Pathogens resistant to antimicrobial agents. Epidemiology, molecular mechanisms, and clinical management

Bacterial Nosocomial Infections: Multidrug Resistance as a Trigger for the Development of Novel Antimicrobials

Nosocomial bacterial infections are associated with high morbidity and mortality, posing a huge burden to healthcare systems worldwide. The ongoing COVID-19 pandemic, with the raised hospitalization of patients and the increased use of antimicrobial agents, boosted the emergence of difficult-to-treat multidrug-resistant (MDR) bacteria in hospital settings. Therefore, current available antibiotic treatments often have limited or no efficacy against nosocomial bacterial infections, and novel therapeutic approaches need to be considered. In this review, we analyze current antibacterial alternatives under investigation, focusing on metal-based complexes, antimicrobial peptides, and antisense antimicrobial therapeutics. The association of new compounds with older, commercially available antibiotics and the repurposing of existing drugs are also revised in this work.

Reversal of heavy metal-induced antibiotic resistance by dandelion root extracts and taraxasterol

Introduction. Metal exposure is an important factor for inducing antibiotic resistance in bacteria. Dandelion extracts have been used for centuries in traditional Chinese and Native American medicine.

Aim. We assessed the effects of dandelion water extracts and taraxasterol on heavy metal-induced antibiotic resistance in Escherichia coli as well as the underlying mechanisms.

Methodology. Dandelion extracts were obtained through 4 h of boiling in distilled water. Bacterial growth was monitored with a spectrophotometer. Biochemical assays were performed to assess the activities and gene transcriptions of β-lactamase and acetyltransferase. Oxidative stress was determined using an oxidation-sensitive probe, H2DCFDA.

Results. The present study demonstrated that higher concentrations of nickel (>5 µg ml−1), cadmium (>0.1 µg ml−1), arsenic (>0.1 µg ml−1) and copper (>5 µg ml−1) significantly inhibited the growth of E. coli . Lower concentrations of nickel (0.5 µg ml−1), cadmium (0.05 µg ml−1) and arsenic (0.05 µg ml−1) had no effect on bacterial growth, but helped the bacteria become resistant to two antibiotics, kanamycin and ampicillin. The addition of dandelion root extracts and taraxasterol significantly reversed the antibiotic resistance induced by these heavy metals. The supplements of antibiotics and cadmium generated synergistic effects on the activities of β-lactamase and acetyltransferase (two antibiotic resistance-related proteins), which were significantly blocked by either dandelion root extract or taraxasterol. In contrast, oxidative stress was not involved in the preventative roles of dandelion root extracts and taraxasterol in heavy metal-induced antibiotic resistance.

Conclusion. This study suggests that heavy metals induce bacterial antibiotic resistance and dandelion root extracts and taraxasterol could be used to help reverse bacterial resistance to antibiotics.

Chemical Constituents of Salix babylonica L. and Their Antibacterial Activity Against Gram-Positive and Gram-Negative Animal Bacteria

The principle of animal wellbeing, which states that animals should be free from pain, injury, and disease, is difficult to maintain, because microorganisms are most frequently found to be resistant or multi-resistant to drugs. The secondary metabolites of plants are an alternative for the treatment of these microorganisms. The aim of this work was to determine the antibacterial effect of Salix babylonica L. hydroalcoholic extract (SBHE) against Escherichia coli, Staphylococcus aureus and Listeria monocytogenes, and identify the compounds associated with the activity. The SBHE showed activity against the three strains, and was subjected to a bipartition, obtaining aqueous fraction (ASB) with moderate activity and organic fraction (ACSB) with good activity against the three strains. The chromatographic separation of ACSB, allowed us to obtain ten fractions (F1AC to F10AC), and only three showed activity (F7AC, F8AC and F10AC). In F7AC, five compounds were identified preliminary by GC-MS, in F8AC and F10AC were identified luteolin (1) and luteolin 7-O-glucoside (2) by HPLC, respectively. The best antibacterial activity was obtained with F7AC (Listeria monocytogenes; MIC: 0.78 mg/mL, MBC: 0.78 mg/mL) and F8AC (Staphylococcus aureus; MIC: 0.39 mg/mL; MBC: 0.78 mg/mL). The results indicated that the compounds obtained from SBHE can be used as an alternative treatment against these microorganisms and, by this mechanism, contribute to animal and human health.

Detection of AmpC β-lactamase producing bacteria isolated in neonatal sepsis

OBJECTIVE

The objective of this study was to determine the occurrence and antimicrobial profile of AmpC β-lactamase producing bacteria.

METHODS

The study was conducted at The Children's Hospital and The Institute of Child Health Lahore, Pakistan, during September 2011 to June 2012. A total number of 1,914 blood samples of suspected neonatal septicemia were processed. Isolates were identified using Gram's staining, API 20E and API 20NE tests. Gram negative isolates were screened for AmpC β-lactamase production against ceftazidime, cefotaxime and cefoxitin resistance and confirmed by inhibitor based method.

