two treatment groups, 96.9 and 95.9 per cent in the ticarcillin/clavulanate and imipenem/cilistatin groups, respectively (P=0.99; 95% confidence interval for the difference was -5.6% to 7.6%). Bacteriologic success at the end of therapy was similar in the two groups, 100 and 98.4 per cent in the ticarcillin/clavulanate and imipenem/ cilistatin groups, respectively (P=0.99; 95% confidence interval for the difference was -1.8% to 4.7%). The occurrence of adverse events related to treatment was similar for the two groups (P=0.31) and led to study withdrawal for four patients (one with ticarcillin/clavulanate and three with imipenem/ cilistatin). Ticarcillin/clavulanate given at 3.1 g every 6 hours is as effective and as safe as imipenem/ cilistatin given at 500 mg every 6 hours for treatment of gangrenous or perforated appendicitis.

Ticarcillin/Clavulanate versus Imipenem/Cilistatin for the Treatment of Infections Associated with Gangrenous and Perforated Appendicitis

The objective of this study was to compare ticarcillin/clavulanate given at 3.1 g every 6 hours with imipenem/cilistatin given at 500 mg every 6 hours for the treatment of infections associated with gangrenous or perforated appendicitis. One hundred thirty-seven patients were found to have gangrenous or perforated appendicitis and received the study medication for 3 to 5 days in a double-blinded, randomized manner. Clinical success was similar for the two treatment groups, 96.9 and 95.9 per cent in the ticarcillin/clavulanate and imipenem/cilistatin groups, respectively (P = 0.99; 95% confidence interval for the difference was -5.6% to 7.6%). Bacteriologic success at the end of therapy was similar in the two groups, 100 and 98.4 per cent in the ticarcillin/clavulanate and imipenem/cilistatin groups, respectively (P = 0.99; 95% confidence interval for the difference was -1.8% to 4.7%). The occurrence of adverse events related to treatment was similar for the two groups (P = 0.31) and led to study withdrawal for four patients (one with ticarcillin/clavulanate and three with imipenem/cilistatin). Ticarcillin/clavulanate given at 3.1 g every 6 hours is as effective and as safe as imipenem/cilistatin given at 500 mg every 6 hours for treatment of gangrenous or perforated appendicitis.

Comparison of Recovery of Anaerobic Bacteria Using the Anoxomat®, Anaerobic Chamber, and GasPak®Jar Systems

The Anoxomat system provides an automated evacuation-replacement technique to create an anaerobic or microaerophilic environment in a jar. We evaluated the Anoxomat system for the growth of obligate anaerobes and for the recovery of anaerobic organisms from clinical specimens, and compared its performance to that of an anaerobic chamber and the GasPak System. Of the 54 stock strains tested, the Anoxomat, the chamber, and the GasPak recovered 95%, 95% and 93% at 24 h, respectively. On 29 occasions (51%), the colonies on the Anoxomat plates were slightly larger than those in the chamber and on 17 (30%) occasions larger than the colonies on the GasPak jar plates. At 48 h, the Anoxomat, the chamber, and the GasPak recovered 93.5%, 94.4% and 88.9%, respectively; of 108 anaerobes isolated from 31 clinical specimens. Methylene blue indicators became decolorized (average of 10 tests) within 2 h inside the Anoxomat jars, 2 h 10 min inside the anaerobic chamber, and 2 h 30 min inside the GasPak jars.

Current susceptibility patterns of anaerobic bacteria

While antibiotic resistance among anaerobes continues to increase, the frequency of antimicrobial susceptibility testing for anaerobes is declining. Because anaerobic infections are often mixed and detailed bacteriology of the organisms involved may take some time, physicians must institute empiric therapy before susceptibility testing results are available. Also, economic realities and prudent use of resources mandate that careful consideration be given to the necessity for routine susceptibility testing of anaerobic bacteria. Determination of appropriate therapy can be based on published antibiograms; however, since patterns may vary within geographic regions and even within hospitals, it is strongly recommended that each hospital center periodically test their isolates to determine local patterns and detect any pockets of resistance. As a general guide, antibiograms from the last several years of susceptibility testing at the Wadsworth Anaerobe Laboratory are reported.

