An Easter outbreak of Salmonella Typhimurium DT 104A associated with traditional pork salami in Italy.

Salmonella enterica is a common cause of gastrointestinal illness in Italy. S. Typhimurium accounts for approximately 40% of isolates, and most of these strains belong to the phage type DT104. We describe the investigation of an outbreak of S. Typhimurium DT104A, a subtype never observed before in Italy, which occurred in Rome during spring 2004.We conducted a matched case control study between 24 July and 9 September 2004. Controls were matched for age and area of residence. Each case had between one and four controls. Odds of exposure to potential risk factors and vehicles for the outbreak were compared between cases and controls. A multivariate analysis was conducted to estimate adjusted Odds Ratios.Sixty-three cases of S. Typhimurium DT 104A infection with onset between 1 April and 5 May 2004 were identified. Sixty-one were residents of Rome and two were residents of a neighbouring region. Twenty-six cases (43%) were enrolled in the study. Their median age was 7.5 years. Fourteen of 26 cases and 16 of 62 controls had eaten pork salami (OR= 25.5; 95% CI 1.6- 416.8). No food samples were available for testing. In northern Italy, two months prior to the outbreak, the veterinary surveillance system identified the first isolation of S. Typhimurium DT104A in a pig isolate. Both human and pig isolates showed indistinguishable PFGE patterns. It was not possible to trace the pig after the sample was taken at slaughter. The epidemiological evidence on the implication of pork salami in this outbreak suggests that pork products can also be a vehicle for salmonella in Italy and underlines the importance of good manufacturing practices for ready-to-eat foods. This investigation highlights the value of laboratory-based surveillance in identifying community-wide outbreaks of uncommon pathogens. It also underlines the need to improve surveillance timeliness, for promptly detecting outbreaks, undergoing field investigation, and implementing control measures. Moreover, our study shows the usefulness of integrated human and animal surveillance in tracing the possible source of infection.

Genomic heterogeneity of environmental and clinical aeromonads.

Thirty-three isolates of Aeromonas from environmental sources and clinical samples were tested and the results, obtained using the pulsed field gel electrophoresis (PFGE) technique, were compared with those obtained by biochemical typing. On the basis of their biochemical characteristics 31 strains was assigned to one of the recognised groups or species within the Aeromonas genus and 2 strains to the species Vibrio fluvialis. These latter were nevertheless found to belong to the Aeromonas genus on the basis of the chromosomal DNA analysis. Among the clinical isolates the biochemical analysis showed greater uniformity. A low correlation between molecular and traditional typing methods was observed with a wider heterogeneity at the genomic level. The results showed the difficulty of discriminating Aeromonas isolates by conventional biochemical methods. The genomic analysis performed by PFGE can be a more effectual technique, which can be used for epidemiological and ecological studies of the microorganisms belonging to the Aeromonas group.

Virulence factors of salmonella ser. enteritidis strains isolated in Italy from food-borne outbreaks.

Twelve Salmonella ser. Enteritidis strains phage type 4 isolated in Italy from different food-borne outbreaks were characterized for the expression of different virulence traits, for antibiotic resistance, and for plasmid DNA profile. All the twelve S. Enteritidis strains were able to invade and multiply within HeLa cell monolayers, even if at a lower efficiency if compared to an invasive Shigella flexneri strain. The strains were not hemolytic and produced only a moderate-level cytotoxic effect on HeLa cell monolayers. Moreover, all the strains examined produced mannose-sensitive hemagglutination with chicken erythrocytes but were not able to adhere to tissue culture cells. The strains did not produce the hydroxamate-type siderophore aerobactin or the specific ferric-aerobactin receptor. The S. Enteritidis strains were resistant only to spectinomycin, and eleven strains harbored a 38 MDa non-conjugative plasmid, while one strain harbored a 64 MDa conjugative plasmid which carried a colicinogenic activity-encoding locus. The uniformity of antibiotic resistance pattern, of the plasmid DNA content, and of the virulence factors produced indicated that the S. Enteritidis clinical isolates examined are clonally-related.

Serotype and phage type distribution of salmonellas from human and non-human sources in Italy in the period 1973-1995.

According to the data collected at the Rome-based National Reference Centre for Enterobacteria, 266,547 Salmonella strains isolated from human sources (226,513) and from non human sources (40,034) were characterised in Italy during the period 1973-1995. The serotype of all isolates, and the antibiotype and phage type of selected isolates were determined. Human-source isolations grew from 4372 in 1973 to 12,310 in 1995: non-human source isolations, from 339 in 1973 to 3459 in 1995. Salm. Typhimurium ranked first in the list of the most common serotypes isolated from both sources in the period 1973-1988 except in the years 1975 and 1976 when it was overtaken by Salm. Wien. Since 1983 Salm. Enteritidis has been among the top ten isolates from animals, and ranked first in the list of isolates from humans in 1988 and from non human sources in 1991. During the last years the number of multidrug-resistant strains, mostly belonging to phage types 104 and 193 of Salm. Typhimurium has been rising. Salmonella strains have also been isolated from numerous extraintestinal infections, almost exclusively caused by Salm. Enteritidis and Typhimurium.

