Research Articles (Medical Microbiology)


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    Association between fluoroquinolone resistance and MRSA genotype in Alexandria, Egypt
    (Nature, 2021-02-19) Alseqely, Mustafa; Newton-Foot, Mae; Khalil, Amal; El-Nakeeb, Mostafa; Whitelaw, Andrew; Abouelfetouh, Alaa
    Antimicrobial stewardship isn’t strictly observed in most Egyptian hospitals, raising antibiotic resistance. Epidemiology of Egyptian MRSA isolates, or associations with resistance to other antibiotics remain largely unknown. We identified MRSA genotypes in Alexandria Main University Hospital (AMUH) and investigated rates of moxifloxacin resistance, an alternative MRSA treatment, among different genotypes. Antibiotic susceptibility of 72 MRSA clinical isolates collected in 2015 from AMUH was determined by disc diffusion and broth microdilution. spa- and Staphylococcal Cassette Chromosome mec (SCCmec) typing were performed; with multi-locus sequence typing conducted on isolates representing major genotypes. Resistance to moxifloxacin, levofloxacin and ciprofloxacin were 69%, 78% and 96%, respectively. spa type t037 (57%) was commonest, followed by t127 (12.5%), t267 (8%) and t688 (6%). SCCmec III predominated (57%), all of these were moxifloxacin resistant and 97.6% t037 (ST241). SCCmec IV, IV E and V represented 15%, 7% and 11% of the isolates, respectively, 79% of these were moxifloxacin susceptible and of different spa types. t127 (ST-1) was associated with SCCmec V in 56% of the isolates, mostly moxifloxacin susceptible. Moxifloxacin resistance was high, most resistant isolates belonged to t037 and SCCmec III, suggesting local dissemination and antibiotic pressure. We recommend caution in treating MRSA infections with moxifloxacin.
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    Comparison of commercial assays and two-step approach to detect Clostridioides difficile in South Africa
    (AOSIS, 2022-09) Singh, Sarishna; Newton-Foot, Mae; Nel, Pieter; Pienaar, Colette
    Background: Clostridioides difficile is the number one cause of hospital-acquired diarrhoea. Accurate diagnosis of C. difficile is of utmost importance as it guides patient management and infection control practices. Studies evaluating the performance of commercially available nucleic acid amplification tests (NAATs) versus algorithms are lacking in resource-limited settings. Objective: This study assessed the performance of three commercially available tests and a two-step approach for the diagnosis of C. difficile infection using toxigenic culture (TC) as the gold standard. Methods: Two hundred and twenty-three non-duplicate loose stool samples were submitted to the National Health Laboratory Service Microbiology Laboratory at Tygerberg Hospital, Cape Town, South Africa, from October 2017 to October 2018. The samples were tested in parallel using the C. DIFF QUIK CHEK COMPLETE enzyme immunoassay (EIA) and two NAATs (Xpert C. difficile and BD MAX Cdiff), and the results were compared to TC. The performance of a two-step approach consisting of the C. DIFF QUIK CHEK COMPLETE followed by the Xpert C. difficile was also determined. Results: Of 223 faecal specimens tested, 37 (16.6%) were TC-positive. The sensitivity and specificity of the C. DIFF QUIK CHEK COMPLETE were 54.1% and 98.9%; Xpert C. difficile, 86.4% and 96.8%; BD MAX Cdiff, 89.2% and 96.8%; and two-step approach, 89.2% and 96.2%. Conclusion: The C. DIFF QUIK CHEK COMPLETE, in a two-step approach with the Xpert C. difficile, performed similarly to the NAATs on their own and offer advantages in terms of cost and workflow in low-resource settings.