RESULTS

Total number of 54 (8.49%) Gram positive and 582 (91.5%) Gram negative bacteria were identified. Among Gram negative isolates 141 (22%) were AmpC producers and found to be 100% resistant to co-amoxiclav, cefoxitin, ceftazidime, cefotaxime, cefuroxime, cefixime, ceftriaxone, cefpodoxime, gentamicin, amikacin and aztreonam. Less resistance was observed against cefepime (30.4%), sulbactam-cefoperazone (24.8%), piperacillin-tazobactam (10.6%), ciprofloxacin (20.5%) and meropenem (2.1%). All the isolates were found sensitive to imipenem. The patients harbored AmpC β-lactamases were on various interventions in which intravenous line was noted among (51.1%), naso-gastric tube (37.6%), ambu bag (8.5%), endotracheal tube (3.5%), ventilator (2.1%) and surgery (0.7%).

CONCLUSION

Extensive use of invasive procedures and third generation cephalosporins should be restricted to avoid the emergence of AmpC beta-lactamases in neonates.

Influence of antibiotic-regimens on intensive-care unit-mortality and liver-cirrhosis as risk factor

AIM: To assess the rate of infection, appropriateness of antimicrobial-therapy and mortality on intensive care unit (ICU). Special focus was drawn on patients with liver cirrhosis.

METHODS: The study was approved by the local ethical committee. All patients admitted to the Internal Medicine-ICU between April 1, 2007 and December 31, 2009 were included. Data were extracted retrospectively from all patients using patient charts and electronic documentations on infection, microbiological laboratory reports, diagnosis and therapy. Due to the large hepatology department and liver transplantation center, special interest was on the subgroup of patients with liver cirrhosis. The primary statistical-endpoint was the evaluation of the influence of appropriate versus inappropriate antimicrobial-therapy on in-hospital-mortality.

RESULTS: Charts of 1979 patients were available. The overall infection-rate was 53%. Multiresistant-bacteria were present in 23% of patients with infection and were associated with increased mortality (P < 0.000001). Patients with infection had significantly increased in-hospital-mortality (34% vs 17%, P < 0.000001). Only 9% of patients with infection received inappropriate initial antimicrobial-therapy, no influence on mortality was observed. Independent risk-factors for in-hospital-mortality were the presence of septic-shock, prior chemotherapy for malignoma and infection with Pseudomonas spp. Infection and mortality-rate among 175 patients with liver-cirrhosis was significantly higher than in patients without liver-cirrhosis. Infection increased mortality 2.24-fold in patients with cirrhosis. Patients with liver cirrhosis were at an increased risk to receive inappropriate initial antimicrobial therapy.

CONCLUSION: The results of the present study report the successful implementation of early-goal-directed therapy. Liver cirrhosis patients are at increased risk of infection, mortality and to receive inappropriate therapy. Increasing burden are multiresistant-bacteria.

A guide to antibiotics for the interventional radiologist

Antibiotics are among the most common pharmaceutical agents used by the interventional radiologist. This article updates some of the practical aspects of the use of antibiotics in interventional radiological practice and provides some general guidelines with respect to indications for and selection of antibiotics. In particular, the objectives of this article are to review the basic pharmacology of the common antibiotic agents, the interventional radiological procedures in which prophylactic antibiotics are usually administered, the specific antimicrobial agents recommended for prophylaxis before common interventional radiological procedures, the appropriate antibiotics for patients allergic to penicillins, and the indications for antibiotic prophylaxis to prevent bacterial endocarditis.

Clonality and antimicrobial resistance gene profiles of multidrug- resistant Salmonella enterica serovar infantis isolates from four public hospitals in Rio de Janeiro, Brazil

In Brazil, Salmonella enterica serovar Infantis resistant to various antimicrobials, including cephalosporins, has been identified as an etiological agent of severe gastroenteritis in hospitalized children since 1994. In this study, 35 serovar Infantis strains, isolated from children admitted to four different Rio de Janeiro, Brazil, hospitals between 1996 and 2001, were characterized by pulsed-field gel electrophoresis (PFGE) and antimicrobial susceptibility testing in order to determine their genetic relatedness and antimicrobial resistance profiles. Thirty-four serovar Infantis strains were resistant to at least two antibiotic classes, and all 35 strains were susceptible to fluoroquinolones, cephamycin, and carbapenem. Extended-spectrum beta-lactamase (ESBL) screening by double-disk diffusion indicated that 32 serovar Infantis strains (91.4%) produced beta-lactamases that were inhibited by clavulanic acid. Antimicrobial resistance gene profiles were determined by PCR for a subset of 11 multidrug-resistant serovar Infantis strains, and putative ESBLs were detected by isoelectric focusing. Ten serovar Infantis strains carried bla(TEM), catI, ant(3")Ia and/or ant(3")Ib, sulI and/or sulII, and tet(D) genes as well as an integron-associated aac(6')-Iq cassette. Eight strains possessed at least four different beta-lactamases with pI profiles that confirmed the presence of both ESBLs and non-ESBLs. Our PFGE profiles indicated that 33 serovar Infantis strains isolated from Rio de Janeiro hospitals came from the same genetic lineage.

