Re-assessment of phenotypic identifications of Bacteroides putredinis to Alistipes species using molecular methods

Alistipes (previously Bacteroides) are strictly anaerobic gram-negative rods that resemble the Bacteroides fragilis group in that most species are bile-resistant and indole-positive; however, they are only weakly saccharolytic and most species produce light brown pigment only on laked rabbit blood agar. In this retrospective study, we re-identified 18 organisms previously identified phenotypically as "Bacteroides putredinis-like", but that did not produce pigment on routine media. The strains were identified with 16S rDNA sequencing and pigment production was evaluated on several different culture media. Only 12/18 strains had molecular identifications of Alistipes species, while the remaining strains phylogenetically resembled Butyricimonas and Odoribacter spp. Pigment production was not a reliable test for those Alistipes strains that are described as pigment producers.

Activity of garenoxacin against 536 unusual anaerobes including 128 recovered from acute pelvic infections

Garenoxacin, a des-(F)6-quinolone, was tested using the agar dilution method against 536 anaerobic bacteria, composed of 408 unusual strains from various sources and 128 pelvic isolates. Only 33/408 (8%) unusual isolates and 6/128 (4.7%) pelvic isolates had garenoxacin MICs ≥ 4 μg/mL, and 18 and 3 (4.4% and 2.3% of the respective totals) had MICs ≥ 8 μg/mL. Less susceptible unusual isolates included 7/15 Veillonella sp. from various clinical sources, 6/14 Fusobacterium varium from predominantly abdominal infections, 5/5 F. russii (cat bites), and 6/9 Actinomyces israelii. Overall, garenoxacin showed good activity against the isolates studied and has potential utility in mixed aerobic/anaerobic infections.

Multi-drug resistant Bacteroides fragilis recovered from blood and severe leg wounds caused by an improvised explosive device (IED) in Afghanistan

This report summarizes the case of a 23 year-old otherwise healthy male that was injured in an improvised explosive device (IED) blast in support of Operation Enduring Freedom (OEF). He sustained bilateral open tibia and fibula fractures in the setting of being exposed to water contaminated with raw sewage. Despite long-term carbapenem therapy, the patient's wounds were repeatedly noted to have purulent drainage during surgical debridement and cultures from these wounds were persistently positive for Bacteroides fragilis. Apparent clinical failure persisted despite the addition of metronidazole to his regimen and an eventual trial of tigecycline. Susceptibility testing of the B. fragilis isolate was performed and resistance to penicillin, clindamycin,metronidazole, cefoxitin, meropenem, imipenem, piperacillin/tazobactam, and tigecycline was confirmed. The presence of a nimE gene on a potentially transferrable plasmid was also confirmed by plasmid sequencing. The only antibiotics that displayed in vitro susceptibility were moxifloxacin and linezolid. These antibiotics were initiated in combination with aggressive irrigation and serial surgical debridement. Conversion to left-sided internal fixation became feasible and his left lower extremity was salvaged without residual evidence of infection. The patient completed an eight week course of combination moxifloxacin and linezolid therapy without adverse event. This B. fragilis isolate displayed simultaneous high-level resistance to multiple antibiotics routinely utilized in anaerobic infections. This was evidenced by clinical failure, in vitro susceptibility testing, and demonstration of genes associated with resistance mechanisms. This case warrants review not only due to the rarity of this event but also the potential implications regarding anaerobic infections in traumatic wounds and the success of a novel treatment regimen utilizing combination therapy with moxifloxacin and linezolid.

Activity of Ceftaroline against Aerobic Gram-Positive and Gram-Negative Pathogens: Effect of Test Method Variability

Ceftaroline is a new cephalosporin with bactericidal activity against methicillin-resistant S. aureus (MRSA) as well as gram-negative pathogens. Variations of in vitro test conditions were found to affect ceftaroline activity, with 5% NaCl inhibiting growth and/or reducing the minimum inhibitory concentrations (MICs) for E. coli, K. pneumoniae, M. catarrhalis, H. influenzae, and streptococci, while an inoculum of 10⁶ CFU/mL raised MICs of some E. coli, K. pneumoniae, and M. catarrhalis strains.

