In vitro and intracellular activities of fosfomycin against clinical strains of Listeria monocytogenes.

This study was designed to evaluate the potential role of fosfomycin as a therapeutic agent in human listeriosis. The in vitro activity of fosfomycin against 154 Listeria monocytogenes clinical isolates under conditions that mimic the induction of prfA expression was determined and was correlated with fosfomycin intracellular antimicrobial activity. In vitro, partial induction of prfA expression is achieved through bacterial growth in brain-heart infusion agar supplemented with activated charcoal (BHIC). A fosfomycin pharmacokinetic/pharmacodynamic breakpoint of ≤64 mg/L was estimated using a Monte Carlo simulation to assess the success of an intravenous fosfomycin dose of 300 mg/kg/day over 5000 individuals. Eighty strains (51.9%) were susceptible to fosfomycin in BHIC, with minimum inhibitory concentrations (MICs) of ≤64 mg/L; 13 strains (8.4%) had the epidemic clone (EC) marker. In addition, 27 strains (17.5%) had a three doubling dilutions reduction in the MIC from ≥1024 mg/L to 128 mg/L (96-128 mg/L by Etest). The fosfomycin modal MIC is lower under prfA expression. However, this effect is smaller in terms of clinical categorisation of isolates and can be influenced by the serotype and clonal type. In A549 cells, the reductions in bacterial inocula of the two susceptible isolates studied after 1h and 24h of incubation with fosfomycin at 0.5× the human maximum serum concentration (Cmax) were 45.8% and 46.6%, and 93.8% and 99.1%, respectively. Slightly higher reductions were found with fosfomycin at 1× Cmax. The resistant strain tested showed significantly lower reductions in all assays.

Quantitative real-time PCR for detection of Acinetobacter baumannii colonization in the hospital environment.

A real-time PCR assay was developed for detecting the presence of Acinetobacter baumannii on hospital equipment and compared to conventional bacterial culture using 100 hospital environmental samples. The real-time PCR detected contaminated surfaces in 4 h with high sensitivity (100%) compared to conventional culture. Thirty-eight percent of samples were positive by real-time PCR and negative by bacterial culture (false positives), possibly indicating the widespread presence of bacterial DNA that is not associated with viable bacteria.

Molecular analysis improves pathogen identification and epidemiologic study of pediatric parapneumonic empyema.

BACKGROUND: Parapneumonic empyema (PPE) is an increasingly common complication of bacterial pneumonia. Epidemiologic study is complicated by the low frequency of positive cultures. We sought to describe the epidemiology of PPE in children using molecular analysis of pleural fluid. METHODS: We performed molecular testing for bacterial pathogens using archived pleural fluid from children hospitalized in 2009 with PPE. Real-time polymerase chain reaction (PCR) to detect Streptococcus pneumoniae, Staphylococcus aureus (including methicillin-resistant), Streptococcus pyogenes, Haemophilus influenzae, and Mycoplasma pneumoniae as well as PCR-based serotyping of S. pneumoniae was performed. Demographic, laboratory, and microbiologic data were abstracted. RESULTS: Pleural fluid specimens from 63 children were available for PCR. By culture, a pathogen was isolated from blood and/or pleural fluid in 22 (35%) patients, with S. pneumoniae in 15 (24%), S. pyogenes in 3 (5%), and methicillin-resistant Staphylococcus aureus in 4 (6%). By PCR, a pathogen was detected in 53 (84%), including S. pneumoniae in 45 (71%). Compared with culture, PCR testing significantly increased detection of any pathogen (35% vs. 84%; P < 0.001) and of S. pneumoniae (24% vs. 71%; P < 0.001). Serotype 7F was the most common pneumococcal serotype detected. Comparison of culture-negative to culture-positive disease showed differences in both the pathogen profile and clinical outcomes. CONCLUSIONS: Molecular analysis of pleural fluid more than doubled the detection of pathogens causing PPE. S. pneumoniae was the most common cause of both culture-positive and culture-negative PPE, although serotype distribution and outcomes differed.