Intra-abdominal anaerobic infections: bacteriology and therapeutic potential of newer antimicrobial carbapenem, fluoroquinolone, and desfluoroquinolone therapeutic agents

Next-generation microbiological testing in intraabdominal infections with PCR technology

PURPOSE

Intraabdominal infections (IAI) are increasing worldwide and are a major contributor to morbidity and mortality. Among IAI, the number of multi-drug resistant organisms (MDRO) is increasing globally. We tested the Unyvero A50® for intraabdominal infections, compared the detected microorganisms and antibiotic resistance, and compared the results with those of routine microbiology.

METHODS

We prospectively compared samples obtained from surgical patients using PCR-based Unyvero IAI cartridges against routine microbiology for the detection of microorganisms. Additionally, we identified clinical parameters that correlated with the microbiological findings. Data were analyzed using the t-test and Mann-Whitney U test.

RESULTS

Sixty-two samples were analyzed. The PCR system identified more microorganisms, mostly Bacteroides species, Escherichia coli, and Enterococcus spp. For bacterial resistance, the PCR system results were fully concordant with those of routine microbiology, resulting in a sensitivity, specificity, and positive and negative predictive value (PPV, NPV) of 100%. The sensitivity, specificity, PPV, and NPV for the detection of microorganisms were 74%, 58%, 60%, and 72%, respectively. CRP levels were significantly higher in patients with detectable microorganisms. We identified more microorganisms and bacterial resistance in hospital-acquired intra-abdominal infections by using the PCR system.

DISCUSSION

IAI warrants early identification of the microorganisms involved and their resistance to allow for adequate antibiotic therapy. PCR systems enable physicians to rapidly adjust their antibiotic treatment. Conventional microbiological culture and testing remain essential for determining the minimal growth inhibition concentrations for antibiotic therapy.

Eubacterium bacteremia - a retrospective observational study of a seldom found anaerobic pathogen

BACKGROUND

Human infections due to Eubacterium are rare and knowledge of the condition is limited. This study aimed to describe clinical characteristics and outcome in patients with Eubacterium bacteremia.

METHODS

Episodes of Eubacterium bacteremia were identified through the clinical microbiology laboratory in Lund, Sweden. Medical records were retrospectively reviewed. Blood isolates of Eubacterium were collected and antibiotic susceptibility testing was performed with agar dilution.

RESULTS

Seventeen patients with Eubacterium bacteremia were identified of whom six had monomicrobial bacteremia. The incidence was 1.7 cases of Eubacterium bacteremia per million inhabitants and year. The median age was 67 years (interquartile range 63-79 years), and six patients had some form of malignancy. Most of the patients an abdominal focus of infection and the 30-day mortality was low (n = 1).

CONCLUSIONS

Invasive infections with Eubacterium have a low incidence. The condition has a low mortality and an abdominal focus of infection, and malignancy, is common.

A tale of two habitats: Bacteroides fragilis, a lethal pathogen and resident in the human gastrointestinal microbiome

Bacteroides fragilis is an obligately anaerobic Gram-negative bacterium and a major colonizer of the human large colon where Bacteroides is a predominant genus. During the growth of an individual clonal population, an astonishing number of reversible DNA inversion events occur, driving within-strain diversity. Additionally, the B. fragilis pan-genome contains a large pool of diverse polysaccharide biosynthesis loci, DNA restriction/modification systems and polysaccharide utilization loci, which generates remarkable between-strain diversity. Diversity clearly contributes to the success of B. fragilis within its normal habitat of the gastrointestinal (GI) tract and during infection in the extra-intestinal host environment. Within the GI tract, B. fragilis is usually symbiotic, for example providing localized nutrients for the gut epithelium, but B. fragilis within the GI tract may not always be benign. Metalloprotease toxin production is strongly associated with colorectal cancer. B. fragilis is unique amongst bacteria; some strains export a protein >99 % structurally similar to human ubiquitin and antigenically cross-reactive, which suggests a link to autoimmune diseases. B. fragilis is not a primary invasive enteric pathogen; however, if colonic contents contaminate the extra-intestinal host environment, it successfully adapts to this new habitat and causes infection; classically peritoneal infection arising from rupture of an inflamed appendix or GI surgery, which if untreated, can progress to bacteraemia and death. In this review selected aspects of B. fragilis adaptation to the different habitats of the GI tract and the extra-intestinal host environment are considered, along with the considerable challenges faced when studying this highly variable bacterium.

Change in antimicrobial susceptibility of pathogens isolated from surgical site infections over the past decade in Japanese nation-wide surveillance study

