Use Of Extended-spectrum Cephalosporins Research Articles

Phylogenomic investigation of an outbreak of fluoroquinolone-resistant Salmonella enterica subsp. enterica serovar Paratyphi A in Phnom Penh, Cambodia.

In early 2020, the Medical Biology Laboratory of the Pasteur Institute of Cambodia isolated an unusually high number of fluoroquinolone-resistant Salmonella enterica subspecies enterica serovar Paratyphi A strains during its routine bacteriological surveillance activities in Phnom Penh, Cambodia. A public-health investigation was supported by genome sequencing of these Paratyphi A strains to gain insights into the genetic diversity and population structure of a potential outbreak of fluoroquinolone-resistant paratyphoid fever. Comparative genomic and phylodynamic analyses revealed the 2020 strains were descended from a previously described 2013-2015 outbreak of Paratyphi A infections. Our analysis showed sub-lineage 2.3.1 had remained largely susceptible to fluoroquinolone drugs until 2015, but acquired chromosomal resistance to these drugs during six separate events between late 2012 and 2015. The emergence of fluoroquinolone resistance was rapidly followed by the replacement of the original susceptible Paratyphi A population, which led to a dramatic increase of fluoroquinolone-resistant blood-culture-confirmed cases in subsequent years (2016-2020). The rapid acquisition of resistance-conferring mutations in the Paratyphi A population over a 3 year period is suggestive of a strong selective pressure on that population, likely linked with fluoroquinolone use. In turn, emergence of fluoroquinolone resistance has led to increased use of extended-spectrum cephalosporins like ceftriaxone that are becoming the drug of choice for empirical treatment of paratyphoid fever in Cambodia.

WGS Analysis of Clonal and Plasmidic Epidemiology of Colistin-Resistance Mediated by mcr Genes in the Poultry Sector in Lebanon.

Poultry and poultry meat are important contributors to the global antimicrobial burden. Unregulated and illegal use of extended-spectrum cephalosporins (ESC) in this sector has long been identified as a major cause of massive spread of ESC-resistant Escherichia coli, and colistin usage is considered a main driver of plasmid-mediated mcr genes dissemination. In Lebanon, the first mcr-1-positive E. coli found in poultry dates back to 2015, followed by a few reports of mcr-1-positive E. coli in poultry, swine, humans, and the environment. On the contrary, a comprehensive picture of the population structure of mcr-1-positive E. coli and mcr-1-bearing plasmids carrying the mcr-1 gene using whole-genome analysis is largely lacking. This study reports the prevalence of mcr-1-positive E. coli in poultry originating from 32 farms across three Lebanese governorates and slaughtered in the same place. We report 27/32 (84.4%) mcr-1 positive farms, leading to a total of 84 non-duplicate E. coli collected, of which 62 presented the mcr-1 gene. Numerous associated resistances were identified, including to ESC through the presence of blaCTX–M or blaCMY genes. The mcr-1 gene was mostly carried by IncX4 (n = 36) and IncI2 (n = 24) plasmids, which are both known for their efficient transfer capacities. A high genetic diversity was detected, arguing for the lack of contamination during the slaughter process. ST744 and ST1011 were the most widely identified clones, which have been both regularly associated to mcr-1-carrying E. coli and to the poultry sector. The wide dissemination of colistin-resistance, coupled to resistances to ESC and numerous other molecules, should urge authorities to implement efficient guidelines for the use of antibiotics in the poultry sector in Lebanon.

Emergence of Nosocomial Pneumonia Caused by Colistin-Resistant Escherichia coli in Patients Admitted to Chest Intensive Care Unit.