Prophylactic Antibiotic Use in Open Fractures: An Evidence-Based Guideline

BACKGROUND

Prolonged courses of broad-spectrum antibiotics are often cited as the standard of care for prevention of infective complications of open fractures. The origins of these recommendations are obscure, however, and multi-drug-resistant systemic infections attributable to antibiotic overuse are common life-threatening problems in current intensive care unit practice.

OBJECTIVE

To review systematically the effects of prophylactic antibiotic administration on the incidence of infections complicating open fractures.

DATA SOURCES

Computerized bibliographic search of published research and citation review of relevant articles.

STUDY SELECTION

All published clinical trials claiming to evaluate, or cited elsewhere as being authoritative regarding, the role of antibiotics in open fracture management were identified and then evaluated according to published guidelines for evidence-based medicine. Only small studies (<20 patients), practice surveys, pharmacokinetic studies, and reviews or duplicative publications presenting primary data already considered were excluded from analysis.

DATA EXTRACTION

Information on demographics, study dates, fracture grade, antibiotic type, duration and route of administration, surgical interventions, infection-related outcomes, and the methodologic quality of the studies was extracted by the authors. The primary results were submitted to the Therapeutic Agents Committee of the Surgical Infection Society for review prior to creation of the final consensus document.

DATA SYNTHESIS

Current antibiotic management of open fractures is based on a small number of studies that generally are more than 30 years old and do not reflect current management priorities in trauma and critical care. With a few noteworthy exceptions, these primary studies suffer from a variety of methodologic problems, including co-mingling of prospective and retrospective data sets, absence of or inappropriate statistical analysis, lack of blinding, or failure of randomization.

CONCLUSIONS

The data support the conclusion that a short course of first-generation cephalosporins, begun as soon as possible after injury, significantly lowers the risk of infection when used in combination with prompt, modern orthopedic fracture wound management. There is insufficient evidence to support other common management practices, such as prolonged courses or repeated short courses of antibiotics, the use of antibiotic coverage extending to gram-negative bacilli or clostridial species, or the use of local antibiotic therapies such as beads. Large, randomized, blinded trials are needed to prove or disprove the value of these traditional approaches. Such trials should be performed in patients with high-grade fractures who (1) are well-stratified according to the degree of local injury and (2) undergo standardized fracture and wound management. Trials also must be powered to study the effects of extended antibiotic coverage on nosocomial infections. Antibiotic regimens confirmed to improve local fracture outcomes in such studies could then be used rationally, balancing the risks of local fracture-related infections and of multi-drug-resistant systemic infections to achieve optimal global outcomes.

Applying antimicrobial pharmacodynamics to resistant gram-negative pathogens

PURPOSE

Guided antibiotic adjustment for the treatment of multidrug-resistant, gram-negative pathogens is explored.

SUMMARY

Multidrug-resistant pathogens are being isolated with increasing frequency, while the production of novel agents to circumvent resistance has slowed to a near halt. Hence, antimicrobial adjustment based on drug pharmacokinetic and pharmacodynamic properties has moved to the forefront of treatment. Pharmacodynamic principles for major classes of antimicrobials are reviewed, and the use of susceptibility reports to optimize pharmacodynamics to treat gram-negative infections is described. The need for the application of antimicrobial pharmacodynamics continues to grow as resistance to the agents becomes more common. Susceptibility reports, including antibiograms, and their limitations are briefly discussed. The resistance profiles of the beta-lactams (including carbapenems), aminoglycosides, fluoroquinolones, tetracyclines and glycylcyclines, and the polymyxins are reviewed, and the pharmacodynamic optimization of these profiles is explored.

CONCLUSION

Various mechanisms account for resistance of bacteria to antibiotics. The appropriate use of pharmacokinetics and pharmacodynamics can guide antibiotic therapy and enhance the likelihood of success.

Predictors of mortality in patients with bloodstream infection due to ceftazidime-resistant Klebsiella pneumoniae