In vitro activity of ceftaroline against 623 diverse strains of anaerobic bacteria

The in vitro activities of ceftaroline, a novel, parenteral, broad-spectrum cephalosporin, and four comparator antimicrobials were determined against anaerobic bacteria. Against Gram-positive strains, the activity of ceftaroline was similar to that of amoxicillin-clavulanate and four to eight times greater than that of ceftriaxone. Against Gram-negative organisms, ceftaroline showed good activity against beta-lactamase-negative strains but not against the members of the Bacteroides fragilis group. Ceftaroline showed potent activity against a broad spectrum of anaerobes encountered in respiratory, skin, and soft tissue infections.

Introduction of ertapenem into a hospital formulary: effect on antimicrobial usage and improved in vitro susceptibility of Pseudomonas aeruginosa

After ertapenem was added to the formulary of a 344-bed community teaching hospital, we retrospectively studied its effect on antimicrobial utilization and on the in vitro susceptibility of various antimicrobial agents against Pseudomonas aeruginosa. Three study periods were defined as preintroduction (months 1 to 9), postintroduction but before the autosubstitution of ertapenem for ampicillin-sulbactam (months 10 to 18), and after the policy of autosubstitution (months 19 to 48) was initiated. Ertapenem usage rose slowly from introduction to a range of 36 to 48 defined daily doses/1,000 patient days (DDD) with a resultant decrease in ampicillin-sulbactam usage due to autosubstitution. Imipenem usage peaked 6 months after the introduction of ertapenem and started to decline coincidently with the increased use of ertapenem. During the second period, imipenem usage decreased (slope = -1.28; P = 0.002). Prior to the introduction of ertapenem, the susceptibility of P. aeruginosa to imipenem increased from 61 to 81% at month 7 but then decreased slightly to 67% at month 9. After the introduction of ertapenem, susceptibility continued to increase; the increasing trend was significant (slope = 1.74; P < 0.001). In the third period, the median susceptibility (interquartile range) was 88% (82 to 95%). This change appeared related to decreased imipenem usage. For every unit decrease in the monthly DDD of imipenem, there was an increase of 0.38% (P = 0.008) in the susceptibility of P. aeruginosa to imipenem in the same month. Ertapenem was effective in our antimicrobial stewardship program and may have helped improve the P. aeruginosa antimicrobial susceptibility to imipenem by decreasing the unnecessary usage and selective pressure of antipseudomonal agents.

Impact of an intervention to control Clostridium difficile infection on hospital- and community-onset disease; an interrupted time series analysis

Strategies to reduce rates of Clostridium difficile infection (CDI) generally recommend isolation or cohorting of active cases and the reduced use of cephalosporin and quinolone antibiotics. Data supporting these recommendations come predominantly from the setting of epidemic disease caused by ribotype 027 strains. We introduced an initiative involving a restrictive antibiotic policy and a CDI-cohort ward at an acute, 820-bed teaching hospital where ribotype 027 strains account for only one quarter of all CDI cases. Antibiotic use and monthly CDI cases in the 12 months before and the 15 months after the initiative were compared using an interrupted time series analysis and segmented regression analysis. The initiative resulted in a reduced level of cephalosporin and quinolone use (22.0% and 38.7%, respectively, both p <0.001) and changes in the trends of antibiotic use such that cephalosporin use decreased by an additional 62.1 defined daily doses (DDD) per month (p <0.001) and antipseudomonal penicillin use increased by 20.7 DDD per month (p = 0.011). There were no significant changes in doxycycline or carbapenem use. Although the number of CDI cases each month was falling before the intervention, there was a significant increase in the rate of reduction after the intervention from 3% to 8% per month (0.92, 95% CI 0.86-0.99, p = 0.03). During the study period, there was no change in the proportion of cases having their onset in the community, nor in the proportion of ribotype 027 cases. CDI cohorting and restriction of cephalosporin and quinolone use are effective in reducing CDI cases in a setting where ribotype 027 is endemic.

Infection after elective colorectal surgery: bacteriological analysis of failures in a randomized trial of cefotetan vs. ertapenem prophylaxis

BACKGROUND

A randomized study comparing single-dose cefotetan and ertapenem prophylaxis for elective colorectal surgery in 1,002 patients found ertapenem to be significantly more effective (p < 0.001). Failures of prophylaxis were thought to involve organisms resistant to both antimicrobial agents, isolated most often from deep or superficial incision sites.