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    The association between pathogen factors and clinical outcomes in patients with Staphylococcus aureus bacteraemia in a tertiary hospital, Cape Town
    (Elsevier, 2019-11) Abdulgader, Shima M.; van Rijswijk, Amike; Whitelaw, Andrew; Newton-Foot, Mae
    Background: Staphylococcus aureus is a serious pathogen, able to cause life-threatening infections such as bacteraemia. The association between S. aureus microbial characteristics and clinical outcomes is under-investigated in African settings. This study aimed to determine the molecular epidemiology and virulence characteristics of S. aureus isolates from bacteraemic patients at Tygerberg Hospital, South Africa, and to investigate the associations between pathogen characteristics and clinical outcomes. Methods: This study included 199 S. aureus isolates collected from blood cultures between February 2015 and March 2017. Methicillin resistance was determined using disc diffusion and all resistant isolates were further characterized by staphylococcal cassette chromosome mec (SCCmec) typing. Genotyping was done using spa and agr typing, and agr functionality was assessed using the phenotypic δ-haemolysin assay. Logistic regression models were performed to describe the associations between strain characteristics and the clinical outcomes methicillin resistance, in-hospital mortality, and length of stay (LOS). Results: Of the 199 S. aureus isolates collected, 27% were MRSA, and the overall crude in-hospital mortality rate was 29%. Seventy-three different spa types were identified, including seven new types. Agr I was the most common type, in 99 (49.7%) isolates, followed by agr II, III, and IV in 57 (28.6%), 37 (18.6%), and six (3%) isolates, respectively. Agr dysfunctionality was observed in 25 (13%) isolates, mostly belonging to spa-clonal complex (CC) 012. Methicillin resistance was significantly associated with hospital-acquired infection (odds ratio (OR) 4.77, 95% confidence interval (CI) 2.09-10.87). A significant increase in mortality was observed with increasing age (OR 7.48, 95% CI 2.82-19.8) and having a hospital-acquired infection (OR 2.26, 95% CI 1.12-4.55). S. aureus strains with a functional agr system showed an association with longer duration of stay (OR 1.66, 95% CI 0.93-2.99). Conclusions: We report the lowest MRSA prevalence at Tygerberg Hospital for the past 10 years, and agr dysfunctionality was shown to be driven by a certain genotype, spa-CC012. Despite the limited available clinical data, the study provided insights into associations between S. aureus epidemiology and agr-related virulence characteristics, and clinical outcomes.
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    Clonal expansion of colistin-resistant Acinetobacter baumannii isolates in Cape Town, South Africa
    (Elsevier, 2020-02) Snyman, Yolandi; Whitelaw, Andrew Christopher; Reuter, Sandra; Dramowski, Angela; Maloba, Motlatji Reratilwe Bonnie; Newton-Foot, Mae
    Objectives: To describe colistin-resistant Acinetobacter baumannii isolates in Cape Town, South Africa. Methods: A. baumannii isolates identified on Vitek 2 Advanced Expert System were collected from Tygerberg Hospital referral laboratory between 2016 and 2017. Colistin resistance was confirmed using broth microdilution and SensiTest. mcr-1-5 were detected using PCR and strain typing was performed by rep-PCR. Whole genome sequencing (WGS) was performed on a subset of isolates to identify chromosomal colistin resistance mechanisms and strain diversity using multilocus sequence typing (MLST) and pairwise single nucleotide polymorphism analyses. Results: Twenty-six colistin-resistant and six colistin-susceptible A. baumannii were collected separately based on Vitek susceptibility; 20/26 (77%) were confirmed colistin-resistant by broth microdilution. Four colistin-resistant isolates were isolated in 2016 and 16 in 2017, from five healthcare facilities. Thirteen colistin-resistant isolates and eight colistin-susceptible isolates were identical by rep-PCR and MLST (ST1), all from patients admitted to a tertiary hospital during 2017. The remaining colistin-resistant isolates were unrelated. Conclusions: An increase in colistin-resistant A. baumannii isolates from a tertiary hospital in 2017 appears to be clonal expansion of an emerging colistin-resistant strain. This strain was not detected in 2016 or from other hospitals. Identical colistin-susceptible isolates were also isolated, suggesting relatively recent acquisition of colistin resistance.
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    Association between clinical and environmental factors and the gut microbiota profiles in young South African children
    (Nature Research (part of Springer Nature), 2021) Nel Van Zyl, Kristien; Whitelaw, Andrew C.; Hesseling, Anneke C.; Seddon, James A.; Demers, Anne‑Marie; Newton‑Foot, Mae
    ENGLISH ABSTRACT: Differences in the microbiota in populations over age and geographical locations complicate cross-study comparisons, and it is therefore essential to describe the baseline or control microbiota in each population. This includes the determination of the influence of demographic, clinical and environmental factors on the microbiota in a setting, and elucidates possible bias introduced by these factors, prior to further investigations. Little is known about the microbiota of children in South Africa after infancy. We provide a detailed description of the gut microbiota profiles of children from urban Cape Town and describe the influences of various clinical and environmental factors in different age groups during the first 5 years of life. Prevotella was the most common genus identified in the participants, and after infancy, the gut bacteria were dominated by Firmicutes and Bacteroidetes. In this setting, children exposed to antibiotics and indoor cooking fires were at the most risk for dysbiosis, showing significant losses in gut bacterial diversity.