Assessment of five screening strategies for optimal detection of carriers of third-generation cephalosporin-resistant Enterobacteriaceae in intensive care units using daily sampling.

There is no consensus on optimal screening procedures for multidrug-resistant Enterobacteriaceae (MDRE) in intensive care units (ICUs). Therefore, we assessed five strategies for the detection of extended-spectrum beta-lactamase (ESBL) and high-level expressed AmpC cephalosporinase (HL-CASE) producers. During a 3-month period, a rectal screening swab sample was collected daily from every ICU patient, from the first 24 h to the last day of ICU stay. Samples were plated on MDRE-selective media. Bacteria were identified using MALDI-TOF mass spectrometry and antibiograms were performed using disk diffusion. MDREs were isolated from 682/2348 (29.0%) screening samples collected from 93/269 (34.6%) patients. Incidences of patients with ESBL and HL-CASE producers were 17.8 and 19.3 per 100 admissions, respectively. In 48/93 patients, MDRE carriage was intermittent. Compared with systematic screening at admission, systematic screening at discharge did not significantly increase the rate of MDRE detection among the 93 patients (62% vs. 70%). In contrast, screening at admission and discharge, screening at admission and weekly thereafter, and screening at admission and weekly thereafter and at discharge significantly increased MDRE detection (77%, p 0.02; 76%, p 0.01; 86%, p<0.001, respectively). The difference in MDRE detection between these strategies relies essentially on the levels of detection of patients with HL-CASE producers. The most reasonable strategy would be to collect two samples, one at admission and one at discharge, which would detect 87.5% of the ESBL strains, 67.3% of the HL-CASE strains and 77.4% of all MDRE strains. This study should facilitate decision-making concerning the most suitable screening policy for MDRE detection in a given ICU setting.

Fighting the spread of AmpC-hyperproducing Enterobacteriaceae: beneficial effect of replacing ceftriaxone with cefotaxime.

OBJECTIVES: Considering the hypothesis that the high biliary elimination of ceftriaxone could be responsible for the selection of Enterobacteriaceae harbouring high-level AmpC ß-lactamase (HL-CASE), the use of ceftriaxone was discontinued in our hospital in 2006 and replaced with cefotaxime. METHODS: Antibiotic consumption, expressed as defined daily dose (DDD)/1000 patient-days (PD), and HL-CASE incidence, expressed as the number of patients carrying HL-CASE/1000 PD, were compared between the pre-intervention period (Period 1, 2001-05) and the post-intervention period (Period 2, 2006-12) using an interrupted time series analysis. RESULTS: The incidence of HL-CASE increased significantly from 0.32 to 0.69/1000 PD during Period 1 (coefficient = 0.082, P < 0.01). A significant inflection of the slope in the incidence curve occurred in Period 2 (coefficient = -0.061, P = 0.05), mainly owing to the stabilization of the HL-CASE incidence of Enterobacteriaceae harbouring chromosomally inducible cephalosporinase (Period 1, 0.27 to 0.64/1000 PD; Period 2, 0.58 to 0.61/1000 PD) and especially for Enterobacter cloacae (Period 1, 0.09 to 0.30/1000 PD; Period 2, 0.26 to 0.27/1000 PD). This deceleration was observed despite a significant increase in the slope of cefotaxime consumption over Period 2 (coefficient = 2.97, P < 0.01). CONCLUSION: Despite the disadvantages of using cefotaxime compared with ceftriaxone (administration three times daily versus once a day), the ecological benefits of this substitution seem sufficiently convincing to preferentially use cefotaxime. Control of HL-CASE incidence is crucial to limiting carbapenem use and preventing the selection of carbapenemase-producing Enterobacteriaceae.

Comparison of five media for detection of extended-spectrum Beta-lactamase by use of the wasp instrument for automated specimen processing.

Overall, 2,337 rectal screening samples (RSSs) were seeded by using the Wasp instrument for automated microbiological processing with five media for detection of extended-spectrum ß-lactamase (ESBL): CHROMagar, ChromID, Brilliance, BD Drigalski, and HEGP media. Of 354 RSSs harboring ESBL-producing isolates, 89.3% were found to be positive on all media. Sensitivity and specificity ranged from 95.5 to 98.3% and from 57.9 to 72.3%, respectively. No medium was perfectly ESBL selective, and non-ESBL-producing strains were mainly Enterobacteriaceae overproducing AmpC ß-lactamase and nonfermenting Gram-negative bacilli, mostly Pseudomonas aeruginosa.

Readmission of known MRSA carriers and MRSA colonization pressure in hospital.

Readmission of asymptomatic methicillin-resistant Staphylococcus aureus (MRSA) carriers may contribute to the hospital reservoir. Using an electronic alert system, we assessed the weight of readmission of known MRSA carriers on MRSA colonization pressure in a hospital setting. During the 2004-2010 period, 2058 alerts were generated for 1060 inpatients. A total of 486/1060 patients (46%) were readmitted at least once, and 330/486 (64·4%) were readmitted <3 months after discharge. A mean of 20 MRSA patients were present on the same day (from 40 in 2004 to eight in 2010). The number of MRSA patient-days was 34 575, i.e. 2·5% of the 1 366 277 patient-days of the study period, and 17 737 (51·3%) MRSA patient-days were due to readmission of known MRSA carriers. The number of new MRSA cases was partly correlated with the number of MRSA patients hospitalized (R 2 = 0·49). Rapid electronic identification of these patients proved essential in decreasing the global burden of MRSA in our hospital.

Differences in daptomycin and vancomycin ex vivo behaviour can lead to false interpretation of negative blood cultures.

In clinical studies on bacteraemia, the negativity of blood cultures is an important endpoint for comparing the efficacy of different therapeutic regimens. In FAN anaerobic blood culture medium (BacT/ALERT system), daptomycin displayed increased MIC against Staphylococcus aureus and improved abolishment of its carryover effect in charcoal when compared with vancomycin. Differences between these two drugs can lead to a false interpretation of negative blood cultures. To compare different antibiotic regimens for the treatment of bacteraemia, preliminary studies are mandatory to ensure that ex vivo antibiotic behaviour is similar in the blood-culture system used.

[Trends in Staphylococcus aureus antimicrobials susceptibilities: is methicillin still a relevant multiresistance marker?]. / Evolution de la sensibilité de Staphylococcus aureus aux antibiotiques: la méticilline est-elle encore un marqueur de multirésistance ?

OBJECTIVE: Recent change was noted in S. aureus epidemiology, especially for none multiresistant methicillinresistant S. aureus (MRSA) and for multiresistant methicillin-susceptible S. aureus (MSSA). So, a six-year retrospective study was conducted to follow trends in antimicrobials resistance and to determine if methicillin remained a relevant multiresistant marker. METHODS: All S. aureus isolates (duplicates excluded) isolated between 2001 and 2006 in a French 800-beds-teaching-hospital were included in the study. RESULTS: Four thousand four hundred and fifty-five isolates providing from 3602 patients were identified between 2001 and 2006. MRSA rate and incidence for 1000 hospitalization-days significantly decreased from 34.7 to 22.6% and 1.3 to 0.6% respectively (p < 0.001). Significant decrease was observed for multiresistant MRSA (72.9 to 46.3%, p < 0.001), while no change was observed for multiresistant MSSA (2.9 to 3.4%). Among the 186 different antibiotic patterns isolated, four MRSA-phenotypes significantly decreased whereas two MSSA-phenotypes significantly increased. The main MRSA phenotype, resistant to kanamycin, tobramycin, macrolides-lincosamides-streptograminesB, and fluoroquinolones, significantly decreased from 11.9 to 5.9% (p < 0.001). Glycopeptide Intermediate S. aureus (GISA) phenotypes disappeared. CONCLUSION: At this date, methicillin remains in our institution a relevant marker of multiresistance but trend is changing.

[Selection of relevant duplicate criteria in the monitoring of Staphylococcus aureus methicillin resistance trends]. / Sélection de critères de doublons pertinents pour le suivi du taux de Staphylococcus aureus résistant à la méticilline.

OBJECTIVE: Monitoring methicillin-resistant Staphylococcus aureus (MRSA) rates is crucial in hospital settings, but its calculation is hampered by variations according to duplicate isolates. The aim of this study was to assess the impact of applying different methods for duplicate isolate removal on the MRSA rates. MATERIALS AND METHODS: Trends in S. aureus resistance were analysed from isolates collected in a teaching hospital during a 4-year period by using a specifically designed software. Reference duplicate (RD) criteria were defined as one major and three minor differences in antibiotic patterns and a 30-day time period between two isolates. Variations in antibiotic patterns and time period were studied and compared to RD. NCCLS recommendations based upon results from the first isolate of a species per patient per study period, and the ONERBA recommendations based on phenotypic method, were also studied. RESULTS: MRSA rate was 31.1% when using RD. When duplicates were not eliminated, the MRSA rate significantly increased to 34.0% (P=0.002). When using NCCLS and ONERBA recommendations, the MRSA rate significantly decreased to 27.6% (P=0.002) and significantly increased to 33.8% (P=0.002) respectively. When no difference was tolerated in antibiotic pattern or when the time period was set at five days, the MRSA rate significantly increased to 34.3 and 34.2%, respectively (p=0.003 for each). CONCLUSIONS: These results suggest that criteria used to remove duplicates should be carefully selected to assess accurate MRSA trends.

[Retrospective study of bacteremia diagnosed in an emergency department: frequency, susceptibility of microorganisms, and impact on therapeutic management]. / Etude rétrospective des bactériémies diagnostiquées aux urgences: fréquence, sensibilité des microorganismes et intérêt dans la prise en charge thérapeutique.

OBJECTIVE: The authors had for aim to determine the prevalence of bacteremia diagnosed in an emergency department (ED), the susceptibility of microorganisms to antibiotics, and the impact on therapeutic management. DESIGN: A retrospective analysis was made on patient features, microbiological ecology, susceptibility to antibiotics, and modalities of antimicrobial therapy in the Georges Pompidou European hospital ED of Hôpital, between 1 November 2001 and 30 June 2002. RESULTS: One thousand four hundred and thirty two blood cultures were obtained from 1069 patients. The rate of positive cultures was 12%, but only 8.7% (n = 125) were proved as true bacteremia. The most frequently identified organisms were: Enterobacteriaceae (n = 63, 39.4%) with a predominance of Escherichia coli (n = 48, 30%), and Streptococcus pneumoniae (n = 16, 10%). Forty two cases of pyelonephritis and 34 of prostatitis both due to E. coli were diagnosed. 76.5% of these were resistant to amoxicillin, 64.7% to amoxicillin-clavulanic acid, 11.8% to ciprofloxacin, and 44% to cotrimoxazole. No resistance to third generation cephalosporin was detected in E. coli isolates. Fourteen S. pneumoniae pneumonia cases were diagnosed. 57.1% of isolates presented with a decreased susceptibility to penicillin (CMI > 0.1 mg/l). Susceptibility to amoxicillin and cefotaxim was 85.7% and 92.9% respectively. Blood culture was the only exam available for bacterial diagnosis in 51.5% of true bacteremia. 1.6% of blood cultures from ED samples had an impact on therapeutic management. CONCLUSIONS: Blood culture is a relevant exam for the diagnosis of infection in patients admitted to the ED.

Vancomycin resistance is associated with serine-containing peptidoglycan in Enterococcus gallinarum.

In Enterococcus gallinarum SC1, a low-level vancomycin-resistant strain, only monomeric muropentapeptides with a C-terminal D-alanine were detected after growth without vancomycin. In contrast, in SC1 induced by vancomycin, as well as in AIB39, a constitutive vancomycin-resistant strain, monomeric and dimeric muropentapeptides with a C-terminal D-serine were detected.