Expression of the MexXY-OprM efflux system in Pseudomonas aeruginosa with discordant cefepime/ceftazidime susceptibility profiles

While MIC distributions and percent susceptibility for cefepime and ceftazidime are generally similar among Pseudomonas aeruginosa, we noted an increasing discordance in susceptibility favoring ceftazidime at our hospital. Quantitative reverse transcriptase-polymerase chain reaction was utilized to explore overexpression of the MexXY-OprM efflux as the mechanism for this phenotype profile. Thirteen of 15 (87%) randomly selected isolates had mexY gene expression levels of 5.8–40.8-fold relative to the wild-type reference strain. While mexY overexpression was noted in the majority of isolates, other resistance mechanisms appear to contribute to the observed phenotypic profile of the Pseudomonas aeruginosa studied. Clinicians must understand not only the magnitude of difference in the MIC profiles between agents, but also the mechanism(s) responsible for these observations if strategies (ie, pharmacodynamic dosing) are to be designed to optimize patient care outcomes in the face of increasing resistance

Acquisition of a natural resistance gene renders a clinical strain of methicillin-resistant Staphylococcus aureus resistant to the synthetic antibiotic linezolid.

Linezolid, which targets the ribosome, is a new synthetic antibiotic that is used for treatment of infections caused by Gram-positive pathogens. Clinical resistance to linezolid, so far, has been developing only slowly and has involved exclusively target site mutations. We have discovered that linezolid resistance in a methicillin-resistant Staphylococcus aureus hospital strain from Colombia is determined by the presence of the cfr gene whose product, Cfr methyltransferase, modifies adenosine at position 2503 in 23S rRNA in the large ribosomal subunit. The molecular model of the linezolid-ribosome complex reveals localization of A2503 within the drug binding site. The natural function of cfr likely involves protection against natural antibiotics whose site of action overlaps that of linezolid. In the chromosome of the clinical strain, cfr is linked to ermB, a gene responsible for dimethylation of A2058 in 23S rRNA. Coexpression of these two genes confers resistance to all the clinically relevant antibiotics that target the large ribosomal subunit. The association of the ermB/cfr operon with transposon and plasmid genetic elements indicates its possible mobile nature. This is the first example of clinical resistance to the synthetic drug linezolid which involves a natural resistance gene with the capability of disseminating among Gram-positive pathogenic strains

Comparison of stool versus rectal swab samples and storage conditions on bacterial community profiles

Abstract Background Sample collection for gut microbiota analysis from in-patients can be challenging. Collection method and storage conditions are potential sources of variability. In this study, we compared the bacterial microbiota from stool stored under different conditions, as well as stool and swab samples, to assess differences due to sample storage conditions and collection method. Methods Using bacterial 16S rRNA gene sequence analysis, we compared the microbiota profiles of stool samples stored and collected under various conditions. Stool samples (2 liquid, 1 formed) from three different patients at two hospitals were each evaluated under the following conditions: immediately frozen at -80°C, stored at 4°C for 12-48 hours before freezing at -80°C and stored at -20°C with 1-2 thaw cycles before storage at -80°C. Additionally, 8 stool and 30 rectal swab samples were collected from 8 in-patients at one hospital. Microbiota differences were assessed using the Yue and Clayton dissimilarity index (θYC distance) and analysis of molecular variance (AMOVA). Results Regardless of the storage conditions, the bacterial communities of aliquots from the same stool samples were very similar based on θYC distances (median intra-sample θYC distance: 0.035, IQR: 0.015-0.061) compared to aliquots from different stool samples (median inter-sample θYC distance: 0.93, IQR: 0.85-0.97) (Wilcoxon test p-value: <0.0001). For the stool and rectal swab comparison, samples from different patients, regardless of sample collection method, were significantly different (AMOVA p-values: <0.001-0.029) compared to no significant difference between all stool and swab samples (AMOVA p-value: 0.976). The θYC dissimilarity index between swab and stool samples was significantly lower within individuals (median 0.17, IQR: 0.10-0.27) than between individuals (median 0.93, IQR: 0.85-0.97) (Wilcoxon test p-value: <0.0001), indicating minimal differences between stool and swab samples collected from the same individual over the sampling period. Conclusion For gastrointestinal microbiota studies based on bacterial 16S rRNA gene sequence analysis, interim stool sample storage at 4 °C or -20 °C, rather than immediate storage at -80 °C, does not significantly alter results. Additionally, stool and rectal swab microbiotas from the same subject were highly similar, indicating that these sampling methods could be used interchangeably to assess the community structure of the distal GI tract.https://deepblue.lib.umich.edu/bitstream/2027.42/136214/1/12866_2017_Article_983.pd

Impact of measurement and feedback on chlorhexidine gluconate bathing among intensive care unit patients: A multicenter study.

