Prevalence of the ermB Gene in Clostridium difficile Strains Isolated at a University Teaching Hospital from 1987 through 1998

Antimicrobial resistance progression in the United Kingdom: A temporal comparison of Clostridioides difficile antimicrobial susceptibilities

OBJECTIVES

Clostridioides difficile (CD) is widely reported as one of the most prevalent multi-drug resistant (MDR) organisms. Assessment of temporally disparate isolate collections can give valuable epidemiological data to further the understanding of antimicrobial resistance progression.

METHODS

A collection of 75 CD isolates (1980-86) was characterised by PCR ribotyping, cell cytotoxicity assay and susceptibility testing with a panel of 16 antimicrobials and compared to a modern surveillance collection consisting of 416 UK isolates (2012-2016). Agar-incorporation was performed to ascertain susceptibility data for vancomycin, metronidazole, rifampicin, fidaxomicin, moxifloxacin, clindamycin, imipenem, chloramphenicol, tigecycline, linezolid, ciprofloxacin, piperacillin/tazobactam, ceftriaxone, amoxicillin, tetracycline and erythromycin. Genomes were obtained using Illumina HiSeq3000 sequencing and assembled using CLC Genomics Workbench. Resistance genes were identified using the Comprehensive Antibiotic Research Database's Resistance Gene Identifier and ResFinder3.0.

RESULTS

Twenty-six known and one previously unobserved ribotype (RT) were detected. RT015 and RT020 dominated; 21.3% and 17.3%, respectively. Three moxifloxacin resistant (16-32 mg/L) RT027 isolates were recovered, pre-dating the earliest reports of this phenotype/genotype. Phenotypic resistance was observed to moxifloxacin (9.3% of isolates), ciprofloxacin (100%), erythromycin (17.3%), tetracycline (9.3%), linezolid and chloramphenicol (4.0%). Phenotypic comparisons with modern strains revealed increasing minimum inhibitory concentrations (MIC), with MIC₅₀ elevations of one doubling-dilution for the majority of compounds, excluding clindamycin and imipenem. Moxifloxacin MIC₉₀ comparisons revealed a two doubling-dilution increase between temporal isolate collections. Historical genomes revealed twenty different resistance determinants, including ermB (8.0% of isolates), tetM (9.3%), cfr (5.3%) and gyrA substitution Thr-82→Ile (9.3%). Seventeen isolates (22.7%) were resistant to ≥3 compounds (MDR), demonstrating ten different combinations. Intra-RT diversity was observed.

CONCLUSIONS

Antibiotic resistance in CD has increased since the early 1980s, across the majority of classes. Moxifloxacin resistance determinants may pre-date its introduction.

Phenotypic characterisation of Clostridium difficile PCR ribotype 251, an emerging multi-locus sequence type clade 2 strain in Australia

The global emergence of epidemic Clostridium difficile PCR ribotype (RT) 027 prompted enhanced surveillance of emerging strains. Recently, there have been reports of severe C. difficile infection in Australia caused by an unusual strain of C. difficile not seen previously. Identified as PCR RT251, this strain produces toxins A (TcdA) and B (TcdB), as well as binary toxin (CDT), and shares a common phylogenetic lineage with RT027. In this study, C. difficile RT251 strains were sourced from various geographical locations and potential virulence factors were evaluated and compared to that of control strains, CD630, VPI10463 and R20291 invitro. C. difficile RT251 strains were motile, germinated and sporulated efficiently, despite producing significantly less TcdA and TcdB compared to all control strains. Genomic analyses revealed three multi-locus sequence types (MLSTs 188, 231 and 365) with four to five loci variants compared to RT027 (ST1) all MLST clade 2. C. difficile RT251 strains were susceptible to metronidazole, vancomycin and moxifloxacin, a fluoroquinolone antimicrobial to which RT027 strains are often resistant. Further studies using whole-genome sequencing are required to determine additional virulence factors that may contribute to the pathogenicity of C. difficile RT251 strains.

The impact of antimicrobial resistance on induction, transmission and treatment of Clostridium difficile infection

Clostridium difficile infection (CDI) of the gastrointestinal (GI) tract is a potentially life-threatening disease that has surpassed multi-drug-resistant Staphylococcus aureus as the commonest antimicrobial-resistant organism associated with healthcare1. This obligate anaerobic spore-forming Gram-positive bacillus colonises the GI tract and its numbers increase after disruption of the commensal GI microbiota often induced by exposure to antimicrobial agents2. Paradoxically, the disease that may follow its outgrowth necessitates further antimicrobial treatment. Already a major challenge to infection prevention and control strategies, there are indications that C. difficile is developing further resistance to currently used antimicrobial agents.

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.

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.

