Gentamicin Susceptibility Research Articles

Accuracy of different methods for susceptibility testing of gentamicin with KPC carbapenemase-producing Klebsiella pneumoniae

Performance of Vitek2, Etest, and TREK broth microdilution (BMD) panels was evaluated versus reference CLSI BMD for gentamicin susceptibility testing with 57 bloodstream isolates of KPC-producing Klebsiella pneumoniae. Compared with reference BMD, the Essential Agreement and Categorical Agreement for TREK panels, Vitek2, and Etest were 91.2%, 31.6%, and 61.4%, respectively, and 86%, 21%, and 52.6%, respectively. Four very major discrepancies occurred with Vitek2. In these 4 strains, gentamicin resistance was associated with the presence of an armA aminoglycoside resistance determinant.

High level gentamicin resistance and susceptibility to Vancomycin in enterococci in a tertiary care hospital of Dhaka City

Vancomycin and high level gentamicin resistant enterococci detection is important for effective treatment and control of nosocomial infection. The present study was undertaken to determine the species distribution of Enterococcus and the rate of vancomycin and high level gentamicin resistant enterococci (HLGRE) in clinical samples in a tertiary care hospital of Dhaka city. Enterococci were identified to species level by standard biochemical and serological methods. Their susceptibilities to antibiotics were determined by disc diffusion method according to CLSI guideline. Minimum inhibitory concentration (MIC) of vancomycin and gentamicin were determined by agar dilution method. The study was conducted from July 2009 to February 2010. Among 80 isolates, 95% and 5% were identified as Enterococcus faecalis and Enterococcus faecium respectively. Out of 80 isolates 72 (90%) were sensitive and 8 (10%) were intermediate resistant to vancomycin (30?g) by disc diffusion method, but all isolates were susceptible by agar dilution MIC method. Out of 80 enterococci, 37 (46.25%) showed high level resistance to gentamicin (MIC: > 500 ?g/ml) by MIC method but, initially six of which showed sensitive result to gentamicin by disc diffusion method using 120 ?g disc. The study indicated high prevalence of HLGRE in our hospital population. MIC method was more accurate in detecting high level gentamycin resistant enterococci compared to disc diffusion method with 120 ?g gentamicin disc. However, none of the enterococcal strains showed resistance to vancomycin. HLGRE should be monitored regularly in clinical samples as it is difficult to treat. DOI: http://dx.doi.org/10.3329/imcj.v7i2.20103 Ibrahim Med. Coll. J. 2013; 7(2): 28-31

Characterisation of Pseudomonas aeruginosa related to bovine mastitis

Pseudomonas aeruginosa is one of the causative pathogens of bovine mastitis. Most P. aeruginosa strains possess the type III secretion system (TTSS), which may increase somatic cell counts (SCCs) in milk from mastitis-affected cows. Moreover, most of P. aeruginosa cells can form biofilms, thereby reducing antibiotic efficacy. In this study, the presence and effect of TTSS-related genotypes on increase of SCCs among 122 P. aeruginosa isolates obtained from raw milk samples from mastitis-affected cows and their antibiotic susceptibility at planktonic and biofilm status were investigated. Based on the presence of TTSS-related genes a total of 82.7% of the isolates were found to harbour exoU and/or exoS genes, including the invasive (exoU-/exoS+, 69.4%), cytotoxic (exoU+/exoS-, 8.3%) and cytotoxic/invasive strains (exoU+/ exoS+, 5.0%). Milk containing exoS-positive isolates had higher SCCs than those containing exoS-negative isolates. The majority of isolates showed gentamicin, amikacin, meropenem and ciprofloxacin susceptibility at planktonic status. However, the susceptibility was decreased at the biofilm status. Based on minimum biofilm eradication concentration (MBEC)/minimum inhibitory concentration (MIC) ratios, the range of change in antibiotic susceptibility varied widely depending on the antibiotics (from ≥ 3.1-fold to ≥ 475.0-fold). In conclusion, most P. aeruginosa isolates studied here had a genotype related to increase in SCCs. The efficiency of antibiotic therapy against P. aeruginosa-related bovine mastitis could be improved by analysing both the MBEC and the MIC of isolates.

