Epidemiological MIC cut-off values for tigecycline calculated from Etest MIC values using normalized resistance interpretation

Comparison of antimicrobial susceptibility of Glaesserella parasuis from different pig production systems in Taiwan between 2015 and 2020

BACKGROUND

Glässer's disease, caused by Glaesserella parasuis (G. parasuis), is a widespread bacterial infection in swine that leads to significant economic losses. G. parasuis, a member of the normal microbiota within the Pasteurellaceae family, exhibits horizontal resistance gene exchange and intracellular invasion capabilities, increasing the risk of developing resistant isolates. Accurate antimicrobial therapy is essential for controlling Glässer's disease. The production systems for exotic crossbred pigs and Taiwan black pigs differ considerably. To inform Glässer disease control and monitor antimicrobial resistance, we assessed the antimicrobial susceptibilities of G. parasuis isolates, analyzed them using normalized resistance interpretation (NRI), and compared findings between the two production systems.

RESULTS

A total of 154 G. parasuis isolates from 106 exotic crossbred pig herds and 48 Taiwan black pig herds were tested against 16 antimicrobial agents between 2015 and 2020. Due to the absence of specific breakpoints for G. parasuis, NRI was utilized to define non-wild-type (non-WT) populations based on minimum inhibitory concentration (MIC) distributions. Non-WT subpopulations of isolates for amoxicillin, ampicillin, ceftiofur, gentamicin, kanamycin, and tiamulin were observed. The highest MIC90 (the concentration at which 90% of isolates were inhibited) was > 256 µg/mL for several antimicrobials, including gentamicin, kanamycin, lincomycin, lincospectin, spectinomycin, and tylosin. In contrast, the lowest MIC90 was observed for ceftiofur (0.5 µg/mL). The MIC values for cephalothin were significantly higher in exotic crossbred pigs than in Taiwan black pigs (p = 0.0016). Conversely, MIC values for florfenicol were significantly higher in Taiwan black pigs than in exotic crossbred pigs (p = 0.003).

CONCLUSIONS

This study provides the susceptibility profile of G. parasuis isolates for both exotic crossbred pigs and Taiwan black pigs in Taiwan and highlights potential antimicrobial resistance for aminocyclitol, aminoglycosides, beta-lactams, lincosamides, macrolides, and pleuromulin. Ceftiofur, cephalothin, doxycycline, and florfenicol could be most suitable for treating early-stage Glässer's disease. Nonetheless, increased attention should be paid to the responsible use of antimicrobials in light of the growing threat of antimicrobial resistance.

Antimicrobial susceptibility rates in gram-positive catalase-negative cocci from sheep and goat genital microbiota

Gram-positive catalase-negative cocci (GPCNCs) are significant components of the genital microbiota in sheep and goats. However, characterizing them can be difficult due to overlapping culture features and the limited information on their susceptibility to antibiotics. In this study, 97 foreskin and 13 vaginal swabs were investigated using a culturomic approach. Of 110 animals, 76 (69.09 %) hosted GPCNCs, including strains from Streptococcaceae (37, 33.64 %), Aerococcaceae (30, 27.27 %), Enterococcaceae (6, 5.45 %) and other minor species. With increasing antimicrobial resistance rates in livestock, surveillance programs are globally required, so we conducted a pilot study on GPCNCs isolated from the genital mucosa surfaces of sheep and goats using the minimal inhibitory concentration assay (MIC). Due to gaps in interpretative standard breakpoints, normalized resistance interpretation was used for setting epidemiological susceptibility cut-off values (COWTs). Of 57 suitable strains, the majority (80.71 %) showed high COWTs with decrease susceptibility to at least one antimicrobial class, with 22.81 % displaying multiresistant profiles. Of interest, combined resistances to beta-lactams, macrolides, lincosamides, and tetracyclines were detected in strains of Streptococcus plurianimalium. Further combinations, including resistance to beta-lactams, pleuromutilins, aminoglycosides, and lincosamides, were also recorded in both Streptococcus uberis and Enterococcus spp. strains. Being beta-lactams, macrolides, and tetracyclines the most used antibiotics in livestock worldwide, our results highlight the need for their prudent use. Collectively, our findings highlight that small ruminant genital microbiota can serve as reservoirs for opportunistic severe pathogens, often zoonotic, carrying multidrug resistances, thus standing for high risks for both animals and humans.

