Activity of telithromycin against erythromycin-susceptible and -resistant Streptococcus pneumoniae isolates from adults with invasive infections

A telithromycin (TEL) kill-kinetics study was conducted with 120 clinically significant Streptococcus pneumoniae isolates (60 susceptible and 60 highly resistant to erythromycin). Time–kill curves were performed using different antibiotic concentrations. The minimum inhibitory concentrations (MICs) of TEL were low for both erythromycin-susceptible (MIC ≤ 0.016 mg/L) and erythromycin-resistant strains (MIC ≤ 0.25 mg/L). TEL showed 99.9% killing of all erythromycin resistant strains at 18–24 h of incubation. Even for strains with erythromycin MICs ≥ 64.0 mg/L, TEL was uniformly bactericidal at 0.25 mg/L.     

Colistin susceptibility testing by Etest and disk diffusion methods

The accuracy of disk susceptibility methods for colistin against 778 bacterial pathogens was evaluated in comparison with Etest using interpretive criteria available from the Clinical and Laboratory Standards Institute (CLSI). Colistin exhibited excellent activity against Acinetobacter baumannii and Escherichia coli isolates (minimum inhibitory concentration for 90% of the organisms (MIC₉₀) = 0.5 mg/L), whilst it was less active both against Enterobacter spp. and Klebsiella pneumoniae (MIC for 50% of the organisms (MIC₅₀) = 0.5 mg/L, MIC₉₀ = 16 mg/L). Colistin also showed good activity against Pseudomonas aeruginosa (MIC₉₀ = 2 mg/L, MIC₅₀ = 1 mg/L) but poor activity against Stenotrophomonas maltophilia (MIC₅₀ = 8 mg/L, MIC₉₀ = 128 mg/L). Only 0.8% of minor errors were observed between the studied methods for P. aeruginosa isolates when the CLSI criteria were applied. All A. baumannii isolates with a zone diameter ≤12 mm were resistant and those with a zone diameter ≥14 mm were susceptible according to MIC breakpoints established by the CLSI. Among nine isolates exhibiting a zone diameter of 13 mm, one was resistant to colistin (MIC = 8 mg/L) and eight isolates were susceptible (MIC = 0.5 mg/L). Applying a MIC breakpoint of ≤2 mg/L for susceptibility in Enterobacteriaceae, all isolates with a zone diameter ≥14 mm were susceptible, whilst all isolates with a zone diameter ≤11 mm were resistant. Among isolates with zone diameters of 12–13 mm, 59% were characterised as susceptible. Major errors were observed only in K. pneumoniae isolates at a rate of 0.8%. The poor agar diffusion characteristics of colistin limit the predictive accuracy of the disk diffusion test and consequently values of 12–13 mm should be confirmed with MIC determination by Etest or broth dilution method.     

Activity of cephalosporin CXA-101 (FR264205) against Pseudomonas aeruginosa and Burkholderia cepacia group strains and isolates

Twenty-five years after its introduction, ceftazidime remains the most active cephalosporin against Pseudomonas aeruginosa. Nevertheless, resistance arises by upregulation of AmpC β-lactamase, by efflux or, less often, via acquisition of additional β-lactamases. Mutational resistance is especially prevalent among cystic fibrosis (CF) isolates. We examined the activity of a novel oxyimino-aminothiazolyl cephalosporin, CXA-101 (FR264205), against P. aeruginosa strains with defined resistance mechanisms as well as against multiresistant clinical CF isolates of P. aeruginosa and Burkholderia cepacia. Minimum inhibitory concentrations (MICs) of CXA-101 were determined by the Clinical and Laboratory Standards Institute agar dilution method and were 0.25–0.5 mg/L for ‘typical’ P. aeruginosa strains without acquired resistance, compared with 1–2 mg/L for ceftazidime. MICs of CXA-101 were 0.5–2 mg/L and 4 mg/L, respectively, for isolates with upregulated efflux or total AmpC derepression, compared with 2–16 mg/L and 32–128 mg/L for ceftazidime. Full activity was retained against OprD mutants resistant to imipenem. Substantive resistance (MICs ≥ 32 mg/L) arose for transconjugants with PER, VEB and OXA extended-spectrum β-lactamases and for metallo-β-lactamase producers, with reduced susceptibility (MIC = 8 mg/L) for transconjugants with OXA-2, OXA-3 and NPS-1 enzymes. MICs of CXA-101 were 2- to 16-fold below those of ceftazidime for multiresistant P. aeruginosa from CF patients, but ranged up to >128 mg/L; values for B. cepacia from CF resembled those for ceftazidime.     

