Third Belgian multicentre survey of antibiotic susceptibility of anaerobic bacteria

Antibiotic Resistance and Mechanisms of Pathogenic Bacteria in Tubo-Ovarian Abscess

A tubo-ovarian abscess (TOA) is a common type of inflammatory lump in clinical practice. TOA is an important, life-threatening disease, and it has become more common in recent years, posing a major health risk to women. Broad-spectrum antimicrobial agents are necessary to cover the most likely pathogens because the pathogens that cause TOA are polymicrobial. However, the response rate of antibiotic treatment is about 70%, whereas one-third of patients have poor clinical consequences and they require drainage or surgery. Rising antimicrobial resistance serves as a significant reason for the unsatisfactory medical outcomes. It is important to study the antibiotic resistance mechanism of TOA pathogens in solving the problems of multi-drug resistant strains. This paper focuses on the most common pathogenic bacteria isolated from TOA specimens and discusses the emerging trends and epidemiology of resistant Escherichia coli, Bacteroides fragilis, and gram-positive anaerobic cocci. Besides that, new methods that aim to solve the antibiotic resistance of related pathogens are discussed, such as CRISPR, nanoparticles, bacteriophages, antimicrobial peptides, and pathogen-specific monoclonal antibodies. Through this review, we hope to reveal the current situation of antibiotic resistance of common TOA pathogens, relevant mechanisms, and possible antibacterial strategies, providing references for the clinical treatment of drug-resistant pathogens.

In Vitro Antimicrobial Susceptibility Profiles of Gram-Positive Anaerobic Cocci Responsible for Human Invasive Infections

The aim of this multicentre study was to determine the in vitro susceptibility to anti-anaerobic antibiotics of Gram-positive anaerobic cocci (GPAC) isolates responsible for invasive infections in humans. A total of 133 GPAC isolates were collected in nine French hospitals from 2016 to 2020. All strains were identified to the species level (MALDI-TOF mass spectrometry, 16S rRNA sequencing). Minimum inhibitory concentrations (MICs) of amoxicillin, piperacillin, cefotaxime, imipenem, clindamycin, vancomycin, linezolid, moxifloxacin, rifampicin, and metronidazole were determined by the reference agar dilution method. Main erm-like genes were detected by PCR. The 133 GPAC isolates were identified as follows: 10 Anaerococcus spp., 49 Finegoldia magna, 33 Parvimonas micra, 30 Peptoniphilus spp., and 11 Peptostreptococcus anaerobius. All isolates were susceptible to imipenem, vancomycin (except 3 P. micra), linezolid and metronidazole. All isolates were susceptible to amoxicillin and piperacillin, except for P. anaerobius (54% and 45% susceptibility only, respectively). MICs of cefotaxime widely varied while activity of rifampicin, and moxifloxacin was also variable. Concerning clindamycin, 31 were categorized as resistant (22 erm(A) subclass erm(TR), 7 erm(B), 1 both genes and 1 negative for tested erm genes) with MICs from 8 to >32 mg/L. Although GPACs are usually susceptible to drugs commonly used for the treatment of anaerobic infections, antimicrobial susceptibility should be evaluated in vitro.

Scrotal Abscess in a Japanese Patient Caused by Prevotella bivia and Streptococcus agalactiae, Successfully Treated with Cefazolin and Amoxicillin: A Case Report

Background

Infections caused by Prevotella bivia, a gram-negative anaerobic bacillus, are rare, with no reported cases in Japan. We present a novel case of scrotal abscess in a Japanese patient co-infected with Prevotella bivia and Streptococcus agalactiae.

Case Presentation

A 41-year-old uncontrolled diabetic man complained of swelling and pain in the scrotum. On examination, computed tomography revealed an abscess of 5-cm diameter in the scrotum. Then, the abscess was incised and drained. He was treated with cefazolin empirically. Prevotella bivia and Streptococcus agalactiae were identified in the pus cultures obtained from the abscess. However, the susceptibility tests for Prevotella bivia could not be submitted. Seven days following admission, the pain reduced, and the drainage slowed. The patient was discharged on day 14 when cefazolin was discontinued and oral amoxicillin (750 mg/day) was started. Amoxicillin was continued until day 42; improvement was confirmed.

Conclusion

To the best of our knowledge, this case is the first report of Prevotella bivia in Japan. We suggest that cephem antibiotics such as cefazolin may be effective against Prevotella bivia in Japan.

Construction of a Mutant in Prevotella melaninogenica Using the Conjugation Transfer Method with Escherichia coli

Prevotella melaninogenica is a bacterium that is resident in the oral cavity and upper respiratory tract and is associated with periodontal disease and aspiration pneumonia. Prevotella mutants are difficult to produce and only few reports have been reported. We examined several methods and many strains and succeeded in producing mutants in Prevotella melaninogenica GAI 07411. In this chapter, we will describe how to create a mutation of a target gene by carrying out conjugation transfer using Escherichia coli S17-1 as a donor and introducing a plasmid into P. melaninogenica.

