Replication of the 50 and 58 moles per cent guanine plus cytosine (%GC) components of R factor 222 in Proteus mirabilis during growth in the presence and absence of chloramphenicol and after shifting exponential- and stationary-phase cells to conditions which inhibit host protein or deoxyribonucleic acid (DNA) synthesis was examined. Chloramphenicol reduced the growth rate but increased the amount of both R-factor components; the 58% GC component showed a larger proportionate increase. This was inferred to indicate reduced synthesis of an inhibitor that acts on both R-factor components and an initiator for replication of the 50% GC component. Replicative patterns observed after shifting exponential- and stationary-phase cells grown with or without chloramphenicol to minimal medium or chloramphenicol for one generation, or puromycin for 3 hr, corroborated this interpretation. After shifts of exponential cells from either medium, replication of the 50% GC components paralleled host replication, thus indicating a requirement for protein synthesis; replication of the 58% GC component increased due to reduced inhibitor synthesis. R-factor DNA remained constant after shifting stationary cells from drug-free medium, thus indicating that the cells contained effective concentrations of the regulatory inhibitor, whereas increased replication of the 58% GC component occurred after identical shifts of chloramphenicol-grown cells of the same chronological age. Similar responses were observed after shifts to 5 C or to medium containing streptomycin or tetracycline. Absence of replication of the 50% GC component after shifting to medium containing nalidixic acid or phenethanol and its hereditary persistence during growth indicated that the 50% GC replicon was attached to the membrane. Thus, in P. mirabilis the three replicons of R factor 222 are regulated as follows: The composite and transfer portion (RTF) replicons represented by the 50% GC component require protein synthesis and membrane attachment and are negatively regulated by an inhibitor; the 58% GC or resistance-determinants replicon exists cytoplasmically and is subject only to negative control.

In young adults with T1DM, geographical separation, socioeconomic disadvantage and risk-taking behaviours did not influence glycaemic control. Longer duration of diabetes identifies young adults at higher risk of poor control, while attendance at a multidisciplinary clinic and engagement in work or study was associated with better glycaemic control. Additional studies are warranted to clarify the role of behavioural interventions to improve diabetes management in young adults.

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A comparative study was done on the transfer frequency of R factors from 90 strains of multiple drug-resistant Aerobacter and 81 strains of Klebsiella to Escherichia coli CSH-2 (F-, met-, pro-, Nal-r). The most common resistance patterns for the Aerobacter isolants were ampicillin streptomycin chloramphenicol tetracycline and ampicillin streptomycin chloramphenicol tetracycline kanamycin neomycin; for the Klebsiella isolants, the most common resistance pattern was ampicillin kanamycin streptomycin tetracycline chloramphenicol neomycin. R factors were isolated from 14.1% of the Aerobacter strains; 61.5% of these R factors harbored R determinants for ampicillin streptomycin tetracycline. R factors were isolated from 79.1% of the Klebsiella strains; four R factors were isolated with significant frequency; streptomycin chloramphenicol kanamycin neomycin, 37.5%; ampicillin streptomycin tetracycline kanamycin neomycin, 14.1%; ampicillin streptomycin tetracycline, 12.5%; and streptomycin chloramphenicol tetracycline, 12.5%. Chloramphenicol, kanamycin, and neomycin resistance was rarely transferred from the Aerobacter strains, although over 50% of the clinical isolants possessed resistance to these antibiotics. In contrast, over 75% of the Klebsiella strains transferred resistance to chloramphenicol, kanamycin, neomycin. Highest frequency of transferred resistance to individual drugs in the Aerobacter strains was to streptomycin (14.8%), whereas in the Klebsiella group resistance to four drugs was transferred at a very high frequency: streptomycin (80.8%), chloramphenicol (78.5%), kanamycin (76.4%7c), and neomycin (75.9%). Within the last 5 years in the Medical College of Virginia hospitals, as in others, there has been a significant increase in infections caused by gramnegative bacteria (2, 7, 14, 15, 17). Particularly, Aerobacter and Klebsiella have demonstrated an increase in resistance to multiple drugs which may be due to episomal resistance transfer factors (1, 8). This type of rapidly appearing multiple drug resistance is known to be mediated by an extrachromosomal deoxyribonucleic acid particle (R factor), which is an independent linkage group composed of genes determining drug resistance (R determinants; 4, 20). The existence of gram-negative bacteria possessing R factors responsible for resistance to numerous antibiotics, i.e., ampicillin (Am), tetracycline (Tc), chloramphenicol (Cm), streptomycin (Sm), kanamycin (Km), the sulfonamides, and neomycin (Nm), has been reported in Japan, Great Britain, the European continent, Israel, and recently in the United States (3, 9, 15, 16, 18). In this communication, the incidence of R factors in clinically isolated multiple drug-resistant strains of Klebsiella and Aerobacter is reported. MATERIALS AND METHODS Sources of bacteria. Strains of multiple drugresistant Klebsiella and Aerobacter were isolated from clinical sources, i.e., urine, sputum, wounds, exudates, and blood, during the period from March to June 1968. No effort was made to distinguish between hospitaland com...

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