Comparison of effects of formoterol and BRL 37344 on isolated term-pregnant rat myometrial strips in vitro

This study was designed to compare the effects of β-adrenoceptor agonists formoterol and BRL 37344 on spontaneous contractions and the levels of cAMP and cGMP of myometrial strips isolated from timed-pregnant rats. Myometrial strips were obtained from term-pregnant Wistar albino rats (n = 12), mounted in organ baths and tested for changes in isometric tension in response to formoterol and BRL 37344. We evaluated the effect of increasing concentrations of formoterol and BRL 37344 on oxytocin-induced myometrial contractions and on contractions of myometrial smooth muscle pretreated with metoprolol, ICI 118.551 and SR 59230A (β₁, β₂, β₃-adrenoceptor antagonist, respectively, 10^− 6 M). Effects of formoterol and BRL 37344 on cAMP and cGMP levels in isolated myometrial strips (n = 6) were evaluated by radioimmunoassay kits. Formoterol (10^− 12–10^− 8 M) and BRL 37344 (10^− 11–10^− 5 M) concentration-dependently decreased the amplitude of oxytocin-induced contractions. E_max value (100%) of formoterol was increased significantly more than E_max value (70.6%) of BRL 37344 (P < 0.05), with no change in pD₂ value (9.54 ± 0.12 and 9.12 ± 0.12, respectively). The inhibition of the amplitude of oxytocin-induced contractions by formoterol was antagonized with ICI 118.551 (10^− 6 M), but they were not changed by metoprolol (10^− 6 M) or SR 59230A (10^− 6 M). The inhibition of the amplitude of oxytocin-induced contractions by BRL 37344 were antagonized with SR 59230A (10^− 6 M), but they were not changed by metoprolol (10^− 6 M) or ICI 118.551 (10^− 6 M). Formoterol and BRL 37344 increased cAMP levels. BRL 37344 increased cGMP levels in BRL 37344 group more than control group, but this increase is less significant than cAMP levels (P > 0.05). Formoterol and BRL 37344 decreased amplitude of myometrial contractions with similar potency, but efficacy of formoterol was better than BRL 37344.     

Evaluation of gatifloxacin pharmacokinetics and pharmacodynamics in severely ill adults in a medical Intensive Care Unit

A prospective, open-label study investigated the steady-state pharmacokinetics of gatifloxacin in 20 adult patients in a medical Intensive Care Unit (ICU). Twelve patients had normal or moderately impaired renal function (creatinine clearance (CrCL) ≥40 mL/min) and received gatifloxacin 400 mg intravenously once daily. Eight patients had CrCL < 40 mL/min and received 200 mg doses. Gatifloxacin plasma and urine concentrations were determined by validated high-performance liquid chromatography. Mean ± standard deviation gatifloxacin elimination half-life (t_1/2), systemic clearance and volume of distribution in patients with CrCL ≥ 40 mL/min were 10.8 ± 1.5 h, 156 ± 29 mL/min and 1.8 ± 0.2 L/kg, respectively. Maximum and minimum serum concentrations (C_max and C_min) and area under the serum concentration–time curve from 0–24 h (AUC_0–24) in these patients were 4.77 ± 0.76 mg/L, 1.08 ± 0.28 mg/L and 44.4 ± 9.2 mg h/L, respectively. Observed t_1/2, C_max and AUC_0–24 following 200 mg doses in patients with poor renal function (CrCL < 40 mL/min) were 18.2 ± 3.3 h, 2.85 ± 0.76 mg/L and 36.6 ± 3.4 mg h/L, respectively. Statistically significant (P < 0.05) increase in AUC_0–24 and decreases in t_1/2 and clearance (total and renal) were observed in ICU patients administered intravenous gatifloxacin compared with previous data in healthy volunteers. Pharmacodynamic evaluation by Monte Carlo simulation indicated that approved gatifloxacin dosage regimens appear to be adequate for most pathogens (minimum inhibitory concentration (MIC) ≤0.5 μg/mL) associated with community-acquired infections in severely ill ICU patients; less susceptible pathogens (MIC ≥ 1 μg/mL) do not appear to be optimally treated with currently approved doses.     

