Antibiotic-resistant Gram-negative Bacilli Research Articles

Antibiotic-Resistant Bacteria in Environmental Water Sources from Southern Chile: A Potential Threat to Human Health

Antimicrobial resistance (AMR) is a critical global issue affecting public and animal health. The overuse of antibiotics in human health, animal production, agriculture, and aquaculture has led to the selection of antibiotic-resistant strains, particularly in Gram-negative bacteria. Mutations and horizontal gene transfer play a significant role in the development of antimicrobial resistance, leading to the reduced efficacy of current antibiotics. Today, AMR in bacteria and antibiotic-resistance genes (ARGs) are increasingly recognized in multiple environmental sources, including recreational and irrigation waters. This study aims to identify Gram-negative bacteria from surface aquatic reservoirs in southern Chile and assess their susceptibility to clinically relevant antibiotics. Water samples were collected from four lakes, five rivers, one waterfall, and one watershed in southern Chile to isolate environmental Gram-negative bacilli (GNB). API-20E and MALDI–TOF were employed for bacterial identification. Kirby–Bauer disc diffusion tests and multiplex PCR were performed to determine their susceptibility profile. A total of 26 GNB strains were isolated from environmental water samples, predominantly belonging to the Pseudomonas (n = 9) and Acinetobacter (n = 7) genera. Among these strains, 96.2% were resistant to ampicillin and cefazoline, while 26.9% and 34.6% showed resistance to ceftazidime and cefepime, respectively. Additionally, 38.5% exhibited resistance to colistin. Two Enterobacter cloacae strains obtained from Cachapoal River (sixth region) and Villarrica Lake (ninth region), respectively, presented a multidrug-resistant (MDR) phenotype and carried at least two extended-spectrum β-lactamase (ESBL) genes. Thus, antibiotic-resistant GNB and ARGs were found in natural water reservoirs, raising concerns about the dissemination of resistance determinants among potentially pathogenic bacteria in environmental microbial communities.

Evaluation of Variability in Interpretation of Disk Diffusion Testing for Cefiderocol Using Different Brands of Mueller-Hinton Agar.

Cefiderocol is a new antibiotic used to treat infections with antibiotic resistant Gram-negative bacilli. The impact of differences between Mueller-Hinton agar (MHA) brands on susceptibility testing is underexplored. Compounding the implementation of cefiderocol susceptibility testing is a lack of harmonization between different regulatory body breakpoint criteria. We performed Kirby-Bauer disk diffusion using BD, Hardy, and Remel MHA, in addition to broth microdilution for Acinetobacter baumannii (n = 25), Enterobacterales (n = 25), Stenotrophomonas maltophilia (n = 24), and Pseudomonas aeruginosa (n = 23). We analyzed disk diffusion diameters and minimum inhibitory concentrations using interpretive criteria from the Clinical and Laboratory Standards Institute (CLSI), US Food and Drug Administration (FDA), and the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Breakpoint criteria impacted interpretation of susceptibly testing results, for example with the broth microdilution we found 8% (2/25) of A. baumannii isolates change interpretation between CLSI and EUCAST and 32% (8/25) change between CLSI and FDA, 12% (3/25) of Enterobacterales change between CLSI and EUCAST, 13% (3/23) of P. aeruginosa interpretations change between CLSI and FDA, and 4% (1/25) S. maltophilia change between CLSI and FDA. There was a significant difference between the zone disk diffusion diameters for P. aeruginosa and S. maltophilia between Hardy and BD; which changed interpretation (using CLSI criteria) for 8.7% (2/23) for P. aeruginosa but 0% (0/24) for S. maltophilia. Breakpoint criteria impact cefiderocol susceptibility testing interpretation for broth microdilution and disk diffusion. Choice of MHA brand can also affect result interpretation.

Optimal empirical antimicrobial therapy in infective endocarditis.

