Enterococcus spp. in a single blood culture: bacteremia or contamination?

We retrospectively evaluated adult cases with Enterococcus spp. in 1 blood culture (BC) (1/1/2010-12/31/2015; n=294) and stratified them into bacteremia or contamination. Contamination frequency was similar in community versus hospital-onset, E. faecalis versus E. faecium, and number of BC drawn per day. Contamination predictors were vancomycin-resistance, ampicillin-resistance, commensal organism copresence, and nonurinary/abdominal sources.

Correlation of methicillin-resistant Staphylococcus aureus vancomycin minimal inhibitory concentration results by Etest and broth microdilution methods with population analysis profile: lack of Etest overestimation of the MIC.

Methicillin-resistant Staphylococcus aureus (MRSA) vancomycin minimum inhibitory concentrations (V-MICs) are sometimes reported to be higher according to Etest versus broth microdilution (BMD). These observations are often interpreted as an Etest overestimation of the actual MIC. We measured V-MIC of 484 MRSA blood isolates using Etest, BMD, and a modified BMD (M-BMD) with incremental dilutions parallel to the Etest scale, correlated the results with population analysis profile-area under the curve (PAP-AUC). All MIC tests were done in parallel. The mean V-MIC was comparable (1.83 ± 0.44 [Etest], 1.88 ± 0.67 [BMD] and 1.75 ± 0.57 mg/L [M-BMD]; p = 0.9 [ANOVA]). The V-MICs/PAP-AUC correlation coefficient was 0.555 (Etest), 0.513 (BMD), and 0.586 (M-BMD). Etest MICs were equal (44.2 %), one dilution higher (21.9 %), two dilutions higher (2.5 %), one dilution lower (29.8 %), and two dilutions lower (1.6 %) than BMD MICs and were equal (61.5 %), one dilution higher (28.3 %), two dilutions higher (0.4 %), one dilution lower (9.5 %), and two dilutions lower (0.2 %) than M-BMD MICs. The mean PAP-AUC for Etest vs M-BMD among isolates with similar Etest/M-BMD MIC values was 0.25 ± 0.15 vs 0.35 ± 0.13 (p = 0.8), 0.46 ± 0.16 vs 0.50 ± 0.17 (p = 0.8), 0.64 ± 0.19 vs 0.67 ± 0.21 (p = 0.9), and 0.90 ± 0.31 vs 0.88 ± 0.25 (p = 1.0) for isolates with V-MIC of ≤ 1, 1.5, 2, and ≥ 3 mg/L respectively. These results suggest that Etest might not overestimate V-MIC in comparison to M-BMD or BMD; Etest and M-BMD tests depict comparable PAP-AUC and have a higher correlation with PAP-AUC than the conventional BMD, probably because of the more detailed results. Etest may be more suitable than conventional BMD for MIC outcome assessment because of the more detailed MICs.

Detection of intermediately vancomycin-susceptible and heterogeneous Staphylococcus aureus isolates: comparison of Etest and Agar screening methods.

Detection of Staphylococcus aureus isolates with intermediate vancomycin susceptibility (VISA) and heteroresistance (hVISA) remains problematic. The population analysis profile/area under the curve (PAP/AUC) is the gold standard but is cumbersome. We compared the performance of two Etest screening methods (macromethod [MAC] and glycopeptide resistance detection [GRD]) plus brain heart infusion (BHI) agars supplemented with 3 (BHI-V3) or 4 (BHI-V4) mg/liter vancomycin in detecting hVISA and/or VISA phenotypes. Etest hVISA screenings were done in parallel for 485 saved methicillin-resistant S. aureus (MRSA) blood isolates according to the manufacturer's instructions. The PAP/AUC was measured for all isolates according to the modified method. PAP/AUC test isolate/Mu3 ratios of <0.9, 0.9 to 1.3, and >1.3 were considered positive for susceptible MRSA (S-MRSA), hVISA, and VISA, respectively. PAP/AUC revealed seven VISA and 33 hVISA phenotypes. MAC screening was positive for 30 (75.0%) hVISA/VISA and 49 (11.0%) S-MRSA isolates. GRD screening was positive for 28 (70.0%) hVISA/VISA and 63 (14.2%) S-MRSA isolates. Growth on BHI-V3 was noted in all hVISA/VISA and 24 (5.4%) S-MRSA isolates. Growth on BHI-V4 was noted in all VISA and four (12.1%) hVISA isolates. None of the S-MRSA isolates grew on BHI-V4 agar. The sensitivity, specificity, and positive (PPV) and negative (NPV) predictive values were 75.0%, 89.0%, 38.0%, and 97.5% for MAC; 70.0%, 85.8%, 30.8%, and 97.0% for GRD; 100%, 94.6%, 62.5%, and 100% for BHI-V3; and 100, 99.2%, 63.6%, and 100% for BHI-V4 (for detecting VISA). These findings suggest that both Etest screening methods have excellent NPV, but positive results require confirmation. BHI-V3 and BHI-V4 agars provide more precise identification of hVISA and VISA, respectively; they may be reasonable alternatives to PAP/AUC.

