Dissemination Of Gram-negative Bacteria Research Articles

Evaluation of a DNA microarray for rapid detection of the most prevalent extended-spectrum β-lactamases, plasmid-mediated cephalosporinases and carbapenemases in Enterobacteriaceae, Pseudomonas and Acinetobacter

The dissemination of Gram-negative bacteria (GNB) producing extended-spectrum β-lactamases (ESBLs), plasmid-encoded cephalosporinases (pAmpCs) and carbapenemases is a matter of great clinical concern. In this study, we evaluated a new low-density DNA array ‘Check-MDR CT103 XL’ (Check-Points, Wageningen, The Netherlands) that identifies the most clinically relevant β-lactamase genes of ESBLs (blaTEM, blaSHV, blaCTX-M, blaBEL, blaPER, blaGES and blaVEB), pAmpCs (blaCMY-2-like, blaDHA, blaFOX, blaACC-1, blaACT/MIR and blaCMY-1-like/MOX) and carbapenemases (blaKPC, blaOXA-48, blaVIM, blaIMP, blaNDM, blaGIM, blaSPM and blaOXA-23, -24 and -58) in cultured bacteria. In total, 223 GNB isolates with well-characterised resistance mechanisms to β-lactams were analysed. A specificity and sensitivity of 100% were recorded for most bla genes, with a slightly lower signal observed for blaIMP. The Check-MDR CT103 XL array proved highly accurate for the identification of epidemiologically relevant ESBL, pAmpC and carbapenemase genes harboured in Enterobacteriaceae, Pseudomonas and Acinetobacter spp. The Check-MDR CT103 XL assay is a significant improvement compared with Check-MDR CT103 and it highlights the ability of this array to evolve rapidly to adjust to the current needs for the detection of resistance mechanisms to β-lactam agents.

English

Resistance to broad spectrum β-lactams mediated by AmpC and metallo beta-lactamases (MBLs) enzymes is a rising problem worldwide. The wide dissemination of Gram negative bacteria harboring these enzymes represents a significant clinical threat during the last decade, which is mainly due to treatment failure and restriction of therapeutic options. This problem should be really estimated in our locality with special emphasis on immunocompromised patients. The aim of this study was to isolate Gram negative bacteria from differrent sites of infection among patients with hematological malignancy, and to examine those isolates for AmpC and MBLs production by phenotypic and genotypic methods. Seventy four Gram negative bacterial strains were isolated from 387 clinical samples collected from different infection sites. Those isolates were screened for the presence of AmpC and MBLs by modified three dimensional test and Imipenem–EDTA combined disc test, respectively. Multiplex PCR was done as a confirmatory step for detection of AmpC and MBLs production by these isolates. Pseudomonas aeroginosa was the most common isolated Gram negative strain that was found to be positive for AmpC and MBL production. DHA gene was the most frequently detected AmpC β-lactamase gene, whereas VIM was the only detected MBL gene among the Gram negative bacterial isolates by multiplex PCR. The strong association found between AmpC production and MBL gene carriage is alarming which necessitate continuous surveillance of such resistance mechanisms among the Gram negative bacteria, especially in patients with hematological malignancy. Key words: AmpC, metallo beta-lactamase (MBL), multiplex polymerase chain reaction, Pseudomonas aeroginosa.

LPS-conditioned dendritic cells confer endotoxin tolerance contingent on tryptophan catabolism

Dendritic cells (DCs) are specialized antigen-presenting cells with a bipolar nature. Depending on environmental factors, DCs will promote either inflammatory or anti-inflammatory effects. Lipopolysaccharide (LPS), a ligand of Toll-like receptor (TLR)4 and a most potent proinflammatory stimulus, is responsible for complex signaling events in different cell types, including DCs. LPS effects range from protective inflammation–capable of counteracting growth and dissemination of gram-negative bacteria – to hyperacute detrimental responses, as it occurs in endotoxic shock. Consistent with the plasticity of TLR4 signaling, a low dosage of LPS will induce a regulatory response capable of protecting mice against a subsequent, otherwise lethal challenge (‘endotoxin tolerance’). By examining CD11c+ DCs (‘conventional’ DCs, or cDCs), we investigated whether DC flexibility in promoting either inflammation or tolerance can be differentially affected by single vs. repeated exposure to LPS in vitro. cDCs stimulated twice with LPS expressed high levels of indoleamine 2,3-dioxygenase 1 (IDO1) – one of the most effective mediator of anti-inflammatory activity by DCs – and of TGF-β, an immunoregulatory cytokine capable of upregulating IDO1 expression and function. In contrast, a single exposure to LPS failed to upregulate IDO1, and it was instead associated with high-level production of IL-6, a cytokine that promotes inflammation and proteolysis of IDO1. When adoptively transferred in vivo, only cDCs on double endotoxin exposure greatly improved the outcome of an otherwise lethal LPS challenge. The protective effect required that the transferred cDCs be fully competent for IDO1 and the host for TGF-β production. Thus cDCs, conditioned by LPS in vitro to mimic an endotoxin-tolerant state, can protect recipients from endotoxic shock, pointing to adoptive transfer of tolerance as a new option for controlling potentially harmful responses to TLR4 signaling.

Vacuum-assisted closure device in intensive care unit patients and dissemination of Gram-negative bacteria

We read with interest the study by Batacchi and colleagues in a recent issue of Critical Care [1]. Vacuum-assisted closure (VAC) decompression is promising for the management of open abdomen, but our limited experience with this system suggests that dissemination of bacteria may occur. Recently, two patients were treated with VAC in our intensive care unit (ICU). Patient 1 was a 62-year-old man who was originally operated on for paraganglioma and underwent left nephrectomy and gastrojejunal anastomosis. Patient 2 was a 54-year-old woman who was admitted to the ICU two months after a complicated laparoscopic sleeve gastrectomy for morbid obesity. In both patients, at a certain point during their course, intra-abdominal sepsis developed, and they were both managed with extensive debridement, drainage, and VAC placement. Both patients developed fistulas, and although dressings and VAC pump containers were meticulously changed, leaks were repeatedly observed around the dressings. Furthermore, 2 to 4 weeks after the placement of VAC, a rise of positive cultures for Gram-negative bacteria was observed in all patients in our ICU (Figure ​(Figure1).1). As depicted in Figure ​Figure2,2, Klebsiella pneumoniae species became prevalent in our flora despite barrier measures and the isolation of both patients in a separate ward. In 12 out of 34 cases, KPC K. pneumoniae was isolated, whereas in one case it was resistant to all antibiotics. Figure 1 Number of positive Gram-negative and Gram-positive cultures in our intensive care unit during the stay of patients 1 (left) and 2 (right). The arrows represent the time of vacuum-assisted closure placement for each patient. Figure 2 Number of Klebsiella pneumoniae-positive cultures during the stay of patients 1 and 2. The solid arrow represents vacuum-assisted closure (VAC) placement in patient 1. The dotted arrow represents VAC placement in patient 2. Recent literature is inconclusive on this subject. We believe that further studies are needed to confirm the dissemination of bacteria from patients with VAC devices and abdominal leaks.

P722 Clonal dissemination of Gram-negative bacteria causing bloodstream infections in patients with haematological malignancies

P722 Clonal dissemination of Gram-negative bacteria causing bloodstream infections in patients with haematological malignancies