Antifungal susceptibility of candida isolates at the American University of Beirut Medical Center

For the first time from Lebanon, the antifungal susceptibility patterns of 70 consecutive clinical candida isolates (each from one patient) representing 48 C. albicans, 12 C. tropicalis, 6 C. parapsilosis, 2 C. kruseii, and 2 C. (Torulopsis) glabrata were studied against amphotericin B (AP), 5-fluorocytosine (FC), ketoconazole (KE), fluconazole (FL), and itraconazole (IT) using the Epsilometer test (E-test; AB Biodisk, Solna, Sweden). The MIC₉₀ (and MIC range, mg/l) determined, at 24 h incubation, for each antifungal agent against C. albicans were: AP 0.032 (≤0.002–0.064), FC 0.75 (0.023–2), KE 0.064 (0.002–>32), FL 2 (0.064–>256), and IT 0.19 (0.012–2), against C. tropicalis were: AP 0.016 (<0.002–0.047), FC 0.125 (0.023–0.19), KE 0.094 (0.012–0.19), FL 2 (0.5–2), and IT 0.5 (0.047–1) and against C. parapsilosis were: AP<0.002 (<0.002–0.002), FC 0.047 (0.003–0.5), KE 0.004 (0.002–0.004), FL 0.125 (0.032–0.19), and IT 0.004 (<0.002–0.004). Based on the NCCLS established MICs breakpoints, resistance was found among C. albicans to FL (MIC ≥6 mg/l) and IT (MIC ≥1 mg/l) in 6 and 4%, respectively, and among C. tropicalis to IT in 17% of the isolates. The susceptibility dependent upon dose (S-DD) was noted only to IT (MIC 0.25–0.5 mg/l) among C. albicans (8%) and C. tropicalis (58%). MICs determination at 48 h incubation were higher, showed more resistance rates and more endpoint trailing particularly with the azoles drugs. The small numbers of C. kruseii and C. glabrata preclude providing meaningful results. Thus, this study indicates that the antifungal susceptibility by E-test can be conveniently incorporated and performed in a hospital-based clinical laboratory. Despite the uniform susceptibility to AP and FC, resistance to azoles drugs is encountered in a range of 4–17% among candida isolates in this country.     

In vitro activity of ceftaroline and comparator antimicrobials against European and Middle East isolates from complicated skin and skin-structure infections collected in 2008-2009

The activities of ceftaroline, the active metabolite of the pro-drug ceftaroline fosamil, a novel anti-meticillin-resistant staphylococcal cephalosporin, and nine comparators were determined against surveillance isolates collected in 2008-2009. Over 3000 isolates associated with complicated skin and skin-structure infections (cSSSIs) were collected from 106 centres in 19 countries. MICs were determined using CLSI broth microdilution methodology. Clonal relatedness of meticillin-resistant Staphylococcus aureus (MRSA) with raised ceftaroline MICs (2mg/L) was assessed by MLST, PFGE and mec typing. The presence of Panton-Valentine leukocidin in these isolates was also determined. Ceftaroline was active against 500 MRSA and 479 meticillin-susceptible S. aureus, with MIC(50/90) values of 0.5/2mg/L and 0.25/0.25mg/L, respectively. For coagulase-negative staphylococci (CoNS), the ceftaroline MIC(50/90) values for meticillin-resistant strains (n=159) were the same as those seen for MRSA. Meticillin-susceptible CoNS (n=113) had the same MIC(90) as that seen with S. aureus, but the MIC(50) was lower at 0.06mg/L. Ceftaroline was also active against β-haemolytic streptococci (n=526; MIC(50/90)=0.004/0.015mg/L), other streptococci (n=75; 0.015/0.06mg/L), common Enterobacteriaceae (n=897; 0.25/≥128mg/L) and Enterococcus faecalis (n=329; 1/16mg/L). Those MRSA with ceftaroline MICs of 2mg/L were found to be from four clonal groups associated with the country of origin. These data confirm the broad-spectrum in vitro activity of ceftaroline against cSSSI pathogens. Ceftaroline is unique among clinically available cephalosporins, having good in vitro activity against MRSA and meticillin-resistant CoNS and moderate activity against Gram-negative bacteria.     