Persistent Staphylococcus aureus bacteremia: incidence and outcome trends over time.

Persistent Staphylococcus aureus bacteremia (SAB-P) is well known but poorly delineated due to unclear definition. We retrospectively studied 78 patients with SAB-P using a stringent definition (bacteremia for > or = 7 d), in a single teaching hospital, during 1 January 2002 to 30 June 2003 and 1 November 2005 to 31 December 2006 to determine whether the frequency, risk factors and outcome changed over time. SAB was encountered in 354 and 259 instances during the 2 periods, respectively. Patients' characteristics changed with increasing organ dysfunction score (2.9+/-1.7 vs 3.4+/-1.4; p <0.001), patients with invasive devices (27.7% vs 41.3%; p=0.001), hemodialysis dependence (19.2% vs 27.8%; p=0.04), MRSA (50.8% vs 64.5%; p=0.001), and vancomycin treatment (57.9% vs 67.2%; p=0.02). SAB-P frequency increased slightly (11.0% vs 15.1%). Risk (associated) factors for SAB-P (identified by logistic regression) were metastatic infection (OR=5.60; 95% CI 3.00 - 10.47), vancomycin treatment (OR=4.17; 95% CI 2.14 - 8.11), endovascular sources (OR=3.35; 95% CI 1.92 - 5.85) and diabetes (OR=2.14; 95% CI 1.26 - 3.64). SAB- and SAB-P-associated case-fatality did not change (23.2% vs 18.5% and 25.6 vs 30.8%, respectively). All survivors ultimately achieved clearance. These findings suggest that patients with SAB are changing over time. Additionally, SAB-P frequency is higher than previously reported. SAB-P rise is probably due to increasing SAB, MRSA, and patients at risk for complications. Innovative approaches should target novel treatment modalities and risk reduction.

High rate of decreasing daptomycin susceptibility during the treatment of persistent Staphylococcus aureus bacteremia.

Daptomycin is bactericidal against Staphylococcus aureus, with susceptibility defined as a minimal inhibitory concentration (MIC) < or =1 microg/ml. Higher MIC developed in a few cases during therapy. The frequency of MIC rise in persistent bacteremia is unknown. We evaluated all patients with S. aureus bacteremia (SAB) treated with daptomycin (> or =2 days) from 1 April 2004 to 30 October 2006. All patients with post-daptomycin-exposure saved isolates were studied. Daptomycin susceptibility was determined (in duplicate) on all pre- and post-daptomycin-exposure isolates by the broth (Mueller-Hinton) microdilution method. Among 74 treatment courses in 67 patients, 18 were for SAB. Ten had persistent bacteremia (median = 11 days; range = 1-21) and post-daptomycin-exposure saved isolates. The patient age was 29-84 years (median = 57.5 years). Intravascular catheter was the most common source (50%). Most patients (90%) failed therapy prior to starting daptomycin. The initial daptomycin dose was 4 mg/kg in four (40%) cases. The pre-exposure MIC was 0.125-0.5 microg/ml. The post-exposure MIC increased in four cases and was elevated in two cases (60%), to 2 microg/ml in five and 4 microg/ml in one. MIC rise was noted within 5-15 days of exposure and persisted up to 247 days after stopping daptomycin. Pulse-field gel electrophoresis (PFGE) band pattern of isolates with increased MIC revealed 1-3-band differences, implying genetic relatedness. All patients with non-susceptible isolates relapsed or failed therapy. These findings illustrate that daptomycin susceptibility often decreases during the treatment of persistent SAB. Therefore, susceptibility should be closely monitored during therapy.

Interinstitutional and intrainstitutional transmission of a strain of Acinetobacter baumannii detected by molecular analysis: comparison of pulsed-field gel electrophoresis and repetitive sequence-based polymerase chain reaction.

Pulsed-field gel electrophoresis and repetitive sequence-based polymerase chain reaction provided comparable strain discrimination with minor discordance in typing Acinetobacter baumannii clinical isolates from patients at our hospital and affiliated institutions. Typing revealed a cluster strain with intrainstitutional and interinstitutional spread during the study period. A long-term acute care facility may have been the reservoir.