Phenotypic and genotypic biotyping of environmental strains of Vibrio cholerae non-O1 isolated in Italy.

The purpose of this study was to characterize strains of Vibrio cholerae non-O1 isolated in Italy from different sources by biochemical and serological assays, antibiotic susceptibility testing, and molecular biotyping. Serotyping and genomic analysis by pulsed-field gel electrophoresis proved to be useful in discriminating the isolates. The data obtained show a wide heterogeneity at the genomic level, and in keeping with this, the serogrouping classification provided evidence of a high variability of the investigated strains. In addition, none of the strains tested produced cholera-like toxins.

Conventional and molecular approaches to isolates of Salmonella hadar from sporadic and epidemic cases.

In September 1994 an outbreak of gastroenteritis occurred in 437 people who had consumed lunch in the canteen of a factory in Central Italy. Salmonella sp. was isolated from stools of 99 patients and in 73 of them Salmonella hadar was identified. This is the first outbreak caused by this serotype described in Italy. In order to examine the genotypic basis of the epidemic strains, molecular typing was applied to sporadic strains isolated before and after the outbreak episode. For this purpose phage type, resistance to antibiotics, DNA plasmid profile and sites of insertion of the mobile element of IS200 were determined. The epidemic strains were genetically distinct from the non-epidemic isolates; they were shown to be phage type 26, harbouring four small plasmids, were resistant to nalidixic acid and showed a unique characteristic IS200 fingerprint. The typing methods used in this study allowed the identification and discrimination of the outbreak strains from related isolates. They can thus be considered as a tool for epidemiological purposes. In addition we should point out the emerging resistance to nalidixic acid, largely used in veterinary medicine, in Salm. hadar.

Foodborne outbreaks caused by Salmonella in Italy, 1991-4.

This report summarizes studies on 1699 foodborne outbreaks, in Italy, reported to the Istituto Superior di Sanità (ISS) (the National Institute of Health of Italy, Rome) during the period 1991-4. The most frequently reported foodborne outbreaks were caused by salmonellae (81%), in particular by Salmonella enteritidis and non-serotyped group D salmonella (34% and 33% of the total salmonella outbreaks, respectively). A vehicle was implicated in 69% of the salmonella outbreaks; eggs were implicated in 77% of the outbreaks for which a vehicle was identified or suspected. Salmonella strains isolated in 54 outbreaks were studied for phenotypic and genotypic characteristics. The isolates belonged to S. enteritidis (50 outbreaks), S. typhimurium (three outbreaks) and S. hadar (one outbreak). In the S. enteritidis outbreaks, phage type 4 was most frequently isolated (64.8%), followed by phage type 1 (14.8%). The virulence plasmid of 38 megadaltons was found in many different phage types of S. enteritidis.

Salmonella enteritidis in Italy.

During the period 1982-1992 the percentages of Salmonella enteritidis isolations in Italy have increased from 2.4 to 57.1% from human beings and from 0.5 to 22.8% from food. Seven hundred and fifty-seven isolates, 702 from man and 55 from food, were characterized. Phage type 4 accounted for the 76.8% of these isolates. The majority of strains were sensitive to the antibiotics tested; only 18 (2.4%) showed resistance to three or more antibiotics by nine different patterns.

Simultaneous infection with three different S. enteritidis strains in a nursing home resident.

A culture taken from a nursing home resident as part of a S. enteritidis outbreak was found to have a mixed infection due to three different strains of S. enteritidis. One of the three strains belonged to phage type (PT) 4, one to PT6 and one reacted with phages but did not conform to any typing scheme (RDNC). All three strains had the 38.9 megadaltons (MDa) plasmid found in the isolates from the outbreak-related cases, in addition the PT6 and RDNC strains harboured a 69.9 MDa plasmid. The importance of phage typing and plasmid analysis for S. enteritidis strain characterization and their epidemiologic and bacterial significance are discussed.

Epidemiological markers of Salmonella typhimurium isolates in Rome.

The phage type, antimicrobial resistance pattern, colicinogenic activity and DNA plasmid content of 172 strains of Salmonella typhimurium isolated in Rome from 1984 to 1986 were determined; 142 isolates were from patients with enteritis, 30 were from asymptomatic subjects. Most of the phage types identified were isolated during 2 or 3 of the study years; others, e.g., PT141, PT 204c and PT 194 were isolated during 1 year only, and only the last of these was isolated in large numbers. Phage typing proved most valuable in identifying epidemiologically related strains; DNA plasmid analysis was most useful in characterising further cultures of the same phage type, especially those isolated during suspected epidemics.

Italian experience in Salmonella enteritidis 1978-1988: characterization of isolates from food and man.

