Median Minimum Inhibitory Concentration Research Articles

Toxicity of Ag, CuO and ZnO nanoparticles to selected environmentally relevant test organisms and mammalian cells in vitro: a critical review.

Nanoparticles (NPs) of copper oxide (CuO), zinc oxide (ZnO) and especially nanosilver are intentionally used to fight the undesirable growth of bacteria, fungi and algae. Release of these NPs from consumer and household products into waste streams and further into the environment may, however, pose threat to the ‘non-target’ organisms, such as natural microbes and aquatic organisms. This review summarizes the recent research on (eco)toxicity of silver (Ag), CuO and ZnO NPs. Organism-wise it focuses on key test species used for the analysis of ecotoxicological hazard. For comparison, the toxic effects of studied NPs toward mammalian cells in vitro were addressed. Altogether 317 L(E)C50 or minimal inhibitory concentrations (MIC) values were obtained for algae, crustaceans, fish, bacteria, yeast, nematodes, protozoa and mammalian cell lines. As a rule, crustaceans, algae and fish proved most sensitive to the studied NPs. The median L(E)C50 values of Ag NPs, CuO NPs and ZnO NPs (mg/L) were 0.01, 2.1 and 2.3 for crustaceans; 0.36, 2.8 and 0.08 for algae; and 1.36, 100 and 3.0 for fish, respectively. Surprisingly, the NPs were less toxic to bacteria than to aquatic organisms: the median MIC values for bacteria were 7.1, 200 and 500 mg/L for Ag, CuO and ZnO NPs, respectively. In comparison, the respective median L(E)C50 values for mammalian cells were 11.3, 25 and 43 mg/L. Thus, the toxic range of all the three metal-containing NPs to target- and non-target organisms overlaps, indicating that the leaching of biocidal NPs from consumer products should be addressed.Electronic supplementary materialThe online version of this article (doi:10.1007/s00204-013-1079-4) contains supplementary material, which is available to authorized users.

Quality control ranges for testing broth microdilution susceptibility of Flavobacterium columnare and F. psychrophilum to nine antimicrobials

A multi-laboratory broth microdilution method trial was performed to standardize the specialized test conditions required for the fish pathogens Flavobacterium columnare and F. psychrophilum. Nine laboratories tested the quality control (QC) strains Escherichia coli ATCC 25922 and Aeromonas salmonicida subsp. salmonicida ATCC 33658 against 10 antimicrobials (ampicillin, enrofloxacin, erythromycin, florfenicol, flumequine, gentamicin, ormetoprim/sulfadimethoxine, oxolinic acid, oxytetracycline, and trimethoprim/sulfamethoxazole) in diluted (4 g l-1) cation-adjusted Mueller-Hinton broth incubated at 28 and 18°C for 44-48 and 92-96 h, respectively. QC ranges were set for 9 of the 10 antimicrobials. Most of the minimal inhibitory concentration (MIC) distributions (16 of 18, 9 drugs at both temperatures) for A. salmonicida ATCC 33658 were centered on a single median MIC ± 1 two-fold drug dilution resulting in a QC range that spanned 3 dilutions. More of the E. coli ATCC 25922 MIC distributions (7 of 16) were centered between 2 MIC dilutions requiring a QC range that spanned 4 dilutions. A QC range could not be determined for E. coli ATCC 25922 against 2 antimicrobials at the low temperature. These data and their associated QC ranges have been approved by the Clinical and Laboratory Standards Institute (CLSI), and will be included in the next edition of the CLSI M49-A Guideline. This method represents the first standardized reference method for testing fish pathogenic Flavobacterium spp.