Bloodstream infection (BSI) due to multidrug-resistant Klebsiella is associated with high rates of morbidity and mortality. The aim of this study was to identify predictors of in-hospital mortality among patients with BSI due to ceftazidime-resistant (CAZ-R) Klebsiella pneumoniae at a tertiary care medical center. Patients with CAZ-R K. pneumoniae BSI were identified by our microbiology laboratory between January 1995 and June 2003. Clinical data were collected retrospectively. Logistic regression was used to identify independent predictors of all causes of in-hospital mortality. Of 779 patients with K. pneumoniae BSI, 60 (7.7%) had BSI due to CAZ-R K. pneumoniae; 43 (72%) of these were nosocomial infections. Pulsed-field gel electrophoresis identified a single predominant strain in 17 (28%) patients. The in-hospital mortality rate was 43% (n = 26). Among patients with CAZ-R K. pneumoniae BSI, those who died were similar to survivors with respect to demographic, clinical, and antimicrobial susceptibility characteristics. Only 43 (72%) patients received effective therapy within 5 days of BSI. In bivariable analysis, delay in initiation of effective therapy for >72 h after diagnosis of BSI was associated with death (P = 0.03). Strain genotype was not predictive of outcome. In multivariable analysis, delay in initiation of effective therapy for >72 h after diagnosis of BSI was an independent predictor of death (odds ratio, 3.32; 95% confidence interval, 1.07 to 10.3). Thus, among patients with BSI due to CAZ-R K. pneumoniae, a delay in the initiation of effective therapy of greater than 72 h after BSI was associated with a >3-fold increase in mortality risk.

Risk factors for ICU-acquired methicillin-resistant Staphylococcus aureus infections

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen that causes severe morbidity and mortality in many hospitals worldwide, and MRSA infections are frequent in intensive care units (ICUs).

OBJECTIVE

A prospective study was implemented to investigate the risk factors for ICU-acquired MRSA infections.

METHODS

This study was conducted in surgical and neurologic ICUs from May to November 2003. The patients staying in ICUs more than 48 hours were included in the study. All of the patients were visited daily, and data were recorded on individual forms for each patient until discharge or death. Nasal swab cultures were done within 48 hours of ICU admission and repeated every week until the patients colonized with MRSA or were discharged from ICUs. ICU-acquired MRSA infection was diagnosed when MRSA was isolated from the infected site.

RESULTS

Overall, 249 patients were followed during the study. MRSA infection was detected in 21 (8.4%) of these patients. The most frequent infection was primary bloodstream infection (10/21, 47%). It was followed by pneumonia (8/21, 38%) and surgical site infection (3/21, 14%). Nasal MRSA colonization was detected in 59 (23.7%) patients, and 12 of them (20.3%) developed MRSA infection. In univariate analysis, hospitalization period in an ICU, intraabdominal and orthopedic pathologies, mechanical ventilation, central venous catheter insertion, total parenteral nutrition, previous antibiotic use, surgical ICU stay, nasal MRSA colonization, and presence of more than 2 patients having nasal colonization in the same ICU at the same time were found significant for MRSA infections. In multivariate analysis; hospitalization period in an ICU (OR, 1.090; 95% CI: 1.038-1.144, P = .001), central venous catheter insertion (OR, 1.822; 95% CI: 1.095-3.033, P = .021), previous antibiotic use (OR, 2.337; 95% CI: 1.326-4.119, P = .003) and presence of more than 2 patients having nasal colonization in the same ICU at the same time (OR, 1.398; 95% CI: 1.020-1.917, P = .037) were independently associated with MRSA infections.

CONCLUSION

According to the our results, hospitalization period in an ICU, presence of patients colonized with MRSA in the same ICU at the same time, previous antibiotic use, and central venous catheter insertion are independent risk factors for ICU-acquired MRSA infections. Detection of these factors helps to decrease the rate of MRSA infections in the ICUs.

Changes of antimicrobial resistance and extended-spectrum beta-lactamase production in Klebsiella spp. strains

Changes of antimicrobial resistance and extended-spectrum beta-lactamase (ESBL) production of Klebsiella spp. strains isolated at the Central Military Hospital, Ruzomberok, Slovakia, with a special focus on the Anesthesiology--Resuscitation and Intensive Medicine Department during the years 1998-2002, were analyzed. Of 3920 gram-negative strains isolated from clinical materials during this period, Klebsiella spp. represented 8%. The incidence of ESBL-producing Klebsiella spp. isolates increased from 29% in 1998 to 69% in 2002. Of 17 antibiotics tested, meropenem was found to be the most effective drug (100%). The overall efficacy of cefotaxime was 31%, that of gentamicin 23%, and that of ciprofloxacin 54%. Analyzed Klebsiella isolates were characterized also by a high degree of multiresistance (53%). The high incidence of reduced antibiotic susceptibility among Klebsiella spp. strains isolated at the intensive-care department suggests that more effective strategies are necessary to control the selection and spread of resistant organisms in this hospital.

