Lifen Hu

In vivo activity of daptomycin/colistin combination therapy in a Galleria mellonella model of Acinetobacter baumannii infection

Antimicrobial treatment of multidrug-resistant Acinetobacter baumannii (MDR-AB) infections continues to pose significant challenges. With limited options, clinicians have been pushed towards using unorthodox combinations of licensed antibiotics. Although daptomycin/colistin combination appears to be a promising treatment option based on in vitro data, further preclinical work is needed. In this study, the A. baumannii-Galleria mellonella system was employed to study the in vivo efficacy of this combination in order to determine whether it should be explored further for the treatment of MDR-AB infections. The antimicrobial activity of colistin alone and in combination with daptomycin was assessed versus an A. baumannii type strain (ATCC 19606) and a MDR-AB clinical strain (GN2231) isolated in Anhui, China. Synergy studies were performed using the microtitre plate chequerboard assay and time-kill methodology. The in vivo activity of daptomycin/colistin combination was assessed using a G. mellonella larvae model. The combination of daptomycin and colistin was bactericidal against both strains tested. In chequerboard assays, daptomycin was highly active against A. baumannii when combined with colistin [fractional inhibitory concentration index (FICI) of <0.5]. Treatment of G. mellonella larvae infected with lethal doses of A. baumannii resulted in significantly enhanced survival rates when daptomycin was given with colistin compared with colistin treatment alone (P<0.05). This work suggests that daptomycin/colistin combination is highly active against A. baumannii both in vitro and in a simple invertebrate model of infection.

Surveillance of antimicrobial susceptibility patterns among Shigella species isolated in China during the 7-year period of 2005-2011.

Background Shigella is a frequent cause of bacterial dysentery in the developing world. Treatment with antibiotics is recommended for shigellosis, but the options are limited due to globally emerging resistance. This study was conducted to determine the frequency and pattern of antimicrobial susceptibility of Shigella in China. Methods We studied the antimicrobial resistance profiles of 308 Shigella spp. strains (260 S. flexneri, 40 S. sonnei, 5 S. boydii, and 3 S. dysenteriae) isolated from fecal samples of patients (age, from 3 months to 92 yr) presenting with diarrhea in different districts of Anhui, China. The antimicrobial resistance of strains was determined by the agar dilution method according to the CSLI guidelines. Results The most common serogroup in the Shigella isolates was S. flexneri (n=260, 84.4%), followed by S. sonnei (n=40, 13.0%). The highest resistance rate was found for nalidixic acid (96.4%), followed by ampicillin (93.2%), tetracycline (90.9%), and trimethoprim/sulfamethoxazole (80.8%). Among the isolates tested, 280 (91.0%) were multidrug resistant (resistant to ≥2 agents). The most common resistance pattern was the combination of ampicillin, tetracycline, and trimethoprim/sulfamethoxazole (70.8%). Resistance to ampicillin and tetracycline were more common among S. flexneri than among S. sonnei isolates. Conclusions S. flexneri is predominant in Anhui, China, and its higher antimicrobial resistance rate compared with that of S. sonnei is a cause for concern. Continuous monitoring of resistance patterns is necessary to control the spread of resistance in Shigella. The recommendations for antimicrobial treatment must be updated regularly based on surveillance results.

Increase in the Prevalence of Resistance Determinants to Trimethoprim/Sulfamethoxazole in Clinical Stenotrophomonas maltophilia Isolates in China

Aims This study was carried to reveal the genetic mechanisms of trimethoprim/sulfamethoxazole (SXT) resistance. Methods Among 300 clinical Stenotrophomonas maltophilia isolates from China, resistance determinants such as sul and dfrA genes, integrons and transposase were examined using PCR, DNA sequencing and thermal asymmetric interlaced PCR (TAIL-PCR). Data were analyzed using SPSS 20.0. Results Of the 300 isolates, 116 (38.7%) were resistant to SXT. An alarming trend of increased resistance to SXT were found over the 10-year period. The positive rates of sul and class 1 integrase (intI1) increased gradually with the development of SXT resistance over the 10-year period. Multiple logistic regression analyses indicated that the genes of qacEΔ1-sul1 (81% vs 46.2%, p = 0.000), sul2 (50.9% vs 9.8%, p = 0.000), intI1 (83.6% vs 65.8%, p = 0.000), dfrA12 (25% vs 3.3%, p = 0.000), dfrA17 (15.5% vs 3.8%, p = 0.000) and dfrA27 (4.3% vs 1.6%, p = 0.01) were more prevalent in SXT-resistant isolates than SXT-susceptible isolates except dfrA1(p = 0.83) and dfrA5(p = 0.18). Sequencing data revealed 12 types of resistance gene cassettes (aar-3-dfrA27, dfrA12–aadA2, dfrA17–aadA5, cmlA1, aacA4, aadA5, arr-3-aacA4, aadA1, aadB–aadA4, aacA4–catB8–aadA1, aadB–aac(6′)-II–blaCARB-8 and aac(6′)-II–blaCARB-8) located in the class 1 integron in 163 isolates (87% SXT-resistant vs 33.7% SXT-susceptible isolates, p = 0.000). A novel finding was the aar-3-dfrA27 (KC748137) gene cassette. The gene of sul2 linked to transposase in 50 SXT- resistant and 7 SXT- susceptible isolates was detected by TAIL-PCR. Conclusions The findings demonstrated a higher prevalence of sul, dfrA, intI1 and resistance gene cassettes in class 1 integron in SXT-resistant clinical S. maltophilia isolates in China. The sul1 and dfrA genes located in integrons and the sul2 linked to transposase may imply wide and rapid dissemination of resistance gene in bacteria.

