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PubMed1986

Characterization of an isogenic set of methicillin-resistant and susceptible mutants of Staphylococcus aureus.

A low affinity penicillin binding protein (PBP2') present in methicillin resistant strains but absent in isogenic sensitive strains of Staphylococcus aureus is responsible for the phenotypic expression of the methicillin resistance. An additional factor controlling methicillin resistance is known to map on the chromosome at the insertion site omega 2003 (chr::Tn551). The influence of this factor on PBP2' synthesis was analysed. Isogenic methicillin sensitive and resistant mutants derived from a Staphylococcus aureus strain carrying methicillin resistance factors and the omega 2003 (chr::Tn551) insertion were characterized by population analysis and restriction analysis of the DNA surrounding the Tn551 insertion site, and their PBP2' content was determined. Both methicillin resistant and sensitive mutants produced levels of PBP2' similar to those of the original methicillin resistant parent. The mere presence of this PBP2' could therefore not be solely responsible for the phenotypic expression of methicillin resistance. The nature and site of action of the additional factor determined by the omega 2003 (chr::Tn551) site controlling expression of methicillin resistance still remains unknown.

Bacterial Proteins↗

PubMed1986

Conversion of a homogeneously methicillin-resistant strain of Staphylococcus aureus to heterogeneous resistance by Tn551-mediated insertional inactivation.

Plasmid pRN3208, thermosensitive for replication, and carrying the erythromycin transposon Tn551, was used for insertional inactivation of methicillin resistance in a highly and homogeneously resistant strain of Staphylococcus aureus. Two kinds of insertionally inactivated cells were obtained. Cultures of the major class contained highly methicillin resistant cells with a frequency of about 10(-3) to 10(-4), produced DNA with methicillin resistance transforming activity, and also produced penicillin binding protein 2a, the 78 kd low affinity penicillin binding protein characteristic of methicillin resistant Staphylococcus aureus, in apparently normal quantities. The single member of class B had no detectable methicillin resistant cells (less than 10(-8)) with an MIC greater than 1 micrograms/ml, contained no DNA with methicillin resistant transforming activity and no penicillin binding protein 2a. The data suggest that in the class A cells insertional inactivation did not affect the structural gene(s) of methicillin resistance but a regulatory locus or loci needed for the homogeneous expression of resistance.

Bacterial Proteins↗

PubMed1982

Effect of subinhibitory antibiotic concentrations on the phagocytosis of Staphylococcus aureus.

The effect of subinhibitory antibiotic concentrations on the phagocytosis of Staphylococcus aureus was studied by pretreating 3H-thymidine labelled bacteria with one-third the minimal inhibitory concentration of clindamycin, doxycyclin, cefotiam, vancomycin, piperacillin and penicillin G, respectively. Pretreatment with clindamycin and doxycyclin resulted in enhanced uptake of the bacteria by polymorphonuclear leukocytes compared to the untreated control. The augmented phagocytosis was still observed at 1/32 the MIC of clindamycin and 1/64 the MIC of doxycyclin, and when the serum was diluted to a concentration of 1%. Pretreatment of the bacteria with penicillin, cefotiam, piperacillin and vancomycin had no effect on phagocytosis. Inhibitors of bacterial protein synthesis induce alterations of Staphylococcus aureus leading to increased phagocytosis, whereas antibiotics acting on cell wall synthesis are without effect.

Anti-Bacterial Agents↗

PubMed1983

Susceptibility of gram-negative bacteria and Staphylococcus aureus to combinations of ticarcillin and clavulanic acid.

Four hundred and fifty-nine blood culture isolates were tested for susceptibility to ticarcillin alone and ticarcillin plus clavulanic acid, a potent beta-lactamase inhibitor. The susceptibilities of the Staphylococcus aureus strains to cloxacillin, methicillin, vancomycin, rifampicin, cefoperazone, ceftriaxone and moxalactam and of the gram-negative strains to Augmentin, azlocillin, mezlocillin, piperacillin, cefoperazone, ceftriaxone, cefotaxime, cefsulodin and tobramycin were also measured. Seventy-one percent of staphylococcal strains were beta-lactamase positive. In the presence of clavulanic acid the ticarcillin spectrum was extended to include beta-lactamase producing Staphylococcus aureus, Serratia marcescens and Klebsiella. All the ticarcillin-resistant Enterobacteriaceae were rendered ticarcillin-sensitive by clavulanic acid. The anti-Pseudomonas activity of ticarcillin plus clavulanic acid differed little from that of azlocillin and piperacillin and was comparable to that of the third generation cephalosporins. The combination of ticarcillin with clavulanic acid should be tested in the treatment of patients with infections caused by ticarcillin-sensitive and ticarcillin-resistant bacteria.