(1) Background: Colistin is a last-resort antibiotic used in treating multidrug-resistant Gram-negative infections. The growing emergence of colistin resistance in Escherichia coli (E. coli) represents a serious health threat, particularly to intensive care unit (ICU) patients. (2) Methods: In this work, we investigated the emergence of colistin resistance in 140 nosocomial E. coli isolated from patients with pneumonia and admitted to the chest ICU over 36 months. Virulence and resistance-related genes and E. coli pathotypes in colistin-resistant and colistin-sensitive isolates were determined. (3) Results: Colistin resistance was observed in 21/140 (15%) of the nosocomial E. coli isolates. The MIC50 of the resistant strains was 4 mg/L, while MIC90 was 16 mg/L. Colistin-resistant isolates were also co-resistant to amoxicillin, amoxicillin/clavulanic, aztreonam, ciprofloxacin, and chloramphenicol. The mechanism of colistin resistance was represented by the presence of mcr-1 in all resistant strains. Respectively, 42.9% and 36.1% of colistin-resistant and colistin-sensitive groups were extended-spectrum β-lactamase (ESBL) producers, while 23.8% and 21% were metallo β-lactamase (MBL) producers. blaTEM-type was the most frequently detected ESBL gene, while blaIMP-type was the most common MBL in both groups. Importantly, most resistant strains showed a significantly high prevalence of astA (76.2%), aggR (76.2%), and pic (52.4%) virulence-related genes. Enteroaggregative E. coli (76%) was the most frequently detected genotype among the colistin-resistant strains. (4) Conclusion: The high colistin resistance rate observed in E. coli strains isolated from patients with nosocomial pneumonia in our university hospital is worrisome. These isolates carry different drug resistance and virulence-related genes. Our results indicate the need for careful monitoring of colistin resistance in our university hospital. Furthermore, infection control policies restricting the unnecessary use of extended-spectrum cephalosporins and carbapenems are necessary.

Antimicrobial-resistant Enterobacteriaceae recovered from companion animal and livestock environments.

Antimicrobial-resistant bacteria represent an important concern impacting both veterinary medicine and public health. The rising prevalence of extended-spectrum beta-lactamase (ESBL), AmpC beta-lactamase, carbapenemase (CRE) and fluoroquinolone-resistant Enterobacteriaceae continually decreases the efficiency of clinically important antibiotics. Moreover, the potential for zoonotic transmission of antibiotic-resistant enteric bacteria increases the risk to public health. Our objective was to estimate the prevalence of specific antibiotic-resistant bacteria on human contact surfaces in various animal environments. Environmental surface samples were collected from companion animal shelters, private equine facilities, dairy farms, livestock auction markets and livestock areas of county fairs using electrostatic cloths. Samples were screened for Enterobacteriaceae expressing AmpC, ESBL, CRE or fluoroquinolone resistance using selective media. Livestock auction markets and county fairs had higher levels of bacteria expressing both cephalosporin and fluoroquinolone resistance than did equine, dairy, and companion animal environments. Equine facilities harboured more bacteria expressing cephalosporin resistance than companion animal shelters, but less fluoroquinolone resistance. The regular use of extended-spectrum cephalosporins in livestock populations could account for the increased levels of cephalosporin resistance in livestock environments compared to companion animal and equine facilities. Human surfaces, as well as shared human and animal surfaces, were contaminated with resistant bacteria regardless of species environment. Detecting these bacteria on common human contact surfaces suggests that the environment can serve as a reservoir for the zoonotic transmission of antibiotic-resistant bacteria and resistance genes. Identifying interventions to lower the prevalence of antibiotic-resistant bacteria in animal environments will protect both animal and public health.

Management of cephalosporin resistance in Neisseria gonorrhoeae

Gonorrhea is a sexually transmitted disease caused by Neisseria gonorrhoeae, and substantially harms human health and socioeconomic development. Due to inappropriate treatment and the presence of drug resistance genes in patients, antibiotic resistance has emerged in Neisseria gonorrhoeae, such as resistance to penicillin, tetracycline, ciprofloxacin, or other antibiotics. Currently, extended-spectrum cephalosporins (ESCs)are the first-line treatment of gonococcal infection. With the wide use of ESCs, the sensitivity of Neisseria gonorrhoeae to ESCs has been decreasing gradually, and there have been reports on cases of treatment failure in clinical practice. In order to control gonorrhea and deal with drug resistance in Neisseria gonorrhoeae, combined therapy, alternative therapy and new drugs have been developed in clinic. Key words: Neisseria gonorrhoeae; Cephalosporins; Drug resistance; Therapeutic uses; Drug substitution

Use of cefuroxime for women with community-onset acute pyelonephritis caused by cefuroxime-susceptible or -resistant Escherichia coli.