The case report of left-sided infective endocarditis (IE) in intravenous drug use (IDU) reminds the importance of recognizing peripheral stigmata of IE with subsequent immediate aggressive management.1 However, the management of this patient, including inappropriate the choice of empirical antibiotics and no consideration of valve surgery (given large size of vegetation and systemic embolization), does not seem appropriate. The current literature recommends empirical antimicrobial coverage of methicillin-resistant Staphylococcus aureus (MRSA) and potentially antibiotic-resistant Gram-negative bacilli (including Pseudomonas spp.) in IDU-IE.2–4 A combination of vancomycin plus gentamicin or cefepime covers these bacteria and other potential agents pending culture results.2,3 MRSA, the commonest cause of both right- and left-sided IDU-IE, was not covered in the index case report before the blood cultures were obtained.2–5 Our large IE study, published from the same center (Postgraduate Institute of Medical Education and Research, Chandigarh), also supports the combination of vancomycin and gentamicin for empirical treatment in IDU-IE.6

Clinico-Microbiological Investigation on Fosfomycin and Tigecycline Resistant Gram-Negative Bacilli Isolated from Urinary Tract Infections: A Potential Resurgence

Background: Traditional antibiotics are no longer as effective as before for controlling pathogens associated with urinary tract infections (UTI), which shows the necessity of developing new and more effective antibiotics. Objectives: The current study aimed to evaluate in vitro susceptibility of fosfomycin and tigecycline towards common antibiotic-resistant Gram-negative bacilli isolated from the urinary tract. Besides, clinico-microbiological on fosfomycin and tigecycline resistant Gram-negative bacilli was investigated. Methods: In this descriptive cross-sectional study, 150 resistant Gram-negative bacilli were isolated from urine specimens send for culture, and antibiotic susceptibility assessment to the Division of Microbiology of Sina Hospital affiliated to Tabriz University of Medical Sciences which were collected from April-September 2017 are included. Antibiotic susceptibilities were evaluated according to the Clinical and Laboratory Standards published by the Institute and the criteria of the Food and Drug Administration. Results: Of 150 isolates, 138 (92%) were susceptible, and 2 (1.3%) were resistant to both fosfomycin and tigecycline, as confirmed by disk diffusion and Epsilonmeter tests. The difference was statistically significant (P = 0.001). Conclusions: Based on the results, resistance to the conventional antibiotics prescribed for the treatment of UTI was significantly high. Fosfomycin and tigecycline have an appropriate antimicrobial activity towards Gram-negative-resistant isolates involved in UTIs.

Risk Factors for the Antibiotic Resistant Gram-Negative Bacilli Associated Infections in Burn Patients and the In-Vitro Susceptibility of Colistin

Background: Burns patients are predisposed to infectious complications. Amongst microbial infections, Gram-negative bacilli are the most prevalent bacteria in the burn units. Objectives: The current study aimed to identify the risk factors associated with antibiotic-resistant Gram-negative bacilli in hospitalized burn patients and determine the in-vitro susceptibility of these organisms to colistin. Methods: Two hundred burn patients hospitalized in the burn unit and ICU burn ward were allocated to two groups (each with 100 patients) of patients with antibiotic-resistant Gram-negative bacilli infections and the other with antibiotic susceptible Gram-negative bacilli associated infections. The susceptibility of Gram-negative bacilli was done towards various antibacterial agents by the Kirby-Bauer method. Susceptibility of colistin was performed using both E-test and disc diffusion methods. Results: The history of antibiotic usage, length of ICU stay, mechanical ventilation, and catheter usage were the most important risk factors for infections associated with antibiotic-resistant Gram-negative bacilli. Pseudomonas aeruginosa and Acinetobacter baumannii were the most prevalent bacteria in the burn unit. Only one A. baumannii isolate was found resistant toward colistin by both disk diffusion and E-test methods. Conclusions: Burn patients are prone to infections, and Gram-negative bacilli predominates in patients harboring risk factors. These findings influence the choice of traditional therapeutic regimens in such patients. Colistin served as an appropriate antibiotic choice.

Shedding of multidrug-resistant gram-negative bacilli by colonized patients during procedures and patient care activities