Comparison of teicoplanin and vancomycin in vitro activity on clinical isolates of Staphylococcus aureus

Ninety-one clinical isolates of Staphylococcus aureus have been tested with the Kirby Bauer and the Etest® method to determine the susceptibility to glycopeptides in the 2007–2010 period. Five strains (5·5%) were resistant to vancomycin and nine (9·9%) to teicoplanin. Teicoplanin showed a median minimal inhibitory concentration (MIC) of 1 mg/l (range 0·125–24 mg/l), an MIC50 of 1 mg/l, and an MIC90 of 2 mg/l; vancomycin had a median MIC of 1·5 mg/l (range 0·38–4 mg/l), an MIC50 of 1·5 mg/l, and an MIC90 of 2 mg/l. More isolates were distributed on higher values of MIC for vancomycin. Inhibition halos induced by vancomycin-impregnated paper diskettes were slightly larger than those by teicoplanin. Glycopeptide resistance among methicillin-resistant Staphylococcus aureus in Italy is an underestimated phenomenon, possibly due to the described underestimation of glycopeptides MICs by the automatic broth microdilution method, when compared to agar MIC assays. A teicoplanin MIC creep, as reported for vancomycin, cannot be assumed.

Association of streptomycin resistance mutations with level of drug resistance and Mycobacterium tuberculosis genotypes

To determine 1) the relationship between specific streptomycin (SM) resistance mutations and the minimum inhibitory concentration (MIC), and 2) whether these mutations are preferentially associated with the Beijing genotype in Viet Nam. A total of 131 consecutive Mycobacterium tuberculosis isolates resistant to either isoniazid (INH) or rifampicin (RMP), collected previously, were tested for SM resistance, spoligotyped and sequenced in the rpsL, rrs and gidB genes. The MIC for 50 mutants was also determined. Overall, 116/131 isolates were SM-resistant. The three most frequently occurring mutation sites in rpsL and rrs were at codon 43 of rpsL (72/116, 62.1%), rpsL88 (22/116, 18.9%) and rrs514 (8/116, 6.9%). Mutations in the rrs910 region were found in two isolates (1.7%), and three isolates had mutations in both rpsL and rrs (2.6%). gidB mutations were found in both resistant and susceptible strains. Among SM-resistant isolates resistant to INH/RMP, the Beijing genotype was strongly associated with rpsL43 mutation (aOR 23.6, 95%CI 2.9-193.4, P = 0.002). The median MIC for each mutation was as follows: rpsL43 = 256 μg/ml, rpsL88 = 16 μg/ml, 515 loop = 4 μg/ml, 910 region = 8 μg/ml, and double mutation = 256 μg/ml. We found a strong association between rpsL43 and high drug resistance levels, with all rpsL43 mutants having an MIC >256 μg/ml (P < 0.001).

Continuous infusion of piperacillin/tazobactam in ventilator-associated pneumonia: a pilot study on efficacy and costs

Ventilator-associated pneumonia (VAP) occurs in nearly one-third of mechanically ventilated patients in the Intensive Care Unit. Piperacillin/tazobactam (TZP) is currently recommended in the empirical treatment of VAP, but intermittent dosing may result in inadequate serum concentrations. The efficacy and costs of continuous infusion (CI) of TZP, using therapeutic drug monitoring for real-time dose adjustment, was assessed in a prospective pilot study of 16 patients with VAP. TZP was given as a loading dose of 2.0/0.25g followed by a CI of 10.0/1.25g daily. Rapid antimicrobial susceptibility testing was used to determine the minimum inhibitory concentration (MIC) of the pathogens. TZP concentrations were determined by high-pressure liquid chromatography before and at 1, 6, 12, 24, 48, 72 and 96h after the onset of administration. Dosages were adjusted to maintain piperacillin concentrations four-fold above the MIC (T>4×MIC) of the pathogen, with a maximum dose of 16.0/2.0g. The cost of the total TZP administered was compared with the cost of a standard TZP regimen (16.0/2.0g) if given over the same period of time. The median MIC for TZP was 1μg/mL (range 0.025–32μg/mL). TZP concentrations were adequate for 71% of pathogens on the first day of therapy. Clinical cure was achieved in 9/10 patients who had adequate drug concentrations and in 3/6 patients with insufficient levels. The daily dose of TZP received by CI was 37.5% less than that of a standard regimen, which corresponds to a saving of €15 on daily therapy costs compared with the standard regimen. In conclusion, CI of TZP achieved optimal drug concentrations in most patients with VAP, with a favourable impact on costs. Adequate drug concentrations were achieved for MIC≤4μg/mL, but higher dosages should be considered for the treatment of pathogens with low susceptibility thresholds.

