Enterococci highly resistant to penicillin and ampicillin: an emerging clinical problem?

Abstract

Sixteen clinical isolates of ampicillin-resistant enterococci (ARE) were recovered from the microbiology laboratory of a 450-bed rehabilitation medical center from January 1981 to September 1987. These isolates were detected when a disk diffusion test using 10 ,ug of ampicillin on a blood agar plate revealed no zones of inhibition. Tube macrodilution tests yielded an MIC of .16 ,ig of ampicillin per ml. None of the isolates were penicillinase producers by the chromogenic cephalosporin disk test. Ten isolates were Enterococcus faecium, four isolates were E. raffinosus, one isolate was E. gallinarum, and one isolate was not identified (lost). There were 6 male and 10 female patients. The sources of isolates were urine (n = 7), wound (n = 5), ascitic fluid (n = 2), blood (n = 2), peritoneal catheter tip (n = 1), Bartholin's cyst abscess (n = 1), rectal swab (n = 2), and pancreatic abscess (n = 1). The organism was isolated from multiple sites in 4 patients, was a pure culture isolate in 5 patients, and was part of a polymicrobial fora in 11 patients. Six patients were diabetic, and four had liver cirrhosis. All but four patients had received at least one antibiotic within 3 weeks of ARE isolation. The MICs (micrograms per milliliter) for 50 and 90% of isolates tested, respectively, were as follows:

Vancomycin resistance emerging in a clonal outbreak caused by ampicillin-resistant Enterococcus faecium

“…Our patients had been hospitalized for a long time prior to ARE‐infection, had high consumption of antibiotics and a high proportion of the patients had severe underlying diseases. These findings are in accordance with those in other outbreaks[5–14,43]. Many cases of multiple‐drug‐resistant enterococcal infections have been described in debilitated patients with prolonged hospital stay[19–45] who have received multidrug regimens or antimicrobial agents for a long time[15–46].…”

“…Several factors have also been suggested as modifiers of the outcome of enterococcal infection, among them ampicillin resistance[5–24]. None of the fatal cases in this study was found in patients without underlying severe and life‐threatening diseases.…”

“…Enterococci have acquired high‐level resistance to aminoglycosides[8–9]. Later, ampicillin‐resistant enterococci[10–11] and eventually vancomycinresistant enterococci (VRE) emerged[12–13]. Multiple‐drug resistant enterococci (MDRE) combine inherent resistance of Enterococcus spp.…”

Risk factors for acquiring ampicillin-resistant enterococci and clinical outcomes at a Canadian tertiary-care hospital

“…Ampicillin resistance among enterococcal isolates was reported to be rare in a survey of 382 isolates in 1969 (35). Since then there have been several reports of a growing clinical problem with ARE (2,3,5,12,30,33). Our study confirms this and illustrates the importance of ARE as nosocomial pathogens.…”

“…High-level resistance to aminoglycosides which results in a lack of bactericidal synergism when combined with cell wallactive agents is now frequently seen worldwide (27,31). Ampicillin-resistant enterococci (ARE) are increasingly common in some centers (2,30,33), and more recently, vancomycin-resistant enterococci have been isolated with greater frequency in the United States and Europe (7,10,15,19). It has been reported that the prevalence of vancomycin-resistant enterococci in hospital intensive care units in the United States increased from 0.8% of enterococcal strains in 1989 to an alarming 13.3% by 1993 (9).…”