Characterization of resistance phenotype and cephalosporin activity in oxacillin-resistant Staphylococcus aureus.

Forty isolates of methicillin-resistant Staphylococcus aureus were tested versus oxacillin at 30 and 35 degrees C with and without 2% NaCl supplementation of Mueller-Hinton broth and classified as having resistance that was low (MIC, less than or equal to 16 micrograms/ml) or high (MIC, greater than or equal to 32 micrograms/ml) and temperature or NaCl dependent. Only three isolates had low-grade resistance at both 30 and 35 degrees C; for two isolates the MICs at 35 degrees C were greater than or equal to 4 X the MICs at 30 degrees C. NaCl usually increased the MICs two- to fourfold. Efficiency of plating studies were performed on strains selected for their level of oxacillin resistance and according to temperature-related difference in MICs. Most strains appeared to represent the heterogeneous resistance phenotype. Cefamandole MICs were little affected by temperature but increased with NaCl. With three exceptions, cefamandole MCBs were less than or equal to 4 X MICs. For only six isolates were cefuroxime MICs less than or equal to 16 micrograms/ml. Four strains that were susceptible to both cefuroxime and cefamandole were selected for time-killing curve studies at inocula of 10(7) CFU/ml. At 8 X MIC, cefuroxime failed to reduce the concentration of any strain by greater than or equal to 3 X log10 CFU/ml. Killing of greater than or equal to 3 X log10 CFU/ml was achieved by cefamandole at 4X and 8 X MIC in one strain, at 8 X MIC only in two strains, and by neither 4 X nor 8 X MIC in one strain. Within therapeutically attainable blood levels, cefuroxime is essentially inactive and cefamandole is variably bactericidal against oxacillin-resistant s. aureus.

Community-acquired febrile illness in patients with prosthetic heart valves.

We prospectively studied 40 patients with prosthetic heart valves and community-acquired febrile illness. The mean age of the group studied was 35.2 +/- 12.8 years, and the mean length of time that the prosthetic valve had been in place was 53.4 +/- 43.7 months. There was a high incidence (37.5%) of infectious endocarditis in the patients studied, with a total mortality of 15% in the group. The presence of a new regurgitant murmur, skin or retinal lesions, splenomegaly, vegetations shown on echocardiograms, and persistent bacteremia was associated with infectious endocarditis (P less than .05). The patients with mechanical Starr-Edwards valves had a significantly higher incidence (P less than .001) of infectious endocarditis than those with other types of prosthetic valves implanted in our hospital. Complete evaluation is mandatory in febrile patients with prosthetic heart valves because of the high risk of prosthetic valve endocarditis as the cause of the fever.

Mycobacterium fortuitum endocarditis after mitral valve replacement with a bovine prosthesis.

We have described a patient who had mitral valve replacement with a bovine prosthesis, followed by infectious endocarditis caused by Mycobacterium fortuitum. We found no previous reports of endocarditis caused by this organism involving a biologic heart prosthesis.

Salmonella bacteremia in patients with prosthetic heart valves.

During 1982 and 1983, five patients with prosthetic heart valves and documented Salmonella bacteremia were admitted to the Instituto Nacional de Cardiolog ía in Mexico City. The clinical and microbiologic features in this group of patients are described, as well as the therapeutic implications when Salmonella bacteremia is present in patients with heart prostheses. None of the patients had evidence of infectious endocarditis; however, all received prolonged parenteral antimicrobial therapy for at least four weeks with ampicillin or chloramphenicol, with excellent clinical response.