Experimental and clinical trials of BRL 25000 (clavulanic acid-amoxicillin) granules in the field of pediatrics

MICs of BRL 25000, a combination of a newly developed beta-lactamase inhibitor CVA and AMPC in the ratio of 1 to 2, were determined against a number of bacterial strains and compared with those of AMPC, CVA, CEX and CCL. The 98 bacterial strains tested included 2-S. aureus, 23-H. influenzae, 25-E. coli, 22-K. pneumoniae and 26-P. mirabilis. In pharmacokinetic studies, BRL 25000 medium granules were administered to groups of 3 male subjects, aged between 7 years 8 months and 9 years 5 months, at doses of 10, 15 and 20 mg/kg, 2 hours after a meal. The resultant serum and urine concentrations and drug recoveries were measured. Furthermore, BRL 25000 was administered to a total 43 patients (2-pharyngitis, 8-tonsillitis, 3-bronchitis, 2-pneumonia and 28-urinary tract infection) whom clinically evaluable. An average daily dosage of 45.3 mg/kg was given, in 3 or 4 divided doses, for a period of 8 days on average. Clinical and bacteriological effects as well as side effects were studied. In the microbiological studies on 98 clinical strains, including beta-lactamase negative bacteria, BRL 25000 showed MICs against the Gram-positive cocci (2-S. aureus) superior to the other 4 drugs at inoculum sizes of 10(8) and 10(6) cells/ml. For the Gram-negative bacilli, against H. influenzae at inoculum sizes of 10(8) and 10(6) cells/ml, BRL 25000 was inferior in the small MIC range but superior in the large MIC range to AMPC, and was superior to the other 3 drugs. Against E. coli at an inoculum of 10(8) cells/ml, BRL 25000 showed antibacterial activity next to AMPC and CCL whilst at an inoculum of 10(6) cells/ml, it was inferior in the small MIC range but superior in the large MIC range to AMPC and CEX and was inferior to CCL but superior to CVA. Against K. pneumoniae at an inoculum of 10(8) cells/ml, BRL 25000 was equal to AMPC, CVA and CEX but inferior to CCL, whilst at an inoculum of 10(6) cells/ml, it was inferior to CCL but superior to the other 3 drugs. Against P. mirabilis at inoculum sizes of 10(8) and 10(6) cells/ml, BRL 25000 was inferior in the small MIC range but equal or superior in the large MIC range to AMPC, and was superior to CVA and CEX.(ABSTRACT TRUNCATED AT 400 WORDS)     

Occurrence of plasmidic AmpC type beta-lactamase-mediated resistance in Escherichia coli: report from the SENTRY Antimicrobial Surveillance Program (North America, 2004)

Among 1429 Escherichia coli isolates collected as part of the SENTRY Antimicrobial Surveillance Program (2004) from 30 North American medical centres, 65 (4.5%) were screen-positive for an extended-spectrum β-lactamase (ESBL). Among the strains with a negative ESBL confirmatory test (n = 26; clavulanic acid inhibition), a CMY-2 enzyme was detected in 13 isolates (50.0%), FOX-5 in 3 isolates (11.5%) and DHA-1 in 1 isolate (3.8%). These AmpC-producing E. coli were cephamycin (cefoxitin)-resistant but susceptible to cefepime (minimum inhibitory concentration (MIC) ≤0.12–4 mg/L). Clearly, the ESBL tests recommended by the Clinical and Laboratory Standards Institute identify only a fraction of E. coli with elevated β-lactam MIC values as ESBL-producing strains; the majority of the remaining strains would be potentially responsive to some other β-lactams, directed by accurately performed and interpreted susceptibility methods.     

Clonal spread of both oxyimino-cephalosporin- and cefoxitin-resistant Klebsiella pneumoniae isolates co-producing SHV-2a and DHA-1 beta-lactamase at a burns intensive care unit

Over a 1-month period, a total of 16 ceftriaxone- and cefoxitin-resistant Klebsiella pneumoniae isolates were isolated from 15 patients hospitalised at a burns intensive care unit (ICU). These isolates showed negative results for extended-spectrum β-lactamase (ESBL) by the Vitek system and were highly resistant to ceftazidime, aztreonam and cefoxitin (minimum inhibitory concentrations ≥128 μg/mL). The bla_SHV-2a and bla_DHA-1 genes were detected by polymerase chain reaction and sequence analysis. Pulsed-field gel electrophoresis profiles of the isolates were identical. AmpC disk tests for AmpC enzymes as well as double-disk tests and Clinical and Laboratory Standards Institute (CLSI) confirmatory disk tests for ESBLs yielded positive results for all the isolates. However, only three isolates (18.8%) were shown to produce ESBL by CLSI confirmatory tests using broth microdilution. We report the first outbreak of colonisations and infections due to K. pneumoniae isolates co-producing an SHV-2a ESBL and a DHA-1 AmpC β-lactamase in a Korean hospital, which were suggested to represent a single clonal spread at a burns ICU. In addition, this report presents problems associated with ESBL detection using broth microdilution in isolates that co-produce an ESBL and an AmpC β-lactamase.     