Salmonella enteritidis accounted for 5.45% of the 118.685 Salmonella isolates from man and for 2.65% of the 3.315 Salmonella isolates from food in Italy in the eleven year period 1978 to 1988. In the years 1978-1982 no S. enteritidis strain was isolated from eggs and poultry; in the years 1983-1988 the 53% of S. enteritidis isolates from food were from eggs and poultry. In 1989 S. enteritidis accounted for 744 isolates from man and 22 from food of which 80% were from eggs and poultry (partial data). In that year 18 outbreaks caused by S. enteritidis were reported to the National Centre of Enteric Pathogens in Rome. Characteristics of 81 S. enteritidis isolates were examined of which 27 were from sporadic cases involving humans and 40 from outbreaks in humans; 14 isolates were from food, all but one connected with the outbreaks. All the isolates studied were sensitive to the antibiotics tested; plasmid profile analysis showed a predominant profile pattern in both epidemic and non-epidemic strains; lysine decarboxylase was present in all the strains tested. Although in at least three epidemics a common supplier of eggs was proved, the source was not identified. Unfortunately it was not possible to determine the phage type of isolates because of the unavailability of specific phages.

Siderophore production by Salmonella species isolated from different sources.

A total of 230 Salmonella strains were screened for enterobactin and aerobactin production, sensitivity to bacteriocins and resistance to antibiotics. All the isolates produced the phenolate siderophore enterobactin. Amongst these, 74 strains, most belonging to S. enteritidis, were sensitive to colicin B. Only 26 isolates, all belonging to S. wien, produced an additional iron chelator, i.e. the siderophore aerobactin, and 22 out of these were sensitive to cloacin DF13. Analysis of iron repressible outer membrane proteins and plasmid profiles in S. wien strains showed that the expression of a 74-kDa iron-repressible outer membrane protein and the presence of large plasmids were associated with multiple antibiotic resistance, aerobactin production and sensitivity to cloacin DF13. The incidence of aerobactin-producing strains among S. wien isolates was higher during years 1974-1985; the epidemiological implications of these results are discussed.

Phage type and DNA plasmid profile of Salmonella typhimurium isolates in the area of Isernia, Italy.

Thirty-eight Salmonella typhimurium strains isolated from December 1987 to March 1988 in Isernia, Central Italy, were characterized on the basis of their phage type, resistance to antimicrobials and plasmid profiles. According to their phage types, the isolates could be assigned to one of six groups, the prevalent one being PT 195 which accounted for 73.6% of isolates. On the basis of their plasmid content, the isolates could be assigned to one of ten groups. The prevalent plasmid profile (60.0; 6.0; 4.3; 4.0; 3.2 megadaltons) was found in 60.4% of isolates. All the isolates from a particular food (salsicce), and as most of isolates from humans who had consumed this food belonged to phage type 195 and were of the same plasmid profile. The combined use of phage typing and DNA plasmid analysis proved to be a useful tool in identifying epidemiologically related isolates in this investigation.

Italian experience in Salmonella spp. isolations from 1973 to 1986.

A total of 150,072 strains of Salmonella were isolated in Italy over a 14-year period. The strains from humans, food, animals and from environmental samples reached the National Centre for Enterobacteria in Rome and the interregional Centres for Enterobacteria in Milan, Palermo and Pisa to be characterized according to their serotype. S. typhimurium was the most frequently isolated serotype from both humans and food in nearly all the years considered. Pork was the source most frequently found to be contaminated by Salmonella. Egg-based foods appear to be involved in such a contamination with increasing frequency.

Salmonella mbandaka isolated in Italy. 1979-1986.

A total of 350 strains of Salmonella mbandaka were isolated in Italy during the period 1979 to 1986. S. mbandaka was a rare serotype in Italy. It was first isolated from water in 1979. Since that year the number of isolates has increased: 1980 (3), 1981 (21), 1982 (21), 1983 (24), 1984 (54), 1985 (108), 1986 (118). 67.1% of the strains were isolated from humans, 14.6% from food, 15.1% from water and 2.9% from animals. Frozen eggs and egg-based products were the most frequently contaminated foods. Of the forty-six strains tested for drug resistance, two were multiresistant to gentamicin, nalidixic acid and nitrofurantoin and to chloramphenicol, kanamycin, tetracycline and tobramycin, respectively.

R-plasmids in Salmonella isolates from sporadic cases of gastroenteritis.

Five-hundred and twenty seven strains of Salmonella isolated from different patients admitted to hospitals in Rome from 1982 to 1985 were screened for their resistance to antimicrobial drugs. Sixty-one strains (11.6%) were found to be resistant to two or more antibiotics; the most frequent resistances were to sulfathiazole, streptomycin, tetracycline, chloramphenicol and ampicillin. Of the thirty-eight strains showing resistance to three or more antibiotics, 17 were able to transfer their resistance to E. coli K 12. The isolates were heterogeneous in plasmid population: only few strains harbored a sole plasmid, most harbored many plasmids ranging between 20 and 120 megadaltons in weight. Most strains were found to carry a conjugative plasmid of incompatibility group Inc H of 100-120 megadaltons and Inc I alpha of 60-70 megadaltons.