Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2022

The elusiveness and significance of clinical isolates of cysteine-requiring Escherichia coli (82412)

Christopher J McIver 1 2 , Sabrina Koentgen 2 , Ryan Pratama 1 , Peter C Taylor 1 2 , Stephen M Riordan 3 4 , Chinmoy Mukerjee 1 2 , Robert Stevens 1 , Georgina Hold 2
  1. Microbiology Department NSW HP, St George Hospital, Sydney, NSW, Australia
  2. School of Medical Sciences, University of NSW, Sydney, NSW, Australia
  3. Gastrointestinal and Liver Unit, Prince of Wales Hospital, Randwick , NSW, Australia
  4. UNSW Medicine and Health, University of New South Wales, Sydney, NSW, Australia

Strains of Escherichia coli requiring cysteine (cys-) for optimal growth are commonly isolated from clinical specimens, especially in urinary tract infections amongst elderly patients with a chronic and debilitating co-morbidity known to be related to increased blood levels of sulphur-containing compounds. Sub-optimal growth on conventional media deficient in cysteine compromises laboratory methods for their detection, identification and susceptibility testing - potentially contributing to an under-appreciation as a pathogen.

Previous studies have showed E. coli cys- to be non-clonal and lack the phenotypic expression of virulence factors commonly associated with prototrophic uropathogenic strains including type-1 fimbriation, haemolysin production, and motility.1 These strains were also shown to be more sensitive to normal human serum than prototrophic strains.1 Further, rates of increased resistance to specific classes of antibiotics have not been reported.2

A random selection of contemporary E. coli cys- isolates (76 urine and 9 blood) was collected for a future investigation into possible association with changes to the intestinal microbiome or disease. We report the characterisation of these strains including identification using the MALDI-TOF MS (Bruker) and PCR detection of E.coli specific alr gene; susceptibility to 10 antibiotics commonly used to treat E. coli infections; the prevalence of three virulence genes commonly associated with uropathgenic strains including PAI, fimH, papAH; and the production of biofilm.

There was complete agreement between the MALDI-TOF MS and the PCR detection of E.coli specific alr for E. coli cys-isolates. Strains were not overtly different to contemporary septic or uropathogenic strains in their antibiotic susceptibility pattern, the prevalence of the virulence genes tested and biofilm formation.3

These observations account for infections occurring in susceptible individuals with decreased resistance due to preserved bacterial virulence. We speculate that the availability of cysteine or related compounds in vivo and the potential metabolic stress exerted by changes to the intestinal microbiome in disease can be conducive to selection and survival. This is the focus of further studies.

  1. 1. McIver C.J. and Tapsall J.W. In vitro susceptibilities of clinical isolates of cysteine-requiring Escherichia coli to 12 antimicrobial agents. Antimicrobial Agents and Chemotherapy 1991; 35:995-97
  2. 2. McIver C.J. and Tapsall J.W. Virulence and other phenotypic characteristics of urinary isolates of cysteine-requiring Escherichia coli. J Med Microbiol 1995; 42:39-42
  3. 3. Johnson J.R. and Stell A.L. Extended virulence genotypes of Escherichia coli strains from patients with urosepsis in relation to phylogeny and host compromise. J Infect Dis 2000; 181:261-72