Clavulanic Acid↗

PubMed1994

National survey of methicillin-resistant Staphylococcus aureus in Belgian hospitals: detection methods, prevalence trends and infection control measures. The Groupement pour le Dépistage, l'Etude et la Prévention des Infections Hospitalières.

A questionnaire survey of Belgian acute care hospitals was conducted to determine the methods used for detection of methicillin-resistant Staphylococcus aureus (MRSA), to estimate the prevalence of this organism during the period 1989-1991 and to describe the infection control measures used locally for limiting its spread. Questionnaires were returned by 144 acute care hospitals, with a coverage of 41 to 72% of hospitals by province. Methods used for detection of MRSA included disk diffusion (91%), microdilution panels (8%) and oxacillin agar screen (9%). Only 34% of laboratories performed disk diffusion testing under optimal conditions for detection of heterogenous resistance. Among 36 hospitals reporting complete susceptibility data of Staphylococcus aureus isolates tested during the study period (n = 24,153), a mean MRSA prevalence of 14% was found (range: 0-70%). The median prevalence increased from 9.5% in 1989 to 13.7% in 1991 and showed a significant linear increase during this period in 30% of these hospitals (p < 0.01). Precautions used for controlling spread of MRSA included hand decontamination using either soap and water or antimicrobial preparations (68% of hospitals), room decontamination (62%), patient isolation (55%) and various barrier precautions (24-49%). Carrier screening was performed in 37% of hospitals, but antibiotic decolonization was attempted in only 24%. This survey identified areas for improvement in MRSA detection methods and underscored the need for multicentric surveillance of MRSA prevalence and a reappraisal of MRSA control strategies in Belgian hospitals.

Bacteriological Techniques↗

PubMed1994

Risk factors for nosocomial bacteremia due to methicillin-resistant Staphylococcus aureus.

In a prospective surveillance study (February 1990-December 1991) performed at a 1000-bed teaching hospital to identify risk factors for nosocomial methicillin-resistant Staphylococcus aureus (MRSA) bacteremia, 309 patients were found to be colonized (n = 103; 33%) or infected (n = 206; 67%) by MRSA. Sixty-three of them developed bacteremia. Compared with 114 patients who had nosocomial bacteremia caused by methicillin-sensitive Staphylococcus aureus during the same period of time, MRSA bacteremic patients had more severe underlying diseases (p < 0.01), were more often in intensive care units (p < 0.01) and had received prior antibiotic therapy more frequently (p < 0.01). To further identify risk factors for MRSA bacteremia, univariate and multivariate analyses of this series of 309 patients were performed using the occurrence of MRSA bacteremia as the dependent variable. Among 14 variables analyzed, intravascular catheterization, defined as one or more intravascular catheters in place for more than 48 h, was the only variable selected by a logistic regression model as an independent risk factor (OR = 2.7, CI = 1.1-6.6). The results of this study reinforce the concept that recent antibiotic therapy may predispose patients to MRSA infection and suggest that among patients colonized or infected by MRSA, those with intravascular catheters are at high risk of developing MRSA bacteremia.

Adult↗

PubMed1995

Variation and persistence of methicillin-resistant Staphylococcus aureus strains among individual patients over extended periods of time.

To determine the strain variation and persistence among isolates of methicillin-resistant Staphylococcus aureus (MRSA) cultured from patients with colonization over extended time spans, pulsed-field gel electrophoresis was used to analyze the isolates from 47 patients for whom at least two mecA-positive isolates collected a minimum of six months apart were available. For 22 (47%) patients, the isolates represented multiple distinct strains of Staphylococcus aureus, while 20 (43%) patients had only a single strain detected; five (11%) patients had similar, genetically related isolates. MRSA were frequently associated with mucocutaneous abnormalities; 29 (62%) patients had focal cutaneous defects, and ten (21%) had chronic dermatitis. Multiple strains of MRSA were detected more frequently than single strains among patients in whom the initial focus of MRSA resolved clinically and another mucocutaneous defect subsequently developed compared to patients with clinically persistent foci (11/15 versus 9/23, respectively; p = 0.05, Fisher's exact test). Among the 21 patients in this series for whom isolates cultured within a two-month time span were available, there were seven (33%) patients with multiple strains of MRSA, including one patient with polyclonal bacteremia. In summary, patients with long-term MRSA colonization often have several different strains of MRSA, which typically change overtime in association with removal or resolution of a colonized focus and the recurrence of mucocutaneous defects.

