The emergence of blaOXA-48 and blaNDM among ESBL-producing Klebsiella pneumoniae in clinical isolates of a tertiary hospital in Iran

The aim of this study was to investigate the prevalence of carbapenem-resistant Klebsiella pneumoniae (CRKP) and the most common types of carbapenemases, metallo-beta-lactamases (MBLs), and extended-spectrum beta-lactamases (ESBLs) among CRKP isolates in a tertiary hospital in Isfahan, Iran. Eighty non-repetitive clinical isolates of K. pneumoniae were obtained from different clinical specimens. Antibiotic resistance pattern of isolates was determined by disk diffusion method and production of carbapenemases and MBLs was confirmed using modified Hodge test and E-test, respectively. Molecular detection of the antibiotic resistance genes was performed using PCR. Fifty-one (63.8%) isolates have decreased susceptibility to carbapenems, of which 46 (90.2%) isolates were as carbapenemase producer and four (7.8%) isolates were positive for MBLs, phenotypically. The results of PCR showed that the prevalence of bla_OXA-48, bla_NDM, bla_SHV, bla_CTX-M, and bla_TEM genes among CRKP isolates were 90.2%, 15.7%, 98%, 96.1%, and 90.2%, respectively. No isolates carrying the bla_KPC, bla_GES, bla_IMI, bla_VIM, and bla_IMP genes were detected. This study showed that the production of OXA-48 is one of the main mechanisms of resistance to carbapenems in CRKP isolates in Isfahan. In addition, the dissemination of NDM-producing CRKP isolates is a potential risk for the health care system of this area in the near future.

Surveillance in Taiwan Using Molecular Epidemiology for Extended-Spectrum Beta-Lactamase-ProducingKlebsiella pneumoniae

Objective:

To evaluate intrahospital and interhospital clonal dissemination of extended-spectrum beta-lactamase (ESBL)-producing strains ofKlebsiella pneumoniae.

Setting:

Eight tertiary-care university hospitals and 16 regional hospitals in Taiwan.

Methods:

Two hundred eleven confirmed ESBL-producing isolates ofK. pneumoniaewere collected from January 1998 to June 2000. The isolates were characterized by various typing methods, including antibiogram (9 antimicrobial agents), computer-based ribotyping, pulsed-field gel electrophoresis (PFGE), and isoelectric focusing of beta-lactamase.

Results:

Ribotyping identified 70 distinct ribogroups among 200 isolates evaluated. Forty-three of these ribogroups were unique. Eleven ribogroups, comprising 115 isolates, were detected in more than one hospital (interhospital dissemination), whereas 16 groups (42 isolates) were detected in more than one patient within a hospital (intrahospital dissemination). The combination of ribotyping and PFGE identified two large epidemic clones, which were called 691.5/PFGE-G and 595.7/PFGE-A. These epidemic clones were detected mainly in the hospitals located in the northern and central regions of Taiwan. However, variation of the profiles of antibiograms and isoelectric focusing was apparent within each clone. In addition, isolates with the same isoelectric focusing profile (isoelectric points 7.9, 8.2, and 8.4) and antibiogram (resistance to 9 compounds evaluated) were present among different molecular-typed clones.

Conclusions:

Our results showed that clonal dissemination (both interhospital and intrahospital dissemination) is occurring in several regions of Taiwan. Rapid computer-based ribotyping associated with PFGE demonstrated multiple epidemic clones of ESBL-producingK. pneumoniaein Taiwan. The combination of phenotypic and molecular methods has proved useful to characterize these epidemic clones.

Extended-spectrum beta-lactamases: a clinical update

Extended-spectrum beta-lactamases (ESBLs) are a rapidly evolving group of beta-lactamases which share the ability to hydrolyze third-generation cephalosporins and aztreonam yet are inhibited by clavulanic acid. Typically, they derive from genes for TEM-1, TEM-2, or SHV-1 by mutations that alter the amino acid configuration around the active site of these beta-lactamases. This extends the spectrum of beta-lactam antibiotics susceptible to hydrolysis by these enzymes. An increasing number of ESBLs not of TEM or SHV lineage have recently been described. The presence of ESBLs carries tremendous clinical significance. The ESBLs are frequently plasmid encoded. Plasmids responsible for ESBL production frequently carry genes encoding resistance to other drug classes (for example, aminoglycosides). Therefore, antibiotic options in the treatment of ESBL-producing organisms are extremely limited. Carbapenems are the treatment of choice for serious infections due to ESBL-producing organisms, yet carbapenem-resistant isolates have recently been reported. ESBL-producing organisms may appear susceptible to some extended-spectrum cephalosporins. However, treatment with such antibiotics has been associated with high failure rates. There is substantial debate as to the optimal method to prevent this occurrence. It has been proposed that cephalosporin breakpoints for the Enterobacteriaceae should be altered so that the need for ESBL detection would be obviated. At present, however, organizations such as the Clinical and Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards) provide guidelines for the detection of ESBLs in klebsiellae and Escherichia coli. In common to all ESBL detection methods is the general principle that the activity of extended-spectrum cephalosporins against ESBL-producing organisms will be enhanced by the presence of clavulanic acid. ESBLs represent an impressive example of the ability of gram-negative bacteria to develop new antibiotic resistance mechanisms in the face of the introduction of new antimicrobial agents.