Epidemiological Cut-Off Values and Multidrug Resistance of Escherichia coli Isolated from Domesticated Poultry and Pigs Reared in Mwanza, Tanzania: A Cross-Section Study

Increasing antimicrobial resistance (AMR) colonizing domesticated animals is a global concern threatening food safety. This study aimed at determining the prevalence of multidrug resistance (MDR) and epidemiological cut-off values (ECVs) of E. coli isolated from poultry and pigs in Mwanza, Tanzania. This cross-sectional study was conducted between June and August 2021, involving 297 pigs, 191 broilers, and 203 layers. Rectal and cloacal swabs were collected and processed following standard guidelines. ECVs were determined using normalized resistance interpretation (NRI), a computer software, and descriptive analysis was performed using STATA version 13.0. The overall prevalence of MDR E.coli was 63.2%, whereas poultry (87.5% layers and 86.3% broilers) were more colonized than pigs (31.8%) (p < 0.001). Based on ECVs of antibiotics tested, E. coli from broilers, layers, and pigs exhibited different resistance patterns hence different populations. Exotic breed (p < 0.001) and recent antimicrobial use (p < 0.001) significantly predicted colonization with MDR E. coli. Veterinary officers should implement regulations that prohibit the inappropriate use of antimicrobial agents in livestock keeping.

Antimicrobial Activity of Silver, Copper, and Zinc Ions/Poly(Acrylate/Itaconic Acid) Hydrogel Matrices

The design and use of new potent and specific antimicrobial systems are of crucial importance in the medical field. This will help relieve, fight, and eradicate infections and thus improve human health. The use of metals in various forms as antimicrobial therapeutics has been known since ancient times. In this sense, polymeric hydrogel matrices as multifunctional materials and in combination with various metal forms can be a great alternative to conventional treatments for infections. Hydrogels possess high hydrophilicity, specific three-dimensional networks, fine biocompatibility, and cell adhesion and are therefore suitable as materials for the loading of active antimicrobial agents and acting in antimicrobial areas. The biocompatible nature of hydrogels’ matrices makes them a convenient starting platform to develop biocompatible, selective, active controlled-release antimicrobial materials. Hydrogels based on acrylate and itaconic acid were synthesized and loaded with silver (Ag+), copper (Cu2+), and zinc (Zn2+) ions as a controlled release and antimicrobial system to test release properties and antimicrobial activity in contact with microbes. The metal ions/hydrogel systems exhibited favorable biocompatibility, release profiles, and antimicrobial activity against methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus aureus, Escherichia coli, and Candida albicans microbes, and have shown that they have the capacity to “fight” with the life-threatening infections. Antimicrobial activity depends on types of metal ions, the composition of polymeric matrices, as well as the types of microbes. Designed metal ions/poly(acrylate/itaconic acid) antimicrobial systems have shown to have good potential as antimicrobial therapeutics and suitable biomaterials for medical applications.

Prudent Use of Tylosin for Treatment of Mycoplasma gallisepticum Based on Its Clinical Breakpoint and Lung Microbiota Shift

The aim of this study was to explore the prudent use of tylosin for the treatment of chronic respiratory infectious diseases in chickens caused by Mycoplasma gallisepticum (MG) based on its clinical breakpoint (CBP) and its effect on lung microbiota. The CBP was established based on the wild-type/epidemiological cutoff value (CO_WT/ECV), pharmacokinetics-pharmacodynamics (PK-PD) cutoff value (CO_PD), and clinical cutoff value (CO_CL) of tylosin against MG. The minimum inhibitory concentration (MIC) of tylosin against 111 MG isolates was analyzed and the CO_WT was 2 μg/ml. M17 with MIC of 2 μg/ml was selected as a representative strain for the PK-PD study. The CO_PD of tylosin against MG was 1 μg/ml. The dosage regimen formulated by the PK-PD study was 3 days administration of tylosin at a dose of 45.88 mg/kg b.w. with a 24-h interval. Five different MIC MGs were selected for clinical trial, and the CO_CL of tylosin against MG was 0.5 μg/ml. According to the CLSI decision tree, the CBP of tylosin against MG was set up as 2 μg/ml. The effect of tylosin on lung microbiota of MG-infected chickens was analyzed by 16S rRNA gene sequencing. Significant change of the lung microbiota was observed in the infection group and treatment group based on the principal coordinate analysis and the Venn diagrams of the core and unique OTU. The phyla Firmicutes and Proteobacteria showed difference after MG infection and treatment. This study established the CBP of tylosin against MG. It also provided scientific data for the prudent use of tylosin based on the evaluation of MG infection and tylosin treatment on the lung microbiota.