Impact of initial antibiotic choice and delayed appropriate treatment on the outcome of Staphylococcus aureus bacteremia.

The study presented here investigated the impact of initial antibiotic choice (beta-lactams vs vancomycin) on the outcome of 342 patients with Staphylococcus aureus bacteremia (50.9% with methicillin-resistant isolates) encountered between 1 January 2002 and 30 June 2003. Initial antibiotics were inappropriate (beta-lactams) in 60 (34.5%) methicillin-resistant cases and suboptimal (vancomycin) in 62 (36.9%) methicillin-susceptible cases. Time to effective antibiotic therapy was longer in methicillin-resistant cases (25.5+/-28.6 vs 9.6+/-16.6 h; p<0.0005). All-cause in-hospital mortality was higher with inappropriate therapy (35.0 vs 20.9%; p=0.02). Initial vancomycin treatment was associated with a higher incidence of delayed clearance (>or=3 days) of methicillin-susceptible bacteremia (56.3 vs 37.0%; p=0.03). The results indicate inappropriate initial therapy is associated with higher in-hospital mortality and initial vancomycin may delay clearance.

Fungal peritonitis at a tertiary care community teaching hospital: epidemiology, treatments, and outcome over a 3 year timespan.

Fungal species isolated from the peritoneal cavity over a 3-year period were equally divided among dialysis and intra-abdominal sources and demonstrated that triazole antifungal susceptible species predominated. The evolution toward triazole-resistant species/strains noted in bloodstream infections has not yet developed in fungal peritonitis. A trend toward non-albicans species in continuous ambulatory peritoneal dialysis (CAPD) cases, however, requires careful monitoring. .

Repeating blood cultures during hospital stay: practice pattern at a teaching hospital and a proposal for guidelines.

Guidelines for blood culture (BC) address the appropriate frequency, number and volume, but no guidelines exist for repeating BCs. The pattern of repeated BCs was studied in all patients hospitalised in December 2001 to determine the extent of and reasons for repeating cultures. BC was repeated in 127 (31.6%) of 405 adults with an initial BC during the study period. All patients with available records (n = 96; 75.6%) were included. The average patient age was 62.2 +/- 15.9 years. In total, 295 BC sets (one to four BCs/set) were obtained, comprising 96 initial and 199 repeats (one to nine repeats/patient). Sixty-nine (34.7%) repeats were taken within 24 h, and 89 (44.7%) within 2-4 days. The most common reason (32.2%) was persistent fever. The result of repeated cultures was: no growth (83.4%), same pathogen (9.1%), new pathogen (2.5%) or contamination (5.0%). Thus, BC repeats accounted for one-third of all BCs handled in the laboratory, with little additional yield. Guidelines for repeating BCs may decrease unnecessary testing.

Limited genetic diversity of Candida albicans in fecal flora of healthy volunteers and inpatients: a proposed basis for strain homogeneity in clinical isolates.

Molecular analysis of Candida albicans isolates from individual patients often yields a single strain at multiple sites. Whether this strain-limitation is due to virulence factors favoring the invasive strain or to lack of genetic diversity in the gastrointestinal reservoir is uncertain. We elected to study C. albicans genotypes in the fecal flora among healthy volunteers and inpatients. Self-obtained stool swabs or stool samples were cultured on inhibitory mold agar. From each subject with C. albicans, nine colonies were randomly selected, individually propagated, and typed utilizing random amplified polymorphic DNA. Colonies were considered identical (all bands matched), related variants (one to three unique bands), or distinct strains (more than three unique bands). Analysis showed a single clone in 33/43 (76.7%) volunteers and 6/18 (33.3%) inpatients (P = 0.018), two to four related variants in eight (18.6%) volunteers and 10 (55.6%) inpatients, and two distinct strains in two volunteers (4.6%) and two inpatients (11.1%). Strain variation was more common in females (33.5 versus 5.6%; P = 0.04) and tended to increase with age (r = 0.245, P = 0.06). These findings illustrate that most healthy subjects harbor a single strain of C. albicans in the fecal flora. This strain may undergo genetic evolution leading to minor clonal variations. The mechanisms for strain selection, maintenance and possible evolution remain to be delineated.

Molecular analysis of coagulase-negative Staphylococcus isolates from blood cultures: prevalence of genotypic variation and polyclonal bacteremia.

