Carbapenem-resistant Gram-negative Bacteria Research Articles

Mortality burden related to infection with carbapenem-resistant Gram-negative bacteria among haematological cancer patients: a retrospective cohort study.

Carbapenem-resistant Gram-negative bacteria (CRGNB) pose a clinical challenge. We attempted to estimate the mortality burden of CRGNB among haematological cancer patients. This was a retrospective cohort study. We included adult patients hospitalized in the haemato-oncological/bone marrow transplantation departments for chemotherapy, between 2008 and 2014, with Gram-negative aerobic bacteraemia. We compared patients with CRGNB and carbapenem-susceptible Gram-negative bacteraemia (CSGNB). The primary outcome was 14 day all-cause mortality. In addition, we assessed 1 year survival. Multivariable logistics regression analysis and adjusted Cox regression analysis were conducted. Analyses were adjusted to the propensity for CRGNB bacteraemia. The cohort included mostly young patients (mean age 50.1 years) with acute leukaemia (264/423, 62.4%) and the median absolute neutrophil count at bacteraemia onset was 0 × 10(9)/L. The unadjusted 14 day mortality rate was higher for patients with CRGNB compared with CSGNB [45.6% (47/103) versus 15% (48/320), respectively (P < 0.001)]. Adjusting to baseline prognostic factors, infection characteristics and the propensity score retained a significant association between CRGNB and 14 day mortality (OR 5.14, 95% CI 2.32-11.38). Including only the first bacteraemic episode per patient, 1 year mortality was 74.7% (68/91) for patients with CRGNB versus 49.8% (119/239) for patients with CSGNB (P < 0.001). Adjusting for risk factors associated with 1 year mortality, the HR for mortality with CRGNB was 1.48 (95% CI 1-2.2). CRGNB bacteraemia was associated with several risk factors for mortality, including inappropriate empirical antibiotic treatment and less effective definitive antibiotics. This study demonstrated a significant adjusted association between CRGNB and mortality up to 1 year among haemato-oncological patients receiving chemotherapy.

Four years of experience with carbapenem-resistant Gram-negative bacteria in two tertiary care hospitals in Crete, Greece

Carbapenem-resistant gram-negative bacteria (CRGNB, Acinetobacter baumannii, Klebsiella pneumoniae, Pseudomonas aeruginosa)) are important nosocomial pathogens in Greece.

Safety and efficacy of intravenous colistin in children.

To observe the safety and efficacy of Colistimethate sodium in children infected with gram-negative bacteria, susceptible only to colistimethate sodium. This prospective observational study done over 2 years observed children who received colistin for >48 h, for renal failure as defined by p-RIFLE criteria. Out of 68 children, 52 (76.5%) survived. There were three children with evidence of acute kidney injury and none had neurotoxicity. Serum creatinine significantly decreased at 48 h and at end of treatment, from that at beginning of therapy (P=0.007). Colistimethate sodium is effective against carbapenem-resistant Gram-negative bacteria, and is safe in children.

Molecular characterization of carbapenemase production among gram-negative bacteria in saudi arabia.

We characterized the molecular basis of carbapenemase production in carbapenem-resistant Gram-negative bacteria isolated from hospitalized patients from Saudi Arabia in the year 2012. Isolates were collected from across the Kingdom and phenotypically tested for carbapenemase production. Polymerase chain reaction detection of carbapenemase genes was also performed. Our results indicate that in Saudi Arabia, OXA-48 and NDM-1 are the dominant carbapenemases among Enterobacteriaceae with low prevalence of VIM. The latter is the most prevalent metallo-beta-lactamase in Pseudomonas aeruginosa, whereas oxacillinases, OXA-23 in particular, are the dominant carbapenemases in Acinetobacter baumannii. No KPC or IMP genes were detected. Our study is the first report of OXA-48, NDM-1, and VIM-4 enzymes in Enterobacter from the Kingdom. Also it is the first report of OXA-72 and NDM-1 in A. baumannii in Saudi Arabia, and the coexistence of blaOXA-23 and blaNDM-1 genes in this species in the country. Awareness of the role of international travel in the spread of carbapenem-resistant determinants in the Kingdom, as well as effective infection control interventions in hospitals and strict antimicrobial stewardship in healthcare facilities and the community are keys to combat the rise of carbapenemase producers in the Kingdom.

