TRANSDUCTION OF RESISTANCE TO SOME MACROLIDE ANTIBIOTICS IN STAPHYLOCOCCUS A UREUS1 P. A. PATTEE AND J. N. BALDWIN Department of Bacteriology, Iowa State University, Ames, Iowa, and Department of Microbiology, Ohio State University, Columbus, Ohio Received for publication June 21, 1962 ABSTRACT among members of this species. Morse (1959), PATTEE, P. A. (Iowa State University, Ames) Edgar and Stocker (1961), and Dowell and AND J. N. BALDWIN. Transduction of resistance Rosenblum (1962) also reported staphylococcal to some macrolide antibiotics in Staphylococcus transductions involving a variety of charac- aureus. J. Bacteriol. 84:1049-1055. 1962.-By use teristics. Pattee and Baldwin (1961) reported of phage 80 of the International Typing Series, that phages 29, 52A, 79, 80, and 53 of the Inter- propagated on appropriate strains of Staphy- national Typing Series were capable of trans- lococcus aureus, two related markers controlling ducing the capacity to produce penicillinase, as resistance to certain macrolide antibiotics well as resistance to chlortetracycline and novo- (erythromycin, oleandomycin, spiramycin, and biocin, among a variety of strains of S. aureus. carbomycin) were transduced among a variety The present report is concerned with the trans- of strains of S. aureus. Unlike the markers duction of resistance to several of the macrolide controlling penicillinase production and resistance antibiotics among strains of S. aureus. to chlortetracycline and novobiocin, the deter- Among the pathogenic staphylococci, resistance minants of resistance to the macrolide antibiotics to the macrolide antibiotics, which include were transduced at normal frequencies (at least erythromycin, oleandomycin, spiramycin, carbo- 300 transductants per 109 phage) only to certain mycin, and leucomycin (Murai et al., 1959), of the recipient strains. One of the markers appears to be controlled by two distinctly differ- studied appears to control an inducible enzyme ent general mechanisms. In vitro adaptation system which is specifically induced by sub- results in a step-wise development of resistance inhibitory concentrations of erythromycin and to the macrolide antibiotics as a group (Jones, which controls resistance to erythromycin, Nichols, and Finland, 1956). Resistance in this oleandomycin, spiramycin, and carbomycin. The instance probably is determined by a series of other marker examined confers resistance to independent mutations and may be similar to erythromycin, oleandomycin, spiramycin, and erythromycin resistance in the pneumococcus carbomycin, and shows no evidence of being (Ravin and Iyer, 1961). The other mechanism of dependent upon an inducible mechanism. resistance, which predominates among naturally resistant strains of S. aureus, was extensively studied by Garrod (1957). His results generally Transduction in Staphylococcus aureus was were in agreement with others (Jones et al., 1956; first reported in 1958 by Ritz and Baldwin Waterworth, 1960; Rantz et al., 1957); i.e., in (1961), who demonstrated that several phages of vitro adaptation to one of the macrolide anti- the International Typing Series were capable of biotics results in a considerable degree of cross transducing the capacity to produce penicillinase resistance to other antibiotics of the macrolide group. During these studies, Garrod (1957) 1 Portions of this study were presented at the encountered certain strains of S. aureus, called 60th Annual Meeting of the American Society dissociated which were resistant for Microbiology, Philadelphia, Pa., May, 1960. strains, naturally This paper is based on portions of a dissertation to erythromycin but apparently sensitive to the submitted by the senior author to the Graduate other macrolide antibiotics. Garrod (1957) was School of Ohio State University, in partial ful- able to show that, while populations of dissociated fillment of the requirements for the degree, Doctor strains consisted primarily of erythromycin- of Philosophy. sensitive cells, such populations did not readily 1049 1050 PATTEE AND BALDWIN J. BACTERIOL. yield erythromycin-sensitive mutants. Further TABLE 1. Designations and phage types examination of dissociated strains revealed that of strains of Staphylococcus aureus growth in broth containing subinhibitory con- Strain designation Phage type centrations of erythromycin resulted in a popula- tion which consisted entirely of cells resistant not U9 (Pase, Tet, Ery) 80/81 only to erythromycin, but also to oleandomycin, U9 (Pase, Tet, Ery, spiramycin, and carbomycin. Reversion of Nov) 80/81 dissociated strains to the original phenotype U9 (Pase, Tet, 01, occurred after several transfers in the absence of Nov) 80/81 erythromycin. Waterworth (1960) reported that U35 (Pase, Tet) 80/81 dissociated strains acquired temporary resistance U40 (Pase, Tet) 80/81 to leucomycin after growth in the presence of U61 (Pase, Tet) 80/81 U66 (Pase, Tet, Ery) 80/81 erythromycin. U91 (Pase, Tet) 80/81 MATERIALS AND METHODS U114 (Pase, Tet) 80/81 461 (Pase, Tet) 80/81 The methods