METHODS

Further testing and analysis of the microbial data was performed. Susceptibility results were correlated with the clinical outcomes reported previously.

RESULTS

Of the 216 aerobes tested, 62.6% were resistant to cefotetan and 44% to ertapenem. Enterococci and methicillin-resistant Staphylococcus epidermidis were the aerobes recovered most frequently, and Bacteroides thetaiotaomicron, Clostridium innocuum, and Eubacterium lentum were the most frequent anaerobes. Enterococcus faecalis usually was associated in mixed culture with Bacteroides fragilis group species. Approximately one-half of the 158 anaerobes (50.7%), including all the species above, were resistant to cefotetan; most of these (61.4%) came from superficial incision sites. Only one anaerobe (Desulfovibrio fairfieldensis), found in a superficial incisional infection, was resistant to ertapenem, and no ertapenem-resistant enteric bacteria were recovered. In vitro resistance was associated with therapeutic failure.

CONCLUSIONS

The in vitro activity of ertapenem was superior to that of cefotetan against all anaerobic and many aerobic bacteria isolated from postoperative cultures of patients who failed prophylaxis with these agents. Our findings help to elucidate the results of the clinical trial.

Mobilization and prevalence of a Fusobacterial plasmid

Fusobacterium nucleatum is a Gram-negative anaerobic rod found in dental plaque biofilms, and is an opportunistic pathogen implicated in periodontitis as well as a wide range of systemic abscesses and infections. Genomic analyses of F. nucleatum indicate considerable genetic diversity and a prominent role for horizontal gene transfer in the evolution of the species. Several plasmids isolated from F. nucleatum, including pFN1, harbor relaxase gene homologs that may function in plasmid mobilization. In this investigation we examined the RP4-mediated mobilization properties of pFN1 and the prevalence of pFN1-related sequences in a panel of F. nucleatum clinical isolates. The fusobacterial plasmid pFN1 was mobilized by RP4 at a high frequency. Deletion analyses were used to delineate the core mobilon of pFN1, which consisted of the relaxase gene (rlx), an upstream open reading frame ORF4 and a region of DNA upstream of ORF4 with potential nic sites. To examine the prevalence of pFN1 in a panel of clinical isolates, total DNA isolated from the strains was hybridized with pFN1 replication (repA) and rlx gene probes. DNA from strains harboring plasmids known to be homologous to pFN1 hybridized with both the repA and rlx probes. Five additional strains were rlx-positive but repA-negative, indicating a greater prevalence of rlx-related genes in comparison with repA-related genes. Plasmid or plasmid-related sequences were identified in 11.5% of the strains examined. These findings demonstrate mobilization properties of a fusobacterial plasmid that may be important in horizontal gene transfer.

A central role for venom in predation by Varanus komodoensis (Komodo Dragon) and the extinct giant Varanus (Megalania) priscus

The predatory ecology of Varanus komodoensis (Komodo Dragon) has been a subject of long-standing interest and considerable conjecture. Here, we investigate the roles and potential interplay between cranial mechanics, toxic bacteria, and venom. Our analyses point to the presence of a sophisticated combined-arsenal killing apparatus. We find that the lightweight skull is relatively poorly adapted to generate high bite forces but better adapted to resist high pulling loads. We reject the popular notion regarding toxic bacteria utilization. Instead, we demonstrate that the effects of deep wounds inflicted are potentiated through venom with toxic activities including anticoagulation and shock induction. Anatomical comparisons of V. komodoensis with V. (Megalania) priscus fossils suggest that the closely related extinct giant was the largest venomous animal to have ever lived.

