Fecal carriage of extended-spectrum beta-lactamase-producing Enterobacterales in healthy Spanish schoolchildren

Background

Extended-spectrum ß-lactamase-producing Enterobacterales (ESBL-E) are a serious threat among emerging antibiotic resistant bacteria. Particularly, the number of cases of ESBL-E infections reported in children has been increasing in recent years, and approved antibiotic treatments for this age group are limited. However, information regarding the prevalence of colonization in European children, risk factors associated with colonization, and the characteristics of the colonizing strains is scarce. The aims of this study were to determine the prevalence of ESBL-E colonization in fecal samples of apparently healthy schoolchildren, to identify lifestyle routines associated with colonization, and to characterize clonal relationships and mechanisms of resistance in ESBL-E isolates.

Methods

A cohort of 887 healthy children (3-13  years old) from seven primary and secondary schools in the Madrid metropolitan area was recruited between April-June 2018, and sociodemographic information and daily habits were collected. Fecal samples were screened for ESBL-E carriage in selective medium. ESBL-E isolates were further characterized by assessing molecular epidemiology (PFGE and MLST), ESBL gene carriage, and antibiotic resistance profile. This information was analyzed in conjunction with the metadata of the participants in order to identify external factors associated with ESBL-E carriage.

Results

Twenty four ESBL-E, all but one Escherichia coli, were detected in 23 children (prevalence: 2.6%; 95% CI: 1.6-3.6%). Of these, seven contained the bla_CTX-M-14 allele, five the bla_CTX-M-15, five the bla_SHV-12, three the bla_CTX-M-27, three the bla_CTX-M-32, and one the bla_CTX-M-9. Significant clonal diversity was observed among the isolates that grouped into 22 distinct clusters (at <85% similarity of PFGE profile). ESBL-producing E. coli isolates belonged to 12 different STs, with ST10 (25%) and ST131 (17%) being the most frequent. Apart from ß-lactams, resistance to trimethoprim/sulfamethoxazole (46%), ciprofloxacin (33%), levofloxacin (33%), tobramycin (21%), and gentamicin (8%) were the most frequently detected.

Conclusion

The prevalence of ESBL-E in the studied cohort of children was lower than the average colonization rate previously detected in Europe for both children and adults. E. coli was the main ESBL-producing species detected and CTX-M were the most frequently identified ESBLs. High ST diversity suggests polyclonal dissemination. Compared to other STs, ST131 isolates were associated with resistance to various antimicrobials.

The classification of Staphylococcus aureus strains by biofilm production differs depending on the method used

INTRODUCTION

Strains can be classified in terms of biofilm production from quantitative absorbance values collectively by dividing strains into tertile ranks or individually by calculating the optical density for the negative control. However, these methods have not been compared in a large sample of Staphylococcus aureus strains. Therefore, our objective was to analyze the agreement between both methods in terms of biomass production and metabolic activity of their biofilm.

METHODS

We classified 233 S. aureus strains by biomass production and metabolic activity using the crystal violet and XTT assays, respectively. Strains were classified as low, moderate, or high biofilm producers according to tertile or optical density.

RESULTS

We found no agreement between both methods (p<0.001 and p=0.028, respectively).

CONCLUSIONS

We consider strains' biofilm classification by optical density to be a more reliable method, as it depends on the individual absorbance of each strain.

Inhibition of LpxC Increases the Activity of Iron Chelators and Gallium Nitrate in Multidrug-Resistant Acinetobacter baumannii

Infections caused by multidrug-resistant Acinetobacter baumannii would benefit from the development of novel treatment approaches. Compounds that interfere with bacterial iron metabolism, such as iron chelators and gallium nitrate, have previously been shown to have antimicrobial activity against A. baumannii. In this study, we characterize the effect of LpxC inhibitors on the antimicrobial activity of previously characterized iron chelators, 2,2′-bipyridyl (BIP) and deferiprone (DFP), and gallium nitrate (Ga(NO₃)₃) against A. baumannii reference strains and multidrug-resistant clinical isolates. The LpxC inhibitor LpxC-2 was synergistic with BIP for 30% of strains tested (FICI values: 0.38–1.02), whereas inhibition with LpxC-4 was synergistic with BIP for 60% of strains tested (FICI values: 0.09–0.75). In time–kill assays, combinations of BIP with both LpxC inhibitors demonstrated synergistic activity, with a more than 3 log₁₀ reduction in bacterial counts compared to BIP alone. LpxC-2 was synergistic with Ga(NO₃)₃ for 50% of strains tested (FICI values: 0.27–1.0), whereas LpxC-4 was synergistic with Ga(NO₃)₃ for all strains tested (FICI values: 0.08–≤0.50). In time–kill assays, combinations of Ga(NO₃)₃ with LpxC-2 and LpxC-4 decreased the growth of both strains compared to each compound separately; however, only the combination with LpxC-4 met the defined criteria for synergy. These results identify a novel synergy between two antimicrobial classes against A. baumannii strains.