Background/Aims:Efforts to decrease the use of extended-spectrum cephalosporins are required to prevent the selection and transmission of multi-drug resistant pathogens, such as extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae. The objectives of this study were to assess the clinical efficacy of intravenous cefuroxime as an empirical antibiotic for the treatment of hospitalized women with acute pyelonephritis (APN) caused by Escherichia coli.Methods:We analyzed the clinical and microbiologic database of 328 hospitalized women with community-onset APN.Results:Of 328 women with APN, 22 patients had cefuroxime-resistant E. coli APN, and 306 patients had cefuroxime-susceptible E. coli APN. The early clinical success rates were significantly higher (p = 0.001) in the cefuroxime-susceptible group (90.8%, 278/306) than in the cefuroxime-resistant group (68.2%, 15/22) at 72 hours. The clinical cure rates at 4 to 14 days after completing antimicrobial therapy were not significantly different in the cefuroxime-resistant or -susceptible groups, with 88.2% (15/17) and 97.8% (223/228; p = 0.078), respectively. The microbiological cure rates were not significantly different and were 90.9% (10/11) and 93.4% (128/137), respectively (p =0.550). The median duration of hospitalization in the cefuroxime-resistant and -susceptible groups was 10 days (interquartile range [IQR], 8 to 13) and 10 days (IQR, 8 to 14), respectively (p =0.319).Conclusions:Cefuroxime, a second-generation cephalosporin, can be used for the initial empirical therapy of community-onset APN if tailored according to uropathogen identification and susceptibility results, especially in areas where the prevalence rate of ESBL-producing uropathogens is low.

Association of veterinary third-generation cephalosporin use with the risk of emergence of extended-spectrum-cephalosporin resistance in Escherichia coli from dairy cattle in Japan.

The use of extended-spectrum cephalosporins in food animals has been suggested to increase the risk of spread of Enterobacteriaceae carrying extended-spectrum β-lactamases to humans. However, evidence that selection of extended-spectrum cephalosporin–resistant bacteria owing to the actual veterinary use of these drugs according to criteria established in cattle has not been demonstrated. In this study, we investigated the natural occurrence of cephalosporin-resistant Escherichia coli in dairy cattle following clinical application of ceftiofur. E. coli isolates were obtained from rectal samples of treated and untreated cattle (n = 20/group) cultured on deoxycholate-hydrogen sulfide-lactose agar in the presence or absence of ceftiofur. Eleven cefazoline-resistant isolates were obtained from two of the ceftiofur-treated cattle; no cefazoline-resistant isolates were found in untreated cattle. The cefazoline-resistant isolates had mutations in the chromosomal ampC promoter region and remained susceptible to ceftiofur. Eighteen extended-spectrum cephalosporin–resistant isolates from two ceftiofur-treated cows were obtained on ceftiofur-supplemented agar; no extended-spectrum cephalosporin–resistant isolates were obtained from untreated cattle. These extended-spectrum cephalosporin–resistant isolates possessed plasmid-mediated β-lactamase genes, including bla CTX-M-2 (9 isolates), bla CTX-M-14 (8 isolates), or bla CMY-2 (1 isolate); isolates possessing bla CTX-M-2 and bla CTX-M-14 were clonally related. These genes were located on self-transmissible plasmids. Our results suggest that appropriate veterinary use of ceftiofur did not trigger growth extended-spectrum cephalosporin–resistant E. coli in the bovine rectal flora; however, ceftiofur selection in vitro suggested that additional ceftiofur exposure enhanced selection for specific extended-spectrum cephalosporin–resistant β-lactamase-expressing E. coli clones

Correlation between antibiotic consumption and carbapenem-resistant Acinetobacter baumannii causing health care-associated infections at a hospital from 2005 to 2010

This study investigated the correlation between antibiotic consumption and the incidence of health care-associated infections (HCAIs) caused by imipenem-resistant Acinetobacter baumannii (IRAB) at a hospital in Taiwan from 2005 to 2010. Data on annual consumption (defined daily dose per 1000 patient-days) of extended-spectrum cephalosporins, β-lactam-β-lactamase inhibitor combinations, carbapenems, aminoglycosides, and fluoroquinolones from 2005 to 2010 were analyzed. Yearly aggregated data on the number of nonduplicate clinical IRAB isolates causing HCAI were collected. The incidence rates of HCAI caused by IRAB were defined as the number of patients infected with IRAB per 1000 inpatient-days. The trend of total consumption (defined daily dose per 1000 patient-days) of extended-spectrum cephalosporins, carbapenems, and fluoroquinolones was significantly increased, but the use of aminoglycosides decreased during 2005 to 2010. During the same period, the incidence of HCAI caused by IRAB gradually increased. The consumptions of carbapenems and fluoroquinolones were positively correlated with the incidence of HCAI caused by IRAB. There was no significant association between the use of extended-spectrum cephalosporins, β-lactam-β-lactamase inhibitor combinations, and aminoglycosides and the incidence of HCAI caused by IRAB. The increasing use of carbapenems and fluoroquinolones was associated with the increasing incidence of HCAI caused by IRAB.

