The evolution of new hospital strains of Staphylococcus aureus

Abstract

srNopsis The emergence of new groups of strains of Staph. aureus as important causes of endemic hospital infection in Great Britain has been followed by the phage typing method. Experiments are reported which suggest the possible origin of one of them.Staphylococcus phage typing is a practical method of characterizing the strains of Staph. aureus frequently isolated from human sources. The basic set of typing phages used for this purpose is chosen so that as many as possible of the important strains pathogenic for man, and particularly those causing endemic sepsis in hospitals, show characteristic patterns of lysis. In the course of time, however, the strains responsible for sepsis in hospitals change, and the new ones may not be typable with the phages in current use. On several occasions since 1950, the appearance of a new organism has made it necessary to introduce a fresh phage into the basic set of typing phages (Blair and Williams, 1961;Parker, 1962; Report, 1963).In order to increase the percentage of typable strains, cultures which show no lysis by the basic set oftyping phages at their routine test dilution (R.T.D.) are tested with the same phages at 1,000 times this strength (R.T.D. x 1,000). The reactions given by these strong phage preparations include, as well as those due to phage lysis, areas of general thinning of bacterial growth where a phage filtrate has been applied. These inhibition reactions (Anderson and Williams, 1956) are believed to be due to phage adsorption which leads to bacterial death but not to the production of new phage particles. They are often difficult to distinguish from true phage lysis with secondary overgrowth, and indeed this can only be done with certainty by titration of the phage on the culture. If the reaction is one of inhibition, the thinning of growth will disappear progressively as the strength of the phage is decreased, without the appearance of plaques; if it is a true lytic reaction separate plaques will be seen at an intermediate dilution.

Bacteriological characters of strains ofStaphylococcus aureussubmitted to a reference laboratory related to methicillin resistance

“…Some of this change may be technical but similar changes have been described for other epidemic strains (Jevons & Parker, 1964). Antibiotic resistance of this strain showed little change between the two periods and was unusual in the inclusion of minocycline resistance and constitutive macrolide resistance as well as other characters.…”

The Multiplication of Staphylococcal Phages in Nonpermissive Hosts

“…Inhibition by turbid-plaque (tu) and virulent (vii) variants are discussed here. Since endemic hospital infections due to untypable strains showing inhibition by group III phages have been reported [6,7], two such staphylococcal strains were examined for similarity to the other systems studied.…”

Methicillin-Resistant Staphylococcus aureus and the Eye: Current Concepts and Management Strategies

“…Methicillin, a semisynthetic derivative of penicillin that is resistant to cleavage by b-lactamase, was introduced for clinical use in 1959. producing penicillin-resistant strains sharply declined [19]. However, within 2 years following the introduction of methicillin, resistant strains were isolated in hospitals in the United Kingdom and subsequently in the United States [19]. Soon after, MRSA became endemic worldwide [13].…”

“…The molecular determinant responsible for penicillin resistance was identified as a plasmid-encoded b-lactamase gene capable of cleaving the b-lactam ring of penicillin [17,18]. Methicillin, a semisynthetic derivative of penicillin that is resistant to cleavage by b-lactamase, was introduced for clinical use in 1959. producing penicillin-resistant strains sharply declined [19]. However, within 2 years following the introduction of methicillin, resistant strains were isolated in hospitals in the United Kingdom and subsequently in the United States [19].…”