Postoperative mediastinitis due to methicillin resistant Staphylococcus epidermidis with low sensitivity to vancomycin

BACKGROUND: Vancomycin is the drug of choice for methicillin-resistant Staphylococcus. Antibiotherapy failure is rarely clinically related to Staphylococcus with vancomycin low susceptibility. CASE REPORT: A surgical cure of an aortic stenosis in a neonate was complicated by a Staphylococcus mediastinitis. After initiation of antibiotherapy with vancomycin and rifampin and surgical debridement, there was a rapid improvement. Few days later, failure of therapy was obvious. Despite continuous infusion of vancomycin, with a serum level of 29 mg/L, blood cultures were positive again to Staphylococcus. There was no endocarditis or inadequate surgical drainage. Susceptibility of the Staphylococcus was tested, looking for a tolerant strain. The vancomycin minimum bactericidal concentration was 30 mg/L (above usual value 2 to 8 mg/L), while the minimum inhibitory concentration was 3.75 mg/L. A higher dosage of vancomycin associated with fusidic acid was rapidly efficient, and total recovery was achieved. CONCLUSION: In case of failure of vancomycin therapy, despite correct serum levels, the susceptibility of the Staphylococcus strain has to be determined. A low susceptibility strain prescribes more prolonged combination of two antibiotics.     

Lysogenic conversion as a factor influencing tolerance to vancomycin in Staphylococcus aureus

The standard, non-lysogenic, bacteriophage-free S. aureus NCTC 8325-4 strain was lysogenized with 15 different, obtained in our laboratory staphylokinase-converting bacteriophages belonging to serological groups A, B and F. MIC and MBC of vancomycin as well as the ratio of MBC to MIC were evaluated for all 15 lysogenic derivatives. The obtained results were compared with those for maternal strain. In the case of eight strains the ratio MBC/MIC showed the presence of tolerance to vancomycin (MBC/MIC > or = 32). Four of the vancomycin-tolerant derivatives were lysogenized with bacteriophages belonging to the serological group A, two were members of group B and two belonged to group F.     

In vitro studies of pharmacodynamic properties of vancomycin against Staphylococcus aureus and Staphylococcus epidermidis

The bactericidal activities of vancomycin against two reference strains and two clinical isolates of Staphylococcus aureus and Staphylococcus epidermidis were studied with five different concentrations ranging from 2x to 64x the MIC. The decrease in the numbers of CFU at 24 h was at least 3 log10 CFU/ml for all strains. No concentration-dependent killing was observed. The postantibiotic effect (PAE) was determined by obtaining viable counts for two of the reference strains, and the viable counts varied markedly: 1.2 h for S. aureus and 6.0 h for S. epidermidis. The determinations of the PAE, the postantibiotic sub-MIC effect (PA SME), and the sub-MIC effect (SME) for all strains were done with BioScreen C, a computerized incubator for bacteria. The PA SMEs were longer than the SMEs for all strains tested. A newly developed in vitro kinetic model was used to expose the bacteria to continuously decreasing concentrations of vancomycin. A filter prevented the loss of bacteria during the experiments. One reference strain each of S. aureus and S. epidermidis and two clinical isolates of S. aureus were exposed to an initial concentration of 10x the MIC of vancomycin with two different half-lives (t1/2s): 1 or 5 h. The post-MIC effect (PME) was calculated as the difference in time for the bacteria to grow 1 log10 CFU/ml from the numbers of CFU obtained at the time when the MIC was reached and the corresponding time for an unexposed control culture. The difference in PME between the strains was not as pronounced as that for the PAE. Furthermore, the PME was shorter when a t1/2 of 5 h (approximate terminal t1/2 in humans) was used. The PMEs at t1/2s of 1 and 5 h were 6.5 and 3.6 h, respectively, for S. aureus. The corresponding figures for S. epidermidis were 10.3 and less than 6 h. The shorter PMEs achieved with a t1/2 of 5 h and the lack of concentration-dependent killing indicate that the time above the MIC is the parameter most important for the efficacy of vancomycin.     