Activity of a novel carbapenem, doripenem, against anaerobic pathogens

Doripenem, a synthetic 1-beta-methyl carbapenem, has a broad-spectrum of activity against almost all species of anaerobic bacteria, including all Bacteroides fragilis group species, most with MIC(90) results at <or=1 microg/mL (with the exception of Sutterella wadsworthensis). Against Clostridium difficile strains, it has a narrow range of inhibitory concentrations (1-4 microg/mL) that "may be achievable in the colon", potentially resulting in lower disease rates. It has been shown to be active in vitro against strains isolated from a variety of clinical infections, including bacteremias, diabetic foot and other soft tissues infections and in intra-abdominal and pelvic sites. In addition, a study of a pyometrium animal model of mixed infections noted a better microbiologic response than with imipenem. Two phase 3 multinational clinical trials of complicated mixed aerobic/anaerobic intra-abdominal infections noted "noninferiority" of doripenem when compared with meropenem, but in vitro against the anaerobes, it was "more potent than meropenem, ertapenem, ... and similar to imipenem". Doripenem activity against anaerobes seems comparable with the other extant carbapenems. Although resistance among anaerobic bacteria to this agent is possible, it remains relatively rare.

Comparative in vitro activity of REP3123 against Clostridium difficile and other anaerobic intestinal bacteria

OBJECTIVES

The aim of this study was to determine the anaerobic spectrum of activity of REP3123, a novel diaryldiamine that inhibits bacterial methionyl-tRNA synthetases in Gram-positive bacteria.

METHODS

Fifty recent clinical isolates of Clostridium difficile from patients diagnosed with C. difficile infection and 223 other intestinal normal flora anaerobes were tested for their susceptibility to REP3123 and four or five comparator agents by the agar dilution method using supplemented Brucella agar with 5% laked sheep blood.

RESULTS

All strains of C. difficile were inhibited by 0.5-1 mg/L REP3123, including those resistant to moxifloxacin and clindamycin. REP3123 lacked activity against many normal flora anaerobes in the gut, including Clostridium ramosum, bifidobacteria, lactobacilli of the Lactobacillus casei-rhamnosus-plantarum group and Gram-negative anaerobes.

CONCLUSIONS

REP3123 demonstrated good potency against C. difficile, but limited activity against many other intestinal anaerobic species, thus, in theory, maintaining the colonization resistance barrier.

Virulence characteristics of community-associated Staphylococcus aureus and in vitro activities of moxifloxacin alone and in combination against community-associated and healthcare-associated meticillin-resistant and -susceptible S. aureus

The increasing prevalence of community-associated meticillin-resistant Staphylococcus aureus (CA-MRSA) poses a challenge for antimicrobial therapy of skin and soft tissue infections (SSTIs). To determine whether another antimicrobial agent might enhance the activity of moxifloxacin against CA-MRSA, this study analysed its activity alone and in chequerboard combination with doxycycline, rifampicin, clindamycin, trimethoprim, sulfamethoxazole/trimethoprim (SXT) and vancomycin against recent SSTI clinical isolates, and also characterized the isolates for Panton–Valentine leukocidin (PVL), agr groups, staphylococcal cassette chromosome mec (SSCmec) types and δ-haemolysin production. For comparison, 25 strains of outpatient meticillin-susceptible S. aureus (MSSA), 24 strains of healthcare-associated (HA)-MRSA and six historical strains of vancomycin-intermediate S. aureus (VISA) were included. It was found that 21/25 CA-MRSA strains tested were PVL-positive, SSCmec type 4 and agr type 1, whilst 4/25 were PVL-negative, SSCmec type 2 and agr type 2. Two of the agr type 2 strains were negative for δ-haemolysin but all other strains were positive. Moxifloxacin MIC50/90 values (μg ml−1) were 1/8 for CA-MRSA, 4/32 for HA-MRSA and ≤0.03/1 for MSSA and MIC50 of 2 for VISA. The D-test for inducible clindamycin resistance was positive for 3/27 CA-MRSA, 5/14 HA-MRSA and none of the MSSA isolates. In chequerboard studies, fractional inhibitory concentration indices (FICIs) showed that most interactions were additive or indifferent (FICI value >0.5 to ≤2) as follows: rifampicin 43/52 strains, clindamycin 44/44, SXT 44/47, trimethoprim 41/42 and vancomycin 37/43. The FICI values for doxycycline were 3–6 for 32/34 strains, indicating antagonism, suggesting that it should not be used in combination with moxifloxacin.

