Comparison of Staphylococcus aureus isolates associated with food intoxication with isolates from human nasal carriers and human infections

Staphylococcus aureus represents an organism of striking versatility. While asymptomatic nasal colonization is widespread, it can also cause serious infections, toxinoses and life-threatening illnesses in humans and animals. Staphylococcal food poisoning (SFP), one of the most prevalent causes of foodborne intoxication worldwide, results from oral intake of staphylococcal enterotoxins leading to violent vomiting, diarrhea and cramps shortly upon ingestion. The aim of the present study was to compare isolates associated with SFP to isolates collected from cases of human nasal colonization and clinical infections in order to investigate the role of S. aureus colonizing and infecting humans as a possible source of SFP. Spa typing and DNA microarray profiling were used to characterize a total of 120 isolates, comprising 50 isolates collected from the anterior nares of healthy donors, 50 isolates obtained from cases of clinical infections in humans and 20 isolates related to outbreaks of staphylococcal food poisoning. Several common spa types were found among isolates of all three sources (t015, t018, t056, t084). DNA microarray results showed highly similar virulence gene profiles for isolates from all tested sources. These results suggest contamination of foodstuff with S. aureus colonizing and infecting food handlers to represent a source of SF

Virulence and antimicrobial resistance genes in human MRSA ST398 isolates in Austria

This study determined the genetic background of virulence and resistance genes of MRSA ST398 in Austria. From 2004 up to 2008 a total of 41 human isolates of MRSA ST398 were investigated for virulence and resistance gene patterns using DNA microarray chip analysis. Highly similar virulence gene profiles were found in 29 (70·7%) of the isolates but genes encoding Panton-Valentine leukocidin, enterotoxins, or toxic shock syndrome toxin were not detected. Genes conferring resistance to tetracycline and erythromycin-lincosamide were common as all but one of the isolates exhibited tetM and/or tetK, which are involved in tetracycline resistance, and 12 (29·9%) were positive for ermC, conferring resistance to erythromycin/lincosamide. SplitsTree analysis showed that 40 isolates were closely related. Changes in virulence and resistance gene patterns were minimal over the observed time perio

A β-galactosidase negative E. coli leading to atypical colonies on RAPID’E.coli 2 agar

In recent years, the use of chromogenic media for detection of coliforms and E. coli increases as they allow fast identification of colonies directly on the plate without further confirmation steps. We obtained an atypical strain from a raw milk sample forming bright red colonies on RAPID'E.coli 2 agar, as opposed to the violet coloration characteristic for E. coli, or blue/green coloration characteristic for coliforms. API32E and MALDI-TOF analysis were used to identify isolate 2099 as E. coli. While API ID 32 E analysis resulted in a biochemical profile characteristic for E. coli, isolate 2099 was found to be phenotypically β-glucuronidase positive but β-galactosidase negative, which resulted in atypical red coloration of its colonies on RAPID'E.coli 2 agar. In order to elucidate possible causes of the β-galactosidase negative phenotype, we sequenced the lacZ gene encoding β-galactosidase. A mutation leading to a premature stop codon at amino acid position 774 was identified, rendering the polypeptide abnormally short and most likely not functional. Considering our findings, not only β-glucuronidase, but also β-galactosidase negative E. coli represent a challenge to routine diagnostic procedures screening for E. coli with chromogenic media that rely on detection of β-glucuronidase and β-galactosidase activity

Effect of food-related stress conditions and loss of agr and sigB on seb promoter activity in S. aureus

publisher: Elsevier articletitle: Effect of food-related stress conditions and loss of agr and sigB on seb promoter activity in S. aureus journaltitle: Food Microbiology articlelink: http://dx.doi.org/10.1016/j.fm.2017.03.006 content_type: article copyright: © 2017 Elsevier Ltd. All rights reserved.publisher: Elsevier articletitle: Effect of food-related stress conditions and loss of agr and sigB on seb promoter activity in S. aureus journaltitle: Food Microbiology articlelink: http://dx.doi.org/10.1016/j.fm.2017.03.006 content_type: article copyright: © 2017 Elsevier Ltd. All rights reserved.publisher: Elsevier articletitle: Effect of food-related stress conditions and loss of agr and sigB on seb promoter activity in S. aureus journaltitle: Food Microbiology articlelink: http://dx.doi.org/10.1016/j.fm.2017.03.006 content_type: article copyright: © 2017 Elsevier Ltd. All rights reserved.publisher: Elsevier articletitle: Effect of food-related stress conditions and loss of agr and sigB on seb promoter activity in S. aureus journaltitle: Food Microbiology articlelink: http://dx.doi.org/10.1016/j.fm.2017.03.006 content_type: article copyright: © 2017 Elsevier Ltd. All rights reserved