Multilocus sequence typing of Klebsiella pneumoniae nosocomial isolates

A multilocus sequence typing (MLST) scheme was developed for Klebsiella pneumoniae. Sequences of seven housekeeping genes were obtained for 67 K. pneumoniae strains, including 19 ceftazidime- and ciprofloxacin-resistant isolates. Forty distinct allelic profiles were identified. MLST data were validated against ribotyping and showed high (96%) discriminatory power. The MLST approach provides unambiguous data useful for the epidemiology of K. pneumoniae isolates.

Molecular serotyping of Klebsiella species isolates by restriction of the amplified capsular antigen gene cluster

The objective of the present work was to develop a molecular method that would enable determination of the capsular serotypes of Klebsiella isolates without the use of antiserum. PCR amplification of the capsular antigen gene cluster (cps) was followed by digestion with the restriction enzyme HincII (cps PCR-restriction fragment length polymorphism [RFLP] analysis). The profiles (C patterns) obtained for 224 strains representing the 77 known K serotypes showed 3 to 13 fragments ranging in size from 0.2 to 4.4 kb. A total of 97 distinct C patterns were obtained; 100% of 61 pairs of samples tested twice showed reproducible C patterns. The C patterns were K-type specific; i.e., the C pattern(s) of any K serotype was distinct from the C patterns of all other K serotypes, with the only exceptions being serotypes K22 and K37, which are known to cross-react. For 12 of 17 K types for which at least two strains were included, C-pattern variations were found among strains with the same K serotype. Therefore, cps PCR-RFLP analysis has a higher discriminatory power than classical K serotyping. C-pattern identity was observed among strains with a given K type that were collected many years apart and from distinct sources, indicating C-pattern stability. Only 4.5% of the strains were nontypeable, because of unsuccessful PCR amplification (whereas 8 to 23% are nontypeable by classical K serotyping). Three of four noncapsulated strains analyzed showed recognizable C patterns. The K serotypes of 18 (82%) of 22 recent Klebsiella pneumoniae clinical isolates could be deduced from their C patterns. In conclusion, cps PCR-RFLP analysis allows determination of the K serotype, while it is easier to perform and more discriminatory than classical serotyping.

Epidemiology of Nosocomial Pneumonia in Infants After Cardiac Surgery

BACKGROUND

The pattern of nosocomial pneumonia (NP) in infants in a pediatric surgical ICU after cardiac surgery may differ from that seen in adult ICUs.

STUDY OBJECTIVES

The primary aim of this study was to describe the epidemiology of NP in infants after cardiac surgery and, secondarily, to describe the changes of the distribution and antibiotic resistance of the pathogen during the last 3 years.

METHODS

Data were collected between June 1999 and June 2002 from 311 consecutive infants who underwent open-heart surgery in our hospital. We retrospectively analyzed the distribution and antibiotic resistance pattern of all the pathogenic microbial isolates cultured from lower respiratory tract aspirations.

RESULTS

Of 311 infants, 67 patients (21.5%) acquired NP after cardiac surgery. The incidence of NP was more frequently associated with complex congenital heart defect (CHD) compared to simple CHD (43% vs 15.9%, chi(2) = 22.47, p < 0.0001). The proportion of late-onset NP was higher in patients with complex CHD (chi(2) = 6.02, p = 0.014). A total of 79 pathogenic microbial strains were isolated. Gram-negative bacilli (GNB) were the most frequent isolates (68 isolates, 86.1%), followed by fungi (6 isolates, 7.6%) and Gram-positive cocci (5 isolates, 6.3%). The main GNB were Acinetobacter baumanii (11 isolates, 13.9%), Pseudomonas aeruginosa (10 isolates, 12.7%); other commonly seen GNB were Flavobacterium meningosepticum (7 isolates, 8.9%), Klebsiella pneumoniae (7 isolates, 8.9%), Escherichia coli (6 isolates, 7.6%), and Xanthomonas maltophilia (5 isolates, 6.2%). The most commonly seen Gram-positive cocci were Staphylococcus aureus (2 isolates, 2.5%) and Staphylococcus epidermidis (2 isolates, 2.5%). The frequent fungi were Candida albicans (5 isolates, 6.3%). Most GNB were sensitive to cefoperazone-sulbactum, piperacillin-tazobactam, imipenem, ciprofloxacin, amikacin. The bacteria producing extended spectrum beta-lactamases were mainly from K pneumoniae and E coli; the susceptibility of ESBL-producing strains to imipenem was 100%. There were one case of methicillin-resistant S aureus (MRSA) and 1 case of methicillin-resistant S epidermidis; their susceptibility to vancomycin, gentamycin, and ciprofloxacin were 100%. From 1999 to 2002 in infants with NP after open-heart surgery, there was a trend of increasing frequency of multiresistant GNB such as A baumanii, P aeruginosa, and K pneumoniae. However, no remarkable changes of distribution were found in Gram-positive cocci and fungi in the 3-year period. Early onset episodes of NP were frequently caused by Haemophilus influenzae, methicillin-sensitive S aureus, and other susceptible Enterobacteriaceae. Conversely, in patients who acquired late-onset NP, P aeruginosa, A baumannii, other multiresistant GNB, MRSA, and fungi were the predominant organisms.