Association between fluoroquinolone resistance and resistance to other antimicrobial agents among Escherichia coli urinary isolates in the outpatient setting: a national cross-sectional study

Sir, Fluoroquinolones are among the most widely prescribed antibiotics. Recent reports show that quinolones are prescribed in nearly half of all outpatient urinary tract infection (UTI) visits in the USA, although current guidelines recommend against their use as first-line treatment for uncomplicated UTIs. As a result, the prevalence of quinolone-resistant pathogens, particularly Gram-negative bacteria, is on the rise globally. Horizontally transferable genes (qnr) borne by plasmids encode low-level quinolone resistance in Escherichia coli. Previous studies have found that plasmid-mediated resistance to low concentrations of ciprofloxacin increases the selection of higher ciprofloxacin resistance, by allowing the bacterial population to survive and grow to a level at which secondary mutations to higher resistance can occur. This low-level resistance, conferred by multiresistance plasmids, would not be detected by the usual breakpoints for susceptibility used in microbiology laboratories. By prescribing a quinolone to patients infected with these apparently susceptible isolates, physicians may inadvertently facilitate the selection of higher-level resistance. There are important clinical and public health implications. First, the treatment of infections caused by Gram-negative bacteria containing these resistance elements may be less effective than the treatment of infections caused by bacteria lacking these genes. Second, the biological linking of quinolone resistance with other resistance types that can be carried by plasmids means that overprescribing of quinolones and other antibiotics is likely to further fuel the dissemination of multidrug-resistant bacteria, for which there are limited available treatment options. To inform the practice of evidence-based prescribing, we aimed in the present study to ascertain whether there was an association between fluoroquinolone resistance among urinary E. coli isolates and resistance to other antimicrobial agents. We conducted a cross-sectional analysis of antimicrobial surveillance data from a nationally representative network of microbiological laboratories (The Surveillance Network Database—USA) described in detail elsewhere. The results of all routine susceptibility tests were reported based on CLSI criteria adopted by the facility at the time of testing. Aminoglycoside (gentamicin) susceptibility was chosen as a marker because resistance to it in E. coli is almost always plasmid mediated and plasmids containing qnr and other quinolone resistance genes (such as qepA) commonly contain genes for aminoglycoside resistance. Since clinicians may be more likely to prescribe a quinolone if an isolate is non-susceptible to other treatment options, we included only isolates that were also susceptible to at least trimethoprim/sulfamethoxazole, ampicillin or nitrofurantoin, which are commonly used for treatment of UTIs. Multivariable Poisson regression with robust error variances was used to estimate the relative risk (RR) of fluoroquinolone non-susceptibility. Statistical analyses were performed using Stata v.12.0, with P values ,0.05 considered significant. The study was exempt from Institutional Review Board review at Harvard University. The study included 1651506 outpatient urine E. coli isolates tested for fluoroquinolone (ciprofloxacin or levofloxacin) and aminoglycoside (gentamicin) susceptibility between 2000 and 2010 (Table S1, available as Supplementary data at JAC Online). The majority of isolates in the sample were from female patients (89.5%) and the mean age was 46 years. Fluoroquinolone and gentamicin resistance increased significantly over the sample period, from 3.2% in 2000 to 18.2% in 2010 (P,0.001) and from 2.3% to 7.4% (P,0.001), respectively. After controlling for age, sex, region and year, isolates that were non-susceptible to gentamicin were seven times more likely to be fluoroquinolone resistant than gentamicin-susceptible isolates (adjusted RR: 7.0; 95% CI: 6.5–7.5; P,0.001) (Table 1) that were also susceptible to ampicillin, nitrofurantoin and trimethoprim/sulfamethoxazole. The risk of fluoroquinolone resistance was higher for isolates susceptible to only ampicillin (adjusted RR: 7.8; 95% CI: 7.5–8.1) or trimethoprim/sulfamethoxazole (adjusted RR: 8.6; 95% CI: 8.5 –8.8). Across all five models, age, isolates tested in the south and year were positively associated with fluoroquinolone resistance. Our findings show that the risk of fluoroquinolone-resistant E. coli infection in the outpatient setting is heightened by nonsusceptibility to an aminoglycoside, even amongst isolates that were susceptible to three other antibiotics commonly used to treat UTIs. We also found that there was some geographic variation in risk, with a nearly 50% increased risk of quinolone resistance among isolates from the south, holding other factors constant. There are a number of limitations, including the lack of patient-level data on antimicrobial use. However, our results correspond favourably with similar associations of fluoroquinolone resistance with other resistances reported previously in intensive care patients. One explanation for this association is the widespread circulation of plasmid-encoded quinolone resistance genes. To our knowledge, these findings are the first national-level

Antimicrobial susceptibility of Gram-negative organisms isolated from patients hospitalised with pneumonia in US and European hospitals: Results from the SENTRY Antimicrobial Surveillance Program, 2009–2012

