The epidemiology of bacterial infection is investigated by the use of identification procedures at a sub-species level by such techniques as serotyping, phage typing, various antigen recognition tests, plasmid profiling and DNA probes. Fungal epidemiology has tended to lag behind in the use of this technology, particularly with the filamentous fungi, though several techniques have been developed for yeasts and especially for Candida albicans. This review will briefly describe the application of these methods to outbreaks of C. albicans infection, describe the limited methods available for the investigation of filamentous fungal infection and indicate the necessity for increased research in this area.

Multiple introductions of methicillin-resistant Staphylococcus aureus (MRSA) strains occurred to a new hospital in Hong Kong. Two years of clinical microbiological surveillance of the resulting outbreaks was combined with laboratory investigation by phage and antibiogram typing, and plasmid profiling. The outbreaks on the special care baby (SCBU) and burns (BU) units were studied in detail, and colonization of staff and contamination of the environment were investigated. MRSA were spread by the hands of staff on the SCBU, where long-term colonization of dermatitis was important, but were probably transmitted on the BU by a combination of the airborne, transient hand-borne and environmental routes. Simple control measures to restrict hand-borne spread on the SCBU were highly effective, but control was not successful on the BU.

Examination of a selection of serum samples from adults from two regions of England showed that 50 % of men in the 16–24 years and over 55 years age groups had high titres of antibody to diphtheria toxin (DT). In contrast, only 11% of women aged 16 to over 55 years had high titres of antibody to DT. All human antisera with high anti-DT titres reacted with a synthetic peptide (SP) corresponding to the amino acids 141–157 of DT fragment A, with sera from men aged 35 to over 55 years showing the highest titres. High antibody titres to fragment A paralleled those to SP in both sexes. Titres of antibody to DT fragment B were highest in individuals with high titres to DT. In sera from both sexes immunoglobulin G1 was the predominant subclass reactive with all three antigens. However, both IgG1 and IgG4 and to a lesser extent IgG2 and IgG3 were present in immunoglobulin concentrates.

Samples of ground beef (225), pork (235) and chicken (200) were randomly selected from meat processing plants in the southwestern Ontario area. Supernatants of broth cultures of the samples were tested for verocytotoxins using a Vero cell assay. Neutralization of cytotoxic activity using antisera specific for three types of verocytotoxin (Verotoxin 1, Verotoxin 2 and Shiga-like toxin II) was performed on positive samples. Isolation of verocytotoxigenic Escherichia coli (VTEC) was attempted from positive samples. VTEC were confirmed as E. coli biochemically, tested for drug resistance, and serotyped. Based on neutralization studies, the prevalance of VTEC in beef and pork was at least 36·4% and 10·6%. respectively. This is much higher than has been reported from a survey of retail meats in which a method designed to detect only E. coli O 157.H7 was used. Isolations of VTEC were made from 10·4 % of the beef samples and 3·8 % of the pork samples. No VTEC were recovered from the chicken samples. The majority of VTEC isolates were susceptible to commonly used antimicrobial agents. A number of the serotypes of the VTEC isolates recovered have been associated with human disease; however, no VTEC of serotype O 157.H7 were isolated.

Piglets between 1 and 40 days of age were inoculated with varying numbers and with different isolates of Streptococcus suis type 2 by the intranasal, intravenous and subarachnoid routes. Less than 100 organisms of an isolate cultured from apparently normal pigs caused subclinical infection in 1-day-old piglets after intranasal inoculation. This infection was naturally transmitted between litter mates. Intravenous inoculation of a similar isolate in 7-week-old pigs resulted in a sub-clinical bacteraemia in 3 of 8 piglets. One other piglet developed a bacteraemia 7 days after inoculation and concurrently developed signs of lameness and nervous dysfunction. Ten piglets were inoculated by the subarachnoid route with a porcine isolate and two with an isolate from a person with clinical disease. Only the latter two pigs developed the classical signs of nervous disease associated with infection by S. suis type 2. It is concluded that strains of S. suis type 2, of varying pathogenicity for both pigs and man, are endemic in New Zealand. It is suggested that the occurrence of disease is associated with both exposure to a pathogenic strain and other, as yet undetermined, secondary factors.

