A Retrospective Analysis of Treatment and Clinical Outcomes among Patients with Methicillin-Susceptible Staphylococcus aureus Bloodstream Isolates Possessing Detectable mecA by a Commercial PCR Assay Compared to Patients with Methicillin-Resistant Staphylococcus aureus Bloodstream Isolates

Molecular Characterization of Clinical Rel Mutations and Consequences for Resistance Expression and Fitness in Staphylococcus aureus

The stringent response (SR) is a universal stress response that acts as a global regulator of bacterial physiology and virulence, and is a contributor to antibiotic tolerance and resistance. In most bacteria, the SR is controlled by a bifunctional enzyme, Rel, which both synthesizes and hydrolyzes the alarmone (p)ppGpp via two distinct catalytic domains. The balance between these antagonistic activities is fine-tuned to the needs of the cell and, in a "relaxed" state, the hydrolase activity of Rel dominates. We have previously shown that two single amino acid substitutions in Rel (that were identified in clinical isolates from persistent infections) confer elevated basal concentrations of (p)ppGpp and consequent multidrug tolerance in Staphylococcus aureus. Here, we explore the molecular details of how these mutations bring about this increase in cellular (p)ppGpp and investigate the wider cellular consequences in terms of resistance expression, resistance development, and bacterial fitness. Using enzyme assays, we show that both these mutations drastically reduce the hydrolase activity of Rel, thereby shifting the balance of Rel activity in favor of (p)ppGpp synthesis. We also demonstrate that these mutations induce high-level, homogeneous expression of β-lactam resistance and confer a significant fitness advantage in the presence of bactericidal antibiotics (but a fitness cost in the absence of antibiotic). In contrast, these mutations do not appear to accelerate the emergence of endogenous resistance mutations in vitro. Overall, our findings reveal the complex nature of Rel regulation and the multifaceted implications of clinical Rel mutations in terms of antibiotic efficacy and bacteria survival.

Antimicrobial resistance determinants are associated with Staphylococcus aureus bacteraemia and adaptation to the healthcare environment: a bacterial genome-wide association study

Staphylococcus aureus is a major bacterial pathogen in humans, and a dominant cause of severe bloodstream infections. Globally, antimicrobial resistance (AMR) in S. aureus remains challenging. While human risk factors for infection have been defined, contradictory evidence exists for the role of bacterial genomic variation in S. aureus disease. To investigate the contribution of bacterial lineage and genomic variation to the development of bloodstream infection, we undertook a genome-wide association study comparing bacteria from 1017 individuals with bacteraemia to 984 adults with asymptomatic S. aureus nasal carriage. Within 984 carriage isolates, we also compared healthcare-associated (HA) carriage with community-associated (CA) carriage. All major global lineages were represented in both bacteraemia and carriage, with no evidence for different infection rates. However, kmers tagging trimethoprim resistance-conferring mutation F99Y in dfrB were significantly associated with bacteraemia-vs-carriage (P=10-8.9-10-9.3). Pooling variation within genes, bacteraemia-vs-carriage was associated with the presence of mecA (HMP=10-5.3) as well as the presence of SCCmec (HMP=10-4.4). Among S. aureus carriers, no lineages were associated with HA-vs-CA carriage. However, we found a novel signal of HA-vs-CA carriage in the foldase protein prsA, where kmers representing conserved sequence allele were associated with CA carriage (P=10-7.1-10-19.4), while in gyrA, a ciprofloxacin resistance-conferring mutation, L84S, was associated with HA carriage (P=10-7.2). In an extensive study of S. aureus bacteraemia and nasal carriage in the UK, we found strong evidence that all S. aureus lineages are equally capable of causing bloodstream infection, and of being carried in the healthcare environment. Genomic variation in the foldase protein prsA is a novel genomic marker of healthcare origin in S. aureus but was not associated with bacteraemia. AMR determinants were associated with both bacteraemia and healthcare-associated carriage, suggesting that AMR increases the propensity not only to survive in healthcare environments, but also to cause invasive disease.

Resistance-Guided Treatment of Gonorrhea: A Prospective Clinical Study

BACKGROUND

Novel treatment strategies to slow the continued emergence and spread of antimicrobial resistance in Neisseria gonorrhoeae are urgently needed. A molecular assay that predicts in vitro ciprofloxacin susceptibility is now available but has not been systematically studied in human infections.

METHODS

Using a genotypic polymerase chain reaction assay to determine the status of the N. gonorrhoeae gyrase subunit A serine 91 codon, we conducted a multisite prospective clinical study of the efficacy of a single oral dose of ciprofloxacin 500 mg in patients with culture-positive gonorrhea. Follow-up specimens for culture were collected to determine microbiological cure 5-10 days post-treatment.