Medical procedures and patient care activities may facilitate environmental shedding of health care-associated pathogens. We conducted a cohort study of hospitalized patients in contact precautions for carriage of extended-spectrum beta-lactamase (ESBL)-producing gram-negative bacilli (N = 38) or carbapenem-resistant gram-negative bacilli (CR-GNB) (N = 22) to determine the frequency of environmental shedding during procedures and care activities. Perirectal, wound, and skin were cultured for ESBL-producing and CR-GNB. High-touch surfaces and portable equipment were disinfected before and cultured after procedures; control cultures were collected in the absence of procedures. Of 60 patients enrolled, 34 (57%) had positive perirectal and/or skin or wound cultures. For these 34 patients, 15 (44%) shed their colonizing organism to surfaces during 1 or more procedures. Patients with shedding had significantly higher concentrations of the pathogens recovered from perirectal swabs than those with no shedding (mean, 3.5 vs 2.2 log10 colony-forming units per swab; P < .01). Environmental shedding occurred more frequently during procedures and care activities than in the absence of a procedure (21 of 117, 18% vs 1 of 61, 2%; P < .01), and 6 of 56 (10%) portable devices used for procedures became contaminated. Environmental shedding of antibiotic-resistant gram-negative bacilli occurs frequently during medical procedures and patient care activities. Decontamination of surfaces and equipment and approaches that reduce the burden of carriage could reduce the risk for dissemination.

Expert Consensus on Polymyxin Antimicrobial Susceptibility Testing and Clinical Interpretation

The polymyxins are important antimicrobial agents against antibiotic-resistant gram-negative bacilli. In 2020, the Clinical and Laboratory Standards Institute modified the clinical breakpoints for polymyxin susceptibility test by eliminating the “susceptible” interpretive category, only reporting intermediate (≤2 mg/L) and resistant (≥4 mg/L). However, the European Committee on Antimicrobial Susceptibility Testing recommended the use of clinical breakpoints of ≥2 mg/L as susceptible and >2 mg/L as resistant. The first-line laboratorians and clinicians in China have been perplexed by the inconsistence of international polymyxin clinical breakpoints and discouraged by the difficulty of conducting polymyxin susceptibility testing. Therefore, it is urgently needed to make it clear for the laboratorians in China to know how to accurately carry out polymyxin susceptibility testing and standardize the interpretation of susceptibility testing results. To this end, the experts from relevant fields were convened to formulate this consensus statement on the testing and clinical interpretation of polymyxin susceptibility. Relevant recommendations are proposed accordingly for laboratorians and clinicians to streamline their daily work.

1145. Sparring With Spores: Ultrasounds as a Vector for Pathogen Transmission in the Intensive Care Unit

BackgroundPortable equipment that is shared among patients can be a potential source of pathogen dissemination. In busy healthcare settings, cleaning of shared medical equipment may be suboptimal. In addition, equipment such as ultrasound probe heads present a challenge because sporicidal cleaning solutions such as bleach cannot be used.MethodsWe conducted a culture survey of ultrasounds in 15 intensive care units (ICUs) at a large tertiary care referral center, including medical, surgical, neurology, cardiology, and cardiovascular ICUs. Multiple high-touch surfaces on different types of ultrasound equipment used in the ICUs were swabbed to assess for the presence of Clostridium difficile and antibiotic-resistant Gram-negative bacilli. To assess cleaning, a fluorescent marker visible only under UV light was placed on high-touch surfaces on each of the cultured ultrasounds and a black light was used determine if the marker was removed after 24 hours and again after 1 week.ResultsOf 15 ultrasounds cultured, 7% were contaminated with C. difficile spores and 7% were contaminated with Gram-negative bacilli. Based on fluorescent marker removal, only 20% of the ultrasounds were cleaned within 24 hours and only 31% were cleaned within 1 week. Ultrasounds with touchscreens were cleaned more frequently than those with no touchscreen. For equipment with a combination of touchscreen features and knobs, the touchscreens were cleaned more often than the knobs which often had residual marker even after 7 days.ConclusionUltrasound equipment can be a vector for transmission of C. difficile and other pathogens in critical care settings. In our facility, cleaning of ultrasound equipment was suboptimal, particularly for ultrasounds that did not have a touchscreen interface. Since ultrasounds are being employed in critical care settings with increasing frequency, there is a need for improved methods for cleaning and disinfection.Disclosures A. Deshpande, 3M: Investigator, Research grant. Clorox: Investigator, Research grant. STERIS: Investigator, Research grant.

Isolation and Characterization of Escherichia coli Sequence Type 131 and Other Antimicrobial-Resistant Gram-Negative Bacilli from Clinical Stool Samples from Veterans.