Exploration of Clinical Breakpoint of Danofloxacin for Glaesserella parasuis in Plasma and in PELF

Background: In order to establish the clinical breakpoint (CBP) of danofloxacin against G. parasuis, three cutoff values, including epidemiological cutoff value (ECV), pharmacokinetic-pharmacodynamic (PK-PD) cutoff value (CO_PD) and clinical cutoff value (CO_CL), were obtained in the present study. Methods: The ECV was calculated using ECOFFinder base on the MIC distribution of danfloxacin against 347 G. parasuis collected from disease pigs. The CO_PD was established based on in vivo and ex vivo PK-PD modeling of danofloxacin both in plasma and pulmonary epithelial lining fluid (PELF) using Hill formula and Monte Carlo analysis. The CO_CL was established based on the relationship between the possibility of cure (POC) and MIC in the clinical trials using the "WindoW" approach, nonlinear regression and CART analysis. Results: The MIC₅₀ and MIC₉₀ of danofloxacin against 347 G. parasuis were 2 μg/mL and 8 μg/mL, respectively. The ECV value was set to 8 μg/mL using ECOFFinder. Concentration-time curves of danofloxacin were fitted with a two-compartment PK model. The PK parameters of the maximum concentration (C_max) and area under concentration-time curves (AUC) in PELF were 3.67 ± 0.25 μg/mL and 24.28 ± 2.70 h·μg/mL, higher than those in plasma (0.67 ± 0.01 μg/mL and 4.47 ± 0.51 h·μg/mL). The peak time (T_max) in plasma was 0.23 ± 0.07 h, shorter than that in PELF (1.61 ± 0.15 h). The CO_PD in plasma and PELF were 0.125 μg/mL and 0.5 μg/mL, respectively. The CO_CL calculated by WindoW approach, nonlinear regression and CART analysis were 0.125-4 μg/mL, 0.428 μg/mL and 0.56 μg/mL, respectively. The 0.5 μg/mL was selected as eligible CO_CL. The ECV is much higher than the CO_PD and CO_CL, and the clinical breakpoint based on data in plasma was largely different from that of PELF. Conclusions: Our study firstly established three cutoff values of danofloxacin against G. parasuis. It suggested that non-wild-type danofloxacin-resistant G. parasuis may lead to ineffective treatment by danofloxacin.

First Report on a Randomized Investigation of Antimicrobial Resistance in Fecal Indicator Bacteria from Livestock, Poultry, and Humans in Tanzania

This study provides an estimate of antimicrobial resistance in intestinal indicator bacteria from humans (n = 97) and food animals (n = 388) in Tanzania. More than 70% of all fecal samples contained tetracycline (TE), sulfamethoxazole (STX), and ampicillin (AMP)-resistant coliforms, while cefotaxime (CTX)-resistant coliforms were observed in 40% of all samples. The average Log₁₀ colony forming units/g of CTX-resistant coliforms in samples from humans were 2.20. Of 390 Escherichia coli tested, 66.4% were resistant to TE, 54.9% to STX, 54.9% to streptomycin, and 36.4% to CTX. Isolates were commonly (65.1%) multiresistant. All CTX-resistant isolates contained bla_CTX-M gene type. AMP- and vancomycin-resistant enterococci were rare, and the average concentrations in positive samples were low (log₁₀ 0.9 and 0.4, respectively). A low-to-moderate resistance (2.1-15%) was detected in 240 enterococci isolates to the drugs tested, except for rifampicin resistance (75.2% of isolates). The average number of sulII gene copies varied between Log₁₀ 5.37 and 5.68 with no significant difference between sample source, while cattle had significantly higher number of tetW genes than humans. These findings, based on randomly obtained samples, will be instrumental in designing antimicrobial resistance (AMR) intervention strategies for Tanzania.