RESULTS

Of the 106 subjects possessing culture-positive infections with wild-type gyrA serine N. gonorrhoeae genotype, the efficacy of single-dose oral ciprofloxacin treatment in the per-protocol population was 100% (95% 1-sided confidence interval, 97.5-100%).

CONCLUSIONS

Resistance-guided treatment of N. gonorrhoeae infections with single-dose oral ciprofloxacin was highly efficacious. The widespread introduction and scale-up of gyrA serine 91 genotyping in N. gonorrhoeae infections could have substantial medical and public health benefits in settings where the majority of gonococcal infections are ciprofloxacin susceptible.

CLINICAL TRIALS REGISTRATION

NCT02961751.

Defining persistent Staphylococcus aureus bacteraemia: secondary analysis of a prospective cohort study

BACKGROUND

Staphylococcus aureus persistent bacteraemia is only vaguely defined and the effect of different durations of bacteraemia on mortality is not well established. Our primary aim was to analyse mortality according to duration of bacteraemia and to derive a clinically relevant definition for persistent bacteraemia.

METHODS

We did a secondary analysis of a prospective observational cohort study at 17 European centres (nine in the UK, six in Spain, and two in Germany), with recruitment between Jan 1, 2013, and April 30, 2015. Adult patients who were consecutively hospitalised with monomicrobial S aureus bacteraemia were included. Patients were excluded if no follow-up blood culture was taken, if the first follow-up blood-culture was after 7 days, or if active antibiotic therapy was started more than 3 days after first blood culture. The primary outcome was 90-day mortality. Univariable and time-dependent multivariable Cox regression analysis were used to assess predictors of mortality. Duration of bacteraemia was defined as bacteraemic days under active antibiotic therapy counting the first day as day 1.

FINDINGS

Of 1588 individuals assessed for eligibility, 987 were included (median age 65 years [IQR 51-75]; 625 [63%] male). Death within 90 days occurred in 273 (28%) patients. Patients with more than 1 day of bacteraemia (315 [32%]) had higher Charlson comorbidity index and sequential organ failure assessment scores and a longer interval from first symptom to first blood culture. Crude 90-day mortality increased from 22% (148 of 672) with 1 day of bacteraemia, to 39% (85 of 218) with 2-4 days, 43% (30 of 69) with 5-7 days, and 36% (10 of 28) with more than 7 days of bacteraemia. Metastatic infections developed in 39 (6%) of 672 patients with 1 day of bacteraemia versus 40 (13%) of 315 patients if bacteraemia lasted for at least 2 days. The second day of bacteraemia had the highest HR and earliest cutoff significantly associated with mortality (adjusted hazard ratio 1·93, 95% CI 1·51-2·46; p<0·0001).

INTERPRETATION

We suggest redefining the cutoff duration for persistent bacteraemia as 2 days or more despite active antibiotic therapy. Our results favour follow-up blood cultures after 24 h for early identification of all patients with increased risk of death and metastatic infection.

FUNDING

None.

Using genomics to understand meticillin- and vancomycin-resistant Staphylococcus aureus infections

Resistance to meticillin and vancomycin in Staphylococcus aureus significantly complicates the management of severe infections like bacteraemia, endocarditis or osteomyelitis. Here, we review the molecular mechanisms and genomic epidemiology of resistance to these agents, with a focus on how genomics has provided insights into the emergence and evolution of major meticillin-resistant S. aureus clones. We also provide insights on the use of bacterial whole-genome sequencing to inform management of S. aureus infections and for control of transmission at the hospital and in the community.

Fatal sepsis caused by mecA-positive oxacillin-susceptible Staphylococcus aureus: First report in a tertiary hospital of southern Brazil

mecA-positive oxacillin phenotypically susceptible Staphylococcus aureus (OS-MRSA) is increasingly reported worldwide. This bacterium poses a therapeutic threat, as it can be misidentified as an oxacillin-susceptible organism by phenotypic methods that are routinely used in the majority of clinical microbiology laboratories. Herein, we report the first case of fatal sepsis in a 43-year-old female patient caused by an OS-MRSA SCCmec type IVa/ST1/CC1 in a tertiary hospital in southern Brazil, which highlights the difficulties involved in diagnosing this bacterium. Blood cultures and phenotypic susceptibility tests on admission yielded a penicillin-resistant S. aureus. Although vancomycin therapy was initiated, this antibacterial was replaced by oxacillin, based on the susceptibility result. However, the clinical conditions of the patient deteriorated rapidly evolving to fatal septic shock. Clinical microbiology laboratories should consider the use of additional tests to accurately distinguish between various antimicrobial phenotypes of S. aureus.