Corynebacterium jeikeium causes septicaemia in neutropenic patients usually after colonizing intravenous lines. This paper reports the results of immunoblotting sera from 14 patients with a C. jeikeium septicaemia. Recovery from the septicaemia was associated with production of both IgM and IgG against antigenic bands of 50, 52 and 110 kDa. Antibody against the 110 kDa band was present in controls but the antibody against the 50 and 52 kDa was specific to those patients who had on-going or previous C. jeikeium infection. A case of C. jeikeium endocarditis is also presented and here recovery was associated with seroconversion to the 50 and 52 kDa bands.

Over the past 5 years Salmonella enteritidis infections in humans have increased on both sides of the Atlantic ocean. The WHO salmonella surveillance data for 1979–87 were reviewed and show that S. enteritidis appears to be increasing on at least the continents of North America, South America, and Europe, and may include Africa. S. enteritidis isolates increased in 24 (69%) of 35 countries between 1979 and 1987. In 1979, only 2 (10%) of 21 countries with reported data reported S. enteritidis as their most common salmonella serotype; in 1987, 9 (43%) of 21 countries reported S. enteritidis as their most common serotype; 8 (89 %) of 9 were European countries. Although the reason for the global increase is not yet clear, investigations in individual countries suggest it is related to consumption of eggs and poultry which harbour the organism.

Mice, rats, guinea-pigs and rabbits were inoculated with isolates of Streptococcus suis type 2. An isolate cultured from the tonsils of a healthy pig, produced disease in rabbits after intravenous inoculation but not in mice, rats or guinea-pigs. An isolate of S. suis type 2, that was pathogenic for pigs and had been cultured from a human patient with clinical disease, produced signs of neurological disease in mice, rats and rabbits following intravenous inoculation. There was an apparent dose response in mice with 31 % of mice receiving more than 106 organisms developing clinical disease, whilst mice receiving less than this did not develop disease. There were no detectable histopathological lesions in the brains or meninges of mice with nervous signs. It is proposed that the disease in mice may mimic that reported in humans and that mice may be a useful indicator species for determining the virulence of isolates cultured from pigs.

The present study has attempted to determine the colonization resistance (CR) of the digestive tract by biotyping Enterobacteriaceae in four faecal samples per subject of five different animal species as well as man. The results indicate that the degree of bacterial contamination with Enterobacteriaceae from the environment may strongly influence the outcome. Both conventionally living chicken and man, showed a much wider range of the ‘confidence limits of the mean’ of the mean number of biotypes per faecal sample between individual subjects, than was found between subjects maintained under laboratory circumstances. Yet there appeared a statistically significant difference in CR between some of the animal species as a group. Man did not differ from monkeys, however, both differed from the rodents species studied. Monkeys differed also from dogs and the latter from rodents. It is concluded that the CR measured by determining the mean number of biotypes of Enterobacteriaceae can only be used for accurate comparison of the CR between subjects, if the ‘bacteriological environment’ is known; i.e. the sources of contamination.

Ninety-six isolates of presumptive or confirmed Listeria monocytogenes were obtained from local clinical (30 isolates) or food laboratories (66 isolates). Minimal biochemical analysis identified only 80% of these isolates as L. monocytogenes the remaining included L. seeligeri, 1%, or the non-haemolytic L. innocua, 19%. The 27 clinical and 50 food isolates, mainly from meat products, frozen confectionaries, and cheeses, confirmed as L. monocytogenes were compared biochemically and serologically. Twenty-one isolates, including some strains of L. innocua and L. seeligeri, were examined for pathogenicity in immunocompromized mice and 44 typed using bacterial restriction endonuclease DNA analysis (BRENDA). Only isolates of L. monocytogenes were found to be pathogenic. Biovar-typing of the isolates was unreliable and provided poor discrimination. Serogroups 1/2 and 4 predominated among clinical and food isolates and BRENDA provided better discrimination among isolates. Ten stable and reproducible restriction patterns were observed among the Listeria sp. isolates studied. Overall, a combination of techniques gave the best discrimination and indicated their potential for use as epidemiological tools.

