Ampicillin and cephalothin susceptibility of community-acquired Enterobacteriaceae

We prospectively evaluated all Enterobacteriaceae isolated at a Veterans Administration medical center during an eight-week period for site of acquisition and antimicrobial susceptibility. Patients from whom isolates were obtained were also evaluated for underlying diseases and other factors possibly pre-disposing to colonization or infection with Enterobacteriaceae. During this period 118 patients were identified in whom 130 strains of Enterobacteriaceae were isolated; 90% of the isolates were identified in urine cultures. Two thirds of the isolates were hospital acquired. Seventeen of 40 CA isolates were resistant to ampicillin, cephalothin, or gentamicin sulfate alone or in combination. Age, underlying diseases, and recent surgery or antibiotic therapy were as common in patients with sensitive organisms as in those with resistant ones in the community setting. In our population of predominantly elderly men with frequent underlying diseases, CA Enterobacteriaceae are frequently resistant to ampicillin (43%) and cephalothin (25%). Therefore, it may be appropriate in such populations to initiate therapy with an aminoglycoside when serious CA Enterobacteriaceae infection is suspected.