Emerging multidrug-resistant (MDR) Gram-negative bacilli (GNB), including Escherichia coli sequence type 131 (ST131) and its resistance-associated H30 subclone, constitute an ever-growing public health threat. Their reservoirs and transmission pathways are incompletely defined. To assess diarrheal stools as a potential reservoir for ST131-H30 and other MDR GNB, we cultured 100 clinical stool samples from a Veterans Affairs Medical Center clinical laboratory (October to December 2011) for fluoroquinolone- and extended-spectrum cephalosporin (ESC)-resistant E. coli and other GNB, plus total E. coli We then characterized selected resistant and susceptible E. coli isolates by clonal group, phylogenetic group, virulence genotype, and pulsotype and screened all isolates for antimicrobial resistance. Overall, 79 of 100 stool samples yielded GNB (52 E. coli; 48 other GNB). Fifteen samples yielded fluoroquinolone-resistant E. coli (10 were ST131, of which 9 were H30), 6 yielded ESC-resistant E. coli (2 were ST131, both non-H30), and 31 yielded susceptible E. coli (1 was ST131, non-H30), for 13 total ST131-positive samples. Fourteen non-E. coli GNB were ESC resistant, and three were fluoroquinolone resistant. Regardless of species, almost half (46%) of the fluoroquinolone-resistant and/or ESC-resistant non-E. coli GNB were resistant to at least three drug classes. Fecal ST131 isolates closely resembled reference clinical ST131 isolates according to virulence genotypes and pulsed-field gel electrophoresis (PFGE) profiles. Thus, a substantial minority (30%) of veterans with diarrhea who undergo stool testing excrete antibiotic-resistant GNB, including E. coli ST131. Consequently, diarrhea may pose transmission risks for more than just diarrheal pathogens and may help disseminate clinically relevant ST131 strains and other MDR GNB within hospitals and the community.

An Argument for the Use of Aminoglycosides in the Empiric Treatment of Ventilator-Associated Pneumonia.

Appropriate empiric antibiotic therapy for ventilator-associated pneumonia improves outcomes. Controversy exists regarding the inclusion of aminoglycosides in empiric therapeutic regimens. The Ovid and Cochrane databases were searched for relevant literature regarding the use of aminoglycosides in combination therapy for ventilator-associated pneumonia. The data supporting the use of aminoglycosides in certain populations and strategies to limit toxicity are summarized. In patients at high risk of infection with antibiotic-resistant gram-negative bacilli and in those with severe illness, aminoglycosides improve clinical outcomes. In critically ill populations, short-duration therapy and high-dose extended-interval dosing of aminoglycosides can improve therapeutic efficacy while limiting nephrotoxicity. In selected populations using appropriate dosing strategies, aminoglycosides should be considered for empiric treatment of ventilator-associated pneumonia.

Effect of Surotomycin, a Novel Cyclic Lipopeptide Antibiotic, on Intestinal Colonization with Vancomycin-Resistant Enterococci and Klebsiella pneumoniae in Mice.

Surotomycin (formerly called CB-183,315) is a novel, orally administered cyclic lipopeptide antibacterial in development for the treatment of Clostridium difficile infection (CDI) that has potent activity against vancomycin-resistant enterococci (VRE) but limited activity against Gram-negative bacilli, including Bacteroides spp. We used a mouse model to investigate the impact of surotomycin exposure on the microbiome, and to test the consequences of the disruption on colonization by vancomycin-resistant enterococci (VRE) and extended-spectrum β-lactamase-producing Klebsiella pneumoniae (ESBL-KP), in comparison with the effects of oral vancomycin and metronidazole. Mice (8 per group) received saline, vancomycin, metronidazole, or surotomycin through an orogastric tube daily for 5 days and were challenged with 10(5) CFU of VRE or ESBL-KP administered through an orogastric tube on day 2 of treatment. The concentrations of the pathogens in stool were determined during and after treatment by plating on selective media. A second experiment was conducted to determine if the antibiotics would inhibit established VRE colonization. In comparison to controls, oral vancomycin promoted VRE and ESBL-KP overgrowth in stool (8 log10 to 10 log10 CFU/g; P < 0.001), whereas metronidazole did not (<4 log10 CFU/g; P > 0.5). Surotomycin promoted ESBL-KP overgrowth (>8 log10 CFU/g; P, <0.001 for comparison with saline controls) but not VRE overgrowth. Surotomycin suppressed preexisting VRE colonization, whereas metronidazole and vancomycin did not. These results suggest that treatment of CDI with surotomycin could reduce levels of VRE acquisition and overgrowth from those with agents such as vancomycin and metronidazole. However, surotomycin and vancomycin may promote colonization by antibiotic-resistant Gram-negative bacilli.

