Intra-abdominal infections: etiology, epidemiology, microbiological diagnosis and antibiotic resistance

Antimicrobial Zeolitic Imidazolate Frameworks with Dual Mechanisms of Action

The horizontal transfer of drug-resistant genes and the formation of biofilm barriers have threatened the therapeutic efficacy of conventional antibiotic drugs. Development of non-antibiotic agents with high delivery efficiency through bacterial biofilms is urgently required. A pyrithione (PT)-loading zeolitic imidazolate framework (ZIF-8@PT) is synthesized to destroy biofilms and improve the sensitivity of bacteria to PT. ZIF-8@PT can target and destroy the biofilm as well as the cell membrane, promoting the intracellular delivery of PT and possibly its interaction with SmpB, a protein that could regulate the drug resistance of bacteria. ZIF-8@PT effectively suppresses abdominal infections induced by multiresistant Aeromonas veronii C4 in rodent models without systemic toxicity. ZIF-8@PT promises wide applications in treating infections caused by multidrug-resistant bacteria through a dual mechanism of action.

The Role of Ertapenem for the Treatment of Complicated Intra-abdominal Infections With a Positive Culture for Enterococcus faecalis

Controversy remains as to whether Enterococcus faecalis recovered from intra-abdominal infections (IAIs) requires targeted therapy. In a multicenter study comparing patients with IAIs from which E. faecalis was identified in intra-abdominal cultures, no difference in clinical outcomes was observed between patients receiving ertapenem vs those receiving piperacillin/tazobactam.

A multicenter epidemiology study on the risk factors and clinical outcomes of nosocomial intra-abdominal infections in China: results from the Chinese Antimicrobial Resistance Surveillance of Nosocomial Infections (CARES) 2007-2016

Objective

This study aimed to determine the risk factors for intra-abdominal infections (IAIs), assess the clinical outcomes of IAIs, and investigate the spectrum and antimicrobial resistance of major pathogens causing IAIs.

Patients and methods

This prospective observational study enrolled patients from the Chinese Antimicrobial Resistance Surveillance of Nosocomial Infections (CARES) program between 2007 and 2016. Data on the clinicopathological factors and causative pathogens were collected. The results of antimicrobial susceptibility tests were interpreted according to the minimum inhibitory concentration (MIC) interpretive breakpoints recommended by the Clinical and Laboratory Standards Institute in 2017.

Results

A total of 2,756 patients were included. The 30-day all-cause mortality was 9.5% (262/2,756). Multivariable analysis showed that the following independent risk factors were associated with the 30-day mortality: age >60 years, pulmonary disease, tracheal cannula, infection occurring in intensive care unit (ICU), prior admission within 3 months, antibiotic use before infection, recent use of immunosuppressants, and multidrug-resistant organisms. In addition, 2,913 clinical isolates were collected. The Gram-negative and Gram-positive bacteria accounted for 70.8% and 29.2% of all isolates, respectively. The most common pathogens were Escherichia coli (33.4%), Klebsiella pneumoniae (10.8%), and Enterococcus faecium (10.7%). Pseudomonas aeruginosa and Acinetobacter baumannii were the most common non-Enterobacteriaceae Gram-negative pathogens. E. faecium, Enterococcus faecalis, and Staphylococcus aureus were the most common Gram-positive pathogens. E. coli, A. baumannii, and Enterobacter cloacae were more commonly found in ICU patients than in non-ICU patients. Overall, the antibiotics tested in the CARES exhibited diminished susceptibility to pathogens over the study period, especially extended spectrum β-lactamase producing isolates.

Conclusion

Considering the current data set and high-level resistance of intra-abdominal pathogens to various antibiotics, further monitoring of the epidemiology of IAIs and their susceptibility to antibiotics through the CARES is warranted.

