Matthew V. N. O'Sullivan

Antibiotic Choice May Not Explain Poorer Outcomes in Patients With Staphylococcus aureus Bacteremia and High Vancomycin Minimum Inhibitory Concentrations

BACKGROUND There are concerns about reduced efficacy of vancomycin in patients with Staphylococcus aureus bacteremia (SAB), especially when the minimum inhibitory concentration (MIC) nears the upper limit of the susceptible range. METHODS We examined the relationship between antibiotic treatment, 30-day mortality, and microbiologic parameters in a large Australasian cohort of patients with SAB. RESULTS We assessed 532 patients with SAB from 8 hospitals. All patients with methicillin-resistant S. aureus (MRSA) bacteremia were treated with vancomycin, and patients with methicillin-susceptible S. aureus (MSSA) bacteremia received either flucloxacillin or vancomycin. Increasing vancomycin MIC was associated with increased mortality in vancomycin-treated patients. However, even in patients with MSSA bacteremia treated with flucloxacillin, mortality was also higher if the vancomycin Etest MIC of their isolate was >1.5 μg/mL, compared with those with lower MIC isolates (26.8% vs 12.2%; P < .001). After adjustment in a multivariate model, age, hospital-onset SAB and vancomycin MIC were independently associated with mortality, but methicillin resistance and antibiotic choice were not. CONCLUSIONS We have confirmed an association between higher vancomycin MIC and increased mortality in patients with SAB, but surprisingly this relationship was not related to the antibiotic treatment received, suggesting that the use of vancomycin per se is not responsible for the poorer outcome.

Proton Nuclear Magnetic Resonance—Based Metabonomics for Rapid Diagnosis of Meningitis and Ventriculitis

BACKGROUND Reduction of mortality associated with bacterial meningitis and postsurgical cerebral ventriculitis is dependent on early diagnosis and institution of appropriate therapy. Metabonomics rapidly defines metabolic profiles of biological fluids through the use of high-throughput analytical techniques combined with statistical pattern recognition tools. METHODS Proton nuclear magnetic resonance (1H NMR)-based metabonomics was applied to (1) lumbar cerebrospinal fluid samples collected prospectively from a cohort of patients with bacterial, fungal, or viral meningitis and from control subjects without neurological disease and (2) ventricular cerebrospinal fluid samples from patients with ventriculitis associated with an external ventricular drain and from control subjects. 1H NMR spectra were analyzed by the unsupervised statistical method of principal components analysis. RESULTS Metabonomic analysis clearly distinguished patients with bacterial or fungal meningitis (11 patients) from patients with viral meningitis (12) and control subjects (27) and clearly distinguished patients with postsurgical ventriculitis (5) from postsurgical control subjects (10). Metabolites of microbial and host origin that were responsible for class separation were determined. Metabonomic data also correlated with the onset and course of infection in a patient with 2 episodes of bacterial ventriculitis and with response to therapy in another patient with cryptococcal meningitis. CONCLUSIONS Metabonomic analysis is rapid, requires minimal sample processing, and is not targeted to specific microbial pathogens, making the platform potentially suitable for use in the diagnostic laboratory. This pilot study indicates that metabonomic analysis of cerebrospinal fluid is feasible and a potentially more powerful diagnostic tool than conventional rapid laboratory indicators for distinguishing bacterial from viral meningitis and for monitoring therapy. This should have important implications for early management, reduced empirical use of antibiotics, and treatment duration.

Combination of Vancomycin and β-Lactam Therapy for Methicillin-Resistant Staphylococcus aureus Bacteremia: A Pilot Multicenter Randomized Controlled Trial

BACKGROUND In vitro laboratory and animal studies demonstrate a synergistic role for the combination of vancomycin and antistaphylococcal β-lactams for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia. Prospective clinical data are lacking. METHODS In this open-label, multicenter, clinical trial, adults with MRSA bacteremia received vancomycin 1.5 g intravenously twice daily and were randomly assigned (1:1) to receive intravenous flucloxacillin 2 g every 6 hours for 7 days (combination group) or no additional therapy (standard therapy group). Participants were stratified by hospital and randomized in permuted blocks of variable size. Randomization codes were kept in sealed, sequentially numbered, opaque envelopes. The primary outcome was the duration of MRSA bacteremia in days. RESULTS We randomly assigned 60 patients to receive vancomycin (n = 29), or vancomycin plus flucloxacillin (n = 31). The mean duration of bacteremia was 3.00 days in the standard therapy group and 1.94 days in the combination group. According to a negative binomial model, the mean time to resolution of bacteremia in the combination group was 65% (95% confidence interval, 41%-102%; P = .06) that in the standard therapy group. There was no difference in the secondary end points of 28- and 90-day mortality, metastatic infection, nephrotoxicity, or hepatotoxicity. CONCLUSIONS Combining an antistaphylococcal β-lactam with vancomycin may shorten the duration of MRSA bacteremia. Further trials with a larger sample size and objective clinically relevant end points are warranted. Australian New Zealand Clinical Trials Registry: ACTRN12610000940077 (www.anzctr.org.au).