环丙沙星和司氟沙星体外诱导肺炎克雷伯菌产生耐药性的研究

目的:了解亲、疏水性氟喹诺酮药物(FQNLs)诱导肺炎克雷伯菌(Kpn)产生耐药性的差异。方法:采用亲水性环丙沙星(CIP)和疏水性司氟沙星(SPFX)对敏感株Kpn909进行分步诱导,并用琼脂平板法测定细菌敏感性。结果:Kpn的耐药性随药物浓度增加而升高。CIP浓度为2×MIC(0·5mg/L)时,诱导菌株MIC较Kpn909升高16倍~32倍,对氧氟沙星、洛美沙星和依诺沙星的MIC分别为8、16、8mg/L;而SPFX获得相同耐药水平菌株的浓度为8×MIC(1mg/L);CIP和SPFX获得耐药株的最大浓度分别为128、64mg/L,细菌对5种FQNLs的MIC分别为≥256mg/L和32~128mg/L。结论:亲水性CIP或疏水性SPFX均可导致Kpn对其它FQNLs产生交叉耐药性;疏水性FQNLs在延缓Kpn产生耐药性方面优于亲水性FQNLs。     

利福霉素等6种抗菌药物对金葡球菌体外抗菌作用比较研究

目的 比较利福霉素、甲氧西林、氟氧头孢、美洛培南、奈替米星、万古霉素对mecA基因阳性和mecA基因阴性的金葡球菌的体外抗菌活性。方法 采用多重PCR方法检测金葡球菌的mecA基因携带情况,采用平皿二倍稀释法进行6种抗菌药物的最低抑菌浓度的测定。结果 6种抗菌药物对mecA 基因阴性的金葡球菌的MIC50和MIC90分别为甲氧西林（2、4mg/L), 利福霉素（0．125、0．25mg/L）,氟氧头孢（0．5、2mg/L）,美洛培南（0．25、0．25mg/L）,奈替米星（2、2mg/L）,万古霉素（2．2mg/L）。对mecA基因阳性的金葡球菌的MIC50和MIC90分别为甲氧西林（＞256、＞256mg/L),利福霉素（0．031、0．031mg/L）,氟氧头隐(32、64mg/L）,美洛培南（64、128mg/L）、奈替米星（32、64mg/L）,万古霉素（4、4mg/L）。结论 6种抗菌药物对mecA基因阴性的金葡球菌均有很强的体外抗菌活性,但对mecA基因阳性且对甲氧西林耐药的金葡球菌,氟氧头孢、美洛培南和奈替米星的体外抗菌活性差,万古霉素和利福霉素具有很强的体外抗菌活性,特别是利福霉素对于MRSS的抗菌活性明显强于MSSA。     

Strategies to overcome extended-spectrum β-lactamases (ESBLs) and AmpC β-lactamases in shigellae

Oral cephalosporins and mecillinam are used to treat Shigella infections, but are compromised by extended-spectrum β-lactamases (ESBLs) and plasmid AmpC β-lactamases. Potential solutions include combining an oral or intravenous cephalosporin with a β-lactamase inhibitor (BLI) or using an oral penem. These strategies were examined using Escherichia coli transconjugants and clinical isolates with ESBLs or AmpC, as a proxy for shigellae. The Clinical and Laboratory Standards Institute agar dilution method was used with inocula of 10(4) and 10(6) colony-forming units/spot. ESBLs conferred resistance to the cephalosporins and mecillinam, at least at high inoculum, although: (i) ceftibuten was significantly compromised only by SHV and CTX-M-15 ESBLs, but not by TEM or CTX-M-9 and -14; (ii) cefdinir was little affected by TEM-type ESBLs, and mecillinam was little affected by CTX-M-9 group enzymes. The BLI clavulanic acid reduced the minimum inhibitory concentrations (MICs) of cephalosporins and mecillinam to ≤2 mg/L for ESBL-producers, even at high inocula; sulbactam in particular and tazobactam were less effective, especially against SHV types. Strains with AmpC were resistant to all cephalosporins±inhibitors, but mecillinam remained active (MIC=1 mg/L) against a strain with AmpC alone, whereas strains with TEM-1+AmpC were susceptible to mecillinam+clavulanic acid at ≤2 mg/L. Faropenem was active against all ESBL- and AmpC-producers at 4 mg/L, with little inoculum effect or inhibitor potentiation. In conclusion, cephalosporin+clavulanic acid combinations overcame ESBLs, with ceftibuten+clavulanic acid being particularly promising. Mecillinam+clavulanic acid and faropenem overcame both ESBLs and AmpC enzymes. Clinical utility will depend also on a drug's ability to reach intracellular shigellae in the intestinal epithelium and this deserves exploration for clavulanic acid and faropenem.     