CONCLUSIONS

The pattern of pathogens and their antibiotic-resistance patterns in NP in infants after cardiac surgery had not shown an increasing prevalence of Gram-positive pathogens as reported by several adult ICUs. GNB still remained the most common pathogens during the last 3 years in our hospital. There was a trend of increasing antibiotic resistance in these isolates.

Impact of antibiotic-resistant Gram-negative bacilli infections on outcome in hospitalized patients

OBJECTIVE

The impact of resistant (vs. nonresistant) Gram-negative infections on mortality remains unclear. We sought to define risk factors for and excess mortality from these infections.

DESIGN

Prospective cohort study.

SETTING

Inpatient surgical wards at a university hospital.

PATIENTS

All patients in the general, transplant, and trauma surgery services diagnosed with Gram-negative rod (GNR) infection.

MEASUREMENTS AND MAIN RESULTS

All culture-proven GNR infections (n = 924) from December 1996 to September 2000 were studied. Characteristics and outcomes were compared between GNR infections with and without antibiotic resistance. Univariate and logistic regression analysis identified factors associated with antibiotic-resistant GNR (rGNR) infection and mortality. rGNR infection (n = 203) was associated with increased Acute Physiology and Chronic Health Evaluation (APACHE) II scores (17.8 +/- 0.5), multiple comorbidities, pneumonia and catheter infection, coexistent infection with antibiotic-resistant Gram-positive cocci and fungi, and high mortality (27.1%). Only seven isolates were resistant in vitro to all available antibiotics. Logistic regression demonstrated that rGNR infection was an independent predictor of mortality (odds ratio, 2.23; 95% confidence interval, 1.35-3.67; p =.002). Analysis of rGNR infection with controls matched by organism, age, APACHE II score, and site of infection, however, revealed that antibiotic resistance was not associated with increased mortality (23.6% vs. 29.2%, p =.35). Furthermore, analysis of all Pseudomonas aeruginosa infections demonstrated no significant difference in mortality between resistant and sensitive strains (18.9% vs. 20.0%, p =.85).

CONCLUSION

rGNRs are associated with prolonged hospital stay and increased mortality. Infection with rGNRs independently predicts mortality; however, this may be more closely related to selection of certain bacterial species with a high frequency of resistance rather than actual resistance to antibiotic therapy. Therefore, altering infection-control practices to limit the dissemination of certain bacterial species may be more effective than attempts to control only antibiotic-resistant isolates.

Natural history of colonization with vancomycin-resistant enterococci, methicillin-resistant Staphylococcus aureus, and resistant gram-negative bacilli among long-term-care facility residents

OBJECTIVE

To determine the natural history of colonization with vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA), and resistant gram-negative bacilli among long-term-care facility (LTCF) residents.

DESIGN

Observational cohort study.

SETTING

A 355-bed LTCF with a ventilator unit and a subacute unit.

PARTICIPANTS

Residents with colonization or infection with VRE, MRSA, or resistant gram-negative bacilli housed at the LTCF between December 1, 1999, and February 29, 2000.

METHODS

Cultures of clinical and surveillance sites were performed at regular intervals. Charts were reviewed for clinical characteristics associated with clearance of colonization. Kaplan-Meier curves were constructed to analyze the number of days to clearance of colonization.

RESULTS

Forty-nine residents had 65 episodes of colonization (27 VRE, 30 MRSA, and 8 resistant gram-negative bacilli). Eighteen (28%) of the episodes cleared. The clearance rate was 2.7 episodes per 1,000 person-days. Clearance occurred significantly more often with resistant gram-negative bacilli colonization compared with VRE or MRSA colonization (6 [75%] vs 12 [21%]; P = .007; relative risk, 4.17; 95% confidence interval, 1.26 to 11.8). There was a trend toward longer use of antimicrobial agents among residents with persistent colonization. Infections occurred most frequently with MRSA. The urinary tract was the most common site of infection.

CONCLUSION

Among LTCF residents, colonization with resistant gram-negative bacilli is four times more likely to clear than colonization with VRE or MRSA. Performance of surveillance cultures at regular intervals may reduce the need for contact precautions for LTCF residents with resistant gram-negative bacilli colonization.

Regional occurrence of plasmid-mediated SHV-7, an extended-spectrum beta-lactamase, in Enterobacter cloacae in Philadelphia Teaching Hospitals

Although the production of extended-spectrum beta-lactamases (ESBLs) by Klebsiella pneumoniae and Escherichia coli is an emerging problem, limited data are available regarding the frequency of ESBL production in other organisms. We provide the only description of regional occurrence of SHV-7 in Enterobacteriaceae other than E. coli or K. pneumoniae in the United States, and we emphasize that, among Enterobacter cloacae strains, not all resistance to extended-spectrum cephalosporins is the result of hyperproduction of AmpC beta-lactamase.