Fifty-seven coagulase-negative Staphylococcus isolates from 22 inpatients who had > or =2 blood cultures that were positive for Staphylococcus within 24 hours were analyzed to determine the frequency of polyclonal bacteremia. Patients were considered to have bacteremia (14 patients) or contamination of sample (8 patients) on the basis of clinical criteria. Nine colonies were randomly selected from each blood culture and genotyped by means of SmaI digestion/pulsed-field gel electrophoresis. Relatedness was determined by calculation of the Dice coefficient of banding-pattern similarity (S(AB)). Analysis of bacteremic isolates demonstrated the presence of a single species in 35 of 41 blood cultures, 1 related variant in 5 blood cultures (87%-92% S(AB)), and an unrelated strain in 1 blood culture (79% S(AB)). Analysis of contaminated samples demonstrated the presence of a single strain in 10 of 16 blood cultures and 1-3 variants (28%-97% S(AB)) in the remainder. Genotype diversity was significantly more common in the contaminated samples (P=.036). Almost all coagulase-negative Staphylococcus bacteremias were monoclonal.

Faecal fungal flora in healthy volunteers and inpatients.

The faecal fungal flora was analysed in healthy volunteers and inpatients. Self-obtained stool swabs from volunteers (n = 228) and inpatient stool-samples (n = 34) were cultured on Inhibitory-Mould-Agar plates. All yeast isolates were identified. Fungi were detected in 51.8% of volunteers; the majority (88.1%) had single species. The prevalence increased steadily with age. Candida albicans was detected in 62.7%, non-albicans Candida species in 22.0%, yeasts--other than Candida in 20.3% and moulds in 8.5% of volunteers with fungi. No gender-related differences were noted in the prevalence or types of yeast. Candida glabrata and C. krusei were detected in adults only. Intra-household species-similarity (excluding C. albicans) was noted in seven of 31 (22.6%) households with fungi in two or more members. Inpatients had higher prevalence of yeast (88.2%) with a single species in the majority (73.3%). Yeasts other than Candida were less common in inpatients (3.3%; P = 0.013) whereas C. glabrata was significantly more prevalent (33.3 versus 2.5%; P < 0.001). This study delineates the faecal fungal flora in volunteers and inpatients. Most subjects harbour a single species that may be shared with other households. The prevalence is somewhat higher in adults and the types of yeast may vary with age. Finally, C. glabrata appears to be acquired nosocomially.

Recurrent vancomycin-resistant Enterococcus bacteremia: prevalence, predisposing factors, and strain relatedness.

We studied the prevalence of recurrent vancomycin-resistant Enterococcus (VRE) bacteremia, predisposing factors, and strain relatedness during a 3 year period at our institution. Of 36 inpatients who had episodes of bacteremia, 3 (8.3%) had recurrent episodes. Predisposing factors were mucositis and neutropenia (1 patient) and chronic renal failure requiring hemodialysis (2). Recurrent episodes separated by < or = 3 months were caused by identical or related strains, and those at greater intervals by distinct strains. Recurrent VRE bacteremia is uncommon.

Limits of detection of Mycobacterium tuberculosis in spiked cerebrospinal fluid using the polymerase chain reaction in tuberculous meningitis.

The limit of detection of Mycobacterium tuberculosis in spiked cerebrospinal fluid (CSF) using polymerase chain reaction (PCR) was compared to that of a radiometric liquid culture. Serial dilutions of clinical isolates of Mycobacterium tuberculosis were prepared in CSF (n=3) or broth (n=11) with estimated concentrations of 0-550 cfu/ml. Each dilution was examined concurrently by PCR and radiometric culture. PCR and radiometric culture detected Mycobacterium tuberculosis DNA in all dilutions with an estimated 2 cfu/ml in the CSF. At lower concentrations (estimated <2 cfu/ml), PCR and radiometric culture were positive in three of five (60%) and five of five (100%) CSF samples, respectively. In comparison to PCR in broth dilutions, no evidence of inhibition or interference was noted. These results imply that PCR can provide a rapid and reliable diagnosis of tuberculous meningitis, although there is a potential for false-negative results to occur in samples containing very few organisms ( < 2 cfu/ml).

Trends in antifungal susceptibility among Candida sp. Urinary isolates from 1994 and 1998.

Antifungal susceptibilities were determined from 80 urinary isolates of Candida species collected in 1994 and 1998. Our findings demonstrate increasing geometric means of fluconazole MICs and fluconazole resistance in Candida albicans and Candida tropicalis (those for Candida glabrata were unchanged) within the 4-year span. Amphotericin B and voriconazole MICs remained constant.

Clinicians' reaction to positive urine culture for Candida organisms.