Inappropriate antimicrobial therapy for surgical site infections (SSIs) can lead to poor outcomes and an increased risk of antibiotic resistance. A nationwide survey was conducted in Japan from 2018 to 2019 to investigate the antimicrobial susceptibility of pathogens isolated from SSIs. The data were compared with those obtained in 2010 and 2014-2015 surveillance studies. Although the rate of detection of extended-spectrum β-lactamase producing strains of Escherichia coli was increased from 9.5% in 2010 to 23% in 2014-2015, the incidence decreased to 8.7% in 2018-2019. Although high susceptibility rates were detected to piperacillin/tazobactam (TAZ), the geometric mean MICs were substantially higher than to meropenem (2.67 vs 0.08 μg/mL). By contrast, relatively low geometric mean MICs (0.397 μg/mL) were demonstrated for ceftolozane/TAZ. Although the MRSA incidence rate decreased from 72% in the first surveillance to 53% in the second, no further decrease was detected in 2018-2019. For the Bacteroides fragilis group species, low levels of susceptibility were observed for moxifloxacin (65.3%), cefoxitin (65.3%), and clindamycin (CLDM) (38.9%). In particular, low susceptibility against cefoxitin was demonstrated in non-fragilis Bacteroides, especially B. thetaiotaomicron. By contrast, low susceptibility rates against CLDM were demonstrated in both B. fragilis and non-fragilis Bacteroides species, and a steady decrease in susceptibility throughout was observed (59.3% in 2010, 46.9% in 2014-2015, and 38.9% in 2018-2019). In conclusion, Japanese surveillance data revealed no significant lowering of antibiotic susceptibility over the past decade in organisms commonly associated from SSIs, with the exception of the B. fragilis group.

Candida spp./Bacteria Mixed Biofilms

The ability to form biofilms is a common feature of microorganisms, such as bacteria or fungi. These consortiums can colonize a variety of surfaces, such as host tissues, dentures, and catheters, resulting in infections highly resistant to drugs, when compared with their planktonic counterparts. This refractory effect is particularly critical in polymicrobial biofilms involving both fungi and bacteria. This review emphasizes Candida spp.-bacteria biofilms, the epidemiology of this community, the challenges in the eradication of such biofilms, and the most relevant treatments.

Antimicrobial susceptibility of common pathogens isolated from postoperative intra-abdominal infections in Japan

The principle of empirical therapy for patients with intra-abdominal infections (IAI) should include antibiotics with activity against Enterobacteriaceae and Bacteroides fragilis group species. Coverage of Pseudomonas aeruginosa, Enterobacter cloacae, and Enterococcus faecalis is also recommended for hospital-associated IAI. A nationwide survey was conducted to investigate the antimicrobial susceptibility of pathogens isolated from postoperative IAI. All 504 isolates were collected at 26 institutions and referred to a central laboratory for susceptibility testing. Lower susceptibility rates to ciprofloxacin and cefepime were demonstrated in Escherichia coli. Among E. coli, 24.1% of strains produced extended-spectrum β-lactamase (ESBL). Carbapenems, piperacillin/tazobactam, cephamycins/oxacephem, aminoglycosides, and tigecycline had high activity against E. coli, including ESBL-producing isolates. Among E. cloacae, low susceptibility rates to ceftazidime were demonstrated, whereas cefepime retained its activity. P. aeruginosa revealed high susceptibility rates to all antimicrobials tested except for imipenem. Among B. fragilis group species, low levels of susceptibility were observed for cefoxitin, moxifloxacin, and clindamycin, and high susceptibility rates were observed for piperacillin/tazobactam, meropenem, and metronidazole. Ampicillin, piperacillin, and glycopeptides had good activity against E. faecalis. Imipenem had the highest activity against E. faecalis among carbapenems. In conclusion, we suggested the empirical use of antimicrobials with the specific intent of covering the main organisms isolated from postoperative IAI. Piperacillin/tazobactam, meropenem, or doripenem, are appropriate in critically ill patients. Combination therapy of cefepime (aztreonam in patients with β-lactam allergy) plus metronidazole plus glycopeptides, imipenem/cilastatin or cephamycins/oxacephem plus ciprofloxacin plus metronidazole are potential therapeutic options.

Candida-Bacteria Interactions: Their Impact on Human Disease

Candida species are the most common infectious fungal species in humans; out of the approximately 150 known species, Candida albicans is the leading pathogenic species, largely affecting immunocompromised individuals. Apart from its role as the primary etiology for various types of candidiasis, C. albicans is known to contribute to polymicrobial infections. Polymicrobial interactions, particularly between C. albicans and bacterial species, have gained recent interest in which polymicrobial biofilm virulence mechanisms have been studied including adhesion, invasion, quorum sensing, and development of antimicrobial resistance. These trans-kingdom interactions, either synergistic or antagonistic, may help modulate the virulence and pathogenicity of both Candida and bacteria while uniquely impacting the pathogen-host immune response. As antibiotic and antifungal resistance increases, there is a great need to explore the intermicrobial cross-talk with a focus on the treatment of Candida-associated polymicrobial infections. This article explores the current literature on the interactions between Candida and clinically important bacteria and evaluates these interactions in the context of pathogenesis, diagnosis, and disease management.

Antimicrobial susceptibility of pathogens isolated from surgical site infections in Japan: Comparison of data from nationwide surveillance studies conducted in 2010 and 2014-2015