Involvement of PorK, a component of the type IX secretion system, in Prevotella melaninogenica pathogenicity

Prevotella melaninogenica is a gram-negative anaerobic commensal bacterium that resides in the human oral cavity and is isolated as a pathogen of suppurative diseases both inside and outside the mouth. However, little is known about the pathogenic factors of P. melaninogenica. The periodontal pathogens Porphyromonas gingivalis and Tanerella forsythia secrete virulence factors such as protease and bacterial cell surface proteins via a type IX secretion system (T9SS) that are involved in pathogenicity. P. melaninogenica also possesses all known orthologs of T9SS. In this study, a P. melaninogenica GAI 07411 mutant deficient in the orthologue of the T9SS-encoding gene, porK, was constructed. Hemagglutination and biofilm formation were decreased in the porK mutant. Furthermore, following growth on skim milk-containing medium, the diameters of the halos surrounding the porK mutant were smaller than those of the wild-type strain, suggesting a decrease in secretion of proteases outside the bacterium. To investigate this in detail, culture supernatants of wild-type and porK mutant strains were purified and compared by two-dimensional electrophoresis. In the mutant strain, fewer spots were detected, indicating fewer secreted proteins. In infection experiments, the mortality rate of mice inoculated with the porK mutant strain was significantly lower than in the wild-type strain. These results suggest that P. melaninogenica secretes potent virulence factors via the T9SS that contribute to its pathogenic ability.

A multicenter survey of antimicrobial susceptibility of Prevotella species as determined by Etest methodology

Knowledge about the antimicrobial susceptibility patterns of different Prevotella species is limited. The aim of this study was to determine the current antimicrobial susceptibility of clinical isolates of Prevotella species from different parts of Europe, Kuwait and Turkey. Activity of 12 antimicrobials against 508 Prevotella isolates, representing 19 species, were tested according to Etest methodology. EUCAST, CLSI and FDA guidelines were used for susceptibility interpretations. All Prevotella species were susceptible to piperacillin/tazobactam, imipenem, meropenem, tigecycline and metronidazole. Ampicillin/sulbactam and cefoxitin also showed good activity. Ampicillin, clindamycin, tetracycline and moxifloxacin were less active; 51.2%, 33.7%, 36.8% and 18.3% of isolates were non-susceptible, respectively. A total of 49 (9.6%) isolates were resistant to three or more antimicrobials. Prevotella bivia was the most prevalent species (n = 118) and accounted for most of the multidrug-resistant isolates. In conclusion, the level of non-susceptibility to antimicrobials, which may be used for treatment of infections involving Prevotella species, are a cause of concern. This data emphasizes the need for species level identification of clinical Prevotella isolates and periodic monitoring of their susceptibility to guide empirical treatment.

Use and Effectiveness of Peri-Operative Cefotetan versus Cefazolin Plus Metronidazole for Prevention of Surgical Site Infection in Abdominal Surgery Patients

BACKGROUND

Current practice guidelines for antimicrobial prophylaxis in surgery recommend a cephamycin or cefazolin plus metronidazole for various abdominal surgeries. In February 2016, cephamycin drug shortages resulted in a change in The Johns Hopkins Hospital's (JHH) recommendation for peri-operative antibiotic prophylaxis in abdominal surgeries from cefotetan to cefazolin plus metronidazole. The primary objective of this study was to quantify the percentage of abdominal surgeries adherent to JHH peri-operative antibiotic prophylaxis guidelines. A sub-group analysis investigated whether prophylaxis with cefazolin plus metronidazole was associated with a lower rate of surgical site infections (SSIs) versus cefotetan.

PATIENTS AND METHODS

This retrospective cohort study included adult inpatients who underwent an abdominal surgery at JHH in September 2015 (Study Period I: cefotetan) or February to March 2016 (Study Period II: cefazolin plus metronidazole).

RESULTS

Two hundred abdominal surgery cases were included in the primary analysis. A subset of 156 surgical cases were included in the sub-group analysis. The overall adherence rate to JHH guidelines was 75% in Study Period I versus 17% in Study Period II (p < 0.001). The largest difference in adherence was attributed to pre-operative administration time (87% vs. 23%, p < 0.001), primarily because of the longer infusion time required for metronidazole. Surgical site infections occurred in 14% (12/83) of surgeries with cefotetan versus 8.2% (6/73) with cefazolin plus metronidazole for prophylaxis (p = 0.19).