High prevalence of blaCTX–M in Enterobacteriaceae isolates from the Kingdom of Bahrain

Objective To determine the molecular epidemiology of extended-spectrum β-lactamase (ESBL) by testing a cohort of clinical ESBL-producing bacterial isolates that were isolated in the Kingdom of Bahrain. Methods ESBL producing Enterobacteriaceae isolates (based on phenotypic tests) were collected from Microbiology Laboratory of the Salmaniya Medical Complex, Bahrain between January-June 2006. Antibiotic susceptibility to a panel of antibiotics was performed and bla CTX-M genes were detected by multiplex PCR. Results A total of 230 isolates ( Escherichia coli, n=180; Klebsiella pneumoniae, n=50) were studied, 98% were CTX-M type. For Escherichia coli isolates, 65 (36.1%) harbored CTXM+TEM combination and 68 (37.8%) had CTX-M alone. In contrast, for Klebsiella pneumoniae isolates only 5 (10.0%) harbored the CTX-M combination, and none had CTX-M only. The bla CTX-M gene was found predominantly in urine isolates ( n=145/230; 63.0%). Sensitivity to imipenem and nitrofurantoin was 100% and 60%, respectively. CTX-M carriage was associated with the resistance to fluoroquinolones, trimethoprim-sulfamethoxazole and aminoglycosides. Conclusions Our study documentes high prevalence of CTX-M ESBL type among Escherichia coli and Klebsiella from the Kingdom of Bahrain. The apparent dissemination of CTX-M producers could represent a substantial barrier in the treatment of community-acquired infections. The use of extended-spectrum cephalosporins, quinolones, and aminoglycosides is compromised, leaving carbapenems as the therapeutic option for severe infections caused by ESBL producers.

Decreased Susceptibility to Ciprofloxacin among Shigella Isolates in the United States, 2006 to 2009

We characterized 20 Shigella isolates with decreased susceptibility to fluoroquinolones. Most patients (80%) from whom a travel history was obtained reported travel to South or Southeast Asia. Mutations within the quinolone resistance determining regions of gyrA and parC and plasmid-mediated resistance determinants (qnrB, qnrS, and aac(6')-Ib-cr) were identified. The rise in antimicrobial resistance among Shigella isolates may necessitate the increased use of extended-spectrum cephalosporins or macrolides in some patients.

Correlation between antimicrobial consumption and resistance among Staphylococcus aureus and enterococci causing healthcare-associated infections at a university hospital in Taiwan from 2000 to 2009

This study investigated the correlation between antibiotic consumption and resistance among Staphylococcus aureus and enterococci causing healthcare-associated infections at a university hospital in Taiwan from 2000 to 2009. Overall, the trend of total consumption (defined daily dose [DDD] per 1,000 patient-days) of glycopeptides, including vancomycin and teicoplanin, significantly increased during 2000 to 2003 and remained stable during 2004-2009. Vancomycin consumption significantly increased during 2003 and decreased after 2004. A significant decrease in the resistance rate with time was found for oxacillin- and gentamicin-resistant S. aureus. In contrast, the rates of vancomycin- and teicoplanin-resistant enterocci increased significantly. A significant correlation was found between the increased use of extended-spectrum cephalosporins, β-lactam-β-lactamase inhibitor combinations, carbapenems and the decreased prevalence of methicillin-resistant S. aureus (MRSA). In contrast, the increased use of teicoplanin, extended-spectrum cephalosporins, β-lactam-β-lactamase inhibitor combinations, and carbapenems was correlated with the increased prevalence of vancomycin-resistant enterococci (VRE). In conclusion, this 10-year study in a single institution identified different correlations between the prescription of antibiotics and the resistance rates of MRSA and VRE. Strict implementation of infection control policy based on these correlates would be helpful in decreasing the presence of these multidrug-resistant pathogens in hospitals.

