Michael Maley

Utility of Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry following Introduction for Routine Laboratory Bacterial Identification

ABSTRACT Matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) was evaluated prospectively in a diagnostic laboratory. Nine hundred twenty-seven organisms were tested in triplicate; 2,351/2,781 (85%) species and 2,681/2,781 (96%) genus identifications were correct. Known issues such as the misidentification of alpha-hemolytic streptococci as Streptococcus pneumoniae were easily corrected. Identifications cost AUD

Short duration of lamivudine for the prevention of hepatitis B virus transmission in pregnancy: lack of potency and selection of resistance mutations

0.45 per isolate and were available in minutes. MALDI-TOF MS is rapid, accurate, and inexpensive.

Prevention of laboratory-acquired brucellosis: significant side effects of prophylaxis.

This study sought to assess the antiviral efficacy of lamivudine (LMV) administered during third trimester to reduce maternal viraemia and to identify the emergence of LMV resistance. A prospective observational analysis was performed on 26 mothers with high viral load (>107 IU/mL). Twenty‐one women received LMV (treated group) for an average of 53 days (range 22–88 days), and the remaining five formed the untreated control group. Serum samples from two time points were used to measure HBV DNA levels and antiviral drug resistance. The LMV‐treated women achieved a median HBV DNA reduction of 2.6‐log10 IU/mL. Although end‐of‐treatment (EOT) HBV DNA in four (18%) LMV‐treated women remained at >107 IU/mL (±0.5 log IU/mL), no mother‐to‐baby transmission was observed. In contrast, a baby from the untreated mother was HBsAg positive at 9 months postpartum. Four technologies were used for drug resistance testing. Only ultra‐deep pyrosequencing (UDPS) was sufficiently sensitive to detect minor viral variants down to <1%. UDPS showed that LMV therapy resulted in increased viral quasispecies diversity and positive selection of HBV variants with reverse transcriptase amino acid substitutions at sites associated with primary LMV resistance (rtM204I/V and rtA181T) in four (19%) women. These viral variants were detected mostly at low frequencies (0.63–5.92%) at EOT, but one LMV‐treated mother had an rtA181T variant that increased from 2.2% pretherapy to 25.59% at EOT. This mother was also infected with the vaccine escape variant (sG145R), which was inhibited by LMV treatment. LMV therapy during late pregnancy only reduced maternal viraemia moderately, and drug‐resistant viral variants emerged.

Impact of source of infection and vancomycin AUC0–24/MICBMD targets on treatment failure in patients with methicillin-resistant Staphylococcus aureus bacteraemia

Reference 1. Lawn S, Wood R. How can earlier entry of patients into antiretroviral programs in low-income countries be promoted? Clin Infect Dis 2006; 42:431–2 (in this issue). Sir—We describe our experience in responding to a laboratory exposure to Bru-cella melitensis—in particular, the high incidence of adverse events associated with antibiotic prophylaxis. This information may be useful to other laboratories with similar exposures. A 45-year-old man returned to Austra-lia from Iraq. He presented to the hospital with a cerebrovascular accident and was noted to be febrile and to have a systo-lic murmur. An echocardiogram demonstrated a vegetation on the aortic valve, and blood cultures grew B. melitensis after 2 days. His condition was treated with a combination of rifampicin, doxycycline, and gentamicin, and he had an uneventful recovery. In the laboratory, the blood cultures were continuously monitored by the BacT/Alert 3D instrument (bioMérieux). When the bottles signaled positive results, they were moved to a class II biological safety cabinet (BSC II), where the bottles were accessed and an aliquot was transferred to a slide and was also placed onto solid agar media. The inoculated media were removed from the cabinet, and plate streaking was performed on an open bench. Initial plate reading and manipulation of the cultures were performed on the open bench, but, within 24 h of the appearance of growth, a presumptive identification of Brucella species was made, after which all further manipulation was performed in the BSC II. The organism was confirmed to be B. melitensis by a reference laboratory. It was thought that staff may have been exposed to the organism during these procedures. Staff were interviewed about their exposure and were assigned to high-, medium-, and low-risk groups. Seven staff members were assigned to the high-risk group. These staff manipulated or handled open-plate cultures or potentially inhaled material from the liquid or plate cultures outside the BSC II (i.e., they sniffed the plate, streaked the plate with flamed loops, inspected open-plate cultures, or performed subcultures or biochemical tests). The medium-risk group members were in close proximity while these procedures were being performed (12 staff), and the low-risk group members were working in other areas of the bacteriology laboratory (25 staff). We decided our response would be similar to that reported by Robichaud et al. [1]. After counseling, the high-risk group was offered antimicrobial prophy-laxis with rifampicin (450 or 600 mg once daily, depending on body …