In Vitro and In Vivo Activity of First Generation Cephalosporins Against Leptospira

Third generation cephalosporins are commonly used in the treatment of leptospirosis. The efficacy of first generation cephalosporins has been less well-studied. Susceptibility testing of 13 Leptospira strains (11 serovars) to cefazolin and cephalexin was conducted using broth microdilution. Median minimal inhibitory concentration (MIC) for cefazolin and cephalexin ranged from < 0.016 to 2 μg/mL (MIC(90) = 0.5 μg/mL) and from 1 to 8 μg/mL (MIC(90) = 8 μg/mL), respectively. Efficacy of cefazolin and cephalexin in an acute lethal hamster model of leptospirosis was studied. Survival rates for cefazolin were 80%, 100%, and 100%, and survival rates for cephalexin were 50%, 80%, and 100% (treated with 5, 25, and 50 mg/kg per day for 5 days, respectively). Each treatment group showed improved survival compared with no treatment (P < 0.01), and none of the therapies, regardless of dose, was statistically significantly different than doxycycline. These results support a potential role for first generation cephalosporins as alternative therapies for leptospirosis.

Changes in Antibiotic Resistance Level of Nosocomial Pseudomonas Aeruginosa Isolates in the Largest University Hospital of Lithuania

The aim was to estimate changes in the resistance rates of Pseudomonas aeruginosa (P. aeruginosa) strains isolated from patients treated in intensive care units of the largest university hospital. Isolates were identified with the Phoenix ID system (Becton Dickinson, USA). The minimum inhibitory concentration (MIC) of ceftazidime, ciprofloxacin, and amikacin were determined by the E-test and evaluated following the recommendations of the Clinical Laboratory Standards Institute. In 2003, the proportion of P. aeruginosa strains resistant to piperacillin was greatest followed by strains resistant gentamicin and ciprofloxacin. In 2008, the resistance rates markedly changed being the highest to ciprofloxacin. An increase in the resistance rates to ciprofloxacin (+24%, P<0.001) and ceftazidime (+8.3%, P<0.05) was documented. In 2003, there were 66.7% of P. aeruginosa strains sensitive to all antibiotics tested, and this percentage decreased to 47.5% in 2008 (P<0.05). During the study, a significant increase in the median MICs for ciprofloxacin and amikacin was observed (P<0.001); however, no significant change was documented for ceftazidime. P. aeruginosa remains an important nosocomial pathogen with relatively high overall resistance to antimicrobial agents, and the resistance level is increasing.

Glycopeptide resistance in coagulase-negative staphylococci isolated in blood cultures from patients with hematological malignancies during three decades

The aim of this study was to determine if there was a long-term increase in glycopeptide minimum inhibitory concentration (MIC) values, MIC creep, among bloodstream isolates of Staphylococcus epidermidis and S. haemolyticus isolated from patients with hematological malignancies. We conducted a retrospective single-center study where all positive blood cultures of S. epidermidis (n = 387) and S. haemolyticus (n = 19) isolated from patients with hematological malignancies during three decades, 1980 to 2009, were re-evaluated for the presence of reduced susceptibility to vancomycin and teicoplanin. Three different methods for the detection of reduced susceptibility to glycopeptides were used; standard Etest, macromethod Etest, and glycopeptide resistance detection (GRD) Etest. The median MIC value for vancomycin was 2 mg/L. MIC values for vancomycin and teicoplanin did not show any statistically significant increase during the study period. The presence of heterogeneously glycopeptide-intermediate staphylococci (hGIS) was analyzed among 405 coagulase-negative staphylococci (CoNS) isolates. hGIS were found in 31-45% of the CoNS isolates by the macromethod Etest and in 53-67% by the GRD Etest during the three decades. In conclusion, we did not observe any long-term glycopeptide MIC creep determined by the standard Etest, although a high and increasing proportion of heterogeneous vancomycin resistance was observed.

