Changing phage typing patterns of epidemic gentamicin-resistant Staphylococcus aureus. Evidence for transmission of gentamicin resistance

Mobility of gentamicin resistance genes from staphylococci isolated in the United States: identification of Tn4031, a gentamicin resistance transposon from Staphylococcus epidermidis

Homologous genes encoding resistance to gentamicin, tobramycin, and kanamycin through the bifunctional acetylating [AAC(6')] and phosphorylating [APH(2")] aminoglycoside-modifying enzyme were identified in staphylococci isolated from patients in the United States. The mobility of gentamicin resistance (Gmr) genes found on a prototype conjugative plasmid (pGO1) was compared with that of genes cloned from chromosomal sites. Plasmid-encoded Gmr genes and flanking sequences were introduced onto a temperature-sensitive plasmid (pRN3208) from pGO1 by homologous recombination between insertion sequence-like elements present on both replicons. Growth of Staphylococcus aureus strains containing the temperature-sensitive recombinant (pGO161) at the nonpermissive temperature for plasmid replication (42 degrees C) revealed no translocation of Gmr from its plasmid location. A transposon (Tn551) resident on the same replicon did translocate. Chromosomal Gmr determinants were cloned, together with the gene for trimethoprim resistance (dfrA), from three geographically distinct S. epidermidis isolates; two were subcloned onto temperature-sensitive Escherichia coli-S. aureus shuttle plasmids as 7.2-kilobase BglII fragments. Growth of both recombination-deficient and-proficient S. aureus strains containing the cloned genes at 42 degrees C allowed detection of transposition of Gmr sequences and identification of insertion into random chromosomal sites. We have designated this 5-kilobase transposon from S. epidermidis as Tn4031.

Plasmid profiles of multi-resistant Staphylococcus aureus at a children's hospital

Twenty-six strains of multi-resistant Staphylococcus aureus (MRSA) recovered from November 1985 to February 1986 were screened for their plasmid profiles. Among them, 11 strains were recovered from 8 patients with definite nosocomial infections. The results showed that one MRSA strain carrying 5 plasmids with molecular weight ranging from 1.75 X 10(6) to 5 X 10(6) daltons was epidemic in our hospital while 3 other distinct strains caused cross infections in both the burn ward and the medical wards. The epidemic strain and two other hospital-acquired strains were found in identical form in the community, suggesting that the pattern of nosocomial MRSA can be affected by strains outside hospital. The plasmid profile analysis was employed to differentiate the epidemic isolates from the coisolates and to study the relation between clinical isolates. The method is apparently superior to antibiogram.

Nosocomial infections with methicillin and tobramycin resistant Staphylococcus aureus--implication of physiotherapy in hospital-wide dissemination

From January 1979 to July 1980, methicillin and tobramycin resistant Staphylococcus aureus was isolated from 45 patients at a Veteran's Administration hospital. Of these 45, 36 (80%) had clinical infections involving non-surgical wounds (16), urinary tract (10), blood (8), surgical wounds (7), and sputum (5). The epidemic strain had a single phage type (47/54/75/77/83A), a single, 16.4 Md plasmid, and produced an aminoglycoside inactivating enzyme (AAD[4']). Compared to a control group of patients with nosocomial antibiotic susceptible S. aureus infections, patients with the epidemic strain had more hospital days before a positive culture (p = .004), more severe underlying disease (p = .006), received antibiotics more often (p = .0018), and underwent physiotherapy more often (p = .00007). Although selected environmental and personnel cultures were negative for the epidemic strain, epidemiologic investigation suggested that hospital-wide dissemination of S. aureus may have occurred through patient contacts in the physiotherapy department with subsequent clusters of cases occurring on several wards.

Occurrence of a nonplasmid-located determinant for gentamicin resistance in strains of Staphylococcus aureus

The occurrence of resistance to gentamicin in strains of Staphylococcus aureus with different phage patterns in two hospitals is described. The data suggest transfer of gentamicin resistance between different strains. In the strains investigated the determinant for resistance to gentamicin (parallel resistance to kanamycin and tobramycin) is located on the chromosome. The transfer of this resistance determinant in a mixed culture of donor and recipient cells in vitro is mediated by transduction because it is dependent upon lysogenicity of the donor for a serogroup-B phage and because it can be inhibited by gamma-globulin. The transfer is always associated with lysogenization of the recipient cells by this phage.

