Defining the phylogenetics and resistome of the major Clostridioides difficile ribotypes circulating in Australia.

Clostridioides difficile infection (CDI) remains a significant public health threat globally. New interventions to treat CDI rely on an understanding of the evolution and epidemiology of circulating strains. Here we provide longitudinal genomic data on strain diversity, transmission dynamics and antimicrobial resistance (AMR) of C. difficile ribotypes (RTs) 014/020 (n=169), 002 (n=77) and 056 (n=36), the three most prominent C. difficile strains causing CDI in Australia. Genome scrutiny showed that AMR was uncommon in these lineages, with resistance-conferring alleles present in only 15/169 RT014/020 strains (8.9 %), 1/36 RT056 strains (2.78 %) and none of 77 RT002 strains. Notably, ~90 % of strains were resistant to MLSB agents in vitro, but only ~5.9 % harboured known resistance alleles, highlighting an incongruence between AMR genotype and phenotype. Core genome analyses revealed all three RTs contained genetically heterogeneous strain populations with limited evidence of clonal transmission between CDI cases. The average number of pairwise core genome SNP (cgSNP) differences within each RT group ranged from 23.3 (RT056, ST34, n=36) to 115.6 (RT002, ST8, n=77) and 315.9 (RT014/020, STs 2, 13, 14, 49, n=169). Just 19 clonal groups (encompassing 40 isolates), defined as isolates differing by ≤2 cgSNPs, were identified across all three RTs (RT014/020, n=14; RT002, n=3; RT056, n=2). Of these clonal groups, 63 % (12/19) comprised isolates from the same Australian State and 37 % (7/19) comprised isolates from different States. The low number of plausible transmission events found for these major RTs (and previously documented populations in animal and environmental sources/reservoirs) points to widespread and persistent community sources of diverse C. difficile strains as opposed to ongoing nationwide healthcare outbreaks dominated by a single clone. Together, these data provide new insights into the evolution of major lineages causing CDI in Australia and highlight the urgent need for enhanced surveillance, and for public health interventions to move beyond the healthcare setting and into a One Health paradigm to effectively combat this complex pathogen.

Candida auris PCR for high-throughput infection control screening.

Candida auris has significant implications for infection control due to its multidrug resistance and spread in healthcare settings. Current culture-based screening methods are laborious and risk muco-cutaneous colonisation of laboratory staff. We describe the adaptation of a published real-time PCR for the identification of C. auris in skin swabs for high-throughput infection control screening. Two published primer and probe sets were analysed utilising serial 10-fold dilutions of 15 C. auris strains to assess the PCR limit of detection. One primer and probe set was compatible with our laboratory workflow and was selected for further development yielding a limit of detection of 1 colony forming unit per reaction. Non-C. auris isolates as well as routine skin swabs (n = 100) were tested by culture and PCR to assess specificity, where no cross-reactivity was detected. Skin swabs from a proven C. auris case (n = 6) were all both culture positive and PCR positive, while surveillance swabs from close contacts (n = 46) were all both culture negative and PCR negative. Finally, the use of a lysis buffer comprising 4 m guanidinium thiocyanate rendered swab-equivalent quantities of C. auris non-viable, providing assurance of the safety benefit of PCR over culture. The development of a PCR assay for high-throughput infection control screening is a promising method for rapid detection of C. auris with utility in an outbreak setting. LAY SUMMARY: Candida auris, a difficult to treat yeast-like fungus, has spread through healthcare facilities globally, posing a serious threat to the health of patients. We evaluated a PCR-based method suitable for screening large numbers of patient samples to rapidly and accurately detect C. auris.

Evaluation of a custom Sensititre YeastOne plate for susceptibility testing of isavuconazole and other antifungals against clinically relevant yeast and mould species in three Australian diagnostic mycology laboratories.

This study aimed to validate the performance of the custom formulated Sensititre YeastOne One (SYO) microdilution plate which includes isavuconazole (AUSNMRC1) to perform susceptibility testing on clinically relevant yeast and mould species across three Australian reference laboratories. The minimum inhibitory concentration (MIC) results were compared with the IVD approved SYO YO10 microdilution plate and isavuconazole gradient strips. A total of 127 isolates were tested on both the YO10 and AUSNMRC1 plates. The overall essential agreement (EA) and categorical agreement (CA) for the eight common drugs was 99.9% and 98.8%, respectively. The EA was 96.9% for the isavuconazole MICs obtained using the AUSNMRC1 plate and gradient strip. The MIC results for all nine antifungals on the AUSNMRC1 panel were highly reproducible for all quality control and reference strains and the overall EA and CA for 45 clinical strains tested across all three participating laboratories were >93% and 94.1%, respectively. These findings demonstrate the SYO AUSNMRC1 plate provides a commercial means to determine isavuconazole MICs by broth microdilution testing.