Between July 1976 and February 1989, 50 incidents of suspected red kidney bean poisoning were reported in the UK. Nine incidents in which nausea, vomiting and diarrhoea developed within 1–7 h of ingestion, were confirmed by the detection of haemagglutinin in the beans. The diagnosis was made on a further 23 incidents on the basis of symptoms, incubation time and the description of preparation of beans prior to consumption. The haemagglutinin (lectin), which occurs naturally in the red kidney bean, is inactivated by thorough cooking of well soaked beans. In many of the outbreaks reported the implicated beans were consumed raw or following an inadequate heat process.

During the 3-year period 1985–7, all strains of Shigella sonnei isolated in Catania, Sicily, showed a high level of resistance to trimethoprim (Tp) which was invariably associated with resistance to other antibiotics.

Plasmid analysis showed 18 different electropherotypes: 35 of 37 strains harboured a plasmid of 70 Megadaltons (MDa), and 29 of 37 strains a plasmid of 130 MDa.

Restriction endonuclease fingerprinting of purified 70 MDa plasmid DNA from different strains demonstrated that these plasmids were similar but not identical.

In some strains with transferable Tp resistance, DNA hybridization analysis demonstrated the presence of genes coding for the production of dihydrofolate reductase (DHFR) type V. In contrast, there was no detectable hybridization with DNA probes specific for genes coding for DHFR types I, II and IV. This is the first report of the DHFR type V gene outside Sri Lanka.

When 168 fresh clinical isolates of Staphylococcus aureus were examined for their reactions on a medium containing 1 part in 100 000 crystal violet 50·6% of strains produced a purple appearance, 39·3% produced a white appearance and 10·1% produced a yellow appearance. Purple-reacting isolates were significantly associated with both invasive infections (P < 0·01) and hospital origin (P < 0·001). There were no significant associations between the crystal violet reactions and either animal contact or other properties previously reported to be characteristic of white and yellow-reacting strains (beta haemolysin and bovine coagulase production). The results of phage typing showed associations between susceptibility to group III phages and purple-reacting strains and between phage group II susceptibility and white and yellow-reacting strains. There was also a highly significant association between white reactions on crystal violet agar and susceptibility to lysis by a combination of all three groups (that is, I + II + III) and white-reacting strains were significantly more susceptible to lysis by phages 94 and/or 96, whether as a restricted pattern or as part of a broader pattern. The purple reaction on crystal violet medium may be a reliable marker of the ‘ hospital Staphylococcus’.

Cell surface hydrophobicity, haemagglutination pattern and adherence to HeLa cells were examined in 230 strains of Escherichia coli collected from women (n = 61 strains) and children (n = 65 strains) with non-obstructive acute pyelonephritis and in 104 faecal control strains of E. coli from healthy adults (n = 71 strains) and children (n = 33 strains). Pyelonephritogenic E. coli strains showed a significantly increased incidence of hydrophobic properties (90%) and mannose resistant haemagglutination (MRHA) of human erythrocytes (83%) than faecal control strains (64 and 23% respectively, P < 0·001 in both cases). Mannose sensitive haemagglutination (MSHA) was observed in 48% of the pyelonephritogenic E. coli strains and in 50% of the faecal control strains (NS). The incidence of adherence to HeLa cells was low both in pyelonephritogenic and faecal control strains, 6 and 7% respectively (NS). The bacterial phenotypes MRHA + MSHA + and MRHA + MSHA− appeared significantly more often in pyelonephritogenic E. coli strains (35 and 48% respectively) than in faecal control strains (5 and 17% respectively, P < 0·001 in both cases). The phenotype MRHA − MSHA + occurred significantly more often in control strains (45%) than in pyelonephritogenic strains (13%, P < 0·001). Eighty-three per cent of the pyelonephritogenic E. coli strains expressing hydrophobic properties showed MRHA and 50% of the hydrophobic strains showed MSHA. There were no significant correlations between cell surface hydrophobic properties and haemagglutination pattern or adherence to HeLa cells in pyelonephritogenic E. coli strains nor in faecal control strains.

