Antimicrobial susceptibility and heteroresistance in Chinese Clostridium difficile strains

Antimicrobial Resistance of Clostridioides difficile in Children from a Tertiary Pediatric Hospital in Shanghai, China

Background

Our previous study reported a high rate of recurrence in children with Clostridioides difficile (C. difficile) infection (CDI) after conventional antibiotic therapy. Here, we aimed to explore whether metronidazole and vancomycin resistant C. difficile isolates are circulating in pediatric CDI.

Methods

Antimicrobial susceptibility testing (AST) using the agar dilution method according to the Clinical and Laboratory Standard Institute (CLSI) were performed on C. difficile isolates collected from children with CDI between 2019 and 2022 at the Shanghai Children's Hospital. Whole-genome sequencing (WGS) was performed on all C. difficile isolates, and the presence of antibiotic resistance genes (ARGs) were identified using Resfinder and the Comprehensive Antibiotic Resistance Database (CARD). The presence of plasmid pCD-METRO was detected using SRST2 (v0.2.0) against 8 pCD-METRO coding sequences.

Results

A total of 50 C. difficile isolates were collected from stools of CDI children. The overall resistance rate on all isolates was 30.00% for metronidazole, 6.00% for vancomycin, 0% for rifaximin, 2.00% for rifampin, 24.00% for meropenem, 100.00% for ceftriaxone and clindamycin, 86.00% for erythromycin, 30.0% for levofloxacin, and 50.0% for tetracycline. Multidrug-resistant (MDR) was presented in 44 isolates (88.00%). Sixteen reported potential ARGs relating with resistance to antibiotic classes of aminoglycoside (AAC(6')-Ie-APH(2")-Ia, aad(6), ANT(6)-Ib, APH(2")-If, APH(3')-IIIa), lincosamide-clindamycin-erythromycin (ErmB, ErmQ), fluoroquinolones (CdeA), glycopeptides (vanRG), nucleoside (SAT-4), tetracycline (tetM, tetA(P), tetB(P), tetO), and trimethoprim (dfrF) were identified. However, the pCD-METRO plasmid and vanA/B were not detected in any isolates.

Conclusion

C. difficile isolates from children with reduced susceptibility to metronidazole and vancomycin are emerging in pediatric CDI in China. The lack of pCD-METRO plasmid and vanA/B associated with reduced antibiotic susceptibility suggests there are additional mechanisms of resistance.

Antimicrobial activity of lipids extracted from Hermetia illucens reared on different substrates

As the problem of antimicrobial resistance is constantly increasing, there is a renewed interest in antimicrobial products derived from natural sources, particularly obtained from innovative and eco-friendly materials. Insect lipids, due to their fatty acid composition, can be classified as natural antimicrobial compounds. In order to assess the antibacterial efficacy of Hermetia illucens lipids, we extracted this component from the larval stage, fed on different substrates and we characterized it. Moreover, we analyzed the fatty acid composition of the feeding substrate, to determine if and how it could affect the antimicrobial activity of the lipid component. The antimicrobial activity was evaluated against Gram-positive Micrococcus flavus and Gram-negative bacteria Escherichia coli. Analyzing the fatty acid profiles of larval lipids that showed activity against the two bacterial strains, we detected significant differences for C4:0, C10:0, C16:1, C18:3 n3 (ALA), and C20:1. The strongest antimicrobial activity was verified against Micrococcus flavus by lipids extracted from larvae reared on strawberry, tangerine, and fresh manure substrates, with growth inhibition zones ranged from 1.38 to 1.51 mm, while only the rearing on manure showed the effect against Escherichia coli. Notably, the fatty acid profile of H. illucens seems to not be really influenced by the substrate fatty acid profile, except for C18:0 and C18:2 CIS n6 (LA). This implies that other factors, such as the rearing conditions, larval development stages, and other nutrients such as carbohydrates, affect the amount of fatty acids in insects. KEY POINTS: • Feeding substrates influence larval lipids and fatty acids (FA) • Generally, there is no direct correlation between substrate FAs and the same larvae FAs • Specific FAs influence more the antimicrobial effect of BSF lipids.

Molecular epidemiology, antimicrobial susceptibility, and toxin production of clinical Clostridioides difficile isolates from a teaching hospital in Northern China

To grasp the epidemiological trend and drug resistance mechanisms of Clostridioides difficile (C. diff) in Beijing, 302 C. diff isolates were obtained from patients with diarrhea. The sequence types (STs) from mainstream strains were all susceptible to metronidazole, vancomycin, piperacillin/tazobactam, meropenem, and tigecycline but almost resistant to ciprofloxacin and clindamycin. The missense mutation of GyrA/GyrB and RpoB resulted in fluoroquinolone and rifamycin resistance, respectively. Toxigenic strains from clade IV were likely to be missed due to the deficiency of tcdA gene. Four tcdC genotypes were first detected in strains from clade III and IV. The truncating mutation of TcdC disabled its function working as a toxin suppressor. In conclusion, the molecular epidemiology of C. diff in Beijing is different from other regions of China. The antimicrobial resistance patterns and toxin-producing abilities of strains with different STs varied greatly, which suggests that continuous surveillance and control are meaningful and urgent.

Prevalence, genetic characteristics, and antimicrobial resistance of Clostridioides difficile isolates from horses in Korea

OBJECTIVES

Clostridioides difficile is an etiological agent of enteric diseases in humans and animals. Animals are considered a potential reservoir due to the genetic and antimicrobial resistance similarities between human and animal C. difficile isolates. In this study, we evaluated the genetic characteristics and antimicrobial resistance profiles of C. difficile isolated from 942 fecal samples collected from horses in South Korea during 2019-2020.

METHODS

The C. difficile isolates were tested for toxin genes including tcdA (A), tcdB (B), and cdtAB (CDT) and deletions of the tcdC gene by PCR. In addition, ribotyping, multilocus sequence typing, and antimicrobial susceptibility tests were performed.

RESULTS

Twenty-three (2.4%) C. difficile isolates were associated with diarrhea in foals under 1 year old during the spring-summer period. Of these, 82.6% were toxigenic strains, determined to be A⁺B⁺CDT⁺ (52.1%) or A⁺B⁺CDT^‒ (30.4%). All isolates were susceptible to metronidazole and vancomycin, and resistant to cefotaxime and gentamicin, and 76.2% were multidrug resistant (MDR). RT078/ST11/Clade 5 was the most common genotype (47.8%), which was also found in animals and humans worldwide. All RT078/ST11/Clade 5 strains were toxigenic and had deletions of the tcdC gene. About half of these strains were resistant to moxifloxacin, and 63.6% were MDR.

CONCLUSIONS

C. difficile isolates in this study consisted mostly of toxigenic and MDR strains, and their genetic properties were highly similar to human C. difficile isolates. These results suggest high possibilities of zoonotic transmission and can provide knowledge for establishing strategies for the treatment and prevention of C. difficile infection.

Clostridioides difficile infection in Africa: A narrative review

Clostridioides (Clostridium) difficile infection (CDI) places a burden on healthcare facilities worldwide. Most research studies have been concentrated in high-income countries in North America, Europe, Asia and Australia, where C. difficile is the leading cause of diarrhoea associated with antimicrobial use. This narrative review summarises African CDI studies, focussing on reports published in the last 20 years. Although relatively sparse, the data suggest that CDI is an important cause of diarrhoea on the continent. African CDI patient populations are often younger than in European and North American settings, probably due to the high prevalence of co-morbid conditions such as tuberculosis, particularly in sub-Saharan Africa. Strain typing data are rare and where reported generally limited to single sites and institutions. Despite challenges, including a lack of facilities and awareness, there is a need for further investigation to more accurately determine the true burden of disease caused by C. difficile in Africa.

Clostridioides difficile epidemiology in the Middle and the Far East

OBJECTIVES

Clostridioides difficile is an important pathogen of healthcare-associated gastrointestinal infections. Recently, an increased number of C. difficile infection (CDI) surveillance data has been reported from Asia. The aim of this review is to summarize the data on the prevalence, distribution and molecular epidemiology of CDI in the Middle and the Far East.

METHODS

Literature was drawn from a search of PubMed up to September 30, 2021.