CTX-M1 ESBL-Producing Klebsiella pneumoniae subsp. pneumoniae Isolated from Cases of Bovine Mastitis

Escherichia coli and Klebsiella spp., followed by Serratia spp. and Enterobacter spp., are the most frequent Gram-negative pathogens isolated from bovine clinical mastitis (8). The incidence of mastitis due to such bacteria has increased in recent years (7). Klebsiella is usually referred as particularly aggressive and prone to cause severe clinical mastitis, which responds poorly to treatment and is likely to have a fatal outcome (6, 13). Klebsiellae are defined as germs that easily produce enzymes like extended-spectrum β-lactamases (ESBL), thanks to their ability to survive longer than other Gram-negative rods in the environment and on the skin and, in particular, to allow ESBL genes to evolve (9). At the onset of clinical mastitis, it is impossible to identify the causative agent; thus, it is necessary to use broad-spectrum intramammary preparations which contain narrow- to extended-spectrum cephalosporins, alone or in combination with other antibiotics (1). The broad-spectrum cephalosporin ceftiofur is used as well in supportive systemic therapy (6). Few recent works have studied Klebsiella isolation and ESBL detection in veterinary medicine (2, 16), and no data are available describing ESBL-mediated resistance in Klebsiella spp. isolated from bovine mastitis. In this research, the antimicrobial susceptibility and ESBL production were evaluated in Klebsiella pneumoniae isolated from animals with bovine clinical mastitis and selected for their resistance to ceftiofur, a broad-spectrum cephalosporin. Susceptibility to a range of antimicrobials, including those approved for both human and animal use (Table ​(Table1),1), was determined by disk diffusion assay according to Clinical and Laboratory Standards Institute interpretative criteria (3). Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923 were used as quality control standards. TABLE 1. Comparison of resistance profiles of the nine isolates From March 2008 to March 2009, 140 klebsiellae were isolated from milk samples, representing 26.6% of the total number of Gram-negative isolates obtained from bovine clinical mastitis. The isolates were subcultured on MacConkey agar supplemented with 8 μg/ml of ceftiofur (5). Nine isolates, identified as Klebsiella pneumoniae, were able to grow in the presence of 8 μg of ceftiofur. All Klebsiella pneumoniae isolates were screened against the panel in Table ​Table11 by the disk diffusion method and for ESBLs by the double-disk diffusion assay. A strain was considered an ESBL producer when it showed the expansion of an inhibition zone between a disk containing amoxicillin-clavulanate (20 and 10 μg) and disks containing, respectively, ceftazidime (30 μg) and cefotaxime (30 μg) placed 25 mm apart (10). All Klebsiella pneumoniae isolates were tested by PCR targeting the Ambler class A β-lactamase genes blaSHV, blaTEM, and blaCTX, identified in Klebsiella pneumoniae animal isolates (16), using previously published primer sets (14, 15). Sequencing of amplified genes completed the study. The complete resistance profiles and the PCR results are summarized in Table ​Table1.1. Only isolate 205, identified as Klebsiella pneumoniae subsp. pneumoniae, had a positive result to the double-disk test and was resistant to all the β-lactams, including cefotaxime and ceftriaxone, and sensitive to amoxicillin-clavulanate. The amplification of a CTX-M class enzyme-encoding gene confirmed such a phenotype, and sequencing of the gene identified the blaCTX-M1 group. To our knowledge, it is the first report about a CTX-M1 enzyme produced by a Klebsiella pneumoniae subsp. pneumoniae isolate in a case of bovine clinical mastitis. Isolate 205 also displayed a positive PCR result for genes blaSHV and blaTEM, and so did isolates 204 and 251. A previous randomized search detected only ESBL-producing E. coli and no Klebsiella spp. (11). The generally low level of in vitro resistance and the low prevalence of ESBL-producing strains (0.7%) should guarantee a good outcome of drug treatment for Klebsiella involved in mastitis, but antimicrobial resistance is not the only factor affecting therapy efficacy (1, 4). However, the described isolation must encourage that attention be paid to a phenomenon which could evolve and be enforced under the pressure of antimicrobial therapy, as the use of extended-spectrum cephalosporins in veterinary medicine may select ESBL producers (12). It is recommended to screen klebsiellae from cases of bovine mastitis in order to keep the prevalence of ESBL producers under control.