Does combination antimicrobial therapy reduce mortality in Gram-negative bacteraemia? A meta-analysis

The use of combination antimicrobial therapy for bacteraemia caused by Gram-negative bacilli is controversial. We did a meta-analysis of published studies to determine whether a combination of two or more antimicrobials reduces mortality in patients with Gram-negative bacteraemia. Criteria for inclusion were: analytic studies of patients with documented Gram-negative bacteraemia that included patients receiving a single antibiotic (monotherapy) and patients receiving two or more antibiotics (combination therapy). Data on mortality (outcome) had to be provided. A pooled odds ratio was calculated with the random effects model of DerSimonian and Laird. Assessment of heterogeneity was done with the Breslow-Day test and reasons for heterogeneity were explored. 17 studies met the inclusion criteria, five prospective cohort studies, two prospective randomised trials, and ten retrospective cohort studies. Most studies used beta-lactams or aminoglycosides alone and in combination. The summary odds ratio was 0.96 (95% CI 0.70-1.32), indicating no mortality benefit with combination therapy. Subgroup analyses adjusting for year of publication, study design, and severity of illness did not change the results. Considerable heterogeneity was present in the main analyses. Analysis of only Pseudomonas aeruginosa bacteraemias showed a significant mortality benefit (OR 0.50, 95% CI 0.30-0.79). Our analysis does not support the routine use of combination antimicrobial therapy for Gram-negative bacteraemia, beyond settings where infection by P aeruginosa is strongly suspected or more than one drug would be desirable to assure in-vitro efficacy.

Antibacterial resistance

Resistance to antimicrobial agents, which was recognized more than 50 years, continues to be a major cause of increased morbidity, mortality and health care cost. Overuse of antibiotics is considered the major contributing factor; however, poor implementation of infection control measures, prolonged hospitalization, admission to intensive care units and the use of invasive procedures are other contributing factors. The authors review the epidemiology, mechanism of resistance, treatment options and prevention measures of infections caused multi-drug resistant S. pneumoniae, methicillin-resistant S. aureus (MRSA), macrolide-resistant S. pyogenes and vancomycin-resistant enterococci (VRE) in pediatric patients. Antibacterial resistance among Gram-negative organisms, including extended spectrum beta-lactamase (ESBL) producing enteric bacteria, and the management and prevention of infections caused by these organisms are also discussed.

Susceptibility patterns of enterococci causing infections

Enterococci are among the common organisms associated with hospital-acquired infections. We examined in vitro activities of different antibiotics to 103 enterococcal isolates. Minimal inhibitory concentrations (MICs) of penicillin G, ampicillin, gentamicin, ciprofloxacin, ofloxacin, levofloxacin, grepafloxacin, trovafloxacin and gemifloxacin were determined by broth microdilution testing method. Among the isolates 71 (69%) were identified as E. faecalis and 32 (31%) as E. faecium. While over 75% of E. faecium isolates were resistant to penicillin and ampicillin, approximately 25% of E. faecalis isolates were resistant to penicillin and ampicillin. None of the E. faecalis and E. faecium isolates were resistant to vancomycin. While 17 (52%) of E. faecium isolates exhibited high-level gentamicin resistance (HLGR), high level streptomycin resistance (HLSR) was detected in 24 (74%) of the isolates. In contrast, HLGR and HLSR rates for E. faecalis were 14 (20%) and 22 (31%), respectively. Both HLGR and HLSR were detected with higher frequency in ampicillin resistant isolates. Among fluoroquinolones, gemifloxacin and trovafloxacin were the most potent antibiotics tested. There was no increase in MIC90 values of the fluoroquinolones in ampicillin resistant isolates in comparison with ampicillin susceptible isolates. Our data suggest newer fluoroquinolones would be good alternative agents to use especially for combination drug therapy where enterococci with ampicillin resistance and HLAR are prevalent.

Bacteremia Due toKlebsiella pneumoniaeIsolates Producing the TEM‐52 Extended‐Spectrum β‐Lactamase: Treatment Outcome of Patients Receiving Imipenem or Ciprofloxacin

The treatment outcome of 35 cases of bacteremia due to Klebsiella pneumoniae isolates producing TEM-52 extended-spectrum beta-lactamase was studied. Twenty-eight cases, classified as "nonfatal disease" using the McCabe and Jackson classification, were investigated with regard to ciprofloxacin and imipenem response. Because ciprofloxacin was active in vitro against 21 of 28 isolates, only the treatment outcome of the ciprofloxacin-susceptible subgroup was evaluated. Eight of 10 cases occurred in patients who experienced a complete response to imipenem; 2 of 10 failed to respond. In contrast, only 2 of 7 cases had a partial response to ciprofloxacin, and, in 5 of 7 cases, the treatment failed. Statistical analysis revealed a significant difference in the treatment outcome of the 2 groups (P=.03). Because the isolates had minimum inhibitory concentrations of ciprofloxacin close to the susceptibility breakpoint, treatment failure could be ascribed to the inability of the drug to reach therapeutic concentrations at infected sites.

Worldwide trends in antimicrobial resistance among common respiratory tract pathogens in children

BACKGROUND

Respiratory tract infections among children are a common reason for health care provider visits and the primary reason for antimicrobial prescribing in this population. The increased prevalence of resistance among Streptococcus pneumoniae and Haemophilus influenzae pathogens poses a serious challenge in the successful treatment of respiratory tract infections caused by these pathogens.