Identification of Specific Components of the Eicosanoid Biosynthetic and Signaling Pathway Involved in Pathological Inflammation during Intra-abdominal Infection with Candida albicans and Staphylococcus aureus

Polymicrobial intra-abdominal infections (IAIs) are a significant cause of morbidity and mortality, particularly when fungal pathogens are involved. Our experimental murine model of IAI involving intraperitoneal inoculation of Candida albicans and Staphylococcus aureus results in synergistic lethality (∼80%) due to exacerbated inflammation. Monomicrobial infection results in no mortality, despite a microbial burden and dissemination similar to those in a coinfection. In the coinfection model, the immunomodulatory eicosanoid prostaglandin E₂ (PGE₂) was determined to be necessary and sufficient to induce mortality, implicating PGE₂ as the central mediator of the amplified inflammatory response. The aim of this study was to identify key components of the PGE₂ biosynthetic and signaling pathway involved in the inflammatory response and explore whether these can be targeted to prevent or reduce mortality. Using selective pharmacological inhibitors of cyclooxygenases (COX) or PGE₂ receptor antagonists in the C. albicans-S. aureus IAI mouse model, we found that inhibition of COX and/or blocking of PGE₂ receptor 1 (EP1) or PGE₂ receptor 3 (EP3) signaling reduced proinflammatory cytokine production, promoted interleukin-10 production, reduced cellular damage in the peritoneal cavity, and, most importantly, significantly improved survival. The greatest effect on survival was obtained by the simultaneous inhibition of COX-1 activity and EP1 and EP3 receptor signaling. Importantly, early inhibition of PGE₂ pathways dramatically improved the survival of fluconazole-treated mice compared with that achieved with fluconazole treatment alone. These findings indicate that COX-1 and the EP1 and EP3 receptors mediate the downstream pathological effects of PGE₂ during polymicrobial IAI and may serve as effective therapeutic targets.

Biocide Selective TolC-Independent Efflux Pumps in Enterobacteriaceae

Bacterial resistance to biocides used as antiseptics, dyes, and disinfectants is a growing concern in food preparation, agricultural, consumer manufacturing, and health care industries, particularly among Gram-negative Enterobacteriaceae, some of the most common community and healthcare-acquired bacterial pathogens. Biocide resistance is frequently associated with antimicrobial cross-resistance leading to reduced activity and efficacy of both antimicrobials and antiseptics. Multidrug resistant efflux pumps represent an important biocide resistance mechanism in Enterobacteriaceae. An assortment of structurally diverse efflux pumps frequently co-exist in these species and confer both unique and overlapping biocide and antimicrobial selectivity. TolC-dependent multicomponent systems that span both the plasma and outer membranes have been shown to confer clinically significant resistance to most antimicrobials including many biocides, however, a growing number of single component TolC-independent multidrug resistant efflux pumps are specifically associated with biocide resistance: small multidrug resistance (SMR), major facilitator superfamily (MFS), multidrug and toxin extruder (MATE), cation diffusion facilitator (CDF), and proteobacterial antimicrobial compound efflux (PACE) families. These efflux systems are a growing concern as they are rapidly spread between members of Enterobacteriaceae on conjugative plasmids and mobile genetic elements, emphasizing their importance to antimicrobial resistance. In this review, we will summarize the known biocide substrates of these efflux pumps, compare their structural relatedness, Enterobacteriaceae distribution, and significance. Knowledge gaps will be highlighted in an effort to unravel the role that these apparent "lone wolves" of the efflux-mediated resistome may offer.

Epidemiology and susceptibility of pathogens from SMART 2011-12 Turkey: evaluation of hospital-acquired versus community-acquired urinary tract infections and ICU- versus non-ICU-associated intra-abdominal infections

Objectives

To describe the epidemiology and susceptibility of pathogens (including ESBL producers) from hospital-acquired (HA) versus community-acquired (CA) urinary tract infections (UTIs) and ICU- versus non-ICU-associated intra-abdominal infections (IAIs) in Turkey as a part of the SMART study.