CONCLUSIONS

Adherence to an institution-specific peri-operative antibiotic prophylaxis guideline for abdominal surgeries was limited primarily by the longer infusion time required for pre-operative metronidazole. A higher percentage of SSIs occurred among abdominal surgeries with cefotetan versus cefazolin plus metronidazole for prophylaxis.

Multicenter study of antimicrobial susceptibility of anaerobic bacteria in Korea in 2012

Background

Periodic monitoring of regional or institutional resistance trends of clinically important anaerobic bacteria is recommended, because the resistance of anaerobic pathogens to antimicrobial drugs and inappropriate therapy are associated with poor clinical outcomes. There has been no multicenter study of clinical anaerobic isolates in Korea. We aimed to determine the antimicrobial resistance patterns of clinically important anaerobes at multiple centers in Korea.

Methods

A total of 268 non-duplicated clinical isolates of anaerobic bacteria were collected from four large medical centers in Korea in 2012. Antimicrobial susceptibility was tested by the agar dilution method according to the CLSI guidelines. The following antimicrobials were tested: piperacillin, piperacillin-tazobactam, cefoxitin, cefotetan, imipenem, meropenem, clindamycin, moxifloxacin, chloramphenicol, metronidazole, and tigecycline.

Results

Organisms of the Bacteroides fragilis group were highly susceptible to piperacillin-tazobactam, imipenem, and meropenem, as their resistance rates to these three antimicrobials were lower than 6%. For B. fragilis group isolates and anaerobic gram-positive cocci, the resistance rates to moxifloxacin were 12-25% and 11-13%, respectively. Among B. fragilis group organisms, the resistance rates to tigecycline were 16-17%. Two isolates of Finegoldia magna were non-susceptible to chloramphenicol (minimum inhibitory concentrations of 16-32 mg/L). Resistance patterns were different among the different hospitals.

Conclusions

Piperacillin-tazobactam, cefoxitin, and carbapemems are highly active β-lactam agents against most of the anaerobes. The resistance rates to moxifloxacin and tigecycline are slightly higher than those in the previous study.

Fusobacterial head and neck infections in children

Fusobacterium species are increasingly recognized as a cause of head and neck infections in children. These infections include acute and chronic otitis, sinusitis, mastoiditis, and tonsillitis; peritonsillar and retropharyngeal abscesses; Lemierre syndrome; post-anginal cervical lymphadenitis; and periodontitis. They can also be involved in brain abscess and bacteremia associated with head and neck infections. This review describes the clinical spectrum of head and neck fusobacterial infection in children and their management.

Antimicrobial susceptibility of clinically isolated anaerobic bacteria in a University Hospital Centre Split, Croatia in 2013

Anaerobic bacteria play a significant role in many endogenous polymicrobial infections. Since antimicrobial resistance among anaerobes has increased worldwide, it is useful to provide local susceptibility data to guide empirical therapy. The present study reports recent data on the susceptibility of clinically relevant anaerobes in a University Hospital Centre (UHC) Split, Croatia. A total of 63 Gram-negative and 59 Gram-positive anaerobic clinical isolates from various body sites were consecutively collected from January to December 2013. Antimicrobial susceptibility testing was performed using standardized methods and interpreted using EUCAST criteria. Patient's clinical and demographic data were recorded by clinical microbiologist. Among 35 isolates of Bacteroides spp., 97.1% were resistant to penicillin (PCN), 5.7% to amoxicillin/clavulanic acid (AMC), 8.6% to piperacillin/tazobactam (TZP), 29.0% to clindamycin (CLI) and 2.9% to metronidazole (MZ). Percentages of susceptible strains to imipenem (IPM), meropenem (MEM) and ertapenem (ETP) were 94.3. Resistance of other Gram-negative bacilli was 76.0% to PCN, 8.0% to AMC, 12.0% to TZP, 28.0% to CLI and 8% to MZ. All other Gram-negative strains were fully susceptible to MEM and ETP, while 96.0% were susceptible to IPM. Clostridium spp. isolates were 100% susceptible to all tested antibiotics except to CLI (two of four tested isolates were resistant). Propionibacterium spp. showed resistance to CLI in 4.3%, while 100% were resistant to MZ. Among other Gram-positive bacilli, 18.2% were resistant to PCN, 9.1% to CLI and 54.5% to MZ, while 81.8% of isolates were susceptible to carbapenems. Gram-positive cocci were 100% susceptible to all tested antimicrobials except to MZ, where 28.6% of resistant strains were recorded. Abdomen was the most common source of isolates (82.5%). The most prevalent types of infection were abscess (22.1%), sepsis (14.8%), appendicitis (13.9%) and peritonitis (6.6%). Twenty four patients (19.7%) received empiric antimicrobial therapy. One hundred and one patients (82.8%) had polymicrobial aerobic/anaerobic isolates cultivated from the same specimens. Almost all aerobic bacteria were of endogenous origin and showed fully susceptible antimicrobial profile; only 8.7% (9/104) were multiresistant and considered as hospital acquired. Based on our findings, β-lactam/β-lactamase inhibitor combinations and metronidazole remain useful antimicrobials for empiric treatment of anaerobic infections, while carbapenems should be reserved for situations were multidrug resistant, aerobic or facultative Gram-negative bacteria are expected. However, a certain percentage of resistant isolates were observed for each of these agents. Therefore, periodic resistance surveillance in anaerobes is highly recommended in order to guide empirical therapy.