Molecular epidemiology of a citywide outbreak of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae infection

Multidrug-resistant strains of Klebsiella pneumoniae are a problem in many hospitals. In 1999, the molecular epidemiology of K. pneumoniae with extended-spectrum beta-lactamases (ESBLs) was studied at 15 hospitals in Brooklyn. Of 824 unique patient isolates, 34% were presumptive ESBL producers. Of this subset, 34% were susceptible to cefoxitin, 42% to ciprofloxacin, 48% to ceftriaxone, 55% to piperacillin-tazobactam, 57% to amikacin, and 86% to cefepime. Ribotype analysis revealed 87 unique types. However, 2 clusters accounted for 35% of isolates and were present in most of the hospitals. One cluster was significantly more resistant to most antibiotics. Although there was a predominance of SHV-5, considerable heterogeneity of beta-lactamases was evident, even among isolates of the same cluster. A correlation was found between the use of cephalosporins and the prevalence of ESBL-producing strains of K. pneumoniae at each hospital. Our data suggest that there is an advanced outbreak of multidrug-resistant K. pneumonia infection that is affecting all Brooklyn hospitals.

A decade of antimicrobial susceptibilities at the University of Kentucky Hospital

OBJECTIVE

To determine the antimicrobial susceptibility rates for key antimicrobial agents and selective bacterial pathogens in the decade of the 1990s.

METHODS

Data from 1990 to 2000 from the University of Kentucky Clinical Microbiology Laboratory were analyzed by linear regression analysis to identify agents and pathogens that show a decline in susceptibility. For selected pathogens and antimicrobial agents, predictions were made for further declines in susceptibility for 2005 and 2010.

RESULTS

Significant declines in susceptibility to selected antimicrobial agents were found for Pseudomonas aeruginosa, Klebsiella pneumoniae, Enterobacter cloacae, Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, and Streptococcus pneumoniae. Further declines were predicted for 2005 and 2010.

CONCLUSIONS

Examination of susceptibility rates over time in a university hospital medical center provides useful data for future planning. In our institution, antimicrobial susceptibility rates have significantly declined during the 1990s for certain antimicrobial agents and bacterial pathogens. We are attempting to change our antimicrobial use patterns through formulary manipulation and clinician education, which may retard or prevent such declines in the future.

Development and spread of bacterial resistance to antimicrobial agents: an overview

Resistance to antimicrobial agents is emerging in a wide variety of nosocomial and community-acquired pathogens. The emergence and spread of multiply resistant organisms represent the convergence of a variety of factors that include mutations in common resistance genes that extend their spectrum of activity, the exchange of genetic information among microorganisms, the evolution of selective pressures in hospitals and communities that facilitate the development and spread of resistant organisms, the proliferation and spread of multiply resistant clones of bacteria, and the inability of some laboratory testing methods to detect emerging resistance phenotypes. Twenty years ago, bacteria that were resistant to antimicrobial agents were easy to detect in the laboratory because the concentration of drug required to inhibit their growth was usually quite high and distinctly different from that of susceptible strains. Newer mechanisms of resistance, however, often result in much more subtle shifts in bacterial population distributions. Perhaps the most difficult phenotypes to detect, as shown in several proficiency testing surveys, are decreased susceptibility to beta-lactams in pneumococci and decreased susceptibility to vancomycin in staphylococci. In summary, emerging resistance has required adaptations and modifications of laboratory diagnostic techniques, empiric anti-infective therapy for such diseases as bacterial meningitis, and infection control measures in health care facilities of all kinds. Judicious use is imperative if we are to preserve our arsenal of antimicrobial agents into the next decade.

Epidemiology and frequency of resistance among pathogens causing urinary tract infections in 1,510 hospitalized patients: a report from the SENTRY Antimicrobial Surveillance Program (North America)

Bacterial urinary tract infections (UTIs) are an important cause of septicemia resulting in high mortality rates, prolonged hospital stays and increased healthcare costs. Periodic reviews of pathogen frequency and susceptibility patterns impact on appropriate antimicrobial usage, leading to more effective prescribing practices. As part of the SENTRY Antimicrobial Surveillance Program (SENTRY, 1998), participants collected 50 consecutive UTI pathogens from patients hospitalized in 31 medical centers (26 in the United States and five in Canada) and forwarded subcultures to the coordinating center. Thirty-four antimicrobial agents were tested including two investigational compounds (quinupristin/dalfopristin [Q/D], gatifloxacin). The rank order of the 32 species identified during the study was: Escherichia coli (46.9%) > Enterococcus spp. (12.8%) > Klebsiella spp. (11.0%) > Pseudomonas aeruginosa (7.5%) > Proteus mirabilis (5.0%) > coagulase-negative staphylococci (CoNS; 3.4%). This pathogen rank order did not change from 1997 to 1998, but resistance patterns changed. Clonal spread of confirmed extended spectrum beta-lactamase-producing strains was not observed, but co-resistance was elevated for aminoglycosides, tetracyclines, sulfonamides, and fluoroquinolones. P. aeruginosa was most susceptible to amikacin (97.3%) > piperacillin +/- tazobactam (92.0-95.6%) > cefepime = imipenem (91.2%) > ceftazidime (85.8%). Fluoroquinolone resistance was greater in P. aeruginosa (24.8-39.8%) > P. mirabilis (5.3-13.3%) > Enterobacter spp. (6.7-8.9%) > Klebsiella spp. (4.2-7.8%) > E. coli (3.0-3.8%). Only 5% of enterococci were resistant to vancomycin. These results emphasize the need for continued surveillance studies for common infections which establish baseline resistance patterns by geographic areas, and have the potential to detect epidemics or direct local epidemiologic interventions.