Clinical Importance of Carbapenemase Production in Gram-Negative Bacteria

Carbapenem resistance is one of the major threats faced in antimicrobial treatment of infections caused by Gram negative organisms. In India and throughout the world the use of carbapenems has increased resulting in an increased resistance of pathogens to this class of antibiotics. Bacteria are capable enough to become resistant to antibiotics by a number of mechanisms both intrinsic and acquired, most common of which include enzymatic degradation of antibiotics. Carbapenem resistant Gram-negative bacteria usually spreads in the hospital settings to other patients and caregivers or relatives by unwashed hands or from contact with soiled equipment and surfaces such as bedrails, tables, chairs, countertops and door handles. These carriers are the ultimate sources of dissemination in the community. Detection of carbapenemase is a crucial infection control issue because they are often associated with extensive antibiotic resistance, treatment failures and infection-associated mortality. For the identification of carbapenemase producers different nonmolecular methods are used such as E- test (Epsilometer Test), Modified hodge test, MIC by Agar Dilution Method, Carba NP Test, EDTA disk synergy test, Boronic Acid Test, 2-mercaptopropionic acid inhibition (2-MPA) test. Molecular techniques remain the gold standard for the precise identification of carbapenemase genes. Most of these techniques are based on PCR and may be followed by a sequencing step if a precise identification of the carbapenemase gene is needed. This review article describes clinical importance and methods used for the identification of carbapenemase producers.

Exploring the epidemiology of carbapenem-resistant Gram-negative bacteria in west London and the utility of routinely collected hospital microbiology data.

The objective of this study was to identify carbapenem-resistant organisms using routinely collected local microbiology data and describe the epidemiology of carbapenem resistance in two London teaching hospitals. Data on inpatients infected or colonized with Gram-negative organisms between March 2009 and February 2012 were extracted. A computer algorithm was developed incorporating internationally recognized criteria to distinguish carbapenem-resistant organisms. Multivariable analysis was conducted to identify factors associated with infection or colonization with carbapenem-resistant organisms. Binomial regression was performed to detect changes in resistance trends over time. Yearly incidence of carbapenem resistance was observed to be increasing, with significant increasing trends in Acinetobacter baumannii (47.1% in 2009-10 to 77.2% in 2011-12; P<0.001) and Enterobacter spp. (2.2% in 2009-10 to 11.5% in 2011-12; P<0.001). Single-variable and multivariable analysis demonstrated differences in the proportion of carbapenem-resistant isolates across all variables investigated, including age, sex and clinical specialty; in the latter organism-specific niches were identified. Patients in the youngest age group (16-24 years old) had the highest odds of being infected or colonized with carbapenem-resistant isolates of Escherichia coli, Klebsiella spp. or Pseudomonas aeruginosa. Furthermore, proportions of carbapenem-resistant organisms differed between the hospitals. Carbapenem resistance is an emerging problem within the UK inpatient healthcare setting. This is not an issue confined to the Enterobacteriaceae and fine-resolution surveillance is needed to identify at-risk groups. Regular analysis of routinely collected data can provide insight into the evolving carbapenem-resistance threat, with the ability to inform efforts to prevent the spread of resistance.

Safety and clinical outcomes of carbapenem de-escalation as part of an antimicrobial stewardship programme in an ESBL-endemic setting.

