Epidemiological and genetical study of drug resistance in Staphylococcus aureus

Gastrointestinal motor-stimulating activity of macrolide antibiotics and analysis of their side effects on the canine gut

For clarification of the nature of the side effects of macrolide antibiotics on the gastrointestinal tract, the motor-stimulating activity of these agents was studied in unanesthetized dogs. The results showed that erythromycin and oleandomycin, the 14-membered macrolides with two side chain sugars combined at C3 and C5 in a glycosidic linkage in parallel, strongly stimulate gastrointestinal motor activity, an action accompanied by vomiting at large doses. On the other hand, leucomycin, acetylspiramycin, and tylosin, belonging to a 16-membered macrolide with two side chain sugars in series combined at C5 of the lactone ring, did not induce contractions of the gastrointestinal tract. Motor-stimulating activity by erythromycin and oleandomycin was greatly inhibited by atropine sulfate. These results point to structure-physiological activity relationships.

Drug resistance plasmids in Lactobacillus acidophilus and Lactobacillus reuteri

Sixteen strains of Lactobacillus reuteri and 20 strains of Lactobacillus acidophilus were tested for resistance to 22 antibiotics by using commercially available sensitivity disks. Evidence suggesting linkage of these resistances to plasmids was obtained by "curing" experiments with acridine dyes and high growth temperatures. Examination of plasmid patterns of agarose gel electrophoresis provided further evidence of loss in plasmid DNA under curing conditions in some of the strains examined.

Drug resistance of Escherichia coli isolated in Nepal

We collected Escherichia coli strains from 59 Nepalese porters in 1971 and surveyed for their drug resistance. Drug-resistant E. coli strains were isolated from four porters. (TC. CM. SM. SA. APC.)-resistant strains were isolated from two porters and SA- or APC-resistant strains were isolated from each of the others. The R factors were demonstrated from the multiple-resistant E. coli strains.

Plasmid-mediated sulfanilamide resistance

Dihydropteroate synthetase (DHPS) is specified by a substrain of Escherichia coli K12, ML1410. This enzyme activity is inhibited by sulfanilamides (Sa) and is known to be heat-stable, i.e., an Sa-sensitive normal enzyme. Another DHPS activity specified by E. coli ML1410 carrying drug resistance plasmids is Sa-resistant but heat-sensitive, i.e., an Sa-resistant enzyme. Most plasmids encoding single Sa or double (Sa. Tc or Sa. Sm) (Tc, tetracycline; Sm, streptomycin) resistance mediate the formation of this type of DHPS. Therefore, E. coli carrying these plasmids becomes diploid for DHPS, i.e., an Sa-resistant and an Sa-sensitive normal enzyme. The biochemical mechanism of Sa resistance mediated by plasmids encoding triple (Cm.Sm.Sa; Tc.Sm.Sa) and quadruple (Cm.Tc.Sm.Sa) resistance is not due to the formation of an altered DHPS but probably due to the decrease in permeation of the drug into the cell. The evolutionary process of the formation of Sa-resistance determinants on plasmids is discussed based on the presence of two types of Sa resistance mechanism.

Antibacterial and inducer activities for tetracycline resistance by its derivates and analogues

Antibacterial and inducer activities of thirteen TC derivates were investigated for tetracycline (TC) resistance in staphylococcus aureus. Four compounds of the TC derivatives were not able to induce the resistance to TC in Staphylococcus aureus MS3937 rms7 (TC) + harboring an inducible TC resistance determinant located on a plasmid. The 12a-hydroxy position seems to be essential for the inducer activity.

Extrachromosomal inheritance in bacteria

Images

Drug resistance of staphylococci. VII. Genetic determinants responsible for the resistance to tetracycline, streptomycin, sulfanilamide, and penicillin

A genetic analysis of resistance to tetracycline (TC), streptomycin (SM), sulfanilamide (SA), and penicillin G was carried out through transduction with phage lysates obtained from a multiply resistant strain of Staphylococcus aureus by ultraviolet irradiation. All transductants acquired resistance to both TC and SA, even when singly selected for either SA or TC resistance. The locus responsible for TC resistance could not be separated genetically from that for SA resistance. On the other hand, in transduction of SM resistance, about 30% of the transductants jointly acquired resistance to both TC and SA. These observations suggest that the loci governing resistance to TC, SA, and SM exist close together on a single genetic unit, this probably being the chromosome.

Drug resistance of staphylococci. VI. Genetic determinant for chloramphenicol resistance

Naturally occurring strains of staphylococci which are resistant to chloramphenicol (CM) inactivate this antibiotic. One of the inactivation products of CM showed the chromatographic behavior of 3-acetoxychloramphenicol. Induction of resistance occurred after prior exposure to subinhibitory concentrations of the antibiotic. The resistance of induced populations, as well as CM-inactivation ability, was decreased when they were grown in CM-free medium. The CM-inactivation property was transduced together with CM resistance. Transductional analysis and CM-resistance elimination experiments indicated that CM resistance in naturally occurring strains of staphylococci is mainly accounted for by inactivation of the drug.