In vitro antimicrobial efficacy of β‐defensin 3 against Staphylococcus pseudintermedius isolates from healthy and atopic canine skin

β-Defensins (BDs) are highly conserved antimicrobial peptides important in innate defence against bacteria. β-Defensin 3 has a specific role in protecting the skin. This study quantified the minimal inhibitory concentration (MIC) of human (h)BD3 against Staphylococcus pseudintermedius isolates from atopic and healthy dogs. Single colony isolates (1 × 10(5) colony-forming units/mL log phase) were cultured with doubling dilutions of hBD3 in sodium phosphate buffer from 0.8 to 50 μg/mL at 37 °C for 2 h, before adding 100 μL of tryptone soy broth and incubating for a further 20 h. Bacterial growth was assessed as the mean optical density at 540 nm corrected for background. The median MIC was 12.5 μg hBD3/mL (range 3.125-25 μg/mL; n=22). Forty-five percent of the isolates were inhibited at ≤ 6.25 μg hBD3/mL, and 90% were inhibited at ≤ 12.5 μg hBD3/mL. Bacterial growth was not inhibited at ≤ 1.6 μg hBD3/mL. There were no significant differences in the inhibition by hBD3 of isolates from atopic (median MIC 12.5 μg/mL, range 6.25-25 μg/mL, n=14) and healthy dogs (median MIC 9.4 μg/mL, range 3.125-12.5 μg/mL, n = 8); from noninfected colonized sites (median MIC 12.5 μg/mL, range 3.125-25 μg/mL, n=16) and infected lesions (median MIC 9.4 μg/mL, range 6.25-12.5 μg/mL, n=6); or between sample sites (nose median MIC 12.5 μg/mL, range 6.25-25 μg/mL, n=5; perineum median MIC 12.5 μg/mL, range 3.125-25 μg/mL, n=7; ear median MIC 6.25 μg/mL, range 6.25-12.5 μg/mL, n=4; lesions median MIC 9.4 μg/mL, range 6.25-12.5 μg/mL, n=6). In conclusion, hBD3 inhibited the growth of canine S. pseudintermedius isolates in vitro irrespective of origin.

Alarming spread of vancomycin resistant enterococci in Sweden since 2007

The total number of persons infected or colonised with vancomycin-resistant enterococci mandatorily reported to the Swedish Institute for Infectious Disease Control increased dramatically during 2007 and 2008. During a period of twenty months from 1 July 2007 to 28 February 2009, a total of 760 cases were reported compared with 194 cases reported during the entire period from 2000 to 2006. This rise was mainly attributed to a wide dissemination of vancomycin resistant enterococci which started in a number of hospitals in Stockholm in the autumn of 2007 and was followed by dissemination in various healthcare facilities (hospitals and homes for the elderly) in a further two Swedish counties in 2008. The majority of the cases (97%) were acquired in Sweden and among these, healthcare-acquired E. faecium vanB dominated (n=634). The majority of these isolates had identical or closely related pulsed-field gel electrophoresis patterns indicating clonal dissemination in the affected counties. The median minimum inhibitory concentration of vancomycin was 32 mg/L (ranging from 4 to >128 mg/L) and of teichoplanin 0.12 mg/L (ranging from 0.06 to 0.25 mg/L). Particular emphasis was placed on countermeasures such as screening, contact tracing, cleaning procedures, education in accurate use of infection control practices as well as increasing awareness of hygiene among patients and visitors. With these measures the dissemination rate decreased substantially, but new infections with the E. faecium vanB strain were still detected.