Molecular prevalence and antibiotics resistance pattern of class A bla CTX-M-1 and bla TEM-1 beta lactamases in uropathogenic Escherichia coli isolates from Pakistan

BACKGROUND/AIM

Extended spectrum beta lactamase (ESBL) production among E. coli is one of the principal mechanisms that augment resistance to antibiotics. In the current study the molecular detection of class A beta lactamases among uropathogenic Escherichia coli was evaluated.

MATERIALS AND METHODS

A total of 355 urine samples were collected from a tertiary care hospital in Peshawar. The ESBL production among E. coli isolates was detected by using the disc synergy diffusion method. Moreover, the molecular detection of bla TEM-1 and bla CTX-M-1 ESBLs, the antibiotic resistance pattern, and the minimum inhibitory concentrations (MICs) were also documented.

RESULTS

Among the 355 urine samples, 157 isolates were E. coli, and 23.56% of the isolates were ESBL E. coli. Among phenotypic ESBL producers, bla CTX-M-1 and bla TEM-1 were found in 59.45% and 40.54% of the isolates, respectively. A high resistance rate was observed against aztreonam (97.29%), while the lowest resistance was observed against imipenem (2.7%). The MICs of ESBLs E. coli for ceftriaxone, ciprofloxacin, and gentamicin was >512 µg/mL, 4 µg/mL to 128 µg/mL, and 1 µg/mL to 14 µg/mL respectively.

CONCLUSION

The present study showed that bla CTX-M-1 ESBL production is more prevalent in our clinical E. coli isolates. More often the ESBLs were resistant to commonly used antibiotics.

Pediatric fecal microbiota harbor diverse and novel antibiotic resistance genes

Emerging antibiotic resistance threatens human health. Gut microbes are an epidemiologically important reservoir of resistance genes (resistome), yet prior studies indicate that the true diversity of gut-associated resistomes has been underestimated. To deeply characterize the pediatric gut-associated resistome, we created metagenomic recombinant libraries in an Escherichia coli host using fecal DNA from 22 healthy infants and children (most without recent antibiotic exposure), and performed functional selections for resistance to 18 antibiotics from eight drug classes. Resistance-conferring DNA fragments were sequenced (Illumina HiSeq 2000), and reads assembled and annotated with the PARFuMS computational pipeline. Resistance to 14 of the 18 antibiotics was found in stools of infants and children. Recovered genes included chloramphenicol acetyltransferases, drug-resistant dihydrofolate reductases, rRNA methyltransferases, transcriptional regulators, multidrug efflux pumps, and every major class of beta-lactamase, aminoglycoside-modifying enzyme, and tetracycline resistance protein. Many resistance-conferring sequences were mobilizable; some had low identity to any known organism, emphasizing cryptic organisms as potentially important resistance reservoirs. We functionally confirmed three novel resistance genes, including a 16S rRNA methylase conferring aminoglycoside resistance, and two tetracycline-resistance proteins nearly identical to a bifidobacterial MFS transporter (B. longum s. longum JDM301). We provide the first report to our knowledge of resistance to folate-synthesis inhibitors conferred by a predicted Nudix hydrolase (part of the folate synthesis pathway). This functional metagenomic survey of gut-associated resistomes, the largest of its kind to date, demonstrates that fecal resistomes of healthy children are far more diverse than previously suspected, that clinically relevant resistance genes are present even without recent selective antibiotic pressure in the human host, and that cryptic gut microbes are an important resistance reservoir. The observed transferability of gut-associated resistance genes to a gram-negative (E. coli) host also suggests that the potential for gut-associated resistomes to threaten human health by mediating antibiotic resistance in pathogens warrants further investigation.

Combination of alpha-melanocyte stimulating hormone with conventional antibiotics against methicillin resistant Staphylococcus aureus

