Β-Lactam resistance in Streptococcus mitis isolated from saliva of healthy subjects

The purpose of this study was to examine the percentage of -lactam-resistant streptococcal carriers in healthy adults, and to investigate the relationships among minimum inhibitory concentrations (MICs) of -lactams, alterations in the penicillin-binding protein genes (pbp genes), and the affinity of penicillin-binding proteins (PBPs) for ampicillin (ABPC) in Streptococcus mitis. We also compared numbers of surviving bacteria at various ABPC concentrations in both ABPC-susceptible and -resistant S. mitis strains. The percentages of subjects carrying ABPC- and cefaclor (CCL)-resistant streptococci were 52% (27 of 52 subjects) and 100%, respectively. S. mitis, including both antibiotic-susceptible and -resistant strains, were classified into five groups according to the pbp gene mutations that resulted in alterations of the deduced amino-acid sequence in the homology boxes of PBPs. All ABPC-resistant strains showed alterations in PBP1A, 2X, and 2B, while no or only PBP2X alterations were detected in the susceptible strains. These results suggest that the accumulation of pbp gene mutations is strongly related to the MIC of ABPC for S. mitis. In the resistant strains, the affinity of PBPs for ABPC was reduced in comparison with that in the susceptible strains, and the bactericidal effect of ABPC was also reduced. Therefore, we should be aware of conditions such as infective endocarditis that are caused by -lactam-nonsusceptible streptococci in the normal oral flora.     

放射性碘标记羟氨苄青霉素用于青霉素结合蛋白的研究

本文报道用放射性~(125)碘对羟氨苄青霉素进行标记后用于青霉素结合蛋白(PBPs)的研究。结果表明:~(125)I-羟氨苄青霉素能较好地与细菌内膜上所有的青霉素结合蛋白结合。进行竞争性结合实验,头孢噻肟的主要靶位是PBP_3,Mecillinam的主要靶位是PBP_2。我们建立的青霉素结合蛋白的测定方法,关键性的材料价廉易得,具有简便、快速、经济等优点,是一个值得继续开发和研究的新途径。     

苯唑西林对金葡球菌ATCC25923青霉素结合蛋白亲和力研究

利用十二烷基硫酸钠—聚丙烯酰胺凝胶电泳、荧光放射自显影术及竞争分析法检测苯唑西林对金葡球菌ＡＴＣＣ２５９２３青霉素结合蛋白的亲和力。结果发现金葡球菌有５条青霉素结合蛋白，即ＰＢＰ１、ＰＢＰ２、ＰＢＰ３、ＰＢＰ４、ＰＢＰ５，分子量范围４１～８７ｋＤ。苯唑西林主要与金葡球菌ＡＴＣＣ２５９２３的ＰＢＰ１和ＰＢＰ２亲和力强，尤其是与ＰＢＰ２亲和力很强。由此说明金葡球菌的ＰＢＰ１和ＰＢＰ２是苯唑西林的主要作用靶位。     

放射性125碘标记阿莫西林研究临床分离MRSA青霉素结合蛋白

目的本文以放射性125碘标记阿莫西林研究临床分离MRSA青霉素结合蛋白(PBPs),探讨高耐药及低耐药不产酶MRSA青霉素结合蛋白的改变.方法用125Ⅰ-阿莫西林与ATCC25923、临床分离MRSA及MSSA结合,SDS-PAGE分离检测PBPs的改变.结果SDS-PAGE分离检测PBPs,高耐药株在78KDa处有放射性,低耐药株放射性低于敏感株.结论125Ⅰ-阿莫西林与MRSA结合降低,高耐药株产生低亲和力的PBP2a,低耐药株PBPs与阿莫西林结合下降.     