Prevalence and characteristics of ertapenem-nonsusceptible Escherichia coli in a Taiwanese university hospital, 1999 to 2007

The present study was conducted to investigate the prevalence and characteristics of ertapenem-nonsusceptible (ETP-NS) Escherichia coli in a Taiwanese university. A total of 9,722 isolates collected in 1999, 2003, 2005, and 2007 were examined. Overall, 1.0% of all isolates from 66 patients were interpreted as ETP-NS on the basis of the disk diffusion test result. Most of these isolates were clonally unrelated and showed low-level ertapenem resistance, the production of CMY-2 cephalosporinase (86.4%), and decreased expression of the OmpF (97.0%) and/or OmpC (56.1%) porins. No carbapenemase was detected. The decreased porin expression was associated with disruptions of ompF or ompC in only about one-third of the ETP-NS isolates. During the study period, the prevalence of ETP-NS strains increased from 0.1 to 1.7%, accompanying an increase (0.8 to 17.6%) in the prevalence of CMY-2 producers. Coexistent or pre-existing clonally related ertapenem-susceptible (ETP-S) E. coli isolates were identified in 47.0% of all case patients, and almost all of the ETP-S isolates had the same β-lactamases as the ETP-NS isolates. Our study results suggest the restricted use of extended-spectrum cephalosporins to hinder the emergence and prevalence of carbapenem resistance in E. coli, which may arise by the accumulation of multiple resistance determinants.

Control of extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae in a children's hospital by changing antimicrobial agent usage policy

This ambidirectional intervention study was performed to examine the impact of a change in antibiotic policy on extended-spectrum beta-lactamase (ESBL) prevalence in a children's hospital with a high prevalence of ESBL production among Escherichia coli and Klebsiella pneumoniae. The use of extended-spectrum cephalosporins was restricted and use of beta-lactam/ beta-lactamase inhibitor combinations was encouraged from 2002. All strains of E. coli and K. pneumoniae isolated from sterile body fluids from 1999 to 2005 were analysed for beta-lactamase production and the prevalences of ESBL production were compared at three periods; pre-intervention (1999-2001), transitional period (2002-03) and post-intervention (2004-05). Comparing the pre- and post-intervention periods, overall piperacillin/tazobactam use increased from 2.2 to 108.0 days on antibiotics/1000 patient admission days/year (AD) (P for trend < 0.001), whereas extended-spectrum cephalosporin use decreased from 175.0 to 96.9 AD (P for trend < 0.001). Among 252 strains of E. coli (n = 128) and K. pneumoniae (n = 124), the overall prevalence of ESBL producers decreased from 39.8% (41/103) to 22.8% (18/79) (P for trend = 0.018). This decreasing trend of ESBL production was more evident for K. pneumoniae (64.1% to 25.6%; P for trend < 0.001) than E. coli (25.0% to 19.4%; P for trend = 0.514). The mortality rates of invasive disease caused by E. coli or K. pneumoniae remained unchanged. The substitution of piperacillin/tazobactam for extended-spectrum cephalosporins successfully decreased the prevalence of ESBL production of K. pneumoniae and E. coli in an institute for children where ESBLs were endemic. The impact of change in antibiotic policy was more evident in K. pneumoniae than E. coli.

Spread of Extended-Spectrum β-Lactamase CTX-M-Producing Escherichia coli Clinical Isolates in Community and Nosocomial Environments in Portugal

ABSTRACT Of the 181 unduplicated Escherichia coli strains isolated in nine different hospitals in three Portuguese regions, 119 were extended-spectrum β-lactamase (ESBL)-CTX-M producers and were selected for phenotype and genotype characterization. CTX-M producer strains were prevalent among community-acquired infections (56%), urinary tract infections (76%), and patients ≥60 years old (76%). In MIC tests, all strains were resistant to cefotaxime, 92% were resistant to ceftazidime, 93% were resistant to quinolones, 89% were resistant to aminoglycoside, and 26% were resistant to trimethoprim-sulfamethoxazole; all strains were sensitive to carbapenems, and 92% of the strains had a multidrug resistance phenotype. Molecular methods identified 109 isolates harboring a bla CTX-M-15 gene, 1 harboring the bla CTX-M-32 gene (first identification in the country), and 9 harboring the bla CTX-M-14 gene. All isolates presented the IS Ecp1 element upstream from the bla CTX-M genes; one presented the IS 903 element (downstream of bla CTX-M-14 gene), and none had the IS 26 element; 85% carried bla TEM-1B , and 84% also carried a bla OXA-30 . Genetic relatedness analysis based on pulsed-field gel electrophoresis defined five clusters and indicated that 76% of all isolates (from cluster IV) corresponded to a single epidemic strain. Of the 47 strains from one hospital, 41 belonged to cluster IV and were disseminated in three main wards. CTX-M-producing E. coli strains are currently a problem in Portugal, with CTX-M-15 particularly common. This study suggests that the horizontal transfer of bla CTX-M genes, mediated by plasmids and/or mobile elements, contributes to the dissemination of CTX-M enzymes to community and hospital environments. The use of extended-spectrum cephalosporins, quinolones, and aminoglycosides is compromised, leaving carbapenems as the therapeutic option for severe infections caused by ESBL producers.