SHOULD HIGHER VANCOMYCIN TROUGH LEVELS BE TARGETED FOR INVASIVE COMMUNITY-ACQUIRED METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS INFECTIONS IN CHILDREN?

Methicillin-resistant Staphylococcus aureus isolates with vancomycin minimal inhibitory concentrations (MICs) >or=1.5 microg/mL have been associated with poorer clinical outcomes and treatment failures in adults. We evaluated vancomycin MICs in 71 invasive pediatric community-acquired MRSA isolates from 2004 to 2008, using the E-test micromethod and the E-test macro-method. The modal MIC by micromethod was 1.5 microg/mL, and median vancomycin MICs did not increase over time.

Comparative in-vitro efficacy of fluoroquinolones against Streptococcus pneumoniae recovered from bacterial keratitis as determined by E-test

The advent of new fluoroquinolones has drawn the attention for reliable methods on the in-vitro susceptibility testing of Streptococccus pneumoniae. This study attempts to determine the minimum inhibitory concentration (MIC) of second-generation (ciprofloxacin and ofloxacin), third-generation (levofloxacin) and the fourth-generation (moxifloxacin and gatifloxacin) fluoroquinolones against S. pneumoniae recovered from bacterial keratitis. In retrospect, the MICs of 50 strains of S. pneumoniae isolated from the corneal scrapes of patients with bacterial keratitis were determined against ciprofloxacin, ofloxacin, levofloxacin, gatifloxacin and moxifloxacin using E-tests. The National Committee of Clinical Laboratory Standards (NCCLS) susceptibility patterns and the potencies of the MICs were statistically compared. The median MIC of ciprofloxacin (0.25microg/ml) was found to be lower than the median MICs of ofloxacin (0.5microg/ml) (P < 0.449) and levofloxacin (1.0microg/ml) (P < 0.001). The median MICs of gatifloxacin (0.1microg/ml) was lower than the median MICs of ciprofloxacin (0.25microg/ml) (P < 0.001), ofloxacin (0.5microg/ml) (P < 0.001) and levofloxacin (1.0microg/ml) (P < 0.001). Moxifloxacin (0.06microg/ml) had showed lower median MICs than gatifloxacin (0.1microg/ml) (P < 0.001) levofloxacin (1.0microg/ml) (P < 0.001), ofloxacin (0.5microg/ml) (P < 0.001) and ciprofloxacin (0.25microg/ml) (P < 0.001). Moxifloxacin (0.06microg/ml) had a lower MIC50 (microg/ml) than gatifloxacin (0.1microg/ml), levofloxacin (1.0microg/ml), ciprofloxacin (0.25microg/ml) and ofloxacin (0.5microg/ml). MIC90 (microg/ml) of moxifloxacin (0.06microg/ml) was found to be lower than the MIC90 (microg/ml) of gatifloxacin (0.5microg/ml), levofloxacin (1.0microg/ml), ofloxacin (0.5microg/ml) and ciprofloxacin (0.5microg/ml). Based on in-vitro testing, the five portrayed fluoroquinolones 100% sensitivity to S. pneumoniae. However, the fourth-generation fluoroquinolone, moxifloxacin appeared to be more effective against S. pneumoniae than gatifloxacin, levofloxacin, ofloxacin and ciprofloxacin.

