Staphylococci in Food and Food Intoxication A Review and an Appraisal of Phage Typing Results

Abstract

SUMMARYA review has been made of published information on the phage groups and types of staphylococci concerned in food‐borne intoxication. It revealed that the majority belonged to phage group III with the types 6 and 47, either alone or, with others, being the most common. In Great Britain the yearly incidence of food‐borne intoxication, from 1950 to 1962, due to strains of phage group III ranged from 64.5 to 94.7%.In food handlers incriminated in outbreaks the nose was the most common focus of infection, and the hand came next.Meat and milk were the foods most commonly incriminated. Group III phages lysed 64.3% of strains found in meat and 58.1% of those in milk. Group IV phage lysed nine times as many milk‐borne as meat‐borne strains, which were also quite common in milk taken direct from cows, with and without mastitis or abnormal secretion.The meager data on staphylococcal contamination of “wholesome” food, meat, milk and fish, were tabulated. A high proportion of these strains were untypable, but one‐fourth to one‐third of the strains were lysed by phages of Group III.The results of phage typing of staphylococci from milk, dairy workers, market milk and dairy products were summarized. Phages obtained from strains of human and animal origin have been used for typing purposes. Of the phages in the “international set” obtained from staphylococci of human origin, 42D, Group IV, lysed more strains than any other phage. A set of phages of bovine origin has not yet been internationally recognized.About two‐thirds of the strains obtained from bovine mastitis but three‐fourths of strains front normal milk were lysed by the typing phages employed. Group III phages lysed two‐and‐one‐half times as many strains from normal as from mastitis secretion.Cheese, butter, butter‐milk, skim milk, cream, ice cream, kefir, and dried and condensed milk have yielded staphylococci lysed mainly by phages of Groups III and IV.Dairy workers, veterinary surgeons, and farmers have yielded strains similarly lysed. Some of the people in these groups as well as the animals they tended have suffered clinical disease processes, due to strains with identical phage reactions.Phage‐typable strains have been found in the noses of cattle, in dogs, pigs and chickens; their human attendants have, in some cases, carried identical strains.The proportion of staphylococci, lysed by the 52/52A/80/81 complex of phages has shown a twofold increase in hospitalized human patients and a two‐and‐one‐half increase in animals in the last few years. Staphylococci lysed by this complex are regarded as particularly invasive in and pathogenie for man.No comparison has appeared on the frequency distribution of staphylococci among the phage groups from food‐borne intoxication and food handlers. A comparison was therefore made of such reported strains from: i) food causing intoxication; ii) the nose; iii) the feces; and iv) superficial lesions of apparently healthy persons. The main features were: a) the low proportion of strains lysed by phages of Group 111 in ii, iii, and iv; b) the low proportion of untypable strains, especially in i.Systematic phage typing of staphylococci from wholesome food, food incriminated in intoxication outbreaks, hospital patients and the general population in defined geographical areas is recommended. Sites such as the nose, hands, feces, and perineum of healthy people and disease processes in hospitalized patients should be searched for staphylococci, which then should be typed by the use of a standard technique with the aid of the international set of phages from strains of human origin, augmented, where necessary, by phages from strains of animal origin.In addition to the international set of “human” phages, it would be useful to establish and use an international set of phages of animal, especially bovine, origin.Phage typing cannot be used to determine whether a given staphylococcus has produced or can be induced to produce enterotoxin; but is an excellent means of assisting in determining whether staphylococci from victims of food‐borne intoxication, suspected food and suspected food handlers are related.