Here we evaluated the frequency of occurrence and antimicrobial susceptibility patterns of Gram-negative bacteria isolated from patients hospitalised with pneumonia in medical centres in the USA (n=28) and Europe and the Mediterranean region (EMR) (n=25) in 2009–2012. Susceptibility testing was performed by reference broth microdilution methods. Overall, 12851 isolates were collected (6873/5978 in USA/EMR). The same top 11 organisms were observed in both geographic regions, but in different rank orders, and Gram-negative organisms represented 61.5/76.1% of strains in USA/EMR. Pseudomonas aeruginosa was the most frequently isolated Gram-negative organism in both regions (20.9/20.9% of cases in USA/EMR) and showed reduced susceptibility to most antimicrobials tested, including ceftazidime (79.6/68.7% susceptibility in USA/EMR), meropenem (76.3/65.8%) and piperacillin/tazobactam (72.9/63.9%). Klebsiella spp. was isolated from 9.7/11.6% of cases and showed extended-spectrum β-lactamase (ESBL) phenotype rates of 19.5/35.1% in USA/EMR. Meropenem and amikacin were active against 62.3/78.7% and 60.8/85.2% of ESBL phenotype Klebsiella spp. from USA/EMR, respectively. Enterobacter spp. ranked fourth in the USA (5.9%) and sixth in EMR (5.5%), whereas Escherichia coli ranked fifth in the USA (5.5%) and third in EMR (11.8%). Acinetobacter spp. and Stenotrophomonas maltophilia combined were isolated from 8.0/10.7% of cases in USA/EMR. A significant increase in P. aeruginosa susceptibility to meropenem and a significant decrease in gentamicin susceptibility among Klebsiella spp. were noted in EMR. These results confirm that very few agents remain broadly active against the most frequently isolated Gram-negative organisms from patients with pneumonia in US and EMR medical centres.

Burkholderia pseudomallei Isolates from Sarawak, Malaysian Borneo, Are Predominantly Susceptible to Aminoglycosides and Macrolides

Melioidosis is a potentially fatal disease caused by the saprophytic bacterium Burkholderia pseudomallei. Resistance to gentamicin is generally a hallmark of B. pseudomallei, and gentamicin is a selective agent in media used for diagnosis of melioidosis. In this study, we determined the prevalence and mechanism of gentamicin susceptibility found in B. pseudomallei isolates from Sarawak, Malaysian Borneo. We performed multilocus sequence typing and antibiotic susceptibility testing on 44 B. pseudomallei clinical isolates from melioidosis patients in Sarawak district hospitals. Whole-genome sequencing was used to identify the mechanism of gentamicin susceptibility. A novel allelic-specific PCR was designed to differentiate gentamicin-sensitive isolates from wild-type B. pseudomallei. A reversion assay was performed to confirm the involvement of this mechanism in gentamicin susceptibility. A substantial proportion (86%) of B. pseudomallei clinical isolates in Sarawak, Malaysian Borneo, were found to be susceptible to the aminoglycoside gentamicin, a rare occurrence in other regions where B. pseudomallei is endemic. Gentamicin sensitivity was restricted to genetically related strains belonging to sequence type 881 or its single-locus variant, sequence type 997. Whole-genome sequencing identified a novel nonsynonymous mutation within amrB, encoding an essential component of the AmrAB-OprA multidrug efflux pump. We confirmed the role of this mutation in conferring aminoglycoside and macrolide sensitivity by reversion of this mutation to the wild-type sequence. Our study demonstrates that alternative B. pseudomallei selective media without gentamicin are needed for accurate melioidosis laboratory diagnosis in Sarawak. This finding may also have implications for environmental sampling of other locations to test for B. pseudomallei endemicity.

P5.094 Evaluation of Gentamicin Susceptibility of Neisseria Gonorrhoeae Isolates in Argentina

IntroductionThe effective treatment of infection by Neisseria gonorrhoeae (Ng) is critical for the individual patient management and essential in the control of gonorrhoea. The emergence of decreased susceptibility to third...

P3.280 Gentamicin Susceptibility Profile of Neisseria Gonorrhoeae Clinical Strains Isolated in Bilbao (Spain) During 2011 and 2012

BackgroundAntimicrobial therapy is essential to control Neisseria gonorrhoeae (NG). The appearance of isolates with decreased susceptibility or resistant to third-generation cephalosporins (TGC) has raised several concerns. Recent clinical trials suggest...