碳青霉烯诱导对多重耐药鲍曼不动杆菌青霉素结合蛋白编码基因表达的影响

目的 探讨碳青霉烯诱导对多重耐药鲍曼不动杆菌(MDR-AB)青霉素结合蛋白(PBPs)编码基因表达的影响。方法 收集2018年6月至2018年12月成都市郫都区人民医院临床分离的19株MDR-AB菌株,聚合酶链式反应(PCR)扩增所有菌株7种PBPs 基因。分别用1 mg/L浓度的亚胺培南、美罗培南、多尼培南对菌株进行诱导处理,对照组为未加任何抗生素的空白组。实时定量荧光PCR(qRT-PCR)检测7种PBPs基因的表达情况,采用相对定量(2^-△△Ct)法比较碳青霉烯诱导后MDR-AB的7种PBPs基因表达量与对照组的差异。结果 19株MDR-AB均携带7种PBPs基因,其中1 mg/L亚胺培南诱导后MDR-AB中pbp1a,pbp2,pbp3,pbp7基因相对表达量分别为(0.41±0.12)、(0.55±0.25)、(0.55±0.46)、(0.62±0.39),与对照组相比基因表达水平下降,差异有统计学意义(P<0.05),pbp1b,pbp5/6,pbp6基因相对表达量分别为(4.31±0.54)、(5.63±1.42)、(8.98±1.14),基因表达水平上调(P<0.05),1 mg/L美罗培南诱导后MDR-AB中pbp2,pbp3基因表达下调,分别为(0.60±0.21)、(0.54±0.47),与对照组比较差异有统计学意义(P<0.05),pbp1b,pbp5/6,pbp6基因相对表达量分别为(2.78±0.21)、(5.66±0.89)、(11.10±1.02),与对照组相比上调,差异有统计学意义(P<0.05),1 mg/L多尼培南诱导后pbp7基因相对表达量为(0.51±0.42),与对照组相比基因表达下降,差异有统计学意义(P<0.05),pbp1b,pbp5/6,pbp6基因相对表达量分别为(7.18±1.20)、(11.66±1.82)、(10.12±0.87),与对照组相比基因表达上调,差异有统计学意义(P<0.05)。结论 MDR-AB普遍携带PBPs基因,亚最小抑菌浓度(MIC)的碳青霉烯诱导可导致MDR-AB的PBPs编码基因表达明显变化。     

In vitro and in vivo antipseudomonal activity, acute toxicity, and mode of action of a newly synthesized fluoroquinolonyl ampicillin derivative

Compounds N-(6,7-difluoroquinolonyl)-ampicillin (AU-1) and N-(6-fluoroquinolonyl)-ampicillin (FQ-1), synthesized by coupling of the carboxyl group of 6,7-difluoroquinolone (FP-3) and 6-fluoroquinolone (FP4), respectively, with the α-amino-group of ampicillin side chain, exhibit antipseudomonal activity similar to and lower acute toxicity than that of norfloxacin, whereas neither ampicillin nor the fluoroquinolone moieties, compound FP-3 or FP4, alone have such activity. Also, AU-1 and FQ-1 are active against tested clinical isolates of Pseudomonas aeruginosa that are highly resistant to norfloxacin, gentamicin, or both. The therapeutic efficacies of FQ-1 and norfloxacin were assessed and compared in neutropenic mice infected with a 90% lethal dose of P aeruginosa. Mice intraperitoneally administered FQ-1 (10 mg/kg) 4, 8, 24, and 48 hours after infection had survival rates as high as 80%, comparable to those of mice treated with norfloxacin at the same dosage and dosing schedule. The study of protoplast formation revealed that FQ-1 did not inhibit cell-wall biosynthesis but did induce cell filamentation of Bacillus subtilis at a level close to its minimal inhibition concentration. Both AU-1 and FQ-1 were able to intercalate into the double-stranded DNA. However, that FQ-1 lost such activity after it was treated with penicillinase suggests that the lactam-ring structure in ampicillin moiety of FQ-1 was hydrolyzed by penicillinase and that the hydrolyzed structure of FQ-1 does not own DNA-intercalation activity.