Our previous studies revealed that alpha-melanocyte stimulating hormone (α-MSH) is strongly active against Staphylococcus aureus (S. aureus) including methicillin resistant S. aureus (MRSA). Killing due to α-MSH occurred by perturbation of the bacterial membrane. In the present study, we investigated the in vitro synergistic potential of α-MSH with five selected conventional antibiotics viz., oxacillin (OX), ciprofloxacin (CF), tetracycline (TC), gentamicin (GM) and rifampicin (RF) against a clinical MRSA strain which carried a type III staphylococcal cassette chromosome mec (SCCmec) element and belonged to the sequence type (ST) 239. The strain was found to be highly resistant to OX (minimum inhibitory concentration (MIC) = 1024 µg/ml) as well as to other selected antimicrobial agents including α-MSH. The possibility of the existence of intracellular target sites of α-MSH was evaluated by examining the DNA, RNA and protein synthesis pathways. We observed a synergistic potential of α-MSH with GM, CF and TC. Remarkably, the supplementation of α-MSH with GM, CF and TC resulted in ≥64-, 8- and 4-fold reductions in their minimum bactericidal concentrations (MBCs), respectively. Apart from membrane perturbation, in this study we found that α-MSH inhibited ∼53% and ∼47% DNA and protein synthesis, respectively, but not RNA synthesis. Thus, the mechanistic analogy between α-MSH and CF or GM or TC appears to be the reason for the observed synergy between them. In contrast, α-MSH did not act synergistically with RF which may be due to its inability to inhibit RNA synthesis (<10%). Nevertheless, the combination of α-MSH with RF and OX showed an enhanced killing by ∼45% and ∼70%, respectively, perhaps due to the membrane disrupting properties of α-MSH. The synergistic activity of α-MSH with antibiotics is encouraging, and promises to restore the lost potency of discarded antibiotics.

National surveillance of methicillin-resistant Staphylococcus aureus in China highlights a still-evolving epidemiology with 15 novel emerging multilocus sequence types

The global spread of methicillin-resistant Staphylococcus aureus (MRSA) is a serious problem, particularly in mainland China. In order to better understand the national molecular epidemiology and resistance profiles of hospital-associated MRSA (HA-MRSA) in China, a laboratory-based multicenter surveillance study was conducted. Sixty-nine hospitals in 45 large cities in 27 provinces were involved, and a total of 1,141 HA-MRSA isolates were collected during the 6-month study period in 2011. All MRSA isolates were characterized by multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec) typing, spa typing, detection of the Panton-Valentine leukocidin (PVL) locus (lukS-PV and lukF-PV), and antibiogram analysis. ST239-III-t030, ST239-III-t037, and ST5-II-t002 were the predominant HA-MRSA clones (overall prevalence rates, 57.1%, 12.9%, and 8.1%, respectively), although the prevalence rates of these major clones varied markedly in different administrative regions. Of note, 6.6% of the HA-MRSA isolates were found to belong to ST59, which had typical community-associated MRSA (CA-MRSA) features, including carriage of SCCmec type IV or V and PVL and less antimicrobial resistance than other major HA-MRSA clones. Moreover, among 36 MLST sequence types (STs) identified, 15 STs, accounting for 3.5% of total isolates, were novel. A novel ST designated ST2590, which is a single-locus variant of ST5-II-t002, was identified in three hospitals in two large cities, with a total of 17 isolates. To further monitor trends in HA-MRSA prevalence, epidemic clonal shifts, clone emergence, and transmission between community and health care settings, longitudinal national MRSA surveillance is required.

Setting interpretive breakpoints for antimicrobial susceptibility testing using disk diffusion

Antimicrobial susceptibility testing plays a key role in clinical microbiology. The disk diffusion test dates back to the 1940s and became standardised from the 1950s, with the International Collaborative Study (ICS) and National Committee for Clinical Laboratory Standards (NCCLS) as the two major standards. Interlaboratory variation of disk test results was recognised early but has never been dealt with in a satisfactory manner. The error-rate bounded method was described in 1974 and its role is discussed. Species-specific susceptibility interpretation was coined in 1980 for Proteus mirabilis and chloramphenicol. In the late 1970s, more extensive use of species-specific breakpoints was introduced in Lund (Sweden). At the same time, P. Mouton constructed species-specific regression lines and pointed out the difficulties with narrow ranges of minimal inhibitory concentration (MIC) values. A more general use of species-specific regression lines was made possible with single-strain regression analysis, using one well-defined strain tested in disk diffusion with a range of disk contents. This method made it possible to calibrate the disk test in an individual laboratory. Other methods to achieve such calibration are also described. A recent method, 'MIC-coloured zone diameter histogram-technique', has proven useful for the validation of species-specific interpretive breakpoints. The microbiological breakpoint proposed by Williams in 1990 has experienced a renaissance with the European Committee on Antimicrobial Susceptibility Testing (EUCAST) epidemiological cut-off value (ECOFF). MIC and zone diameter distributions with accompanying ECOFFs for species-antimicrobial combinations are published on the EUCAST website. A method for the reconstruction of wild-type zone diameter populations, namely normalised resistance interpretation, is described. This method can produce resistance figures that are truly comparable between laboratories.