The Effect on Peritoneal Dialysis Pathogens of Changing Topical Antibiotic Prophylaxis

Prophylactic gentamicin 0.1% cream has demonstrated efficacy in preventing both exit-site infection (ESI) and peritonitis attributable to gram-positive and gram-negative organisms; however, the effect of this practice on the gentamicin susceptibility patterns of bacterial pathogens isolated from such infections is unknown. We therefore examined the effect of a change in our prophylactic topical antibiotic exit-site protocol (from mupirocin 2% cream to gentamicin 0.1% cream) on infection rates and susceptibility patterns. This retrospective observational cohort study examined two periods of time: before and after the change in exit-site protocol. Each period was 30 months in duration, with a 2-month implementation period between, during which patient data were excluded. Demographic, clinical, and microbiology data were collected for each patient and episode of infection. Overall, 377 patients were evaluated. In the mupirocin period (MUP), 145 infections occurred in 79 patients, and in the gentamicin period, 145 infections occurred in 93 patients. No significant effect was found either in overall episodes of infection (0.53 per year) or in episodes of peritonitis (0.429 vs 0.375 per year), but episodes of ESI increased significantly (0.098 vs 0.153 per year; p = 0.024; odds ratio: 1.55; 95% confidence interval: 1.05 to 2.28). Episodes of Staphylococcus aureus peritonitis increased by 38% (0.018 vs 0.025 per year), and episodes of S. aureus ESI increased significantly by 150% (0.022 vs 0.055 per year; p = 0.03; hazard ratio: 3.00; 95% confidence interval: 1.09 to 8.26). Episodes of pseudomonal peritonitis declined by 68% (0.022 vs 0.007 per year), and episodes of pseudomonal ESI increased by 150% (0.007 vs 0.018 per year). The gentamicin susceptibility for gram-positive isolates demonstrated no significant change; however, the gentamicin susceptibility for Enterobacteriaceae decreased by 12% and for Pseudomonas, by 14%. The significant increase in episodes of ESI and the decrease in susceptibility for both Enterobacteriaceae and Pseudomonas isolates represent a concerning trend. Centers should examine trends in infection rates and in bacterial susceptibilities to determine the most appropriate agent for ESI prophylaxis.

Adaptation of Salmonella enterica Hadar under static magnetic field: effects on outer membrane protein pattern

BackgroundSalmonella enterica serovar Hadar (S. Hadar) is a highly prevalent foodborne pathogen and therefore a major cause of human gastroenteritis worldwide. Outer membrane proteins whose production is often regulated by environmental conditions also play important roles in the adaptability of bacterial pathogens to various environments.ResultsThe present study investigated the adaptation of S. Hadar under the effect of acute static magnetic field exposure (200 mT, 9 h) and the impact on the outer membrane protein pattern. Via two-dimensional electrophoresis (2-DE) and LC-MS/MS spectrometry, we compared the proteome of enriched-outer membrane fraction before and after exposure to a magnetic field. A total of 11 proteins, displaying more than a two-fold change, were differentially expressed in exposed cells, among which 7 were up-regulated and 4 down-regulated. These proteins were involved in the integrity of cell envelope (TolB, Pal), in the response to oxidative stress (OmpW, dihydrolipoamide dehydrogenase, UspF), in the oxidative stress status (bacterioferritin), in virulence (OmpX, Yfgl) or in motility (FlgE and UspF). Complementary experiments associated the down-regulation of FlgE and UspF with an alteration of swarming, a flagella-driven motility, under SMF. Furthermore, the antibiotic disc diffusion method confirmed a decrease of gentamicin susceptibility in exposed cells. This decrease could be partly associated with the up-regulation of TolC, outer membrane component of an efflux pump. OmpA, a multifunctional protein, was up-regulated.ConclusionsSMF (200 mT) seems to maintain the cell envelope integrity and to submit the exposed cells to an oxidative stress. Some alterations suggest an increase of the ability of exposed cells to form biofilms.

Change of Antimicrobial Susceptibility amongEscherichia coliStrains Isolated from Female Patients with Community-Onset Acute Pyelonephritis

PurposeThere is a concern on which antimicrobials are appropriate as empirical agents for community-onset acute pyelonephritis (APN) in regions where the fluoroquinolone resistance rate is high, such as in Korea.Materials and MethodsThree hundred and two strains of E. coli in 2001-2002 and 349 strains in 2008-2009 were isolated from the urine cultures of female adult APN patients, and the antimicrobial susceptibility was compared according to each study period. All the patients were classified as uncomplicated or complicated APN, and a subgroup analysis was done thereafter.ResultsThe E. coli strains isolated in 2008-2009 showed improved susceptibility to trimethoprim-sulfamethoxazole compared to those isolated in 2001-2002. However, the third generation cephalosporin and gentamicin susceptibility was worsened. Of the 232 isolates from the uncomplicated APN patients, there was no difference between the two different time periods. On the other hand, of the 419 isolates from the complicated APN patients, the susceptibility to third generation cephalosporin, gentamicin and ciprofloxacin was significantly worsened.ConclusionThe antimicrobial susceptibility of E. coli changed over the study period, however, this change occurred mainly in the complicated APN patients. In Korea, ciprofloxacin is still useful as an empirical agent for uncomplicated APN patients, but this is not the case for patients with complicated APN because of high resistance rate to ciprofloxacin in these patients. For the complicated APN patients, the rate of resistance to ciprofloxacin is already more than 30%.

