LXA-1: a new plasmid-mediated β-lactamase giving low-level resistance

Abstract LXA-1, a novel plasmid-mediated β-lactamase, was observed in clinical isolates of Klebsiella oxytoca, Klebsiella pneumoniae, Citrobacter freundii and Enterobacter cloacae . All the strains additionally produced TEM-1 β-lactamase. LXA-1 had an M _r of 24 000 and a pI of 6.7. It hydrolysed benzyl-penicillin, ampicillin, carbenicillin and first generation cephalosporins, but not methicillin, oxacillin or cefotaxime. Clavulanate and cloxacillin were inhibitors. Studies of one of the E. cloacae isolates showed that LXA-1 was encoded by a 41-MDa IncFII plasmid distinct from that encoding TEM-1 enzyme in the strain. Transconjugants which acquired LXA-1 production, but not TEM-1, exhibited only low-level resistance to substrate β-lactams.     

Insecticidal bacterium isolated from an ant lion larva from Munakata,Japan

Twenty bacteria were isolated from four ant lion larvae. The isolates were classified into three groups by biological characteristics. Since Group I, Group II and Group III were isolated from individual larvae Kuo1, Kuo3, 4 and Kuo2, respectively, with exception of one isolate Kuo2‐1, each ant lion tested had its own dominant bacterial flora. Groups I and II were closer to Serratia liquefaciens and Enterobacter cloacae, respectively, whereas Group III could not be identified by the test used. The phylogenetic analysis of GroEL amino acid sequences revealed that Group I, II and III were related to those of Serratia spp., E. cloacae and Salmonella spp. –Escherichia/Shigella spp., respectively. Among these groups, Group I was highly virulent against Bombyx mori and Periplaneta americana, and caused 100% mortality within 24 h. The other two groups (Group II and III) were avirulent to these insect species. The culture filtrate of Group I caused killing activity to B. mori larvae and the insecticidal substance was purified from culture filtrate of Group I bacterium. Since the insecticidal activity highly correlated with proteolytic activity in the chromatographies, Group I bacterium may secret insecticidal proteinase in vitro.     

Characterisation of local isolates of Enterobacteriaceae from Turkey

20 local isolates of enterics belonging to the genera Salmonella, Enterobacter, Proteus, Citrobacter from human, chicken and/or egg were characterised for their antibiotic resistance patterns, plasmid profiles, phage types, outer membrane proteins, and lipopolysaccharide patterns. Relatedness of these characteristics for epidemiological analysis was assessed. 18 (90%) strains were resistant to at least one antibiotic and those (multi-drug resistant ones) resisting to two or more antibiotics constituted 50% of all isolates. A common 54 kb plasmid was harboured by 55% of the isolates. 14 isolates showed smooth type lipopolysaccharide. 60% of the 20 isolates contained outer membrane proteins in a molecular weight range of 34.6 to 30.6 kDa. The data reveal the lack of correlation between the characteristics investigated.     

Enterobacteriaceae facilitate the anaerobic degradation of glucose by a forest soil

Anoxic micro zones that occur in soil aggregates of oxic soils may be temporarily extended after rainfall and thus facilitate the anaerobic degradation of organic compounds in soils. The microbial degradation of glucose by anoxic slurries of a forest soil yielded acetate, CO₂, H₂, succinate, and ethanol, products indicative of mixed acid fermentation. Prokaryotes involved in this process were identified by time-resolved 16S rRNA gene-targeted stable isotope probing with [¹³C-U]-glucose. All labeled phylotypes from the ¹³C-enriched 16S rRNA gene were most closely related to Rahnella and Ewingella , enterobacterial genera known to catalyze mixed acid fermentation. These results indicate that facultative aerobes, in particular Enterobacteriaceae , (1) can outcompete obligate anaerobes when conditions become anoxic in forest soils and (2) may be involved in the initial decomposition of monosaccharides in anoxic micro zones of aerated forest soils.     