Methods

: For this report, Gram-negative pathogens (363 from UTIs and 458 from IAIs) were collected in 2011 and 2012 at six hospitals in Turkey. HA versus CA UTIs and ICU- versus non-ICU-associated IAIs were compared for the species isolated, percentage of ESBL-positive isolates by species and susceptibility for overall and individual Gram-negative species.

Results

: Escherichia coli was the most common pathogen identified in HA (40.2%) and CA (73.9%) UTIs and ICU-associated (25.8%) and non-ICU-associated (43.3%) IAIs. The rate of ESBL-positive E. coli was significantly higher in HA than in CA UTIs (50.5% versus 38.2%, P  <   0.001) and in non-ICU-associated than in ICU-associated IAIs (52.5% versus 29.2%, P  = 0.029). Of the drugs studied, only amikacin was active against ≥90% of pathogens in UTIs, while ertapenem, imipenem and amikacin were active against ≥90% of E. coli ; and imipenem, amikacin and cefoxitin were active against ≥90% of Klebsiella pneumoniae in IAIs.

Conclusions

Our findings demonstrated that E. coli continues to be the principal pathogen of UTIs and IAIs in Turkey. Along with a high rate of ESBL-positive isolates, high antimicrobial resistance among Gram-negative bacilli from either UTIs or IAIs was noted particularly in the case of HA UTIs and ICU-associated IAIs, with a higher likelihood of carbapenem- or amikacin-based therapy to provide the broadest activity against bacterial pathogens.

Multidrug efflux pumps and their role in antibiotic and antiseptic resistance: a pharmacodynamic perspective

INTRODUCTION

Worrying levels of bacterial resistance have been reported worldwide involving the failure of many available antibiotic treatments. Multidrug resistance (MDR) in Gram-negative bacteria is often ascribed to the presence of multiple and different resistance mechanisms in the same strain. RND efflux pumps play a major role and are an attractive target to discover new antibacterial drugs. Areas covered: This review discusses the prevalence of efflux pumps, their overexpression in clinical scenarios, their polyselectivity, their effect on the intracellular concentrations of various antibiotics associated with the alteration of the membrane permeability and their involvement in pathogenicity are discussed. Expert opinion: Efflux pumps are new targets for the development of adjuvant in antibiotic treatments by of efflux pump inhibition. They may allow us to rejuvenate old antibiotics acting on their concentration inside the bacteria and thus potentiating their activity while blocking the release of virulence factors. It is a pharmacodynamic challenge to finalize new combined therapy.

Intra-abdominal Infections: The Role of Anaerobes, Enterococci, Fungi, and Multidrug-Resistant Organisms

BACKGROUND

Intra-abdominal infections (IAI) constitute a common reason for hospitalization. However, there is lack of standardization in empiric management of (1) anaerobes, (2) enterococci, (3) fungi, and (4) multidrug-resistant organisms (MDRO). The recommendation is to institute empiric coverage for some of these organisms in "high-risk community-acquired" or in "healthcare-associated" infections (HCAI), but exact definitions are not provided.

METHODS

Epidemiological study of IAI was conducted at Assaf Harofeh Medical Center (May-November 2013). Logistic and Cox regressions were used to analyze predictors and outcomes of IAI, respectively. The performances of established HCAI definitions to predict MDRO-IAI upon admission were calculated by receiver operating characteristic (ROC) curve analyses.

RESULTS

After reviewing 8219 discharge notes, 253 consecutive patients were enrolled (43 [17%] children). There were 116 patients with appendicitis, 93 biliary infections, and 17 with diverticulitis. Cultures were obtained from 88 patients (35%), and 44 of them (50%) yielded a microbiologically confirmed IAI: 9% fungal, 11% enterococcal, 25% anaerobic, and 34% MDRO. Eighty percent of MDRO-IAIs were present upon admission, but the area under the ROC curve of predicting MDRO-IAI upon admission by the commonly used HCAI definitions were low (0.73 and 0.69). Independent predictors for MDRO-IAI were advanced age and active malignancy.