Molecular and Epidemiological Evaluation of Strain Replacement in Patients Previously Harboring Gentamicin-Resistant MRSA

Gentamicin-susceptible methicillin-resistant Staphylococcus aureus (GS-MRSA) clones have gradually replaced gentamicin-resistant MRSA (GR-MRSA) clones in many European countries. We studied molecular and epidemiological aspects of MRSA strain replacement in individual patients. All patients from whom at least 2 MRSA strains showing different gentamicin susceptibility patterns were isolated between 1996 and 2008 were retrospectively identified. Staphylococcal cassette chromosome mec (SCCmec) type and clonality between isolates were determined using molecular methods. Risk factors for individual GR-MRSA SCCmec I (prevalent clone) strain replacement with GS-MRSA non-SCCmec I types were studied in a nested case-crossover study (n = 55 patients). MRSA strain replacement was observed in 127 patients, 85 (67%) of whom were initially colonized with GR-MRSA replaced subsequently by GS-MRSA. Most GS-MRSA replacement strains (50; 59%) possessed SCCmec IV. All MRSA isolate pairs from the same patient that consisted of different gentamicin susceptibility and SCCmec types were also genotypically different. Exposure to domiciliary nursing assistance (odds ratio [OR], 8.1; 95% confidence interval [CI], 1.2 to 53.7) and high Charlson scores (OR, 7.1; 95% CI, 1.1 to 46.8) were associated with individual strain replacement. In individual patients, exogenous acquisition of a different MRSA strain was responsible for strain replacement in most cases. Domiciliary nursing assistance could be a target for specific control measures to prevent transmission of GS-MRSA in our setting.

Ciprofloxacin use and susceptibility of Gram-negative organisms to quinolone and non-quinolone antibiotics

A Trust strategy to reduce ciprofloxacin use was implemented at a University hospital. This study aimed to investigate whether the susceptibility of Gram-negative organisms (GNO) to alternative antimicrobials (co-amoxiclav, doxycycline, aztreonam, piperacillin/tazobactam, meropenem and gentamicin) changed, and whether there was any relationship between GNO susceptibility to these antimicrobials and ciprofloxacin usage. The first isolate of each GNO from blood cultures, sputum and urine of hospitalized adults, between January 2008 and August 2009, was included. Antibiotic usage and GNO susceptibility were investigated using linear regression. The association between defined daily dose/1000 occupied bed days (DDD/1000 OBD) and susceptibility was assessed using Pearson correlation and linear regression. Ciprofloxacin use decreased significantly by 4.37 DDD/1000 OBD per month [95% confidence interval (CI) 2.99, 5.75; P < 0.001], while aztreonam and gentamicin use increased significantly (aztreonam: 0.22 DDD/1000 OBD increase per month; 95% CI 0.10, 0.34; P = 0.001; gentamicin: 0.46 DDD/1000 OBD increase per month; 95% CI 0.12, 0.79; P = 0.01). There was no change in meropenem, co-amoxiclav, doxycycline or piperacillin/tazobactam use. When DDD/1000 OBD for all non-quinolone antimicrobials were pooled, use increased significantly by 3.33 DDD/1000 OBD per month (95% CI 0.79, 5.87; P = 0.013). There were 5410 GNO isolates. A significant increase was recorded in the proportion of GNO susceptible to ciprofloxacin (0.55% increase in susceptibility per month; 95% CI 0.38, 0.72; P < 0.001), aztreonam (1.87% susceptibility increase per month; 95% CI 1.18, 2.55; P < 0.001), piperacillin/tazobactam (0.18% susceptibility increase per month; 95% CI 0.03, 0.33; P = 0.021), meropenem (0.27% susceptibility increase per month; 95% CI 0.08, 0.47; P = 0.009) and gentamicin (0.17% susceptibility increase per month; 95% CI 0.04, 0.29; P = 0.011). An inverse association between ciprofloxacin use and susceptibility to ciprofloxacin (P < 0.001), piperacillin/tazobactam (P = 0.12), aztreonam (P= 0.002), meropenem (P = 0.015) and gentamicin (P = 0.034) is suggested. These data demonstrate reduced ciprofloxacin usage and concomitant increasing GNO susceptibility to β-lactams. While definitive evidence of a causal relationship is beyond the capability of a single-centre study, the results suggest that reducing quinolone exposure may exert a favourable effect on the quinolone, β-lactam and gentamicin susceptibility of GNO.

