Mechanism of aminoglycoside resistance among beta-lactam-resistant Escherichia coli in the United States

We examined aminoglycoside (AG) resistance in ampicillin-resistant Escherichia coli obtained from nine hospitals participating in the National Nosocomial Infections Study. The isolates were tested to 25 antimicrobials using broth microdilution methods. If the organism was intermediate or resistant to gentamicin, tobramycin, netilmicin, or amikacin, we determined the class of aminoglycoside-modifying enzyme (AME) using the phosphocellulose paper binding assay. Of 423 E. coli, 21 (5%) were intermediate or resistant to one or more of the AGs. All but two of these E. coli isolates had at least one AME. Twelve isolates had phosphotransferase (APH) enzymes; seven had adenyltransferase (ANT) enzymes (all ANT[2"]); and four had acetyltransferase (AAC) enzymes. The seven ANT[2"]-producing isolates were more likely to be acquired in the community than in the hospital (4/7 ANT[2"]-producing E. coli versus one of 14 of the other AG-resistant E. coli, p = 0.03, Fisher's exact test). These findings suggest that for E. coli resistant to both ampicillin and an AG, APH enzymes are the predominant AME class. Additionally, isolates with certain AMEs may be acquired both in the community and in the hospital.

Illness with fatalities in premature infants: association with an intravenous vitamin E preparation, E-Ferol

Three clusters of an unusual syndrome in premature infants were investigated in three intensive care nurseries in 1984. A retrospective cohort study of 68 infants weighing less than or equal to 1,250 g at birth and surviving at least 72 hours revealed that in 13 infants ascites developed and in four at least two of the following abnormal laboratory values were found within a seven-day period: serum direct bilirubin greater than or equal to 2 mg/dL, blood urea nitrogen greater than or equal to 40 mg/dL or serum creatinine greater than or equal to 2 mg/dL, and platelet count less than or equal to 60,000/microL. All cases occurred after the introduction and use of intravenous E-Ferol, a vitamin E preparation that was new on the market when the clusters were reported. All 17 case infants but only 23 of 51 (45%) noncase infants received E-Ferol (P less than .0001). Case and noncase infants were similar with respect to other complications and to receipt of medications and parenteral nutrition. A dose-response relationship was found; cases occurred in infants receiving E-Ferol dosages of greater than 20 U/kg/d. Case infants who had higher daily doses of E-Ferol had a shorter latency. No new cases were reported after use of E-Ferol was stopped. Results of these investigations led to a nationwide recall of intravenous E-Ferol.

Antibiotic-resistant flora in nursing home patients admitted to the hospital

To study carriage of multiply resistant gram-negative bacilli, 50 patients admitted to the hospital from nursing homes (NHs) and 50 control admissions not from NHs were matched for age and recent antibiotic use. Their antibiotic resistance patterns were similar: 20 NH patients and 14 controls had resistant strains. However, significantly more patients (64%) from NHs with large numbers of "skilled beds" had resistant bacteria than did patients from small NHs (21%) or controls (28%). Also, more patients from NHs had members of the Proteus-Providencia-Morganella group in their urine than did controls. Discriminant analysis showed that residence in NHs with large numbers of skilled beds, recent antibiotic use, and bladder dysfunction (indwelling catheter or incontinence) were independently important in predicting carriage of resistant strains in NH and control patients. Over 75% of resistant isolates were from rectal specimens, emphasizing the occult way that such strains are brought into the hospital.

The role of host factors in an outbreak of necrotizing enterocolitis

During an outbreak investigation of necrotizing enterocolitis (NEC) in a neonatal intensive care unit, we identified nine definite and six suspected cases of NEC on the basis of histopathologic, clinical, and roentgenographic findings. Neonates of low birth weight (less than 1,250 g) had the highest incidence of NEC, supporting a role for prematurity in this disease. Patients with definite NEC and those with severe clinical features had significantly lower birth weights and postconception ages (gestational age at birth plus postnatal age at onset of NEC) than the patients with suspected NEC. In a case-control study using birth weight-matched control subjects, maternal toxemia was identified as a possible protective factor for NEC. To our knowledge, this is the first report of the relationship between NEC disease severity and postconception age. These findings also suggest that toxemia may be an important protective factor in NEC and should be examined in subsequent studies.

A nursery outbreak of multiple-aminoglycoside-resistant Escherichia coli

In the neonatal intensive care unit (NICU) of one hospital, 16 infants became colonized or infected with multiply-resistant Escherichia coli (MR-E.coli) over an 8-month period. Isolates were obtained from blood, urine, and sputum of three patients and from rectal surveillance cultures of 13 patients. The one patient with the blood isolate died. A matched case-control study identified continuous feeding (nine of 16 cases vs. one of 16 controls, p less than or equal to 0.001) and receipt of aminoglycosides (p less than or equal to 0.03) as risk factors. For case-babies not exposed to continuous feeding, duration of bolus feeding was significantly greater than for their controls (cases, 22 days; controls, 7 days; p less than or equal to 0.02). All 16 isolates were the same serotype and were resistant to amikacin, tobramycin, kanamycin, and gentamicin. The epidemiologic investigation suggested that MR-E. coli may have spread from person-to-person on the hands of personnel and that MR-E. coli persisted in the NICU for 8 months until effective control measures were instituted.

Control of aminoglycoside resistance by barrier precautions

The efficacy of antibiotic resistance (barrier) precautions for control of aminoglycoside resistance was evaluated from 1978 to 1981. Despite increasing aminoglycoside use and a 13-fold increase in aminoglycoside-resistant isolates on a newly opened oncology unit, the hospital-wide frequency of aminoglycoside resistant Enterobacteriaceae remained low, supporting the continued value of barrier precautions which were initiated in our hospital in 1974. This control enabled us to focus on exceptions to the effectiveness of barrier precautions. These were traced to environmental reservoirs, very chronic and heavily infected patients, asymptomatic carriers of Serratia, and oncology patients receiving oral non-absorbable aminoglycosides. In addition, resistance in Pseudomonas aeruginosa paralleled aminoglycoside use and, as in our prior experience, continued to rise. With increasing adoption of barrier precautions by others such exceptions should be anticipated.

Prosthetic valve endocarditis caused by Histoplasma capsulatum

Previously reported cases of Histoplasma capsulatum infection of prosthetic heart valves have been first diagnosed at autopsy. A patient had an H capsulatum infection that was diagnosed by serologic means 1 1/2 years before involvement of the patient's prosthetic mitral valve was found at surgery. Numerous previous attempts to demonstrate organisms by culture and histologic study of bone marrow and liver biopsy specimens were unsuccessful. Various serologic tests were used in the diagnosis and evaluation of treatment of H capsulatum endocarditis. The management of this case was compared with 29 other previously reported cases of endocarditis caused by H capsulatum.