Reduced fluoroquinolone susceptibility in Salmonella enterica isolates from travelers, Finland.

We tested the fluoroquinolone susceptibility of 499 Salmonella enterica isolates collected from travelers returning to Finland during 2003-2007. Among isolates from travelers to Thailand and Malaysia, reduced fluoroquinolone susceptibility decreased from 65% to 22% (p = 0.002). All isolates showing nonclassical quinolone resistance were from travelers to these 2 countries.

Territorial waters of the Baltic Sea as a source of infections caused by Vibrio cholerae non-O1, non-O139: report of 3 hospitalized cases.

A fatal infection with temporal relation to 2 other febrile infections caused by Vibrio cholerae non-O1, non-O139 (NCV) occurred in Finland in 2003. All infections were associated with contact with seawater. The patient who died had also eaten home-salted whitefish, tested positive for NCV, preceding his symptoms. All patients had compromising factors, and all strains were distinguishable by pulsed-field gel electrophoresis and negative for the ctx gene. These 3 cases illustrate that, despite being uncommon in Finland, NCVs can cause clinically significant and even fatal infections.

Application of molecular genetic methods in diagnostics and epidemiology of food-borne bacterial pathogens.

Salmonella enterica, Campylobacter and Yersinia species, Shiga toxin-producing Escherichia coli (STEC), Listeria monocytogenes and Clostridium perfringens are the bacterial pathogens constituting the greatest burden of food-borne disease in Finland. Several molecular genetic methods have been applied to diagnose, discriminate and survey these bacteria. PCR, PCR-RFLP and PFGE are the most widely and successfully used. However, these methods are unable to replace conventional and internationally standardised phenotyping. Electronic database libraries of the different genomic profiles will enable continuous surveillance of infections and detection of possible infection clusters at an early stage. Furthermore, whole-genome sequence data have opened up new insights into epidemiological surveillance. Laboratory-based surveillance performed in a timely manner and exploiting adequate methods, and co-operation at local, national and international levels are among the key elements in preventing food-borne diseases. This paper reviews different applications of molecular genetic methods for investigating enteric bacterial pathogens and gives examples of the methods successfully used in diagnostics and epidemiological studies in Finland.

Genomic identity of pyelonephritogenic Escherichia coli isolated from blood, urine and faeces of children with urosepsis.

Chromosomal genotypes of Escherichia coli isolates from blood, urine and faeces of infants with urosepsis were studied to find possible clonality of the isolates. The isolates were analysed by PCR for class I, II and III alleles of the pyelonephritis-associated adhesin gene papG. The macrorestriction profiles of the papG-positive isolates were analysed by pulsed-field gel electrophoresis and their O serogroups were determined. Genetically identical E. coli isolates from the blood, urine and faeces of the same infant were found in 8 of 10 infants. This finding confirmed the results of previous phenotypic studies that the reservoir of pyelonephritogenic E. coli is indeed the colon.

Genomic diversity within phage types of Salmonella enterica ssp. enterica serotypes Enteritidis and Typhimurium.

The diversity among 1354 strains of Salmonella enterica subsp. enterica, serotype Enteritidis (n = 847) and Typhimurium (n = 507) isolated in Finland in 1991-2002 (n = 608) and in 2003 (n = 746) were studied. The former strains were studied retrospectively by phage typing and pulsed-field gel electrophoresis (PFGE) harmonized in the European Salm-gene project. The latter strains were studied prospectively, and the results correlated to their antimicrobial susceptibility and association with travel to popular tourist destinations. During both periods, S. Enteritidis phage types (PTs) PT1 and PT4, and S. Typhimurium definite types (DTs) DT1 and DT104 were the major phenotypes. SENTXB.0001 was the dominating single PFGE type among S. Enteritidis strains (40% in 1991-2002; 57% in 2003), and accounted correspondingly for 23% and 63% of the PT1 strains, and 81% and 88% of the PT4 strains. No PFGE types dominated among the S. Typhimurium strains but a correlation was found between certain phage and PFGE types: among DT1 strains, STYMXB.0098 accounted for 66% (1991-2002) and 98% (2003) and among the DT104 strains STYMXB.0001 accounted for 84% and 97% in the two time periods, respectively. Of the S. Enteritidis strains isolated in 2003, 91% were associated with travel, most commonly to Spain, Greece, and Bulgaria. SENTXB.0001 was the major Salmonella PFGE type in these countries. In contrast, most (55%) S. Typhimurium strains were of domestic origin. While only 1.3% of the S. Enteritidis strains were multiresistant and 24% were resistant to nalidixic acid only, 30% of the S. Typhimurium strains were multiresistant. Among the multiresistant S. Typhimurium strains, R-type ACSSuT and PFGE type STYMXB.0001 of the DT104 complex dominated.