METHODS

This paper reviews worldwide trends in antimicrobial resistance among common respiratory tract pathogens, highlighting data obtained from the pediatric population where available.

RESULTS

S. pneumoniae resistance to beta-lactams is mediated through alterations in the penicillin-binding proteins and macrolide resistance to acquisition of efflux or methylation genes. The mechanisms of resistance to the fluoroquinolones include target enzyme alterations via genetic mutations and transport out of the bacterial cell via an efflux pump. Beta-lactamase production is the primary mechanism of resistance to penicillins among H. influenzae isolates. Although S. pneumoniae with reduced susceptibility to penicillin was first documented > 30 years ago, resistance has increased at an alarming rate worldwide in the past decade. According to recent surveillance data, the worldwide prevalence of S. pneumoniae with reduced susceptibility to penicillin is 18.2%. Beta-lactamase production among H. influenzae ranges from approximately 4% in Russia to 26% in the United States and to 31% in France. The prevalence of beta-lactamase-negative, ampicillin-resistant H. influenzae remains very low (< 1%) worldwide, except in Japan, where the incidence is higher. In general, the highest rates of resistance are observed in isolates obtained from children, and risk factors for infection with a resistant pathogen include young age, the site of infection, day-care center attendance and recent antimicrobial use.

CONCLUSIONS

Increased prevalence of antimicrobial resistance among respiratory tract pathogens isolated from children and adults is evident worldwide. Treatment of infections caused by S. pneumoniae and H. influenzae with older agents or ineffective dosing regimens may not eradicate infections and may contribute to the spread of resistance. These observations confirm the need for appropriate antimicrobial use to halt or at least limit the spread of resistance.

Antimicrobial prophylaxis in the surgical patient

The primary prophylactic measure against postoperative infection is antiseptic technique in patient preparation, during surgery, and in postoperative patient care. Antimicrobial prophylaxis against postoperative infection is not indicated for procedures with a low infection rate because the expected benefit of antimicrobial treatment is less than the risk of an adverse medication reaction. Antimicrobial prophylaxis has been demonstrated to be of greater benefit than risk in some procedures with higher infection rates; however, because the problem is complex and the data are limited, extra-polating these findings to the practitioner's setting and the individual patient remains a challenge (Table 1). Although antimicrobial prophylaxis for bacterial endocarditis is not effective for most patients, the seriousness of the potential infection has driven the creation of guidelines recommending prophylaxis for at-risk patients undergoing at-risk procedures. Applying these guidelines appropriately could help to reduce unwarranted use of antimicrobials. In the prophylactic use of antimicrobials, as in many medical interventions, the difficulty is balancing the risks of the intervention with the potential benefits. Although we do not have either the randomized, controlled trials or the detailed, patient-specific information to estimate this balance precisely, there are general guidelines to help the clinician choose treatment for most patients.

Serratia bacteremia in a large university hospital: trends in antibiotic resistance during 10 years and implications for antibiotic use

OBJECTIVE

To identify antibiotic resistance trends and risk factors for resistance of Serratia species to third-generation cephalosporins.

DESIGN

Retrospective survey of medical records.

SETTING

A 2,200-bed, tertiary-care hospital.

PATIENTS

One hundred twenty-two patients with Serratia bacteremia between January 1991 and June 2001.

METHODS

Infectious disease physicians collected data from medical records regarding patient demographics, underlying disease or condition, portal of entry, microorganism, antibiogram, complications, antibiotics received, and outcome.

RESULTS

Among 122 Serratia isolates, 117 (95.9%) were Serratia marcescens and 110 (90.2%) were of nosocomial origin. During the study period, the 122 isolates showed a high rate of resistance to third-generation cephalosporins (45.9%) and extended-spectrum penicillins (56.6%). The resistance rate to ciprofloxacin was 32.0%. The resistance rate to third-generation cephalosporins increased from 31.7% for 1991 to 1995 to 54.9% for 1996 to 1998 and 50.0% for 1999 to 2001. In the multivariate analysis, prior use of a second-generation cephalosporin (adjusted odds ratio [OR], 5.90; 95% confidence interval [CI90], 1.41 to 24.6; P = .015) or a third-generation cephalosporin (OR, 3.26; CI95, 1.20 to 8.87; P = .020) was a strong independent risk factor for resistance to third-generation cephalosporins. The overall case-fatality rate was 25.4% (Serratia bacteremia-related case-fatality rate, 13.1%).

CONCLUSION

Prior use of a second- or third-generation cephalosporin was the most important risk factor for bacteremia with Serratia resistant to third-generation cephalosporins, suggesting the need for antibiotic control. The potential role of patient-to-patient spread could not be fully evaluated in this retrospective study.