Influence of Disk Separation Distance on Accuracy of the Disk Approximation Test for Detection of Inducible Clindamycin Resistance in Staphylococcus spp.

ABSTRACT We undertook this study to assess the accuracy of the clindamycin-erythromycin disk approximation test (D-test) for detection of inducible clindamycin resistance in Staphylococcus spp. One hundred sixty-three Staphylococcus aureus and 68 coagulase-negative Staphylococcus (CoNS) spp. which were erythromycin nonsusceptible but clindamycin susceptible were tested using the D-test performed at both 15-mm and 22-mm disk separations and compared with genotyping as the “gold standard.” The rate of inducible clindamycin resistance was 96.3% for S. aureus and 33.8% for CoNS spp. The sensitivities of the D-tests performed at 15 mm and 22 mm were 100% and 87.7%, respectively, and specificities were 100% for both. The use of 22-mm disk separation for the D-test to detect inducible clindamycin resistance results in an unacceptably high very major error rate (12.3%). All isolates with false-negative results harbored the ermA gene, and the majority were methicillin-resistant Staphylococcus aureus. False-negative results were associated with smaller clindamycin zone sizes and double-edged zones. We recommend using a disk separation distance of ≤15 mm. There is wide geographic variation in the rates of inducible clindamycin resistance, and each laboratory should determine the local rate before deciding whether to either perform the D-test routinely or else report that all erythromycin-resistant S. aureus isolates are also clindamycin resistant.

National Surveillance of Methicillin-Resistant Staphylococcus aureus in China Highlights a Still-Evolving Epidemiology with 15 Novel Emerging Multilocus Sequence Types

ABSTRACT The global spread of methicillin-resistant Staphylococcus aureus (MRSA) is a serious problem, particularly in mainland China. In order to better understand the national molecular epidemiology and resistance profiles of hospital-associated MRSA (HA-MRSA) in China, a laboratory-based multicenter surveillance study was conducted. Sixty-nine hospitals in 45 large cities in 27 provinces were involved, and a total of 1,141 HA-MRSA isolates were collected during the 6-month study period in 2011. All MRSA isolates were characterized by multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec) typing, spa typing, detection of the Panton-Valentine leukocidin (PVL) locus (lukS-PV and lukF-PV), and antibiogram analysis. ST239-III-t030, ST239-III-t037, and ST5-II-t002 were the predominant HA-MRSA clones (overall prevalence rates, 57.1%, 12.9%, and 8.1%, respectively), although the prevalence rates of these major clones varied markedly in different administrative regions. Of note, 6.6% of the HA-MRSA isolates were found to belong to ST59, which had typical community-associated MRSA (CA-MRSA) features, including carriage of SCCmec type IV or V and PVL and less antimicrobial resistance than other major HA-MRSA clones. Moreover, among 36 MLST sequence types (STs) identified, 15 STs, accounting for 3.5% of total isolates, were novel. A novel ST designated ST2590, which is a single-locus variant of ST5-II-t002, was identified in three hospitals in two large cities, with a total of 17 isolates. To further monitor trends in HA-MRSA prevalence, epidemic clonal shifts, clone emergence, and transmission between community and health care settings, longitudinal national MRSA surveillance is required.

Emergence and control of an outbreak of infections due to Panton-Valentine leukocidin positive, ST22 methicillin-resistant Staphylococcus aureus in a neonatal intensive care unit

Methicillin resistant Staphylococcus aureus (MRSA) infection can cause significant morbidity and mortality in neonates. We investigated a nosocomial MRSA outbreak in a neonatal intensive care unit (NICU), using a novel typing method. Following two fatal cases, in May 2011, a prospective outbreak investigation was conducted, involving neonates, mothers and healthcare workers in a large tertiary NICU in Sydney. MRSA isolates were characterized by antimicrobial susceptibility testing, a multiplex PCR-based reverse line blot (mPCR/RLB) binary typing system and other molecular typing methods. Over 7 months, 14 neonates were colonized with MRSA and six infected: three with superficial lesions and three with life-threatening disease, including the two index cases, who died despite empirical treatment with vancomycin. Isolates from 15 neonates were indistinguishable by RLB typing and identified as a PVL-producing ST22 SCCmec IV MRSA strain, which was resistant to gentamicin and trimethoprim-sulphamethoxazole. The outbreak strain was also isolated from one healthcare worker, one environmental swab and one father, but the source remained obscure. During the same period several different non-multiresistant and multiresistant MRSA strains were isolated from five neonates, five mothers (including two whose infants were colonized with the outbreak strain), one father, three healthcare workers and two environmental swabs. Rapid turnaround time of typing results allowed us to recognize and define the outbreak and implement targeted infection control interventions. PVL-producing ST22 SCCmec IV MRSA appears to be a virulent and highly transmissible pathogen in the NICU, which was difficult to control.

