Mycobacterium mucogenicum and other non-tuberculous mycobacteria in potable water of a trauma hospital: a potential source for human infection.

This study examined the frequency of occurrence of non-tuberculous mycobacteria (NTM) in potable water samples from a main trauma hospital in Mexico City. Sixty-nine potable water samples were collected, 23 from each source: cistern, kitchen tap and bathroom showers. Of the 69 samples, 36 harboured NTM species. Twenty-nine of the 36 isolates were Mycobacterium mucogenicum, two Mycobacterium rhodesiae, one Mycobacterium peregrinum, one Mycobacterium fortuitum and three were Mycobacterium spp. Hospital potable water harbouring NTM represents a potential source for nosocomial infections, therefore we suggest that hospital potable water microbiological guidelines should include testing for NTM species.

In vivo transfer of plasmid pRAS1 between Aeromonas salmonicida and Aeromonas hydrophila in artificially infected Cyprinus carpio L.

This study investigated the possible in vivo transfer of plasmid pRAS1 between Aeromonas salmonicida and A. hydrophila inhabiting two different organs of Cyprinus carpio L. To distinguish transconjugants from naturally occurring antibiotic resistant bacteria, twelve luminescent transposon-tagged A. hydrophila strains using mini Tn5luxCDABEKm2 transposon were generated. In conjugal transfer experiments, fish were conditioned with the donor bacteria and subsequently immersed in water containing the recipient strain. Bacteria were recovered from gills and intestines and isolated by growth on selective plates. Transconjugants were identified by their resistance to the pRAS1 encoded antimicrobials and by light emission. In vivo transfer frequencies ranged between 10(-3) and 10(-6) and were somewhat lower in intestines, compared to gills. Transfer frequencies were also smaller relative to those obtained in vitro. The minimal amount of donor and recipient bacteria needed to yield detectable transconjugants in vivo was 1 x 10(4) CFU mL(-1). Implications of this plasmid transfer in natural settings and its possible consequences to human health are discussed.

Characterisation of Aeromonas spp. isolated from frozen fish intended for human consumption in Mexico.

A total of 82 strains of presumptive Aeromonas spp. were identified biochemically and genetically (16S rDNA-RFLP). The strains were isolated from 250 samples of frozen fish (Tilapia, Oreochromis niloticus niloticus) purchased in local markets in Mexico City. In the present study, we detected the presence of several genes encoding for putative virulence factors and phenotypic activities that may play an important role in bacterial infection. In addition, we studied the antimicrobial patterns of those strains. Molecular identification demonstrated that the prevalent species in frozen fish were Aeromonas salmonicida (67.5%) and Aeromonas bestiarum (20.9%), accounting for 88.3% of the isolates, while the other strains belonged to the species Aeromonas veronii (5.2%), Aeromonas encheleia (3.9%) and Aeromonas hydrophila (2.6%). Detection by polymerase chain reaction (PCR) of genes encoding putative virulence factors common in Aeromonas, such as aerolysin/hemolysin, lipases including the glycerophospholipid-cholesterol acyltransferase (GCAT), serine protease and DNases, revealed that they were all common in these strains. Our results showed that first generation quinolones and second and third generation cephalosporins were the drugs with the best antimicrobial effect against Aeromonas spp. In Mexico, there have been few studies on Aeromonas and its putative virulence factors. The present work therefore highlights an important incidence of Aeromonas spp., with virulence potential and antimicrobial resistance, isolated from frozen fish intended for human consumption in Mexico City.

[Investigation of the presence of Staphylococcus aureus in cooked ham using 3 methods (preliminary study)]. / Investigación de la presencia de Staphylococcus aureus en jamón cocido empleando tres métodos (estudio preliminar).

Fifty-one cooked ham samples were analized by three methods for investigation of Staphylococcus aureus; Modified Van Doorne and American Public Health Association; The Official Mexican Method. The first two are enrichment methods and in all three a comparison between Baird Parker agar and salt milk agar was done. The modified Van Doorne technique was the best for isolation of S. aureus from cooked ham. In Baird Parker agar it was possible to demonstrate the presence of S. aureus in all positive samples. The study shows the importance of using Baird Parker broth as an enrichment medium for the isolation of S. aureus from products in which a thermal treatment and addition of salts as sodium chloride and nitrites, inhibit the growth of this microorganism.

[Isolation of Staphylococcus aureus by the Baird Parker method from powdered milk]. / Aislamiento de Staphylococcus aureus por el método de Baird Parker a partir de leche en polvo.

There are many media recommended for the isolation of Staphylococcus aureus from foods, but only with some media one can obtain a good growth started with stressed cells. The Baird Parker (BP) medium is considered the best choice to recover stressed cells, however, it is not as good a medium to isolate Staphylococcus aureus from powder milk. Therefore, it is important to count with alternative media to enhance the chance for Staphylococcus aureus to grow from dehydrated products. Thirty-one powder milk samples contaminated with Staphylococcus aureus were analysed by Baird Parker method, employing four culture media: Baird Parker (BP), Baird Parker + tween + MgCl2 (BPTM), Pork plasma with bovine fibrinogen agar (PPF) and Salt Milk agar (SL). Staphylococcus aureus was isolated in SL, 38.7%; in BP, 3.2%; in BPTM, 6.4%; and PPF, 0%.

[Demonstration of staphylococcal thermonuclease from powdered milk]. / Demostración de termonucleasa (TNasa) estafilocócica a partir de leche en polvo.

Demonstration of Staphylococcal Thermonuclease (TNase) from Powder Milk. Some authors have reported that the number of Staphylococcus aureus needed to produce a food-poisoning is 10(6) CFU per gram of food, however, other authors have reported foods without microorganisms but these have produced food-poisoning. Because the methods for staphylococcal enterotoxins demonstration in foods are laborious and expensive procedures, in this paper we tried to demonstrate the thermonuclease (TNase) presence in foods directly, as a helper test for screening foods suspected to be contaminated with this microorganism. To 112 powder milk samples were determined TNase presence by Tatini's et al (1976) and Lachica's (1972) technics, 31 of this samples had S. aureus. Only with Lachica's technique it could be possible to demonstrate TNase in 17 of 112 analyzed samples, 14 of these had viable S. aureus.