Airway bacterial colonization in patients with non-small cell lung cancer and the alterations during the perioperative period.

To observe the alterations in airway bacterial colonization during the perioperative period in patients with non-small cell lung cancer (NSCLC) and evaluate their clinical implications. Patients with resectable primary NSCLC were enrolled from October 2011 to April 2012. Airway secretions were harvested for microbiological study after admission, immediately after surgery, and before endotracheal extubation. Spontaneous sputum was collected when patients presented with signs of postoperative pneumonia (POP). Detailed data on the isolated pathogens were carefully recorded. Risk factors for airway colonization and POP were analyzed. A total of 78 consecutive patients were enrolled. Fourteen patients (17.9%) had airway colonization at admission, including four cases of fungi and ten cases of Gram-negative bacilli (GNB). Five patients (6.4%) had colonized pathogens at the end of surgery, including three cases of GNB and two cases of Gram-positive cocci. Nine (11.5%) patients had positive culture of airway secretions collected before extubation, including seven cases of GNB and two cases of fungi. Eighteen patients (23.1%) had POP, of whom one suffered from bronchopleural fistula and one died of POP. Pathogens of POP were confirmed in 11 patients, including nine cases of GNB and two cases of fungi. Three patients had the same pathogens as preoperative colonization. The proportion of more antibiotic-resistant strains increased gradually. Advanced age [odds ratio (OR), 2.263; 95% confidence interval (95% CI), 1.030-4.970] and smoking (OR, 2.163; 95% CI, 1.059-4.429) were risk factors for airway colonization. Decreased diffusion capacity of the lung for carbon monoxide (OR, 5.838; 95% CI, 1.318-25.854), prolonged operation time (OR, 6.366; 95% CI, 1.349-30.033), and preoperative airway colonization (OR, 9.448; 95% CI, 2.206-40.465) were risk factors of POP. Airway colonized pathogens altered and more antibiotic-resistant GNB emerged during the perioperative period. These pathogens played an important role in the presence of POP.

Emergence and Control of Antibiotic-resistant Gram-negative Bacilli in Older Adults

The prevalence of multidrug resistant Gram-negative organisms is increasing worldwide. The Infectious Diseases Society of America has previously singled out groups of pathogens with the highest threat, the majority of which are Gram-negative bacilli. These isolates are prevalent not only in intensive-care units of acute-care facilities, but are also found among residents of long-term care facilities with various levels of care, and occasionally among patients without exposure to healthcare systems. Advanced age is an independent predictor for carriage of many of these organisms, and elderly patients are subjected to worse outcomes following the acquisition of resistant Gram-negatives. Due to their frequent admissions and transfers across different healthcare facilities within a region, the elderly constitute important epidemiological reservoirs for these bacteria. Containing the acquisitions of resistant Gram-negatives among the elderly could be achieved through reduction of either 1) selective pressure (e.g. less antibiotics) or 2) colonization pressure (e.g. less exposure to resistant bacteria). This manuscript will review the present situation of multidrug resistant Gram-negative organisms, especially among the elderly, and the infection control interventions that might mitigate their further spread.

A New Metric of Antibiotic Class Resistance in Gram-Negative Bacilli Isolated from Hospitalized Children

The purpose of this study was to describe patterns of infection or colonization with antibiotic-resistant gram-negative bacilli (GNB) in hospitalized children utilizing an electronic health record. Tertiary care facility. Pediatric patients 18 years of age or younger hospitalized from January 1, 2006, to December 31, 2008. Children were identified who had (1) at least 1 positive culture for a multidrug-resistant (MDR) GNB, defined as a GNB with resistance to 3 or more antibiotic classes; or (2) additive drug resistance, defined as isolation of more than 1 GNB that collectively as a group demonstrated resistance to 3 or more antibiotic classes over the study period. Differences in clinical characteristics between the 2 groups were ascertained, including history of admissions and transfers, comorbid conditions, receipt of procedures, and antibiotic exposure. Of 56,235 pediatric patients, 46 children were infected or colonized with an MDR GNB, of which 16 were resistant to 3 classes and 30 were resistant to 4 classes. Another 39 patients had positive cultures for GNB that exhibited additive drug resistance. Patients with additive drug resistance were more likely than patients with MDR GNB to have had previous admissions to a long-term facility (8 vs 2; P = .04) and had more mean admissions (7 vs 3; P < .01) and more mean antibiotic-days (P < .01 to P = .02). Six patients with additive drug resistance later had a positive culture with an MDR GNB. An electronic health record can be used to track antibiotic class resistance in GNB isolated from hospitalized children over multiple cultures and hospitalizations.