Clinicians' reaction to isolating Candida organisms in urine culture (> or = 10(4) CFU ml-1) was assessed in a retrospective review of 133 consecutive in-patients (> or = 15 years-of-age) over a 5 month period. The average age was 68.8 years and male/female ratio was 0.36 (35/98). Most (78.2%) patients had an indwelling catheter, and many (35.3%) were in the intensive care unit (ICU). In response to culture-result, clinicians initiated antifungal therapy in 80 instances (60.2%). Treatment was often based on a single culture without documenting the infection (n = 53/80, 66.3%) in the absence of risk for invasive disease. Removing the indwelling-catheter was never attempted and antibiotics were rarely discontinued or modified (1.3%). Fluconazole was most frequently utilized (n = 42, 52.5%), followed by amphotericin-B bladder-irrigation (n = 26, 32.5%), and combined fluconazole/amphotericin-B bladder-irrigation (n = 12, 15%). Therapy was more frequently initiated in ICU-cases (76.6 versus 55.6%; P = 0.023) and less often in non-catheterized individuals (40.7 versus 69%; P = 0.012) and patients with 10(4) CFU ml-1 (25.9 versus 72.7%; P < 0.0001). These findings show that clinicians nowadays do not follow current guidelines for the management of candiduria. Efforts to increase clinicians' awareness of these guidelines, which are intended to confirm the diagnosis and stratify treatment according to patient risk factors, appear to be necessary.

Strain relatedness in persistent and recurrent candiduria.

PURPOSE: We assessed the value of determining strain relatedness in differentiating persistent from recurrent candiduria. MATERIALS AND METHODS: Prospective monitoring of patients with candiduria (10(4) or greater colony forming units per ml.) during a 5-month period. All patients with persistent or recurrent infection after documented clearance were selected. Pair isolates were typed using restriction endonuclease analysis of genomic deoxyribonucleic acid with SfiI. Isolates were considered related if all deoxyribonucleic acid bands matched. RESULTS: We encountered 22 and 5 patients with persistent and recurrent infection, respectively. The isolates were recovered 1 to 140 days apart (21.56 +/- 28.97). Most patients were women (85.2%) with a mean age of 66.41 +/- 18.11 years. Risk factors included antibiotics (100%), indwelling catheter (88.9%) and diabetes mellitus (40.7%). Of 15 individuals who received antifungal therapy candiduria persisted in 10 and resolved but recurred within 4 to 26 days (13.00 +/- 9.08) after treatment in 5. Candida albicans accounted for 34 of 58 isolates (58.6%), and it was mixed with other species in 4 cultures. Paired strains were genetically identical in 26 of 27 patients. Strain persistence was documented in 21 of 22 cases with persistent infection and in all 5 patients with recurrent disease. CONCLUSIONS: These findings show that strain persistence is exceedingly frequent in candiduria. These results imply that determining strain relatedness of Candida urinary isolates may not be reliable in differentiating persistent from recurrent infection.

Clustering of Candida infections in the neonatal intensive care unit: concurrent emergence of multiple strains simulating intermittent outbreaks.

BACKGROUND: Clusters of Candida albicans and Candida parapsilosis infections were noted intermittently in our neonatal intensive care unit (NICU). We attempted to determine whether these clusters represented single strain outbreaks or coincidental emergence of unrelated strains. METHODS: A retrospective examination of the frequency of candidemia during a 9-year period, two point prevalence studies of colonization and assessment of strain relatedness of individual infant isolates during and in between clusters during a 2-year period with karyotyping and restriction endonuclease analysis of genomic DNA (REAG). RESULTS: C. albicans and C. parapsilosis infections emerged in a scattered pattern (1 to 2 cases every few months) with intermittent clustering of 3 cases/month. The colonization rate was 50% 5 weeks after an apparent cluster, equally distributed between C. albicans and C. parapsilosis, and 17.6% (exclusively with C. parapsilosis) 4 months after absence of invasive disease. Utilizing REAG or karyotyping singly we noted 12 and 16 DNA banding patterns, respectively, among 23 infant isolates. Few patterns were observed repeatedly over 2- to 20-month periods, implying recurrent emergence of the same strains. Combining karyotyping with REAG revealed a different epidemiologic pattern. It identified 20 distinct composites with identical composites in 3 infant pairs. All infants with identical composites were in the NICU concurrently. The frequency of strain relatedness was comparable among clustered cases (16.7%), scattered cases (7.7%) and simultaneously colonized infants (16.7%). CONCLUSIONS: These findings illustrate that Candida infections clustered periodically in our NICU but that these clusters were often caused by unrelated strains with infrequent cross-infection during and between clusters. With suboptimal typing this pattern of emergence can be mistaken for same strain outbreaks.