Characterization of conjugative plasmids carrying antibiotic resistance genes encoding 16S rRNA methylase, extended-spectrum beta-lactamase, and/or plasmid-mediated AmpC beta-lactamase

In this study, we identified extended-spectrum β-lactamase (ESBL) and plasmid-mediated AmpC β-lactamase which were associated with 16S rRNA methylase gene on the conjugative plasmid. Among 82 clinical isolates of Enterobacteriaceae that carry 16S rRNA methylase gene (64 strains, armA, and 18 strains, rmtB), bla _SHV-12 was detected either alone or combined with bla _DHA-1, bla _CTX-M-3, and bla _CTX-M-14 in 30 strains carrying armA and 6 strains carrying rmtB. The bla _CTX-M-3 was detected in 13 of 64 strains carrying armA but no strains carrying rmtB. Whereas bla _CTX-M-14 was detected in 15 of 18 strains carrying rmtB but only 2 of 64 strains carrying armA. Overall, bla _SHV-12 and bla _CTX-M-14 was the most common ESBL gene which was associated with armA and rmtB, respectively. In addition, we found that bla _CTX-M-3 localized with armA on the same IncL/M plasmid and bla _CTX-M-14 localized with rmtB on the same IncA/C plasmid. Restriction fragment length polymorphism of conjugative plasmids and pulsed-field gel electrophoresis of genomic DNAs revealed that intercellular horizontal transfer of conjugative plasmid and clonal transmission have been occurred at the same time.     

Heat resistance of coliform species isolated from cooked ham, snail flesh, and 'bouchées à la reine'

AIMS: In this study, the heat resistance of coliform species isolated from cooked ham and ready-made meals was determined. METHODS AND RESULTS: Thirteen coliform strains belonging to 12 different species were studied using laboratory medium in order to determine delta (first decimal reduction time) and z(T) values (temperature increase leading to a 10-fold reduction of delta) using the Weibull model. For seven strains, delta-values were determined at temperatures ranging from 55 to 60 degrees C, with, delta values between 0.52 and 2.98 min, at 59 degrees C. For the other six strains, lower temperature values were determined with delta-values ranging from 0.47 to 1.64 min at 54 degrees C. z(T) values calculated for the 13 strains were 3.1 to 7.5 degrees C. For eight strains, plotting of the log of survivors was not linear but rather showed shoulders or shoulders and tails. CONCLUSIONS: Coliform species were sensitive to heat treatment with a decimal reduction time under 2 min at 60 degrees C. SIGNIFICANCE AND IMPACT OF THE STUDY: The better knowledge of coliform heat resistance by determining thermal resistance parameters with confidence intervals will be useful for evaluating the efficiency of industrial thermal processes.     

Outer membrane lipoprotein Lpp is Gram-negative bacterial cell surface receptor for cationic antimicrobial peptides

Antimicrobial peptides/proteins (AMPs) are important components of the host innate defense mechanisms. Here we demonstrate that the outer membrane lipoprotein, Lpp, of Enterobacteriaceae interacts with and promotes susceptibility to the bactericidal activities of AMPs. The oligomeric Lpp was specifically recognized by several cationic α-helical AMPs, including SMAP-29, CAP-18, and LL-37; AMP-mediated bactericidal activities were blocked by anti-Lpp antibody blocking. Blebbing of the outer membrane and increase in membrane permeability occurred in association with the coordinate internalization of Lpp and AMP. Interestingly, the specific binding of AMP to Lpp was resistant to divalent cations and salts, which were able to inhibit the bactericidal activities of some AMPs. Furthermore, using His-tagged Lpp as a ligand, we retrieved several characterized AMPs, including SMAP-29 and hRNase 7, from a peptide library containing crude mammalian cell lysates. Overall, this study explores a new mechanism and target of antimicrobial activity and provides a novel method for screening of antimicrobials for use against drug-resistant bacteria.     