RESULTS

The meta-analysis of data from 111 studies revealed the pooled CDI prevalence rate in the Middle and the Far East of 12.4% (95% CI 11.4-13.3); 48 studies used PCR for CDI laboratory diagnoses. The predominant types (RT)/sequence type (ST) differ between individual countries (24 studies, 14 countries). Frequently found RTs were 001, 002, 012, 017, 018 and 126; RT017 was predominant in the Far East. The epidemic RT027 was detected in 8 countries (22 studies), but its predominance was reported only in three studies (Israel and Iran). The contamination of vegetable and meat or meat products and/or intestinal carriage of C. difficile in food and companion animals have been reported; the C. difficile RTs/STs identified overlapped with those identified in humans.

CONCLUSIONS

A large number of studies on CDI prevalence in humans from the Middle and the Far East have been published; countries with no available data were identified. The number of studies on C. difficile from non-human sources is limited. Comparative genomic studies of isolates from different sources are needed.

Antibiotic Resistances and Molecular Characteristics of Clostridioides difficile in ICUs in a Teaching Hospital From Central South China

Clostridioides (C.) difficile is a major healthcare-associated pathogen inducing infectious diarrhea. Approximately 25–33% of patients with antibiotic-associated diarrhea (AAD) and 90% of patients with pseudomembranous enteritis are caused by C. difficile infection (CDI). Stool samples were collected from hospitalized adults with presumptive AAD in four nonneonatal intensive care units (ICUs). Diagnosis of CDI was based on both clinical symptoms and laboratory results. The stool specimens were transferred onto CDIF (C. difficile agar), and C. difficile was finally confirmed by the latex agglutination test. Toxin-producing genes tcdA (A), tcdB (B), and cdt (CDT) were detected by PCR, and all isolates were performed multilocus sequence typing analysis. The antibiotic susceptibility of C. difficile isolates was assessed by the agar dilution method. A total of 184 C. difficile were isolated from 857 specimens in our study, the isolation rate of C. difficile was 21.5% (184/857). The 184 C. difficile were isolated from 179 patients, among these 115 patients were toxin-positive, giving the incidence of CDI being 58.0/10,000 patient days in the four ICUs. Among these 115 toxin-positive C. difficile isolates, 100 (87.0%) isolates produced two toxins (A+B+CDT-), three (2.6%) isolates were A+B+ with binary toxin-producing (A+B+CDT+), and 12 (10.4%) isolates only produced one toxin (A-B+CDT-). A total of 27 sequencing types (STs) were obtained. The most prevalent was ST3 (34 isolates), followed by ST39 (27 isolates), ST54 (19 isolates), ST26 (16 isolates), ST35 (15 isolates), and ST2 (13 isolates). All the ST26 isolates were nontoxigenic. Meanwhile, five STs were newly discovered. Although multidrug resistance was present in ≥50% of these C. difficile isolates, all of them were susceptible to tigecycline, fidaxomicin, metronidazole, and vancomycin. In conclusion, C. difficile isolates producing two toxins (A+B+CDT-) were dominant in our hospital. The most prevalent was ST3, and all ST26 isolates were NTCD. Although multidrug resistance was present in ≥50% of the C. difficile isolates, metronidazole, tigecycline, fidaxomicin, and vancomycin were still effective treatments for CDI in our hospital.

Genomic evolution and virulence association of Clostridioides difficile sequence type 37 (ribotype 017) in China

Clostridioides difficile sequence type (ST) 37 (ribotype 017) is one of the most prevalent genotypes circulating in China. However, its genomic evolution and virulence determinants were rarely explored. Whole-genome sequencing, phylogeographic and phylogenetic analyses were conducted for C. difficile ST37 isolates. The 325 ST37 genomes from six continents, including North America (n = 66), South America (n = 4), Oceania (n = 7), Africa (n = 9), Europe (n = 138) and Asia (n = 101), were clustered into six major lineages, with region-dependent distributions, harbouring an array of antibiotic-resistance genes. The ST37 strains from China were divided into four distinct sublineages, showing five importation times and international sources. Isolates associated with severe infections exhibited significantly higher toxin productions, tcdB mRNA levels, and sporulation capacities (P < 0.001). Kyoto Encyclopedia of Genes and Genomes analysis showed 10 metabolic pathways were significantly enriched in the mutations among isolates associated with severe CDI (P < 0.05). Gene mutations in glycometabolism, amino acid metabolism and biosynthesis virtually causing instability in protein activity were correlated positively to the transcription of tcdR and negatively to the expression of toxin repressor genes, ccpA and codY. In summary, our study firstly presented genomic insights into genetic characteristics and virulence association of C. difficile ST37 in China. Gene mutations in certain important metabolic pathways are associated with severe symptoms and correlated with higher virulence in C. difficile ST37 isolates.

Molecular epidemiology and antimicrobial resistance of Clostridioides difficile in Germany, 2014-2019

Clostridioides difficile is a Gram positive spore-forming rod and mainly responsible for nosocomial diarrhea in developed nations. Molecular and antimicrobial surveillance is important for monitoring the strain composition including genotypes of high epidemiological importance such as ribotype 027 (RT027) and corresponding resistance patterns. 1535 isolates obtained from samples sent between 2014 and 2019 to the German National Reference Center (NRC) for diagnostic reasons (NRC strain set), and 1143 isolates from a Tertiary Care University Center in Saarland, Germany (non-NRC strain set), were evaluated using antibiotic susceptibility testing and ribotyping. In the NRC strain set, RT027 overtook RT001, the main RT found in the preceding studies, and dominated with 36.2%, followed by RT001 (13.3%), and RT014 (8.5%). Of note, since 2016 a constant decrease of RT027 could be noticed. In the non-NRC strain set a large strain diversity was present with RT014 (18%) and RT001 (8.9%) being most prevalent. In NRC samples, resistance towards metronidazole, vancomycin, moxifloxacin, clarithromycin and rifampicin was 2.7%, 0%, 57.1%, 53.2% and 19.2%, respectively. Metronidazole resistance was almost exclusively found in RT027 isolates. Rifampicin resistance was also observed predominantly in isolates of RT027, constituting an almost four-fold increase, when compared to preceeding studies in this region. In conclusion these data demonstrate that RT027 is a driver for rifampicin and metronidazole resistance, underlining the importance of continuous surveillance efforts.

Functional analyses of epidemic Clostridioides difficile toxin B variants reveal their divergence in utilizing receptors and inducing pathology

Clostridioides difficile toxin B (TcdB) is a key virulence factor that causes C. difficile associated diseases (CDAD) including diarrhea and pseudomembranous colitis. TcdB can be divided into multiple subtypes/variants based on their sequence variations, of which four (TcdB1-4) are dominant types found in major epidemic isolates. Here, we find that these variants are highly diverse in their receptor preference: TcdB1 uses two known receptors CSPG4 and Frizzled (FZD) proteins, TcdB2 selectively uses CSPG4, TcdB3 prefers to use FZDs, whereas TcdB4 uses neither CSPG4 nor FZDs. By creating chimeric toxins and systematically switching residues between TcdB1 and TcdB3, we determine that regions in the N-terminal cysteine protease domain (CPD) are involved in CSPG4-recognition. We further evaluate the pathological effects induced by TcdB1-4 with a mouse intrarectal installation model. TcdB1 leads to the most severe overall symptoms, followed by TcdB2 and TcdB3. When comparing the TcdB2 and TcdB3, TcdB2 causes stronger oedema while TcdB3 induces severer inflammatory cell infiltration. These findings together demonstrate divergence in the receptor preference and further lead to colonic pathology for predominant TcdB subtypes.

Clostridioides difficile is a major cause of nosocomial and community-associated gastrointestinal infections. The bacterium produces three exotoxins including TcdA, TcdB, and CDT, of which TcdB is known as a key virulence factor causing the diseases. Since C. difficile was first linked to antibiotic-associated infections in 1978, a large number of clinically relevant strains were characterized and many of them were found to harbor some variant forms of TcdB. In this study, we examined four predominant TcdB variants from epidemic C. difficile strains. We found that these variants are highly diverse in preference to the known receptors, CSPG4 and Frizzled proteins. By conducting a systematically designed mutagenesis study, we determined that TcdB interacts with CSPG4 via regions across multiple domains. We also found that TcdB variants could induce distinguishable pathological phenotypes in a mouse model, suggesting C. difficile strains harboring divergent TcdB variants might exhibit different disease progression. Our study provides new insights into the toxicology and pathology of C. difficile toxin variants.