Variations in the prevalence of strains expressing an extended-spectrum beta-lactamase phenotype and characterization of isolates from Europe, the Americas, and the Western Pacific region

To evaluate the prevalence of extended-spectrum beta-lactamase (ESBL)-producing strains among species of Enterobacteriaceae, a microdilution susceptibility test was performed with strains of Klebsiella pneumoniae, Escherichia coli, Proteus mirabilis, and Salmonella species that were isolated as part of the SENTRY project. The highest percentage of ESBL phenotype (defined as a minimum inhibitory concentration [MIC] > or =2 microg/mL for ceftazidime, ceftriaxone, or aztreonam) was detected among K. pneumoniae strains from Latin America (45%), followed by those from the Western Pacific region (25%), Europe (23%), the United States (8%), and Canada (5%). P. mirabilis and E. coli strains for which MICs of extended-spectrum cephalosporins or monobactams were elevated also were more prominent in Latin America. Testing with ceftazidime revealed more isolates with elevated MICs than did testing with ceftriaxone or aztreonam. ESBL strains showed high levels of co-resistance to aminoglycosides, tetracycline, trimethoprim-sulfamethoxazole, and ciprofloxacin. Imipenem remains highly effective against ESBL strains. Organisms expressing an ESBL are widely distributed worldwide, although prevalence rates are significantly higher in certain geographic regions.

Integration of molecular characterization of microorganisms in a global antimicrobial resistance surveillance program

The SENTRY Antimicrobial Surveillance Program has incorporated molecular strain typing and resistance genotyping as a means of providing additional information that may be useful for understanding pathogenic microorganisms worldwide. Resistance phenotypes of interest include multidrug-resistant pathogens, extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci, and fluoroquinolone-resistant (FQR) strains of gram-negative bacilli and Streptococcus pneumoniae. Clusters of > or =2 isolates within a given resistance profile that are linked temporally and by hospital location are flagged for DNA fingerprinting. Further characterization of organisms with respect to resistance genotype is accomplished with use of polymerase chain reaction and DNA sequencing. This process has been highly successful in identifying clonal spread within clusters of multiresistant pathogens. Between 50% and 90% of MRSA clusters identified by phenotypic screening contained evidence of clonal spread. Among the Enterobacteriaceae, ESBL-producing strains of Escherichia coli and Klebsiella pneumoniae are the most common pathogens causing clusters of infection, and approximately 50% of recognized clusters demonstrate clonal spread. Clusters of Pseudomonas aeruginosa, Acinetobacter species, and Stenotrophomonas maltophilia have been noted with clonal spread among patients with urinary tract, respiratory, and bloodstream infections. Characterization of mutations in the FQR-determining region of phenotypically susceptible isolates of E. coli and S. pneumoniae has identified first-stage mutants among as many as 40% of isolates. The ability to characterize organisms phenotypically and genotypically is extremely powerful and provides unique information that is important in a global antimicrobial surveillance program.

Evolution and clinical importance of extended-spectrum beta-lactamases

In the process of evolution, bacteria have acquired well-developed mechanisms of resistance to an extensive array of hostile substances. This time-tempered system of defense is so intricate and adaptable that contemporary medicine has been hard-pressed to maintain an advantage. In this article, the processes responsible for bacterial resistance to extended-spectrum cephalosporins are reviewed. Particular emphasis is placed on the extended-spectrum beta-lactamases that have emerged to provide bacteria with formidable resistance to modern drugs. Avoidance of this problem requires limitations on extended-spectrum cephalosporin usage. While carbapenems are clearly the treatment of choice for infections caused by these pathogens, empirical use of beta-lactam/beta-lactamase inhibitors such as piperacillin/tazobactam has been associated with reduction in the prevalence of cephalosporin resistance.