The classification of Staphylococcus aureus strains by biofilm production differs depending on the method used

INTRODUCTION

Strains can be classified in terms of biofilm production from quantitative absorbance values collectively by dividing strains into tertile ranks or individually by calculating the optical density for the negative control. However, these methods have not been compared in a large sample of Staphylococcus aureus strains. Therefore, our objective was to analyze the agreement between both methods in terms of biomass production and metabolic activity of their biofilm.

METHODS

We classified 233 S. aureus strains by biomass production and metabolic activity using the crystal violet and XTT assays, respectively. Strains were classified as low, moderate, or high biofilm producers according to tertile or optical density.

RESULTS

We found no agreement between both methods (p<0.001 and p=0.028, respectively).

CONCLUSIONS

We consider strains' biofilm classification by optical density to be a more reliable method, as it depends on the individual absorbance of each strain.

How should microbiology laboratories interpret cultures of the sonicate of closed needleless connectors?

INTRODUCTION

Our objective was to determine whether there is a cut-off in the needleless connectors' (NCs) cultures that when combined with skin cultures it was as efficient as conventional superficial cultures to rule-out catheter colonization (CC) and catheter-related bloodstream infection (CRBSI).

METHODS

During 10 months, we collected samples and then we analyzed the validity values of skin+NCs cultures for CC and CRBSI considering the best cut-off showing at least >90% of specificity to have a high negative predictive value using a ROC curve.

RESULTS

We collected a total of 167 catheters. The optimal cut-off of NCs culture was 1000cfu/NC. The validity values for CC and CRBSI combining skin cultures and NCs cultures using the selected cut-off were, respectively: S, 42.9%/16.7%; SP, 83.6%/75.8%; PPV, 27.3%/2.5%; and NPV, 91.0%/96.0%.

CONCLUSIONS

The combination of skin cultures and quantitative NCs cultures could be used for ruling-out CC and CRBSI.

Can dalbavancin be used as a catheter lock solution?

Purpose. The new lipoglycopeptide dalbavancin has only been approved for acute bacterial skin and skin structure infections. However, its alternative use as a catheter lock solution could facilitate the conservative management of catheter-related bloodstream infection. Our objective was to assess the stability and activity of dalbavancin alone and in combination with heparin against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus epidermidis (MRSE) biofilms. We also compared the results with those obtained with vancomycin alone and in combination with heparin.Methodology. We used a 96-well plate in vitro model based on 24 h biofilms of MRSA and MRSE (ATCC 43300, ATCC 35984 and one clinical strain of each). The biofilms were exposed to dalbavancin (0.128 mg ml^-1) and vancomycin (5 mg ml^-1) alone and in combination with heparin (60 IU). The median percentage reductions in metabolic activity, biomass, bacterial load, and cell viability for each solution were compared.Results. Dalbavancin combined with heparin significantly reduced the median [interquartile range (IQR)] percentage of metabolic activity in MRSA biofilms compared with vancomycin [90.0 % (70.4-92.9 %) versus 35.0 % (14.8-59.6 %), P=0.006]. For the remaining variables studied, the combination was not inferior to vancomycin for MRSA and MRSE.Conclusions. Dalbavancin proved to be active against MRSA and MRSE biofilms. The combination of dalbavancin with heparin is a promising catheter lock solution that has the advantage of locking the catheter at home for 7 days.

Randomized clinical trial analyzing maintenance of peripheral venous catheters in an internal medicine unit: Heparin vs. saline

Background

Peripheral venous catheters (PVCs) require adequate maintenance based on heparin or saline locks in order to prevent complications. Heparin has proven effective in central venous catheters, although its use in PVCs remains controversial. Our hypothesis was that saline locks are as effective as heparin locks in preventing problems with PVCs. The objective of the present study was to compare phlebitis and catheter tip colonization rates between PVCs locked with saline and those locked with heparin in patients admitted to an internal medicine department (IMD).

Methods

We performed a 19-month prospective, controlled, open-label, randomized clinical study of patients with at least 1 PVC admitted to the IMD of our hospital. The patients were randomized to receive saline solution (PosiFlush^®, group A) or heparin (Fibrilin^®, group B) for daily maintenance of the PVC. Clinical and microbiological data were monitored to investigate the frequency of phlebitis, catheter tip colonization, and catheter-related bloodstream infection (C-RBSI), as well as crude mortality, days of hospital stay, and days of antimicrobial treatment.

