Lantibiotic Nisin and Its Detection Methods

The type A lantibiotic nisin produced by several Lactococcus lactis strains, and one Streptococcus uberis strainis a small antimicrobial peptide that inhibits the growth of a wide range of gram-positive bacteria, such as Bacillus, Clostridium, Listeria and Staphylococcus species. It is nontoxic to humans and used as a food preservative (E234) in more than 50 countries including the EU, the USA, and China. National legislations concerning maximum addition levels of nisin in different foods vary greatly. Therefore, there is a demand for non-laborious and sensitive methods to identify and quantify nisin reliably from different food matrices. The horizontal inhibition assay, based on the inhibitory effect of nisin to Micrococcus luteus is the base for most quantification methods developed so far. However, the sensitivity and accuracy of the agar diffusion method is affected by several parameters. Immunological tests have also been described. Taken into account the sensitivity of immunological methods to interfering substances within sample matrices, and possible cross-reactivities with lantibiotics structurally close to nisin, their usefulness for nisin detection from food samples remains limited. The proteins responsible for nisin biosynthesis, and producer self-immunity are encoded by genes arranged into two inducible operons, nisA/Z/QBTCIPRK and nisFEG, which also contain internal, constitutive promoters PnisI and PnisR. The transmembrane histidine kinase NisK and the response regulator NisR form a two-component signal transduction system, in which NisK autophosphorylates after exposure to extra cellular nisin, and subsequently transfers the phosphate to NisR. The phosphorylated NisR then relays the signal downstream by binding to two regulated promoters in the nisin gene cluster, i.e the nisA/Z/Qand the nisF promoters, thus activating transcription of the structural gene nisA/Z/Q and the downstream genes nisBTCIPRK from the nisA/Z/Q promoter, and the genes nisFEG from the nisF promoter. In this work two novel and highly sensitive nisin bioassays were developed. Both of these quantification methods were based on NisRK mediated, nisin induced Green Fluorescent Protein (GFP) fluorescence. The suitabilities of these assays for quantifica¬tion of nisin from food samples were evaluated in several food matrices. These bioassays had nisin sensitivities in the nanogram or picogram levels. In addition, shelf life of nisin in cooked sausages and retainment of the induction activity of nisin in intestinal chyme (intestinal content) was assessed.

Äidinmaito - terveysjuomaa ja normaalibakteereita

The chemical composition of breast milk has been studied in detail in the past decades. Hundreds of new antibacterial and antiviral components have been found. Several molecules have been found to promote the proper function of neonatal intestine. However, microbiological studies of breast milk have been, until recently, focused mainly on detecting harmful and pathogenic bacteria and viruses. Natural microbial diversity of human milk has not been widely studied before the work reported in this thesis. This is mainly because breast milk has traditionally been thought to be sterile - even if a certain amount of commensal bacteria have usually been detected in milk samples. The first part of this licentiate thesis contains a short literature review about the anatomy and physiology of breast feeding, human milk chemical and microbiological composition, mastitis, intestinal flora and bacteriocins. The second part reports on the experiments of the licentiate work, concentrating on the microbial diversity in the milk of healthy breast-feeding mothers, and the ability of these bacteria to produce antibacterial substances against pathogenic bacteria. The results indicate that human milk is a source of commensal bacteria for infant intestine. 509 random isolates from 40 breast milk samples were isolated and identified by 16S rRNA sequencing. Median bacterial count was about 600 colony forming units per milliliter. Over half of the isolates were staphylococci, and almost one third streptococci. The most common species were skin bacteria Staphylococcus epidermidis and oral bacteria Streptococcus salivarius and Streptococcus mitis. Lactic acid bacteria, identified as members of Lactobacillus-, Lactococcus- and Leuconostoc -genera, were found in five milk samples. Enterococci were found in three samples. A novel finding in this study is the capability of these commensal bacteria to inhibit the growth of pathogens. In 90 precent of the milk samples commensal bacteria inhibiting the growth of Staphylococcus aureus were found. In 40 precent of samples the colonies could block the growth completely. One fifth of the isolated Staph. epidermidis strains, half of Str. salivarius strains, and all lactic acid bacteria and enterococci could inhibit or block the growth of Staph. aureus. In further study also Listeria innocua- and Micrococcus luteus active isolates were found in 33 and 11 precent of milk samples (out of 140). Furthermore, two Lactococcus lactis isolates from the breast milk were shown to produce bacteriocin nisin, which is an antimicrobial molecule used as a food preservative. The importance of these human milk commensal bacteria in the development of newborn intestinal flora and immune system, as well as in preventing maternal breast infections, should be further explored.