Low Frequency of Endemic Patient-to-Patient Transmission of Antibiotic-Resistant Gram-Negative Bacilli in a Pediatric Intensive Care Unit

We sought to determine the frequency of horizontal transmission of antibiotic-resistant gram-negative bacilli (ARGNB) in a pediatric intensive care unit during a nonoutbreak period. Among 5,300 admissions over 39 consecutive months, 13 ARGNB clusters involving 35 children were identified by pulsed-filed gel electrophoresis analysis, which suggests that person-to-person transmission was uncommon.

Prospective Audit of Febrile Neutropenia Management at a Tertiary University Hospital in Singapore

Febrile neutropenia (FN) remains a major cause of morbidity and mortality in Oncology/Haematology units. We launched a new protocol for FN management that incorporates risk stratification at our institute from October 2008. An audit was performed concurrently to evaluate the protocol and to define the epidemiology of FN locally. Case records of all inpatients with FN between October 2008 and June 2009 were reviewed prospectively. Clinical and microbiological characteristics were collated along with outcomes and programme adherence. Statistical testing was performed using Stata 10.1. There were 178 FN episodes (50 in patients with solid cancers) from 131 patients. Forty-two (23.6%) episodes were classified as high-risk according to MASCC criteria. Initial blood cultures were positive in 49 (27.5%) episodes, of which gram-negative bacilli (GNB) predominated. Overall compliance to the protocol was 56.7%, with the main issue being disinclination to use oral antibiotics as fi rst-line empirical therapy for low-risk episodes. Overall mortality was 7.3% and infection-related mortality was 4.5%. High-risk FN and the presence of central venous catheters were independently associated with bacteraemia on multivariate analysis, but there were no independent predictors of infection-related mortality. GNB accounted for the majority of bloodstream infections at our institute, unlike data from developed countries. Uptake of the new FN protocol was satisfactory, although the use of oral antibiotics as fi rst-line empirical therapy can be improved. A better method for predicting infections caused by antibiotic-resistant GNB is urgently required, and antibiotic resistance trends should be monitored to enable the implementation of more appropriate antibiotic regimens over time.

Meropenem use and colonization by antibiotic-resistant Gram-negative bacilli in a pediatric intensive care unit*

The carbapenems are broad-spectrum beta-lactam antibiotics with activity against most organisms encountered in the pediatric intensive care unit (PICU). In anticipation of their increased use in critically ill children, we measured the effect of sustained meropenem use on the pattern of Gram-negative bacillus colonization in patients admitted to a tertiary care PICU. : Prospective preintervention/postintervention comparison. Medical/surgical PICU. Consecutive PICU admissions over 2.5 yrs. After a 6-mo baseline period, all children with serious infections admitted to the PICU during the subsequent 2 yrs were administered meropenem. The incidence of colonization by Gram-negative bacilli resistant to one of a battery of broad-spectrum parenteral agents, and by organisms resistant specifically to meropenem, during the baseline period was compared with the period of preferred meropenem use. During the period of preferred meropenem use, the amount of meropenem used increased >seven-fold, whereas the use of other advanced generation beta-lactams was reduced by nearly 80%. The mean prevalence of colonization by antibiotic-resistant bacilli in general was not statistically altered during the period of meropenem preference (7.3 organisms/100 patient-days, vs. 9.4 organisms/100 patient-days at baseline, p < 0.09). The prevalence of colonization by Gram-negative organisms resistant specifically to meropenem was 0.61 organisms/100 patient-days during the baseline period vs. 1.04 organisms/100 patient-days during the period of meropenem preference (p < 0.30). The incidence of nosocomial infections did not change, and the prevalence of nosocomial infections caused by meropenem-resistant organisms was always <1% of all admissions during the period of meropenem preference. There was no statistically detectable effect on the prevalence of colonization by Gram-negative organisms resistant to one or more classes of broad-spectrum parenteral antibiotics, or to colonization by organisms resistant specifically to meropenem, when meropenem was the preferred antibiotic in a PICU.