Resistance determinants in strains of Clostridium difficile from two geographically distinct populations

Ninety-three clinical isolates of Clostridium difficile, comprising 65 from Royal Gwent Hospital, Newport and 28 from Southmead Hospital, Bristol were examined to determine the prevalence of genes coding for macrolide resistance and to explore differences in susceptibility patterns. Antibiogram testing produced similar results for both sets of strains with respect to amoxicillin, tetracycline, erythromycin and cefotaxime. Results differed for rifampicin, where 53% of the Bristol isolates were resistant, compared with 3% of the Newport isolates. Clindamycin disc susceptibility testing produced similar resistance rates. However, clindamycin MIC determinations revealed that 53% of the Bristol strains exhibited high-level resistance (MIC > 256 mg/L), whereas strains from Newport had clindamycin MICs ranging from 0.25 to 3 mg/L. erm (B) was present in 15 of the strains from Bristol and in none of the Newport strains. erm (F) and erm (Q) were not detected in either population. The two geographically distinct populations of C. difficile differed considerably in their susceptibility to antibiotics. The possibility that C. difficile may serve as a conservator for resistant determinants subsequent to exposure to antimicrobial agents, has important implications for infection control.     

Susceptibility of Borrelia afzelii strains to antimicrobial agents

The aim of the present study was to determine the susceptibility of Borrelia afzelii strains to antibiotics, and to test the hypothesis that persistence of borrelia in skin, after therapy, is a consequence of resistance to the antibiotic used for treatment. Ten B. afzelii strains isolated from skin of seven adult patients (two with acrodermatitis chronica atrophicans, five with erythema migrans) were studied. In three patients B. afzelii was isolated from erythema migrans lesion before antibiotic therapy and 2–3 months after treatment with cefuroxime axetil (two patients) or with ceftriaxone (one patient). MICs and MBCs for amoxicillin, azithromycin, ceftriaxone, cefuroxime, doxycycline and amikacin were measured. There was total resistance to amikacin but isolates were susceptible to all other antibiotics except one isolate that was resistant to cefuroxime, MIC >4 mg/L. Comparison of MBC values after 3 and 6 weeks’ incubation revealed comparible results for azithromycin and ceftriaxone while for amoxicillin, cefuroxime and doxycycline, some differences were found. In one of the patients from whom there were borrelia isolated before and after treatment with cefuroxime axetil, both isolates were resistant to cefuroxime. In the other two patients, the paired isolates were susceptible to the antibiotic used for therapy.     

Interpreting streptomycin susceptibility test results for Salmonella enterica serovar Typhimurium

Resistance or susceptibility of Salmonella enterica to streptomycin is widely used as an epidemiological marker. However, there is no clear consensus on the interpretation of streptomycin susceptibility test results. Comparison of results obtained with the Clinical and Laboratory Standards Institute (CLSI) disk diffusion method, the minimum inhibitory concentration (MIC) determined by Etest and streptomycin resistance genotype for 90 isolates of S. enterica serovar Typhimurium suggests that appropriate interpretive criteria for MIC results are susceptible at ≤8 mg/L and resistant at ≥16 mg/L. For CLSI disk diffusion, we propose susceptible at a zone diameter ≥13 mm and resistant at ≤10 mm.     

Involvement of cholinergic system in suppression of formalin-induced inflammatory pain by cobratoxin

Aim:

To investigate the analgesic effect of cobratoxin (CTX), a long-chain α-neurotoxin from Thailand cobra venom, in a rat model of formalin-induced inflammatory pain.

Methods:

Inflammatory pain was induced in SD rats via injecting 5% formalin (50 μL) into the plantar surface of their right hind paw. CTX and other agents were ip administered before formalin injection. The time that the animals spent for licking the injected paw was counted every 5 min for 1 h.