To evaluate the safety and clinical outcomes of patients who received carbapenem de-escalation as guided by an antimicrobial stewardship programme (ASP) in a setting where ESBL-producing Enterobacteriaceae are endemic. Patients receiving meropenem or imipenem underwent a prospective ASP review for eligibility for de-escalation according to defined institutional guidelines. Patients in whom carbapenem was de-escalated or not de-escalated, representing the acceptance and rejection of the ASP recommendation, respectively, were compared. The primary outcome was the clinical success rate; secondary outcomes included the 30 day readmission and mortality rates, the duration of carbapenem therapy, the incidence of adverse drug reactions due to antimicrobials, the acquisition of carbapenem-resistant Gram-negative bacteria and the occurrence of Clostridium difficile-associated diarrhoea (CDAD). The de-escalation recommendations for 300 patients were evaluated; 204 (68.0%) were accepted. The patient demographics and disease severity were similar. The clinical success rates were similar [de-escalated versus not de-escalated, 183/204 (89.7%) versus 85/96 (88.5%), P=0.84], as was the survival at hospital discharge [173/204 (84.8%) versus 79/96 (82.3%), P=0.58]. In the de-escalated group, the duration of carbapenem therapy was shorter (6 versus 8 days, P<0.001), the rate of adverse drug reactions was lower [11/204 (5.4%) versus 12/96 (12.5%), P=0.037], there was less diarrhoea [9/204 (4.4%) versus 12/96 (12.5%), P=0.015], there was a lower incidence of carbapenem-resistant Acinetobacter baumannii acquisition [4/204 (2.0%) versus 7/96 (7.3%), P=0.042] and there was a lower incidence of CDAD [2/204 (1.0%) versus 4/96 (4.2%), P=0.081]. This study suggests that the ASP-guided de-escalation of carbapenems led to comparable clinical success, fewer adverse effects and a lower incidence of the development of resistance. This approach is safe and practicable, and should be a key component of an ASP.

Molecular characteristics of carbapenem-resistant gram-negative bacteria in southern China.

A total of 368 nonreplicate gram-negative bacteria with resistance to imipenem or meropenem were collected to search for carbapenemase genes, class 1 integrons, and insertion sequence with common region 1 (ISCR1). The carbapenemase genes blaIMP-4, blaKPC-2, and blaNDM-1 were found in two Enterobacteriaceae and seven Pseudomonas aeruginosa isolates, nine Klebsiella pneumoniae isolates, and seven Enterobacteriaceae and two Acinetobacter spp. isolates. The class D OXA-type carbapenemase genes blaOXA-23-like, blaOXA-24-like, blaOXA-58, and blaOXA-51-like were detected in 59 (34.9%), 2 (1.2%), 16 (9.5%), and 126 (74.6%) Acinetobacter strains. This is the first description of blaNDM-1 in Enterobacter hormaechei and Acinetobacter genomic species 13TU. Of the integrase-positive strains, 135 (90.0%) Acinetobacter spp., 22 (61.1%) P. aeruginosa, and 14 (100%) Enterobacteriaceae isolates were identified by five, ten, and four different gene cassette arrays, respectively. Three novel gene cassette arrays aadB-aadA1, dfrA25, and dfrA16-aadA2 were reported for the first time in some species. Of the ISCR1-positive strains, the nonfermentative strains (102 Acinetobacter spp. and 13 P. aeruginosa. isolates) contained the same arrangement blaPER-1-putative glutathione-S-transferase-novel type ABC transporter, and three Enterobacteriaceae isolates harbored three different arrangements. Four distinct complex class 1 integron structures were observed. The complex class 1 integron detected in New Delhi, metallo-β-lactamase (NDM-1)-producing E. hormaechei, was found to coexist in the NDM-1-carrying plasmid. Our results suggested that we should pay more attention to the strict implementation of infection control measures and active antibiotic resistance surveillance to avoid the rapid spread or outbreak of carbapenemase-producing gram-negative bacteria.

Bloodstream infections in patients with hematological malignancies: which is more fatal - cancer or resistant pathogens?