Resistance patterns among nosocomial pathogens: trends over the past few years

Multiple surveillance studies have demonstrated that resistance among prevalent pathogens is increasing at an alarming rate, leading to greater patient morbidity and mortality from nosocomial infections. Among Gram-positive organisms, the most important resistant pathogens are methicillin- (oxacillin-)resistant Staphylococcus aureus, beta-lactam-resistant and multidrug-resistant pneumococci, and vancomycin-resistant enterococci. Important causes of Gram-negative resistance include extended-spectrum beta-lactamases (ESBLs) in Klebsiella pneumoniae, Escherichia coli, and Proteus mirabilis, high-level third-generation cephalosporin (Amp C) beta-lactamase resistance among Enterobacter species and Citrobacter freundii, and multidrug-resistance genes observed in Pseudomonas aeruginosa, Acinetobacter, and Stenotrophomonas maltophilia. In selecting an empiric treatment for a nosocomial infection, one should consider the prevalent resistance patterns. Antimicrobials used for the treatment of nosocomial infections should be effective against any likely resistant pathogens and should not further promote the development of resistance. Recent data suggest that because of ESBLs and high-level amp C beta-lactamase resistances, use of third-generation cephalosporins may be ineffective in many patients with nosocomial infections. In addition, use of these agents may allow overgrowth of inherently resistant enterococci. The role of fluoroquinolones in the empiric treatment of nosocomial infections is also being limited by new resistance patterns and increasing resistance levels. Available antimicrobials with good activity against many resistant pathogens include the carbapenems, piperacillin/tazobactam, and cefepime. In addition, several new agents with good activity against Gram-positive organisms are in development or have been recently released. Appropriate antimicrobial selection, surveillance systems, and effective infection-control procedures are key partners in limiting antimicrobial-resistant pathogen occurrence and spread.

Evaluation of current activities of fluoroquinolones against gram-negative bacilli using centralized in vitro testing and electronic surveillance

Given the propensity for Enterobacteriaceae and clinically significant nonfermentative gram-negative bacilli to acquire antimicrobial resistance, consistent surveillance of the activities of agents commonly prescribed to treat infections arising from these organisms is imperative. This study determined the activities of two fluoroquinolones, levofloxacin and ciprofloxacin, and seven comparative agents against recent clinical isolates of Enterobacteriaceae, Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia using two surveillance strategies: 1) centralized in vitro susceptibility testing of isolates collected from 27 hospital laboratories across the United States and 2) analysis of data from The Surveillance Network Database-USA, an electronic surveillance network comprising more than 200 laboratories nationwide. Regardless of the surveillance method, Enterobacteriaceae, P. aeruginosa, and A. baumannii demonstrated similar rates of susceptibility to levofloxacin and ciprofloxacin. Susceptibilities to the fluoroquinolones approached or exceeded 90% for all Enterobacteriaceae except Providencia spp. (</=65%). Approximately 70% of P. aeruginosa and 50% of A. baumanii isolates were susceptible to both fluoroquinolones. Among S. maltophilia isolates, 50% more isolates were susceptible to levofloxacin than to ciprofloxacin. Overall, the rate of ceftazidime nonsusceptibility among Enterobacteriaceae was 8.7%, with fluoroquinolone resistance rates notably higher among ceftazidime-nonsusceptible isolates than ceftazidime-susceptible ones. Multidrug-resistant isolates were present among all species tested but were most prevalent for Klebsiella pneumoniae and Enterobacter cloacae. No gram-negative isolates resistant only to a fluoroquinolone were encountered, regardless of species. Thus, while levofloxacin and ciprofloxacin have maintained potent activity against Enterobacteriaceae, the potential for fluoroquinolone resistance, the apparent association between fluoroquinolone and cephalosporin resistance, and the presence of multidrug resistance in every species examined emphasize the need to maintain active surveillance of resistance patterns among gram-negative bacilli.

Epidemiological analysis of bacterial strains involved in hospital infection in a university hospital from Brazil

Hospital infections cause an increase in morbidity and mortality of hospitalized patients with significant rise in hospital costs. The aim of this work was an epidemiological analysis of hospital infection cases occurred in a public University Hospital in Rio de Janeiro. Hence, 238 strains were isolated from 14 different clinical materials of 166 patients hospitalized in the period between August 1995 and July 1997. The average age of the patients was 33.4 years, 72.9% used antimicrobials before having a positive culture. The most common risk conditions were surgery (19.3%), positive HIV or AIDS (18.1%) and lung disease (16.9%). 24 different bacterial species were identified, S. aureus (21%) and P. aeruginosa (18.5%) were predominant. Among 50 S. aureus isolated strains 36% were classified as MRSA (Methicillin Resistant S. aureus). The Gram negative bacteria presented high resistance to aminoglycosides and cephalosporins. A diarrhea outbreak, detected in high-risk neonatology ward, was caused by Salmonella serovar Infantis strain, with high antimicrobial resistance and a plasmid of high molecular weight (98Mda) containing virulence genes and positive for R factor.

Association of antibiotic utilization measures and control of multiple-drug resistance in Klebsiella pneumoniae

OBJECTIVE

To study the association of antibiotic-utilization measures and control of multidrug-resistant (MDR) Klebsiella pneumoniae after emergence in two hospitals in our medical center.

DESIGN AND SETTING

Rates of MDR K. pneumoniae at two hospitals were compared before and after acute interventions, including emphasis on Contact Precautions and education in antibiotic utilization. Antipseudomonal beta-lactam antibiotic use was measured before and after the interventions at both hospitals. Pulsed-field gel electrophoresis of whole cell DNA was used as a marker of strain identity.