Influence of different Mueller-Hinton agars and media age on Etest susceptibility testing of tigecycline

This study investigated the effect of different Mueller-Hinton agars and media age on tigecycline MICs, obtained by Etest. Variations in MIC values on different Mueller-Hinton were noted, which may result in changes in categoric susceptibility. The use of stored Mueller-Hinton media had minimal effect on MIC values.

Normalized resistance interpretation as a tool for establishing epidemiological MIC susceptibility breakpoints

Normalized resistance interpretation (NRI) utilizes the fact that the wild-type population on the sensitive side is not affected by resistance development, and therefore a normalized reconstruction of the peak can be performed. The method was modified for MIC distributions by the introduction of helper variables, in-between values assigned the mean of the neighboring numbers of isolates. This method was used on Staphylo- coccus aureus and Escherichia coli MIC distributions for 27 antimicrobials each and obtained from the EUCAST (European Committee on Antimicrobial Susceptibility Testing) website (http://www.eucast.org/mic_distributions/). The number of isolates in each of the 54 distributions ranged from 40 to 124,472. NRI produced normalized distributions in all cases. Cutoff values were calculated for +2.0 and +2.5 standard deviations (SD) above the means and then rounded up to nearest regular MIC dilution step. EUCAST also show cutoff values, ECOFF values, which were used as the reference. The NRI generated +2.0 SD values showed the best agreement with 26 of 27 within ±1 dilution step and 17 exactly on the ECOFF values for Staphylococcus aureus, and 25 of 27 within ±1 dilution step and 14 right on the ECOFF values for Escherichia coli. NRI offers an objective method for the reconstruction of the wild-type population in an MIC distribution for a given bacterial species and an antimicrobial agent. This method offers a new tool in comparative susceptibility studies such as global surveillance of resistance, as well as in quality control in individual laboratories.

Spread of community-acquired meticillin-resistant Staphylococcus aureus skin and soft-tissue infection within a family: implications for antibiotic therapy and prevention

Outbreaks or clusters of community-acquired meticillin-resistant Staphylococcus aureus (CA-MRSA) within families have been reported. We describe a family cluster of CA-MRSA skin and soft-tissue infection where CA-MRSA was suspected because of recurrent infections which failed to respond to flucloxacillin. While the prevalence of CA-MRSA is low worldwide, CA-MRSA should be considered in certain circumstances depending on clinical presentation and risk assessment. Surveillance cultures of family contacts of patients with MRSA should be considered to help establish the prevalence of CA-MRSA and to inform the optimal choice of empiric antibiotic treatment.

Tigecycline use in cancer patients with serious infections: a report on 110 cases from a single institution

Tigecycline, the first in a new class of glycylcyclines, has been approved for the treatment of complicated skin and skin structure and intraabdominal infections in adults. However, clinical data on its safety and effectiveness in cancer patients are lacking. We reviewed the records of all cancer patients treated with tigecycline for more than 48 hours between June 2005 and September 2006 at our institution and identified 110 consecutive cases (median age, 58 yr; range, 18-81 yr). We collected data on demographics, cancer type, tigecycline indication, microbiologic characteristics, side effects, and outcome. Sixty-four (58%) patients had hematologic malignancies; 27 patients had undergone hematopoietic stem cell transplantation. Thirty-one (28%) patients had neutropenia, and 62 (56%) were in the intensive care unit at the start of therapy. Most patients (106 [96%]) received tigecycline as a second-line agent (after not responding to other broad-spectrum antibiotics), and 101 (92%) received it in combination with an antipseudomonal drug. The mean duration of therapy was 11 days (range, 3-35 d). Sixty-six (60%) patients received tigecycline for refractory pneumonia, 19 (17%) had bacteremia, 9 (8%) had intraabdominal infections, and 7 (6%) had complicated skin and soft tissue infections. Fifty (45%) patients had microbiologically documented infections, and the remaining patients had negative cultures at the start of therapy.An overall clinical response was noted in 70 (64%) patients. More clinical responses were seen in patients with bacteremia than in those with pneumonia (79% vs. 51%; p = 0.029). Patients with microbiologically documented infections had significantly higher clinical response rates than patients with non-microbiologically documented infections (73% vs. 55%; p = 0.047). Forty (36%) patients did not respond to treatment; 36 of these patients died of active infection during tigecycline therapy. Patients with pneumonia had a significantly higher mortality rate than patients with bacteremia (44% vs. 16%; p = 0.026). During the 60 days of follow-up from the date of clinical response, patients with pneumonia had significantly shorter survival durations than patients with other infections. Of the 42 patients who were not on antiemetics or ventilator support at the start of tigecycline therapy, 2 (5%) experienced mild nausea, and 1 (2%) experienced nausea and vomiting. Only 4 (4%) patients overall experienced diarrhea during tigecycline therapy, all of whose stools were negative for Clostridium difficile toxin. No serious adverse events related to tigecycline use were identified. The combination of tigecycline and an antipseudomonal drug may be appropriate for treating refractory infections and multidrug-resistant organisms in cancer patients, including hematopoietic stem cell transplant recipients. Patients with refractory pneumonia had a relatively low clinical response rate in our study.