In vitro activity of levofloxacin against a selected group of anaerobic bacteria isolated from skin and soft tissue infections

The in vitro activity of levofloxacin was compared to the activities of ofloxacin, ciprofloxacin, ampicillin-sulbactam (2:1), cefoxitin, and metronidazole for a selected group of anaerobes (n = 175) isolated from skin and soft tissue infections by using the National Committee for Clinical Laboratory Standards-approved Wadsworth method. Ampicillin-sulbactam and cefoxitin inhibited 99% of the strains of this select group, levofloxacin and ofloxacin inhibited 73 and 50%, respectively, at 2 microg/ml, and ciprofloxacin inhibited 51% at 1 microg/ml. The geometric mean MIC of levofloxacin was lower than those of ofloxacin and ciprofloxacin for every group except Veillonella.

Cellular fatty acid composition, soluble-protein profile, and antimicrobial resistance pattern of Eubacterium lentum

Phenotypic heterogeneity among isolates of Eubacterium lentum has been recognized for many years. To better delineate their taxonomic relatedness, 29 clinical isolates of E. lentum were examined for soluble-protein content, cellular fatty acid profile, and antimicrobial resistance pattern in order to ascertain whether differences in these characteristics could be correlated with differences in biochemical activities. Among 29 isolates we could identify 6 that were different from all the others. These strains were coccobacilli with translucent colonies; they were catalase and H2S negative, not fluorescent under UV light, and susceptible to beta-lactam drugs; growth was not stimulated by arginine; and fatty acid analysis revealed the presence of straight-chain fatty acids. The remainder of the strains, including the type species, were pleomorphic bacilli with speckled colonies and were catalase and H2S positive; all but two were fluorescent under UV light; they were resistant to beta-lactam antibiotics; growth was greatly stimulated by arginine; and they demonstrated saturated branched-chain fatty acids. Our data suggest that E. lentum can be further differentiated into different types.

Biochemical and genetic characterization of a Prevotella intermedia/nigrescens-like organism

Thirty-three previously non-typable faintly pigmented Gram-negative anaerobic bacterial isolates, biochemically most closely related to Prevotella intermedia and Prevotella nigrescens, were analysed for enzymic reactions, cellular fatty acid (CFA) composition, electrophoretic mobility of malate and glutamate dehydrogenases, hybridization with P. intermedia and P. nigrescens species-specific oligonucleotide probes and, for genetic heterogeneity, by arbitrarily primed PCR (AP-PCR). P. intermedia ATCC 25611T and P. nigrescens ATCC 33563T were run in parallel for comparison. Twenty-nine isolates originated from the normal oral flora of 18 subjects (including five mother-child pairs), and four isolates from various infections. Except for a negative lipase reaction, enzymic profiles of the test isolates were similar to those of P. intermedia and P. nigrescens. Clustering of CFAs, electrophoretic mobility patterns, hybridization with DNA probes for P. intermedia and P. nigrescens, and AP-PCR band patterns of the test isolates differed from those of the type strains of P. intermedia and P. nigrescens, suggesting the existence, in humans, of a new anaerobic species of pigmented, moderately saccharolytic, indole-positive Gram-negative rods.

Perspective on susceptibility testing of anaerobic bacteria

Physicians must use empirical treatment initially for anaerobic infections. However, such treatment can be targeted if clinicians establish the nature of the infection and know the usual infecting flora of that type of infection and how the flora may have been modified by the use of antimicrobials. Physicians must also be aware of the usual susceptibility patterns of various anaerobes and nonanaerobes in the hospitals in which they work. Despite cost containment, it is still important to isolate all anaerobes present, to provide at least general identification (and specific identification of key organisms such as the Bacteroides fragilis group), and to keep the organisms alive so that they may be referred elsewhere for definitive identification and susceptibility testing, if indicated. Because resistance is increasing among anaerobes, susceptibility testing is very important. Susceptibility testing should be done when patients are seriously ill, when patients do not respond to therapy or relapse, when there are few data available on a species, when the organisms isolated are frequently resistant, and when patients require prolonged therapy. Periodic surveys of susceptibility patterns should be done on isolates from individual hospitals. Tests most useful for individual patient isolates are the Etest (AB BIODISK, Solna, Sweden), an expensive test, and the microbroth dilution test. Testing should be done on organisms that are the most virulent and most resistant to antimicrobial agents.