《碳青霉烯耐药革兰阴性杆菌感染预防与控制技术指引》解读

细菌耐药是全球关注的公共卫生问题,给人类健康、发展和安全造成根本性威胁。因此采取积极有效的控制策略和措施、预防和控制多重耐药菌感染的发生与传播具有现实紧迫性,势在必行。近期,中华预防医学会医院感染控制分会、中华医学会感染病学分会、中国医院协会医院感染管理专业委员会、中国老年医学学会感染管理质量控制分会、中华护理学会医院感染管理专业委员会、国家医院感染管理专业质控中心联合发布了《碳青霉烯耐药革兰阴性杆菌感染预防与控制技术指引》(下文简称《指引》),对碳青霉烯耐药革兰阴性杆菌的医院感染精准防控提出了建议,内容包括集束化措施、合理使用抗菌药物、手卫生、主动监测、接触预防、患者隔离和环境清洁消毒。为更好地理解和落实《指引》,本文对其进行解读,期望对临床工作有一定的指导作用。     

医院肺炎克雷伯菌耐药及分子流行病学特征研究

摘要 目的：了解医院肺炎克雷伯菌的耐药及分子流行特点,分析其基因同源性,为医院感染控制提供实验室依据。方法：收集2017年10月-2018年12月医院分离的耐碳青霉烯类肺炎克雷伯菌和碳青霉烯类敏感肺炎克雷伯菌,用梅里埃VITEK 2 Compact 全自动微生物分析系统进行细菌鉴定和药敏分析,K-B法药敏予以补充;采用赛沛Xpert?Carba-R试剂盒检测耐碳青霉烯类肺炎克雷伯菌碳青霉烯耐药基因;采用多位点序列分析技术检测菌株7个管家基因型别及其ST型别,使用eBURST软件对ST数据进行亲缘性关系分析。结果：共分离到63株耐碳青霉烯类肺炎克雷伯菌和211株碳青霉烯类敏感肺炎克雷伯菌（随机选取30株作研究）;耐药组对青霉素类、大环内酯类、头孢菌素类、喹诺酮类、含酶抑制剂类、四环素类耐药率显著高于敏感组;63株耐药株中,96.83%（61/63）产KPC酶,1.59%（1/63）产KPC酶和NDM酶,1.59%（1/63）未检测到5种碳青霉烯酶基因;耐碳青霉烯类组获得8个ST型别,包括ST11（54/63,85.71%）、ST15（2/63,3.17%）、ST392（2/63,3.17%）、ST45（1/63,1.59%）、ST147（1/63,1.59%）,ST659（1/63,1.59%）、ST3228（1/63,1.59%）、STr1（1/63,1.59%）,STr1为新发现型别,属于克隆复合体11;30株碳青霉烯敏感组获得25个ST型别,包括ST35（3/30,10.00%）,ST659（3/30,10.00%）,ST147（2/30,6.67%）,ST485、 ST34、 ST395、ST370、ST2388、ST893、ST11、ST2176、ST221、ST86、ST380、ST65、ST920、ST268、ST25、ST2154、ST2229以及5个新ST型别（STs1,STs2,STs3,STs4,STs5）各1株,分别占3.33%,两组比较,耐药组ST型别集中而敏感组离散,差异明显。结论：医院耐碳青霉烯肺炎克雷伯菌具有基因同源相关性,并呈现水平传播的趋势。     

Prevalence of plasmid-mediated quinolone resistance determinants among oxyiminocephalosporin-resistant Enterobacteriaceae in Argentina

High quinolone resistance rates were observed among oxyiminocephalosporin-resistant enterobacteria. In the present study, we searched for the prevalence of plasmid-mediated quinolone resistance (PMQR) genes within the 55 oxyiminocephalosporin-resistant enterobacteria collected in a previous survey. The main PMQR determinants were aac(6'')-Ib-cr and qnrB, which had prevalence rates of 42.4% and 33.3%, respectively. The aac(6'')-Ib-cr gene was more frequently found in CTX-M-15-producing isolates, while qnrB was homogeneously distributed among all CTX-M producers.