RESULTS

Clonal strain dissemination was the major mechanism of emergence at hospital A; emergence was polyclonal at hospital B. Antibiotic-utilization interventions at both institutions included physician education regarding the association of ceftazidime use and MDR K. pneumoniae. At hospital A, ceftazidime use decreased from 4,301 g in the preintervention period, to 1,248 g in the postintervention period. Piperacillin-tazobactam use increased from 12,455 g to 17,464 g. Ceftazidime resistance in K. pneumoniae decreased from 110 (22%) of 503 isolates to 61 (15%) of 407 isolates (P<.05); piperacillin-tazobactam resistance decreased from 181 (36%) of 503 to 77 (19%) of 407 isolates (P<.05). At hospital B, ceftazidime use decreased from 6,533 g in the preintervention period to 4,792 g in the postintervention period. Piperacillin-tazobactam use increased from 58,691 g to 67,027 g. Ceftazidime resistance in K. pneumoniae decreased from 42 (10%) of 415 isolates to 19 (5%) of 383 isolates (P<.05). Piperacillin-tazobactam resistance decreased from 91 (22%) of 415 isolates to 54 (14%) of 383 isolates (P<.05). Follow-up data showed continued decrease in piperacillin-tazobactam resistance despite increased use at both hospitals.

CONCLUSIONS

Antibiotic-use measures may be particularly important for control of MDR K. pneumoniae, whether emergence is clonal or polyclonal.

Clinical and molecular epidemiology of chromosome-mediated resistance to third-generation cephalosporins in Enterobacter isolates in eastern France

OBJECTIVE

To determine both the prevalence of group I beta-lactamase-related resistance and the clinical setting in which resistance to expanded-spectrum cephalosporins occurs.

METHODS

Isolates of Enterobacter spp. were sensitivity tested to a range of antibiotics, and selected isolates were DNA fingerprinted by pulsed-field gel electrophoresis. The medical records of all patients with positive cultures for Enterobacter spp. were reviewed to determine the effect of previous antibiotic treatment on the susceptibility profile of these organisms.

RESULTS

The crude incidence of colonization/infection (n = 315) was 0.51 per 100 patients and 0.73 per 1000 days of hospitalization. The 4-day and 7-day Kaplan-Meier rates of colonization/infection with Enterobacter were estimated to be 7.57% (standard deviation (SD = 3.26%) and 4.16% (SD = 2.88%)), respectively. The time lag to colonization/infection with isolates producing large amounts of Bush group 1 beta-lactamase (HLBL) (27.35 +/- 27.30 days) was significantly different from that to colonization/infection with wild-type isolates (13.59 +/- 17.93 days) (P = 0.036). Ninety-six isolates (30.5%) demonstrated acquired resistance to expanded-spectrum cephalosporins: 34 isolates (10.8%) produced extended-spectrum beta-lactamase, and 62 isolates (19.7%) produced HLBL. The 89 Enterobacter isolates susceptible to third-generation cephalosporins yielded 84 major DNA patterns, and the 45 HLBL isolates yielded 38 major DNA patterns. The risk of colonization/infection with HLBL-producing Enterobacter was higher in cases of antimicrobial treatment with third-generation cephalosporins or a fluoroquinolone, and in cases of urinary tract colonization/infection.

CONCLUSIONS

The judicious use in hospitals of both expanded-spectrum cephalosporins and other antibiotics such as fluoroquinolones is necessary to curtail the emergence of resistance in Enterobacter spp.

Outbreak of a multiresistant Klebsiella pneumoniae strain in an intensive care unit: antibiotic use as risk factor for colonization and infection

An observational study was undertaken to describe a nosocomial outbreak caused by multiresistant Klebsiella pneumoniae (MRKP). Ten patients in the pediatric intensive care unit (ICU) at a hospital in Madrid were colonized by or infected with MRKP from October 1997 to April 1998. Thirty-two patients with MRKP-negative surveillance cultures who were admitted to the ICU during the outbreak period were selected as control patients. Random amplified polymorphic DNA analysis of MRKP isolates revealed patterns that were indistinguishable from each other. After identification of colonized patients by surveillance cultures and implementation of standard and contact precautions, the outbreak was controlled. An age <12 weeks (odds ratio [OR], 13.1) and previous treatment with third-generation cephalosporins and aminoglycosides (OR, 31.2) were independently associated with MRKP colonization and/or infection. Individual exposure to antibiotics, irrespective of other clinical determinants, is a risk factor for MRKP acquisition. Screening high-risk patients during outbreaks and reducing the use of third-generation cephalosporins and aminoglycosides contribute to the control of these epidemics.