Recently described clinically important anaerobic bacteria: medical aspects

There is still inadequate information on the role of certain newly described or reclassified anaerobes in disease processes, on their normal sites of carriage, and on their antimicrobial susceptibilities. Herein, we summarize this information (most of the literature reviewed is from the past 5 years, but a few of the articles are approximately 10 years old). Porphyromonas species had seemed to be relatively nonpathogenic, but recent work indicates that this belief is incorrect. P. gingivalis, P levii-like organisms, and P. endodontalis-like organisms have been recovered from a variety of oral and extraoral infections. P. macacae has been recovered from infected cat bite wounds. Sutterella wadsworthensis, recently differentiated from Campylobacter gracilis, has been found in a variety of infections. Bilophila wadsworthia has also been recovered from a wide variety of infections. Newly described anaerobic cocci, gram-positive nonsporeforming rods, and clostridia have also been isolated from various infections.

Characteristics of an unusual anaerobic pigmented gram-negative rod isolated from normal and inflamed appendices

During our studies of the bacterial etiology of appendicitis, we often isolated a previously undescribed anaerobic gram-negative rod. This organism resembled the Bacteroides fragilis group because it was resistant to bile and because of its special-potency-disk pattern (resistant to vancomycin, kanamycin, and colistin), but unlike the B. fragilis group, this bacterium produced brown pigment on media containing hemolysed blood. The cellular fatty acid pattern, with iso-C15:0 being the predominant acid, was most closely related to the fatty acid profile of Porphyromonas species; however, this organism differed from Porphyromonas species by being bile-resistant and by not producing butyrate as a metabolic endproduct. Enzymatic activities of 31 isolates were determined with use of the API ZYM system and Rosco diagnostic tablets. These profiles were different from those of Prevotella, Porphyromonas, and related species. This organism was isolated from 40% of appendiceal tissue samples; no obvious qualitative or quantitative difference in rates of isolation from patients with inflamed or normal appendices was observed.

Present studies of therapy for anaerobic infections

Therapeutic approaches to anaerobic infections are changing. Debridement, drainage, and other surgical approaches remain extremely important. Resistance to antimicrobial agents currently used for treatment of anaerobic infections is increasing. However, promising new agents are being introduced. We review the current status of therapy for anaerobic infections and discuss the potential role of these new agents. We stress an empirical approach to therapy that is based on the usual infecting flora in various types of infections.

Analysis of trends in antimicrobial resistance patterns among clinical isolates of Bacteroides fragilis group species from 1990 to 1994

Antimicrobial resistance, including plasmid-mediated resistance, among Bacteroides fragilis group species is well documented. A 5-year (1990-1994) prospective, eight-center survey of 3,177 clinical isolates of Bacteroides species was undertaken to review trends in resistance, using the breakpoints for full and intermediate susceptibility established by the National Committee for Clinical Laboratory Standards. No documented resistance to either metronidazole or chloramphenicol was found in this survey. Among B. fragilis isolates virtually no resistance was seen to imipenem, meropenem, ampicillin/sulbactam, piperacillin/tazobactam, or ticarcillin/clavulanate. Significant increases in resistance among B. fragilis isolates to cefotetan, ceftizoxime, and clindamycin (p < .01) were noted. Resistance to cefoxitin remained unchanged. Among the non-fragilis species of the B. fragilis group, there was virtually no resistance to imipenem, meropenem, chloramphenicol, or metronidazole. The three beta-lactamase inhibitors had increasing levels of resistance, although 95%-98% of strains were susceptible (p < .05). There was a significant decline in cefoxitin, cefmetazole, and clindamycin activity over time against these strains (p <.01). There was a significant (P < .001) increase in geometric mean minimum inhibitory concentration for most drugs and species tested from 1990 to 1994. Clusters in the eight institutions could not account for this rise in resistance. This survey demonstrates that rates of resistance of B. fragilis and non-fragilis species of B. fragilis group are increasing.

In vitro activities of trovafloxacin against 557 strains of anaerobic bacteria

The antimicrobial activity of trovafloxacin for 557 strains of anaerobic bacteria was determined by the National Committee for Clinical Laboratory Standards-approved Wadsworth agar dilution technique. The species tested included Bacteroides fragilis (n = 91), other members of the B. fragilis group (n = 130), Campylobacter gracilis (n = 15), other Bacteroides spp. (n = 16), Prevotella spp. (n = 49), Porphyromonas spp. (n = 15), Fusobacterium spp. (n = 62), Bilophila wadsworthia (n = 24), Sutterella wadsworthensis (n = 21), Clostridium spp. (n = 61), Peptostreptococcus spp. (n = 38), and gram-positive non-spore-forming rods (n = 35). Trovafloxacin inhibited all strains of B. fragilis at < or = 0.5 microgram/ml, 99% of other B. fragilis group species at < or = 2 micrograms/ml, and 96% of all anaerobes tested at < or = 2 micrograms/ml.

