Antimicrobial susceptibilities of coagulase-negative staphylococci isolated from urinary infections

Coagulase-negative staphylococci: incidence, pathogenicity, and treatment in the 1990s

Coagulase-negative staphylococci (CNS), which historically have been viewed as contaminants when recovered in culture media, are now recognized as opportunistic pathogens of increasing importance in hospital-acquired infections. They are frequently found colonizing prosthetic devices and intravenous lines. CNS are capable of producing a variety of infections including deep-seated infections such as endocarditis and meningitis. Staphylococcus epidermidis is the most commonly isolated CNS and it appears to be the most resistant to antibiotics, making antimicrobial therapy challenging. Treatment of the infection will very often require removal of a prosthetic device, if present. An adequate infection control program is imperative in prophylaxis against this infection.

Netilmicin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Netilmicin is a semisynthetic aminoglycoside derived from sisomicin. It is active against most Gram-negative and some Gram-positive bacteria, including many gentamicin-resistant strains. Netilmicin has proved to be effective in Gram-negative infections of the urinary tract, skin and skin structure, and lower respiratory tract, as well as in intra-abdominal infections, septicaemia and other miscellaneous infections. In some trials, the more easily implemented once daily administration of netilmicin has been as effective as multiple dosing regimens. However, further investigation is required to confirm that efficacy and safety are not compromised with once daily administration. Comparative studies have generally revealed similar clinical and bacteriological efficacies between netilmicin and gentamicin, amikacin or tobramycin. As with other aminoglycosides, the principal adverse effects of netilmicin are nephrotoxicity and ototoxicity. Although animal studies strongly suggest that these are less common with netilmicin than with related drugs, there appears to be no difference in their incidence in clinical use; in clinical trials the incidence of nephrotoxicity and ototoxicity has been low, with the symptoms in many cases being minor and reversible. Netilmicin is, therefore, an effective antibacterial drug for the parenteral treatment of severe infections, offering theoretical advantages in safety which may indicate its use for patients believed to be at risk of adverse effects.

In vitro susceptibilities of four species of coagulase-negative staphylococci

The in vitro susceptibilities of 260 strains of coagulase-negative staphylococci to penicillin G, oxacillin, nafcillin, methicillin, cephalothin, and seven non-beta-lactam antimicrobial agents were determined and compared with the susceptibilities of 54 strains of Staphylococcus aureus with known patterns of susceptibility. Penicillin G susceptibility for S. aureus, Staphylococcus epidermidis, Staphylococcus haemolyticus, and Staphylococcus hominis was readily determined by using beta-lactamase tests with induced cells and with a standardized microdilution test. MIC criteria for susceptibility used for S. aureus were applicable to the coagulase-negative species. Percentages of organisms susceptible were as follows: S. epidermidis, 7%; S. haemolyticus, 5%; and S. hominis, 47%. Oxacillin susceptibility for these four species was readily determined by using a modification of the microdilution test. MIC criteria for susceptibility used for S. aureus were applicable to S. haemolyticus and S. hominis, but alternate criteria were necessary for S. epidermidis. Percentages of organisms susceptible were as follows: S. epidermidis, 29%; S. haemolyticus, 36%; and S. hominis, 97%. Staphylococcus saprophyticus differed from the other staphylococcal species; all strains were beta-lactamase negative and were penicillin susceptible but had higher penicillin G MICs than did susceptible strains of the other species. There was total cross resistance among the penicillinase-resistant penicillins and cephalothin for the coagulase-negative staphylococci as well as for S. aureus; oxacillin MICs were more reliable than MICs of the other drugs or a standardized disk diffusion test for distinguishing resistant from susceptible strains. Vancomycin, rifampin, and ciprofloxacin were consistently active against all staphylococci. Erythromycin, clindamycin, gentamicin, and trimethoprim-sulfamethoxazole were more active against oxacillin-susceptible staphylococci than against oxacillin-resistant staphylococci.

Vancomycin: an update

Vancomycin is a narrow-spectrum glycopeptide antibiotic with potent antistaphylococcal activity. It is primarily active against gram-positive organisms. Bacterial resistance rarely develops due to its numerous modes of action. The toxic potential of vancomycin is less significant than previously thought. "Red neck syndrome" seems to be the most common side effect and appears to be caused by rapid intravenous infusion. It is characterized by erythema at the base of the neck and the upper back; hypotensive episodes may also occur. Nephrotoxicity and ototoxicity are rare. Relationships between toxicities and serum concentrations have not been established. The disposition of vancomycin after intravenous administration proceeds biphasically--rapid distribution followed by elimination. The drug is excreted primarily unchanged in the urine by glomerular filtration. Vancomycin clearance is reduced and elimination half-life is prolonged in patients with renal insufficiency. Various methods have been published to aid in dosing the drug in these patients. Vancomycin is the drug of choice in the treatment of methicillin-resistant staphylococcal infections. It is also useful in the treatment of gram-positive endocarditis and has been used as alternative therapy in the treatment of prophylaxis of gram-positive infections in penicillin-allergic patients. Oral vancomycin is the preferred therapy in antibiotic-associated colitis.

Concentrations of fusidic acid, cloxacillin, and cefamandole in sera and atrial appendages of patients undergoing cardiac surgery

The concentrations of cefamandole, cloxacillin and fusicid acid were measured in the serum and heart tissue of 100 recipients of these drugs before cardiac surgery. During cardiopulmonary bypass, mean (+/- standard deviation) peak concentrations in serum of all patients were 63.0 +/- 34.0 micrograms of cefamandole per ml, 30.8 +/- 17.7 micrograms of cloxacillin per ml, and 32.4 +/- 10.8 micrograms of fusidic acid per ml. Mean (+/- standard deviation) concentrations in atrial appendages taken 1 h (+/- 15 min) after infusion were 21.3 +/- 11.0 micrograms of cefamandole per g, 23.8 +/- 17.3 micrograms of cloxacillin per g, and 10.7 +/- 4.2 micrograms of fusidic acid per g. No cloxacillin could be detected in 5 of 39 heart specimens. Mean tissue-to-serum ratios at 1 h for cefamandole, cloxacillin, and fusidic acid were respectively 0.35, 0.73, and 0.33. Fusidic acid, a drug which is highly effective in vitro against both methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis, was detectable in heart tissue in concentrations which were 12 times higher than the MICs of this agent against these resistant microorganisms.

Erythromycin: a microbial and clinical perspective after 30 years of clinical use (1)

Erythromycin is a macrolide that acts by inhibiting the translocation reaction during protein synthesis. Erythromycin is inactive against the Enterobacteriaceae and Pseudomonas aeruginosa except under alkaline conditions. Erythromycin is active against most gram-positive bacteria; some gram-negative bacteria, including Neisseria, Bordetella, Brucella, Campylobacter, and Legionella; and Treponema, Chlamydia, and Mycoplasma. The emergence of resistance to erythromycin is closely associated with its use and is often plasmid mediated. After its oral or parenteral administration, erythromycin diffuses readily into intracellular fluids and is actively concentrated intracellularly by polymorphonuclear leukocytes and alveolar macrophages.