Antimicrobial resistance surveillance of Clostridioides difficile in Australia, 2015-18.

BACKGROUND: Clostridioides difficile was listed as an urgent antimicrobial resistance (AMR) threat in a report by the CDC in 2019. AMR drives the evolution of C. difficile and facilitates its emergence and spread. The C. difficile Antimicrobial Resistance Surveillance (CDARS) study is nationwide longitudinal surveillance of C. difficile infection (CDI) in Australia. OBJECTIVES: To determine the antimicrobial susceptibility of C. difficile isolated in Australia between 2015 and 2018. METHODS: A total of 1091 strains of C. difficile were collected over a 3 year period by a network of 10 diagnostic microbiology laboratories in five Australian states. These strains were tested for their susceptibility to nine antimicrobials using the CLSI agar incorporation method. RESULTS: All strains were susceptible to metronidazole, fidaxomicin, rifaximin and amoxicillin/clavulanate and low numbers of resistant strains were observed for meropenem (0.1%; 1/1091), moxifloxacin (3.5%; 38/1091) and vancomycin (5.7%; 62/1091). Resistance to clindamycin was common (85.2%; 929/1091), followed by resistance to ceftriaxone (18.8%; 205/1091). The in vitro activity of fidaxomicin [geometric mean MIC (GM) = 0.101 mg/L] was superior to that of vancomycin (1.700 mg/L) and metronidazole (0.229 mg/L). The prevalence of MDR C. difficile, as defined by resistance to ≥3 antimicrobial classes, was low (1.7%; 19/1091). CONCLUSIONS: The majority of C. difficile isolated in Australia did not show reduced susceptibility to antimicrobials recommended for treatment of CDI (vancomycin, metronidazole and fidaxomicin). Resistance to carbapenems and fluoroquinolones was low and MDR was uncommon; however, clindamycin resistance was frequent. One fluoroquinolone-resistant ribotype 027 strain was detected.

Laboratory-Based Surveillance of Clostridium difficile Infection in Australian Health Care and Community Settings, 2013 to 2018.

In the early 2000s, a binary toxin (CDT)-producing strain of Clostridium difficile, ribotype 027 (RT027), caused extensive outbreaks of diarrheal disease in North America and Europe. This strain has not become established in Australia, and there is a markedly different repertoire of circulating strains there compared to other regions of the world. The C. difficile Antimicrobial Resistance Surveillance (CDARS) study is a nationwide longitudinal surveillance study of C. difficile infection (CDI) in Australia. Here, we describe the molecular epidemiology of CDI in Australian health care and community settings over the first 5 years of the study, 2013 to 2018. Between 2013 and 2018, 10 diagnostic microbiology laboratories from five states in Australia participated in the CDARS study. From each of five states, one private (representing community) and one public (representing hospitals) laboratory submitted isolates of C. difficile or PCR-positive stool samples during two collection periods per year, February-March (summer/autumn) and August-September (winter/spring). C. difficile was characterized by toxin gene profiling and ribotyping. A total of 1,523 isolates of C. difficile were studied. PCR ribotyping yielded 203 different RTs, the most prevalent being RT014/020 (n = 449; 29.5%). The epidemic CDT+ RT027 (n = 2) and RT078 (n = 6), and the recently described RT251 (n = 10) and RT244 (n = 6) were not common, while RT126 (n = 17) was the most prevalent CDT+ type. A heterogeneous C. difficile population was identified. C. difficile RT014/020 was the most prevalent type found in humans with CDI. Continued surveillance of CDI in Australia remains critical for the detection of emerging strain lineages.

Detection and identification of dermatophyte fungi in clinical samples using a commercial multiplex tandem PCR assay.