Antibiotics and gastrointestinal colonization by vancomycin-resistant enterococci

Although several classes of antimicrobial agents have been associated with colonization or infection with glycopeptide-resistant enterococci (GRE) in individual clinical studies, the agents most commonly implicated are extended-spectrum cephalosporins and compounds with potent activity against anaerobic bacteria, including ticarcillin-clavulanic acid. In some clinical studies, formulary alterations designed to minimize the use of extended-spectrum cephalosporins or ticarcillin-clavulanic acid have resulted in significant decreases in colonization and infection by GRE. Experimental data using a mouse model of GRE gastrointestinal colonization indicate that persistence of high-level GRE colonization of the mouse gastrointestinal tract is promoted by exposure to agents with potent activity against anaerobic bacteria, suggesting that reduction of competing flora is the major factor leading to persistence of high-level colonization. One study performed in humans is consistent with this model and suggests that high levels of colonization may promote spread of resistant organisms in the nosocomial setting. Establishing colonization with GRE in uncolonized mice correlates with exposure to agents that are (a) secreted into the bile in significant concentrations and (b) have negligible activity against the colonizing enterococcal strain. Differences between piperacillin-tazobactam and ceftriaxone in the establishment model can be attributed directly to differences in their anti-enterococcal activity. Modification of antimicrobial prescribing practices may play an important role in facilitating successful infection control efforts to limit GRE in the nosocomial setting.

Risk Factors for Antimicrobial Resistance and Influence of Resistance on Mortality in Patients with Bloodstream Infection Caused byPseudomonas aeruginosa

This study was conducted to evaluate risk factors for antimicrobial resistance and influence of resistance on mortality in Pseudomonas aeruginosa bacteremia. Data on 190 patients with P. aeruginosa bacteremia were analyzed retrospectively. Antimicrobial resistance to antipseudomonal antibiotics was evaluated. The main outcome measure was 30-day mortality. In P. aeruginosa bacteremia, resistance rates to piperacillin (PIP), ceftazidime (CAZ), ciprofloxacin (CIP), and imipenem (IPM) were 29 (56/190), 19 (36/190), 17 (32/190) and 15% (28/190), respectively. Prior uses of fluoroquinolones or carbapenems were independent risk factors for resistance to CIP and IPM, and prior use of extended-spectrum cephalosporins was a risk factor for PIP-R. An indwelling urinary catheter was a risk factor for PIP-R, CAZ-R, and CIP-R. An invasive procedure was a risk factor for CIP-R and IPM-R. The 30-day mortality rate was 44% (33/75) in patients infected by strains resistant to any of the antipseudomonal antibiotics, but 33.9% (39/115) in those by strains susceptible to all antipseudomonal antibiotics (p = 0.161). Among patients with bloodstream infection due to antimicrobial-resistant P. aeruginosa, those infected by IPM-R strains had the highest mortality (IPM-R, 53.6% vs. CAZ-R, 47.2% vs. CIP-R 46.9%, PIP-R, 39.3%). In this study regarding P. aeruginosa bacteremia, prior uses of fluoroquinolones, carbapenems, or extended-spectrum cephalosporins, a prior invasive procedure, and an indwelling urinary catheter were found to be associated with antimicrobial resistance. The patients with bloodstream infection caused by antimicrobial-resistant P. aeruginosa, especially to imipenem, had a tendency toward higher mortality than those infected by susceptible strains.

Relationship between ceftriaxone use and resistance to third-generation cephalosporins among clinical strains of Enterobacter cloacae.