BackgroundThe primary objective of this study was to report the incidence of bloodstream infections (BSIs) and clinically or microbiologically proven bacterial or fungal BSIs during neutropenic episodes in patients with hematological malignancies.MethodsIn this retrospective observational study, all patients in the hematology department older than 14 years who developed febrile neutropenia during chemotherapy for hematological cancers were evaluated. Patients were included if they had experienced at least one neutropenic episode between November 2010 and November 2012 due to chemotherapy in the hematology ward.ResultsDuring 282 febrile episodes in 126 patients, 66 (23%) episodes of bacteremia and 24 (8%) episodes of fungemia were recorded in 48 (38%) and 18 (14%) patients, respectively. Gram-negative bacteria caused 74% (n=49) of all bacteremic episodes. Carbapenem-resistant Gram-negative bacteria (n=6) caused 12% and 9% of Gram-negative bacteremia episodes and all bacteremia episodes, respectively. Carbapenem-resistant Gram-negative bacteria included Acinetobacter baumannii (n=4), Pseudomonas aeruginosa (n=1), and Serratia marcescens (n=1). Culture-proven invasive fungal infection occurred in 24 episodes in 18 cases during the study period, with 15 episodes in ten cases occurring in the first study year and nine episodes in eight cases in the second study year. In 13 of 18 cases (72%) with bloodstream yeast infections, previous azole exposure was recorded. Candida parapsilosis, C. glabrata, and C. albicans isolates were resistant to voriconazole and fluconazole.ConclusionBSIs that occur during febrile neutropenic episodes in hematology patients due to Gram-negative bacteria should be treated initially with non-carbapenem-based antipseudomonal therapy taking into consideration antimicrobial stewardship. Non-azole antifungal drugs, including caspofungin and liposomal amphotericin B, should be preferred as empirical antifungal therapy in the events of possible or probable invasive fungal infections with an absence of pulmonary findings due to increase azole resistance.

Patient safety -- mission for the future: Healthcare-associated infections and antibiotic resistance

Healthcare-associated infections (HAI) are considered as one of the major challenges for modern health care. In the context of demographic change and the expected increase of invasive and complex patient treatment and concommittantrise in numbers of patients with underlying diseases with susceptibility to infections, quality of care and patient safety will in the near future depend strongly on the prevention of HAI. To avoid preventable HAI in terms of improved quality of care is beyond question, therefore mainly the prevalence of highly resistant microorganisms (HRMO) will becrucial for the success of treatment of unpreventable HAI. In addition to MRSA, the greatest danger in relation to antibiotic resistance worldwide are now considered tob e carbapenem-resistant Enterobacteriaceae (CRE) or multidrug-resistant Gram-negative (4MRGN) bacteria. In case oft he uncontrolled spread of HRMO unpreventable infections become also untreatable. The prevalence of HRMO varies between different countries. Especially in the Netherlands and Denmark HRMO such as MRSA, VRE and CRE/4MRGN are still significantly less common than in Germany or France. The reason lies in the fact that in nearly all Dutch hospitals anintegrative infectious disease service (clinical microbiology and/or infectious diseaseas wellinfection prevention) was established already years ago, while in Germany - with few exceptions - in most hospitals only a basic infectious disease services (consulting hygienist, microbiological diagnosis is held by laboratories often far away from the patient). As hospitals are connected with each other with respect to theircommon care of patients, one of the most important challenges in future infection prevention will be the implementation of regional and intersectoral infection prevention and control.

Carbapenem and multidrug resistance in Gram-negative bacteria in a single centre in Italy: Considerations on in vitro assay of active drugs

In intensive care units (ICUs), the most important causes of nosocomial bacterial infections are mainly multidrug-resistant (MDR) and extensively drug-resistant (XDR) Acinetobacter baumannii and Klebsiella pneumoniae strains. Mortality related to these infections is very high due to lack of effective therapy and the severity of patient conditions. This study aimed to assess the prevalence of carbapenem resistance genes in 77 carbapenem-resistant Gram-negative bacteria isolated from severe infections (bloodstream, pulmonary and urinary tract) during the period 1 January to 31 July 2013 in a general ICU in Catania, Italy, and to examine their susceptibility to tigecycline and colistin using two different methods. In total, 52 A. baumannii belonging to the same sequence type (ST) 2 clone and carrying the blaOXA-23 gene as well as 25 K. pneumoniae carrying blaKPC-3 were isolated. Four distinct pulsotypes were identified in K. pneumoniae, which correlated with four distinct STs: ST258 and ST512, spread worldwide, and ST147 and ST395 detected for the first time in Italy. A. baumannii isolates showed an XDR profile and were fully susceptible only to colistin; all KPC-producing K. pneumoniae isolates were MDR, whilst colistin was active against 19 of 25 strains. These results show that broth microdilution (BMD) is a reliable in vitro susceptibility test for colistin, above all K. pneumoniae, whilst both the gradient test and BMD are suitable for tigecycline susceptibility testing of A. baumannii.

Combination therapy for carbapenem-resistant Gram-negative bacteria.

