B. Rowe

International increase in Salmonella enteritidis: a new pandemic?

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.

An adhesive factor found in strains ofEscherichia coli belonging to the traditional infantile enteropathogenic serotypes

Escherichia coli strains isolated from outbreaks of diarrheal disease were tested for the presence of adhesive factors. Fifty-one of these strains belonged to traditional infantile entero-pathogenic serotypes (EPEC) and 17 belonged to other serotypes. None of these strains were enterotoxigenic and none possessed colonization factors CFA/I or CFA/II, which have been described among strains of enterotoxigenicE. coli (ETEC). EnterotoxigenicE. coli strains from patients with diarrhea and strains which were neither EPEC nor ETEC from subjects without diarrhea were also examined. By means of a tissue culture technique using HEp-2 cells, a new adhesive factor was found to occur with greater frequency in EPEC strains. The adhesive factor was found less frequently in the other groups ofE. coli studied. It was distinct from type 1 pili and was not inhibited by the presence ofD-mannose.

A phage-typing scheme for Salmonella enteritidis

For many years phage typing has proved invaluable in epidemiological studies on Salmonella typhi, S. paratyphi A and B, S. typhimurium and a few other serotypes. A phage-typing scheme for S. enteritidis is described. This scheme to date differentiates 27 types using 10 typing phages.

Salmonella enteritidis phage type 4 from the contents of intact eggs: a study involving naturally infected hens

Two small flocks of egg-laying hens, naturally infected with Salmonella enteritidis, were housed in individual cages so that their eggs could be identified. During a longitudinal study where the contents of 1,119 eggs were examined, 11 were positive for S. enteritidis. One isolate was phage type (PT) 33 the others were PT4. The production of infected eggs was clustered though intermittent. The positive eggs, which were produced by 10 of the 35 hens, were all found to contain fewer than 10 salmonellas. Some birds were also apparently carrying S. hadar PT14 as this organism was isolated from the contents of six cracked eggs.

Verotoxin producing Escherichia coli O 157 infections associated with the consumption of yoghurt.

Sixteen cases of verotoxin producing Escherichia coli (VTEC) O 157:H7 Phage Type 49 infection were identified in the North West of England from 1 September to 1 November 1991, eight of whom lived in or around the same large town. Eleven of the cases were aged 10 years or less, and five of the affected children developed haemolytic uraemic syndrome. A case control study demonstrated a strong association between VTEC O 157:H7 PT 49 infection and the consumption of a locally produced live yoghurt. This is the first time that an outbreak of VTEC O 157 infection has been linked to the consumption of yoghurt and this vehicle of infection should be considered when investigating such outbreaks in future.

Characterization of plasmids conferring resistance to gentamicin and apramycin in strains of Salmonella typhimurium phage type 204c isolated in Britain

In Salmonella typhimurium phage type 204c isolated in Britain, gentamicin resistance is specified by plasmids of the I1 compatibility group which also confer resistance to apramycin. These plasmids have been subdivided into three types within the I1 group on the basis of their antibiotic resistance specificity, their ability to produce colicin Ib and their restriction enzyme digest fragmentation patterns. All three have been identified in strains from cattle, but as yet only two types have been found in strains from humans. It is suggested that the use of apramycin in animal husbandry is responsible for the appearance of gentamicin resistance in multiresistant strains of phage type 204c, a phage type already epidemic in bovine animals and with an increasing incidence in humans.

An outbreak of Salmonella saint-paul infection associated with beansprouts.

In March 1988, there was an outbreak of infection by a strain of Salmonella saint-paul with a distinctive antigenic marker. A total of 143 reports were received between 1 March and 7 June. Preliminary investigations suggested that raw beansprouts were a possible source of infection and a case-control study confirmed the association. S. saint-paul of the epidemic type was isolated from samples of beansprouts on retail sale in different cities in the United Kingdom and from mung bean seeds on the premises of the producer who was most strongly associated with cases. In addition, Salmonella virchow PT34 was isolated from samples of raw beansprouts and was subsequently associated with seven cases of infection. Four other serotypes of salmonella were also isolated from beansprouts. On 8 April the public were advised to boil beansprouts for 15 seconds before consumption, and the premises of the one producer associated with many cases were closed. As a result of these actions there was a significant decrease in the number of infections with S. saint-paul.

Vero cytotoxin-producing strains of Escherichia coli from children with haemolytic uraemic syndrome and their detection by specific DNA probes

Faecal specimens from 66 children with haemolytic uraemic syndrome in the United Kingdom were examined for strains of Escherichia coli producing Vero cytotoxin (VT). Initially, conventional bacteriological methods were used to identify colonies of E. coli which were then tested for VT production. Subsequently, specific DNA probes for VT1 and VT2 were used in hybridisation tests to detect VT-producing E. coli (VTEC). VTEC strains were isolated from 19 cases and in 15 they belonged to serogroup O157. Fourteen of these O157 strains possessed the flagellar antigen H7 and one was non-motile. The VTEC strains from the remaining four cases belonged to serotypes O26:H11, O104:H2, O153:H25, and O163:H19 together with a rough VT+ strain with flagellar antigen H51. The O157 strains hybridised with either the VT2 probe or both VT1 and VT2 probes. The other VTEC strains hybridised with either the VT1 or VT2 probe. Confirmation of the production of VT1 and VT2 in vivo was obtained by the neutralisation of faecal VT with specific antisera raised against these two cytotoxins.

Heterogeneity of Escherichia coli phages encoding Vero cytotoxins: comparison of cloned sequences determining VT1 and VT2 and development of specific gene probes.

Phages coding for production of Vero cytotoxins VT1 or VT2 in strains of Escherichia coli serotype O157.H7 or O157.H- were morphologically indistinguishable. Their genome size and restriction enzyme digests of the phage DNA were similar. These phages were clearly different in these respects from a VT1-encoding phage isolated from a strain of E. coli O26.H11 (H19). However the VT1 region cloned from the phage originating in the E. coli O157.H7 strain was identical to the VT1 region previously cloned from the phage carried by H19. Sequences encoding VT2 that were cloned from the phage in E. coli O157.H- have been mapped and the VT2 region identified by transposon insertion. The cloned regions coding for VT1 or VT2 production had no similarities in the presence of restriction enzyme sites over a distance of about 2 kb, and two VT1-specific probes spanning a region of about 1.4 kb did not hybridize under stringent conditions with cloned VT2 DNA. A 2 kb HincII fragment contained the VT2 genes but hybridized to VT1-encoding phages and recombinant plasmids via flanking phage DNA. A 0.85 kb AvaI-PstI fragment was a specific probe for VT2 sequences and did not hybridize under stringent conditions to phages or plasmid recombinants encoding VT1.

OUTBREAK OF SALMONELLA NAPOLI INFECTION CAUSED BY CONTAMINATED CHOCOLATE BARS

An outbreak of Salmonella napoli infection in England and Wales in 1982 was detected by the surveillance of routine reports of salmonella infections from hospital and public-health laboratories. Epidemiological investigation quickly identified two types of small chocolate-covered bars, imported from Italy, as the vehicles of infection, and subsequently both were found to be contaminated with the organism. The prompt recognition of this outbreak and rapid identification of the vehicle of infection enabled four-fifths of the consignment of contaminated chocolate to be withdrawn from the market. The 245 reported cases resulted from the sale of 600 000 bars; as these were presumably only a small fraction of the total number of cases, it is likely that many thousands of infections were prevented.