Anti-Bacterial Agents↗

PubMed1995

Use of ribotyping to investigate tracheal colonisation by Staphylococcus epidermidis as a source of bacteremia in ventilated newborns.

Ribotyping was used to determine whether a relationship exists between endotracheal tube colonisation with Staphylococcus epidermidis and bacteremia with this organism. Over a three-week period, four mechanically ventilated preterm babies presented with five episodes of infection and bacteremia. For each blood specimen obtained for culture a tracheal aspirate sample was collected at the same time by suctioning. After DNA extraction and cleavage by EcoRI, hybridisation was performed with a digoxigenin-labelled 16S-rDNA probe from Escherichia coli. Five different band patterns were recognised on the membrane. In two children the same band pattern was found in Staphylococcus epidermidis isolated from both blood and tracheal aspirate. Ribotyping thus could be used to differentiate a series of infections from an outbreak and showed that a relationship may exist between tracheal colonisation and bacteremia in mechanically ventilated newborns.

Bacteremia↗

PubMed1995

Diversity of methicillin-resistant Staphylococcus aureus isolated in a Canadian hospital.

Three neonates and three other patients located elsewhere in the hospital became infected with Staphylococcus aureus. Initial automated microdilution susceptibility testing with oxacillin and disk diffusion testing with amoxicillin-clavulanic acid indicated the isolates had borderline oxacillin resistance (MICs 4 micrograms/ml), presumably due to hyperproduction of beta-lactamase. Chromosomal DNA restriction fingerprinting and phage typing revealed the neonatal isolates to be identical; whereas, the other patients were infected with three different strains. Further analysis of the four strains by Southern hybridization with a mecA specific oligoprobe and a quantitative beta-lactamase assay demonstrated that two strains carried the mecA gene (coding for low affinity penicillin-binding protein 2a), and two strains were hyperproducers of beta-lactamase, including one which was mecA gene positive. One strain neither carried the mecA gene nor hyperproduced beta-lactamase. The two mecA gene positive strains displayed oxacillin MICs of 16 micrograms/ml on dilution susceptibility testing in 4% NaCl supplemented Mueller-Hinton agar. Hence, they were considered intrinsically methicillin-resistant Staphylococcus aureus. Both oxacillin and amoxicillin-clavulanic acid MICs were increased on NaCl supplementation. Results of amoxicillin-clavulanic acid disk diffusion susceptibility testing did not correlate with quantitative beta-lactamase production. It is recommended that clinical laboratories do not use amoxicillin-clavulanic acid disk diffusion assays to differentiate suspected borderline resistance due to beta-lactamase hyperproduction from mecA gene expression of PBP-2a since additional mechanisms may account for resistance.

Adult↗

PubMed1997

Tumor necrosis factor alpha and interleukin 6 release induced by antibiotic killing of Pseudomonas aeruginosa and Staphylococcus aureus.

Using a recently described ex vivo model, tumor necrosis factor-alpha and interleukin-6 released by peripheral blood monocytes after killing of Pseudomonas aeruginosa and Staphylococcus aureus by ceftazidime, imipenem, and meropenem was measured. Cytokine release was highest with ceftazidime and lowest with imipenem for both bacteria (p < 0.05), although cytokine concentrations were much lower after killing of Staphylococcus aureus. Differences in cytokine release rates induced by various cell-wall active antibiotics have not yet been described for gram-positive organisms and should be studied further.

Anti-Bacterial Agents↗

PubMed1995

The effect of salinomycin and lasalocid on laboratory cultures of Enterococcus faecium and Staphylococcus gallinarum strains.