Sutterella wadsworthensis gen. nov., sp. nov., bile-resistant microaerophilic Campylobacter gracilis-like clinical isolates

Campylobacter gracilis (formerly Bacteroides gracilis) is an asaccharolytic, nitrate-positive, urease-negative organism that requires formate and fumarate or hydrogen as a growth additive and may pit agar media. Clinical isolates that were obtained primarily from appendiceal and peritoneal fluid specimens and initially were identified in our laboratory as B. gracilis were later found to include "unusual" strains that could be distinguished by biochemical and genetic criteria. These unusual C. gracilis strains were bile resistant, could not reduce tetrazolium chloride under aerobic conditions if formate and fumarate were added to the medium, and could grow in the presence of 2 or 6% oxygen if no blood was added to the medium. C. gracilis, other campylobacters, and the unusual strains produced distinctive dehydrogenase patterns when gels were incubated anaerobically. A cellular fatty acid analysis revealed that the cluster formed by the unusual organisms was distinct from the (separate) clusters formed by C. gracilis, Bacteroides ureolyticus, and other Campylobacter species. 16S rRNA sequence data indicated that these organisms are not related phylogenetically to either C. gracilis or other Campylobacter species; the most closely related taxa as determined by rRNA sequence analysis were unrelated aerobes (members of the genera Bordetella, Alcaligenes, Rhodocyclus, and Comamonas). DNA homology data confirmed that these taxa are separate groups. Our data indicate that the unusual organisms are members of a new genus and new species, for which we propose the name Sutterella wadsworthensis. The type strain of S. wadsworthensis is strain WAL 9799 (= ATCC 51579).

Comparison of spiral gradient endpoint and agar dilution methods for susceptibility testing of anaerobic bacteria: a multilaboratory collaborative evaluation

A multilaboratory collaborative study was carried out to assess the utility of the spiral gradient endpoint (SGE) method for the determination of the antimicrobial susceptibilities of anaerobes and to evaluate the equivalence of the MICs obtained by the SGE method with those obtained by the reference agar dilution method of the National Committee for Clinical Laboratory Standards. The standard deviation of the MIC obtained by the SGE method for the five participating laboratories was +/- 0.26 of a twofold dilution, whereas it was +/- 1 twofold dilution by the reference method. The interlaboratory reproducibility of the results for two control strains tested with imipenem, chloramphenicol, and metronidazole indicated that 96% of the measurements fell within +/- 1 twofold dilution of the mode. The equivalence of the SGE method with the agar dilution method was assessed with a wide variety of anaerobic organisms. The MICs by both methods were within 1 doubling dilution in 93% of the measurements (n = 1,074). Discrepancies generally occurred with those organism-drug combinations that resulted in tailing endpoints (Fusobacterium nucleatum, 86% agreement) or in cases of light growth (Peptostreptococcus spp., 86% agreement).

Bacteriology of skin and soft-tissue infections: comparison of infections in intravenous drug users and individuals with no history of intravenous drug use

The bacteriology of cutaneous or subcutaneous abscesses (86 specimens) among intravenous drug users (IVDUs) was compared with the bacteriology of abscesses (74 specimens) in patients with no history of intravenous drug use (non-IVDUs). The IVDU abscesses yielded 173 aerobes and 131 anaerobes. Staphylococcus aureus was the most common aerobe isolated (50% of specimens yielded this isolate), followed by "Streptococcus milleri" (46%). The commonly encountered anaerobes were Fusobacterium nucleatum (17%), pigmented Prevotella species (22%), Peptostreptococcus micros (17%), Actinomyces odontolyticus (15%), and Veillonella species (13%). The non-IVDU isolates included 116 aerobes and 106 anaerobes. S. aureus was isolated from 53% of these specimens, followed by coagulase-negative staphylococci (19%), "S. milleri" (19%), and Streptococcus pyogenes (16%). The main groups of anaerobes were Peptostreptococcus species (35%), Bacteroides species (19%), and gram-positive bacilli (31%). Overall, 67% of the IVDU isolates were of oral origin, compared with 25% of the non-IVDU isolates. Of the specimens from IVDUs and non-IVDUs, 48% and 67%, respectively, yielded only aerobes, and 2% and 4%, respectively, yielded only anaerobes. Sixty-four percent of the patients had one or more beta-lactamase-producing organisms.