Antimicrobial activity of tigecycline and comparative agents against clinical isolates of staphylococci and enterococci from ICUs and general hospital wards at three Swedish university hospitals

The activities of tigecycline and comparative agents on staphylococci and enterococci isolated from patients at general hospital wards (GHWs) and intensive care units (ICUs) at 3 university hospitals in Sweden were investigated. Oxacillin disc diffusion and minimal inhibitory concentration with E-test were used. The presence of mecA, vanA or vanB genes was determined with PCR. Statistically significant higher incidence of clindamycin, fusidic acid, rifampicin and multidrug-resistant CoNS was found at ICUs compared to GHWs. Resistance rates were low among S. aureus. Tigecycline, linezolid and vancomycin were the only agents with high activity against methicillin-resistant S. aureus and multidrug-resistant CoNS. Resistance rates were low among E. faecalis, except for high-level gentamicin-resistant (HLGR) E. faecalis. E. faecium showed high resistance rates to ampicillin, piperacillin/tazobactam and imipenem. The HLGR rates among E. faecium were lower than the rates for E. faecalis. Tigecycline and linezolid were the only drugs with high activity against all enterococci including vancomycin-resistant enterococci. No statistically significant differences in susceptibility rates were found between the ward levels for S. aureus and enterococcal isolates and no statistically significant differences were found between the hospitals.

Antimicrobial susceptibility in Escherichia coli of human and avian origin--a comparison of wild-type distributions

In the present study, the antimicrobial susceptibilities of 97 Escherichia coli isolates from birds, and 100 clinical isolates from blood cultures, were determined by disk diffusion. The wild-type distributions were defined by the normalized resistance interpretation method. It is shown that the avian and clinical inhibition zone diameter distributions of wild-type E. coli are indistinguishable.

Tigecycline for the treatment of multidrug-resistant Enterobacteriaceae: a systematic review of the evidence from microbiological and clinical studies

OBJECTIVES

Antimicrobial drug resistance is spreading among Enterobacteriaceae, limiting the utility of traditionally used agents. We sought to systematically review the microbiological activity and clinical effectiveness of tigecycline for multidrug-resistant (MDR) Enterobacteriaceae, including those resistant to broad-spectrum beta-lactams due to the expression of extended-spectrum beta-lactamases (ESBLs), AmpC enzymes and carbapenemases (including metallo-beta-lactamases).

METHODS

PubMed was searched for articles including relevant data.

RESULTS

Twenty-six microbiological and 10 clinical studies were identified. Tigecycline was active against more than 99% of 1936 Escherichia coli isolates characterized by any of the above resistance patterns (including 1636 ESBL-producing isolates) using the US Food and Drug Administration (FDA) breakpoint of susceptibility (MIC < or = 2 mg/L). Findings were not different using the European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoint (< or = 1 mg/L). Susceptibility rates for Klebsiella spp. with any of the above resistance patterns were 91.2% for 2627 isolates by the FDA criteria and 72.3% for 1504 isolates by the EUCAST criteria (92.3% for 2030 and 72.3% for 1284 ESBL-producing isolates, by the FDA and EUCAST criteria, respectively). The degree of microbiological activity of tigecycline against 576 MDR Enterobacter spp. isolates was moderate. In clinical studies, 69.7% of the 33 reported patients treated with tigecycline achieved resolution of an infection caused by a carbapenem-resistant or ESBL-producing or MDR Enterobacteriaceae.