Fourth Belgian multicentre survey of antibiotic susceptibility of anaerobic bacteria

Objectives

To collect recent data on the susceptibility of anaerobes to antimicrobial agents with known activity against anaerobes, and to compare them with results from previous Belgian multicentre studies.

Methods

Four hundred and three strict anaerobic clinical isolates were prospectively collected from February 2011 to April 2012 in eight Belgian university hospitals. MICs were determined by one central laboratory for 11 antimicrobial agents using Etest methodology.

Results

According to EUCAST breakpoints, >90% of isolates were susceptible to amoxicillin/clavulanate (94%), piperacillin/tazobactam (91%), meropenem (96%), metronidazole (92%) and chloramphenicol (98%), but only 70% and 40% to clindamycin and penicillin, respectively. At CLSI recommended breakpoints, only 71% were susceptible to moxifloxacin and 79% to cefoxitin. MIC₅₀/MIC₉₀ values for linezolid and for tigecycline were 1/4 and 0.5/4 mg/L, respectively. When compared with survey data from 2004, no major differences in susceptibility profiles were noticed. However, the susceptibility of Prevotella spp. and other Gram-negative bacilli to clindamycin decreased from 91% in 1993–94 and 82% in 2004 to 69% in this survey. Furthermore, the susceptibility of clostridia to moxifloxacin decreased from 88% in 2004 to 66% in 2011–12 and that of fusobacteria from 90% to 71%.

Conclusions

Compared with previous surveys, little evolution was seen in susceptibility, except a decline in activity of clindamycin against Prevotella spp. and other Gram-negative bacteria, and of moxifloxacin against clostridia. Since resistance was detected to all antibiotics, susceptibility testing of anaerobic isolates is indicated in severe infections to confirm appropriateness of antimicrobial therapy.

Fusobacterial infections in children

Fusobacteria are members of the oral and gastrointestinal flora and are important potential pathogens in children. They are increasingly recognized as a cause of infections in children. These include infections of the head and neck (Lemierre syndrome, acute and chronic mastoiditis, chronic otitis and sinusitis, tonsillitis, peritonsillar and retropharyngeal abscesses, postanginal cervical lymphadenitis, periodontitis), brain, lungs, abdomen, pelvis, bones, joints, and blood. This review describes the clinical spectrum of fusobacterial infection in children and their management.

Five-year retrospective epidemiological survey of anaerobic bacteraemia in a university hospital and rewiew of the literature

In spite of the developments in microbiological methods, blood cultures remain the cornerstone for the diagnosis of bacteraemia. Classically, minimum of two bottles are collected on a routine basis: an aerobic bottle, allowing preferential growth of aerobic and facultative anaerobic microorganisms, and an anaerobic bottle, providing suitable environment for strict anaerobic bacteria. Recent reports have documented a decrease in anaerobic bacteraemias and have questioned the need for routine anaerobic blood cultures. Bacteraemia due to anaerobic organisms occurs in 0.5-12% of blood cultures worldwide; however, recent studies from Europe and the USA presented inconsistent data regarding the prevalence of anaerobic bacteraemias between 1993 and 2006. The aims of this retrospective survey were to determine the prevalence of bacteraemias due to anaerobic bacteria and evaluate the importance of anaerobic blood cultures in a university hospital in Szeged, Hungary. We examined the occurrence of bacteraemias due to anaerobic bacteria during a 5-year period, from January 2005 to 2009, in order to identify current trends of anaerobic bacteraemias in our university.

Species identification of clinical Prevotella isolates by matrix-assisted laser desorption ionization-time of flight mass spectrometry

The performance of matrix-assisted laser desorption-ionization time of flight mass spectrometry (MALDI-TOF MS) for species identification of Prevotella was evaluated and compared with 16S rRNA gene sequencing. Using a Bruker database, 62.7% of the 102 clinical isolates were identified to the species level and 73.5% to the genus level. Extension of the commercial database improved these figures to, respectively, 83.3% and 89.2%. MALDI-TOF MS identification of Prevotella is reliable but needs a more extensive database.