CONCLUSIONS

Multidrug-resistant organism-IAIs are common, and empiric broad-spectrum coverage is important among elderly patients with active malignancy, even if the infection onset was outside the hospital setting, regardless of current HCAI definitions. Outcomes analyses suggest that empiric regimens should routinely contain antianaerobes (except for biliary IAI); however, empiric antienterococcal or antifungals regimens are seldom needed.

In vitro and in vivo efficacy, toxicity, bio-distribution and resistance selection of a novel antibacterial drug candidate

A synthetic antimicrobial peptide was identified as a possible candidate for the development of a new antibacterial drug. The peptide, SET-M33L, showed a MIC₉₀ below 1.5 μM and 3 μM for Pseudomonas aeruginosa and Klebsiella pneumoniae, respectively. In in vivo models of P. aeruginosa infections, the peptide and its pegylated form (SET-M33L-PEG) enabled a survival percentage of 60–80% in sepsis and lung infections when injected twice i.v. at 5 mg/Kg, and completely healed skin infections when administered topically. Plasma clearance showed different kinetics for SET-M33L and SET-M33L-PEG, the latter having greater persistence two hours after injection. Bio-distribution in organs did not show significant differences in uptake of the two peptides. Unlike colistin, SET-M33L did not select resistant mutants in bacterial cultures and also proved non genotoxic and to have much lower in vivo toxicity than antimicrobial peptides already used in clinical practice. The characterizations reported here are part of a preclinical development plan that should bring the molecule to clinical trial in the next few years.

Effects of acute intra-abdominal hypertension on multiple intestinal barrier functions in rats

Intra-abdominal hypertension (IAH) is a common and serious complication in critically ill patients for which there is no well-defined treatment strategy. Here, we explored the effect of IAH on multiple intestinal barriers and discussed whether the alteration in microflora provides clues to guide the rational therapeutic treatment of intestinal barriers during IAH. Using a rat model, we analysed the expression of tight junction proteins (TJs), mucins, chemotactic factors, and Toll-like receptor 4 (TLR4) by immunohistochemistry. We also analysed the microflora populations using 16S rRNA sequencing. We found that, in addition to enhanced permeability, acute IAH (20 mmHg for 90 min) resulted in significant disturbances to mucosal barriers. Dysbiosis of the intestinal microbiota was also induced, as represented by decreased Firmicutes (relative abundance), increased Proteobacteria and migration of Bacteroidetes from the colon to the jejunum. At the genus level, Lactobacillus species and Peptostreptococcaceae incertae sedis were decreased, whereas levels of lactococci remained unchanged. Our findings outline the characteristics of IAH-induced barrier changes, indicating that intestinal barriers might be treated to alleviate IAH, and the microflora may be an especially relevant target.

Do Polymicrobial Intra-Abdominal Infections Have Worse Outcomes than Monomicrobial Intra-Abdominal Infections?

BACKGROUND

Numerous studies have demonstrated microorganism interaction through signaling molecules, some of which are recognized by other bacterial species. This interspecies synergy can prove detrimental to the human host in polymicrobial infections. We hypothesized that polymicrobial intra-abdominal infections (IAI) have worse outcomes than monomicrobial infections.

METHODS

Data from the Study to Optimize Peritoneal Infection Therapy (STOP-IT), a prospective, multicenter, randomized controlled trial, were reviewed for all occurrences of IAI having culture results available. Patients in STOP-IT had been randomized to receive four days of antibiotics vs. antibiotics until two days after clinical symptom resolution. Patients with polymicrobial and monomicrobial infections were compared by univariable analysis using the Wilcoxon rank sum, χ(2), and Fisher exact tests.

RESULTS

Culture results were available for 336 of 518 patients (65%). The durations of antibiotic therapy in polymicrobial (n = 225) and monomicrobial IAI (n = 111) were equal (p = 0.78). Univariable analysis demonstrated similar demographics in the two populations. The 37 patients (11%) with inflammatory bowel disease were more likely to have polymicrobial IAI (p = 0.05). Polymicrobial infections were not associated with a higher risk of surgical site infection, recurrent IAI, or death.