The designer proline-rich antibacterial peptide A3-APO is effective against systemic Escherichia coli infections in different mouse models

Antimicrobial peptides are considered to be viable alternatives to conventional antibiotics. However, they rarely show systemic efficacy in animal models when added at non-toxic doses. The dimer A3-APO was designed to attack both the bacterial membrane and the Enterobacteriaceae-specific domain of the heat shock protein DnaK in order to reduce toxicity whilst maintaining activity. The peptide exhibited a minimal inhibitory concentration (MIC) range of 2–128 mg/L against 28 clinical Escherichia coli, Klebsiella pneumoniae and Salmonella enterica serovar Typhimurium strains, with a median MIC of 30 mg/L. At this concentration, A3-APO was bactericidal to E. coli 5770, a fluoroquinolone-resistant extended-spectrum β-lactamase-producing strain. The No Observed Adverse Effect Limit (NOAEL) at repeated intraperitoneal peptide administration was 20 mg/kg. When administered at this dose three times starting immediately after E. coli Neumann infection, A3-APO cured 100% of mice in a standard bacteraemia model used by the pharmaceutical industry. In a more stringent assay, when treatment started after E. coli 5770 bacteraemia had already been established, three doses of 10 mg/kg A3-APO prolonged early survival at a rate similar to that of imipenem and reduced the bacterial counts to base level. When the second assay was repeated in kidney clearance conditions resembling those in humans, 10 mg/kg A3-APO was as efficacious as imipenem in the long-term. The increased in vivo efficacy compared with the in vitro bactericidal figures can potentially be explained by the generally observable immunostimulatory properties of antimicrobial peptides. Peptide A3-APO shows promising features as a member in our antibiotic arsenal against multidrug-resistant bacterial pathogens.

Communication: Antimicrobial Activity of SMAP28 with a Targeting Domain for Porphyromonas gingivalis

Antibiotic therapy is often used with mechanical therapy to treat periodontal disease. However, complications associated with antibiotic use can occur. A 'bacteria-specific' targeted approach would eliminate some of these complications and kill specific periodontopathogens without harming the commensal bacteria. One such approach is to couple antimicrobial peptides to a ligand, pheromone, or antibody specific for the periodontopathogen, Porphyromonas gingivalis. To assess the feasibility of this approach, we attached PQGPPQ, a peptide from proline-rich protein 1 to either the N-terminus of SMAP28 (peptide ZS37-37) or the C-terminus of SMAP28 (peptide ZS37-38) to see whether it has potential as a carrier ligand to deliver SMAP28 to the surface of P. gingivalis. For Escherichia coli and Aggregatibacter actinomycetemcomitans, the median minimal inhibitory concentration (MIC) of ZS37-37 was higher than the median of SMAP28 alone, although the median MIC of ZS37-38 was lower than that of SMAP28 alone. For P. gingivalis, there was no difference in the median MIC values. For S. aureus, the median MIC was higher for ZS37-37 and ZS37-38 compared to SMAP28 alone, particularly for ZS37-38. For Fusobacterium nucleatum, the median MIC values were equal for ZS37-37 and ZS37-38 and higher than the median MIC for SMAP28 alone. Attaching PQGPPQ to SMAP28 did not greatly increase the antimicrobial activity of ZS37-37 or ZS37-38 for P. gingivalis nor substantially decrease the antimicrobial activity of ZS37-37 or ZS37-38 for the four other microorganisms tested. This is an initial step to develop a selective antimicrobial agent that has 'targeted' antimicrobial activity without adverse reactions often associated with the use of broad-spectrum antibiotics.

Minimum Inhibitory Concentration and Postantibiotic Effect of Amikacin for Equine Isolates of Methicillin‐Resistant Staphylococcus aureus In Vitro

