Current status and future perspectives in HER2 positive advanced gastric cancer.

Gastric cancer is one of the most common malignancy worldwide with a prognosis less than 1 year in unresectable or metastatic disease. HER2 expression is the main biomarker to lead the addition of trastuzumab to first line systemic chemotherapy improving the overall survival in advanced HER2-positivegastric adenocarcinoma. The inevitable development of resistance to trastuzumab remains a great problem inasmuch several treatment strategies that have proven effective in breast cancer failed to show clinical benefit in advanced gastric cancer. In this review, we summarize the available data on the mechanisms underlying primary and secondary resistance toHER2-targeted therapy and current challenges in the treatment of HER2-positive advanced gastric cancer refractory to trastuzumab. Further, we describe the prognostic value of new non-invasive screening techniques, the current development of novel agents such us HER2 antibody-drug conjugates and bispecific antibodies, and the strategies with antitumor activity on going.

First record of the genus Zygina from a Neotropical region on Populus spp.: taxonomic and biological characteristics.

The typhlocybine, Zygina nivea Mulsant & Rey 1855, was found in urban areas of Argentina colonizing trees of poplar (Populus alba L. and P. nigra L.). This is the first mention of the genus Zygina Fieber from the Neotropical region. In this paper redescription of the male, description of the female, distributional and host plant data, and behavioural observations of this species are given.

Helicobacter spp. from gastric biopsies of stranded South American fur seals (Arctocephalus australis).

Gastrointestinal lesions with uncertain etiology have been widely described among pinnipeds. The aim of our study was to investigate the presence of Helicobacter spp. in the gastric mucosa of South American fur seals (Arctocephalusaustralis). Gastric biopsies from thirteen seals, stranded on the shores of the Southwestern Atlantic Ocean in Argentina, were evaluated for the presence of Helicobacter spp. by PCR and DNA sequence analysis. Six gastric biopsies were positive for Helicobacter spp. Pairwise sequence comparisons showed less than 95% identity to novel Helicobacter spp. described from pinnipeds from North America and Australia. However, phylogenetic analysis revealed that the South American fur seal sequences clustered with 99-100% homology with H. cetorum, a species isolated from dolphins and whales. The presence of H. cetorum in pinnipeds, if confirmed by its isolation from the gastric mucosa of these mammals, demonstrates the wide host range of this bacterium in the marine environment.

Detection of Helicobacter and Campylobacter spp. from the aquatic environment of marine mammals.

The mechanism by which Helicobacter species are transmitted remains unclear. To examine the possible role of environmental transmission in marine mammals, we sought the presence of Helicobacter spp. and non-Helicobacter bacteria within the order Campylobacterales in water from the aquatic environment of marine mammals, and in fish otoliths regurgitated by dolphins. Water was collected from six pools, two inhabited by dolphins and four inhabited by seals. Regurgitated otoliths were collected from the bottom of dolphins' pools. Samples were evaluated by culture, PCR and DNA sequence analysis. Sequences from dolphins' water and from regurgitated otoliths clustered with 99.8-100% homology with sequences from gastric fluids, dental plaque and saliva from dolphins living in those pools, and with 99.5% homology with H. cetorum. Sequences from seals' water clustered with 99.5% homology with a sequence amplified from a Northern sea lion (AY203900). Control PCR on source water for the pools and from otoliths dissected from feeder fish were negative. The findings of Helicobacter spp. DNA in the aquatic environment suggests that contaminated water from regurgitated fish otoliths and perhaps other tissues may play a role in Helicobacter transmission among marine mammals.

Methicillin-resistant Staphylococcus aureus strains in Buenos Aires teaching hospitals: replacement of the multidrug resistant South American clone by another susceptible to rifampin, minocycline and trimethoprim-sulfamethoxazole.

The aim of this study was to characterize methicillin-resistant Staphylococcus aureus (MRSA) isolates recovered from different infectious sites of hospitalized patients at two university hospitals. Fourteen isolates were analyzed by repetitive sequence based PCR (Rep-PCR), randomly amplified polymorphic DNA assay (RAPD-PCR), and pulsed-field gel electrophoresis (PFGE). We found that a prevalent clone of MRSA, susceptible to rifampin, minocycline, and trimethoprim/sulfamethoxazole (RIF(s), MIN(s), TMS(s)) was present in both hospitals in replacement of the multiresistant MRSA South American clone, previously described in these hospitals. The staphylococcal chromosomal cassette (SCCmec) type I element was detected in this new clone.