CONCLUSION

Contrary to our hypothesis, polymicrobial IAI do not have worse outcomes than monomicrobial infections. These results suggest polymicrobial IAI can be treated the same as monomicrobial IAI.

Development of resistance of mutans streptococci and Porphyromonas gingivalis to chlorhexidine digluconate and amine fluoride/stannous fluoride-containing mouthrinses, in vitro

OBJECTIVE

The aim if this study was to determine the minimal inhibitory concentrations of chlorhexidine digluconate and an amine fluoride/stannous fluoride-containing mouthrinse against Porphyromonas gingivalis and mutans streptococci during an experimental long-term subinhibitory exposition.

MATERIAL AND METHODS

Five P. gingivalis strains and four mutans streptococci were subcultivated for 20-30 passages in subinhibitory concentrations of chlorhexidine digluconate or an amine fluoride/stannous fluoride-containing mouthrinse.

RESULTS

Pre-passaging minimal inhibitory concentrations for chlorhexidine ranged from 0.5 to 2 mg/l for mutans streptococci and from 2 to 4 mg/l for the P. gingivalis isolates. For the amine fluoride/stannous fluoride-containing mouthrinse minimal inhibitory values from 0.125 to 0.25% for the mutans streptococci and from 0.063 to 0.125% for the P. gingivalis isolates were determined. Two- to fourfold increased minimal inhibitory concentrations against chlorhexidine were detected for two of the five P. gingivalis isolates, whereas no increase in minimal inhibitory concentrations was found for the mutans streptococci after repeated passaging through subinhibitory concentrations. Repeated exposure to subinhibitory concentrations of the amine fluoride/stannous fluoride-containing mouthrinse did not alter the minimally inhibitory concentrations of the bacterial isolates tested.

CONCLUSION

Chlorhexidine and the amine fluoride/stannous fluoride-containing mouthrinse are effective inhibitory agents against the oral bacterial isolates tested. No general development of resistance against chlorhexidine or the amine fluoride/stannous fluoride-containing mouthrinse was detected. However, some strains showed potential to develop resistance against chlorhexidine after prolonged exposure.

CLINICAL RELEVANCE

The use of chlorhexidine should be limited to short periods of time. The amine fluoride/stannous fluoride-containing mouthrinse appears to have the potential to be used on a long-term basis.

Abdominal infections in the intensive care unit: characteristics, treatment and determinants of outcome

BACKGROUND

Abdominal infections are frequent causes of sepsis and septic shock in the intensive care unit (ICU) and are associated with adverse outcomes. We analyzed the characteristics, treatments and outcome of ICU patients with abdominal infections using data extracted from a one-day point prevalence study, the Extended Prevalence of Infection in the ICU (EPIC) II.

METHODS

EPIC II included 13,796 adult patients from 1,265 ICUs in 75 countries. Infection was defined using the International Sepsis Forum criteria. Microbiological analyses were performed locally. Participating ICUs provided patient follow-up until hospital discharge or for 60 days.

RESULTS

Of the 7,087 infected patients, 1,392 (19.6%) had an abdominal infection on the study day (60% male, mean age 62 ± 16 years, SAPS II score 39 ± 16, SOFA score 7.6 ± 4.6). Microbiological cultures were positive in 931 (67%) patients, most commonly Gram-negative bacteria (48.0%). Antibiotics were administered to 1366 (98.1%) patients. Patients who had been in the ICU for ≤ 2 days prior to the study day had more Escherichia coli, methicillin-sensitive Staphylococcus aureus and anaerobic isolates, and fewer enterococci than patients who had been in the ICU longer. ICU and hospital mortality rates were 29.4% and 36.3%, respectively. ICU mortality was higher in patients with abdominal infections than in those with other infections (29.4% vs. 24.4%, p < 0.001). In multivariable analysis, hematological malignancy, mechanical ventilation, cirrhosis, need for renal replacement therapy and SAPS II score were independently associated with increased mortality.