National hospital survey of anaerobic culture and susceptibility methods: III

To assess the current status of anaerobic bacteriology in the United States, we surveyed, by means of a questionnaire, 150 hospitals selected at random with bed capacities of 200-1000 and we received responses from 98 (65%). Ninety-eight percent processed anaerobic culture specimens with 21% sending them to reference laboratories. Almost all these hospitals processed blood and wound cultures for anaerobes and all used selective media for identification, including BBE (52%), LKV (77%), and PEA (53%) agars. All hospital laboratories attempted identification of blood culture isolates including 80% that attempted speciation. Wound cultures for anaerobic bacteria and sterile site cultures were also processed for anaerobes by almost all labs. Identification of B. fragilis group species to species level was performed only in 56% of labs always and 37% sometimes. Preformed enzyme kits were used by 66% of labs and 30% used special potency disks for identification. Susceptibility testing was performed in-house by 21% of hospital labs and sent out to reference labs an additional 20%. Susceptibility testing was attempted for all blood culture isolates by both hospital (21% of total labs) and reference laboratories, but only performed by 17% for sterile body site and 14% of the time for wound isolates. Etest was used most often followed by broth microdilution. No labs used the agar dilution or disk elution methods. The antimicrobials most often tested in hospital labs, predicated on the commercial panel used, were penicillin/ampicillin and clindamycin (15/18; 83%; 15% of total labs), metronidazole (16/18; 89%; 16% of total labs) and cefotetan and ampicillin/sulbactam (12/18; 67%; 12% of total labs), piperacillin/tazobactam (7/18; 39%; 7% of total labs), cefoxitin (9/18; 50%), imipenem (8/18; 44%), and chloramphenicol (6/18; 33%). Our current survey suggests that while many labs are processing anaerobic cultures, especially blood cultures, the identification of isolates and the performance of antimicrobial susceptibility testing of isolates are in disarray and in dire need of improvement.

Serum bactericidal activities of moxifloxacin and levofloxacin against aerobic and anaerobic intra-abdominal pathogens

We studied the serum bactericidal activity (SBA) of moxifloxacin and levofloxacin against common pathogens associated with complicated intra-abdominal infections. Ten healthy volunteers received a single dose of moxifloxacin (400 mg) and levofloxacin (750 mg) and serum samples were collected at 2, 4, 8, 12, and 24h after the dose of each drug. Bactericidal titers in serum over time were determined for aerobic gram-negative bacilli (Escherichia coli, Klebseilla pneumoniae, and Enterobacter cloacae) and anaerobic bacteria (Bacteroides fragilis, Bacteroides thetaiotaomicron, Prevotella bivia, and Finegoldia magna). Both fluoroquinolones provided rapid (2h) attainment and prolonged (24h) SBA (titers > or = 1:8) against each of the aerobic bacilli studied. SBA was observed for at least 12h against B. fragilis strains with MICs < or = 2 microg/ml to moxifloxacin and < or = 4 microg/ml to levofloxacin. Prolonged (12h) SBA (titers > or = 1:2) was also observed against isolates of B. thetaiotaomicron, P. bivia, and F. magna with moxifloxacin < or = MICs 2 microg/ml.

Development of Tyrocidine A analogues with improved antibacterial activity

The development of new antibacterial therapeutic agents capable of halting microbial resistance is a chief pursuit in clinical medicine. Classes of antibiotics that target and destroy bacterial membranes are attractive due to the decreased likelihood that bacteria will be able to generate resistance to this mechanism. The amphipathic cyclic decapeptide, Tyrocidine A, is a model for this class of antibiotics. Tyrocidine A is composed of a hydrophobic and a hydrophilic face, allowing for insertion into bacterial membranes, creating porous channels and destroying membrane integrity. We have used a combination of molecular modeling and solid phase synthesis to prepare Tyrocidine A and analogues 1-8. The minimum inhibitory concentrations (MICs) of these compounds were determined for a host of gram positive species and E. coli as a representative gram negative bacterium. Analogues 2 and 5 demonstrated moderate 2- to 8-fold increases in antibacterial activity over the parent Tyrocidine A for a variety of pathogenic microbes (best MICs for E. coli 32 microg/mL and 2 microg/mL for most gram positives). Examination of the structure- activity relationship between the analogues demonstrated a preference for increased amphipathicity but did not show a clear preference for increasing hydrophilicity versus hydrophobicity in improving antibacterial activity. Of note, movement of positively charged lysine residues or neutral pentafluorophenyl residues to different positions within the cyclopeptide ring system demonstrated improvements in antibacterial activity.

