Naomi Datta

R factors from Proteus rettgeri.

SUMMARY: Of 12 R factors transferred from wild strains of Proteus rettgeri to Escherichia coli K12, all were fi - Five were of the N-compatibility group; three belonged to a newly defined group T, of which Rts1 is the prototype; one belonged to group W. The other three constituted at least one compatibility group, not previously described. The replication of two of the T plasmids, like that of Rts1, was temperature sensitive. This set of R factors is significantly different from those derived from bacteria of other genera.

Trimethoprim Resistance Conferred by W Plasmids in Enterobacteriaceae

SUMMARY: High-level resistance to trimethoprim (minimum inhibitory concentration > 1000 μ/ml) was conferred by R factors of the W compatibility group in Escherichia coli and Klebsiella spp. isolated from patients in three London hospitals. We suggest that we are observing the early stages in the spread of a new R factor.

Host Ranges of R Factors

SUMMARY: All R factors so far described can be transmitted to Escherichia coli. F-like R factors are transmissible to the Proteus group but not to the Pseudomonadaceae. Among fi - R factors, I-like plasmids are not transferable to Proteus although they mediate conjugation, allowing transfer of other plasmids to this group. They are not transmissible to the Pseudomonadaceae. P-group plasmids are transmissible to both taxa. Plasmids of groups N and W are transmissible to Proteus (transfer to Pseudomonas was not tested because of lack of suitable markers).

Sex pili and the classification of sex factors in the enterobacteriaceae.

The properties of sex pili determined by different plasmids of the Enterobacteriaceae suggest that there may be only two major classes of sex factor, typified by F and the factor of colicin factor lb.

R factors from Proteus morganii.

Summary: Twenty-eight R factors transmissible to Escherichia coli K12 were derived from 178 naturally occurring strains of Proteus morganii and evidence was found of non-transmissible resistance plasmids in some strains. Nine plasmids were assigned to group N; one P. morganii strain carried two N plasmids which were incompatible in reference strains of E. coli or P. morganii. Six fi + R factors of group FII were found. One was unique among F-like plasmids in conferring hspII restriction. Entry exclusion by these R factors had a specificity distinct from that of FII plasmids previously described. Three R factors of compatibility group FI were the first recognized plasmids of this group with repressed pilus synthesis. Two fi + R factors incompatible with R6K (and with this plasmid constituting group X) were identified, as were one plasmid of group P and an R factor compatible with plasmids of all groups so far described and therefore assigned to a new group (M). Similarities and differences between the R factor sets of P. morganii and P. rettgeri are discussed.

Distribution of Genes for Trimethoprim and Gentamicin Resistance in Bacteria and their Plasmids in a General Hospital

The incidence of trimethoprim resistance in enterobacteria causing infection in a London hospital increased from 5.6% in 1970 to 16% in 1979. The proportion of gentamicin-resistant aerobic Gram-negative bacilli had risen to 6.5% by 1979. During a 5-month period in 1977, during which no epidemic was recognized, all isolates resistant to either trimethoprim, gentamicin, tobramycin or amikacin were studied. The proportion of enterobacteria resistant to both trimethoprim and gentamicin (3.8% of the total) was significantly higher than expected assuming no correlation between acquisition of resistance characters. The resistance was transferable in 23% of trimethoprim-resistant and 76% of gentamicin-resistant strains. Trimethoprim resistance was carried by plasmids of seven different incompatibility groups and in at least four instances was part of a transposon. Gentamicin resistance was determined by plasmids of three groups - IncC, IncFII and IncW. Transposition of gentamicin resistance was not shown, though this may have been the means of evolution of the gentamicin R plasmids of InW, which determined aminoglycoside acetyltransferase, AAC(3). Some bacterial strains with their plasmids were endemic. There was evidence for these plasmids (i) acquiring new resistance genes by transposition, (ii) losing resistance genes by deletion and (iii) being transferred between bacterial species in the hospital.

Polynucleotide sequence relationships among plasmids of the I compatibility complex.

SUMMARY: Plasmids determining I pili show a variety of intricate compatibility relationships. None the less, all I plasmids tested showed a ‘core’ of common DNA sequences of approximately 30 x 106 daltons. Plasmids of the O compatibility group do not appear to specify for the synthesis of I-like pili and yet they held about 20 % of their sequences in common with all tested I plasmids, suggesting a common phylogenetic origin. Members of the I complex (including group O) do not hold a significant proportion of their sequences in common with representative plasmids of other compatibility groups. We propose that the regions of similar polynucleotide sequences of the different I complex plasmids are due to phylogenetic homology between genes governing pili biosynthesis and/or transfer functions. The regions determining compatibility of the I complex plasmids in some cases may be either unrelated to or have diverged from a common ancestor.

SALMONELLA TYPHI IN VIVO ACQUIRES RESISTANCE TO BOTH CHLORAMPHENICOL AND CO-TRIMOXAZOLE

Salmonella typhi in the bowel of a patient with enteric fever treated with chloramphenicol and later co-trimoxazole acquired resistance to these drugs. Chloramphenicol and sulphonamide resistances were determined by one plasmid, of IncH, whose carriage also changed the Vi phage type. Trimethoprim resistance was determined by a transposon, Tn7, carried in another plasmid, of IncI. The same resistance genes were identified in a strain of klebsiella isolated from the patient.

Plasmids determining I pili constitute a compatibility complex.

SUMMARY: Plasmids which determine I pili were subdivided by their compatibility properties. The original examples, R64, R144 and Col Ib-P9, together with others more recently isolated, constituted one group, termed Iα. Another group, Iβ, was compatible with Iα plasmids. The 1β group was represented by some newly observed trimethoprim-resistance factors. A group incompatible with both of these (possibly the ancestral form) was designated Iω. Yet another group, designated Iγ was compatible with all the above plasmids, and with members of all other known compatibility groups. Its exemplar repressed piliation by some, but not all, mutant Iα plasmids derepressed for pilus synthesis. Exclusion was not necessarily correlated with incompatibility.

Plasmid-determined Fusidic Acid Resistance in the Enterobacteriaceae

SUMMARY: A number of R factors have been shown to determine resistance to fusidic acid, an antibiotic effective against Gram-positive bacteria. Among several R factors examined for this property only one was fi−; the remainder were fi+ and of the FII compatibility group.