A nationwide survey was conducted in Japan from 2014 to 2015 to investigate the antimicrobial susceptibility of pathogens isolated from surgical site infections (SSI). The resulting data were compared with that obtained in an earlier survey, conducted in 2010. Seven main organisms were collected, and 883 isolates were studied. A significant reduction in methicillin resistance was observed among Staphylococcus aureus isolates, dropping from 72.5% in 2010 to 53.8% in 2014-2015 (p < 0.001). MRSA isolates with a vancomycin minimum inhibitory concentration (MIC) of 2 μg/mL accounted for 1.2% of all MRSA isolates, which was significantly lower than in 2010 (9.7%, p = 0.029). Of the Escherichia coli isolates, 23.0% produced an extended spectrum β-lactamase (ESBL) in the 2014-2015 survey, which was a significant increase from 9.5% in 2010 (p = 0.011). The geometric mean MICs for ESBL-producing isolates were 0.07 μg/mL for meropenem, 9.51 μg/mL for tazobactam/piperacillin, 0.15 μg/mL for flomoxef, and 1.56 μg/mL for gentamycin. There was a significant increase in the isolation rate of non-fragilis Bacteroides among Bacteroides fragilis group species between the two study periods (35.2% vs. 53.1%, p = 0.007). More than 90% of isolates belonging to the B. fragilis group remained susceptible to tazobactam/piperacillin, meropenem, and metronidazole. In contrast, lower levels of susceptibility were observed for cefmetazole (49.6%), moxifloxacin (61.9%), and clindamycin (46.9%). Non-fragilis Bacteroides isolates had lower rates of antibiotic susceptibility compared with B. fragilis. Overall, the surveillance data clarified trends in antimicrobial susceptibility for organisms commonly associated with SSI.

Morphology-Independent Virulence of Candida Species during Polymicrobial Intra-abdominal Infections with Staphylococcus aureus

Intra-abdominal polymicrobial infections cause significant morbidity and mortality. An experimental mouse model of Candida albicans-Staphylococcus aureus intra-abdominal infection (IAI) results in 100% mortality by 48 to 72 h postinoculation, while monomicrobial infections are avirulent. Mortality is associated with robust local and systemic inflammation without a requirement for C. albicans morphogenesis. However, the contribution of virulence factors coregulated during the yeast-to-hypha transition is unknown. This also raised the question of whether other Candida species that are unable to form hyphae are as virulent as C. albicans during polymicrobial IAI. Therefore, the purpose of this study was to evaluate the ability of non-albicans Candida (NAC) species with various morphologies and C. albicans transcription factor mutants (efg1/efg1 and cph1/cph1) to induce synergistic mortality and the accompanying inflammation. Results showed that S. aureus coinoculated with C. krusei or C. tropicalis was highly lethal, similar to C. albicans, while S. aureus-C. dubliniensis, S. aureus-C. parapsilosis, and S. aureus-C. glabrata coinoculations resulted in little to no mortality. Local and systemic interleukin-6 (IL-6) and prostaglandin E2 (PGE2) levels were significantly elevated during symptomatic and/or lethal coinfections, and hypothermia strongly correlated with mortality. Coinoculation with C. albicans strains deficient in the transcription factor Efg1 but not Cph1 reversed the lethal outcome. These results support previous findings and demonstrate that select Candida species, without reference to any morphological requirement, induce synergistic mortality, with IL-6 and PGE2 acting as key inflammatory factors. Mechanistically, signaling pathways controlled by Efg1 are critical for the ability of C. albicans to induce mortality from an intra-abdominal polymicrobial infection.

Efficacy and safety of moxifloxacin in hospitalized patients with secondary peritonitis: pooled analysis of four randomized phase III trials

BACKGROUND

Secondary peritonitis is an advanced form of complicated intra-abdominal infection (cIAI) requiring hospitalization, surgical source control, and empiric antibiotic therapy against causative aerobic and anaerobic bacteria.

METHODS

This pooled analysis of four prospective, active-controlled randomized clinical trials compared the efficacy and safety of moxifloxacin with that of comparator antibiotics in patients with confirmed secondary peritonitis. The primary efficacy endpoint was clinical success rate at test-of-cure (TOC) between day 10 and 45 post-therapy in the per-protocol (PP) population. Safety and clinical efficacy were assessed also in the intent-to-treat population (ITT). Bacteriological success was assessed at TOC in the microbiologically-valid population as a secondary efficacy endpoint.

RESULTS

Overall clinical success rates at TOC were 85.3% (431 of 505 patients) in the moxifloxacin and 88.4% (459 of 519 patients) in the comparator treatment groups (PP population, point estimate for the difference in success rates: -3.0%; 95% CI -7.06%, 1.05%), respectively. Similar clinical success rates between moxifloxacin and comparators were observed by anatomical site of infection, and ranged from 80.6% to 100% for moxifloxacin and from 71.4% to 96.6% for comparators, respectively. Bacteriologic success rates were similar with moxifloxacin (82.4%) and comparators (86.8%), respectively. The proportion of patients experiencing any treatment-emergent adverse events was slightly higher with moxifloxacin (67.3%) versus comparators (59.8%). Rates of drug-related adverse events (20.9% versus 20.0%) and deaths (4.3% versus 3.4%) were similar in moxifloxacin and comparator groups; none of the deaths were drug-related.

CONCLUSIONS

The data suggests that once-daily IV (or IV/PO) moxifloxacin has a comparable efficacy and safety profile to antibiotic regimens approved previously in the subgroup of patients with secondary peritonitis of mild-to-moderate severity.

Efficacy of moxifloxacin monotherapy versusgatifloxacin monotherapy, piperacillin-tazobactam combination therapy, and lindamycin plus gentamicin combination therapy: An experimental study in a rat model of intra-abdominal sepsis induced by fluoroquinolone-resistant Bacteroides fragilis

BACKGROUND

In intra-abdominal infections, the activity of antimicrobial agents against Bacteroides fragilis and phenotypically related organisms, and the increasing resistance of these organisms, are of particular importance and concern to surgeons. In vitro data suggest that moxifloxacin is more active than other quinolones against obligately anaerobic organisms, including Bacteroides spp.