Antimicrobial resistance in Clostridioides (Clostridium) difficile derived from humans: a systematic review and meta-analysis

Background

Clostridioides (Clostridium) difficile is an important pathogen of healthcare- associated diarrhea, however, an increase in the occurrence of C. difficile infection (CDI) outside hospital settings has been reported. The accumulation of antimicrobial resistance in C. difficile can increase the risk of CDI development and/or its spread. The limited number of antimicrobials for the treatment of CDI is matter of some concern.

Objectives

In order to summarize the data on antimicrobial resistance to C. difficile derived from humans, a systematic review and meta-analysis were performed.

Methods

We searched five bibliographic databases: (MEDLINE [PubMed], Scopus, Embase, Cochrane Library and Web of Science) for studies that focused on antimicrobial susceptibility testing in C. difficile and were published between 1992 and 2019. The weighted pooled resistance (WPR) for each antimicrobial agent was calculated using a random- effects model.

Results

A total of 111 studies were included. The WPR for metronidazole and vancomycin was 1.0% (95% CI 0–3%) and 1% (95% CI 0–2%) for the breakpoint > 2 mg/L and 0% (95% CI 0%) for breakpoint ≥32 μg/ml. Rifampin and tigecycline had a WPRs of 37.0% (95% CI 18–58%) and 1% (95% CI 0–3%), respectively. The WPRs for the other antimicrobials were as follows: ciprofloxacin 95% (95% CI 85–100%), moxifloxacin 32% (95% CI 25–40%), clindamycin 59% (95% CI 53–65%), amoxicillin/clavulanate 0% (0–0%), piperacillin/tazobactam 0% (0–0%) and ceftriaxone 47% (95% CI 29–65%). Tetracycline had a WPR 20% (95% CI 14–27%) and meropenem showed 0% (95% CI 0–1%); resistance to fidaxomicin was reported in one isolate (0.08%).

Conclusion

Resistance to metronidazole, vancomycin, fidaxomicin, meropenem and piperacillin/tazobactam is reported rarely. From the alternative CDI drug treatments, tigecycline had a lower resistance rate than rifampin. The high-risk antimicrobials for CDI development showed a high level of resistance, the highest was seen in the second generation of fluoroquinolones and clindamycin; amoxicillin/clavulanate showed almost no resistance. Tetracycline resistance was present in one fifth of human clinical C. difficile isolates.

The tcdA-negative and tcdB-positive Clostridium difficile ST81 clone exhibits a high level of resistance to fluoroquinolones: a multi-centre study in Beijing, China

Clostridium difficile infection (CDI) is the leading cause of antibiotic-associated diarrhoea worldwide. In order to gain a better understanding about the molecular epidemiology of C. difficile in Beijing, China, molecular typing, antimicrobial susceptibility testing and drug resistance gene sequencing were performed on 174 strains of C. difficile collected from four large tertiary hospitals in Beijing. In total, 31 sequence types (STs) were identified among the 174 strains. ST81 was found to be the most prevalent (26.4%, 46/174), followed by ST2 (16.7%, 29/174) and ST54 (9.8%, 17/174). All isolates were susceptible to metronidazole and vancomycin. The test strains displayed resistance rates of 97.1%, 44.3% and 44.3% for ciprofloxacin, levofloxacin and moxifloxacin, respectively. ST81 isolates displayed a drug resistance rate of 97.8% for levofloxacin and moxifloxacin, which was significantly higher than ST2 (0%), ST54 (17.6%) and ST42 (0%) isolates (P<0.05). An amino acid mutation (T82I) was identified in GyrA, and the total mutation rate of the C. difficile strains was 40.8% (71/174). The mutation rate of ST81 isolates was 95.7% (44/46). Three amino acid mutations (D426N, S366A and D426V) were identified in GyrB, and the total mutation rate of GyrB was 39.1%. A double-site mutation in GyrB (S366A+D426V) was identified in all ST81 (n=46) isolates. In conclusion, the C. difficile ST81 clone showed a high level of resistance to fluoroquinolones in Beijing, highlighting the need for nationwide surveillance of CDI.

Recommendations for the diagnosis and treatment of Clostridioides difficile infection: An official clinical practice guideline of the Spanish Society of Chemotherapy (SEQ), Spanish Society of Internal Medicine (SEMI) and the working group of Postoperative Infection of the Spanish Society of Anesthesia and Reanimation (SEDAR)

This document gathers the opinion of a multidisciplinary forum of experts on different aspects of the diagnosis and treatment of Clostridioides difficile infection (CDI) in Spain. It has been structured around a series of questions that the attendees considered relevant and in which a consensus opinion was reached. The main messages were as follows: CDI should be suspected in patients older than 2 years of age in the presence of diarrhea, paralytic ileus and unexplained leukocytosis, even in the absence of classical risk factors. With a few exceptions, a single stool sample is sufficient for diagnosis, which can be sent to the laboratory with or without transportation media for enteropathogenic bacteria. In the absence of diarrhoea, rectal swabs may be valid. The microbiology laboratory should include C. difficile among the pathogens routinely searched in patients with diarrhoea. Laboratory tests in different order and sequence schemes include GDH detection, presence of toxins, molecular tests and toxigenic culture. Immediate determination of sensitivity to drugs such as vancomycin, metronidazole or fidaxomycin is not required. The evolution of toxin persistence is not a suitable test for follow up. Laboratory diagnosis of CDI should be rapid and results reported and interpreted to clinicians immediately. In addition to the basic support of all diarrheic episodes, CDI treatment requires the suppression of antiperistaltic agents, proton pump inhibitors and antibiotics, where possible. Oral vancomycin and fidaxomycin are the antibacterials of choice in treatment, intravenous metronidazole being restricted for patients in whom the presence of the above drugs in the intestinal lumen cannot be assured. Fecal material transplantation is the treatment of choice for patients with multiple recurrences but uncertainties persist regarding its standardization and safety. Bezlotoxumab is a monoclonal antibody to C. difficile toxin B that should be administered to patients at high risk of recurrence. Surgery is becoming less and less necessary and prevention with vaccines is under research. Probiotics have so far not been shown to be therapeutically or preventively effective. The therapeutic strategy should be based, rather than on the number of episodes, on the severity of the episodes and on their potential to recur. Some data point to the efficacy of oral vancomycin prophylaxis in patients who reccur CDI when systemic antibiotics are required again.

Surveillance of antimicrobial susceptibilities reveals high proportions of multidrug resistance in toxigenic Clostridium difficile strains in different areas of Poland

Two hundred and fifty-three non-duplicate toxigenic Clostridium difficile isolates, collected from February 2012 to December 2014, were evaluated for phenotypic resistance to ten antimicrobial drugs with the E-test gradient diffusion method. All strains of C. difficile were susceptible to metronidazole, vancomycin, and tigecycline. The metronidazole MIC values of the hyperepidemic PCR-ribotypes RT027 and RT176 were higher than those of non-epidemic PCR-ribotypes (p < 0.05, as evidenced by Mann-Whitney U test). In contrast, vancomycin susceptibility did not differ between hyperepidemic and non-epidemic strains, although the difference was almost significant (p = 0.065). Clostridium difficile RT027 and RT176 isolates could be assessed to five and four different susceptibility patterns, respectively, representing various combinations of resistance to different antimicrobial classes. A single point mutation (Thr82Ile) in the gyrA gene was detected in 11 (78.6%) of 14 isolates with high level of resistance to ciprofloxacin and moxifloxacin and four different types of single point mutations (Arg447Lys, Ser416Ala, Asp426Val, Asp426Asn) in the gyrB gene were detected in 4 strains, also with high level of resistance to ciprofloxacin and moxifloxacin. Four different point mutations were detected in the rpoB gene in 21 rifampicin-resistant strains of which one has not been reported previously, Gln489Leu. This study demonstrates the presence of multidrug-resistant C. difficile strains in Polish hospitals over the study period, irrespective of geographical location or reference level of the hospital.