CONCLUSIONS

The characteristics, microbiology and antibiotic treatment of abdominal infections in critically ill patients are diverse. Mortality in patients with isolated abdominal infections was higher than in those who had other infections.

Bacterial species-specific hospital mortality rate for intra-abdominal infections

BACKGROUND

Intra-abdominal infections (IAIs) are a major cause of morbidity and death. We hypothesized that the involvement of specific organisms would predict death independently.

PATIENTS AND METHODS

All patients with IAIs treated at an academic tertiary-care facility over eight years (June 1999-June 2007) were included. The data collected were demographics, co-morbidities, source of infection, intra-abdominal culture results, type of infection (community-acquired vs. nosocomial), type of intervention (operative vs. percutaneous drainage), and outcome. The Charlson Comorbidity Index and multiple organ dysfunction score (MODS) were used in the analysis.

RESULTS

A total of 389 patients were admitted for 452 infection episodes (IEs) during the study period. None of the 129 patients with appendiceal-related infections died, and these patients were excluded from further analysis. Thus, 323 non-appendiceal IEs were evaluated. The overall mortality rate was 8.7%. The mean age of the patients was 54 y, and 50% of them were male. Intra-abdominal cultures were obtained from 303 IEs (93.8%). The most common cause of IAI was post-operative infection (44%). There were 49 distinct species isolated. The most common were Enterococcus (105), Escherichia coli (75), Streptococcus (62), Staphylococcus (51), and Bacteroides (46). Bivariable analysis revealed multiple risk factors associated with death. Logistic regression demonstrated that independent risk factors for death were age ≥65 years (odds ratio [OR] 3.92), cardiac event (OR=8.17), catheter-related blood stream infection (OR=6.16), and growth of Clostridium (OR=13.03). The growth of Streptococcus was predictive of survival. The C statistic was 0.89.

CONCLUSIONS

In addition to age and intrinsic patient factors, the presence of specific bacterial organisms independently predicts death in patients with non-appendiceal IAI.

A 10 year surveillance for antimicrobial susceptibility of Escherichia coli and Klebsiella pneumoniae in community- and hospital-associated intra-abdominal infections in China

The objective of this study was to investigate the susceptibility of hospital-associated (HA) and community-associated (CA) Escherichia coli and Klebsiella pneumoniae isolated from patients with intra-abdominal infections (IAIs) in China. From 2002 to 2011, the minimum inhibitory concentrations (MICs) of 12 antibiotics against 3074 E. coli and 1025 K. pneumoniae from 23 centres located in 16 cities were determined by the broth microdilution method. During the 10 year study period, ertapenem, imipenem, amikacin and piperacillin-tazobactam retained high and stable activity against E. coli and K. pneumoniae isolates regardless of whether their source was HA or CA and regardless of their extended-spectrum beta-lactamase (ESBL) production. However, the susceptibility of E. coli to cephalosporins and ampicillin-sulbactam decreased dramatically during the 10 years, especially for the CA isolates. Fluoroquinolones showed low activity against E. coli. During the whole study period, the ESBL rates for E. coli isolates from IAIs increased from 36.1 % in 2002–2003 to 68.1 % in 2010–2011 (P<0.001). Correspondingly, the ESBL rates in HA isolates increased from 52.2 % in 2002–2003 to 70.0 % in 2010–2011 (P = 0.001), and in CA isolates from 19.1 % in 2002–2003 to 61.6 % in 2010–2011 (P<0.001). The ESBL-positive rate in K. pneumoniae remained between 30.1 and 39.3 % of the total isolates with no significant change during the 10 years. In conclusion, carbapenems retained the highest susceptibility rates against HA and CA E. coli and K. pneumoniae. High prevalence of ESBL in HA E. coli and fast-growing resistance in CA E. coli severely limit the empirical use of the third- and fourth-generation cephalosporins in the therapy of IAIs.