Gentamicin-resistant staphylococci: genetics of an outbreak in a dermatology department

The genetics of gentamicin resistance in Staphylococcus aureus strains isolated during an outbreak of infection in dermatology department have been studied. The predominant strain of S. aureus did not appear to possess a plasmid mediating gentamicin resistance though one isolate yielded a plasmid coding for penicillin and gentamicin. Three distinct plasmids were isolated from other phage types of S. aureus which appeared towards the end of the epidemic. There appeared to be a stepwise loss of gentamicin resistance in the predominant strain.

Clinical and laboratory studies of nosocomial Staphylococcus aureus resistant to methicillin and aminoglycosides

A methicillin/aminoglycoside-resistant strain of Staphylococcus aureus (MARS) was likely introduced by transfer of a patient from another hospital. Over the next year, 20 other patients were colonized or infected with MARS of the same phage type, although antibiograms varied. Affected patients usually had serious underlying disease and were in intensive care units. Vancomycin therapy was frequently delayed and MARS may have contributed to the death of some patients. The mode of spread was not definitively delineated, but two nurses were found to be colonized. Institution of isolation procedures was difficult, but the problem gradually waned. Susceptibility testing showed vancomycin to be the most active agent. Synergy studies showed no consistent effect of combining methicillin with an aminoglycoside. This experience illustrates the problem of MARS spread between hospitals and wards, the need for institution of effective control measures, and consideration of early empiric use of vancomycin.

Common R-plasmids in Staphylococcus aureus and Staphylococcus epidermidis during a nosocomial Staphylococcus aureus outbreak

During a 7-month period in 1978 to 1979, 31 patients and personnel at a Kentucky hospital were colonized or infected with a Staphylococcus aureus strain resistant to clindamycin, erythromycin, gentamicin, methicillin, penicillin, and tetracycline. S. epidermidis with similar antibiotic resistance patterns had been isolated in this hospital in the year before the S. aureus outbreak. A 32-megadalton R-plasmid, pUW3626, mediating resistance to penicillin and gentamicin, was present in these isolates and in coisolated S. epidermidis from the same outbreak. By colony hybridization, pUW3626 was homologous to gentamicin R-plasmids from staphylococci isolated in other geographic areas. Our studies suggest that the emergency of antibiotic resistance in S. Aureus may result from genetic transfer from S. epidermidis as well as from the interhospital spread of resistant staphylococci.

Epidemic neonatal gentamicin-methicillin--resistant Staphylococcus aureus infection associated with nonspecific topical use of gentamicin

One hundred sixteen infants in an intensive care nursery acquired Staphylococcus aureus resistant to gentamicin and methicillin; 54 patients acquired S. aureus sensitive to gentamicin and methicillin. Topical application of gentamicin ointment was significantly associated with acquisition of GMRS. Of 78 infants who acquired GMRS, 38 had received GmO before GMRS was first cultured, whereas only one of 49 infants with GMSS had previously received GmO (P = 8.6 X 10(-8)). Infants with GMRS were also more likely than patients with GMSS to have had a lower mean birth weight, Apgar score, and gestational age; systemic antibiotic therapy and incubator care were significantly prolonged for patients with GMRS, but these factors did not explain susceptibility to GMRS infection. Multivariate logistic regression analysis showed that use of GmO was the single most important risk factor.

Methicillin-resistant Staphylococcus aureus: interstate spread of nosocomial infections with emergence of gentamicin-methicillin resistant strains

A methicillin-resistant strain of Staphylococcus aureus (MRSA, phage type 84/85) was introduced into City of Memphis Hospital by a burn patient who had recently been treated for MRSA bacteremia in another institution 500 miles distant. Despite prompt recognition of the problem and institution of isolation procedures, six other patients developed secondary colonization during the ensuing six months, and five of these experienced clinically significant infections with MRSA. Three of the patients originally infected with MRSA, as well as two additional patients, subsequently developed colonization with staphylococcal strains of phage type 84/85 that were resistant to both methicillin and gentamicin (MRGRSA). Spread of the staphylococcal strains was most likely accomplished primarily via passive transfer from person to person. The hydrotherapy unit, which became contaminated with both MRSA and MRGRSA, may have played a secondary role. As illustrated by this outbreak, patients carrying potentially dangerous bacterial strains should be identified and informed of the problems posed by such carriage. It may be imprudent to admit such patients to hospitals that are free of the potential pathogen. The outbreak described here exemplifies a number of potential problems associated with control of nosocomial staphylococcal infections: (a) interhospital spread of methicillin-resistant strains; (b) secondary patient-to-patient intrahospital spread; and (c) emergence of even more resistant strains, possibly associated with selective pressures exerted by widespread use of broad-spectrum antimicrobial agents.