Prevalence and characterization of Clostridioides difficile isolates from retail food products (vegetables and meats) in Japan

The present study aimed to elucidate the prevalence of Clostridioides difficile in Japanese retail food products. For this purpose, retail food samples (242 fresh vegetables and 266 retail meat samples: 89 chicken meat; 28 chicken liver; 200 pork meat; 24 pig liver; 127 beef meat) were collected from 14 supermarkets between 2015 and 2019. C. difficile was isolated from eight (3.3%) fresh vegetable, six (6.7%) chicken meat, one (3.6%) chicken liver, one (0.5%) pork meat, and two (1.6%) beef meat samples; it was not isolated from pig liver. Of these isolates, 35% were toxigenic. All isolates were typable by PCR ribotyping and were resolved into 12 PCR ribotypes. Among these isolates, ribotype 014, which is distributed worldwide including in Japanese clinical cases, was detected among vegetable isolates. Therefore, although the C. difficile contamination rate in Japanese retail foods was low, these sources can be contaminated and could transmit these bacteria to humans.

Clostridium difficile ribotype 017 - characterization, evolution and epidemiology of the dominant strain in Asia

Clostridium difficile ribotype (RT) 017 is an important toxigenic C. difficile RT which, due to a deletion in the repetitive region of the tcdA gene, only produces functional toxin B. Strains belonging to this RT were initially dismissed as nonpathogenic and circulated largely undetected for almost two decades until they rose to prominence following a series of outbreaks in the early 2000s. Despite lacking a functional toxin A, C. difficile RT 017 strains have been shown subsequently to be capable of causing disease as severe as that caused by strains producing both toxins A and B. While C. difficile RT 017 strains can be found in almost every continent today, epidemiological studies suggest that the RT is endemic in Asia and that the global spread of this MLST clade 4 lineage member is a relatively recent event. C. difficile RT 017 transmission appears to be mostly from human to human with only a handful of reports of isolations from animals. An important feature of C. difficile RT 017 strains is their resistance to several antimicrobials and this has been documented as a possible factor driving multiple outbreaks in different parts of the world. This review summarizes what is currently known regarding the emergence and evolution of strains belonging to C. difficile RT 017 as well as features that have allowed it to become an RT of global importance.

Helicobacter pylori and Its Antibiotic Heteroresistance: A Neglected Issue in Published Guidelines

"Heteroresistance" is a widely applied term that characterizes most of the multidrug-resistant microorganisms. In microbiological practice, the word "heteroresistance" indicates diverse responses to specific antibiotics by bacterial subpopulations in the same patient. These resistant subpopulations of heteroresistant strains do not respond to antibiotic therapy in vitro or in vivo. Presently, there is no standard protocol available for the treatment of infections caused by heteroresistant Helicobacter pylori in clinical settings, at least according to recent guidelines. Thus, there is a definite need to open a new discussion on how to recognize, how to screen, and how to eliminate those problematic strains in clinical and environmental samples. Since there is great interest in developing new strategies to improve the eradication rate of anti-H. pylori treatments, the presence of heteroresistant strains/clones among clinical isolates of the bacteria should be taken into account. Indeed, increased knowledge of gastroenterologists about the existence of heteroresistance phenomena is highly required. Moreover, the accurate breakpoints should be examined/determined in order to have a solid statement of heteroresistance among the H. pylori isolates. The primary definition of heteroresistance was about coexistence of both resistant and susceptible isolates at the similar gastric microniche at once, while we think that it can be happened subsequently as well. The new guidelines should include a personalized aspect in the standard protocol to select a precise, effective antibiotic therapy for infected patients and also address the problems of regional antibiotic susceptibility profiles.

High prevalence and diversity of tcdA-negative and tcdB-positive, and non-toxigenic, Clostridium difficile in Thailand

Studies on the prevalence and diversity of Clostridium difficile in Thailand have been limited to those derived from a few tertiary hospitals in Central Thailand. In this study, 145 C. difficile isolates collected in 13 provinces in Thailand during 2006-2018 were characterized by ribotyping and detection of toxin genes. Minimum inhibitory concentrations of eight antimicrobial agents were determined also for all 100 C. difficile strains collected from 2006 until 2015. Of the 145 strains of C. difficile, 71 (49%) were non-toxigenic, 46 (32%) were toxin A-negative, toxin B-positive (A-B+) and 28 (19%) were A+B+. No binary toxin-positive strain was found. The most common ribotype (RT) was RT 017 (A-B+CDT-, 19%, 28/145). Besides RT 017, 20 novel non-toxigenic and A-B+ ribotyping profiles, which may be related to RT 017 by the similarity of ribotyping profile, were identified. All C. difficile strains remained susceptible to metronidazole and vancomycin, however, a slight increase in MIC for metronidazole was seen in both toxigenic and non-toxigenic strains (overall MIC_50/90 0.25/0.25 mg/L during 2006-2010 compared to overall MIC_50/90 1.0/2.0 mg/L during 2011-2015). There was a high rate of fluoroquinolone resistance among RT 017 strains (77%), but there was little resistance among non-toxigenic strains. These results suggest that RT 017 is endemic in Thailand, and that the misuse of fluoroquinolones may lead to outbreaks of RT 017 infection in this country. Further studies on non-toxigenic C. difficile are needed to understand whether they have a role in the pathogenesis of C. difficile infection in Asia.

Epidemiology of Clostridium difficile infection in hospitalized adults and the first isolation of C. difficile PCR ribotype 027 in central China

Background

Clostridium difficile infection (CDI) is an emerging healthcare problem in the world. The purpose of this study was to perform a systematic epidemiological research of CDI in Tongji hospital, the central of China.

Methods

Stool samples from hospitalized adults suspected of CDI were enrolled. The diagnosis of CDI were based on the combination of clinical symptoms and laboratory results. Clinical features of CDI and non-CDI patients were compared by appropriate statistical tests to determine the risk factors of CDI. Multilocus sequence typing (MLST) was employed for molecular epidemiological analysis. Susceptibility testing and relevant antimicrobial agent resistance genes were performed as well.

Results

From June 2016 to September 2017, 839 hospitalized adults were enrolled. Among them, 107 (12.8%, 107/839) patients were C. difficile culture positive, and 73 (8.7%, 73/839) were infected with toxigenic C. difficile (TCD), with tcdA + tcdB+ strains accounting for 90.4% (66/73) and tcdA-tcdB+ for 9.6% (7/73). Meanwhile, two TCD strains were binary toxin positive and one of them was finally identified as CD027. Severe symptoms were observed in these two cases. Multivariate analysis indicated antibiotic exposure (p = 0.001, OR = 5.035) and kidney disease (p = 0.015, OR = 8.329) significantly increased the risk of CDI. Phylogenetic tree analysis demonstrated 21 different STs, including one new ST (ST467); and the most dominant type was ST54 (35.6%, 26/73). Multidrug-resistant (MDR) TCD were 53.4% (39/73); resistance to ciprofloxacin, erythromycin, and clindamycin were > 50%. Other antibiotics showed relative efficiency and all strains were susceptible to metronidazole and vancomycin. All moxifloxacin-resistant isolates carried a mutation in GyrA (Thr82 → Ile), with one both having mutation in GyrB (Ser366 → Ala).

Conclusions

Knowledge of epidemiological information for CDI is limited in China. Our finding indicated tcdA + tcdB+ C. difficile strains were the dominant for CDI in our hospital. Significant risk factors for CDI in our setting appeared to be antibiotic exposure and kidney disease. Metronidazole and vancomycin were still effective for CDI. Although no outbreak was observed, the first isolation of CD027 in center China implied the potential spread of this hypervirulent clone. Further studies are needed to enhance our understanding of the epidemiology of CDI in China.

Electronic supplementary material

The online version of this article (10.1186/s12879-019-3841-6) contains supplementary material, which is available to authorized users.

Epidemiological investigation of Clostridioides difficile colonization in Chinese community infants

Clostridioides difficile is a colonizer of the human gut; asymptomatic colonization has been reported to be more common in infants and is highly variable across regions even with no symptoms of diarrhea or death. Antibiotic treatment strategies might increase the antibiotic resistance of C. difficile. We performed a one-point study involving 1098 healthy infants (0-36 months) to address the deficiency of reports on C. difficile colonization in Chinese community infants. The C. difficile colonization rate was 22.8% (250/1098), and more than half of the strains (55.2%) were toxigenic isolates. Among the 138 toxigenic isolates, 111 were of the A⁺B⁺CDT^- genotype, 26 strains were A^-B⁺CDT^-, and one strain was A⁺B⁺CDT⁺. Fifteen different PCR ribotypes were found among the 250 isolates, and PCR-ribotype HB03 appeared to be dominant type, accounting for 19.6% (49/250). High levels of resistance to antimicrobial agents were observed. Our study showed that age and hospitalization before stool collection were positively correlated with the C. difficile colonization rate, whereas the delivery term was negatively related to the colonization rate. Particular attention should be paid to the increasing resistance of C. difficile to rifamycin.