OBJECTIVE

The aim of this study was to compare the efficacy of moxifloxacin monotherapy versus gatifloxacin monotherapy and 2 combination therapies (piperacillin-tazobactam and clindamycin plus gentamicin) in a rat model of intra-abdominal sepsis. The end point was marked by the incidence of mortality and intra-abdominal abscesses at necropsy 7 days after bacterial challenge.

METHODS

Three different strains of B fragilis with different degrees of resistanceto moxifloxacin (minimum inhibitory concentrations [MICs]: 4, 8, and 16 pg/mL) were added to the challenge inoculum in 3 separate experiments. Groups of 20 animals were used in each experiment. Group 1 served as saline-treated controls; group 2 received moxifloxacin 15 mg QD; group 3 received gatifloxacin 25 mg QD; group 4 received piperacillin-tazobactam 93 mg (-83 mg of piperacillin) QD; and group 5 received a combination of clindamycin 15 mg TID plus gentamicin 2 mg TID. All treatments were given intramuscularly. For all antimicrobials, dose was based on peak and trough serum drug concentrations determined by prior testing, with animal doses adjusted based on the ratio of body surface area to body weight, and comparing these doses and levels with studies in humans.

RESULTS

In all 3 experiments, the mortality rate with moxifloxacin was significantlylower or statistically similar compared with antibiotic active comparators (P ≤ 0.024). In addition, there were no significant differences in the incidence of abscess with moxifloxacin versus its comparators or between the 3 moxifloxacin groups across experiments. The best results for moxifloxacin were found in the experiment in which the B fragilis strain with MIC 16 μg/mL was added to the inoculum.

CONCLUSION

The results of this study in an animal model of intra-abdominalsepsis induced by fluoroquinolone-resistant B fragilis suggest that moxifloxacin monotherapy performs as well as combination regimens such as piperacillin-tazobactam and clindamycin plus gentamicin, and is as effective as other fluoroquinolones with antianaerobic activity, such as gatifloxacin.

Antianaerobic antimicrobials: spectrum and susceptibility testing

Susceptibility testing of anaerobic bacteria recovered from selected cases can influence the choice of antimicrobial therapy. The Clinical and Laboratory Standards Institute (CLSI) has standardized many laboratory procedures, including anaerobic susceptibility testing (AST), and has published documents for AST. The standardization of testing methods by the CLSI allows comparisons of resistance trends among various laboratories. Susceptibility testing should be performed on organisms recovered from sterile body sites, those that are isolated in pure culture, or those that are clinically important and have variable or unique susceptibility patterns. Organisms that should be considered for individual isolate testing include highly virulent pathogens for which susceptibility cannot be predicted, such as Bacteroides, Prevotella, Fusobacterium, and Clostridium spp.; Bilophila wadsworthia; and Sutterella wadsworthensis. This review describes the current methods for AST in research and reference laboratories. These methods include the use of agar dilution, broth microdilution, Etest, and the spiral gradient endpoint system. The antimicrobials potentially effective against anaerobic bacteria include beta-lactams, combinations of beta-lactams and beta-lactamase inhibitors, metronidazole, chloramphenicol, clindamycin, macrolides, tetracyclines, and fluoroquinolones. The spectrum of efficacy, antimicrobial resistance mechanisms, and resistance patterns against these agents are described.

Nationwide surveillance of antimicrobial susceptibility patterns of pathogens isolated from surgical site infections (SSI) in Japan

To investigate the trends of antimicrobial resistance in pathogens isolated from surgical site infections (SSI), a Japanese surveillance committee conducted the first nationwide survey. Seven main organisms were collected from SSI at 27 medical centers in 2010 and were shipped to a central laboratory for antimicrobial susceptibility testing. A total of 702 isolates from 586 patients with SSI were included. Staphylococcus aureus (20.4 %) and Enterococcus faecalis (19.5 %) were the most common isolates, followed by Pseudomonas aeruginosa (15.4 %) and Bacteroides fragilis group (15.4 %). Methicillin-resistant S. aureus among S. aureus was 72.0 %. Vancomycin MIC 2 μg/ml strains accounted for 9.7 %. In Escherichia coli, 11 of 95 strains produced extended-spectrum β-lactamase (Klebsiella pneumoniae, 0/53 strains). Of E. coli strains, 8.4 % were resistant to ceftazidime (CAZ) and 26.3 % to ciprofloxacin (CPFX). No P. aeruginosa strains produced metallo-β-lactamase. In P. aeruginosa, the resistance rates were 7.4 % to tazobactam/piperacillin (TAZ/PIPC), 10.2 % to imipenem (IPM), 2.8 % to meropenem, cefepime, and CPFX, and 0 % to gentamicin. In the B. fragilis group, the rates were 28.6 % to clindamycin, 5.7 % to cefmetazole, 2.9 % to TAZ/PIPC and IPM, and 0 % to metronidazole (Bacteroides thetaiotaomicron; 59.1, 36.4, 0, 0, 0 %). MIC₉₀ of P. aeruginosa isolated 15 days or later after surgery rose in TAZ/PIPC, CAZ, IPM, and CPFX. In patients with American Society of Anesthesiologists (ASA) score ≥3, the resistance rates of P. aeruginosa to TAZ/PIPC and CAZ were higher than in patients with ASA ≤2. The data obtained in this study revealed the trend of the spread of resistance among common species that cause SSI. Timing of isolation from surgery and the patient's physical status affected the selection of resistant organisms.