CONCLUSIONS

Tigecycline is microbiologically active against almost all of the ESBL or MDR E. coli isolates and the great majority of ESBL or MDR Klebsiella spp. isolates. Further evaluation of its clinical utility against such resistant Enterobacteriaceae, particularly regarding non-labelled indications, is warranted.

Setting and revising antibacterial susceptibility breakpoints

Clinical microbiology laboratories need to communicate results of antibacterial susceptibility testing to prescribers. Sophisticated prescribers who are knowledgeable of the pharmacokinetics and pharmacodynamics of antibacterials may desire no more information than the MIC of the drug in question. However, most prescribers require interpretation of antibacterial susceptibility testing results. Breakpoints can assist in determining if an antibacterial is potentially useful in the treatment of a bacterial infection. Breakpoints should be set prior to an antibacterial being used clinically. Breakpoint setting requires integration of knowledge of the wild-type distribution of MICs, assessment of the pharmacokinetics/pharmacodynamics of the antibacterial, and study of the clinical outcome of infections when the antibacterial is used. It is mandatory that breakpoints be reviewed when antibacterial agents have been in clinical use for some time, particularly if mechanisms of bacterial resistance to the drug have been described. In general, greater amounts of information on the pharmacokinetics and pharmacodynamics of an antibacterial are available when breakpoints need to be revised. However, the opportunity to conduct randomized clinical studies of an antibacterial declines after the drug has been released commercially. Well-designed observational clinical studies are therefore necessary in order to provide reliable data to inform those reevaluating breakpoints. Breakpoint-setting organizations may also play a role in developing phenotypic tests for detection of resistance mechanisms, as this information may complement use of the breakpoint in some circumstances.

Statistical methods for establishing quality control ranges for antibacterial agents in Clinical and Laboratory Standards Institute susceptibility testing

Quality control (QC) ranges for antimicrobial agents against QC strains for both dilution and disk diffusion testing are currently set by the Clinical and Laboratory Standards Institute (CLSI), using data gathered in predefined structured multilaboratory studies, so-called tier 2 studies. The ranges are finally selected by the relevant CLSI subcommittee, based largely on visual inspection and a few simple rules. We have developed statistical methods for analyzing the data from tier 2 studies and applied them to QC strain-antimicrobial agent combinations from 178 dilution testing data sets and 48 disk diffusion data sets, including a method for identifying possible outlier data from individual laboratories. The methods are based on the fact that dilution testing MIC data were log normally distributed and disk diffusion zone diameter data were normally distributed. For dilution testing, compared to QC ranges actually set by CLSI, calculated ranges were identical in 68% of cases, narrower in 7% of cases, and wider in 14% of cases. For disk diffusion testing, calculated ranges were identical to CLSI ranges in 33% of cases, narrower in 8% of cases, and 1 to 2 mm wider in 58% of cases. Possible outliers were detected in 8% of diffusion test data but none of the disk diffusion data. Application of statistical techniques to the analysis of QC tier 2 data and the setting of QC ranges is relatively simple to perform on spreadsheets, and the output enhances the current CLSI methods for setting of QC ranges.

Multicenter studies of tigecycline disk diffusion susceptibility results for Acinetobacter spp

Acinetobacter sp. isolates having multidrug resistance (MDR) patterns have become common in many medical centers worldwide, limiting therapeutic options. A five-center study tested 103 contemporary clinical Acinetobacter spp., including MDR strains, by reference broth microdilution and disk diffusion (15-mug disk content) methods against tigecycline. Applying U.S. Food and Drug Administration tigecycline breakpoint criteria for Enterobacteriaceae (susceptibility at < or =2 microg/ml [< or =1 microg/ml by the European Committee on Antimicrobial Susceptibility Testing]; disk diffusion breakpoints at > or =19 mm and < or =14 mm) to Acinetobacter spp. led to an unacceptable error rate (23.3%). However, an adjustment of tigecycline disk diffusion breakpoints (susceptible/resistant) to > or =16/ < or =12 mm reduced intermethod errors to an acceptable level (only 9.7%, all minor).