Antimicrobial Resistance and Reduced Susceptibility in Clostridium difficile: Potential Consequences for Induction, Treatment, and Recurrence of C. difficile Infection

Clostridium difficile infection (CDI) remains a substantial burden on healthcare systems and is likely to remain so given our reliance on antimicrobial therapies to treat bacterial infections, especially in an aging population in whom multiple co-morbidities are common. Antimicrobial agents are a key component in the aetiology of CDI, both in the establishment of the infection and also in its treatment. The purpose of this review is to summarise the role of antimicrobial agents in primary and recurrent CDI; assessing why certain antimicrobial classes may predispose to the induction of CDI according to a balance between antimicrobial activity against the gut microflora and C. difficile. Considering these aspects of CDI is important in both the prevention of the infection and in the development of new antimicrobial treatments.

Clostridium difficile and the disease it causes

Clostridium difficile is a spore-forming, toxin-producing, anaerobic bacterium abundant in soils and water. Frequent and early colonization of the human intestinal flora is common and often asymptomatic. Antimicrobials given commonly disrupt the intestinal microflora and through proliferation in colon and production of toxin A and B it precipitates C. difficile infection (CDI). The enterocytic detachment and bowel inflammation provoke C. difficile-associated diarrhoea (CDAD) sometimes developing into severe pseudomembranous colitis (PMC) and paralytic ileus. Infection is acquired from an endogenous source or from spores in the environment, most easily facilitated during hospital stay. In the elderly, comorbidity, hospitalization and antimicrobial treatment present as major risk factors and the slow recolonization of the normal flora likely responsible for single or multiple recurrences of CDI (25-50%) post therapy. The key procedure for diagnosis is toxin detection from stool specimens and sometimes in combination with culture to increase sensitivity. In mild cases stopping the offending antimicrobial will lead to resolution (25%) but standard therapy still consist of either oral metronidazole or vancomycin. Alternative agents are presently being developed and fidaxomicin, as well as nitrothiazolide are promising. Furthermore, host factors like low antitoxin A levels in serum relates to increased risk of recurrence and small numbers of patients have received immunoglobulin with good results. An immunogenic toxoid vaccine has been developed and human colostrum rich in specific secretory Ig A also support the future use of immunotherapy. Today we experience a tenfold increase of CDI incidence in the western world and both epidemics and therapeutic failure of metronidazole is contributing to morbidity and mortality. The current epidemic of the C. difficile strain NAP1/027 emerging in 2002 in Canada and the USA has now spread to most parts of Europe and virulence factors like high toxin production and sporulation challenge the therapeutic situation and cause great concern among infection control workers. Excessive use of modern fluoroquinolones is thought to play an important role in facilitating this epidemic since NAP1/027 was shown to have acquired moxifloxacin resistance compared to historical strains of the same genotype. Both the current epidemic like this and other local outbreaks from resistant or virulent strains warrant culture to be routinely performed enabling susceptibility testing and typing of the pathogen. Genotyping is most commonly done today by pulse-field gel electrophoresis (PFGE) or PCR ribotyping but multilocus variable-number tandem-repeat analysis (MLVA) seems promising. Epidemiological surveillance using all these tools will help us to better understand the global spread of C. difficile.

Colitis due to Clostridium difficile toxins: underdiagnosed, highly virulent, and nosocomial

Clostridium difficile colitis is a major complication of antibiotic therapy. Antibiotics cause a reduction in bacteria that normally reside in the colon. If an antibiotic-treated patient ingests C. difficile bacteria, this organism may proliferate in the colon because it is resistant to most antibiotics and because it does not have to compete with the normal bacteria for nutrients. If the C. difficile organism has the gene for toxin production, the toxin can produce a colitis. In addition to antibiotics, other proposed risk factors for development of C. difficile colitis include advanced age, contact with infected patients and with their health care providers, impaired immune function, suppression of gastric acid secretion by a proton pump inhibitor, and postpyloric tube feeding. Many of the risk factors become simultaneously focused on patients admitted to the hospital. The incidence of C. difficile disease has been rising, and strains have become more virulent. In some forms of the disease, the patient doesn't have diarrhea, and in such patients C. difficile can be deadly but difficult to diagnose. The standard treatment, with metronidazole or vancomycin, fails to work in up to 25% of patients with the fulminant form of colitis. Since C. difficile causes only 20% of cases of antibiotic-associated diarrhea, a specific test is needed to diagnose this organism. Toxigenic cultureis highly specific but not available at most institutions. The tests that are available--enzyme-linked immunosorbent assay and fecal cytotoxicity assay--have high false-negative rates, even in patients with severe clinical disease, creating a diagnostic dilemma. The only proven way to reduce the risk of C. difficile disease is implementation of an antibiotic management program in conjunction with enhanced infection control procedures.