Clostridium difficile in Asia: Opportunities for One Health Management

Clostridium difficile is a ubiquitous spore-forming bacterium which causes toxin-mediated diarrhoea and colitis in people whose gut microflora has been depleted by antimicrobial use, so it is a predominantly healthcare-associated disease. However, there are many One Health implications to C. difficile, given high colonisation rates in food production animals, contamination of outdoor environments by use of contaminated animal manure, increasing incidence of community-associated C. difficile infection (CDI), and demonstration of clonal groups of C. difficile shared between human clinical cases and food animals. In Asia, the epidemiology of CDI is not well understood given poor testing practices in many countries. The growing middle-class populations of Asia are presenting increasing demands for meat, thus production farming, particularly of pigs, chicken and cattle, is rapidly expanding in Asian countries. Few reports on C. difficile colonisation among production animals in Asia exist, but those that do show high prevalence rates, and possible importation of European strains of C. difficile like ribotype 078. This review summarises our current understanding of the One Health aspects of the epidemiology of CDI in Asia.

Molecular epidemiology and antimicrobial susceptibility of human Clostridium difficile isolates from a single institution in Northern China

Because the epidemiology of Clostridium difficile infection (CDI) is region-specific, the present study was undertaken to examine the epidemiology of C difficile outbreaks in Beijing, China.Eighty nonduplicate isolates were collected from March, 2016 to December, 2016. The molecular type and phylogenetic analysis were evaluated by multilocus sequence typing (MLST). The minimum inhibitory concentrations (MICs) for 11 antibiotics and the resistance mechanisms were investigated.Sixty-five toxigenic strains (81.25%), including 22 tcdABCDT strains (27.5%) and 43 tcdABCDT strains (53.75%), and also 15 nontoxigenic strains (tcdABCDT; 18.75%) were detected. MLST identified 21 different sequence types (STs), including 2 novel types (ST409 and ST416). All isolates were susceptible to metronidazole, vancomycin, fidaxomicin, piperacillin/tazobactam, and meropenem, and all were effectively inhibited by emodin (MICs 4-8 μg/mL). The resistance rates to rifaximin, ceftriaxone, clindamycin, erythromycin, and ciprofloxacin were 8.75%, 51.25%, 96.25%, 81.25%, and 96.25%, respectively; 81.25% (65/80) of isolates were multidrug-resistant. Amino acid mutations in GyrA and/or GyrB conferred quinolone resistance. One novel amino acid substitution, F86Y in GyrA, was found in 1 CIP-intermediate strain. The erm(B) gene played a key role in mediating macrolide-lincosamide-streptogramin B (MLSB) resistance. Erm(G) was also found in erm(B)-negative strains that were resistant to both erythromycin and clindamycin. RpoB mutations were associated with rifampin resistance, and 2 new amino mutations were identified in 1 intermediate strain (E573A and E603N).Regional diversity and gene heterogeneity exist in both the ST type and resistant patterns of clinical C difficile isolates in Northern China.

Prevalence of Clostridium difficile isolated from various raw meats in Korea

Clostridium difficile is an anaerobic, toxin-producing pathogen that causes human infection possibly through the consumption of meat. Clostridium difficile was isolated from 45 of 415 (10.8%) various raw meat samples collected in nationwide markets in Korea between 2013 and 2014. Among the 45 isolated strains, the highest prevalence rate was found in September (28.6%) and detected in chicken (16.4%), pork (8.3%) and beef (6.8%). According to an antibiotic resistance test, resistance was found only for clindamycin (2.2%). The genetic similarity of ribotypes O78 and O27 and strains isolated from raw meats was determined using DiversiLab. Among the isolates studied, four different rep-PCR types were identified, genetically distinct from ribotypes O78 and O27. An ELISA reaction confirmed that the two strains have toxin A and toxin B and showed 89% genetic similarity. This study suggests that food animals could be potential routes of foodborne transmission in C. difficile-associated human infection.

Use of matrix-assisted laser desorption ionization-time of flight mass spectrometry to identify MLST clade 4 Clostridium difficile isolates

Clostridium difficile is the leading cause of health care-associated infections. Previous studies suggest that C. difficile MLST clade 4 strains with higher drug resistance rates constitute the major clone spreading in China. Thus development of a rapid and accurate typing method for these strains is needed to monitor the epidemiology of this clone and to guide clinical treatment. A total of 160 non-duplicate C. difficile isolates recovered from three large teaching hospitals in Beijing were studied. All the 41 clade 4 C. difficile isolates clustered together on the PCA dendrogram. Spectra peak statistics revealed that five markers (2691.43Da, 2704.91Da, 2711.93Da, 3247.27Da and 3290.76Da) can easily and reliably distinguish between clade 4 and non-clade 4 isolates, with area under the curve (AUC) values of 0.991, 0.997, 0.973, 1 and 1, respectively. In conclusion, MALDI-TOF MS is a very simple and accurate method for identifying C. difficile MLST clade 4 strains.

Aliyu S, F. Hadjirin N, A. Holmes M, Török E, M. Brown N, Parkhill J, Peacock S. Genomic survey of Clostridium difficile reservoirs in the East of England implicates environmental contamination of wastewater treatment plants by clinical lineages

There is growing evidence that patients with Clostridiumdifficile-associated diarrhoea often acquire their infecting strain before hospital admission. Wastewater is known to be a potential source of surface water that is contaminated with C. difficile spores. Here, we describe a study that used genome sequencing to compare C. difficile isolated from multiple wastewater treatment plants across the East of England and from patients with clinical disease at a major hospital in the same region. We confirmed that C. difficile from 65 patients were highly diverse and that most cases were not linked to other active cases in the hospital. In total, 186 C. difficile isolates were isolated from effluent water obtained from 18 municipal treatment plants at the point of release into the environment. Whole genome comparisons of clinical and environmental isolates demonstrated highly related populations, and confirmed extensive release of toxigenic C. difficile into surface waters. An analysis based on multilocus sequence types (STs) identified 19 distinct STs in the clinical collection and 38 STs in the wastewater collection, with 13 of 44 STs common to both clinical and wastewater collections. Furthermore, we identified five pairs of highly similar isolates (≤2 SNPs different in the core genome) in clinical and wastewater collections. Strategies to control community acquisition should consider the need for bacterial control of treated wastewater.

Molecular characterization, toxin detection and resistance testing of human clinical Clostridium difficile isolates from Lebanon

Clostridium (Clostridioides) difficile is the main cause for nosocomial diarrhoea in industrialised nations. Epidemiologic data on the pathogen's occurrence in other world regions are still scarce. In this context we characterized with phenotypic and molecular genetic methods C. difficile isolates stemming from hospitalised patients with diarrhoea in Lebanon. From 129 stool samples of symptomatic patients at a tertiary care University hospital in Lebanon, a total of 107 C. difficile strains were cultivated and underwent ribotyping, toxin gene detection and antibiotic resistance testing. Ribotype 014 (RT014, 16.8%) predominated, followed by RT002 (9.3%), RT106 (8.4%) and RT070 (6.5%). Binary toxin gene-positive isolates (RT023, RT078 and RT126) were rarely detected and RT027 was absent. Interestingly, within one isolate only the toxin A gene (tcdA) was detected. Multiple-locus variable-number tandem repeat analysis (MLVA) revealed strong strain diversity in most RTs. The isolates were sensitive to metronidazole and vancomycin, and only a small proportion of strains displayed resistance against moxifloxacin, rifampicin, and clarithromycin (5.6%, 1.9%, and 2.8%), respectively. The data indicate that the genetic strain composition of Lebanese strains differs markedly from the situation seen in Europe and North America. Especially the epidemic RTs seen in the latter regions were almost absent in Lebanon. Interestingly, most strains showed almost no resistance to commonly used antibiotics that are suspected to play a major role in the development of C. difficile infection, despite frequent use of these antibiotics in Lebanon. Thus, the role of antimicrobial resistance as a major driving force for infection development remains uncertain in this area.