Methicillin-resistant Staphylococcus aureus strains in Buenos Aires Teaching Hospitals: replacement of the multidrug resistant South American clone by another susceptible to rifampin, minocycline and trimethoprim-sulfamethoxazole / Staphylococcus aureus meticilina-resistente en hospitales universitarios de Buenos Aires: reemplazo del clon Sudamericano multi-resistente por otro sensible a rifampicina, minociclina y trimetoprima-sulfametoxazol

The aim of this study was to characterize methicillin-resistant Staphylococcus aureus (MRSA) isolates recovered from different infectious sites of hospitalized patients at two university hospitals. Fourteen isolates were analyzed by repetitive sequence based PCR (Rep-PCR), randomly amplified polymorphic DNA assay (RAPD-PCR), and pulsed-field gel electrophoresis (PFGE). We found that a prevalent clone of MRSA, susceptible to rifampin, minocycline, and trimethoprim/sulfamethoxazole (RIF S, MIN S, TMS S) was present in both hospitals in replacement of the multiresistant MRSA South American clone, previously described in these hospitals. The staphylococcal chromosomal cassette (SCCmec) type I element was detected in this new clone.

El objetivo de este trabajo fue la caracterización de aislamientos de Staphylococcus aureus meticilina-resistentes (SAMR), provenientes de diferentes procesos infecciosos de pacientes internados en dos hospitales universitarios. Catorce aislamientos fueron analizados mediante la PCR de secuencias repetitivas (Rep-PCR), la amplificación al azar de ADN polimórfico (RAPD-PCR) y la electroforesis de campo pulsado (PFGE). Encontramos que un clon prevalente de SAMR, sensible a rifampicina, minociclina y trimetoprima-sulfametoxazol (RIF S, MIN S, TMS S) estaba presente en ambos hospitales, reemplazando al clon SAMR y multi-resistente previamente descrito en estos mismos hospitales. En este nuevo clon se detectó el cassette cromosómico estafilocócico SCCmec tipo I.

Methicillin-resistant Staphylococcus aureus strains in Buenos Aires teaching hospitals: replacement of the multidrug resistant South American clone by another susceptible to rifampin, minocycline and trimethoprim-sulfamethoxazole.

The aim of this study was to characterize methicillin-resistant Staphylococcus aureus (MRSA) isolates recovered from different infectious sites of hospitalized patients at two university hospitals. Fourteen isolates were analyzed by repetitive sequence based PCR (Rep-PCR), randomly amplified polymorphic DNA assay (RAPD-PCR), and pulsed-field gel electrophoresis (PFGE). We found that a prevalent clone of MRSA, susceptible to rifampin, minocycline, and trimethoprim/sulfamethoxazole (RIF(s), MIN(s), TMS(s)) was present in both hospitals in replacement of the multiresistant MRSA South American clone, previously described in these hospitals. The staphylococcal chromosomal cassette (SCCmec) type I element was detected in this new clone.

Genetic characterisation of Helicobacter pylori isolates from an Argentinean adult population based on cag pathogenicity island right-end motifs, lspA-glmM polymorphism and iceA and vacA genotypes.

Isolates of Helicobacter pylori from 88 patients were characterised by cagA status, cagA pathogenicity island (PAI) right-end motifs, iceA, vacA and lspA-glmM genotypes, primarily by PCR-based analysis, to investigate whether Argentinean isolates differed from those recovered in southern Europe or other Latin American countries. PCR-based analysis of vacA alleles was confirmed by reverse hybridisation in 56 cases, while sequence analysis was performed either when iceA and vacA genotypes could not be determined by PCR, or to investigate PCR and reverse hybridisation vacA genotyping discordance. Typing by lspA-glmM restriction fragment length polymorphism was performed with HhaI and AluI. The pattern of cag PAI right-end motifs and the prevalence of type Ia were similar to those in isolates from southern European countries, with cagA(+)/iceA1/vacA-s1 m1 being the commonest genotype. Reverse hybridisation identified a vacA-s1a/s1b recombinant allele, confirmed by sequencing analysis. Analysis of lspA-glmM genotypes identified at least 73 unrelated strains. Few mixed infections were identified, but in one case, isolates from a single biopsy exhibiting two vacA alleles were shown by lspA-glmM fingerprints to be two unrelated strains. No associated effect on ulcer disease risk was demonstrated by analysis of cagA, vacA and iceA status. Overall, the isolates of H. pylori from Argentina were similar to isolates from southern Europe or Latin American countries, and infections were associated mainly with single H. pylori strains.