In vitro activities of co-amoxiclav at concentrations achieved in human serum against the resistant subpopulation of heteroresistant Staphylococcus aureus: a controlled study with vancomycin

The effects of concentrations that simulated those in human serum after a single intravenous dose of amoxicillin (2 g), amoxicillin-clavulanic acid (2,000 and 200 mg, respectively), or vancomycin (500 mg), on the viability and beta-lactamase activity of two isogenic (beta-lactamase and non-beta-lactamase producer) heteroresistant Staphylococcus aureus strains were studied in an in vitro pharmacodynamic model. A reduction of > or = 97% of the initial inoculum was obtained with vancomycin and amoxicillin-clavulanic acid against both strains, with respect to the total bacterial population and the oxacillin-resistant subpopulation. The same pattern was observed with amoxicillin and the beta-lactamase-negative strain. beta-Lactamase activity in the beta-lactamase-positive strain changed over time parallel to viability, decreasing with amoxicillin-clavulanic acid or vancomycin and increasing in the amoxicillin and control groups. Clavulanic acid concentrations achievable in serum that changed over time allowed amoxicillin to act against the beta-lactamase-producing methicillin-resistant S. aureus to a similar extent as vancomycin.     

Various possible pathogenicity factors in Staphylococcus aureus (proceedings)

Parametric and symptomatologic studies of the EEG in large populations have served to define stages of maturation and criteria of "normality". The younger the subjects, however, the wider are the variations. In the first stage of life only massive cerebral lesions afford unquestionable EEG evidence: in evaluating dysrhythmias it is necessary to bear in mind their high incidence in normal subjects. Hence their meaning is to be understood only by prolonged longitudinal studies. The reference here is not only to diffuse or focal slow anomalies, but also to specific pathologic rhythms. The difficulty of interpreting such anomalies is particularly evident when epileptogenic potentials are found, since they may be signs of a lesion but their clinical correlations are uncertain. The concept of "masked epilepsy" must be rejected. Only the diagnoses of latent or proven epilepsy are admissible, and these epilepsies may be without direct relationship to the clinical, psychiatric or central nervous findings in the affected subject. Numerous genetic, afferential, emotional or biologic factors are involved in the development of non-lesional disorders. Accordingly, the EEG has only a minor contribution to make in the definition of mild focal or diffuse pathologic anatomy of the brain in the very young subject.     

Staphylococcus aureus and Candida albicans infection (animal experiments)

During a certain period of the course of infection in white mice inoculated intraperitoneally with the pure culture of a proteolysing strain of Candida albicans, Staphylococcus aureus and C. albicans both, were isolated simultaneously from the peritoneal abscesses, especially those adhering to the stomach, duodenum, pancreas and the upper part of small intestine. This concommitant occurrence of the two pathogens was further corroborated by histopathological examination which revealed large number of staphylococci present in the close neighbourhood of Candida cells, usually in the center of the granulomata caused by the fungus. In view of the facts that the proteolytic end-products of C. albicans can offer a good substratum for the growth of S. aureus and the latter may be isolated from the intestinal tract of apparently healthy mice, possibly as a constituent of the transient microflora, the co-existence of these two important aetiologic agents of endogenous infections as encountered during this study appears to be of great clinical interest. Furthermore, these observations also demonstrate the importance of controlling the bacterial flora of mice for pure mycological studies.     

Spread and control of methicillin resistant Staphylococcus aureus in a department of dermatology

Patients with skin diseases caused a spread of methicillin-resistant Staphylococcus aureus (MRSA) to 17 patients in our Department of Dermatology, because of their heavily scaly skin. Patients with severe dermatosis are regularly treated with dicloxacillin. The resistance of bacteria strain concerned suggests a selection because of the use of dicloxacillin in the Department. The strain is sensitive to gentamicin, which differentiates it from strains imported from abroad. Increased hygienic precautions, isolation of infected patients, staff and management efforts and a close contact with the microbiologists prevented MRSA from spreading to other hospital wards.     

