Chromosomal localization of resistance to fosfomycin and aminocyclitol antibiotics in hospital strains of Staphylococcus aureus

The chromosomal localization of fosfomycin resistance genes in three hospital Staphylococcus aureus strains and in the standard strain NCTC 8507 was shown. Moreover, the chromosomal locus of the gene determining resistance to three aminocyclitol antibiotics: gentamycin, kanamycin and tobramycin in the one of hospital strains was determined. The possibility of transducing this resistance and the absence of plasmid DNA in the obtained transductants, suggest transposomal nature of the gene determining gentamycin, kanamycin and tobramycin resistance in the investigated strain.     

Staphylococcus aureus resistance to antibiotics: key points in 2010

Staphylococcus aureus has a strong adaptive capacity and thus acquired various types of resistance to antistaphylococcal agents. More than 90% of isolates produce a penicillinase. Oxacillin remains active against these strains, but hospital associated staphylococci and more recently community acquired staphylococci have developed crossed resistance between methicillin (MRSA), oxacillin and other beta-lactams by production of a penicillin binding protein (PBP) with low affinity for beta-lactams, PBP2a. The gene encoding PBP2a, mecA is carried by a chromosomal element which also contains other resistance genes to heavy metals and other antibiotics thus explaining the multiresistant profile of hospital associated MRSA. By contrast, community acquired MRSA (CA-MRSA) are only resistant to kanamycin, fusidic acid and tetracycline, in addition to methicillin. This profile is specific of the European CA-MRSA ST80 clone which also encodes for a very particular virulence factor, the Panton-Valentine leukocidin. Glycopeptides, vancomycin and teicoplanin, are alternatives to oxacillin in case of resistance or intolerance. Strains with decreased susceptibility to glycopeptides have been reported. Their detection is difficult but necessary because vancomycin MIC creep seems linked to poor outcome in patients.     

脑卒中患者院内获得性肺炎的病原学特点及耐药性分析

目的 确定脑卒中患者院内获得性肺炎(hospital acquired pneumonia,HAP)的病原学特点及耐药性.方法 对浙江大学医学院附属第一医院2009年1月至2012年6月重症监护病房脑卒中患者发生的医院感染360例进行回顾性分析.结果 360例肺炎患者中,分离出病原菌640株,G-菌396株,前三位的是鲍曼不动杆菌,铜绿假单胞菌,肺炎克雷伯菌.G+菌184株.真菌60株,以白色念珠菌最多.结论 综合ICU病房中脑卒中患者院内获得性肺炎的主要病原菌是:鲍曼不动杆菌,铜绿假单胞菌,金黄色葡萄球菌.     

Peptidoglycan synthesis and structure in Staphylococcus haemolyticus expressing increasing levels of resistance to glycopeptide antibiotics.

The structures of cytoplasmic peptidoglycan precursor and mature peptidoglycan of an isogenic series of Staphylococcus haemolyticus strains expressing increasing levels of resistance to the glycopeptide antibiotics teicoplanin and vancomycin (MICs, 8 to 32 and 4 to 16 microg/ml, respectively) were determined. High-performance liquid chromatography, mass spectrometry, amino acid analysis, digestion by R39 D,D-carboxypeptidase, and N-terminal amino acid sequencing were utilized. UDP-muramyl-tetrapeptide-D-lactate constituted 1.7% of total cytoplasmic peptidoglycan precursors in the most resistant strain. It is not clear if this amount of depsipeptide precursor can account for the levels of resistance achieved by this strain. Detailed structural analysis of mature peptidoglycan, examined for the first time for this species, revealed that the peptidoglycan of these strains, like that of other staphylococci, is highly cross-linked and is composed of a lysine muropeptide acceptor containing a substitution at its epsilon-amino position of a glycine-containing cross bridge to the D-Ala 4 of the donor, with disaccharide-pentapeptide frequently serving as an acceptor for transpeptidation. The predominant cross bridges were found to be COOH-Gly-Gly-Ser-Gly-Gly-NH2 and COOH-Ala-Gly-Ser-Gly-Gly-NH2. Liquid chromatography-mass spectrometry analysis of the peptidoglycan of resistant strains revealed polymeric muropeptides bearing cross bridges containing an additional serine in place of glycine (probable structures, COOH-Gly-Ser-Ser-Gly-Gly-NH2 and COOH-Ala-Gly-Ser-Ser-Gly-NH2). Muropeptides bearing an additional serine in their cross bridges are estimated to account for 13.6% of peptidoglycan analyzed from resistant strains of S. haemolyticus. A soluble glycopeptide target (L-Ala-gamma-D-iso-glutamyl-L-Lys-D-Ala-D-Ala) was able to more effectively compete for vancomycin when assayed in the presence of resistant cells than when assayed in the presence of susceptible cells, suggesting that some of the resistance was directed towards the cooperativity of glycopeptide binding to its target. These results are consistent with a hypothesis that alterations at the level of the cross bridge might interfere with the binding of glycopeptide dimers and therefore with the cooperative binding of the antibiotic to its target in situ. Glycopeptide resistance in S. haemolyticus may be multifactorial.     