Role of moxifloxacin for the treatment of community-acquired [corrected] complicated intra-abdominal infections in Taiwan

Complicated intra-abdominal infections (cIAIs) are common yet serious infections that can potentially lead to substantial morbidity and morbidity. As an essential adjunct to source control, the goals of antimicrobial therapy are to promote patient recovery, reduce recurrence risk, and prevent antimicrobial resistance. The current international guidelines on the empirical treatment of community-acquired complicated IAIs were published by the Infectious Diseases Society of America (IDSA) and Surgical Infections Society (SIS) in 2010. These guidelines all recommend the use of a fluoroquinolone (ciprofloxacin or levofloxacin) plus metronidazole for mild-to-moderate- and high-severity cases. Moxifloxacin monotherapy is recommended by the current IDSA/SIS guidelines for the treatment of mild-to-moderate complicated IAIs. Moxifloxacin has demonstrated a broad spectrum coverage of both aerobic and anaerobic pathogens, good tissue penetration into the gastrointestinal tract, and a good tolerability profile. Clinical data have demonstrated that moxifloxacin is at least as effective as other standard therapeutic regimens recommended by current clinical guidelines. Due to the high rates of extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae and fluoroquinolone-resistant Enterobacteriaceae among isolates causing community-acquired IAIs in Asia, any fluoroquinolones (including moxifloxacin) are not recommended as drugs of choice for the empirical treatment of community-acquired IAIs, particularly in countries (China, India, Thailand, and Vietnam) with fluoroquinolone resistance rates among Escherichia coli isolates of >20%. Given the low rates of fluoroquinolone-resistant (<20%) and extended-spectrum β-lactamase (ESBL)-producing (<10%) Enterobacteriaceae isolates associated community-acquired IAIs in Taiwan, it appears that moxifloxacin is considered an appropriate first-line therapy for patients with community-acquired complicated IAIs in this country.

Complicated intra-abdominal infections: a focus on appendicitis and diverticulitis

Severe abdominal pain is a common complaint encountered by primary care and emergency room physicians. Caused by many conditions, including appendicitis and diverticulitis, severe abdominal pain may be a diagnostic challenge. Although different in many ways, appendicitis and diverticulitis are caused by obstruction of a blind pouch that leads to inflammation of the structure and surrounding tissue. Appendicitis and diverticulitis are 2 of the most frequently diagnosed causes of complicated intra-abdominal infections. Combined, appendicitis and diverticulitis comprise > 80% of all community-acquired complicated intra-abdominal infections. These conditions are serious and require prompt diagnosis and treatment. Because complicated intra-abdominal infections are typically polymicrobial, a wide variety of causative pathogens are identified, including Gram-positive and Gram-negative aerobic and anaerobic microorganisms. Treatment for these disorders often requires surgical and medical management. Although surgical intervention can be the definitive treatment for complicated intra-abdominal infections, successful management of appendicitis and diverticulitis will depend on appropriate selection of antimicrobials and optimal duration of therapy to maximize the coverage of potential causative pathogens and to minimize the development of resistance. Guidelines for empiric treatment of complicated intra-abdominal infections recommend broad-spectrum antimicrobials as monotherapy or in combinations, including standard antimicrobial regimens, such as piperacillin/tazobactam, imipenem/cilastatin, and piperacillin-tazobactam/amoxicillin-clavulanate regimens, and fluoroquinolone-based regimens. This review article compares the presentations and treatments of these common complicated intra-abdominal infections.

Potent in vitro activity of tomopenem (CS-023) against methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa

Tomopenem (formerly CS-023) is a novel 1beta-methylcarbapenem with broad-spectrum coverage of gram-positive and gram-negative pathogens. Its antibacterial activity against European clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa was compared with those of imipenem and meropenem. The MICs of tomopenem against MRSA and P. aeruginosa at which 90% of the isolates tested were inhibited were 8 and 4 microg/ml, respectively, and were equal to or more than fourfold lower than those of imipenem and meropenem. The antibacterial activity of tomopenem against MRSA was correlated with a higher affinity for the penicillin-binding protein (PBP) 2a. Its activity against laboratory mutants of P. aeruginosa with (i) overproduction of chromosomally coded AmpC beta-lactamase; (ii) overproduction of the multidrug efflux pumps MexAB-OprM, MexCD-OprJ, and MexEF-OprN; (iii) deficiency in OprD; and (iv) various combinations of AmpC overproduction, MexAB-OprM overproduction, and OprD deficiency were tested. The increases in the MIC of tomopenem against each single mutant compared with that against its parent strain were within a fourfold range. Tomopenem exhibited antibacterial activity against all mutants, with an observed MIC range of 0.5 to 8 microg/ml. These results suggest that the antibacterial activity of tomopenem against the clinical isolates of MRSA and P. aeruginosa should be ascribed to its high affinity for PBP 2a and its activity against the mutants of P. aeruginosa, respectively.