Results

We assessed 339 PVCs (241 patients), of which 192 (56.6%) were locked with saline (group A) and 147 (43.4%) with heparin (group B). The main demographic characteristics of the patients were distributed equally between the 2 study groups. The median (IQR) catheter days was 5 (3–8) for both groups (p = 0.64). The frequency of phlebitis was 17.7% for group A and 13.3% for group B (p = 0.30). The frequency of colonization of PVC tips was 14.6% and 12.2% in groups A and B, respectively (p = 0.63). Only 2 episodes of C-RBSI were detected (1 patient in group A). Saline lock was not an independent factor for phlebitis or catheter colonization.

Conclusions

Our study revealed no statistically significant differences in the frequency of phlebitis and catheter tip colonization between PVCs locked with saline and PVCs locked with heparin. We suggest that PVC can be maintained with saline solution, as it is safer and cheaper than heparin.

Activity of maltodextrin and vancomycin against staphylococcus aureus biofilm

We aimed to assess the anti-biofilm activity of vancomycin, maltodextrin, and their combination against vancomycin resistant Staphylococcus aureus (VRSA) and vancomycin-susceptible S. aureus (VSSA) strains based on an in vitro static model. Biofilms of 4 VSSA and 2 VRSA strains were grown in a 96-well static model. Vancomycin 2 mM, maltodextrin 10 mM, and both in combination were tested using tetrazolium salt (XTT), resazurin, and cfu/well counts. The efficacy of the antimicrobial solutions was expressed as the percentage reduction in metabolic activity with each method. Overall percentage reduction in the metabolic activity of VSSA was 79.3%, 34%, and 75.7% for vancomycin, maltodextrin, and their combination (p<0.001). Overall percentage reduction in metabolic activity of VRSA was 46.7%, 27.8%, and 34.6% for vancomycin, maltodextrin, and their combination (p>0.05). Maltodextrin did not improve the anti-biofilm efficacy of vancomycin in VSSA or in VRSA biofilms. XTT cannot replace cfu counts as a means of quantifying cell viability. Futures studies are needed to assess the synergistic effects of other non-antimicrobial molecules combined with vancomycin.

Biofilm production is not associated with poor clinical outcome in 485 patients with Staphylococcus aureus bacteraemia

OBJECTIVES

Staphylococcus aureus biofilm may constitute a major cause of virulence. Our main objective was to analyse whether there was an association between biofilm production and poor outcome in patients with S. aureus bacteraemia.

METHODS

We studied 485 S. aureus strains isolated from the blood of patients with bacteraemia from 2012 to 2015. We assessed in vitro biomass production using crystal violet assay and metabolic activity using tetrazolium salt assay. Strains were classified in tertile ranks as follows: low biomass producers, moderate biomass producers, high biomass producers, low metabolic activity, moderate metabolic activity and high metabolic activity. We excluded from analysis strains with moderate crystal violet and tetrazolium salt values. We defined poor outcome as fulfillment of one or more of the following conditions: 30-day attributable mortality, infective endocarditis, persistent bacteraemia and recurrent bacteraemia.

RESULTS

Outcome was poor in 199 (41.0%) of 485 S. aureus bacteraemia episodes. The distribution of poor outcome with respect to biomass production and metabolic activity was as follows: low biomass producers, 36.6% vs. high biomass producers, 43.2% (p 0.26); and low metabolic activity, 43.5% vs. high metabolic activity, 36.2% (p 0.91). The presence of methicillin-resistant S. aureus was the only characteristic that was more likely to be present in the high metabolic activity group (17.4% vs. 39.3%, p < 0.001).

CONCLUSIONS

Biofilm production, as determined by any of the methods used in the present study, is not associated with poor outcome in patients with S. aureus bacteraemia.

Does biomass production correlate with metabolic activity in Staphylococcus aureus?

We assessed agreement between the crystal violet binding assay and the XTT assay in the classification of biofilm production in 492 Staphylococcus aureus strains from bacteremic patients. We found that the overall correlation between the procedures was 46.5%. Biomass production and metabolic activity must be assessed simultaneously.