Results:

CTX (25, 34, and 45 μg/kg) exhibited a dose-dependent analgesic effect during the phase 1 (0–15 min) and phase 2 (20–60 min) response induced by formalin. Pretreatment with naloxone (0.5 or 2.5 mg/kg) did not block the analgesic effect of CTX. Pretreatment with atropine at 5 mg/kg, but not at 2.5 mg/kg, antagonized the analgesic effect of CTX. Treatment with the nonselective nAChR antagonist mecamylamine (3 mg/kg) inhibited the analgesic effects of CTX in Phase 1 and Phase 2 responses, while with the selective α7-nAChR antagonist methyllycaconitine (3 mg/kg) antagonized the effect of CTX only in the Phase 1 response. Treatment with the α7-nAChR agonist PNU282987 (3 mg/kg) significantly reduced the formalin-induced phase 2 pain response, but only slightly reduced the Phase 1 pain response.

Conclusion:

The results suggest that CTX exerts an antinociceptive effect in formalin-induced inflammatory pain, which appears to be mediated by mAChR and α7-nAChR.     

Experimental and clinical studies on BRL 25000 (clavulanic acid-amoxicillin) in the pediatric field

Fundamental and clinical studies on BRL 25000 granules were carried out in the pediatric field. BRL 25000 is a formulation comprising 1 part of clavulanic acid (CVA) and 2 parts of amoxicillin (AMPC). The MICs of BRL 25000 and AMPC were assessed against 24 clinically isolated strains of S. aureus (including 23 beta-lactamase producing strains), 22 S. pyogenes, 20 E. coli (8 beta-lactamase producing strains), 24 K. pneumoniae (24 beta-lactamase producing strains), 20 H. influenzae (6 beta-lactamase producing strains). BRL 25000 showed MIC80 (cumulatively 80% of strains were inhibited) at 6.25 micrograms/ml against S. aureus, less than or equal to 0.10 micrograms/ml against inst S. pyogenes, 12.5 micrograms/ml against E. coli, 6.25 micrograms/ml against K. pneumoniae and 0.39 micrograms/ml against H. influenzae. BRL 25000 showed no improvement in MIC terms against beta-lactamase nonproducing strains compared with AMPC. However, BRL 25000 was markedly more effective against beta-lactamase producing strains. Thus BRL 25000 was up to 8 fold more active against S. aureus, 2 to 64 fold against E. coli, 4 to 128 fold against K. pneumoniae, 4 to 16 fold against H. influenzae than AMPC. Following oral administration of BRL 25000 granules (at a dose level of 12.5 mg/kg) to 2 children aged 9 and 11 years, the mean peak serum concentrations of AMPC and CVA were 8.33 +/- 2.43 micrograms/ml and 4.44 +/- 1.65 micrograms/ml respectively 1 hour after dosing. The half-lives of AMPC and CVA were 1.35 +/- 0.42 hours and 0.91 +/- 0.05 hour, respectively. The urinary excretion was 48.21 +/- 3.83% for AMPC and 16.90 +/- 7.06% for CVA in the first 6 hours after administration. In clinical studies, 23 pediatric patients aged 2 months to 12 years with bacterial infections were treated with BRL 25000 granules and the clinical effectiveness, bacteriological response and side effects were evaluated. The clinical response was assessed in 23 cases, 3 with acute rhinitis, 6 with acute purulent tonsillitis, 5 with acute bronchitis, 4 with acute pneumonia, 3 with impetigo, 1 with furunculosis and 1 with periproctal abscess. Results were excellent in 13 cases, good in 7, fair in 3 and hence the efficacy rate (excellent and good cases) was 87.0% (20/23). In particular the clinical response in 9 cases with infections due to beta-lactamase producing organisms was excellent in 6, good in 2, fair in 1 and the efficacy rate was 88.9% (8/9).(ABSTRACT TRUNCATED AT 400 WORDS)     

Antimicrobial susceptibility of well-characterised multiresistant CTX-M-producing Escherichia coli: failure of automated systems to detect resistance to piperacillin/tazobactam