Treatment of anaerobic infection

Anaerobic bacteria are the predominant flora in the normal human skin and mucous membranes and are, therefore, a common cause of endogenous infections. Since anaerobic infections are generally polymicrobial, where anaerobes are mixed with aerobic organisms, therapy should provide coverage of both types of pathogens. The isolation of anaerobes requires appropriate methods of collection, transportation and cultivation of specimens. The lack of use of any of these methods can lead to inadequate recovery of anaerobes and inappropriate therapy. Treatment of anaerobic infection is complicated by the slow growth of these organisms and the growing resistance of anaerobic bacteria to antimicrobials. The primary role of antimicrobials is to limit the local and systemic spread of infection. Surgical drainage is of primary importance. This includes debriding of necrotic tissue, draining the pus, improving circulation, alleviating obstruction and increasing tissue oxygenation. The most effective antimicrobials against anaerobic organisms are metronidazole, the carbapenems (imipenem, meropenem and ertapenem), chloramphenicol, the combinations of a penicillin and a beta-lactamase inhibitor (ampicillin or ticarcillin plus clavulanate, amoxicillin plus sulbactam, and piperacillin plus tazobactam), tigecycline and clindamycin.

Antimicrobial treatment for intra-abdominal infections

Treatment of patients with complicated intra-abdominal infections involves antimicrobial therapy, generally in conjunction with an interventional procedure to control the source of the infection. Antimicrobial regimens effective against common gram-negative and anaerobic enteric pathogens are the mainstay of therapy. For patients with community-acquired intra-abdominal infections, efficacy is comparable among the various single-agent or combination regimens recommended for therapy. Narrower-spectrum antimicrobial agents with a low potential for iatrogenic complications are appropriate for these patients. Patients with nosocomially-acquired, intra-abdominal infections are more likely to harbor resistant pathogens. Inadequate empiric antimicrobial therapy is associated with treatment failure and death. Therefore, broader spectrum antimicrobial regimens are recommended for these patients. In addition to coverage of more resistant gram-negative bacilli and anaerobes, use of agents effective against enterococci, resistant staphylococci and Candida should be considered. De-escalation of an initially broad antimicrobial regimen should be undertaken once definitive culture results are available.

Evaluating Empiric Treatment Options for Secondary Peritonitis Using Pharmacodynamic Profiling

BACKGROUND

Selecting an appropriate agent for empiric antibiotic therapy for secondary peritonitis is challenging. The pathogens responsible, aerobic gram-negative bacilli in particular, are becoming more resistant to antibiotics. The purpose of this study was to predict the ability of common antimicrobial regimens to achieve optimal pharmacodynamic exposure against aerobic bacteria implicated in secondary peritonitis, while considering current national resistance trends.

METHODS

Monte Carlo simulation was used to model pharmacodynamic endpoints and compare the cumulative fraction of response (CFR) for imipenem-cilastatin, meropenem, ertapenem, piperacillin/tazobactam, ceftazidime, ceftriaxone, ciprofloxacin, and levofloxacin against isolates of species associated with secondary peritonitis. Minimum inhibitory concentration (MIC) distributions for isolates collected in North America were obtained from the 2004 MYSTIC database. Pharmacokinetic parameters were derived from the literature; the endpoints evaluated included free drug time above the MIC (fT(>MIC)) and the area under the concentration-time curve to MIC ratio (AUC:MIC).

RESULTS

The simulation predicted that several compounds would have a superior probability of providing appropriate coverage of aerobic bacteria: Imipenem-cilastatin (98.6% CFR at 1 g q8h), meropenem (98.2% CFR at 1 g q8h), ertapenem (91.7% CFR at 1 g q24h), piperacillin/ tazobactam (93.7% CFR at 3.375 g q6h), ceftazidime (91.1% CFR at 2 g q8h), and cefepime (92.9% CFR at 1 g q12h and 95.8% CFR at 2 g q12h). Ceftriaxone, ciprofloxacin, and levofloxacin exhibited CFRs < 82%.

CONCLUSIONS

Considering contemporary susceptibility data for aerobic bacteria, monotherapy with any of the three carbapenems or piperacillin/tazobactam 3.375 g q6h would provide optimal exposure for the pathogens commonly encountered in secondary peritonitis. Cefepime (in combination with metronidazole to provide anti-anaerobic coverage) also would be an acceptable choice, as would ceftazidime given at 2 g q8h (again in combination with metronidazole). Despite the popularity of combination therapy based on ciprofloxacin, levofloxacin, or ceftriaxone with metronidazole, these choices appear to be inferior to the other options because of emerging antibiotic resistance, particularly in E. coli.

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

OBJECTIVES

Routine susceptibility testing of all anaerobic organisms is not advocated, but it is useful for laboratories to test periodically for anaerobic organisms and provide local susceptibility data to guide therapy. This study reports the national trend of antibiotic susceptibility of clinically significant anaerobes in New Zealand.

METHODS

Clinical isolates were tested using standardized methods against a range of antibiotics commonly used to treat anaerobic infections. Susceptibility was determined using NCCLS criteria. The change in susceptibility trends between this study and earlier studies was measured by comparing the geometric mean of the MIC.

RESULTS

A total of 364 anaerobes were tested. Penicillin had poor activity against Bacteroides spp., Prevotella spp., Eubacterium spp., Clostridium tertium and Veillonella spp. In general, Fusobacterium spp., Bacteroides ureolyticus, Propionibacterium spp., Clostridium perfringens and anaerobic streptococci isolates, with the exception of Peptostreptococcus anaerobius, were penicillin susceptible. Amoxicillin/clavulanate showed good activity against most anaerobes, but resistance was seen with Bacteroides fragilis group and P. anaerobius isolates. Cefoxitin was more active than cefotetan, particularly against non-B. fragilis species, Eubacterium spp. and P. anaerobius. Meropenem and imipenem showed good activity against all anaerobes, with only 2 and 4% of Bacteroides spp., respectively, showing resistance. With the exception of Propionibacterium acnes isolates, which are predictably resistant, metronidazole was active against all anaerobes tested. There has been little change in susceptibility since 1997.