Clostridium difficile Infections: A Global Overview of Drug Sensitivity and Resistance Mechanisms

Clostridium difficile (C. difficile) is the most prevalent causative pathogen of healthcare-associated diarrhea. Notably, over the past 10 years, the number of Clostridium difficile outbreaks has increased with the rate of morbidity and mortality. The occurrence and spread of C. difficile strains that are resistant to multiple antimicrobial drugs complicate prevention as well as potential treatment options. Most C. difficile isolates are still susceptible to metronidazole and vancomycin. Incidences of C. difficile resistance to other antimicrobial drugs have also been reported. Most of the antibiotics correlated with C. difficile infection (CDI), such as ampicillin, amoxicillin, cephalosporins, clindamycin, and fluoroquinolones, continue to be associated with the highest risk for CDI. Still, the detailed mechanism of resistance to metronidazole or vancomycin is not clear. Alternation in the target sites of the antibiotics is the main mechanism of erythromycin, fluoroquinolone, and rifamycin resistance in C. difficile. In this review, different antimicrobial agents are discussed and C. difficile resistance patterns and their mechanism of survival are summarized.

Surveillance of antibiotic resistance among common Clostridium difficile ribotypes in Hong Kong

Incidence of Clostridium difficile infection (CDI) is rapidly increasing and it poses a major health burden globally. However, data regarding the epidemiology of CDI in Asia are limited. We aimed to characterize the antimicrobial susceptibility patterns of common ribotypes of toxigenic C. difficile in Hong Kong. Fifty-three PCR ribotypes were identified among 284 toxigenic C. difficile clinical isolates. The five most prevalent ribotypes were 002 (13%), 017 (12%), 014 (10%), 012 (9.2%), and 020 (9.5%). All tested C. difficile strains remained susceptible to metronidazole, vancomycin, meropenem and piperacillin/tazobactam, but highly resistant to cephalosporins. Of the fluoroquinolones, highest resistance to ciprofloxacin was observed (99%), followed by levofloxacin (43%) and moxifloxacin (23%). The two newly emerged PCR ribotypes, 017 and 002, demonstrated high levels of co-resistance towards clindamycin, tetracycline, erythromycin and moxifloxacin. PCR ribotypes 017 and 002 with multi-drug resistance are rapidly emerging and continuous surveillance is important to monitor the epidemiology of C. difficile to prevent outbreaks of CDI.

Molecular epidemiology and antimicrobial susceptibility of Clostridium difficile isolated from hospitals during a 4-year period in China

OBJECTIVE

The aim of this study was to perform molecular characterization for and determine the antimicrobial susceptibility profiles of Clostridium difficile collected from hospitals during a 4-year period (2009-2013) in China.

METHODS

Strains of toxigenic C. difficile were isolated from patients with diarrhoea, and this was followed by typing using multilocus sequence typing (MLST) and testing for susceptibility to 10 antimicrobials by using the E-test. The mechanisms of resistance to moxifloxacin, erythromycin, clindamycin and tetracycline were investigated by PCR.

RESULTS

A total of 405 non-duplicate toxigenic C. difficile isolates were identified, while 31 sequence types (STs) were identified. A predominant type, ST-54, accounted for 20.2 % of the STs, followed by ST-35 (16.3 %) and ST-37 (13.6 %). We found that 6.2 % of the isolates were binary toxin genes-positive, and 83.7 % of these belonged to ST-5. All of the isolates demonstrated 100 % susceptibility to first-line Clostridium difficile infection (CDI) therapies (i.e. metronidazole and vancomycin), while the resistance rates varied for the other antibiotics tested. Two hundred and ninety three (72.3 %) isolates were susceptible to moxifloxacin. All 112 moxifloxacin-resistant isolates had mutations resulting in an amino acid substitution in gryA and/or gyrB. The ermB gene was detected in 86.7 % (241/278) of the erythromycin- and clindamycin-resistant isolates, while the tetM gene was present in 97.1 % (85/87) of the tetracycline-resistant isolates.

CONCLUSION

MLST typing revealed a wide variety of STs causing CDI, while ST-54 was the most common ST. All of the isolates were susceptible to metronidazole and vancomycin, while the resistance rates varied for the other antibiotics tested. There were no changes in the trends for the STs and antibiotic susceptibility profiles over 4 years.

Community-acquired infection with hypervirulent Clostridium difficile isolates that carry different toxin and antibiotic resistance loci: a case report

Background

Clostridium difficile infection (CDI) leads to the onset of antibiotic-associated diarrhea (AAD) and a wide range of gastrointestinal pathologies. Currently, CDI is one of the most important opportunistic infections at the intrahospital level and an exponential increase in community-acquired infections has been reported. Herein, we evaluated the relationships (at phylogenetic and genetic population structure levels), as well as the molecular toxigenic and antibiotic resistance profiles of a set of isolates established from a case of community acquired-CDI.

Case presentation

A 30-year-old woman with no history of hospitalization who was exposed to antibiotics (ampicillin/sulbactam and metronidazole) after a cat-bite wound was presented. The patient had a continuous episode of diarrhea; a stool sample was then collected and community acquired-CDI was confirmed by molecular tests and in vitro culture. Seven isolates were established and subsequently subjected to: (i) Multilocus sequence typing, all isolates belonging to ST-1 (associated with hypervirulent strain (027/BI/NAP1); (ii) description of their toxigenic profile: two of the isolates (Gcol.49 and Gcol.91) were positive for the genes coding for the major toxins (tcdA and tcdB) and their negative regulator (tcdC). All isolates were positive for the cdtB gene encoding one of the binary toxin subunits, while only two (Gcol.51 and Gcol.52) were positive for cdtA; and (iii) identification of antibiotic resistance molecular markers, where there was no difference in gyrA or gyrB gene polymorphisms (related to quinolone resistance), but rather at loci presence/absence, being just one isolate negative, whereas the others showed a differential presence of the tet, ermB and Tn916 regions. The former was associated with resistance to tetracycline and the other two for erythromycin/clindamycin.

Conclusions

This case represents the first report of community acquired-CDI in Colombia associated with hypervirulent strains and shows that isolates obtained from a single patient can carry different toxin and antibiotic resistance loci.

Electronic supplementary material

The online version of this article (10.1186/s13099-017-0212-y) contains supplementary material, which is available to authorized users.

Double-Serine Fluoroquinolone Resistance Mutations Advance Major International Clones and Lineages of Various Multi-Drug Resistant Bacteria

The major international sequence types/lineages of methicillin-resistant Staphylococcus aureus (MRSA), extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae and ESBL-producing E. coli were demonstrated to have been advanced by favorable fitness balance associated with high-level resistance to fluoroquinolones. The paper shows that favorable fitness in the major STs/lineages of these pathogens was principally attained by the capacity of evolving mutations in the fluoroquinolone-binding serine residues of both the DNA gyrase and topoisomerase IV enzymes. The available information on fitness balance incurred by individual and various combinations of mutations in the enzymes is reviewed in multiple species. Moreover, strong circumstantial evidence is presented that major STs/lineages of other multi-drug resistant bacteria, primarily vancomycin-resistant Enterococcus faecium (VRE), emerged by a similar mechanism. The reason(s) why the major ST/lineage strains of various pathogens proved more adept at evolving favorable mutations than most isolates of the same species remains to be elucidated.

Identification and Antimicrobial Susceptibility Testing of Anaerobic Bacteria: Rubik's Cube of Clinical Microbiology?

Anaerobic bacteria have pivotal roles in the microbiota of humans and they are significant infectious agents involved in many pathological processes, both in immunocompetent and immunocompromised individuals. Their isolation, cultivation and correct identification differs significantly from the workup of aerobic species, although the use of new technologies (e.g., matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, whole genome sequencing) changed anaerobic diagnostics dramatically. In the past, antimicrobial susceptibility of these microorganisms showed predictable patterns and empirical therapy could be safely administered but recently a steady and clear increase in the resistance for several important drugs (β-lactams, clindamycin) has been observed worldwide. For this reason, antimicrobial susceptibility testing of anaerobic isolates for surveillance purposes or otherwise is of paramount importance but the availability of these testing methods is usually limited. In this present review, our aim was to give an overview of the methods currently available for the identification (using phenotypic characteristics, biochemical testing, gas-liquid chromatography, MALDI-TOF MS and WGS) and antimicrobial susceptibility testing (agar dilution, broth microdilution, disk diffusion, gradient tests, automated systems, phenotypic and molecular resistance detection techniques) of anaerobes, when should these methods be used and what are the recent developments in resistance patterns of anaerobic bacteria.