Vastasyntyneen varsan sepsis osa II - Infektion diagnosoiminen, aiheuttajamikrobit ja mikrobilääkeresistenssi

Sepsis eli infektion aiheuttama yleistynyt tulehdusreaktio on merkittävä kuolleisuuden aiheuttaja vastasyntyneillä varsoilla. Kirjallisuuskatsauksessa on käsitelty sepsiksen patofysiologiaa ja kliinisiä oireita vastasyntyneillä varsoilla sekä sepsikselle altistavia tekijöitä. Vastasyntyneen varsan sepsiksen diagnosoimisessa kliinisten oireiden arvioinnilla on keskeinen merkitys sairauden varhaisessa tunnistamisessa ja hoidon aloittamisessa. Sairauden nopean etenemisen ja veriviljelytulosten hitaan valmistumisen vuoksi antibioottihoito joudutaan aloittamaan jo ennen viljelytulosten valmistumista. Veriviljelyllä on kuitenkin tärkeä merkitys sepsisdiagnoosin ja valitun antibioottihoidon varmistamisessa. Sairaalakohtaisten veriviljelynäytetulosten seuranta mahdollistaa ensisijaisen mikrobilääkkeen valinnan aiemmin eristettyjen aiheuttajamikrobien esiintyvyyden ja mikrobilääkeherkkyyksien perusteella. Yleisimpiä vastasyntyneen varsan sepsiksen aiheuttajia ovat kirjallisuuden mukaan suolistoperäiset gram-negatiiviset bakteerit. Escherichia colin osuus vastasyntyneiltä varsoilta otetuista veriviljelynäytteistä eristetyistä bakteerikannoista on vaihdellut eri tutkimuksissa 18,7 - 50,0 %. Pohjois-Amerikassa tehdyissä tutkimuksissa varsojen veriviljelynäytteistä eristettyjen E.coli -kantojen herkkyys yleisesti käytetylle trimetopriimi-sulfadiatsiinille on ollut huono (57–71 %). Penisilliinin ja gentamisiinin yhdistelmälle enterobakteerien herkkyyden on raportoitu olevan hyvä. Suomessa tilanteen on arvioitu olevan parempi. Tutkimuksessa kartoitettiin retrospektiivisesti veriviljelyn käyttöä varsojen sepsiksen diagnostiikassa, sepsiksen aiheuttajamikrobien esiintymistä ja mikrobilääkkeiden käyttöä Yliopistollisessa eläinsairaalassa (YES) vuosina 2004–2006. Tutkimusaineisto koostuu yhteensä 90 korkeintaan 10 päivän ikäisenä YES:aan tuodun varsan potilastiedoista. Sairaalaan saapuneista varsoista 30 % oli otettu veriviljelynäyte. Veriviljelynäytteistä positiivisia oli 62,5 %. 60 % positiivisista näytteistä kasvoi vähintään kahta bakteerilajia. Yleisin aiheuttajabakteeri oli Escherichia coli (23,1 %). Yksi eristetyistä E.coli -kannoista oli resistentti ampisilliinille, gentamisiinille ja trimetopriimi-sulfadiatsiinille. Aineiston pienen koon vuoksi tutkimus ei kuitenkaan anna luotettavaa kuvaa eristettyjen aiheuttajamikrobien mikrobilääkeherkkyydestä laajemmin. Sekakasvujen osuus oli suuri ja tyypillisten veriviljelynäytteitä kontaminoivien bakteerilajien (Streptococcus viridans sp., Micrococcus sp., koagulaasinegatiiviset stafylokokit) osuus oli yli 30 % eristetyistä bakteerikannoista. Tämä viittaa ongelmiin veriviljelynäytteenottotekniikassa riittävän aseptiikan saavuttamien osalta. Koagulaasinegatiiviset stafylokokit voivat myös aiheuttaa sepsiksen, mutta niiden merkitys vastasyntyneiden varsojen sepsiksen aiheuttajina on epäselvä.