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

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

First national survey of antibiotic susceptibility of the Bacteroides fragilis group: emerging resistance to carbapenems in Argentina

The antibiotic susceptibility rates of 363 clinical Bacteroides fragilis group isolates collected from 17 centers in Argentina during the period from 2006 to 2009 were as follows: piperacillin-tazobactam, 99%; ampicillin-sulbactam, 92%; cefoxitin, 72%; tigecycline, 100%; moxifloxacin, 91%; and clindamycin, 52%. No metronidazole resistance was detected in these isolates during this time period. Resistance to imipenem, doripenem, and ertapenem was observed in 1.1%, 1.6%, and 2.3% of B. fragilis group strains, respectively. B. fragilis species showed a resistance profile of 1.5% to imipenem, 1.9% to doripenem, and 2.4% to ertapenem. This is the first report of carbapenem resistance in Argentina. The cfiA gene was present in 8 out of 23 isolates, all of them belonging to the B. fragilis species and displaying reduced susceptibility or resistance to carbapenems (MICs ≥ 4 μg/ml). Three out of eight cfiA-positive isolates were fully resistant to carbapenems, while 5 out of 8 isolates showed low-level resistance (MICs, 4 to 8 μg/ml). The inhibition by EDTA was a good predictor of the presence of metallo-β-lactamases in the fully resistant B. fragilis strains, but discrepant results were observed for low-level resistant isolates. B. fragilis was more susceptible to antimicrobial agents than other Bacteroides species. Bacteroides vulgatus species was the most resistant to ampicillin-sulbactam and piperacillin-tazobactam, and B. thetaiotaomicron/ovatus strains showed the highest level of resistance to carbapenems, with an unknown resistance mechanism. B. vulgatus and the uncommon non-Bacteroides fragilis species were the most resistant to moxifloxacin, showing an overall resistance rate of 15.1%.

Antimicrobial susceptibility of Bacteroides fragilis group isolates in Europe: 20 years of experience

The susceptibilities of 824 Bacteroides fragilis group isolates against nine antibiotics were evaluated in a Europe-wide study involving 13 countries. Species determination, by different methods, was carried out on all but one isolate. Resistance rates were evaluated according to species and geographical areas via CLSI and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints. The present data were compared with those obtained 10 and 20 years ago at a European level. High-level resistance (MIC ≥ 64 mg/L) to ampicillin was observed in 44.5% of the strains, which is a significant increase relative to 20 years ago (16%). Piperacillin/tazobactam was more active than amoxicillin/clavulanic acid (3.1% and 10.4% resistance, respectively), again with a resistance increase relative to earlier studies. Dramatic increases in resistance were observed for cefoxitin, clindamycin and moxifloxacin, with rates of 17.2%, 32.4% and 13.6%, respectively. The lowest resistances were found for imipenem, metronidazole and tigecycline (1.2%, <1% and 1.7%). Nonsusceptible strains to imipenem and metronidazole were more resistant to other anti-anaerobic drugs. Differences were detected between geographical areas, with higher resistance rates for moxifloxacin in Scandinavian countries (21.4%) than in Mediterranean countries (5.4%), whereas, for clindamycin, the resistance rates were higher in Mediterranean (41.8%) and lower in Scandinavian countries (22.5%). Piperacillin/tazobactam resistance was also higher in Scandinavian countries.

New insights into Prevotella diversity and medical microbiology

In light of recent studies based on cultivation-independent methods, it appears that the diversity of Prevotella in human microbiota is greater than was previously assumed from cultivation-based studies, and that the implication of these bacteria in several human diseases was unrecognized. While some Prevotella taxa were found during opportunistic infections, changes in Prevotella abundance and diversity were discovered during dysbiosis-associated diseases. As member of the microbiota, Prevotella may also be considered as a reservoir for resistance genes. Greater knowledge on Prevotella diversity, as well as new insights into its pathogenic potential and implication in dysbiosis are expected from the use of human microbe identification microarrays, from whole-genome sequence analyse, and from the NIH Human Microbiome Project data. New approaches, including molecular-based methods, could contribute to improve the diagnosis of Prevotella infections.

Differentiation of cfiA-negative and cfiA-positive Bacteroides fragilis isolates by matrix-assisted laser desorption ionization-time of flight mass spectrometry

Carbapenem resistance in Bacteroides fragilis is associated with cfiA-encoded class B metallo-beta-lactamase. cfiA-negative and cfiA-positive isolates belong to genotypically distinct groups. Of a total of 248 B. fragilis isolates included in this study, 214 were susceptible, 10 were intermediate, and 24 were resistant to meropenem. We show that matrix-assisted laser desorption ionization-time of flight mass spectrometry is able to differentiate between cfiA-negative and cfiA-positive isolates and predict carbapenem resistance in a routine laboratory setting.