Bacteriology of moderate-to-severe diabetic foot infections and in vitro activity of antimicrobial agents

As part of a United States-based multicenter clinical trial, conducted from 2001 to 2004, that compared ertapenem to piperacillin-tazobactam for the treatment of moderate-to-severe diabetic foot infections (DFIs), we obtained 454 pretreatment specimens from 433 patients. After debridement, the investigators collected wound specimens, mostly by curettage or biopsy, and sent them to the R. M. Alden Research Laboratory for aerobic and anaerobic culture. Among the 427 positive cultures, 83.8% were polymicrobial, 48% grew only aerobes, 43.7% had both aerobes and anaerobes, and 1.3% had only anaerobes. Cultures yielded a total of 1,145 aerobic strains and 462 anaerobic strains, with an average of 2.7 organisms per culture (range, 1 to 8) for aerobes and 2.3 organisms per culture (range, 1 to 9) for anaerobes. The predominant aerobic organisms were oxacillin-susceptible Staphylococcus aureus (14.3%), oxacillin-resistant Staphylococcus aureus (4.4%), coagulase-negative Staphylococcus species (15.3%), Streptococcus species (15.5%), Enterococcus species (13.5%), Corynebacterium species (10.1%), members of the family Enterobacteriaceae (12.8%), and Pseudomonas aeruginosa (3.5%). The predominant anaerobes were gram-positive cocci (45.2%), Prevotella species (13.6%), Porphyromonas species (11.3%), and the Bacteroides fragilis group (10.2%). Pure cultures were noted for 20% of oxacillin-resistant Staphylococcus aureus cultures, 9.2% of Staphylococcus epidermidis cultures, and 2.5% of P. aeruginosa cultures. Two or more species of Staphylococcus were present in 13.1% of the patients. Ertapenem and piperacillin-tazobactam were each active against >98% of the enteric gram-negative rods, methicillin-sensitive S. aureus, and anaerobes. Among the fluoroquinolones, 24% of anaerobes, especially the gram-positive cocci, were resistant to moxifloxacin; 27% of the gram-positive aerobes but only 6% of the members of the family Enterobacteriaceae were resistant to levofloxacin. Moderate-to-severe DFIs are typically polymicrobial, and almost half include anaerobes. Our antibiotic susceptibility results can help to inform therapeutic choices.

Anaerobic bacteria cultured from the tongue dorsum of subjects with oral malodor

The bacteria on the dorsum of the tongue are the most frequent cause of oral malodor; however, the bacterial flora of the tongue has not been well defined. Although recent studies have used DNA probes to detect the presence of certain periodontal pathogens, cultural studies have been limited because of the complexity of the flora of the tongue dorsum. The purpose of this study was to grow and to identify maximum numbers of capnophylic Gram-negative bacilli and anaerobic micro-organisms by culturing tongue samples on to several selective and non-selective media. The most frequently isolated species included Peptostreptococcus anaerobius, Collinsella aerofaciens, Eubacterium group, Actinomyces spp., Eikenella corrodens, Veillonella spp., Fusobacterium nucleatum, pigmented Prevotella spp. and Selenomonas spp. Reported for the first time are Actinomyces turicensis, Collinsella aerofaciens, Eubacterium saburreum, E. timidum, Prevotella tannerae, Campylobacter concisus, Campylobacter mucosalis, Leptotrichia buccalis, Selenomonas flueggei, and Centipeda periodontii. Species not previously reported in studies that used only molecular techniques were identified in the present study.

Bacteriology of human bite wound infections

This study was designed to define the bacteriology of infected soft-tissue wounds from human bites, and to compare this with the bacteriology of infected animal bites in humans as determined in previous studies. The specimens were collected from 57 patients presenting to emergency rooms at 12 locations around the country. Three hundred and eighty organisms were isolated (224 aerobes and 156 anaerobes), for an average of 6.6 per specimen. The most prevalent anaerobes recovered were Prevotella spp. (34%), while streptococci comprised 44% of all aerobic organisms, over half of which were in the "Streptococcus milleri" group, particularly S. anginosus. The study demonstrated that the pathogens in human bite infections differ considerably from those present in animal bites.