Corrigendum to "sonicating multi-lumen sliced catheter tips after the roll-plate technique improves the detection of catheter colonization in adults" [J. Microbiol. Methods 122 (2016) 20-22]

The Maki technique is the standard method for detecting catheter tip (CT) colonization. However, some "multi-lumen" catheters finish in a vaulted fornix and end at different distances from the CT. Therefore, we compared the traditional Maki technique with the sonication method using several cross-cut fragments of the CT. Our objective was to assess the yield of the Maki technique followed by sonication in the detection of adult CT colonization and catheter-related bloodstream infection (C-RBSI). For 3months, we prospectively performed CT cultures of polyurethane catheters from adult patients admitted to our institution. First, we performed CT culture using the Maki technique on blood agar plates and then sonicated small fragments of CTs in 5ml of BHI followed by culture of 100μl of the sonicate. We included a total of 252 CVCs, with overall colonization and C-RBSI rates of 14.3% (36/252) and 5.9% (15/252). Of the 36 colonized CVCs, 21 (58.3%) were detected both by Maki and sonication, 6 (16.7%) were detected only by Maki technique, and 9 (25.0%) only by sonication method. Among 15 episodes with concomitant bacteremia, both techniques were positive and concordant in 11 cases (73.3%) and in 4 cases (26.7%) sonication was the only positive technique. Our study shows that both techniques are complementary. We recommend sonicating fragments of the CT from patients with bacteremia of unknown origin and a negative CT culture by the Maki technique.

Vascular catheter colonization: surveillance based on culture of needleless connectors

Background

Superficial culture has a high negative predictive value in the assessment of catheter tip colonization (CC) and catheter-related bloodstream infection (C-RBSI). However, the process of hub culture requires the hubs to be swabbed, and this carries a risk of dislodging the biofilm. At present, most catheter hubs are closed by needleless connectors (NCs) that are periodically replaced. Our objective was to compare the yield of SC (skin + hub culture) with that of skin + NC culture in the assessment of CC and C-RBSI.

Methods

During 5 months, we included the patients on the Major Heart Surgery ICU when a central venous catheter (CVC) remained in place ≥7 days after insertion. SCs were taken simultaneously when the NC was withdrawn and processed by the semi-quantitative method, even when the catheter was not removed. All catheter tips were cultured. All NCs belonging to a single catheter lumen were individually flushed with 100 μl of brain-heart infusion (BHI) broth. We considered the lumen to be colonized when ≥1 NC culture from the lumen flush was positive. We collected a total of 60 catheters.

Results

The overall CC rate was 15.0 %, and we confirmed two episodes of C-RBSI. The validity values after the comparison of SCs with skin + NC culture for prediction of CC were the following: sensitivity 66.7 % vs. 77.8 %, and negative predictive value 93.6 % vs. 93.1 %. The sensitivity and negative predictive value for prediction of C-RBSI was 100 % for both SC and skin + NC culture.

Conclusion

The combination of skin and flushed NC culture can be an alternative to conventional SC for ruling out CC and C-RBSI.

The Tego™ needleless connector for hemodialysis catheters may protect against catheter colonization

Catheter connectors used in hemodialysis patients are those with open caps to manage high blood flows. However, current guidelines for the prevention of catheter infections recommend closed connectors. Tego™ is a closed connector designed to enable high blood flows. We used an in vitro model to compare the efficacy of Tego™ against contamination with that of standard caps in a real-life practice scenario. The model consisted of 200 blood culture bottles (BCB) with an inserted cannula closed either with Tego™ (100) or with open caps (100). BCB were manipulated using two different methods: under aseptic conditions and with gloves contaminated with a 0.05 McFarland Staphylococcus aureus solution. The BCB were incubated at 37 °C under continuous shaking for up to 7 days or until positive. When a BCB turned positive, 100 μL of the fluid was cultured. The positivity rate and time to positivity of the BCB in each method were compared. Overall, 4.0 % of BCB with Tego™ and 52.0 % of BCB with open caps were positive in the sterile model (p < 0.001), whereas all BCB in the contamination model were positive. We did not find differences regarding the median time (hours) to positivity between Tego™ and the standard cap in the contamination model (19.04 vs. 17.87, p = 0.465). In our model, Tego™ proved to be better than the standard cap for the prevention of contamination when the device was handled under optimal conditions. Moreover, it was as efficient as the standard catheter cap in the contamination model.

Assessment of central venous catheter colonization using surveillance culture of withdrawn connectors and insertion site skin

BACKGROUND

Culture of catheter hubs and skin surrounding the catheter entry site has a negative predictive value for catheter tip colonization. However, manipulation of the hub for culture requires the hubs to be swabbed, introducing potential dislodging of biofilm and subsequent migration of microorganisms. Hubs are usually closed with needleless connectors (NCs), which are replaced regularly. Our objective was to evaluate whether culture of flushed withdrawn NCs is an alternative to hub culture when investigating central venous catheter colonization.