employed for determining the 588 (Pase, Tet) 80/81 characteristics possessed by strains of S. aureus, 655 (Pase, Tet, Ery) 29/52A/79/7/83/47/ the methods used for the maintenance of bacteria 53/54/73/77 and bacteriophages, and the transduction 4A (Pase, Tet, Ery) 79/83/53/54/77 techniques have been described in detail (Pattee Ps 42B 42B and Baldwin, 1961). The strains of S. aureus Ps 29 29 employed were originally isolated from several Ps 52 52 C-72 29/52A/79/80 different sources, and all were of human origin. Ch-50 80 The genetic markers possessed by these strains W-26 29/80 are included in the strain designations, and N-135 29 include the capacity to produce sufficient peni- 608 52A/80/81 cillinase to grow on Brain Heart Infusion (BHI; 1 52A/80/81 Difco) agar containing 100 units of penicillin per 769 81 ml (Pase marker), and the ability to grow on BHI D-1 52A/80 agar containing either 75 ,ug of chlortetracycline 152 52A/79/80 per ml (Tet marker) or 20 jig of novobiocin per 112 29/52A/79/83/42E/ ml (Nov marker). Strains exhibiting erythromycin 80/81 resistance of the dissociated type possess the 248 52A/80 Ery marker. From strain U9(Pase, Tet, Ery, Nov), a mutant was isolated by the gradient- phage 80 propagated on donor strain U9(Pase, plate technique (Szybalski, 1952), which was Tet, Ery) was designated 80/U9(Pase, Tet, Ery). resistant to oleandomycin. This mutant was Briefly, the transduction procedure involved resistant to 800 MAg of oleandomycin per ml of combining 1.0 ml of a cell-free phage lysate BHI agar (01 marker) and was designated (1010 plaque-forming units per ml) with between U9(Pase, Tet, 01, Nov). The designations and 2 and 6 X 1010 cells of the recipient strain sus- phage types of the strains employed are given pended in 1.0 ml of P and D broth (nutrient in Table 1. broth containing 0.25% K2HPO4 and 0.2 % The bacteriophages of the International dextrose). The mixture was then shaken for 1 Typing Series used in this study were originally hr at 37 C, after which the cells were washed once obtained from John E. Blair and were main- 1 in 1.0 tained in the Department of Microbiology, Ohio with ml of P and D broth, resuspended State University. Phages 29, 52A, 79, 80, and 53 ml of P and D broth, and 0.05-ml quantities were employed for transduction after propagation spread over the surface of each plate of the on appropriate donor strains. The designation of selective medium with the aid of a sterile bent the transducing phages includes both the inter- glass rod. Control suspensions consisted of an national number designation of the phage and the identical suspension of recipient cells shaken with designation of the donor strain. Accordingly, 1.0 ml of sterile P and D broth. VOL. 84, 1962 TRANSDUCTION OF RESISTANCE IN S. AUREUS 1051 RESULTS expression of resistance to erythromycin in a Characteristics of strains possessing the Ery and strain possessing the Ery marker. When the 01 markers. When a heavy (109 cells) inoculum of colonies obtained on BHI agar containing strain U9(Pase, Tet, Ery), prepared from an erythromycin were replicated with velveteen to overnight BHI agar slant culture, was inoculated BHI agar containing 100 ,ug of oleandomycin, onto BHI agar containing 800 Mg of erythromycin spiramycin, or carbomycin per ml, they all were per ml, apparent uninhibited growth was ob- found to be resistant to these antibiotics. When tained. Oleandomycin, spiramycin, and carbo- similar colonies were replicated serially three mycin (10 ,g per ml of BHI agar) were inhibitory times on BHI agar at 24-hr intervals, and then to identical inocula, except for a few resistant replicated to BHI agar containing 100 Mg of mutants present in the cell population. In con- oleandomycin, spiramycin, or carbomycin per trast, strain U9(Pase, Tet, 01, Nov) was capable ml, the majority of the colonies failed to develop. of uninhibited growth on BHI agar containing Those few colonies which retained resistance to either 800 ,g per ml of oleandomycin or erythro- these antibiotics were resistant mutants, a result mycin, or 400 Mg per ml of spiramycin or carbo- which was expected in view of the high mutation mycin. Strains U9(Pase, Tet, Ery) and U9(Pase, frequency previously observed with strain Tet, 01, Nov) were then examined for resistance, U9(Pase, Tet, Ery). by performing plate counts on BHI agar and Transduction of oleandomycin resistance. Trans- BHI agar containing 25 Mug per ml of erythro- duction of resistance to oleandomycin was mycin, oleandomycin, or spiramycin. The results performed by using as a selective medium BHI of this experiment (Table 2) indicate that strain agar containing 25 Mug of oleandomycin per ml. U9(Pase, Tet, Ery) consisted primarily of Control suspensions of erythromycin-sensitive erythromycin-sensitive cells. In contrast, strain recipient strains yielded approximately 20 U9(Pase, Tet, 01, Nov) consisted entirely of cells resistant mutants per 109 cells when BHI agar resistant to all of the macrolide antibiotics containing either 3 or 5 Mig of oleandomycin per examined.