A profile of methicillin resistant Staphylococcus aureus infection in the burn center of the Sultanate of Oman

A retrospective study of patterns of infection in 168 patients admitted during 1995 and 1996 in the burns-unit of Khoula hospital at Muscat, Oman was performed. Out of 819 isolates positive for pathogenic bacterial culture, there were 326 (39.8%) isolates positive for methicillin resistant Staphylococcus aureus (MRSA) infection. Incidence of MRSA infection was marginally more than that of Pseudomonas aeroginosa. The proportion of patients developing MRSA infection sometime or the other during their burns-unit stay ranging from 1 to 112 days rose from 48% in 1995 to 52.7% in 1996. No sophisticated tests were done to identify the MRSA strain but study of the antibiograms of each MRSA positive isolate showed very similar patterns of sensitivity to different antibiotics. This suggests the source of infection to be common and in all probability 'noscomial', since all patients acquired MRSA infection in the hospital. The susceptibility of MRSA to ciprofloxacin, cotrimoxazole and fucidin was 76, 51 and 37% of isolates in 1995, and 59, 44 and 26% in 1996 were susceptible to these drugs. Vancomycin was the antibiotic to which most MRSA cultures were susceptible, but partial resistance was reported due to very low susceptibility observed in 1.4% of the isolates in 1995 and 1.1% of the isolates in 1996. The control measures being practiced in the burns-unit of Khoula Hospital, especially mechanical cleaning and chemical disinfection of all surfaces, are discussed in detail. This paper emphasizes the need for preventive measures against MRSA infection in the burns-unit.     

Levofloxacin versus ciprofloxacin, flucloxacillin, or vancomycin for treatment of experimental endocarditis due to methicillin-susceptible or -resistant Staphylococcus aureus

Levofloxacin is the L isomer of ofloxacin, a racemic mixture in which the L stereochemical form carries the antimicrobial activity. Levofloxacin is more active than former quinolones against gram-positive bacteria, making it potentially useful against such pathogens. In this study, levofloxacin was compared to ciprofloxacin, flucloxacillin, and vancomycin for the treatment of experimental endocarditis due to two methicillin-susceptible Staphylococcus aureus (MSSA) and two methicillin-resistant S. aureus (MRSA) isolates. The four test organisms were susceptible to ciprofloxacin, the levofloxacin MICs for the organisms were low (0.12 to 0.25 mg/liter), and the organisms were killed in vitro by drug concentrations simulating both the peak and trough levels achieved in human serum (5 and 0.5 mg/liter, respectively) during levofloxacin therapy. Rats with aortic endocarditis were treated for 3 days. Antibiotics were injected with a programmable pump to simulate the kinetics of either levofloxacin (350 mg orally once a day), ciprofloxacin (750 mg orally twice a day), flucloxacillin (2 g intravenously four times a day), or vancomycin (1 g intravenously twice a day). Levofloxacin tended to be superior to ciprofloxacin in therapeutic experiments (P = 0.08). More importantly, levofloxacin did not select for resistance in the animals, in contrast to ciprofloxacin. The lower propensity of levofloxacin than ciprofloxacin to select for quinolone resistance was also clearly demonstrated in vitro. Finally, the effectiveness of this simulation of oral levofloxacin therapy was at least equivalent to that of standard treatment for MSSA or MRSA endocarditis with either flucloxacillin or vancomycin. This is noteworthy, because oral antibiotics are not expected to succeed in the treatment of severe staphylococcal infections. These good results obtained with animals suggest that levofloxacin might deserve consideration for further study in the treatment of infections due to ciprofloxacin-susceptible staphylococci in humans.     