Building PulseNet International: an interconnected system of laboratory networks to facilitate timely public health recognition and response to foodborne disease outbreaks and emerging foodborne diseases.

PulseNet USA, the national molecular subtyping network for foodborne disease surveillance, began functioning in the United States in 1996 and soon established itself as a critical early warning system for foodborne disease outbreaks, particularly those in which cases may be geographically dispersed. The PulseNet network is now being replicated in different ways in Canada, Europe, the Asia Pacific region, and Latin America. These independent networks work together in PulseNet International allowing public health officials and laboratorians to share molecular epidemiologic information in real-time and enabling rapid recognition and investigation of multi-national foodborne disease outbreaks. Routine communication between the various international PulseNet networks will provide early warning on foodborne disease outbreaks to participating public health institutions and countries.

Molecular epidemiology of Clostridium perfringens related to food-borne outbreaks of disease in Finland from 1984 to 1999.

From 1975 to 1999, Clostridium perfringens caused 238 food-borne disease outbreaks in Finland, which is 20% of all such reported outbreaks during these years. The fact that C. perfringens is commonly found in human and animal stools and that it is also widespread in the environment is a disadvantage when one is searching for the specific cause of a food-borne infection by traditional methods. In order to strengthen the evidence-based diagnostics of food poisonings suspected to be caused by C. perfringens, we retrospectively investigated 47 C. perfringens isolates by PCR for the cpe gene, which encodes enterotoxin; by reversed passive latex agglutination to detect the enterotoxin production; and by pulsed-field gel electrophoresis (PFGE) to compare their genotypes after restriction of DNA by the enzymes SmaI and ApaI. The strains were isolated during 1984 to 1999 from nine food-borne outbreaks of disease originally reported as having been caused by C. perfringens. In seven of the nine outbreaks our results supported the fact that the cause was C. perfringens. Our findings emphasize the importance of a more detailed characterization of C. perfringens isolates than mere identification to the species level in order to verify the cause of an outbreak. Also, to increase the probability of finding the significant cpe-positive C. perfringens strains, it is very important to isolate and investigate more than one colony from the fecal culture of a patient and screen all these isolates for the presence of the cpe gene before further laboratory work is done.

Listeria monocytogenes isolates from invasive infections: variation of sero- and genotypes during an 11-year period in Finland.

Listeria monocytogenes strains that were isolated from 314 human listeriosis cases in Finland during an 11-year period were analyzed by O:H serotyping and pulsed-field gel electrophoresis (PFGE). Serotyping divided the isolates into five serotypes, the most common being 1/2a (53%) and 4b (27%). During the study period, the number of cases caused by serotype 1/2a increased from 22% in 1990 to 67% in 2001, and those caused by serotype 4b decreased from 61 to 27%, respectively. PFGE with restriction enzyme AscI divided the strains into 81 PFGE genotypes; among strains of serotypes 1/2a and 4b, 49 and 18 PFGE types were seen, respectively. PFGE type 1 (serotype 1/2a) was the most prevalent single type (37 strains). Together with six other, closely related PFGE types, PFGE type 1 formed a group of 71 strains, representing 23% of all 314 strains. Strains of PFGE type 1 have also been isolated from cold smoked fish, suggesting a source of human infections caused by this type. Moreover, PFGE type 24 (serotype 1/2c) was significantly associated with gender: 5% of 180 male subjects but none of 132 female subjects (P = 0.012). An electronic database library was created from the PFGE profiles to make possible the prompt detection of new emerging profiles and the tracing of potential infection clusters in the future.

Technical improvement to prevent DNA degradation of enteric pathogens in pulsed-field gel electrophoresis.

This study used a modified pulsed-field gel electrophoresis (PFGE) method with HEPES as a running buffer to prevent electrophoresis-related DNA degradation of nine Salmonella enterica subsp. enterica serovar Ohio, seven Salmonella serovar Newport, and two enterohemorrhagic Escherichia coli (non-O157) strains. All strains yielded identifiable bands with this method in contrast to a commonly applied PFGE method using Tris buffer.