An evaluation of gentamicin susceptibility of Neisseria gonorrhoeae isolates in Europe

The emergence of decreased susceptibility to third-generation, extended-spectrum cephalosporins in Neisseria gonorrhoeae and associated treatment failures highlights the need to consider alternatives for future therapeutic use, such as gentamicin. The three laboratories surveying gonococcal antimicrobial susceptibility as part of the European Network for Sexually Transmitted Infections Surveillance compared agar dilution and Etest to determine gentamicin MICs and performed the first survey of gentamicin susceptibility on 1366 gonococcal isolates from 17 European Union/European Economic Area (EU/EAA) countries in 2009. Sentinel surveillance of gentamicin susceptibility showed that 95% of European isolates were within a narrow MIC range (4-8 mg/L), with 79% showing an MIC of 8 mg/L. Most countries showed little variation, but wider MIC ranges were observed in Greece (1-16 mg/L) and France, Norway and Sweden (2-16 mg/L). While MICs for both methods generally differed by just one doubling dilution, they were lower by Etest. This is the first reported evidence that the European gonococcal population susceptibility to gentamicin is similar to that reported in other world regions. Clinical trials to evaluate the therapeutic efficacy of gentamicin may be warranted.

High Prevalence of Carbapenem-Resistant Acinetobacter baumannii Carrying the bla OXA-143 Gene in Brazilian Hospitals

A recent article by Higgins et al. reported the identification of a novel carbapenem-hydrolyzing class D β-lactamase (CHDL), defined as OXA-143, in a carbapenem-resistant Acinetobacter baumannii strain isolated in Brazil in 2004 (5). This enzyme, which has 88% identity with OXA-40, is the first representative of a novel subgroup of CHDLs whose prevalence remains to be determined (5). In an attempt to carry out this task, we have conducted a surveillance study of carbapenem-resistant A. baumannii isolates in order to determine the antimicrobial susceptibility patterns and prevalence of blaOXA-type carbapenemase genes in medical centers in both the southeastern and southern regions of Brazil. We report here a high prevalence of carbapenem-resistant A. baumannii carrying the blaOXA-143 and blaOXA-23 genes, along with the first isolation of strains carrying the blaOXA-72 (OXA-72 is a single-amino-acid variant of OXA-40) and blaOXA-58 genes in Brazilian hospitals. From 2004 to 2008, 36 carbapenem-resistant A. baumannii isolates recovered from different patients hospitalized in eight medical centers were screened for the presence of genes encoding metallo-β-lactamases (MβLs) and OXA-type β-lactamases (6, 15). Flanking sequences of blaOXA-type genes were characterized by PCR using primers targeting ISAba-1 or -3 (12). PCR products were confirmed by sequencing, and the genetic diversity of blaOXA-positive strains was determined by enterobacterial repetitive intergenic consensus (ERIC)-PCR analysis (11). All isolates were found to be resistant to imipenem, meropenem, ceftazidime, aztreonam, piperacillin-tazobactam, and ciprofloxacin. Tobramycin (61.1%), ampicillin-sulbactam (61.1%), gentamicin (47.2%), amikacin (27.8%), and cefepime (11.1%) susceptibility rates were determined. MβL-encoding genes were not identified, whereas a high prevalence of blaOXA genes was noticed among carbapenem-resistant isolates (Table ​(Table1).1). In this regard, 21 strains (58.3%) carried the blaOXA-143 gene, 15 strains (41.7%) carried the ISAba-1/blaOXA-23 gene array, one strain carried the ISAba-3/blaOXA-58/ISAba-3 gene array, and two isolates carried the blaOXA-72 gene (GenBank accession no. {type:entrez-nucleotide,attrs:{text:FJ628170,term_id:223585696,term_text:FJ628170}}FJ628170, {type:entrez-nucleotide,attrs:{text:FJ492877,term_id:219563065,term_text:FJ492877}}FJ492877, {type:entrez-nucleotide,attrs:{text:FJ969387,term_id:238866561,term_text:FJ969387}}FJ969387, and {type:entrez-nucleotide-range,attrs:{text:HM804278 to HM804281,start_term:HM804278,end_term:HM804281,start_term_id:308737170,end_term_id:308737176}}HM804278 to HM804281). Although the presence of the blaOXA-51 and ISAba-1 genes was confirmed in all of the isolates, no colinearity of the two genes (i.e., ISAba-1 adjacent to the blaOXA-23 gene) was observed. Isolates harboring the blaOXA-143, blaOXA-72, and blaOXA-58 genes were restricted to hospitals located in Sao Paulo (the largest and most populous metropolitan area in southeastern Brazil), while blaOXA-23-harboring A. baumannii isolates were obtained from hospitals in Sao Paulo and Parana (in southern Brazil), confirming previous reports of widespread dissemination of OXA-23-producing A. baumannii in this region (2, 9). Finally, ERIC-PCR typing revealed genetic diversity among blaOXA-143- and blaOXA-23-positive A. baumannii isolates. TABLE 1. Characteristics of carbapenem-resistant A. baumannii isolates carrying blaOXA-type genes encoding class D carbapenemasesa In summary, the blaOXA-143 gene was commonly identified among the carbapenem-resistant A. baumannii isolates surveyed in this study. Also, we report the first isolation of blaOXA-72- and blaOXA-58-carrying strains in Brazilian hospitals. OXA-143 is a new subgroup of CHDL identified in isolates of A. baumannii from Brazil (5). We would only bring to mind that the blaOXA-72 gene was first reported from an A. baumannii strain in Thailand in 2004 (GenBank accession no. {type:entrez-nucleotide,attrs:{text:AY739646,term_id:52699554,term_text:AY739646}}AY739646), and so far it has been restricted to Acinetobacter sp. isolates from Asian and Mediterranean countries (1, 4, 7, 8, 14).