Inhibition of cell wall turnover and autolysis by vancomycin in a highly vancomycin-resistant mutant of Staphylococcus aureus

A highly vancomycin-resistant mutant (MIC = 100 microg/ml) of Staphylococcus aureus, mutant VM, which was isolated in the laboratory by a step-pressure procedure, continued to grow and synthesize peptidoglycan in the presence of vancomycin (50 microg/ml) in the medium, but the antibiotic completely inhibited cell wall turnover and autolysis, resulting in the accumulation of cell wall material at the cell surface and inhibition of daughter cell separation. Cultures of mutant VM removed vancomycin from the growth medium through binding the antibiotic to the cell walls, from which the antibiotic could be quantitatively recovered in biologically active form. Vancomycin blocked the in vitro hydrolysis of cell walls by autolytic enzyme extracts, lysostaphin and mutanolysin. Analysis of UDP-linked peptidoglycan precursors showed no evidence for the presence of D-lactate-terminating muropeptides. While there was no significant difference in the composition of muropeptide units of mutant and parental cell walls, the peptidoglycan of VM had a significantly lower degree of cross-linkage. These observations and the results of vancomycin-binding studies suggest alterations in the structural organization of the mutant cell walls such that access of the vancomycin molecules to the sites of wall biosynthesis is blocked.     

Severe methicillin-resistant Staphylococcus aureus infections. Emergence of resistance to fusidic acid or fosfomycin during treatment with continuous infusion of vancomycin

OBJECTIVES: To evaluate the development of resistance to fosfomycin or fucidic acid in severe infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and to assess the relationship with serum levels of vancomycin METHODS: A retrospective study was performed in patients hospitalized in our intensive care unit during a 3-year period (1993-1995) who were treated for severe MRSA infection with continuous infusion vacomycin and fosfomycin or fucidic acid. We analyzed the development of resistance and serum levels of vancomycin. RESULTS: During this period, only 20 patients received continuous infusion vancomycin plus fucidic acid or fosfomycin. MSRA resistant to fucidic or fosfomycin developed in 9. Vancomycin serum levels were significantly lower in patients who developed resistance to focidic acid or fosfomycin, both during the first 5 days of treatment (16.68 +/- 1.07 micrograms/ml vs. 22.64 +/- 1.05 mg/ml, p < 0.01) and throughout treatment duration (17.29 +/- 1.07 micrograms/ml vs. 21.85 +/- 0.78 microgram/ml, p < 0.01). CONCLUSIONS: Our findings confirm that in spite of continuous vancomycin infusion at an initial rate of 2 g/24 h, Staphylococcus aureus resistance to fosfomycin or fucidic acid an develop during ongoing treatment. Vancomycin levels of at least 20 micrograms/ml should be obtained as rapidly as possible.     

Staphylococcus aureus binding to human nasal mucin

Colonization of human nasal mucosa with Staphylococcus aureus sets the stage for subsequent systemic infection. This study characterizes S. aureus adhesion to nasal mucosa in vitro and investigates the interaction of S. aureus with human nasal mucin. S. aureus binding to cell-associated and cell-free mucus was greater than to nonmucin-coated epithelial cells. Scanning electron microscopy of S. aureus incubated with human nasal mucosal tissue showed minimal binding to ciliated respiratory epithelium. In a solid-phase assay, S. aureus bound to purified human nasal mucin-coated wells significantly more than to bovine serum albumin-coated microtiter wells. Binding to mucin was saturable in a dose- and time-dependent fashion. Staphylococcal adherence to human nasal mucin was inhibited by bovine submaxillary mucin but not by fibrinogen. Pretreatment of mucin with periodate but not with pronase reduced adherence. Trypsin treatment of the bacteria significantly reduced adherence to mucin. 125I-labelled nasal mucin bound to two surface proteins (138 and 127 kDa) of lysostaphin-solubilized S. aureus. Binding to human nasal mucin occurs in part via specific adhesin-receptor interactions involving bacterial proteins and the carbohydrate moiety in mucin. These experiments suggest that S. aureus binding to mucin may be critical for colonization of the nasopharyngeal mucosa.     