To report the minimum inhibitory concentration (MIC) of amikacin sulfate for equine clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and characterize the initial kill and duration of the postantibiotic effect (PAE) for selected strains. Experimental study. Isolates of MRSA (n=35) had their amikacin MIC determined using the E-test agar diffusion method. Two isolates with MICs>256 microg/mL limit were further characterized using broth macrodilution. Six distinct isolates with amikacin MICs of 32, 48, 128 (2 isolates) and 500 (2 isolates) microg/mL had PAE determinations made over a range of amikacin concentrations from 31.25-1000 microg/mL using standard culture-based techniques. Median MIC of the 35 isolates was 32 microg/mL (range 2 to >256 microg/mL). Mean PAE of selected MRSA strains had an overall mean (all amikacin doses) of 3.43 hours (range 0.10-9.57 hours). PAE for MRSA exposed to amikacin at 1000 microg/mL was 6.18 hours (range 3.30-9.57 hours), significantly longer than that for all other concentrations (P<.0001). There was no statistically significant effect of isolate MIC on PAE. Isolates had a wide range of MIC; however, growth of all 6 selected strains were inhibited within the range of concentrations tested, including 2 strains with MICs of 500 microg/mL. PAE duration was not influenced by the MIC of amikacin but was significantly longer with treatment at 1000 microg/mL than at lower concentrations. Clinical isolates of MRSA are susceptible to amikacin at concentrations achieved by regional perfusion: however, the modest duration of PAE observed suggest that further laboratory and in vivo evaluation be conducted before recommending the technique for clinical use.

A novel bactericidal fabric coating with potent in vitro activity against meticillin-resistant Staphylococcus aureus (MRSA)

We evaluated the antistaphylococcal activity of Cliniweave® (CW), a commercially available textile treatment designed for use in healthcare environments. In tests on genetically diverse isolates of Staphylococcus aureus, including 49 meticillin-resistant S. aureus (MRSA), the median minimum inhibitory concentration of the liquid compound was found to be 1μg/L (range 0.5–2μg/L). Comparison of the antimicrobial activity of CW-treated polyester with three other commercially available silver-based antimicrobial fabrics showed that after exposure of cultures of ca. 106 colony-forming units/mL of S. aureus, only CW-treated fabric showed any significant antibacterial activity, severely reducing bacterial numbers within 1h. Time–kill analysis of liquid CW in culture showed 2log and 3log reductions of S. aureus numbers within 30min and 240min, respectively, and 2log reductions were observed within 60min using treated fabric. CW-treated fabrics are strongly biocidal and may be useful in helping reduce the burden of nosocomial bacterial infection.

Tigecycline for the Treatment of Acinetobacter Infections: A Case Series

Acinetobacter infections resistant to multiple classes of antibiotics have become prevalent in many institutions. Tigecycline has in vitro activity against Acinetobacter spp. and has been suggested as a therapeutic option in these infections. To describe the clinical and microbiologic outcomes of patients who received tigecycline for the treatment of infections caused by Acinetobacter spp. at our institution. A retrospective review was conducted of the medical records of 29 sequential patients who received tigecycline for treatment of Acinetobacter infections. The outcomes assessed for efficacy were clinical improvement or cure and microbiologic cure in evaluable patients. Patients received tigecycline a median of 30 days into hospitalization for a median of 11 days. Common indications were pneumonia (15 pts.), bacteremia (6), and urinary tract infection (3). Positive clinical outcomes (clinical cure or improvement) were seen in 8 (28%) of 29 patients. Of the 25 microbiologically evaluable patients, 11 (44%) had resolution of their cultures. Eleven patients had susceptibility testing performed, and the median minimum inhibitory concentration was 4 microg/mL (range 3-8). In this case series, most patients did not have clinically or microbiologically favorable outcomes with tigecycline therapy. No patient had an isolate that was fully susceptible to tigecycline. Data from more studies are needed before tigecycline can be recommended for the treatment of Acinetobacter infections.

Antimicrobial drug resistance of Escherichia coli isolated from poultry abattoir workers at risk and broilers on antimicrobials