NAD-Glycohydrolase Production and speA and speC Distribution in Group A Streptococcus (GAS) Isolates Do Not Correlate with Severe GAS Diseases in the Australian Population

Despite recent controversies about toxicity and reduced efficacy, vancomycin remains the current treatment of choice for methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia. The parameter associated with treatment success is the vancomycin 24-h area under concentration-time curve to MIC ratio (AUC0-24/MIC). We aimed to determine the utility of calculated AUCs and explore the optimal AUC0-24/MIC targets associated with treatment success. In this single-centre retrospective observational cohort study of 127 patients with MRSA bacteraemia, forty-five (35.4%) did not respond to vancomycin treatment. Patient characteristics were essentially the same between those who did not respond to vancomycin treatment and those with treatment success, with independent predictors of treatment failure being source of bacteraemia (odds ratio (OR), 4.29; 95% confidence interval (CI), 1.50-12.26; p 0.007) and not achieving an AUC0-24/MICBMD (using broth microdilution) target of ≥398 (OR, 11.4; 95% CI, 4.57-28.46; p< 0.001). Bacteraemic source-specific thresholds were observed with a higher AUC0-24/MICBMD target of 440 required for high-risk sources (e.g. infective endocarditis) compared with 330 for low-risk sources (line related bacteraemia). Overall treatment success in patients with MRSA bacteraemia was associated with a vancomycin AUC0-24/MICBMD target of ≥398, with source-specific targets observed. Future vancomycin practice guidelines will need to take into account MIC methodology, source of bacteraemia and patient populations prior to setting targets and monitoring recommendations.

Clostridium difficile Testing: Have We Got It Right?

ABSTRACT Streptococcus pyogenes isolates from a tropical region and a subtropical region of Australia with high and low incidences of severe streptococcal diseases, respectively, were analyzed for speA, speB, and speC gene distributions and NAD-glycohydrolase expression. No direct correlation of these characteristics with a propensity to cause invasive diseases was observed.

Glycopeptide use is associated with increased mortality in Enterococcus faecalis bacteraemia

We read with interest the recent article by Kaltsas et al. which retrospectively evaluated the impact of converting to a nucleic acid amplification test (NAAT)-based assay for Clostridium difficile detection ([1][1]). The authors described several possible consequences of such an approach as a

Establishment of an AUC0–24 Threshold for Nephrotoxicity Is a Step towards Individualized Vancomycin Dosing for Methicillin-Resistant Staphylococcus aureus Bacteremia

OBJECTIVES Enterococci are an important cause of nosocomial and community-acquired infections, with bacteraemia being one of the most common presentations. Although inappropriate antimicrobial therapy has been associated with poorer outcomes in Enterococcus faecalis (EF) bacteraemia, the impact of antimicrobial choice, namely β-lactam versus glycopeptide therapy, has not been well described. We sought to determine whether choice of antibiotic affects patient outcomes in EF bacteraemia. PATIENTS AND METHODS This retrospective cohort study was conducted at Liverpool and Bankstown Lidcombe Hospitals, Sydney, Australia between 2006 and 2013. Medical records and laboratory data for consecutive EF bacteraemias were reviewed. Clinical and microbiological data were obtained for all patients who received appropriate antimicrobial therapy with either a β-lactam or a glycopeptide antibiotic. Outcomes and predictors of mortality were determined and treatment groups were compared. RESULTS One hundred and seventy-two episodes of clinically significant EF bacteraemias received appropriate antimicrobial therapy with a β-lactam (n = 126) or a glycopeptide (n = 46). All-cause 30 day mortality was 15.1%, with mortality significantly higher in patients receiving glycopeptide therapy compared with β-lactam therapy (26.1% versus 11.1%, P = 0.015). Glycopeptide therapy remained an independent predictor of 30 day mortality [OR 2.46 (95% CI 1.01-6.02), P = 0.048]. APACHE II score [OR 1.10 (95% CI 1.02-1.18), P = 0.011] and malignancy [OR 2.58 (95% CI 1.03-6.49), P = 0.044] were also independent predictors of 30 day mortality. CONCLUSIONS Glycopeptide use is associated with increased mortality in patients with EF bacteraemia. In the treatment of β-lactam-susceptible EF bacteraemia, β-lactams should be considered first-line therapy.

Emergence of Klebsiella pneumoniae liver abscesses in South-western Sydney.