Carbapenem-resistant Gram-negative bacteria (CR-GNB) represent an increasing hazard in healthcare settings. A central question concerning the treatment of invasive infections caused by CR-GNB involves the use of combination therapy. Potential advantages of combination therapy include improved efficacy due to synergy, while the disadvantages include adverse events and increased antibiotic use with a potential drive towards resistance. Several observational studies have examined whether combination therapy offers an advantage over colistin/polymyxin monotherapy. We highlight the inherent limitations of these studies related to their observational design and sample size to show why they do not at present provide an answer to the question of combination versus monotherapy. This distinction is important to guide clinical practice until solid evidence has been obtained and to enable the recruitment of patients into randomized controlled trials. A few randomized controlled trials examining specific combinations have recently been completed or are ongoing. Currently, however, there is no evidence-based support for most combination therapies against CR-GNB, including colistin/carbapenem combination therapy.

Development and Testing of Health Information Exchange Methods for Alerting Infection Preventionists About Multi-Drug Resistant Organisms: Making Unstructured Microbiology Culture Data Usable

Recent outbreaks of carbapenem-resistant gram-negative bacteria among hospitalized patients elicited national attention and underscored the danger of healthcare-associated infections. Whenever patients visit more than one hospital, a multidrug-resistant organism (MDRO) may spread. Within hospitals, spread is also a scourge. Our goal is to build a regional system that parses microbiology culture data to make it usable for decision-support, and then alerts hospitals when a patient with a history of MDRO is admitted.

Which Multidrug-Resitant Bacteria are Emerging in Patients with Hematological Malignancies?: One-Year Report.

The aim of this retrospective, observational study was to evaluate the outcomes of bacteremia attacks during neutropenic episodes caused by chemotherapy in patients with hematological cancers by assessing mortality, involved pathogens, antimicrobial therapy and treatment responses. Patients who were older than 14years of age and developed at least one neutropenic episode after chemotherapy to treat hematological cancer between November 2011 and November 2012 were included in the study. We retrospectively collected demographic, treatment, and survival data for 68 patients with 129 neutropenic episodes. The mean age was 59.36±15.22years (range 17-80years), and 41 cases were male. The mean Multinational Association of Supportive Care in Cancer score was 19.56±9.04. A total of 37 (28%) bacteremia attacks were recorded in 20 cases (29%). Fatality rates were 50% in the six cases with bacteremia caused by carbapenem-resistant Gram-negative bacteria; death occurred in two patients with carbapenem-resistant Acinetobacter baumannii and in one patient with carbapenem-resistant Pseudomonas aeruginosa. Clinical and microbiological responses were achieved using PIP-TAZ or CEP-SUL treatment in 80% (16/20) of the cases with bacteremia caused by carbapenem-sensitive Gram-negative bacteria (CS-GNB). During 547 colonization-days in 21 (30%) vancomycin-resistant enterococci (VRE)-colonized cases among 68 patients, vancomycin-resistant Enterococcus faecium bacteremia developed in two patients. Non-carbapenem-based therapy can cure most bacteremia attacks caused by CS-GNB in patients with hematological cancer. However, bacteremia and other infections caused by drug-resistant pathogens, such as A. baumannii, P. aeruginosa, and VRE, are a growing concern in hematological patients.

Association between genotypic and phenotypic pyrazinamide resistance in Mycobacterium tuberculosis

Background: Carbapenem-resistant Gram-negative bacteria (CR GNB) are subject of public health concerns and may be associatedwithworse outcomes. In this studyweaimed to assess 28-days survival of patientswith bacteraemia due toGramnegative species. Methods & Materials: Cross-sectional multicentre study was performed in patients with drug-resistant Gram-negative bacteraemia in Slovakia in November 2011January 2012. Antibiotic susceptibility testing was performed according to the European Committee on Antimicrobial Susceptibility Testing. Kaplan-Meier curves were used to assess 28-days survival and were analysed with Log rank test to compare survival of patientswith andwithout infection caused by CR GNB. Results: Altogether, 257 cases with drug-resistant GNB bacteraemia were identified (59,4% males; median age 62 years, IQR 50-75), of them 45 (17,5%)were due to CR GNB. Twenty-eight-days mortality, was significantly higher in group of CR GNB cases (42,2% vs. 25,5%, p=0,029), while in overall mortality there was no statistically significant difference (64,4% vs. 49,06%, p=0,086). Median time from positive blood culture to death was 9,5 days in CR GNB group, and 34,5 days in carbapenem-susceptible group (p=0,042). Also, significant difference in28-days survivalwasnoticed comparing patients with carbapenem susceptible and CR GNB infection (Log rank test p=0,033). Regarding the risk factors, polymicrobial infection (p=0,019), hospitalization in intensive care unit (p<0,001) andhospitalizationduring thewinter and/or spring (p=0,054),were associated with CR infection. Conclusion: In this study, carbapenem-resistance in GNB species causing bloodstream infection was associated with significantly worse outcome and decreased probability of survival. This is underscoring importance of careful control strategies to avoid spread of CR GNB among patients. (This study was partially supported with Trnava University Grant, No 7/TU/12).