OBJECTIVE: To assess whether measurement and feedback of chlorhexidine gluconate (CHG) skin concentrations can improve CHG bathing practice across multiple intensive care units (ICUs). DESIGN: A before-and-after quality improvement study measuring patient CHG skin concentrations during 6 point-prevalence surveys (3 surveys each during baseline and intervention periods). SETTING: The study was conducted across 7 geographically diverse ICUs with routine CHG bathing. PARTICIPANTS: Adult patients in the medical ICU. METHODS: CHG skin concentrations were measured at the neck, axilla, and inguinal region using a semiquantitative colorimetric assay. Aggregate unit-level CHG skin concentration measurements from the baseline period and each intervention period survey were reported back to ICU leadership, which then used routine education and quality improvement activities to improve CHG bathing practice. We used multilevel linear models to assess the impact of intervention on CHG skin concentrations. RESULTS: We enrolled 681 (93%) of 736 eligible patients; 92% received a CHG bath prior to survey. At baseline, CHG skin concentrations were lowest on the neck, compared to axillary or inguinal regions (P &lt; .001). CHG was not detected on 33% of necks, 19% of axillae, and 18% of inguinal regions (P &lt; .001 for differences in body sites). During the intervention period, ICUs that used CHG-impregnated cloths had a 3-fold increase in patient CHG skin concentrations as compared to baseline (P &lt; .001). CONCLUSIONS: Routine CHG bathing performance in the ICU varied across multiple hospitals. Measurement and feedback of CHG skin concentrations can be an important tool to improve CHG bathing practice

Direct Ertapenem Disk Screening Method for Identification of KPC-Producing Klebsiella pneumoniae and Escherichia coli in Surveillance Swab Specimens ▿

Klebsiella pneumoniae carbapenemase (KPC) production in Gram-negative bacilli is an increasing problem worldwide. Rectal swab surveillance is recommended as a component of infection prevention programs, yet few screening methods are published. We compared detection of KPC-producing Klebsiella pneumoniae and Escherichia coli in surveillance specimens by 2 methods: (i) inoculation of swabs in tryptic soy broth containing 2 μg/ml imipenem followed by plating to MacConkey agar (MAC) (method 1) and (ii) streaking swabs on MAC onto which a 10-μg ertapenem disk was then placed (method 2). Simulated rectal swab specimens of challenge isolates from a collection of well-characterized K. pneumoniae and E. coli strains and salvage rectal swab specimens collected from patients at 4 different health care facilities over a 7-month period were tested. The gold-standard comparator was blaKPC PCR testing of isolates. Method 1 detected 4/9 (44%) KPC-positive challenge isolates. By method 2, 9/9 KPC-positive challenge isolates exhibited zones of inhibition of ≤27 mm; all KPC-negative isolates exhibited zones of inhibition greater than 27 mm. The sensitivity and specificity of method 1 for detection of KPC-positive K. pneumoniae and E. coli in 149 rectal swab specimens were 65.6% (95% confidence interval [CI], 46.8% to 80.8%) and 49.6% (95% CI, 40.3% to 58.9%), respectively. With method 2, a zone diameter of ≤27 mm had a sensitivity of 97.0% (95% CI, 82.5% to 99.8%) and specificity of 90.5% (95% CI, 83.3% to 94.9%) for detection of KPC in rectal swab specimens. Direct ertapenem disk testing is simpler, more sensitive, and more specific than selective broth enrichment with imipenem for detection of KPC-producing K. pneumoniae and E. coli in surveillance specimens

SME-3, a Novel Member of the Serratia marcescens SME Family of Carbapenem-Hydrolyzing β-Lactamases

Imipenem-resistant Serratia marcescens isolates were cultured from a lung transplant patient given multiple antibiotics over several months. The strains expressed SME-3, a β-lactamase of the rare SME carbapenem-hydrolyzing family. SME-3 differed from SME-1 by a single amino acid substitution of tyrosine for histidine at position 105, but the two β-lactamases displayed similar hydrolytic profiles

Multicity outbreak of carbapenem-resistant Acinetobacter baumannii isolates producing the carbapenemase OXA-40

During 2005 we detected a multicity outbreak of infections or colonization due to high-level imipenem-resistant Acinetobacter baumannii (MIC, 64 microg/ml). One hundred isolates from diverse sources were obtained from seven acute-care hospitals and two extended-care facilities; 97% of the isolates belonged to one clone. Susceptibility testing of the first 42 isolates (January to April 2005) revealed broad resistance profiles. Half of the isolates were susceptible to ceftazidime, with many isolates susceptible only to colistin. The level of AmpC beta-lactamase expression was stronger in isolates resistant to ceftazidime. PCR and subsequent nucleotide sequencing analysis identified bla(OXA-40). The presence of an OXA-40 beta-lactamase in these isolates correlated with the carbapenem resistance. By Southern blot analysis, a bla(OXA-40)-specific probe revealed that the gene was both plasmid and chromosomally located. This is the first time in the United States that such carbapenem resistance in A. baumannii has been attributable to a carbapenemase

First Identification of Pseudomonas aeruginosa Isolates Producing a KPC-Type Carbapenem-Hydrolyzing β-Lactamase

In Medellin, Colombia, three Pseudomonas aeruginosa isolates with high-level carbapenem resistance (MIC ≥ 256 μg/ml) and an isolate of Citrobacter freundii with reduced susceptibility to imipenem produced the plasmid-mediated class A carbapenemase KPC-2. This is the first report of a KPC-type β-lactamase identified outside of the family Enterobacteriaceae