Prevalence and drug susceptibility of pathogens causing bloodstream infections in northern Italy: a two-year study in 16 hospitals

The epidemiology of bacterial pathogens causing bloodstream infection was studied in 16 hospitals in Lombardy (northern Italy) over a 2-year period (1999 and 2000). Overall, 2924 microorganisms causing significant bacteremia were collected. The most frequent isolates were Escherichia coli ( n=663; 22.7%), Staphylococcus aureus ( n=534; 18.3%), Staphylococcus epidermidis ( n=242; 8.2%), and Pseudomonas aeruginosa ( n=176; 6.0%). Unlike Escherichia coli, which was usually acquired from the community, Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa were usually acquired in hospitals. Rates of resistance to oxacillin and its associated traits were significantly higher among hospital-acquired staphylococci as compared to those of isolates from the community. Escherichia coli was highly susceptible to extended-spectrum cephalosporins, with a very low percentage of strains producing extended-spectrum ss-lactamases (ESBLs). On the contrary, production of ESBL appeared to be an important mechanism of resistance among nosocomial isolates of Klebsiella pneumoniae. Resistance to ciprofloxacin was widespread in several members of the family Enterobacteriaceae, with rates often exceeding 10%. Moreover, with regard to ciprofloxacin, there were no significant differences between rates of resistance among Enterobacteriaceae causing hospital-acquired infections versus those causing community-acquired infections. Multidrug resistance was commonly observed in Pseudomonas aeruginosa, indicating the need for new antimicrobial agents that are more active against nonfermentative gram-negative bacteria. In conclusion, epidemiological studies of the prevalence and antimicrobial susceptibility patterns of blood isolates in northern Italy appear to provide useful information for both empirical treatment of suspected infections and better management of patients.

Effect of Lactobacillus johnsonii La1 and antioxidants on intestinal flora and bacterial translocation in rats with experimental cirrhosis

BACKGROUND/AIMS

Probiotics and antioxidants could be alternatives to antibiotics in the prevention of bacterial infections in cirrhosis. The aim of the present study was to determine the effect of Lactobacillus johnsonii La1 and antioxidants on intestinal flora, endotoxemia, and bacterial translocation in cirrhotic rats.

METHODS

Twenty-nine Sprague-Dawley rats with cirrhosis induced by CCl(4) and ascites received Lactobacillus johnsonii La1 10(9)cfu/day in vehicle (antioxidants: vitamin C+glutamate) (n=10), vehicle alone (n=11), or water (n=8) by gavage. Another eight non-cirrhotic rats formed the control group. After 10 days of treatment, a laparotomy was performed to determine microbiological study of ileal and cecal feces, bacterial translocation, endotoxemia, and intestinal malondialdehyde (MDA) levels as index of intestinal oxidative damage.

RESULTS

Intestinal enterobacteria and enterococci, bacterial translocation (0/11 and 0/10 vs. 5/8, P<0.01), and ileal MDA levels (P<0.01) were lower in cirrhotic rats treated with antioxidants alone or in combination with Lactobacillus johnsonii La1 compared to cirrhotic rats receiving water. Only rats treated with antioxidants and Lactobacillus johnsonii La1 showed a decrease in endotoxemia with respect to cirrhotic rats receiving water (P<0.05).

CONCLUSIONS

Antioxidants alone or in combination with Lactobacillus johnsonii La1 can be useful in preventing bacterial translocation in cirrhosis.

Methicillin resistant Staphylococcus aureus (MRSA) in the intensive care unit

Methicillin resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen that causes severe morbidity and mortality worldwide. MRSA strains are endemic in many American and European hospitals and account for 29%-35% of all clinical isolates. Recent studies have documented the increased costs associated with MRSA infection, as well as the importance of colonisation pressure. Surveillance strategies have been proposed especially in high risk areas such as the intensive care unit. Pneumonia and bacteraemia account for the majority of MRSA serious clinical infections, but intra-abdominal infections, osteomyelitis, toxic shock syndrome, food poisoning, and deep tissue infections are also important clinical diseases. The traditional antibiotic therapy for MRSA is a glycopeptide, vancomycin. New antibiotics have been recently released that add to the armamentarium for therapy against MRSA and include linezolid, and quinupristin/dalfopristin, but cost, side effects, and resistance may limit their long term usefulness.

Occurrence of extended-spectrum beta-lactamases in members of the family Enterobacteriaceae in Italy: implications for resistance to beta-lactams and other antimicrobial drugs