Antimicrobial usage in food animals increases the prevalence of antimicrobial drug resistance among their enteric bacteria. It has been suggested that this resistance can in turn be transferred to people working with such animals, e.g., abattoir workers. Antimicrobial drug resistance was investigated for Escherichia coli from broilers raised on feed supplemented with antimicrobials, and the people who carry out evisceration, washing and packing of intestines in a high-throughput poultry abattoir in Gauteng, South Africa. Broiler carcasses were sampled from 6 farms, on each of which broilers are produced in a separate 'grow-out cycle'. Per farm, 100 caeca were randomly collected 5 minutes after slaughter and the contents of each were selectively cultured for E. coli. The minimum inhibitory concentration (MIC) of each isolate was determined for the following antimicrobials: doxycycline, trimethoprim, sulphamethoxazole, ampicillin, enrofloxacin, fosfomycin, ceftriaxone and nalidixic acid. The same was determined for the faeces of 29 abattoir workers and 28 persons used as controls. The majority of isolates from broilers were resistant, especially to antimicrobials that were used on the farms in the study. Overall median MICs and the number of resistant isolates from abattoir workers (packers plus eviscerators) tended to be higher than for the control group. However, no statistically significant differences were observed when the median MICs of antimicrobials used regularly in poultry and percentage resistance were compared, nor could an association between resistance among the enteric E. coli from packers and those from broilers be demonstrated.

Changes in the expression pattern of structural proteins after exposure of Borrelia burgdorferi to penicillin G and doxycycline

The numerous genes and proteins encoded in the borrelial genome have been shown to undergo differential expression in response to environmental cues. To gain a better understanding of possible interactions between antimicrobial agents and Borrelia, we investigated here the effects of increasing concentrations of penicillin G and doxycycline on the protein expression of the Borrelia burgdorferi s.s. isolate LW2 after 24 and 48 h of incubation. For 14 protein spots in Borrelia exposed to penicillin G at 0.25 and 0.5 μg/ml and for 5 protein spots in Borrelia exposed to doxycycline at 0.5 and 1 μg/ml, differences in spot intensity were identified by use of high resolution two-dimensional electrophoresis (2-DE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). At concentrations of both antimicrobial agents around the median minimal inhibitory concentration (0.5 μg/ml), all but one of the detected spots showed a considerable down-regulation as revealed by a ⩾50% decrease of spot intensity in comparison to untreated controls. Most of the spots identified thus far belong to proteins that are encoded by genes localized on the borrelial chromosome and are known to be involved in the different pathways of bacterial cell metabolism. Interestingly, one spot, identified as triosephosphate isomerase, was clearly up-regulated in the presence of doxycycline. Our data provide for the first time scientific evidence that B. burgdorferi s.l., although it possesses a small genome and extremely limited biosynthetic capabilities, shows a variable but distinct physiological response to exposure with penicillin G and doxycycline.

Modified allele‐specific primer–polymerase chain reaction method for analysis of susceptibility of Helicobacter pylori strains to clarithromycin

Most clarithromycin-resistant strains of Helicobacter pylori have a mutation from adenine (A) to guanine (G) at position 2142 or 2143 of the 23S rRNA gene. Our aim in this study was to develop a polymerase chain reaction (PCR)-based assay that could determine these mutations in a single reaction tube. We designed the forward primer FP2143G and the reverse primer RP2142G, which specifically anneal with the 2143G- and 2142G-mutated sequences, respectively, of the 23S rRNA gene of H. pylori. We also designed the forward primer FP-1 and reverse primer RP-1 upstream and downstream from the positions 2142 and 2143, respectively, to distinguish the wild-type A2142G and A2143G mutations from each other by amplicon sizes. DNA was extracted from 292 gastric tissue samples positive for rapid urease test, and the DNA underwent the PCR reaction. The results were compared with minimum inhibitory concentrations (MIC) for clarithromycin. Helicobacter pylori strains with A2142G, A2143G and wild type could be distinguished by amplicon sizes by a single PCR reaction. The genotyping results were correlated well with the MIC values for clarithromycin. The median MIC for clarithromycin of the wild-type strains was <0.015 microg/mL. Those of strains with 2142G or 2143G were > or =1.0 microg/mL. Our new PCR-based assay for 23S rRNA mutations of H. pylori is a useful method for detecting clarithromycin-resistant strains of H. pylori easily.