Ability of Staphylococcus cohnii strains to adhere to epithelial cells and solid surfaces in the hospital environment

Presented study describes abilities of staphylococci to adhere to exfoliated cheek and uroepithelial epithelium cells and to various surfaces such as plastics, glass and steel. The subject of the study were strains of Staphylococcus cohnii ssp. cohnii and Staphylococcus cohnii ssp. urealyticus isolated from Intensive Care Unit of Pediatric Hospital. Staphylococcus cohnii ssp.cohnii adhered in great number to epithelial cells. However, the adhesion differed by individual strains. We did not find relationship between slime production and adherence to epithelial cell. Most of investigated strains adhered closely to surfaces--especially of plastics and glass. This phenomenon was stronger in the presence of culture medium and phosphate buffer.     

Mechanisms of resistance to antibiotics

Microbial resistance to antibiotics is manifested by changes in antibiotic permeability, alteration of target molecules, enzymatic degradation of the antibiotics, and efflux of antimicrobials from the cytosol. Bacteria and other microorganisms use all of these mechanisms to evade the toxic effects of antibiotics. Recent research on the molecular aspects of these mechanisms, often informed by atomic resolution structures of proteins, enzymes and nucleic acids involved in these processes, has deepened our understanding of antibiotic action and resistance and, in several cases, spurred the development of strategies to overcome resistance in vitro and in vivo.     

Localization of genes conferring resistance to selected groups of antibiotics in methicillin-resistant strains of Staphylococcus aureus

Localization of genes conferring resistance to MLS, tetracyclines, chloramphenicol, gentamycin and neomycin in 80 MRSA strains isolated from hospital specimens was determined. The obtained results were compared to DNA patterns of the examined strains after digestion with SmaI and separation in pulsed field electrophoresis (PFGE). It was shown that genes of resistance to MLS (ErmI+) in the case of 13 strains were located on chromosome and in the case of 37 strains on plasmids (16 strains had ErmI+ and 21 strains had ErmI-). Genes determining resistance to tetracyclines were localised on chromosome in the case of 39 (23 strains possessed TetK, 11 strains had TetM and 5 strains possessed both TetK and TetM determinants) and in the case of 32 strains on plasmids. Chloramphenicol resistance genes were localised on plasmids in all 30 resistant strains. Genes conferring resistance to gentamycin were present in 31 of the investigated strains on chromosome and in two strains on plasmids. Neomycin resistance genes were plasmid in 34 strains. It was shown that the localization of the resistance genes and the PFGE patterns of the investigated strains were highly correlated.     

Staphylococcus epidermidis strains isolated from breast milk of women suffering infectious mastitis: potential virulence traits and resistance to antibiotics

Background  

AlthoughStaphylococcus aureusis considered the main etiological agent of infectious mastitis, recent studies have suggested that coagulase-negative staphylococci (CNS) may also play an important role in such infections. The aims of this work were to isolate staphylococci from milk of women with lactational mastitis, to select and characterize the CNS isolates, and to compare such properties with those displayed by CNS strains isolated from milk of healthy women.     

Decreased resistance to antibiotics and plasmid loss in plasmid-carrying strains of Staphylococcus aureus treated with ascorbic acid

The effect of ascorbic acid on plasmid-coded antibiotic resistance in Staphylococcus aureus was investigated. Several strains of S. aureus were cultured in the presence of 1 mM ascorbate for 6 h. This treatment induced an increased loss of resistance markers in 4 of 6 strains tested, and agarose gel electrophoresis showed this disappearance of plasmid DNA in ascorbate-induced susceptible colonies. The presence of ascorbate induced a 50-75% decrease in minimal inhibitory concentrations of different antibiotics for resistant strains. When ascorbate is added, formerly subinhibitory concentrations of penicillin or tetracycline have an increased inhibitory effect on resistant strains and even induced the death of 25-93% of the initial population. These results suggest that ascorbate can induce the loss of several plasmids of S. aureus, and that the levels of antibiotic resistance are also affected by the presence of this compound.     

Beta-lactamases and bacterial resistance to antibiotics

The efficiency of β-lactam antibiotics, which are among our most useful chemotherapeutic weapons, is continuously challenged by the emergence of resistant bacterial strains. This is most often due to the production of β-lactamases by the resistant cells. These enzymes inactivate the antibiotics by hydrolysing the β-lactam amide bond. The elucidation of the structures of some β-lactamases by X-ray crystallography has provided precious insights into their catalytic mechanisms and revealed unsuspected similarities with the DD-transpeptidases, the bacterial enzymes which constitute the lethal targets of β-lactams. Despite numerous kinetic, structural and site-directed mutagenesis studies, we have not completely succeeded in explaining the diversity of the specificity profiles of β-lactamases and their surprising catalytic power. The solutions to these problems represent the cornerstones on which better antibiotics can be designed, hopefully on a rational basis.