MRSA (methicillin-resistant Staphylococcus aureus) infections in patients with pulmonary diseases

Methicillin-resistant Staphylococcus aureus (MRSA) has become a major nosocomial pathogen. We investigated MRSA-infections in patients with pulmonary diseases referring to epidemiological aspects. Between 9/92 and 2/92 we found MRSA-infections in our hospital in 24 patients (11 female, 13 male, average age 54.6 years). Clinical presentation, main and accompanying disorders and previous antibiotic therapy regimens were registered. Strains were typed using DNA-RFLP and lysotyping. MRSA detection were done in specimen from sputum (12/24) and from the bronchial secret (9/24). In 18/24 cases the MRSA-colonisation was associated with infection. In 15/24 cases the first acquisition of MRSA happened in our hospital, 6/24 times the germ was carried off other institutions and in 3/24 cases it was possibly community acquired. Most frequently patients suffered from bronchial cancer (6/24), from chronical bronchitis (5/24), from pneumonia (4/24) or Cystic fibrosis (4/24). Usually the patients showed other severe comorbidity. 13/24 patients had an antibiotic course before detecting MRSA. Typing revealed a strain already known in different hospitals of Berlin, another known strain of northern Germany and two so far unknown strains. Of interest was a different behaviour of resistance and the lost of resistance of strains in the course. MRSA-infection in pulmonary medicine emerged as a problem mostly in patients with multimorbidity and severe underlying diseases. Change of resistance in strains and new strains were observed.     

Studies of the repressor (BlaI) of beta-lactamase synthesis in Staphylococcus aureus

Purified BlaI, the putative repressor of the beta-lactamase operon in Staphylococcus aureus, binds specifically to two regions of dyad symmetry (operators) located in the blaZ-blaR1 intergenic region. BlaI binds with similar affinity to the two regions and to the related sequence upstream of the mec gene found in methicillin-resistant strains of S. aureus, providing physical evidence for the cross-talk previously observed between these systems. A change from a lysine in the N-terminus of BlaI to an alanine or deletion of the C-terminal 23 amino acids severely reduces its DNA-binding ability, demonstrating the functional importance of both the N- and C-termini. An operator DNA-protein complex observed with crude cell lysates from repressed cells, indistinguishable from that observed with purified BlaI, was eliminated by induction of the beta-lactamase operon. Furthermore, BlaI is proteolytically cleaved in response to the addition of inducer in a blaR1-dependent manner, providing primary evidence for the molecular basis of induction. Thus, BlaI is shown to be the repressor of the beta-lactamase system.     

Formation of extracellular protein A by Staphylococcus aureus

Staphylococcus aureus contains cell wall protein A as well as extracellular protein A. The two types of protein A have very similar amino acid compositions, electrophoretic mobilities and sizes. The release of extracellular protein A from exponentially growing bacteria is dependent on protein synthesis de novo and protein A is released directly after being synthesized on the ribosomes. Bacteria in the stationary phase, however, release protein A as a result of cell lysis. Protoplasts have been isolated which produce protein A as extensively as the intact bacteria but because of the absence of of the formation of extracellular protein A is observed from cells also producing cell wall protein A.     

Sensitivity of Staphylococcus aureus to unsaturated fatty acids

Some unsaturated fatty acids were found to inhibit the growth of Staphylococcus aureus. Their effectiveness was related both to the degree of unsaturation and to the configuration of the molecule about the double bonds. Both linoleic acid and linolenic acid increased the proportion of plasmid-negative bacteria in a growing culture of bacteria containing a penicillinase plasmid. This was not due to a 'curing' effect of the fatty acids but was the result of greater sensitivity of the growth of bacteria containing penicillinase plasmid to inhibition by the unsaturated fatty acids. The presence of a plasmid conferring resistance to tetracycline, however, did not make the bacterium more sensitive to inhibition by linoleic or linolenic acids.