CONCLUSIONS

Metronidazole, cefoxitin, piperacillin/tazobactam and amoxicillin/clavulanate remain good empirical choices when anaerobes are expected in our setting. No clinically relevant changes in susceptibility over time were found.

Do antimicrobial susceptibility patterns of colonic isolates of Bacteroides species change after antibiotic prophylaxis with cefoxitine during elective abdominal surgery?

The objectives of the study were to investigate and compare the susceptibility profiles of preoperative and postoperative intestinal Bacteroides fragilis and Bacteroides thetaiotaomicron strains against antimicrobials to evaluate their resistance development patterns due to prophylactic antibiotic administration. Preoperative and postoperative stool samples were obtained from patients undergoing elective abdominal surgery with a "clean-contaminated" wound categorization. All patients received cefoxitin 2 g as prophylaxis. Isolates of Bacteroides species were identified. Susceptibility tests against ampicillin, piperacillin, cefoxitin, clindamycin, chloramphenicol, metronidazole, imipenem, and amoxicillin-clavulanate were performed. Stool samples were collected from 40 patients at two settings: before and after the operation. Most of the patients (53%) were operated on because of colorectal carcinoma and underwent surgery that included colectomy or anterior resection. Bacteroides fragilis and Bacteroides thetaiotaomicron were isolated in both samples obtained from 22 and 34 patients, respectively. In the present study 95% to 100%, 50% to 74%, 46% to 64%, and 18% to 35% of preoperatively isolated Bacteroides species were resistant to ampicillin, cefoxitin, clindamycin, and piperacillin, respectively. Although there were no statistically significant difference, postoperative strains were more resistant than preoperative isolates, and the resistance rates were found to be 95% to 100%, 55% to 82%, 46% to 86%, and 37% to 41%, respectively. Both Bacteroides species isolated from all specimens before and after the surgery were uniformly susceptible to amoxicillin-clavulanate, imipenem, metronidazole, and chloramphenicol.Our data revealed that Bacteroides strains revealed high resistance to ampicillin, cefoxitin, piperacillin, and clindamycin. Metronidazole, imipenem, and amoxicillin-clavulanate seem highly effective against both Bacteroides species. Cefoxitin prophylaxis did not significantly increase the resistance patterns against antimicrobial agents.

Empiric Treatment of Nosocomial Intra-Abdominal Infections: A Focus on the Carbapenems

BACKGROUND

Serious nosocomial intra-abdominal infections are associated with high morbidity and mortality and represent a substantial drain on healthcare resources. Effective management of this type of infection requires the early use of appropriate, broad-spectrum empiric antimicrobial therapy. The consequences of delayed or inappropriate antimicrobial treatment can be severe-leading to an increased risk of death, re-operation, or prolonged hospitalization. Therefore, it is necessary to begin treatment as soon as possible with the most appropriate regimen, in terms of spectrum, timing, and duration.

METHODS

Review of pertinent English-language literature.

RESULTS

Serious nosocomial intra-abdominal infections require broad-spectrum coverage because of the wide range of possible pathogens, which include difficult-to-treat organisms such as Pseudomonas aeruginosa and Bacteroides spp., and resistant strains of Klebsiella spp., Escherichia coli, and methicillin-resistant Staphylococcus aureus acquired from the hospital flora. The early use of appropriate, broad-spectrum empiric antimicrobial therapy for treating high-risk patients with intra-abdominal infections is considered, and appropriate use of the carbapenems, meropenem, and imipenem/cilastatin, is described.

CONCLUSION

The carbapenems meropenem and imipenem/cilastatin have a spectrum of antimicrobial activity that covers the majority of expected pathogens, including anaerobes, as well as difficult-to-treat and resistant gram-negative strains. Early and appropriate use can reduce mortality and morbidity. Data from published clinical trials support the clinical effectiveness of these two carbapenems in intra-abdominal infections.

Levofloxacin plus metronidazole administered once daily versus moxifloxacin monotherapy against a mixed infection of Escherichia coli and Bacteroides fragilis in an in vitro pharmacodynamic model