The growth of Enterococcus faecium strains CCM 4231 and EF 26, and Staphylococcus gallinarum SG 31 was inhibited by salinomycin and lasalocid at concentrations of 25 and 50 mg/L. Staphylococcus gallinarum was more sensitive to the additives used than were enterococci. Maximum inhibition (90%) was measured after the growth with the SG 31 strain in the presence of both ionophores. Growth of organisms was more inhibited by salinomycin at 25 mg/L (67.5%) than at 50 mg/L (63%). The inhibitory effect in enterococcal strains reached after the addition of salinomycin and lasalocid (on average) 63 and 58%, respectively. The CCM 4231 strain was more inhibited by salinomycin as well as by lasalocid than was the EF 26 strain.

Enterococcus faecium↗

PubMed1999

Computerized antibiogram for methicillin-resistant Staphylococcus aureus in chest surgery.

BACKGROUND: An increasing number of cases of postoperative morbidity involving methicillin-resistant Staphylococcus aureus have been reported in thoracic surgery. To prevent its outbreak, cluster analysis using a personal computer was employed. METHODS: A total of 120 patients undergoing operations on the lung and mediastinum were included into this study. Materials were isolates of methicillin-resistant Staphylococcus aureus newly recovered from across the hospital. The cluster analysis used antimicrobial susceptibility in 12 drugs, which were categorically valued to produce Euclidean distance to form clusters of similarity. RESULTS: Six of the 120 patients were found to be positive for the microbe before or after thoracotomy. A total of two patients (1.7%) became symptomatic postoperatively, i.e., one of four preoperatively-positive patients and one of two postoperatively-positive cases. The analysis suggested that preoperative patients shared the strains in the same non-surgical ward. DISCUSSION: A computerized antibiogram does not always strictly type Staphylococcal strains but has advantages in typing with ease and at decreased cost. The current analysis suggested that patient harboring the strains migrated across wards. CONCLUSION: Computerized antibiograms for Staphylococcal strains may assist to prevent an outbreak of their infection in chest surgery.

Adult↗

PubMed2001

Highly epidemic strains of methicillin-resistant Staphylococcus aureus not distinguished by capsule formation, protein A content or adherence to HEp-2 cells.

In order to investigate whether highly epidemic methicillin-resistant Staphylococcus aureus (EMRSA) strains possess special properties that favour their dissemination and survival, a study was undertaken that examined methicillin-sensitive and methicillin-resistant strains of Staphylococcus aureus isolated in the UK. Included in the study were EMRSA types 1, 2, 3, 15 and 16. Phage types EMRSA-15 and -16, in particular, have emerged as significant hospital pathogens in the UK, resisting standard methods of control and spreading widely, while the incidence of other epidemic types has either declined or not changed. All of the strains included in the study were examined for capsule formation, the amount of bound protein A produced, and quantitative adherence to the human continuous epithelial cell line HEp-2. Although all of these properties varied amongst the strains examined, there was no relationship between any of them and methicillin resistance or epidemic type and, incidentally, no relationship between cell wall-bound protein A content and adherence.

Bacterial Adhesion↗

PubMed2001

Ciprofloxacin- and methicillin-resistant staphylococcus aureus susceptible to moxifloxacin, levofloxacin, teicoplanin, vancomycin and linezolid.

In order to determine the comparative efficacy of vancomycin, teicoplanin, levofloxacin, moxifloxacin, and linezolid against methicillin- and ciprofloxacin-resistant Staphylococcus aureus, each agent was tested against 65 genetically different strains using the microbroth dilution method. All of the isolates were typed using the enterobacterial repetitive intergenic consensus polymerase chain reaction to exclude multiple isolates of epidemic clones. Susceptibility testing revealed that all of the isolates were susceptible to vancomycin and teicoplanin. Linezolid exhibited minimum inhibitory concentration (MIC) levels ranging from 1 to 4 mg/l (MIC90, 4 mg/l). The MICs of moxifloxacin and levofloxacin ranged from 0.01 to 8 mg/l (MIC90, 8 mg/l) and 0.25 to 32 mg/l (MIC90. 16 mg/l), respectively. Thus, linezolid is active against methicillin- and ciprofloxacin-resistant Staphylococcus aureus, whereas moxifloxacin may need to be administered at a dose higher than recommended in order to successfully treat serious infections.

Acetamides↗

PubMed2001

[Chronic fistulating wound infection after Lichtenstein repair of inguinal hernia, caused by a small colony variant of Staphylococcus aureus].