An Italian nationwide survey was carried out to assess the prevalences and the antimicrobial susceptibilities of members of the family Enterobacteriaceae producing extended-spectrum beta-lactamases (ESBLs). Over a 6-month period, 8,015 isolates were obtained from hospitalized patients and screened for resistance to extended-spectrum cephalosporins and monobactams. On the basis of a synergistic effect between clavulanate and selected beta-lactams (ceftazidime, aztreonam, cefotaxime, cefepime, and ceftriaxone), 509 isolates were found to be ESBL positive (6.3%). Colony blot hybridization with bla(TEM) and bla(SHV) DNA probes allowed one to distinguish four different genotypes: TEM-positive, SHV-positive, TEM- and SHV-positive, and non-TEM, non-SHV ESBL types. MICs for each isolate (E-test) were obtained for widely used beta-lactams, combinations of beta-lactams with beta-lactamase inhibitors, aminoglycosides, and fluoroquinolones. Among ESBL-positive strains, Klebsiella pneumoniae, Proteus mirabilis, and Escherichia coli accounted for 73.6% of isolates. Overall, TEM-type ESBLs were more prevalent than SHV-type enzymes (234 versus 173), whereas the prevalence of strains producing both TEM- and SHV-type ESBLs was similar to that of isolates producing non-TEM, non-SHV enzymes (55 and 38, respectively). In vitro, all but one of the ESBL-producing isolates remained susceptible to imipenem. Susceptibility to other drugs varied: piperacillin-tazobactam, 91%; amoxicillin-clavulanic acid, 85%; cefoxitin, 78%; amikacin, 76%; ampicillin-sulbactam, 61%; ciprofloxacin, 58%; and gentamicin, 56%. Associated resistance to aminoglycosides and ciprofloxacin was observed most frequently among TEM-positive strains. Since therapeutic options for multiresistant Enterobacteriaceae are limited, combinations of beta-lactams and beta-lactamase inhibitors appear to represent an important alternative for treating infections caused by ESBL-producing ENTEROBACTERIACEAE:

Characterization of clinical isolates of Klebsiella pneumoniae from 19 laboratories using the National Committee for Clinical Laboratory Standards extended-spectrum beta-lactamase detection methods

Extended-spectrum beta-lactamases (ESBLs) are enzymes found in gram-negative bacilli that mediate resistance to extended-spectrum cephalosporins and aztreonam. In 1999, the National Committee for Clinical Laboratory Standards (NCCLS) published methods for screening and confirming the presence of ESBLs in Klebsiella pneumoniae, Klebsiella oxytoca, and Escherichia coli. To evaluate the confirmation protocol, we tested 139 isolates of K. pneumoniae that were sent to Project ICARE (Intensive Care Antimicrobial Resistance Epidemiology) from 19 hospitals in 11 U.S. states. Each isolate met the NCCLS screening criteria for potential ESBL producers (ceftazidime [CAZ] or cefotaxime [CTX] MICs were > or =2 microg/ml for all isolates). Initially, 117 (84%) isolates demonstrated a clavulanic acid (CA) effect by disk diffusion (i.e., an increase in CAZ or CTX zone diameters of > or =5 mm in the presence of CA), and 114 (82%) demonstrated a CA effect by broth microdilution (reduction of CAZ or CTX MICs by > or =3 dilutions). For five isolates, a CA effect could not be determined initially by broth microdilution because of off-scale CAZ results. However, a CA effect was observed in two of these isolates by testing cefepime and cefepime plus CA. The cefoxitin MICs for 23 isolates that failed to show a CA effect by broth microdilution were > or =32 microg/ml, suggesting either the presence of an AmpC-type beta-lactamase or porin changes that could mask a CA effect. By isoelectric focusing (IEF), 7 of the 23 isolates contained a beta-lactamase with a pI of > or =8.3 suggestive of an AmpC-type beta-lactamase; 6 of the 7 isolates were shown by PCR to contain both ampC-type and bla(OXA) genes. The IEF profiles of the remaining 16 isolates showed a variety of beta-lactamase bands, all of which had pIs of < or =7.5. All 16 isolates were negative by PCR with multiple primer sets for ampC-type, bla(OXA), and bla(CTX-M) genes. In summary, 83.5% of the K. pneumoniae isolates that were identified initially as presumptive ESBL producers were positive for a CA effect, while 5.0% contained beta-lactamases that likely masked the CA effect. The remaining 11.5% of the isolates studied contained beta-lactamases that did not demonstrate a CA effect. An algorithm based on phenotypic analyses is suggested for evaluation of such isolates.

Multidrug-resistant Pathogens: Mechanisms of Resistance and Epidemiology

Resistance to antimicrobial agents among bacteria and fungi is a persistent problem complicating the management of critically ill patients. To understand the issues involved in resistance in critical care, it is essential to understand the epidemiology and mechanisms of resistance. beta-lactam resistance in pneumococci, and penicillin and chloramphenicol resistance in Neisseria meningitidis, have complicated the management of meningitis. Vancomycin resistance in enterococci and methicillin resistance in Staphylococcus aureus have disseminated among hospitals, nursing homes and, in some cases, community patients. Glycopeptide resistance in S. aureus has recently been described in clinical isolates; the potential for spread of this resistance trait is concerning. Resistance to broad-spectrum cephalosporins is a persistent challenge in the management of infections caused by Pseudomonas areuginosa, and Enterobacter species, as well as other Enterobacteriaceae. Azole resistance in Candida species. has also complicated the treatment of nosocomial infections. Resistance to antimicrobial drugs is a persistent and emerging problem and presents major therapeutic challenges.