Detection and reporting of organisms producing extended-spectrum beta-lactamases: survey of laboratories in Connecticut

Extended-spectrum beta-lactamases (ESBLs) are enzymes produced in some gram-negative bacilli that mediate resistance to extended-spectrum cephalosporins and aztreonam. They are most common in Klebsiella spp. and Escherichia coli but are present in a variety of Enterobacteriaceae. Resistance mediated by these enzymes can be difficult to detect depending on the antimicrobial agents tested. AmpC beta-lactamases are related to the chromosomal enzymes of Enterobacter and Citrobacter spp. and also mediate resistance to extended-spectrum cephalosporins and aztreonam in addition to cephamycins, such as cefoxitin. Unlike ESBLs, however, AmpC beta-lactamases are not inhibited by clavulanic acid or other similar compounds. To assess the abilities of various antimicrobial susceptibility testing methods to detect ESBLs, we sent three ESBL-producing organisms, one AmpC-producing organism, and a control strain that was susceptible to extended-spectrum cephalosporins to 38 laboratories in Connecticut for testing. Eight (21.0%) of 38 labs failed to detect extended-spectrum cephalosporin or aztreonam resistance in any of the ESBL- or AmpC-producing isolates. Errors were encountered with both automated and disk diffusion methods. Conversely, seven (18.4%) labs categorized at least some of the four resistant isolates as potential ESBL producers and reported the results with the extended-spectrum cephalosporins and aztreonam as resistant as suggested by current National Committee for Clinical Laboratory Standards (NCCLS) guidelines. The percentage of laboratories that failed to detect resistance in the ESBL or AmpC isolates ranged from 23.7 to 31.6% depending on the type of enzyme present in the test organism. This survey suggests that many laboratories have difficulty detecting resistance in ESBL and AmpC-producing organisms and may be unaware of the NCCLS guidelines on modifying susceptibility testing reports for ESBL-producing strains.

Control of a prolonged outbreak of extended-spectrum beta-lactamase-producing enterobacteriaceae in a university hospital

Extended-spectrum beta-lactamase-producing Enterobacteriaceae (ESBLPE) were isolated from clinical specimens from 130 to 140 patients/year in 1989-1991 in our hospital. In February 1992, a control program was initiated: screening tests in 3 intensive care units (ICUs) and contact-isolation precautions in all units. The septic surgical unit served as an isolation ward for surgical patients from whom ESBLPE was isolated. In 1992, the incidence of ESBLPE acquisition failed to decrease, and most acquisitions occurred in 3 ICUs. Critical evaluation of implementation of isolation procedures in these ICUs prompted corrective measures for barrier precautions. The incidence of acquired cases subsequently decreased, and a second evaluation determined that these measures had been correctly applied. The incidence of acquired cases in the septic surgical unit was lower than those in the other units. Decreases were also found in the incidence of acquisition of other hand-transmitted multidrug-resistant organisms. Barrier precautions, screening tests for ICU patients, and grouping of cohorts after ICU discharge are effective in controlling the spread of multidrug-resistant microorganisms by cross-contamination. The outbreak was effectively controlled without restricting antimicrobial use.

RAPD typing of Klebsiella pneumoniae, Klebsiella oxytoca, Serratia marcescens and Pseudomonas aeruginosa isolates using standardized reagents

OBJECTIVE: To perform quality assessment of standardized random amplified polymorphic DNA (RAPD) analysis for epidemiologic typing of Klebsiella pneumoniae, K. oxytoca, Serratia marcescens and Pseudomonas aeruginosa. METHODS: Thirty K. pneumoniae, 15 K. oxytoca, 30 S. marcescens and 33 P. aeruginosa epidemiologically unrelated isolates and four collections of clinically related isolates of each species were included in the study. RAPD analysis was performed using Ready-To-Go RAPD Analysis beads with primer ERIC-1R and Ready-To-Go primer 2 for K. pneumoniae and K. oxytoca, primer set ERIC-2/1026 and Ready-To-Go primer 2 for S. marcescens, and primers D-10514 and D-14306 for P. aeruginosa. RESULTS: All epidemiologically unrelated K. pneumoniae and K. oxytoca isolates were distinguished. Twenty-nine types were distinguished among the 30 unrelated S. marcescens isolates and 32 types among the 33 unrelated P. aeruginosa isolates. Indistinguishable banding patterns were obtained in repeated analyses of two isolates and from 11 serial subcultures of three isolates of each species included in the study. The RAPD data from the clinically related isolates correlated with the epidemiologic origin of the isolates. CONCLUSIONS: The use of Ready-To-Go RAPD Analysis beads resulted in reproducible and stable banding patterns with a high discriminatory capacity, and the RAPD typing results corresponded with the epidemiologic origin of the isolates.

Extended-spectrum beta-lactamase-producing Klebsiella pneumoniae strains causing nosocomial outbreaks of infection in the United Kingdom

Representative isolates from 10 distinct extended-spectrum beta-lactamase-producing strains of Klebsiella pneumoniae that caused hospital outbreaks in the United Kingdom from 1991 to 1994 were examined for relationships between their enzymes and plasmids. The beta-lactamases were identified by a combination of isoelectric focusing and gene sequencing. SHV-2 beta-lactamase was produced by isolates from four outbreaks, SHV-5 was involved in three, and SHV-4, TEM-15, and TEM-26 were involved in one outbreak each. All of the extended-spectrum beta-lactamases were encoded by self-transmissible plasmids, with sizes ranging from about 70 to 160 kb. No similarities between the restriction digest patterns of the extended-spectrum beta-lactamase-encoding plasmids were detected, except to some extent between those that produced TEM-15 and TEM-26. Thus, outbreaks of hospital infection with these organisms in the United Kingdom from 1991 to 1994 involved distinct organisms and resistance plasmids and appeared to be unrelated.