Antimicrobial resistance and prevalence of resistance genes in intestinal Bacteroidales strains

OBJECTIVE

This study examined the antimicrobial resistance profile and the prevalence of resistance genes in Bacteroides spp. and Parabacteroides distasonis strains isolated from children's intestinal microbiota.

METHODS

The susceptibility of these bacteria to 10 antimicrobials was determined using an agar dilution method. β-lactamase activity was assessed by hydrolysis of the chromogenic cephalosporin of 114 Bacteriodales strains isolated from the fecal samples of 39 children, and the presence of resistance genes was tested using a PCR assay.

RESULTS

All strains were susceptible to imipenem and metronidazole. The following resistance rates were observed: amoxicillin (93%), amoxicillin/clavulanic acid (47.3%), ampicillin (96.4%), cephalexin (99%), cefoxitin (23%), penicillin (99%), clindamycin (34.2%) and tetracycline (53.5%). P-lactamase production was verified in 92% of the evaluated strains. The presence of the cfiA, cepA, ermF, tetQ and nim genes was observed in 62.3%, 76.3%, 27%, 79.8% and 7.8% of the strains, respectively.

CONCLUSIONS

Our results indicate an increase in the resistance to several antibiotics in intestinal Bacteroides spp. and Parabacteroides distasonis and demonstrate that these microorganisms harbor antimicrobial resistance genes that may be transferred to other susceptible intestinal strains.

Anaerobic infections: update on treatment considerations

Anaerobic bacteria are the predominant indigenous flora of humans and, as a result, play an important role in infections, some of which are serious with a high mortality rate. These opportunistic pathogens are frequently missed in cultures of clinical samples because of shortcomings in collection and transport procedures as well as lack of isolation and susceptibility testing of anaerobes in many clinical microbiology laboratories. Correlation of clinical failures with known antibacterial resistance of anaerobic bacteria is seldom possible. Changes in resistance over time, and the discovery and characterization of resistance determinants in anaerobic bacteria, has increased recognition of problems in empirical treatment and has even resulted in changes in treatment guidelines. This review discusses the role of anaerobic bacteria in the normal flora of humans, their involvement in different mixed infections, developments in antibacterial resistance of the most frequent anaerobic pathogens and possible new treatment options.

Vitek 2 ANC card versus BBL Crystal Anaerobe and RapID ANA II for identification of clinical anaerobic bacteria

The Vitek 2 Anaerobe and Corynebacterium Identification Card (ANC) was recently evaluated in a multicentre study. In the present work, this system was compared with the BBL Crystal Anaerobe and RapID ANA II panels. These kits were tested using 196 strains of anaerobes that had been previously identified by gas-liquid chromatography. Identification to the species or to the genus level was 75.0%, 81.1% and 70.9% for Crystal, RapID and Vitek, respectively. Vitek ANC failed to provide any identification in 20.4% of the strains, but it had fewer misidentifications than RapID. The confidence factors provided on the results report of each kit were not always correlated with a lower risk of major errors, with the exception of Vitek 2 in which a confidence factor higher than 0.86 excluded the risk of misidentification in more than 87% of isolates. The lower rate of identification by the Vitek and Crystal panels is mostly due the lower ability of these systems to identify the Clostridia. Overall, the three panels are comparable but need improvement to a better accuracy.

Identification of clinically important anaerobic bacteria by an oligonucleotide array

Anaerobic bacteria can cause a wide variety of infections, and some of these infections can be serious. Conventional identification methods based on biochemical tests are often lengthy and can produce inconclusive results. An oligonucleotide array based on the 16S-23S rRNA intergenic spacer (ITS) sequences was developed to identify 28 species of anaerobic bacteria and Veillonella. The method consisted of PCR amplification of the ITS regions with universal primers, followed by hybridization of the digoxigenin-labeled PCR products to a panel of 35 oligonucleotide probes (17- to 30-mers) immobilized on a nylon membrane. The performance of the array was determined by testing 310 target strains (strains which we aimed to identify), including 122 reference strains and 188 clinical isolates. In addition, 98 nontarget strains were used for specificity testing. The sensitivity and the specificity of the array for the identification of pure cultures were 99.7 and 97.1%, respectively. The array was further assessed for its ability to detect anaerobic bacteria in 49 clinical specimens. Two species (Finegoldia magna and Bacteroides vulgatus) were detected in two specimens by the array, and the results were in accordance with those obtained by culture. The whole procedure of array hybridization took about 8 h, starting with the isolated colonies. The array can be used as an accurate alternative to conventional methods for the identification of clinically important anaerobes.