Toll-like receptor 9 promotes cardiac inflammation and heart failure during polymicrobial sepsis

Background. Aim was to elucidate the role of toll-like receptor 9 (TLR9) in cardiac inflammation and septic heart failure in a murine model of polymicrobial sepsis. Methods. Sepsis was induced via colon ascendens stent peritonitis (CASP) in C57BL/6 wild-type (WT) and TLR9-deficient (TLR9-D) mice. Bacterial load in the peritoneal cavity and cardiac expression of inflammatory mediators were determined at 6, 12, 18, 24, and 36 h. Eighteen hours after CASP cardiac function was monitored in vivo. Sarcomere length of isolated cardiomyocytes was measured at 0.5 to 10 Hz after incubation with heat-inactivated bacteria. Results. CASP led to continuous release of bacteria into the peritoneal cavity, an increase of cytokines, and differential regulation of receptors of innate immunity in the heart. Eighteen hours after CASP WT mice developed septic heart failure characterised by reduction of end-systolic pressure, stroke volume, cardiac output, and parameters of contractility. This coincided with reduced cardiomyocyte sarcomere shortening. TLR9 deficiency resulted in significant reduction of cardiac inflammation and a sustained heart function. This was consistent with reduced mortality in TLR9-D compared to WT mice. Conclusions. In polymicrobial sepsis TLR9 signalling is pivotal to cardiac inflammation and septic heart failure.

In vitro activity of tigecycline and comparators against organisms associated with intra-abdominal infections collected as part of TEST (2004-2009)

As part of the Tigecycline Evaluation and Surveillance Trial (TEST), bacterial isolates were collected consecutively from centers globally between 2004 and 2009. MICs were determined locally using Clinical and Laboratory Standards Institute broth microdilution methodology. A total of 3114 anaerobic and 99,256 aerobic isolates were included in this study. The most active agents against Gram-negative anaerobes were metronidazole and meropenem (resistance ranges 0.0-0.5% and 0.0-0.9%, respectively); piperacillin-tazobactam was also active (resistance range 0.5-9.4%). Among Gram-positive anaerobes, resistance rates were lowest for meropenem, piperacillin-tazobactam, and metronidazole (ranges 0.0-0.5%, 0.0-1.8%, and 0.0-3.2% respectively). Tigecycline MIC(90) values for anaerobes ranged from 0.12 to 2 μg/mL. The most active antimicrobial agent against Gram-negative aerobes (excluding Pseudomonas aeruginosa) was tigecycline, with resistance ranging from <0.01% to 1.4%. Resistance was also low for imipenem (0.3-9.4%) and meropenem (0.7-15.1%). Extended-spectrum beta-lactamases were produced by 12.2% and 19.7% of E. coli and K. pneumoniae isolates, respectively.

Broad-specificity efflux pumps and their role in multidrug resistance of Gram-negative bacteria

Antibiotic resistance mechanisms reported in Gram-negative bacteria are causing a worldwide health problem. The continuous dissemination of 'multidrug-resistant' (MDR) bacteria drastically reduces the efficacy of our antibiotic 'arsenal' and consequently increases the frequency of therapeutic failure. In MDR bacteria, the overexpression of efflux pumps that expel structurally unrelated drugs contributes to the reduced susceptibility by decreasing the intracellular concentration of antibiotics. During the last decade, several clinical data have indicated an increasing involvement of efflux pumps in the emergence and dissemination of resistant Gram-negative bacteria. It is necessary to clearly define the molecular, functional and genetic bases of the efflux pump in order to understand the translocation of antibiotic molecules through the efflux transporter. The recent investigation on the efflux pump AcrB at its structural and physiological levels, including the identification of drug affinity sites and kinetic parameters for various antibiotics, may pave the way towards the rational development of an improved new generation of antibacterial agents as well as efflux inhibitors in order to efficiently combat efflux-based resistance mechanisms.