Concordance of Gastrointestinal Tract Colonization and Subsequent Bloodstream Infections With Gram-negative Bacilli in Very Low Birth Weight Infants in the Neonatal Intensive Care Unit

Gram-negative bacilli (GNB) cause as many as 20% of episodes of late-onset sepsis among very low birth weight (VLBW, birth weight < or =1500 g) infants in the neonatal intensive care unit. As the gastrointestinal (GI) tract can serve as a reservoir for GNB, we hypothesized that VLBW infants with prior GI tract colonization with gentamicin-susceptible GNB who developed bloodstream infections (BSI) would do so with gentamicin-susceptible GNB. A prospective cohort study of VLBW infants was performed in 2 level III neonatal intensive care units from September 2004 to October 2007. GI tract surveillance cultures were obtained weekly. Risk factors for GNB BSI and for GI tract colonization with GNB were assessed. Fifty-one (7.3%) of 698 subjects experienced 59 GNB BSIs of which 34 occurred by 6 weeks of life and 625 (90%) of 698 subjects were colonized with GNB. Overall, 25% of BSI and 16% of GI tract isolates were nonsusceptible to gentamicin and colonization with the same species and same gentamicin susceptibility profile preceded 98% of GNB BSIs. Vaginal delivery, birth weight < or =750 g, GI tract pathology, increased use of central venous catheters, use of vancomycin, mechanical ventilation, and H2 blockers/proton pump inhibitors were associated with GNB BSI. Vaginal delivery, birth weight >1000 g, and treatment with carbapenem agents were associated with GNB colonization. These data support the use of empiric gentamicin to treat late-onset sepsis in infants colonized with gentamicin-susceptible GNB. Targeted GI tract surveillance cultures of infants with specific risk factors during weeks 2 to 6 of life could be used to guide empiric therapy for late-onset sepsis.

Improved susceptibility of Gram-negative bacteria in an intensive care unit following implementation of a computerized antibiotic decision support system

Emergence of multiresistant Gram-negative organisms in intensive care units (ICUs) throughout the world is a concerning problem. Therefore we undertook a study to follow the resistance patterns of the most common clinically isolated Gram-negative organisms within our ICU following an antibiotic stewardship intervention to evaluate whether a reduction in broad-spectrum antibiotics improves local antibiotic resistance patterns. This prospective study was conducted over a 7 year period within an ICU at a tertiary teaching hospital in Melbourne, Australia. All clinically isolated Gram-negative organisms were identified and extracted from the hospital pathology system. Three monthly antibiograms were created. The pre-interventional period occurred between January 2000 and June 2002 (10 quarters) and the post-interventional period was defined from July 2002 to December 2006 (18 quarters). Segmented linear regression was used to analyse for a difference in the rates of change in susceptibility. A total of 2838 Gram-negative organisms were isolated from clinical sites from ICU patients during the study period. There was significant improvement in susceptibility of Pseudomonas to imipenem 18.3%/year [95% confidence interval (CI): 4.9-31.6; P = 0.009] and gentamicin 11.6%/year (95% CI: 1.8-21.5; P = 0.02) compared with the pre-intervention trend. Significant changes in the rates of gentamicin and ciprofloxacin susceptibility were also observed in the inducible Enterobacteriaceae group although these were less clinically significant. This study demonstrates improved antibiotic susceptibility of ICU Gram-negative isolates including Pseudomonas following an intervention aimed at reducing broad-spectrum antibiotics.