We report a case of chronic wound infection (abscess, fistula) after a Lichtenstein repair of inguinal hernia. After surgical treatment (mesh explantation), a small-colony variant (SCV) of Staphylococcus aureus was cultured microbiologically. SCV represent subpopulations of Staphylococcus aureus which are associated with chronic infections and which respond poorly to usual treatment regimes. In this case surgery and specific antibiotic treatment with flucloxacillin and rifampicin were successful.

Abscess↗

PubMed1998

[Cutaneous Staphylococcus aureus colonisation of atopic eczema. Mechanisms, pathophysiological importance and therapeutic consequences].

Mechanisms for the increased Staphylococcus aureus colonization in atopic eczema are only partially known. From the aspect of the bacterium, the presence of various extracellular matrix components seems important. In the host epidermal lipid deficencies disturbing barrier dysfunction are important. Staphylococcus aureus' immunological and inflammatory effects include the release of superantigens, additional exotoxins and exoenzymes and perhaps bacterial DNA-triggered mechanisms. Therapeutic possibilities include the use of systemic antibiotics in cases of generalized superinfected atopic eczema, the use of corticosteroids and specific antibiotic-antiseptic combinations in cases of localised superinfected atopic eczema and the wide-spread use of topical antiseptics in cases of microbial-laden atopic eczema.

Animals↗

PubMed2001

[Methicillin-resistant Staphylococcus aureus (MRSA). Current status and significance of preventing infection in technical orthopedics].

Many patients of the Clinic for Technical Orthopedics and Rehabilitation of the Munster University are facing several risk factors at the same time, which have to be considered for infection registration and therapy accordingly. The interaction of the known late consequences of diabetes mellitus creates the prerequisites which give way for infections of the soft parts and bones. Very often, patients are only being transferred to special university clinics after long-lasting pre-treatments as day-patients or inpatients. The integrity of patients physiological barriers is often broken through by the already existing morphological damages, and the function of the immune systems defence possibly is affected by already existing basic diseases. Parallel to the increasing importance of Staphylococcus aureus (S. aureus) being the pathogen for nosocomial infections, the resistance situation towards a lot of antibiotics has significantly and increasingly deteriorated. The methicillin resistance of S. aureus, i.e. the resistance of the pathogen towards so-called staphylococcus-effective penicillinase-resistant penicillins (isoxazolylpenicillins), is presently creating the especially for the clinical practice problematic resistance mechanisms. The methicillin (oxacillin)-resistant S. aureus (MRSA, ORSA) stems usually present the phenomenon of multiresistance, i.e. the resistance towards substances of several classes of antibiotics, and, therefore, are not only resistant to all beta-lactamantibiotics (penicillins, cephalosporins, carbapenems). Thus, MRSA infections become a significant risk factor for the respective patients. In many cases there are only a very few options left for an antibiotic therapy. The increasing and often unquestioned use of "reserve substances" is leading to a selection of pathogens creating resistances to the corresponding substances. This results in a resistance spiral which makes an antibiotic therapy more and more difficult.

Cross Infection↗

PubMed2003

Nasal carriage of Staphylococcus aureus on admission to intensive care: incidence and prognostic significance.

We retrospectively studied the prevalence of the nasal carriage of methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) on admission to a medical surgical intensive care unit (ICU). We also compared the intensive care survival of MSSA carriers with non-carriers. Records of 678 patients admitted over a 24-month period were retrospectively reviewed. Nasal swabs were taken from 565 patients on admission to the ICU. MSSA was isolated from the anterior nares of 126 (22%) patients, MRSA was isolated in 16 (3%) patients and 423 (75%) patients had no nasal carriage identified. MSSA carriers were more likely to have been admitted to the ICU after less than 24 h hospital stay (28% non-carriers, 44% MSSA carriers) and were significantly younger (mean age of 50 years) than non-carriers (mean age 55 years). The median survival (with confidence intervals (CI)) was 29 days (CI 14-44) in non-carriers, 16 days (CI 10-22) in MSSA carriers and 6 days (CI 4-8) for the MRSA carriers. This difference was significant when MSSA carriers were compared with non-carriers ( p=0.003). The ICU mortality was also significantly higher ( p=0.004) in MSSA carriers (88 of the 423 (21%) non-carriers and 40 of 126 (32%) MSSA carriers died prior to ICU discharge).

Carrier State↗