We evaluated the performance of a commercial multiplex tandem polymerase chain reaction (PCR) for detection of dermatophytes and other fungi in skin and nail specimens by (1) testing a range of fungal and bacterial reference cultures, (2) retrospectively testing a set of skin and nail specimens with known microscopy and culture results, and (3) prospectively testing skin and nail specimens in parallel to microscopy and culture. The AusDiagnostics Dermatophytes and Other Fungi assay accurately detected and identified a range of common dermatophytes to species, species complex or genus level, as well as Candida, Aspergillus and Scopulariopsis spp. It was unable to detect uncommon dermatophytes such as Nannizzia fulva (previously Microsporum fulvum), and Paraphyton cookei (previously Microsporum cookei). PCR identified a dermatophyte in 25.9% of prospective specimens which were culture negative. Sensitivity, specificity, positive predictive value, and negative predictive value were highest where microscopy and PCR results were combined, versus microscopy and culture combined, which highlights the significant contribution of microscopy in the diagnostic pathway. This assay has the potential to reduce the workload and results turnaround time associated with culturing and identification of dermatophytes, although microscopy remains important.

Cost-effective implementation of a custom MALDI-TOF library for the identification of South Australian Nocardia isolates.

Mass spectrometry plays a significant role in the routine identification of micro-organisms and provides the ability to incorporate newly found pathogens into the database in a cost-effective fashion. This work aims to highlight the role of mass spectrometry through improved identification of Nocardia species in a diagnostic clinical microbiology laboratory. Prior to this study we constructed a custom in-house matrix-assisted laser desorption ionisation-time of flight (MALDI-TOF) library for Nocardia isolates consisting of isolates identified to the species level. Subsequently over a period of 5 years, we isolated a further 153 Nocardia clinical isolates, of which 91.5% (140/153) were identified correctly with the custom MALDI-TOF library and 8.5% (13/153) needed further molecular sequencing for final identification. We estimate our cost savings to be approximately 9,800 AUD overall with this implementation over the study period. Continued expansion and maintenance of this custom library will eventually result in little or no 16S ribosomal DNA sequencing needed for specific identification of Nocardia isolates.

Mycobacterial inactivation protein extraction protocol for matrix-assisted laser desorption ionization time-of-flight characterization of clinical isolates.

Background: Rapid identification of mycobacteria has been made possible with matrix assisted laser desorption ionization time-of-flight (MALDI-TOF) in recent years. Working with high concentrations of mycobacteria in a PC-3 containment facility makes MALDI-TOF cumbersome and costly. Therefore removing the inactivated isolate's protein extract from the PC-3 facility is needed for efficient identification in a routine PC-2 laboratory. Methods: This work describes a novel chemical and mechanical disruption protein extraction method, which provides reliable MALDI-TOF results from solid and liquid media, while ensuring laboratory safety. Results: When compared to sequencing results, 93.9% of the clinical isolates were identified in LJ media and 89% of the clinical isolates were identified in MGIT media. Conclusion: The MIPE protocol produces a high quality protein extract with improved isolate identification without compromising result turn-around-times or laboratory safety.

Surveillance for antimicrobial resistance in Australian isolates of Clostridium difficile, 2013-14.

OBJECTIVES: The objective of this study was to determine the activity of fidaxomicin and comparator antimicrobials against Clostridium difficile isolated from patients with C. difficile infection (CDI) in Australian hospitals and in the community. METHODS: One private and one public laboratory from five states in Australia submitted a total of 474 isolates/PCR-positive stool samples during three collection periods in August-September 2013 (n = 175), February-March 2014 (n = 134) and August-September 2014 (n = 165). Isolate identification was confirmed by selective culture for C. difficile and a proportion of isolates from each state were characterized by PCR for toxin genes and PCR ribotyping. MICs of fidaxomicin and eight comparator antimicrobials were determined for all isolates using agar methodology. RESULTS: Site collection yielded 440 isolates of C. difficile and PCR revealed a heterogeneous strain population comprising 37 different PCR ribotypes (RTs), 95% of which were positive for tcdA and tcdB (A+B+). The most common RTs were 014 (29.8%) and 002 (15.9%). Epidemic RT 027 was not identified; however, small numbers of virulent RTs 078 and 244 were found. Resistance to vancomycin, metronidazole and fidaxomicin was not detected and resistance to moxifloxacin was very low (3.4%). Fidaxomicin showed potent in vitro activity against all 440 isolates (MIC50/MIC90 0.03/0.12 mg/L) and was superior to metronidazole (MIC50/MIC90 0.25/0.5 mg/L) and vancomycin (MIC50/MIC90 1/2 mg/L). CONCLUSIONS: These data confirm the potent in vitro activity of fidaxomicin against C. difficile. Moreover, this study provides an important baseline for ongoing long-term surveillance of antimicrobial resistance and prospective tracking of prominent and emerging strain types.

First human case of fatal Halicephalobus gingivalis meningoencephalitis in Australia.