Genotypic analysis of Staphylococcus aureus from milk of dairy cows with mastitis in Argentina.

Staphylococcus aureus is the most prevalent pathogen causing mastitis of dairy ruminants. This study was developed to ascertain the genotypes and genealogical relationship among strains isolated from milk of bovines with mastitis in Argentina. Molecular epidemiological analysis of S. aureus was performed on 112 isolates from 21 districts. Clonality was assessed by SmaI pulsed-field gel electrophoresis (PFGE) typing, automated EcoRI ribotyping and restriction enzyme analysis of plasmid (REAP) DNA profiles. A total of 22 band patterns distributed in four clusters were found by SmaI PFGE analysis. The similarity of clusters 2, 3 and 4 with cluster 1 was 0.73, 0.69 and 0.33, respectively, and 101 of 112 isolates belonged in cluster 1. PFGE band patterns from 42 isolates within cluster I were indistinguishable from each other (type A). The second largest group of isolates with indistinguishable PFGE band patterns was subtype A11, which was composed of 19 isolates. Automated ribotyping assigned the 112 isolates into 13 ribotypes. Among these, the most prevalent ribotypes I and VI were composed of 49 and 35 isolates respectively. Although there was certain correspondence between PFGE genotypes and ribotypes, further discrimination was achieved by combining both methods. REAP DNA profile analysis was useful to provide even further discrimination between isolates with identical PFGE genotype and ribotype. The most prevalent S. aureus strains A/I and A11/VI were widely distributed in the country and were not restricted to individual nearby locations. Prevalence of these two strains varied consecutively within a period of 8 years. Whether the shift in type prevalence was due to selection of a phenotypic trait remains undisclosed.

Efficacy of two DNA fingerprinting methods for typing Acinetobacter baumannii isolates.

Performance of macrorestriction and repetitive extragenic palindromic DNA sequence-based PCR (REP-PCR) to type Acinetobacter baumannii isolates was quantitatively estimated using a test population of 54 outbreak-related, 29 endemic infection-related and 17 epidemiologically-unrelated isolates. Reproducibility and stability for macrorestriction were 100%, and REP-PCR showed only slightly lower stability. Macrorestriction resolved 18 fingerprints and REP-PCR 10 DNA patterns, forming eight and seven clusters at 75% of similarity level, respectively. Intercluster band variation was > 7 bands for both methods. Although, all endemic isolates, except one, were concordantly grouped by both methods, macrorestriction distinguished a greater number of subtypes over one year study. For outbreaks, the epidemiologic concordance for both methods was 88%. The discriminatory index for macrorestriction and REP-PCR was 0.884 and 0.877, respectively. In conclusion, both methods showed similar efficacy as epidemiological markers, and by concordance, this study demonstrated that for REP-PCR typing, a > or = 7 bands difference seemed an appropriate threshold to identify unrelated strains.

Helicobacter pylori vacA genotypes, cagA status and ureA-B polymorphism in isolates recovered from an Argentine population.

Several reports have evidenced geographic differences in the prevalence of vacA (vacuolating cytotoxin gene) alleles and cagA (cytotoxin-associated gene) status among Helicobacter pylori isolates. We investigated the occurrence of these virulence-associated genes status among our isolates, and their relationship with ulcer disease outcome. Besides, ureA-B polymorphism was studied. One hundred isolates, comprising 32 from patients with ulcer disease (UD) and 68 from patients with non-ulcer dyspepsia (NUD), were analyzed. