Performance and impact of a rapid method combining mass spectrometry and direct antimicrobial susceptibility testing on treatment adequacy of patients with ventilator-associated pneumonia.

Inappropriate antibiotic therapy in ventilator-associated pneumonia (VAP) is associated with increased mortality. Using broad-spectrum antibiotics for 48 h until the results of conventional cultures and antimicrobial susceptibility testing (AST) are available, may promote the emergence of drug-resistant bacteria. Performing AST directly on clinical respiratory samples would hasten the process by at least 24 h. Here, we analysed the diagnostic performance of a rapid method combining mass spectrometry and direct AST (DAST), and compared it with the conventional method (mass spectrometry with conventional AST (CAST)). Additionally, we assessed its potential impact on antimicrobial use in patients. Over a period of 18 months, the two methods were performed on 85 bronchoalveolar lavages obtained from intensive care unit patients with suspected VAP, and in which Gram-negative bacilli were observed on direct examination. Only the CAST results were reported to the clinicians. DAST produced useable results in 85.9% of the patients. The sensitivity and negative predictive values of DAST were 100% for all antibiotics tested, except gentamicin (97.1%, (95% CI 93.3-101) and 97.4% (93.7-101), respectively) and amikacin (88.9% (81.7-96.1) and 96.4% (92.1-100.7), respectively), compared with CAST. Specificity and positive predictive values ranged from 82.9 (74.2-91.5) to 100%, and from 86.4 (78.5-94.2) to 100%, respectively. If the DAST results had been reported to the clinicians, treatment could have been optimized 24 h earlier in 35/85 (41.2%) patients, with 17 carbapenem patient-days saved. Overall, routine use of the DAST method could help optimize earlier antibiotic treatment in patients with suspected VAP.

Impact of imipenem and amikacin pharmacokinetic/pharmacodynamic parameters on microbiological outcome of Gram-negative bacilli ventilator-associated pneumonia.

OBJECTIVES: Despite recent advances, antibiotic therapy of ventilator-associated pneumonia (VAP) in ICU patients is still challenging. We assessed the impact of imipenem and amikacin pharmacokinetic and pharmacodynamic parameters on microbiological outcome in these patients. PATIENTS AND METHODS: Patients with Gram-negative bacilli (GNB) VAP were prospectively included. Blood samples for pharmacokinetic analysis were collected after empirical administration of a combination of imipenem three times daily and one single dose of amikacin. MICs were estimated for each GNB obtained from respiratory samples. Microbiological success was defined as a ≥10(3) cfu/mL decrease in bacterial count in quantitative cultures between baseline and the third day of treatment. RESULTS: Thirty-nine patients [median (min-max) age = 60 years (28-84) and median SAPS2 at inclusion = 40 (19-73)] were included. Median MICs of imipenem and amikacin were 0.25 mg/L (0.094-16) and 2 mg/L (1-32), respectively. Median times over MIC and over 5× MIC for imipenem were 100% (8-100) and 74% (3-100), respectively. The median C1/MIC ratio for amikacin was 23 (1-76); 34 patients (87%) achieved a C1/MIC ≥10. Microbiological success occurred in 29 patients (74%). No imipenem pharmacodynamic parameter was significantly associated with the microbiological success. For amikacin, C1/MIC was significantly higher in the microbiological success group: 26 (1-76) versus 11 (3-26) (P = 0.004). CONCLUSIONS: In ICU patients with VAP, classic imipenem pharmacodynamic targets are easily reached with usual dosing regimens. In this context, for amikacin, a higher C1/MIC ratio than previously described might be necessary.

Multilocus sequence typing (MLST) shows that the 'Iberian' clone of methicillin-resistant Staphylococcus aureus has spread to France and acquired reduced susceptibility to teicoplanin.

Infection by methicillin-resistant Staphylococcus aureus (MRSA) presents a serious problem, as these organisms are resistant to a wide range of antibiotics. Moreover, MRSA with reduced susceptibility to glycopeptides (GISA) have emerged in recent years. In our hospital we were faced with an outbreak of GISA between January and March 2000, involving six patients who were free of MRSA when the GISA isolate emerged, and five of whom had not been given glycopeptides. The initial GISA isolate from the six patients was compared with six 'historical' multiple-resistant MRSA isolates (1996-1999), which had not been found to be GISA by the routinely used method. Antibiotic susceptibility was studied through the disc diffusion method, and MICs of glycopeptides were determined by Etest, agar and broth dilution techniques. Molecular strain typing was done by PFGE and multilocus sequence typing (MLST). All 12 isolates that belonged to the gentamicin-resistant group of MRSA were susceptible to vancomycin, but showed reduced susceptibility to teicoplanin through at least one MIC method. PFGE typing yielded five different but closely related profiles, and eight of the 12 clinical isolates were classified into a single PFGE type. MLST yielded an identical allelic profile for all 12 isolates, corresponding to the profile (3-3-1-12-4-4-16) of the 'Iberian' clone HPV107 of MRSA. MLST allowed us to confirm the presence of the 'Iberian' MRSA clone HPV107 with the same allelic profile in our hospital for several years. We can now note that strains of this clone have acquired reduced susceptibility to teicoplanin.