Halicephalobus gingivalis (previously Micronema deletrix) is a free-living nematode known to cause opportunistic infections, mainly in horses. Human infections are very rare, but all cases described to date involved fatal meningoencephalitis. Here we report the first case of H. gingivalis infection in an Australian human patient, confirmed by nematode morphology and sequencing of ribosomal DNA. The implications of this case are discussed, particularly, the need to evaluate real-time PCR as a diagnostic tool.

Emergence of class 1 integron-associated GES-5 and GES-5-like extended-spectrum beta-lactamases in clinical isolates of Pseudomonas aeruginosa in South Africa.

Several different Guiana extended-spectrum (GES) enzymes have been described occurring in Enterobacteriaceae and Pseudomonas aeruginosa worldwide. Polymerase chain reaction and gene sequencing analysis confirmed bla(GES) genes identified in three P. aeruginosa clinical isolates from South Africa as bla(GES-5) and bla(GES-5)-like, respectively. Compared with GES-1, the GES-5-like protein exhibited an A21E amino acid change, a novel mutation not previously described in this family. Integron structures identified upstream from the bla(GES-5) and bla(GES-5)-like genes were found to be identical to bla(GES-2)-carrying integrons described previously from the same geographical region. These findings confirm the establishment and persistence of integron-associated GES-type extended-spectrum beta-lactamases (ESBLs) in the South African nosocomial environment. This study describes the first isolation of class 1 integron-associated bla(GES-5) and the emergence of a novel GES-5-like ESBL in South Africa.

Rapid detection and sequence-specific differentiation of extended-spectrum beta-lactamase GES-2 from Pseudomonas aeruginosa by use of a real-time PCR assay.

The LightCycler was compared to nested PCR for the detection of bla(GES/IBC) genes from 100 Pseudomonas aeruginosa clinical isolates. The real-time PCR assay detected a bla(GES/IBC) gene product from 83 isolates, exhibiting a sensitivity and specificity of 94.3 and 100% respectively, compared to nested PCR and DNA sequencing.

Sequence-selective recognition of extended-spectrum beta-lactamase GES-2 by a competitive, peptide nucleic acid-based multiplex PCR assay.

Extended-spectrum beta-lactamases (ESBLs) in Pseudomonas aeruginosa, such as GES-2, which compromises the efficacy of imipenem, tend to be geographically restricted. The CC-to-AA base pair substitution at positions 493 and 494 of the bla(GES-2)-coding region distinguishes this ESBL from bla(GES-1) and the bla(IBC)-type genes, making it an ideal target for the development of a novel sequence-specific, peptide nucleic acid (PNA)-based multiplex PCR detection method. By using two primer pairs in conjunction with a PNA probe, this method provided an accurate means of identification of bla(GES-2) compared to standard PCR and gene sequencing techniques when it was used to test 100 P. aeruginosa clinical isolates as well as previously published, well-described control strains encompassing all presently known genes in the bla(GES-IBC) ESBL family. This novel method has the potential to be used in large-scale, cost-effective screening programs for specific or geographically restricted ESBLs.

Molecular detection of GES-2 extended spectrum Beta-lactamase producing Pseudomonas aeruginosa in Pretoria, South Africa.

Screening for and detection of the novel extended spectrum Beta-lactamase (ESBL), GES-2 produced by Pseudomonas aeruginosa remains a problem in the clinical microbiology laboratory. This study aimed to compare the normally used ESBL screening agent ceftazidime, with molecular detection, to demonstrate the presence of GES-2 ESBL production in clinical isolates of P. aeruginosa. Ceftazidime was found unreliable as an ESBL screening agent, with a specificity of 34.4%, when National Committee for Clinical Laboratory Standards resistance criteria for P. aeruginosa were employed. An improved PCR detection method was devised, that amplified a 371 bp segment of bla(GES-2). This should lead to more cost-effective DNA sequencing and sequence interpretation in the laboratory.

Integrons and beta-lactamases--a novel perspective on resistance.

The understanding of microbial resistance to the beta-lactam class of antibiotics in the form of beta-lactamases has come a long way since the early discoveries of narrow-spectrum penicillinases. Integron-borne beta-lactamases co-occurring with a wide array of non-beta-lactam resistance genes, particularly pose an increasing threat to the nosocomial environment, giving rise to multi-drug resistant microbes with complex resistance patterns. Selection of potent beta-lactamases through the use of non-beta-lactam agents may be possible through integron-mediated resistance. It has become imperative that we should continuously strive to understand these complex mechanisms of antimicrobial resistance, not only to overcome them, but to avoid them from evolving further.