ABSTRACT Unlike vancomycin trough concentrations, data on the utility of vancomycin pharmacokinetic (PK) parameters, namely, the area under the concentration-time curve from 0 to 24 h (AUC0–24), in predicting acute kidney injury (AKI) are limited. Our aim was to investigate this relationship in patients receiving vancomycin therapy for methicillin-resistant Staphylococcus aureus bacteremia (MRSA-B). A single-center retrospective observational cohort study involving 127 consecutive MRSA-B patients was conducted to examine the incidence of AKI (defined as serum creatinine of ≥0.5 mg/liter and a 50% increase from baseline) and vancomycin exposure parameters associated with nephrotoxicity. Bayesian estimation was used to predict individual vancomycin AUC0–24. All patients received vancomycin monotherapy for a minimum of 14 days following the diagnosis of MRSA-B. AKI was observed in 15.7% of patients (20/127). Clinical characteristics were similar between patients with and without AKI. At steady state, higher vancomycin trough concentrations were associated with AKI (17.2 mg/liter versus 13.1 mg/liter; P = 0.003). A vancomycin AUC0–24 threshold for AKI of >563 mg · h/liter was detected by classification and regression tree (CART) analysis; patients with exposures above this threshold were significantly more likely to experience AKI than patients with lower vancomycin exposures (40% [8/20] versus 11.2% [12/107]; P = 0.002). This parameter remained an independent predictor of AKI on multivariate logistic regression (odds ratio [OR], 5.07; 95% confidence interval [CI], 1.57 to 16.29; P = 0.006) and was a better predictor of nephrotoxicity than vancomycin trough concentrations. Overall, AKI is associated with higher vancomycin exposure as measured by AUC0–24. These results suggest that individualized patient dosing may be possible with dose modifications directed toward established pharmacodynamic targets while balancing AKI risks.

Relentless spread and adaptation of non-typeable vanA vancomycin-resistant Enterococcus faecium: a genome-wide investigation

Klebsiella pneumoniae liver abscess (KPLA) with metastatic infection has been recognised as an emerging infectious disease since being described originally from Taiwan (where it accounts for up to 78.5 % of all liver abscesses), subsequently from other Asian countries and, more recently, from non-Asian countries [1, 2]. The risk of metastatic infection with KPLA has been linked to APACHE II scores C20 and septic shock [1]. In non-Asian countries, KPLA syndrome cases have arisen predominantly in patients of Asian ethnicity [3, 4]. South-western Sydney is ethnically diverse, with 28 % of the total population and 12 % of regional hospital admissions being of Asian ethnicity (Australian Bureau of Statistics census data 2011; Clinical Information Department Statistics). We retrospectively reviewed patient files for this KPLA syndrome to determine their age, gender, ethnicity, travel history as recorded in formal infectious disease consultation, contact history, presenting features, APACHE II scores, diabetic status, baseline investigations, management and outcomes by the time of discharge. Data were analysed using SAS version 5.1 for Windows (Cary, NC, USA) and study approval was granted by the South Western Sydney Local Health District (SWSLHD) ethics committee (QA2010/015). From 01/01/2001 to 31/12/2010, 180 patients were identified with liver abscess using ICD-10 (International Classification of Diseases) admission codes from SWSLHD hospitals. After excluding cases without radiologically proven liver abscess, 21 cases of KPLA (12 % of all liver abscesses) were identified by cross-referencing microbiology computer records of Klebsiella pneumoniae (KP) isolates in blood cultures or liver aspirates over the same period. This represents the largest study to date of KPLA in Australia. In two Sydney-based, 10-year reviews of liver abscess in general, one study had only 11 KPLA patients, whereas the other study documented 13 KP microbiological isolates without specifying the number of patients with KPLA [5, 6]. Of our 21 cases, 5 patients (24 %) developed metastatic infection (see Table 1), which is comparable to rates of 20–28 % in other KPLA case series from non-Asian countries [2, 4, 7]. There was a single death in the non-metastatic KPLA group, giving a 5 % mortality rate, which is at the lower end of the reported range varying from 4 to 10 % [2, 7]. Of this case series, 71 % (15 patients) were of Asian ethnicity, which is higher than the baseline of 28 %, supporting an association with KPLA, as has been found with other studies from non-Asian countries [3, 4, 7]. This association could be due to genetic susceptibility or KP being more frequent in the local microbiota. Using a significance threshold of P B 0.05, diabetes mellitus, high APACHE II score and septic shock were not significantly associated with metastatic disease, possibly because of the small patient numbers. However, large abscess size, intra-abscess gas formation and history of Asian travel were significantly associated with metastatic infection. Speculatively, the former two factors correlate with high organism burden and, Part of this study was presented in a poster format at the 22nd European Congress of Clinical Microbiology and Infectious Diseases (ECCMID), London, UK, March/April 2012.