Moxifloxacin has been suggested as an option for monotherapy of intra-abdominal infections. Recent data support the use of a once-daily metronidazole regimen. The purpose of this study was to investigate the activity of levofloxacin (750 mg every 24 h [q24h]) plus metronidazole (1,500 mg q24h) compared with that of moxifloxacin (400 mg q24h) monotherapy in a mixed-infection model. By using an in vitro pharmacodynamic model in duplicate, Escherichia coli and Bacteroides fragilis were exposed to peak concentrations of 8.5 mg of levofloxacin/liter q24h, 32 mg of metronidazole/liter q24h, and 2 mg for moxifloxacin/liter q24h for 24 h. The activities of levofloxacin, metronidazole, moxifloxacin, and levofloxacin plus metronidazole were evaluated against E. coli, B. fragilis, and E. coli plus B. fragilis. The targeted half-lives of levofloxacin, metronidazole, and moxifloxacin were 8, 8, and 12 h, respectively. Time-kill curves were analyzed for time to 3-log killing, slope, and regrowth. Pre- and postexposure MICs were determined. The preexposure levofloxacin, metronidazole, and moxifloxacin MICs for E. coli and B. fragilis were 0.5 and 1, >64 and 0.5, and 1 and 0.25 mg/liter, respectively. Levofloxacin and moxifloxacin achieved a 3-log killing against E. coli and B. fragilis in all experiments, as did metronidazole against B. fragilis. Metronidazole did not decrease the starting inoculum of E. coli. The area under the concentration-time curve/MIC ratios for E. coli and B. fragilis were 171.7 and 85.9, respectively, for levofloxacin and 26 and 103.9, respectively, for moxifloxacin. Levofloxacin plus metronidazole exhibited the fastest rates of killing. The levofloxacin and moxifloxacin MICs for B. fragilis increased 8- to 16-fold after the organism was exposed to moxifloxacin. No other changes in the postexposure MICs were found. Levofloxacin plus metronidazole administered once daily exhibited activity similar to that of moxifloxacin against the mixed E. coli and B. fragilis infection. A once-daily regimen of levofloxacin plus metronidazole looks promising for the treatment of intra-abdominal infections.

Ertapenem versus ceftriaxone and metronidazole as treatment for complicated intra-abdominal infections

BACKGROUND

Prompt surgical intervention supplemented by appropriate antimicrobial therapy is usually required for successful treatment of complicated intra-abdominal infections. The objective of this study was to further evaluate the efficacy and safety of ertapenem relative to ceftriaxone/metronidazole as treatment for complicated intra-abdominal infections.

METHODS

Adult patients with intra-abdominal infections requiring surgery were eligible for this open-label randomized trial comparing ertapenem 1 g daily with ceftriaxone 2 g daily plus metronidazole 30 mg/kg/day. The primary efficacy outcome was the clinical response rate in clinically and microbiologically evaluable participants at the test-of-cure (TOC) visit 2 weeks after discontinuation of therapy. All treated patients were included in the safety analysis.

RESULTS

Participant demographics, disease characteristics, and duration of therapy in both treatment groups were generally similar. Escherichia coli was the most commonly isolated baseline pathogen, recovered in 52% of cases in each treatment group. Favorable clinical responses were achieved at TOC in 143 (96.6%) of 148 ertapenem recipients and in 146 (96.7%) of 151 ceftriaxone/metronidazole recipients. The frequencies of drug-related adverse events, most commonly nausea, diarrhea, vomiting, and elevated platelet count, were generally comparable in both treatment arms. Four ertapenem recipients (1.8%) and one ceftriaxone/metronidazole recipient (0.4%) experienced serious drug-related adverse events.

CONCLUSIONS

In this study, ertapenem and ceftriaxone/metronidazole were comparably effective treatments for adult patients with complicated intra-abdominal infections.

In vitro activities of moxifloxacin against 900 aerobic and anaerobic surgical isolates from patients with intra-abdominal and diabetic foot infections

The in vitro activities of moxifloxacin, ciprofloxacin, levofloxacin, gatifloxacin, imipenem, piperacillin-tazobactam, clindamycin, and metronidazole against 900 surgical isolates were determined using NCCLS testing methods. Moxifloxacin exhibited good to excellent antimicrobial activity against most aerobic (90.8%) and anaerobic (97.1%) microorganisms, suggesting that it may be effective for the treatment of polymicrobial surgical infections.

Ertapenem: a review of its use in the management of bacterial infections

Ertapenem, a carbapenem antibacterial, has in vitro activity against many Gram- negative (including Enterobacteriaceae) and Gram-positive aerobic and anaerobic bacteria that are commonly associated with various infections.Once-daily parenteral (intravenous or intramuscular) ertapenem 1g was as effective as comparator antimicrobial agents (piperacillin/tazobactam or ceftriaxone +/- metronidazole) in patients with bacterial infections in randomised, double-blind, multicentre clinical trials. Response rates with ertapenem were 84% and 87% (combined microbiological and clinical) in patients with complicated intra-abdominal infections (CIAI), 82% (clinical) in patients with complicated skin and skin structure infections (CSSSI), 86% and 92% (microbiological) in patients with complicated urinary tract infections (CUTI), 92% (clinical) in patients with community-acquired pneumonia (CAP) associated with typical pathogens and 94% (clinical) in patients with acute pelvic infection. Respective response rates were statistically equivalent to those with comparators (81-94%). The efficacy of ertapenem was equivalent to that of piperacillin/tazobactam in patients infected with Enterobacteriaceae or anaerobes and to ceftriaxone in patients infected with Enterobacteriaceae. Ertapenem was generally well tolerated by patients with bacterial infections, with most adverse events being mild to moderate in severity. The most common ertapenem-associated adverse events were diarrhoea, infused vein complication, nausea, headache, vaginitis in females, phlebitis and/or thrombophlebitis and vomiting.

CONCLUSION

Ertapenem is a broad-spectrum parenteral antibiotic with activity against many Gram-negative (including Enterobacteriaceae) and Gram-positive aerobic and anaerobic bacteria and is suitable for once-daily administration. Ertapenem has a role in the treatment of CAP associated with typical respiratory pathogens and is of particular value in the treatment of polymicrobial infections (such as CIAI, CSSSI, CUTI and acute pelvic infections), especially where Enterobacteriaceae and anaerobic bacteria are involved.