To investigate the potential correlation between the use of extended-spectrum cephalosporins (ESCs) and resistance to this antibiotic class among clinical isolates of Enterobacter cloacae in a university-affiliated hospital. Data on antimicrobial resistance and antimicrobial use concerning E. cloacae and ESCs were collected over a 4 year period. Various statistical tools were used to explore the potential relationship. From 1999 to 2002, the proportion of E. cloacae isolates resistant to ESCs increased from 24.3% to 29.6%. (P=0.04), and the quantity of ESCs prescribed and given did not change. Within the subclass constituted by first-line ESCs, the proportion of ceftriaxone increased from 64.3% to 77.6% and the proportion of cefotaxime decreased accordingly, from 35.7% to 22.4%. Statistical analyses showed that E. cloacae resistance to ESCs correlated with ceftriaxone use regardless of the other ESCs. For every defined daily dose of ceftriaxone per 1000 patient days used in our hospital, resistance of E. cloacae isolates to ESCs increased by 1.36%. This study demonstrates a specific correlation between ceftriaxone use and the development of resistance in E. cloacae clinical isolates. The high biliary elimination of ceftriaxone compared with other ESCs may be responsible for a greater impact of this antibiotic on the digestive flora.

Haemophilus influenzae bla(ROB-1) mutations in hypermutagenic deltaampC Escherichia coli conferring resistance to cefotaxime and beta-lactamase inhibitors and increased susceptibility to cefaclor.

The clinical use of cefaclor has been shown to enrich Haemophilus influenzae populations harboring cefaclor-hydrolyzing ROB-1 beta-lactamase. Such a selective process may lead to the increased use of extended-spectrum cephalosporins or beta-lactams plus beta-lactamase inhibitors and, eventually, resistance to these agents, which has not previously been observed in H. influenzae. In order to establish which bla(ROB-1) mutations, if any, could confer resistance to extended-spectrum cephalosporins and/or to beta-lactamase inhibitors, a plasmid harboring bla(ROB-1) was transformed into hypermutagenic strain Escherichia coli GB20 (DeltaampC mutS::Tn10), and this construct was used in place of H. influenzae bla(ROB-1). Strain GB20 with the cloned gene was submitted to serial passages in tubes containing broth with increasing concentrations of selected beta-lactams (cefotaxime or amoxicillin-clavulanate). Different mutations in the bla(ROB-1) gene were obtained during the passages in the presence of the different concentrations of the selective agents. Mutants resistant to extended-spectrum cephalosporins harbored either the Leu169-->Ser169 or the Arg164-->Trp164 substitution or the double amino acid change Arg164-->Trp164 and Ala237-->Thr237. ROB-1 mutants that were resistant to beta-lactams plus beta-lactamase inhibitors and that harbored the Arg244-->Cys244 or the Ser130-->Gly130 replacement were also obtained. The cefaclor-hydrolyzing efficiencies of the ROB-1 variants were strongly decreased in all mutants, suggesting that if bla(ROB-1) mutants were selected by cefaclor, this drug would prevent the further evolution of this beta-lactamase toward molecular forms able to resist extended-spectrum cephalosporins or beta-lactamase inhibitors.

Plasmid-mediated Extended-spectrum beta-Lactamases in Organisms Other Than Klebsiella pneumoniae and Escherichia coli: A Hidden Reservoir of Transferable Resistance Genes.

Resistance due to AmpC β-lactamases and ESBLs in gramnegative bacillary pathogens is a growing and important problem and is tied to extensive use of extended-spectrum cephalosporins The emergence of these β-lactamases is then amplified by spread of resistant clones or resistant genes among patients within institutions or among patients who move between institutions within a region. Genes encoding β-lactamases are frequently linked to resistance genes for other classes of antibiotics. Thus, use of any one class of antibiotic may select for emergence of resistance to another. Treatment of infections caused by these multidrug-resistant pathogens is often problematic. One strategy to circumvent β-lactamase production has been use of β-lactam/β-lactamase inhibitor combinations, but AmpC β-lactamases and hyperproduction of ESBLs evade this therapeutic strategy. Use of carbapenems and cefepime, which are the most stable of all β-lactam antibiotics to hydrolysis by ESBLs and AmpC β-lactamases, can be expected eventually to select for emergence of resistance to these drugs as well.