Susceptibility of strict and facultative anaerobes Isolated from endodontic infections to metronidazole and beta-lactams

Endodontic infections are mixed aerobic-anaerobic infections and several microbial groups associated to these pathologies are also involved in orofacial infections. The goal of this study was to evaluate the susceptibility of microorganisms isolated from endodontic infections to beta-lactams and metronidazole and verify the production of beta-lactamases. Clinical specimens were collected from 58 endodontic infections of 52 patients. The microorganisms were isolated in selective and non-selective culture media, under anaerobiosis and aerobiosis, and identified using biochemical methods. In the susceptibility tests, it was used an agar dilution method, and Wilkins-Chalgren agar enriched with blood, hemin and menadione for the anaerobes, while Mueller-Hinton agar was employed for the facultative anaerobes. The production of beta-lactamases was evaluated through the biological and chromogenic cephalosporin methods. All tested isolates were sensitive to imipenem and 99.3% to amoxicillin/clavulanate association, while 16.1% showed resistance to amoxicillin and penicillin G, and 4.89% to cefoxitin. Resistance to metronidazole was just found in facultative anaerobes. Production of beta-lactamases was detected in 18.2% of the isolates and presented a correlation with resistance to beta-lactams.

Management of complicated infections in the era of antimicrobial resistance: the role of tigecycline

BACKGROUND

Increasing antimicrobial resistance and infection complications pose challenges to optimal antibiotic therapy. Paucity of new antibiotics (and the eventual bacterial resistance they face) highlights the critical need for more appropriate use of broadly effective agents, which may help to thwart the dramatic rise in global resistance. Single agents that can be combined effectively with others, if needed, promise the simplest overall utility. Approved in 2005 to treat complicated skin and intra-abdominal infections, tigecycline is a novel extended-spectrum minocycline derivative that circumvents bacterial resistance, as it is unaffected by efflux pumps and ribosomal protection. However, tigecycline should not be used as empiric monotherapy for treatment of health-care associated infections known or suspected to be owing to Pseudomonas aeruginosa or Proteus spp.

OBJECTIVE

This article summarizes the demonstrated clinical utility of tigecycline so far.

METHODS

A MEDLINE search examined authoritative published clinical studies, reviews and case reports detailing the clinical record of tigecycline since 2004.

RESULTS/CONCLUSION

Tigecycline continues to maintain satisfactory profiles of safety, efficacy and antimicrobial resistance avoidance. Regardless, continued surveillance is needed to detect reduced susceptibility and resistance against both community and nosocomial pathogens. Judicious use of agents reserved for multidrug resistant pathogens is vital to preserve their effectiveness.

Anaerobic Culture of Diabetic Foot Infections: Organisms and Antimicrobial Susceptibilities

Introduction: The prevalence of diabetes mellitus is high in Singapore. Infections of the lower limb are significant causes of morbidity in this population. Although the aerobic bacteriology of these infections is well-documented, there is less data available on the anaerobic pathogens involved. This study sets out to describe the anaerobic bacteria associated with diabetic foot infections, and evaluates the susceptibility to 3 antimicrobials with anaerobic activity. Materials and Methods: Anaerobic culture was performed on operative samples taken from diabetic foot infections. Organisms were identified through standard microbiological methods and commercial identification kits. Antimicrobial susceptibility testing to clindamycin, metronidazole and imipenem was performed by agar dilution. Results: One hundred and two strains of strict anaerobic bacteria were isolated from 30 unique specimens. The predominant anaerobic isolates were Peptostreptococcus spp. (46%) and Bacteroides fragilis group (19%). Antibiotic resistance was detected for clindamycin (18%), metronidazole (1%) and imipenem (2%). Conclusion: Multiple anaerobic species can be isolated from diabetic foot infections. A significant proportion of isolates are resistant to clindamycin, while resistance to imipenem and metronidazole remains low. Key words: Anaerobe, Antibiotic resistance, Bacterial

Evaluation of a new meropenem-EDTA double-ended Etest strip for the detection of the cfiA metallo-beta-lactamase gene in clinical isolates of Bacteroides fragilis

Thirty-five Bacteroides fragilis clinical isolates with varying susceptibility to meropenem were analysed with a prototype of a double-ended Etest strip containing meropenem +/- EDTA, designed for the detection of the CfiA metallo-beta-lactamase. Phenotypic results obtained with this new Etest strip were related to the genotype and compared to the results of the Etest containing imipenem +/- EDTA. Whereas the Etest with imipenem +/- EDTA only allowed detection of isolates with high-level resistance (both MICs of imipenem and meropenem >32 mg/L), reflecting the possible underestimation of CfiA prevalence in B. fragilis, the Etest with meropenem +/- EDTA proved to be more accurate, particularly for isolates with low-level carbapenem resistance, suggesting its potential for broader detection of CfiA production.