The epidemiological data on shigellosis in Teknaf, a coastal area of Bangladesh, were reviewed for a 10-year period (1975–84). Certain similarities and differences were observed in the epidemiology of the disease in Teknaf when compared with urban Dhaka and rural Matlab. Similarities included: round-the-year infection with two peaks, one in the monsoon period and the other in the winter period; high male to female attendance ratio at the treatment centre: the predominance of infection in the under-15-year age group; high mortality rate in the under-5-year age group of both sexes and in females of all age groups; the multiple drug resistance of organisms. Differences included the higher isolation rate of organisms in Teknaf (42·1 % as against 11–12% in Dhaka and Matlab) and the preponderance of Shigella dysenteriae 1 infection in females in Teknaf. The unusually high isolation rate of shigella makes Teknaf the area with the highest incidence of shigellosis in Bangladesh.

This study attempts to determine whether or not livestock are becoming more susceptible to epidemics of salmonella infections by the analysis of published data on the annual number of reported infections in various animals. The number of incidents reported each year may be subject to a variety of biases due to temporal and geographical differences in reporting practices. This study analysed these reports by the calculation of diversity indices which are not subject to some of these potential biases. The relationship between the ecological concept of niche width and the diversity of species or types occupying that niche is discussed. The diversity of salmonella types reported in fowl has shown a highly significant decline over the 13-year period 1976–88. It is suggested that this declining diversity may be related to the declining niche width of the biotope available to this pathogen. Although speculative, this reduction in niche width could be related to a declining genetic diversity in the host animals or to an increasing intensification of animal husbandry.

DNA restriction endonuclease (Hae III and Hind III) total digest and 16S and 23S ribosomal (r)RNA gene patterns (ribopatterns) were determined for 18 isolates of Campylobacter jejuni from three separate outbreaks of diarrhoea in the north of England. Strains were also characterized by biotyping, serotyping and phage typing. Comparisons of the DNA patterns by visual and numerical methods revealed five distinct strain groupings with clear differences between isolates from different outbreaks as well as some heterogeneity between strains within the community outbreak and one of the school outbreaks. An excellent correlation was observed between the genomic DNA fingerprints data and the Preston bacteriophage group, both of which gave better discrimination than biotyping and serotyping alone or in combination. Only one phage group (PG 37) was not confirmed by the DNA data. DNA fingerprints therefore provide additional information of value in studying the epidemiology of outbreaks of C. jejuni.

Shigellosis is endemic in Central Australia and the infections are predominantly due to Shigella flexneri 6, Shigella flexneri 2a and Shigella sonnei. Plasmid profiles of isolates collected from 1985–9, suggested that infections caused by Shigella flexneri 6 were predominantly due to a single clone, whereas those caused by Shigella flexneri 2a and Shigella sonnei were due to several genetically diverse strains, although strains with identical plasmid profiles were found in widely separated geographical areas and in different years.

Sixty-one isolates of Aeromonas spp. from the faeces of pigs, cows and a variety of associated environmental sources were examined for the characteristics that are reputed to have roles in pathogenicity. Most isolates of Aeromonas hydrophila were cytotoxic (96·4%) and were capable of producing cell elongation factor (75%) and haemagglutinins (67·9%). In contrast few of the Aeromonas caviae isolates produced these three markers (13·6 %, 27·3% and 36·4% respectively). In general, Aeromonas sobria occupied an intermediate position (36·4%, 27·3% and 54·5%), but they did produce the highest mean invasion index for HEp-2 cells. Statistical analysis revealed significant associations between the carriage of these factors and it was clear that many isolates of aeromonads from water and animals possessed the full battery of putative virulence factors.

In an epidemiological survey, plasmid profiles and antimicrobial susceptibility testing of 100 shigella isolates in Lagos, Nigeria was done. All the isolates were sensitive to nalidixic acid, nitrofurantoin and ciprofloxacin. The commonest antimicrobial susceptibility pattern was resistance to ampicillin, colistin sulphate, co-trimoxazole, streptomycin and tetracycline. All but 4 of 100 isolates screened contained one or more plasmids. Plasmid profile analysis distinguished more strains than did antimicrobial susceptibility patterns. A total of 36 isolates was able to transfer resistance plasmids to Escherichia coli K-12 by conjugation. Using in vitro transformation, seven isolates transferred resistance. These plasmids specified resistance to tetracycline, streptomycin, sulphonamide, trimethoprim and ampicillin.