Staphylococcus aureus related to bovine mastitis in Switzerland: Clonal diversity, virulence gene profiles, and antimicrobial resistance of isolates collected throughout 2017

taphylococcus aureus can be associated with subclinical, acute, chronic, and toxic cases of bovine intramammary infections, leading to considerable financial losses for the dairy industry in Switzerland and worldwide. In addition, milk products are one of the most common food categories implicated in staphylococcal food poisoning in humans. Detailed information on the population structure, as well as the virulence and resistance characteristics of Staph. aureus originating from bovine mastitis milk is needed to allow for source attribution and risk assessment of Staph. aureus in a food poisoning context and to improve therapeutic approaches in cattle. Our objective was to assess the population structure, phenotypic resistance patterns, and virulence and resistance gene profiles of Staph. aureus isolates from bovine mastitis milk in Switzerland. To this end, 58 Staph. aureus strains were characterized. The DNA microarray was used to test for the presence or absence of virulence and resistance genes. In addition, minimum inhibitory concentrations of various antimicrobial agents were determined by microdilution. To assess the population structure of the isolates, we determined clonal complexes (CC) using DNA microarray hybridization profiles and performed multilocus sequence typing and spa typing. The strains were assigned to 7 clonal complexes, 10 sequence types, and 11 spa types, with CC705 (43%), CC97 (33%), and CC20 (12%) representing the most common lineages and t529 (43%) and t267 (21%) representing the most common spa types. Only 1 isolate was assigned to CC8, a clonal lineage linked to high within-herd prevalence of mastitis. A total of 14% (n = 8) of strains were classified as resistant to penicillin, and 1 strain each was classified as oxacillin and pirlimycin resistant. Although no clinical breakpoints are available for the combination of kanamycin/cefalexin, growth of all strains was inhibited by the lowest combination of kanamycin/cefalexin concentrations tested (4 µg/mL of kanamycin and 0.4 µg/mL of cefalexin). One strain assigned to CC20, ST389, and t2094 exhibited resistance to penicillin, oxacillin, and pirlimycin as well as intermediate susceptibility to erythromycin and high minimum inhibitory concentration for several antimicrobial agents, for which no breakpoints were available

Short communication: Characterization of Staphylococcus aureus isolated along the raw milk cheese production process in artisan dairies in Italy

Staphylococcus aureus is a common cause of food-borne intoxications. Several staphylococcal food poisoning outbreaks have been linked to consumption of raw milk cheeses and artisanal cheese production. However, information on Staph. aureus isolated from artisanal raw milk cheeses and small-scale dairy production environments is very limited. Therefore, we aimed to characterize Staph. aureus isolated along the artisanal raw milk production chain by determining (1) the population structure, and (2) the presence/absence of enterotoxin genes, mecA/C, and pvl. We collected 276 samples from different production stages (raw milk, whey, curd, brine, drying worktops, and cheese) at 36 artisan dairies in Italy. A total of 102 samples from 25 dairies tested positive for Staph. aureus, with 80% positive samples among the tested artisan cheeses. All isolates were further characterized by spa typing and PCR screening for staphylococcal enterotoxin genes, the mecA/mecC genes characteristic for methicillin-resistant Staph. aureus, and the pvl gene encoding Panton-Valentine leukocidin. The 102 isolates represented 15 different spa types and were assigned to 32 different Staph. aureus strains. The spa type most frequently detected was t2953 (30%), which is associated with genotype B strains causing high within-herd levels of bovine mastitis. In addition, 3 novel spa types (t13269, t13277, and t13278) were identified. Although none of the strains harbored mecA/mecC or pvl, 55% of the isolates exhibited at least one enterotoxin gene. Many strains were present in samples from multiple dairies from different regions and years, highlighting the spread of Staph. aureus in small-scale cheese production plants. Our findings demonstrate that enterotoxigenic Staph. aureus and in particular t2953 (genotype B) isolates commonly occur in artisanal dairies and raw milk cheeses in Italy. It is particularly alarming that 80% of the artisan cheeses sampled in our study were positive for Staph. aureus. These findings stress the need for effective measures preventing staphylococcal food poisoning by limiting Staph. aureus growth and enterotoxin formation along the production chain and in the final product