Detection of plasmid-mediated quinolone resistance determinants and the emergence of multidrug resistance in clinical isolates of Shigella in SiXian area, China

A total of 123 Shigella isolates were collected from SiXian area in Anhui, China. Screening was carried out by polymerase chain reaction (PCR) amplification of plasmid-mediated quinolone resistance (PMQR) determinants. Different β-blactamases genes, plasmid-borne bla(AmpC), 16S rRNA methylase genes, integrons, and mutations in quinolone resistance-determining regions were analysed by PCR for the PMQR-positive isolates.

Plasmid-Mediated Quinolone Resistance in Extended-Spectrum-β-Lactamase- and AmpC β-Lactamase-Producing Serratia marcescens in China

ABSTRACT We investigated the prevalence of plasmid-mediated quinolone resistance (PMQR) determinants and examined the association of these determinants with extended-spectrum β-lactamases (ESBLs) and/or plasmid-mediated AmpC β-lactamases (pAmpCs) in Serratia marcescens isolates in China. In this study, the presence of PMQR determinants was significantly related to the coproduction of ESBLs and/or pAmpCs (CTX-M-14, SHV-5, DHA-1, and ACT-1), among which CTX-M-14 was the most common gene type.

In vivo activity of vancomycin combined with colistin against multidrug-resistant strains of Acinetobacter baumannii in a Galleria mellonella model.

Abstract Background: With increasing antibiotic resistance, the selection of effective treatment of A. baumannii infections is particularly challenging. Methods: This study assessed the activities of the combination of vancomycin and colistin combination in vitro and in vivo using a Galleria mellonella model against four colistin-susceptible or colistin-resistant A. baumannii strains. Results: In checkerboard assays, synergy was observed between vancomycin and colistin for all four strains tested (0.156 ≤ Fractional inhibitory concentration indices [FICI] ≤ 0.281). In time-kill assays, the combination showed continued bactericidal activity and synergy after 24 h for colistin-susceptible strains. For colistin-resistant strains, the combination resulted in bactericidal activity within 8 h, but sustained bacterial re-growth was then observed. Treatment of G. mellonella larvae infected with lethal doses of A. baumannii (except 19606R) resulted in significantly increased survival rates when vancomycin was given with colistin compared to colistin treatment alone (p < 0.05). Conclusions: These findings suggest that regimens containing vancomycin may be useful for infections due to multidrug-resistant Acinetobacter baumannii.

Comparative study of the mutant prevention concentrations of vancomycin alone and in combination with levofloxacin, rifampicin and fosfomycin against methicillin-resistant Staphylococcus epidermidis

