Dennis R. Schaberg

Major trends in the microbial etiology of nosocomial infection

To determine trends in the microbial etiology of nosocomial infections in the 1980s, surveillance data on the microbiology of documented nosocomial infection reported to the National Nosocomial Infections Surveillance System and from the University of Michigan Hospital were analyzed. Antimicrobial susceptibility data on selected pathogens from both sources were also reviewed. Overall, Escherichia coli decreased from 23% of infections in 1980 to 16% in 1986-1989, Klebsiella pneumoniae dropped from 7% to 5%, whereas coagulase negative staphylococci increased from 4% to 9% and Candida albicans increased from 2% to 5%. Staphylococcus aureus, Pseudomonas aeruginosa, Enterobacter species and enterococci had minor increases, but antimicrobial resistant strains for these pathogens as well as coagulase-negative staphylococci were seen more frequently. In contrast to the 1970s, major shifts in the etiology of nosocomial infection have occurred in the decade of the 1980s. Taken as a whole, the shifts are away from more easily treated pathogens toward more resistant pathogens with fewer options for therapy. These shifts underscore the continued need for prevention and control to accompany new developments in therapy.

Increasing resistance of enterococci to ciprofloxacin.

We determined that resistance to ciprofloxacin has emerged in enterococci over the last 5 years in our hospital, mainly in strains demonstrating the phenotype of high-level gentamicin resistance. All high-level-gentamicin-resistant isolates from 1985 and 1986 were susceptible, whereas 24% of isolates from 1989 and 1990 were resistant to ciprofloxacin. Plasmid and genomic DNA typing showed at least six unique strains exhibiting resistance, but one type accounted for 80% of recent resistant isolates, suggesting a role for cross infection in the emergence of resistance.

Experimental spinal epidural abscess: a pathophysiological model in the rabbit

To define the pathophysiology of spinal cord dysfunction associated with spinal epidural abscess formation, we developed an experimental model. Spinal epidural abscesses were produced in rabbits by injecting Staphylococcus aureus into the posterior thoracolumbar epidural space under direct vision. Progressive neurological deficits were detected in 18 of 20 animals; severe paraparesis or paraplegia occurred in 75%, and sphincter dysfunction occurred in 55%. Clinical data, including the results of plain spine roentgenography, myelography, and biochemical and bacteriological examination of the cerebrospinal fluid, were recorded. Epidural abscesses with varying degrees of spinal cord compression were confirmed pathologically in 95% of the experimental group. Spinal cord white matter changes included vacuolization, loss of myelin, and axonal swelling. The gray matter of the spinal cords was relatively preserved. There was no microscopic evidence of thrombosis or vasculitis in the major blood vessels supplying the spinal cords. Histopathological changes detected in the spinal cords were more consistent with direct compression of neural tissue than with infarction. The progressive clinical course and the histopathological changes in the spinal cord after compression by abscess closely resembled those of experimental compression of the spinal cord by epidural neoplasm.

Detection and characterization of mupirocin resistance in Staphylococcus aureus.

Fourteen mupirocin-resistant Staphylococcus aureus strains were isolated over 18 months; 12 exhibited low-level resistance, while two showed high-level resistance. Highly mupirocin-resistant strains contained a large plasmid which transferred mupirocin resistance to other S. aureus strains and to Staphylococcus epidermidis. This plasmid and pAM899-1, a self-transferable gentamicin resistance plasmid, have molecular and biologic similarities. Images

Efficacy of ampicillin versus trimethoprim-sulfamethoxazole in a mouse model of lethal enterococcal peritonitis.

Lethal enterococcal peritonitis in mice was used to compare trimethoprim-sulfamethoxazole (TMP-SMX) therapy with ampicillin therapy. Peritoneal fluid showed a 10(3)-CFU decrease in enterococci with ampicillin compared with TMP-SMX. Mortality of the untreated mice was 100%, compared with 40% for ampicillin and 95% for TMP-SMX, despite adequately measured levels in serum and peritoneal fluid.

Ciprofloxacin versus vancomycin in the therapy of experimental methicillin-resistant Staphylococcus aureus endocarditis.

We compared the efficacy of ciprofloxacin with that of vancomycin by using the rabbit model of methicillin-resistant Staphylococcus aureus endocarditis. Endocarditis was treated with ciprofloxacin (25 mg/kg [body weight] intravenously every 8 h) or vancomycin (17.5 mg/kg intravenously every 6 h) for 3 days. Vancomycin and ciprofloxacin were equally efficacious in clearing bacteremia. Both reduced vegetation bacterial counts by 5 log10 CFU/g and renal and splenic bacterial counts by more than 3 log10 CFU/g as compared with untreated control rabbits after 26 h of infection (P less than 0.001). Both antimicrobial agents were able to eradicate the infectious process in an equivalent proportion of animals. No methicillin-resistant S. aureus that was recovered from ciprofloxacin-treated rabbits developed resistance to ciprofloxacin during therapy. Peak concentrations of ciprofloxacin in the sera of rabbits with endocarditis were significantly higher than those predicted by single-dose studies in uninfected rabbits. This finding was likely due to changes in the pharmacokinetics of the drug with multiple dosing and in infected versus uninfected rabbits. This study demonstrated that intravenously administered ciprofloxacin is as efficacious as vancomycin is in an in vivo model of a serious systemic methicillin-resistant S. aureus infection.