Trends in antibiotic susceptibility of bloodstream pathogens in hospitalized patients in France, 1996 to 2007

Nationwide surveys of antimicrobial susceptibility of bacteria isolated from bloodstream infections are required to fit empiric therapy to recent trends and detect emerging resistance. We report the results of a French national prospective survey based on the College of Bacteriology–Virology and Hygiene study group network performed each October during the 1996 to 2007 period, with focus on Enterobacteriaceae (7708 isolates) and Staphylococcus aureus (2271 isolates). The most relevant antimicrobial susceptibilities trends were i) a decrease in fluoroquinolones susceptibility among Enterobacteriaceae (96–90%, P < 0.0001) and Escherichia coli isolates (98–89%, P < 0.0001), respectively, ii) the slight but significant decrease in cefotaxime susceptibility among E. coli ( P = 0.016), and iii) the significant increase in gentamicin susceptibility among S. aureus strains ( P = 0.016). This survey reports antibiotic susceptibility of bloodstream pathogens in France. The empiric use of fluoroquinolones in severe infections should be cautiously monitored by thorough clinical and microbiologic follow-up.

Antimicrobial susceptibility, inducible macrolide-lincosamide-streptogramin B, and clonal diversity patterns of nosocomial methicillin-resistant Staphylococcus aureus strains isolated in Hacettepe University adult hospital

Aim: Nosocomial infections due to methicillin resistant Staphylococcus aureus (MRSA) are an important problem with limited therapeutic options. The aim of this study was to determine the vancomycin, teicoplanin, linezolid, tigecycline, erythromycin, gentamicin, ciprofloxacin, rifampin, trimethoprim/sulfamethoxazole, and clindamycin susceptibility, inducible macrolide-lincosamide-streptogramin B (iMLS_B) resistance, and clonal diversity patterns of 109 mecA positive Staphylococcus aureus strains isolated from patients with nosocomial infections in Hacettepe University Adult Hospital between 2002 and 2004. Materials and methods: The nosocomial isolates of S. aureus from various clinical samples (58 blood, 45 pus, 6 catheter) were identified by Sceptor (Becton Dickinson, USA) automated system. Polymerase chain reaction (PCR) was performed for the presence of mecA gene of the MRSA isolates. The susceptibility to vancomycin, teicoplanin, linezolid, and tigecycline was determined by Etest (AB Biodisk, Sweden) and to the other antibiotics by disk diffusion methods according to the CLSI recommendations. Inducible macrolide-lincosamide-streptogramin B (iMLS_B) resistance phenotypes were determined by the double disk method. Pulse field gel electrophoresis (PFGE) was performed to examine the clonal diversity. Results: All MRSA strains were susceptible to vancomycin, teicoplanin, linezolid, and tigecycline with MIC_{90} (µg/mL) values of 2, 2, 2, and 0.25, respectively. The isolates were highly resistant (≥90%) to gentamicin, ciprofloxacin, and rifampin, whereas the susceptibility to trimethoprim/sulfamethoxazole was 89%, to clindamycin was 62%, and to erythromycin was 46%. iMLS_B resistance was determined among 13% of the MRSA strains. Thirteen different clones were shown by PFGE, whereas 80% of the isolates were in a dominant clone. Conclusion: Vancomycin, teicoplanin, linezolid, and tigecycline were highly active against nosocomial isolates of MRSA in our hospital. Although these are effective therapeutic options for MRSA, the high rate of cross-contamination of the patients is a matter of concern. We should pay more attention to infection control practices.

Gentamicin susceptibility in Escherichia coli related to the genetic background: problems with breakpoints

In total, 120 Escherichia coli isolates positive for one of the gentamicin resistance (GEN(R)) genes aac(3)-II, aac(3)-IV or ant(2'')-I were tested for gentamicin susceptibility by the agar dilution method. Isolates positive for aac(3)-IV or ant(2'')-I had an MIC distribution of 8-64 mg/L, whereas isolates positive for aac(3)-II had MICs of 32 to >512 mg/L, suggesting a relationship between the distribution of MICs and the specific GEN(R) mechanism. The MIC distribution, regardless of the GEN(R) mechanism, was 8 - >512 mg/L, which supports the clinical breakpoint of MIC >4 mg/L suggested by EUCAST and questions the breakpoint recommended by the CLSI (> or =16 mg/L).