Antimicrobial susceptibility of anaerobic bacteria in Belgium as determined by E-test methodology

The objective was to collect recent data on the antibiotic susceptibility of clinically significant anaerobes in Belgium. A total of 333 anaerobic clinical isolates from various body sites were prospectively collected between 2005 and 2007 at two tertiary care hospitals in Belgium. The minimal inhibitory concentrations (MICs) were determined using the E-test method for nine anti-anaerobic antibiotics. Sixty-one percent of the isolates were beta-lactamase producers, which explains the poor activity of penicillin. Amoxicillin/clavulanic acid, piperacillin/tazobactam, metronidazole and meropenem were very active against most anaerobes, but around 10% of the Bacteroides fragilis group strains were non-susceptible to the two beta-lactam/beta-lactamase inhibitors. No resistance was observed to metronidazole, while 3% of the Bacteroides spp. had decreased susceptibility to meropenem (MIC > or = 4 mg/L). Cefoxitin, clindamycin and moxifloxacin were less active, with 33%, 52% and 57% of the B. fragilis group being non-susceptible respectively. Tigecycline showed consistently good activity against most anaerobes with MIC(50) and MIC(90) of 0.25 and 2 mg/L. Metronidazole, amoxicillin/clavulanate, piperacillin/tazobactam and meropenem remain good empirical choices when anaerobes are expected in our setting. Because of the occurrence of resistance to most classes of current anti-anaerobic antibiotics, it is recommended that the antimicrobial resistance patterns be monitored regularly in order to guide empirical therapy.

Increasing trends in antimicrobial resistance among clinically important anaerobes and Bacteroides fragilis isolates causing nosocomial infections: emerging resistance to carbapenems

This study reports data on the susceptibilities to five commonly used antianaerobic agents of five clinically frequently encountered anaerobes from 2000 to 2007 and to Bacteroides fragilis isolates causing nosocomial infections from 1990 to 2006. There was a trend of decreasing susceptibilities of these anaerobes to ampicillin-sulbactam, cefmetazole, chloramphenicol, and clindamycin with time during the study period. The rates of susceptibility to clindamycin and cefmetazole for all clinical isolates of Bacteroides fragilis isolates were higher than those of isolates associated with nosocomial infections. The MICs of 207 anaerobic blood isolates collected in 2006 to 14 antimicrobial agents were determined by the agar dilution method. The rates of nonsusceptibility to imipenem and meropenem were 7% and 12% for B. fragilis isolates (n = 60), 7% and 3% for Bacteroides thetaiotamicron isolates (n = 30), 4% and 4% for Fusobacterium species (n = 27), 6% and 0% for Prevotella species (n = 16), 15% and 0% for Clostridium species (n = 28), and 0% and 0% for Peptostreptococcus species (n = 32). The rates of susceptibility to moxifloxacin were 90% for B. fragilis isolates, 87% for B. thetaiotaomicron isolates, 81% for Fusobacterium species, 75% for Prevotella species, 93% for Clostridium species, and 78% for Peptostreptococcus species. Thirty-six percent of Clostridium species and 12% of Peptostreptococcus species were not susceptible to metronidazole. Comparison of the data with the data from a previous survey from the same institute in 2002 revealed higher rates of nonsusceptibility to carbapenems, especially for B. fragilis, Fusobacterium species, and Prevotella species isolates. The high rates of nonsusceptibility to commonly used antianaerobic agents mandate our attention, and periodic monitoring of the trend of the resistance is crucial.

Resistance trends of the Bacteroides fragilis group over a 10-year period, 1997 to 2006, in Madrid, Spain

The changes in susceptibilities of Bacteroides fragilis group strains isolated in our hospital from 1997 to 2006 were studied. A total of 1,343 clinical strains were included. The study showed differences in the resistance rates in the different species of the group. Increasing resistance to clindamycin and moxifloxacin was observed. Susceptibility to imipenem, piperacillin-tazobactam, and metronidazole remained unchanged.

Is the incidence of anaerobic bacteremia decreasing? Analysis of 114,000 blood cultures over a ten-year period

The number of positive anaerobic blood culture results per 1,000 blood cultures performed decreased from 12.6 in the period from 1997 to 2001 to 7.0 in the period from 2002 to 2006 (P < 0.001), as did the proportion of isolated anaerobic organisms compared to the number of all organisms isolated from blood cultures (7.6% to 4.3% [P < 0.001]), while positive aerobic cultures remained stable. In contrast, the proportion of Bacteroides fragilis group members and gram-positive cocci within the anaerobic group increased (26.8% to 36.7% [P = 0.004] and 5.4% to 12% [P < 0.001], respectively). The number of patients with anaerobic bacteremia decreased from 122 patients in 1997 to 69 in 2006.