Failure of the BD GeneOhm StaphS/R Assay for Identification of Australian Methicillin-Resistant Staphylococcus aureus Strains: Duplex Assays as the “Gold Standard” in Settings of Unknown SCCmec Epidemiology

Identification and susceptibility testing of presumed staphylococci in blood cultures require >24 h by routine phenotypic methods. Delayed appropriate antibiotic therapy results in increased mortality in critically ill patients, while unnecessary vancomycin use may result in suboptimal therapy and

Genetic and Molecular Predictors of High Vancomycin MIC in Staphylococcus aureus Bacteremia Isolates

ABSTRACT An elevated vancomycin MIC is associated with poor outcomes in Staphylococcus aureus bacteremia (SAB) and is reported in patients with methicillin-susceptible S. aureus (MSSA) bacteremia in the absence of vancomycin treatment. Here, using DNA microarray and phenotype analysis, we investigated the genetic predictors and accessory gene regulator (agr) function and their relationship with elevated vancomycin MIC using blood culture isolates from a multicenter binational cohort of patients with SAB. Specific clonal complexes were associated with elevated (clonal complex 8 [CC8] [P < 0.001]) or low (CC22 [P < 0.001], CC88 [P < 0.001], and CC188 [P = 0.002]) vancomycin MIC. agr dysfunction (P = 0.014) or agr genotype II (P = 0.043) were also associated with an elevated vancomycin MIC. Specific resistance and virulence genes were also linked to an elevated vancomycin MIC, including blaZ (P = 0.002), sea (P < 0.001), clfA (P < 0.001), splA (P = 0.001), and the arginine catabolic mobile element (ACME) locus (P = 0.02). These data suggest that inherent organism characteristics may explain the link between elevated vancomycin MICs and poor outcomes in patients with SAB, regardless of the antibiotic treatment received. A consideration of clonal specificity should be included in future research when attempting to ascertain treatment effects or clinical outcomes.

Vancomycin minimum inhibitory concentration, host comorbidities and mortality in staphylococcus aureus bacteraemia

We reported an association between elevated vancomycin MIC and 30-day mortality in patients with Staphylococcus aureus bacteraemia (SAB), including patients with methicillin-susceptible S. aureus (MSSA) treated with flucloxacillin. A detailed analysis of comorbidities and disease severity scores in the same cohort of patients was performed to ascertain if unknown clinical parameters may have influenced these results. The association between elevated vancomycin MIC and 30-day mortality in SAB remained significant (p 0.001) on multivariable logistic regression analysis even when accounting for clinical factors. In addition, the association persisted when restricting analysis to patients with MSSA bacteraemia treated with flucloxacillin. This suggests that elevated vancomycin MIC is associated with but not causally linked to an organism factor that is responsible for increased mortality.

Staphylococcus aureus ST398 detected in pigs in Australia

Alackoftargeted surveillance means that the presence of MRSA inAustralian food-producing animals may have gone undetected.We report here the first detection of MRSA in Australian pigs, themolecularcharacteristicsoftherecoveredisolatesandtheimpacton our understanding of the global epidemiology of this prioritypathogen.Nasal swabs were collected from 324 pigs in five commercialherds and one feral herd between January 2009 and October2010. Swabs were obtained from herds in Western Australia(feral pigs, Herd 1), Queensland (Herd 2), Victoria (Herd 3) andNew South Wales (Herds 4–6). The collection of nasal samplesfrom pigs was approved by the Animal Ethics Committee of theElizabeth Macarthur Agricultural Institute, Menangle, New SouthWales (reference M10/06). Swabs were suspended in 2 mL ofbrain heart infusion broth (Oxoid, Adelaide, Australia) containing20% (v/v) glycerol and stored at 2808C. Pools containing 100 mLeach of five nasal samples were prepared in 2 mL of Mueller–Hintonbroth(Oxoid)containing6.5%NaClandenrichedovernightat 358C. Each pool was analysed by PCR for markers indicative ofMRSA (femB and mecA).