Impact of carbapenem-resistance on 28-days survival in patients with Gram-negative bacteraemia

Multidrug resistant (MDR) Gram-negative bacteria (GNB) are one of the most serious public health threats. Carbapenem-resistant Gram-negative bacteria (CR GNB) may be associated with worse outcomes [1,2]. Aim of this study was to assess 28-days survival of patients with bacteraemia due to Gram-negative species. Cross-sectional multicentre study was performed in patients with drugresistant Gram-negative bacteraemia in Slovakia in November 2011January 2012. Antibiotic susceptibility testing was performed according to the European Committee on Antimicrobial Susceptibility Testing. KaplanMeier curves were used to assess 28-days survival and were analysed with log rank test to compare survival of patients with and without infection caused by CR GNB.

Risk factors for hospital-acquired pneumonia caused by carbapenem-resistant Gram-negative bacteria in critically ill patients: a multicenter study in Korea

We performed a case–control study to identify risk factors of carbapenem-resistant Gram-negative bacteria (CRGNB) as an increasing cause of hospital-acquired pneumonia (HAP). The study included critically ill adult patients with HAP whose microbial etiology was identified at eight tertiary centers in Korea between June 2008 and December 2009. Eighty two patients with 86 isolates of CRGNB (62 Acinetobacter baumannii, 14 Pseudomonas aeruginosa, and 10 Stenotrophomonas maltophilia) were included in the case group, and 122 patients with carbapenem-susceptible Gram-negative bacteria were included in the control group. Diabetes mellitus (adjusted odds ratio [aOR] 2.82, 95% confidence interval [95% CI] 1.25–6.38), radiologic score ≥5 (aOR 4.56, 95% CI 2.36–8.81), prior fluoroquinolone (aOR 2.39. 95% CI = 1.07–5.35), or carbapenem usage (aOR 2.82, 95% CI 1.75–17.83) were found to be independent risk factors. Fluoroquinolone and carbapenem should be cautiously used to avoid HAP caused by CRGNB.

Bacterial infection after liver transplantation.

Infectious complications are major causes of morbidity and mortality after liver transplantation, despite recent advances in the transplant field. Bacteria, fungi, viruses and parasites can cause infection before and after transplantation. Among them, bacterial infections are predominant during the first two months post-transplantation and affect patient and graft survival. They might cause surgical site infections, including deep intra-abdominal infections, bacteremia, pneumonia, catheter-related infections and urinary tract infections. The risk factors for bacterial infections differ between the periods after transplant, and between centers. Recently, the emergence of multi-drug resistant bacteria is great concern in liver transplant (LT) patients. The instructive data about effects of infections with extended-spectrum beta lactamase producing bacteria, carbapenem-resistant gram-negative bacteria, and glycopeptide-resistant gram-positive bacteria were reported on a center-by-center basis. To prevent post-transplant bacterial infections, proper strategies need to be established based upon center-specific data and evidence from well-controlled studies. This article reviewed the recent epidemiological data, risk factors for each type of infections and important clinical issues in bacterial infection after LT.