METHODS

The study population comprised 49 intensive care unit patients whose central venous catheters had been in place for at least 7 days. Cultures of NCs and skin were obtained weekly.

RESULTS

We included 82 catheters with more than 7 days' indwelling time. The catheter tip colonization rate was 18.3% (15/82). Analysis of skin and NC cultures revealed a 92.5% negative predictive value for catheter colonization. Three episodes of catheter-related bloodstream infection (C-RBSI) occurred in patients with colonized catheters.

CONCLUSION

Surveillance of NC and skin cultures could help to identify patients at risk for C-RBSI.

MALDI-TOF is not useful in the diagnosis of catheter colonization based on superficial cultures: results from an in vitro study

We compared in an vitro model the yields of matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and conventional culture (CC) for the detection of catheter colonization with superficial catheter samples (SS). We used blood culture bottles (BCB) with an inserted cannula and incubated at 37 °C. The BCB were manipulated with different contaminations and when a BCB turned positive, SS were obtained to perform both techniques. To compare both techniques we analyzed the mean time to colonization (MTC) and the mean time to a result (MTR). The MTC (SD, days) by CC and MALDI-TOF was as follows: hub, 0.59 (0.79) versus 1.07 (1.39), P=0.06; surface: 0.62 (0.67) versus 0.82 (0.81), P<0.001. The MTR (SD, days) of CC and MALDI-TOF was as follows: hub: 1.58 (0.79) versus 2.25 (1.48), P=0.04; surface: 1.62 (0.67) versus 1.95 (0.80), P<0.001. In general, the use of MALDI-TOF performed directly with SS was no better than CC and did not anticipate colonization results.

Stickers used for the identification of intravenous lines could be a portal of entry of microorganisms through the catheter: Results from a clinical study

We evaluated the colonization of stickers used to identify intravenous access lines in a clinical practice setting. We isolated the same microorganisms in colonized catheters and on the stickers in 77.8% of cases. Therefore, stickers could be a portal of entry of microorganisms through the catheter. Alternative methods for labeling intravenous lines are required.

Stickers used for identification of intravenous lines may be a source of contamination

This study assessed in an in vitro model the effect of 2% alcohol clorhexidine for the disinfection of stickers used for intravenous line identification. Nonadhesive sticker sides were associated with higher numbers of colony-forming units when manipulation was performed without 2% alcohol clorhexidine disinfection. Future clinical studies are needed to validate these data and design policies for daily sticker disinfection.

Colonization of stickers used for the identification of intravenous lines: results from an in vitro study

BACKGROUND

Clear differentiation of arterial and intravenous (IV) lines is a safety strategy recommended by the World Health Organization, and signaling stickers attached to IV lines are implemented in many institutions. However, the risk of colonization of the stickers' surface has not been evaluated. Our objective was to assess the colonization rate of stickers used for IV lines identification in an in vitro model using 3 different contamination degrees.

METHODS

A set of 30 stickers used for IV lines identification were exposed to low, medium, and high contamination degrees for up to 15 days. Twice a day, a single manipulator vigorously touched the surface of the stickers simulating the daily handling. Surface cultures of all stickers were performed daily. The microorganisms recovered were counted and identified by phenotypic characteristics.

RESULTS

Colonization occurred after 5 days in low and medium manipulation models and after 3 days in the high manipulation model. Nonadhesive sticker sides were associated with greater significant numbers of colony forming units when manipulation was performed without gloves.

CONCLUSION

Stickers used for the identification of IV lines may become potential reservoirs of catheter colonization. Clinical studies to validate these data and design policies of stickers' changes are required.

Deletion of the Correia element in the mtr gene complex of Neisseria meningitidis

The mtr gene complex in Neisseria meningitidis encodes an efflux pump that is responsible for export of antibacterial hydrophobic agents. The promoter region of the mtrCDE operon harbours an insertion sequence known as a Correia element, and a binding site for the integration host factor (IHF) is present at the centre of the Correia element. It has been suggested that the expression of the mtrCDE operon in meningococci is subject to transcriptional regulation by the IHF and post-transcriptional regulation by cleavage in the inverted repeat of the Correia element. The promoter region of the mtrCDE operon as well as the association of changes at that point with decreased susceptibility to antimicrobial drugs in 606 Neisseria meningitidis strains were analysed in this study. Two different deletions were present in the analysed region. The first one, found in seven strains, corresponded to absence of the Correia element. The second one, affecting the −10 region and first 100 bp of the mtrR gene and present in 57 isolates, was only found in ST-1624 isolates. None of the deletions were associated with decreased susceptibility to antimicrobial drugs. Although most of the meningococcal strains carry the Correia element at that position, its deletion is not an exception.