No mutant-prevention concentration (MPC) with methicillin-resistant Staphylococcus epidermidis (MRSE) has been reported. The study aimed to evaluate the propensity of vancomycin individually and in combination to prevent MRSE from mutation. A total of 10 MRSE clinical isolates were included in the study. Susceptibility testing demonstrated that the susceptibility rates to vancomycin, rifampicin, levofloxacin and fosfomycin were 100, 100, 50 and 90%, respectively. The fractional inhibition concentration indices (FICI) for vancomycin combined with rifampicin, levofloxacin or fosfomycin were ⩾1.5 but ⩽2, ⩾1.5 but ⩽2, and >0.5 but ⩽1.5, respectively, implying indifferent interactivity. The MPC with susceptible strains was determined to be the lowest antibiotic concentration inhibiting visible growth among 1010 CFU on four agar plates (9 cm in diameter) after a 72-h incubation at 37 °C. The MPCs were 16∼32, >64, ⩾64 and 4∼16 μg ml−1 for vancomycin, rifampicin, fosfomycin and levofloxacin, respectively. The vancomycin MPCs of combinations with fosfomycin (32 μg ml−1), levofloxacin (2 μg ml−1) and rifampicin (2 or 4 μg ml−1) were 1∼4, 16∼32 and 16∼32 μg ml−1, respectively. Against mutants selected by vancomycin, rifampicin, levofloxacin and fosfomycin individually, antibiotics had standard MICs of 2∼4 μg ml−1 for vancomycin, >64 μg ml−1 for rifampicin, 4∼8 μg ml−1 for levofloxacin and ⩾64 μg ml−1 for fosfomycin. Thus single-step mutation can lead to resistance of MRSE to rifampicin, levofloxacin and fosfomycin, rather than non-susceptibility to vancomycin. Vancomycin–fosfomycin combination might be a superior alternative to vancomycin in blocking the growth of MRSE mutants, especially for high-organism-burden infections.

Prevalence of plasmid-mediated quinolone resistance determinants in association with β-lactamases, 16S rRNA methylase genes and integrons amongst clinical isolates of Shigella flexneri.

Shigellosis remains a public health concern throughout the world (Kotloff et al., 1999). However, the emergence of multidrug resistance (MDR) amongst clinical isolates has made the selection of effective antimicrobial therapy more difficult (Niyogi, 2007). Quinolones are among the most important antibacterial agents used extensively for the treatment of shigellosis. Recently, quinolone resistance has been rising among Shigella isolates (Xiong et al., 2010). Quinolone resistance mainly results from chromosomal mutations in the quinolone resistance-determining regions (QRDRs) of DNA gyrase and topoisomerase IV (Dutta et al., 2005). However, since 1998, three kinds of plasmid-mediated quinolone resistance (PMQR) determinants have been described: Qnr, Aac(69)-Ib-cr and QepA. These mechanisms are prevalent amongst common clinical isolates and have been detected conferring low-level resistance to quinolones (Cattoir & Nordmann, 2009). Co-existence of resistance genes, such as blactamase genes, 16S rRNA methylase genes and integrons, on the same plasmid could, in part, explain the appearance of MDR strains. These responsible genes are primarily located on transferable plasmids and could enhance the acquisition and dissemination of antimicrobial resistance genes by horizontal transfer (Luo et al., 2011; Hu et al., 2011). We investigated the prevalence of PMQR determinants in clinical isolates of Shigella flexneri, and assessed the relatedness of b-lactamase genes, 16S rRNA methylase genes and integrons with PMQR determinants within the same strain.

Detection of the plasmid-mediated quinolone resistance determinants in clinical isolates of Acinetobacter baumannii in China

We examined the prevalence of plasmid–mediated quinolone resistance (PMQR) determinants among Acinetobacter baumannii in Anhui, China. And β–lactamase genes and mutations in quinolone resistance–determining regions (QRDRs) were also investigated among the PMQR-positive isolates. Among the 39 A. baumannii isolates, 3 (7.7%) isolates harbored qnrB and 1 (2.6%) harbored qnrS. Mutations in the QRDRs of gyrA were identified in 2 isolates amongst the 4 PMQR-positive isolates. Quinolone resistance could be transferred by conjugation from all 4 PMQR-positive donors. In conclusion, more attention should be taken to prevent the transmission of PMQR genes among A. baumannii.

Susceptibility of Stenotrophomonas maltophilia clinical strains in China to antimicrobial combinations

Abstract We aimed to investigate the activity levels of several combinations of antimicrobials against Stenotrophomonas maltophilia. In this study, the antimicrobial susceptibility of S. maltophilia clinical isolates was determined, and the synergistic activity of three pairs of antimicrobial combinations was evaluated by the fractional inhibitory concentration index (FICI). The antimicrobial susceptibility in vitro against 83 S. maltophilia strains was greater for minocycline (80·7%) than for trimethoprim–sulfamethoxazole (51·8%), and levofloxacin (50·6%). The rate of resistance was highest for ticarcillin–clavulanate and ceftazidime (63·8%) and resistance to trimethoprim–sulfamethoxazole (TMP–SMX) was 48·2%. All three combinations were tested against susceptible isolates. Two of the combinations, TMP–SMX+ceftazidime and levofloxacin+ceftazidime were more effective than the combination of TMP–SMX+levofloxacin. We recommend acquiring more clinical data in order to explore combination therapy, which is a promising treatment of S. maltophilia infections.