Rifaximin-resistant Clostridium difficile strains isolated from symptomatic patients

BACKGROUND

Rifaximin has been proposed as an alternative treatment for specific cases of Clostridium difficile infection (CDI) and intestinal decontamination. Rifaximin-resistant C. difficile has occasionally been reported. Antibiotic susceptibility testing relies on anaerobic agar dilution (reference method), which is cumbersome and not routinely used. There is no commercial test for detection of resistance to rifaximin.

OBJECTIVES

To assess resistance to rifaximin by C. difficile and to evaluate the correlation between the results of the rifampicin E-test and susceptibility to rifaximin.

METHODS

We compared the in vitro susceptibility of clinical CDI isolates to rifaximin over a 6-month period using the agar dilution method with susceptibility to rifampicin using the E-test. All isolates were characterized using PCR-ribotyping. Clinical data were recorded prospectively.

RESULTS

We recovered 276 consecutive C. difficile isolates and found that 32.2% of episodes were caused by rifaximin-resistant strains. The MICs for rifaximin ranged from <0.0009-256 mg/L, with a geometric mean (GM) of 0.256 mg/L, an MIC_50/90 of 0.015/>256 mg/L. Rifaximin and rifampicin MICs were comparable, and all strains classed as resistant by agar dilution were correctly classified as resistant by E-test. The most common ribotypes were 001 (37.2%), 078/126 (14.3%), and 014 (12.0%). Ribotype 001 exhibited the highest MICs for rifaximin.

CONCLUSIONS

Resistance to rifaximin was common; resistance rates were higher in ribotype 001 strains. Susceptibility to rifaximin determined by agar dilution correlated with susceptibility to rifampicin determined using the E-test, including rifaximin-resistant strains. Our results suggest that the rifampicin E-test is a valid method for the prediction of rifaximin-resistant C. difficile.

Susceptibilities of clinical Clostridium difficile isolates to antimicrobials: a systematic review and meta-analysis of studies since 1970

OBJECTIVES

Although exposure to antibiotics can cause Clostridium difficile infection, certain antibiotics are used to treat C. difficile. Measurements of antimicrobial C. difficile activity could help to identify antibiotic risk and emergent resistance. Here, we describe publication patterns relating to C. difficile susceptibilities and estimate minimum inhibitory concentrations (MIC) for antibiotic classes in the published literature between January 1970 and June 2014.

METHODS

We queried PUBMED and EMBASE for studies reporting antibiotic C. difficile MIC in English or French. We used mixed-effects models to obtain pooled estimates of antibiotic class median MIC (MIC₅₀), 90th percentile of MIC (MIC₉₀), and MIC₉₀:MIC₅₀ ratio.

RESULTS

Our search identified 182 articles that met our inclusion criteria, of which 27 were retained for meta-analysis. Aminoglycosides (MIC₅₀ 120 mg/L, 95% CI 62-250), 3rd (MIC₅₀ 75 mg/L, 95% CI 39-130) and 2nd generation cephalosporins (MIC₅₀ 64 mg/L, 95% CI 27-140) had the least C. difficile activity. Rifamycins (MIC₅₀ 0.034 mg/L, 95% CI 0.012-0.099) and tetracyclines (MIC₅₀ 0.29 mg/L, 95% CI 0.054-1.7) had the highest level of activity. The activity of 3rd generation cephalosporins was more than three times lower than that of 1st generation agents (MIC₅₀ 19 mg/L, 95% CI 7.0-54). Time-trends in MIC₅₀ were increasing for carbapenems (70% increase per 10 years) while decreasing for tetracyclines (51% decrease per 10 years).

CONCLUSIONS

We found a 3500-fold variation in antibiotic C. difficile MIC₅₀, with aminoglycosides as the least active agents and rifamycins as the most active. Further research is needed to determine how in vitro measures can help assess patient C. difficile risk and guide antimicrobial stewardship.

Comparative Genome Analysis and Global Phylogeny of the Toxin Variant Clostridium difficile PCR Ribotype 017 Reveals the Evolution of Two Independent Sublineages

The diarrheal pathogen Clostridium difficile consists of at least six distinct evolutionary lineages. The RT017 lineage is anomalous, as strains only express toxin B, compared to strains from other lineages that produce toxins A and B and, occasionally, binary toxin. Historically, RT017 initially was reported in Asia but now has been reported worldwide. We used whole-genome sequencing and phylogenetic analysis to investigate the patterns of global spread and population structure of 277 RT017 isolates from animal and human origins from six continents, isolated between 1990 and 2013. We reveal two distinct evenly split sublineages (SL1 and SL2) of C. difficile RT017 that contain multiple independent clonal expansions. All 24 animal isolates were contained within SL1 along with human isolates, suggesting potential transmission between animals and humans. Genetic analyses revealed an overrepresentation of antibiotic resistance genes. Phylogeographic analyses show a North American origin for RT017, as has been found for the recently emerged epidemic RT027 lineage. Despite having only one toxin, RT017 strains have evolved in parallel from at least two independent sources and can readily transmit between continents.

The incidence and drug resistance of Clostridium difficile infection in Mainland China: a systematic review and meta-analysis

It has been widely reported that the incidence and severity of Clostridium difficile infection (CDI) have increased dramatically in North America and Europe. However, little is known about CDI in Mainland China. In this study, we aimed to investigate the incidence of CDI and the main epidemic and drug-resistant strains of C. difficile in Mainland China through meta-analysis of related studies published after the year 2010. A total of 51 eligible studies were included. The pooled incidence of toxigenic C. difficile among patients with diarrhoea was 14% (95% CI = 12–16%). In Mainland China, ST-37 and ST-3 were the most prevalent strains; fortunately, hypervirulent strains, such as ST-1 (BI/NAP1/027) and ST-11 (RT 078), have only occurred sporadically to date. The rates of C. difficile resistance to ciprofloxacin (98.3%; 95% CI = 96.9–99.7%), clindamycin (81.7%; 95% CI = 76.1–87.3%) and erythromycin (80.2%; 95% CI = 73.5–86.9%) are higher than in other counties; however, none of the C. difficile isolates reported in Mainland China were resistant to metronidazole (n/N = 0/960), vancomycin (n/N = 0/960), tigecycline (n/N = 0/41) or piperacillin/tazobactam(n/N = 0/288).

Molecular Epidemiology and Antimicrobial Susceptibility of Clostridium difficile Isolates from a University Teaching Hospital in China

While the developed world has seen a significant increase in the number of scientific articles on Clostridium difficile infection (CDI), the developing world still lags behind on this subject due to limited laboratory capacity, low awareness, and limited surveillance of this problem. As such, CDI is considered a neglected but potentially huge problem in developing countries. The major aim of this study was to systemically evaluate the utility of several molecular typing tools for CDI, including their relevance in epidemiological studies in developing countries such as China. A total of 116 non-repetitive toxigenic C. difficile isolates from Chinese patients, were studied. The isolates comprised 83 (71.6%) A+B+CDT- isolates, 27 (23.3%) A-B+CDT- isolates, and 6 (5.1%) A+B+CDT+ isolates. Typing methods evaluated included multilocus variable-number tandem-repeat analysis, PCR ribotyping, multilocus sequence typing, and sequencing of slpA and tcdC genes, which identified 113, 30, 22, 18, and 8 genotypes each and exhibited discriminatory powers of 0.999, 0.916, 0.907, 0.883, and 0.765, respectively. Compared to A+B+ strains, A-B+ strains exhibited higher prevalence of drug resistance to clindamycin, erythromycin, levofloxacin, rifampicin, rifaximin, and tetracycline. Furthermore, drug resistance rates of strains with different PCR ribotypes differed, supporting the importance of molecular typing in management and control of CDI. Based on our earlier suggestion to improve the diagnostic laboratory capacity of CDI in developing countries, setting up efficient surveillance programs complemented by relevant molecular typing methods is warranted.