Prevalence of Carbapenem Resistance among Gram-Negative Bacteria in a Tertiary Care Hospital in North-East India

Introduction: Carbapenems are considered to be the last choice for drug resistant Gramnegative bacteria but emergence of carbapenem resistant Gram-negative bacteria worldwide due to the production of carbapenemase has jeopardize their use. Aims and objectives: To detect the prevalence of carbapenem resistance in Gram-negative bacteria and carbapenemase production by Modified Hodge Test. Materials and Methods: A total of 160 isolates of Gram-negative bacteria from November 2012 to October 2014, from different clinical samples were included in the study. Those isolates with intermediate or resistant zone to meropenem and doripenem by disc diffusion methods according to CLSI guidelines were confirmed by E-test and were again tested for carbapenemase production by Modified Hodge Test (MHT). Results: Out of 160 isolates, 48 (30%) showed resistance to carbapenem by disc diffusion and E-test. Carbapenem resistance was higher in female patients 41.6% than in male patients 15.5% and among ICU patients 57.1%, ward patients 33.3% and among OPD patients 13.8%. Maximum number of carbapenem resistant isolate was obtained from urine sample n= 20, followed by pus n=13 and wound swab n=7. MHT for carbapenemase production was positive in 29 (60.4%) of the isolates. Carbapenemase production by MHT was highest with Acinetobacter spp. with n=5 (83.3%), followed by Pseudomonas spp. n= 6 (75%) and E.coli spp. n=16 (65.5%) and nil among Citrobacter spp. Conclusions: Carbapenem resistance due to production of carbapenemase is prevalent in our hospital. MHT is a simple test in the routine lab for detection of carbapenemases.

Colistin susceptibility testing: time for a review

Sir, Colistin has re-emerged as an important antimicrobial in recent times owing to limited therapeutic options against carbapenemresistant Gram-negative bacteria. Current guidelines (BSAC, CLSI and EUCAST) recommend routine colistin susceptibility testing by estimation of MIC because the disc diffusion test does not reliably detect low-level resistance. – 5 Broth microdilution (BMD) is widely used as a method of MIC estimation in Europe and the USA. Colistin exhibits a varying degree of adherence to organic and inorganic materials due to its polycationic nature, resulting in loss during experimental conditions. Also, polysorbate 80 (P-80), a surfactant widely used as a dispersing agent in BMD panels, may influence the free drug concentration of colistin and hence MIC results. We evaluated the impact of the use of different BMD panels and the presence of P-80 on colistin MIC estimation. A total of 146 clinical isolates collected from a variety of sources and stored at 2708C were evaluated in this study. The isolates included 56 Pseudomonas aeruginosa, 29 Acinetobacter spp. and 61 Enterobacteriaceae. The MIC testing was carried out on two different types of polystyrene microtitre trays (MTTs), namely non-coated V-bottom MTTs (NMTTs; costar 3896; Corning, NY, USA) and tissue-culture-coated round-bottom MTTs (TCMTTs; costar 3799; Corning). The MICs of colistin for the isolates were determined using the CLSI broth dilution method using colistin sulphate. MIC determination was carried out by using an initial bacterial inoculum of 5×10 cfu/mL in Mueller–Hinton broth with or without P-80 (final P-80 concentration of 0.002%) on both types of MTT. The experiments were done in triplicate, and quality control was assured by concurrent testing of P. aeruginosa ATCC 27853 as a control, with all results within the range published by the CLSI. MICs for the isolates in both types of MTT with or without P-80 are shown in Table 1. The NMTT MICs (mean 0.54+0.58) were significantly lower than the TCMTT MICs (mean 2.84+1.93) (P,0.0001; 95% CI –2.5 to –2.1). The tissue coating on MTTs, achieved by means of excess negative electric charge, resulted in an overall 5.3-fold increase in MIC value, probably due to decreased free colistin concentration within the microwells. The differences in MIC results were seen among all types/groups of isolates (3.2, 5.5 and 9.4, respectively, for P. aeruginosa, Enterobacteriaceae and Acinetobacter spp.). The addition of P-80 to NMTTs significantly decreased the colistin MIC (mean 0.09+0.09) by 6-fold (P,0.0001; 95% CI 0.4 –0.5). Although there was a relatively smaller decrease (1.24-fold) in the mean MIC determined using TCMTTs with added P-80 (mean 2.3+1.5), this was also statistically significant (P,0.001; 95% CI 20.31 to 20.75). Comparing the MICs determined using NMTTs and