This study was designed to determine the in vitro activities of several antimicrobial agents against well-characterised CTX-M-producing Escherichia coli strains isolated from clinical specimens. Minimum inhibitory concentrations (MICs) were determined for 202 extended-spectrum beta-lactamase (ESBL)-producing E. coli using microbroth dilution and Vitek methods according to Clinical and Laboratory Standards Institute criteria. Molecular characterisation was performed using isoelectric focusing and polymerase chain reaction (PCR) with sequencing, whilst strain relatedness was determined by pulsed-field gel electrophoresis (PFGE) using XbaI. Of the 202 ESBL-producing E. coli, 2 produced VEB-1, 12 produced TEM-52, 32 produced SHV types (including SHV-2 and -12) and 156 produced CTX-M types (including CTX-M-2, -3, -14, -15, -24, -27 and -30). The MIC(50) and MIC(90) (MIC for 50% and 90% of the organisms, respectively) for the antimicrobial agents tested were, respectively: piperacillin/tazobactam (TZP), 32mg/L and >256mg/L; ciprofloxacin, 16mg/L and 32mg/L; gentamicin, 8mg/L and 128mg/L; amikacin, 2mg/L and 16mg/L; ertapenem, 0.03mg/L and 0.12mg/L; imipenem, 0.03mg/L and 0.12mg/L; meropenem, 0.03mg/L and 0.03mg/L; and tigecycline 0.12mg/L and 0.5mg/L. Vitek Legacy and Vitek 2 failed to detect TZP resistance in 91 (90%) and 75 (74%) of 101 TZP-resistant ESBL-producing strains, respectively, especially CTX-M-15-producing isolates that co-produced OXA-1. The carbapenems, amikacin and tigecycline had good in vitro activities against multiresistant CTX-M-producing E. coli. We recommend that laboratories using Vitek should employ alternative susceptibility testing methods for TZP before reporting the activity of this agent against ESBL-producing E. coli.     

Intrapulmonary pharmacokinetics and pharmacodynamics of meropenem

The objective of this study was to determine the plasma and intrapulmonary pharmacokinetic parameters of intravenously administered meropenem in healthy volunteers. Four doses of 0.5 g, 1.0 g or 2.0 g meropenem were administered intravenously to 20, 20 and 8 healthy adult subjects, respectively. Standardised bronchoscopy and timed bronchoalveolar lavage (BAL) were performed following administration of the last dose. Blood was obtained for drug assay prior to drug administration and at the time of BAL. Meropenem was measured in plasma, BAL fluid and alveolar cells (ACs) using a combined high pressure liquid chromatographic–mass spectrometric technique. Plasma, epithelial lining fluid (ELF) and AC pharmacokinetics were derived using non-compartmental methods. C_max/MIC₉₀ (where C_max is the maximum plasma concentration and MIC₉₀ is the minimum inhibitory concentration required to inhibit 90% of the pathogen), AUC/MIC₉₀ (where AUC is the area under the curve for the mean concentration–time data), intrapulmonary drug exposure ratios and percent time above MIC₉₀ during the dosing interval (%T > MIC₉₀) were calculated for common respiratory pathogens with MIC₉₀ values of 0.12–4 μg/mL. In the 0.5 g dose group, the C_max (mean ± S.D.), AUC_0–8 h and half-life for plasma were, respectively, 25.8 ± 5.8 μg/mL, 28.57 μg h/mL and 0.77 h; for ELF the values were 5.3 ± 2.5 μg/mL, 12.27 μg h/mL and 1.51 h; and for ACs the values were 1.0 ± 0.5 μg/mL, 4.30 μg h/mL and 2.61 h. In the 1.0 g dose group, the C_max, AUC_0–8 h and half-life for plasma were, respectively, 53.5 ± 19.7 μg/mL, 55.49 μg h/mL and 1.31 h; for ELF the values were 7.7 ± 3.1 μg/mL, 15.34 μg h/mL and 0.95 h; and for ACs the values were 5.0 ± 3.4 μg/mL, 14.07 μg h/mL and 2.17 h. In the 2.0 g dose group, the C_max, AUC_0–8 h and half-life for plasma were, respectively 131.7 ± 18.2 μg/mL, 156.7 μg h/mL and 0.89 h. The time above MIC in plasma ranged between 28% and 78% for the 0.5 g dose and between 45% and 100% for the 1.0 g and 2.0 g doses. In ELF, the time above MIC ranged from 18% to 100% for the 0.5 g dose and from 25% to 88% for the 1.0 g dose. In ACs, the time above MIC ranged from 0% to 100% for the 0.5 g dose and from 24% to 100% for the 1.0 g dose. Time above MIC in ELF and ACs for the 2.0 g dose was not calculated because of sample degradation. The prolonged T > MIC₉₀ and high intrapulmonary drug concentrations following every 8 h administration of 0.5–2.0 g doses of meropenem are favourable for the treatment of common respiratory pathogens.