Rapid detection of ermB gene in Clostridium difficile by loop-mediated isothermal amplification

Macrolide-lincosamide-streptogramin B resistance in Clostridium difficile is mostly due to the ermB resistance determinant. Here, we describe a sensitive and rapid molecular method to detect ermB in C. difficile to contribute to the wider epidemiological study. Five sets of loop-mediated isothermal amplification (LAMP) primers were designed and optimized for rapid detection of ermB. The specificity and sensitivity of the primers for ermB were detected, and the ermB LAMP assay was compared to conventional PCR with 80 clinical isolates of C. difficile. Real-time monitoring of turbidity and chromogenic reaction were used to determine negative and positive results. A total of 26 pathogenic bacterial strains of different species were found to be negative for ermB, which indicated the high specificity of the primers. ermB was detected in 78.8 % (63/80) of the clinical isolates by both LAMP and conventional PCR. The detection limit of LAMP was 36.1  pg DNA μl- 1 and its sensitivity was 10-fold greater than that of conventional PCR. This study is the first report regarding the development and application of the LAMP assay for detection of the ermB gene in C. difficile strains. The developed LAMP method is sensitive, specific and provides a user-friendly visual approach for the rapid detection of ermB-bearing C. difficile.

Genomic Epidemiology of a Protracted Hospital Outbreak Caused by a Toxin A-Negative Clostridium difficile Sublineage PCR Ribotype 017 Strain in London, England

Clostridium difficile remains the leading cause of nosocomial diarrhea worldwide, which is largely considered to be due to the production of two potent toxins: TcdA and TcdB. However, PCR ribotype (RT) 017, one of five clonal lineages of human virulent C. difficile, lacks TcdA expression but causes widespread disease. Whole-genome sequencing was applied to 35 isolates from hospitalized patients with C. difficile infection (CDI) and two environmental ward isolates in London, England. The phylogenetic analysis of single nucleotide polymorphisms (SNPs) revealed a clonal cluster of temporally variable isolates from a single hospital ward at University Hospital Lewisham (UHL) that were distinct from other London hospital isolates. De novo assembled genomes revealed a 49-kbp putative conjugative transposon exclusive to this hospital clonal cluster which would not be revealed by current typing methodologies. This study identified three sublineages of C. difficile RT017 that are circulating in London. Similar to the notorious RT027 lineage, which has caused global outbreaks of CDI since 2001, the lineage of toxin-defective RT017 strains appears to be continually evolving. By utilization of WGS technologies to identify SNPs and the evolution of clonal strains, the transmission of outbreaks caused by near-identical isolates can be retraced and identified.

Doxycycline and Tigecycline: Two Friendly Drugs with a Low Association with Clostridium Difficile Infection

Clostridium difficile infection (CDI) is known to be associated with prior exposure to many classes of antibiotics. Standard therapy for CDI (i.e., metronidazole and vancomycin) is associated with high recurrence rates. Although tetracycline derivatives such as tetracycline, doxycycline or tigecycline are not the standard therapeutic choices for CDI, they may serve as an alternative or a component of combination therapy. Previous tetracycline or doxycycline usage had been shown to have less association with CDI development. Tigecycline, a broad-spectrum glycylcycline with potency against many gram-positive or gram-negative pathogens, had been successfully used to treat severe or refractory CDI. The in vitro susceptibility of C. difficile clinical isolates to tigecycline in many studies showed low minimal inhibitory concentrations. Tigecycline can suppress in vitro toxin production in both historical and hypervirulent C. difficile strains and reduce spore production in a dose-dependent manner. Tetracycline compounds such as doxycycline, minocycline, and tigecycline possess anti-inflammatory properties that are independent of their antibiotic activity and may contribute to their therapeutic effect for CDI. Although clinical data are limited, doxycycline is less likely to induce CDI, and tigecycline can be considered one of the therapeutic choices for severe or refractory CDI.

Antimicrobial heteroresistance: an emerging field in need of clarity

"Heteroresistance" describes a phenomenon where subpopulations of seemingly isogenic bacteria exhibit a range of susceptibilities to a particular antibiotic. Unfortunately, a lack of standard methods to determine heteroresistance has led to inappropriate use of this term. Heteroresistance has been recognized since at least 1947 and occurs in Gram-positive and Gram-negative bacteria. Its clinical relevance may be considerable, since more resistant subpopulations may be selected during antimicrobial therapy. However, the use of nonstandard methods to define heteroresistance, which are costly and involve considerable labor and resources, precludes evaluating the clinical magnitude and severity of this phenomenon. We review the available literature on antibiotic heteroresistance and propose recommendations for definitions and determination criteria for heteroresistant bacteria. This will help in assessing the global clinical impact of heteroresistance and developing uniform guidelines for improved therapeutic outcomes.

In vitro activity of surotomycin against contemporary clinical isolates of toxigenic Clostridium difficile strains obtained in Spain

OBJECTIVES

Clostridium difficile infection (CDI) is the leading cause of hospital-acquired diarrhoea in developed countries. Metronidazole and vancomycin are the mainstay of treatment, although they are associated with treatment failure and recurrence. Novel agents have emerged to address these shortcomings. We investigated the in vitro activity of a novel agent, surotomycin (formerly CB-183,315), and seven other antimicrobial agents against clinical C. difficile isolates.

METHODS

Antimicrobial susceptibility to surotomycin, fidaxomicin, metronidazole, vancomycin, clindamycin, rifaximin, moxifloxacin and tigecycline was determined for 100 contemporary clinical isolates of C. difficile collected in 2013. MICs were determined by agar dilution according to CLSI procedures. In addition, 10 strains with reduced susceptibility to metronidazole (n = 6) and vancomycin (n = 4) were also tested. Strains were PCR ribotyped.

RESULTS

The MICs of surotomycin for the 100 isolates ranged from ≤0.06 to 2 mg/L, with a geometric mean (GM) of 0.31 mg/L and an MIC50/90 of 0.25/0.5 mg/L. The MIC range of surotomycin was 0.25-1 mg/L (GM = 0.45 mg/L) for isolates with reduced metronidazole susceptibility and 0.125-0.5 mg/L (GM = 0.25 mg/L) for isolates with reduced vancomycin susceptibility. The three most common ribotypes were 001 (31.0%), 014/020 (17.0%) and 078/126 (17.0%). Ribotype 014/020 exhibited the lowest MICs of surotomycin (GM = 0.22 mg/L); the highest MICs were for ribotype 078/126 (GM = 0.72 mg/L).

CONCLUSIONS

Surotomycin exhibited potent in vitro activity against all the isolates tested, including those with elevated metronidazole and vancomycin MICs. The potential role of this agent in the treatment of CDI requires further clinical evaluation.

Comparison of Clostridium difficile isolates from individuals with recurrent and single episode of infection

PURPOSE

Recurrent Clostridium difficile infection (CDI) is an increasing problem, yet reasons for this are poorly understood. Attention has been paid to the role of strain, with conflicting association of ribotype 027 and recurrences.

METHODS

Stool samples and medical records data were collected from 60 patients: 27 with recurrent CDI and 33 with single episode CDI. C. difficile was isolated and ribotyped, and minimum inhibitory concentrations of metronidazole and vancomycin were determined by Etest.

RESULTS

Twenty-seven ribotypes were identified, but only four (027, 014 and two internally designated strains) were found in more than one patient. Ribotype 027 predominated and was significantly over-represented in the recurrent CDI group (70%) versus the single episode CDI group (30%) (P = 0.004). Female gender and the presence of ribotype 027 were significantly associated with recurrent CDI in the multivariable model. Metronidazole MICs for recurrent isolates were significantly higher compared to single episode isolates (P ≤ 0.024). A general linear model indicated that the difference in MIC was associated with ribotype 027 (P = 0.0023), not whether the isolate was from recurrent or single episode disease (P = 0.25).

CONCLUSIONS

Ribotype 027 was associated with recurrent disease. While there was no difference in the prevalence of metronidazole resistance, isolates from recurrent CDI patients had significantly higher metronidazole MICs, because of higher MICs in ribotype 027. This study provides further support to the clinical importance of ribotype 027 and raises questions about the potential impact of decreased metronidazole susceptibility on the pathophysiology of recurrent CDI.