Resistance in gram-negative bacilli in a cardiac intensive care unit in India: Risk factors and outcome

The objective of this study was to compare the risk factors and outcome of patients with preexisting resistant gram-negative bacilli (GNB) with those who develop sensitive GNB in the cardiac intensive care unit (ICU). Of the 3161 patients ( n=3,161) admitted to the ICU during the study period, 130 (4.11%) developed health care-associated infections (HAIs) with GNB and were included in the cohort study. Pseudomonas aeruginosa (37.8%) was the most common organism isolated followed by Klebsiella species (24.2%), E. coli (22.0%), Enterobacter species (6.1%), Stenotrophomonas maltophilia (5.7%), Acinetobacter species (1.3%), Serratia marcescens (0.8%), Weeksella virosa (0.4%) and Burkholderia cepacia (0.4%). Univariate analysis revealed that the following variables were significantly associated with the antibiotic-resistant GNB: females (P=0.018), re-exploration (P=0.004), valve surgery (P=0.003), duration of central venous catheter (P<0.001), duration of mechanical ventilation (P<0.001), duration of intra-aortic balloon counter-pulsation (P=0.018), duration of urinary catheter (P<0.001), total number of antibiotic exposures prior to the development of resistance (P=0.014), acute physiology and age chronic health evaluation score (APACHE II), receipt of anti-pseudomonal penicillins (piperacillin-tazobactam) (P=0.002) and carbapenems (P<0.001). On multivariate analysis, valve surgery (adjusted OR=2.033; 95% CI=1.052-3.928; P=0.035), duration of mechanical ventilation (adjusted OR=1.265; 95% CI=1.055-1.517; P=0.011) and total number of antibiotic exposure prior to the development of resistance (adjusted OR=1.381; 95% CI=1.030-1.853; P=0.031) were identified as independent risk factors for HAIs in resistant GNB. The mortality rate in patients with resistant GNB was significantly higher than those with sensitive GNB (13.9% vs. 1.8%; P=0.03). HAI with resistant GNB, in ICU following cardiac surgery, are independently associated with the following variables: valve surgeries, duration of mechanical ventilation and prior exposure to antibiotics. The mortality rate is significantly higher among patients with resistant GNB.

P1368 Correlation between colonisation and infection with antibiotic-resistant Gram-negative bacilli in the neonatal intensive care unit

P1368 Correlation between colonisation and infection with antibiotic-resistant Gram-negative bacilli in the neonatal intensive care unit

Comparative Effects of Single-Dose Ceftriaxone Versus Three Oral Antibiotic Regimens on Stool Colonization by Resistant Bacilli in Children

The use of short-term intramuscular ceftriaxone for pediatric ambulatory conditions raises concerns regarding the promotion of resistance among colonizing enteric bacteria. This study was designed to assess the prevalence of stool colonization with resistant Gram-negative bacilli after single-dose ceftriaxone treatment compared with other regimens for acute otitis media. Children age 3 months to 7 years and diagnosed with acute otitis media were randomized to receive treatment with single-dose ceftriaxone or with oral cefprozil, amoxicillin or azithromycin. Stool samples were obtained at enrollment and then 3-5 days, 10-14 days, and 28-30 days after therapy was initiated and screened for the presence of facultative Gram-negative bacilli resistant to ceftriaxone, cefprozil, amoxicillin, piperacillin, piperacillin-tazobactam and tobramycin. Mean prevalence of colonization by resistant organisms for each treatment group was compared at each time point. One thousand nine subjects were enrolled. The prevalence of colonization by a Gram-negative bacillus resistant to at least 1 of the screening antibiotics decreased after receipt of ceftriaxone but returned close to values measured at study entry by 30 days. A qualitatively similar pattern was noted for the 3 other regimens, but a quantitatively greater decrease in the prevalence of colonization by a resistant bacterium was noted at the 3- to 5-day and 10- to 14-day visits among azithromycin recipients (P < 0.001). Colonization by a Gram-negative bacillus resistant specifically to ceftriaxone was unusual at each study visit, regardless of treatment assignment. A single intramuscular dose of ceftriaxone had a similar effect on the prevalence of antibiotic-resistant Gram-negative facultative bacilli in the stool of healthy children when compared with commonly used oral agents.