Retrospective chart review was undertaken for 480 patients who underwent a total of 506 valve replacements or repair procedures for infective endocarditis. The influence of preoperative antimicrobial treatment on culture, Gram stain, and histopathological examination findings for resected valve specimens was examined. When valves were removed before the end of treatment, organisms were seen on the Gram stain of ground valve material performed in the microbiology laboratory and on Gram-stained histopathological sections in 231 (81%) of 285 and 140 (67%) of 208 specimens, respectively (P=.0007). Gram-positive cocci were either cultured from or observed in excised valve tissue in 42 (67%) of 63 episodes involving negative preoperative blood cultures. Positive Gram stain results for microbiological specimens should be reintroduced into the definite pathological criteria for infective endocarditis. When deciding on how long to continue antimicrobial therapy after valve replacement for endocarditis, valve culture results should be the only laboratory finding taken into account, because it takes months for dead bacteria to be removed from sterile vegetations.

Relapse is an uncommon event following surgery for endocarditis. Commonly suggested indications for prolonging postoperative treatment are not associated with higher relapse rates, and their relevance is debatable. We conclude that it is unnecessary to continue treatment for patients with negative valve culture results for an arbitrary 4-6-week period after surgery. Two weeks of treatment appears to be sufficient, and, for those operated on near the end of the standard period of treatment, simply completing the planned course should suffice.

No abstract

Coagulase-negative staphylococci were tested for susceptibility to methicillin, cephradine, ceftriaxone, cephalothin, and cefamandole by standard broth microdilution. Most of the 26 methicillin-resistant isolates were susceptible to cephalothin and cefamandole, but very few were susceptible to ceftriaxone, and none was susceptible to cephradine. The proportion of bacterial cells that grew in the presence of 128 micrograms of methicillin per ml was calculated for each methicillin-resistant isolate. Those with every cell or 1 in 10 cells resistant to 128 micrograms of methicillin per ml included the isolates that were most resistant to the cephalosporins and highly resistant to methicillin. Those with 1 cell resistant in 10(5) or 10(6) cells were the isolates most susceptible to the cephalosporins, and their methicillin MICs were lower. When cells resistant to 128 micrograms of methicillin per ml were used as inocula for broth microdilution tests, resistance to cephradine remained the same, but resistance to ceftriaxone, cephalothin, and cefamandole increased significantly. Cefamandole was the only cephalosporin which retained antibacterial activity against some methicillin-resistant isolates (12 of 26). Cephradine, ceftriaxone, cephalothin, and cefamandole resistance appeared to be expressed by the same cells that expressed methicillin resistance. In this way, cross resistance was demonstrated between methicillin and the cephalosporins.

Colonization of a patient by methicillin-resistant Staphylococcus aureus (MRSA) of a single phage-type for over four years is described. During this period we observed the appearance and disappearance of resistance to erythromycin, clindamycin, gentamicin, kanamycin, tobramycin, neomycin and mupirocin. We also saw stepwise increases in methicillin resistance and reversible changes in physical appearance and the colonizer pathogen role. Correlation of clinical observations, details of antibiotic therapy and laboratory studies demonstrated that adaptation of MRSA during antibiotic therapy favoured MRSA establishment and predominance.