Colonization and transmission of high-level gentamicin-resistant enterococci in a long-term care facility.

OBJECTIVES To assess the prevalence of high-level gentamicin-resistant enterococcus (HGRE) colonization, transmission patterns, and spectrum of illness among residents of a long-term care facility. DESIGN Monthly surveillance for HGRE colonization of wounds, rectum, and perineum over a 1-year period. SETTING A Veterans Affairs long-term care facility attached to an acute-care facility. PATIENTS All 341 patients in the facility during the observation period. RESULTS Over the 1-year period, 120 patients (35.2%) were colonized with HGRE at least once, with an overall monthly colonization rate of 20 +/- 1.5%. HGRE were isolated from rectum (12.8%), wounds (11.7%), and perineum (9.3%). Patients with the poorest functional status had the highest rate of colonization (P < 0.0005). HGRE-colonized patients were more likely to be colonized with methicillin-resistant Staphylococcus aureus (51% versus 25%; P < 0.0005). Seventy-four patients (21.7%) were colonized at admission or at the start of the study. Another 46 patients (13.5%) acquired HGRE during the study, including 36 who acquired HGRE while in the long-term care facility and 10 who were positive when transferred back from the acute-care hospital. Based on plasmid profiles, only two patients appeared to have isolates similar to those of current or previous roommates. Carriage of HGRE was transient in most cases. Only 20 patients were colonized for 4 or more months, and those patients usually carried different strains intermittently. Infections were infrequent, occurring in only 4.1% of total patients. CONCLUSIONS In our long-term care facility, HGRE were endemic, and new acquisition of HGRE occurred frequently. However, only two patients had evidence of acquisition from a roommate, suggesting that cross-infection from a roommate was not a major route of spread of HGRE.

Artery, periarterial adipose tissue, and blood microbiology during vascular reconstructive surgery: Perioperative and early postoperative observations

The presence and clinical significance of bacteria in the arterial wall, periarterial adipose tissue, and blood samples acquired during elective vascular operations were assessed in this study. Specimens were obtained from a random series of 84 patients (56 men, 28 women) undergoing 75 primary and 9 secondary arterial reconstructions. Operations performed most frequently included abdominal aortic aneurysmectomy (42), aortofemoral bypass reconstruction (15), and lower extremity bypass surgery for occlusive disease (7). Perioperative antibiotics were administered to all but one patient. A sample of artery, adjacent adipose tissue, and blood were obtained for microbial analysis during the vascular anastomosis or arteriotomy. This yielded a total of 152 artery, 139 adipose tissue, and 129 blood samples for study. Each specimen was divided and placed in blood agar plates, thioglycolate broth, and brain-heart infusion broth. Tissues yielding growth of the same organism(s) in two or more different media were considered positive for the presence of bacteria. Bacteria were present in at least one of the three tissues studied in 32/84 patients (38%). The frequency of positive cultures in primary (29/75, 39%) and secondary procedures (3/9, 33%) were similar. One positive culture site occurred in 26/32 (81%) patients, two positive culture sites existed in 5/32 (16%) patients, and three positive sites were found in 1/22 (3%) patients. Eighteen individual artery (18/152, 12%) and 19 adipose tissue samples (19/139, 14%) harbored bacteria, whereas only two blood cultures were positive (2/129, 2%). Organisms identified included coagulase-negative staphylococci (71%), gamma-streptococci (7%), diphtheroids (7%), Micrococcus (5%), alpha-streptococci (5%), Staphylococcus aureus (2%), and Pseudomonas picketti (2%).(ABSTRACT TRUNCATED AT 250 WORDS)

Bordetella bronchiseptica pneumonia in a patient with chronic lymphocytic leukemia

This case report describes two episodes of pneumonia caused by Bordetella bronchiseptica in a patient with chronic lymphocytic leukemia. There was discrepancy between the in vitro sensitivity testing of the organism and subsequent clinical response to several antimicrobial agents. Human infection with B bronchiseptica is almost always associated with severe underlying disease and contact with an appropriate animal reservoir.

Clostridium difficile plasmid isolation as an epidemiologic tool

A large hospital outbreak ofClostridium difficile diarrhea at the Minneapolis Veterans Administration Medical Center (MVAMC) was studied by plasmid profile typing. Plasmids were obtained from 30 (37 %) of 82 clinical isolates from MVAMC patients and 10 (67 %) of 15 non-MVAMC isolates. While bacteriophage plus bacteriocin typing and polyacrylamide gel electrophoresis (PAGE) plus bacterial agglutination typing proved more universally applicable, plasmid profiles may be useful for tracing isolated epidemic outbreaks, reinfections and relapses caused by plasmid-bearing strains.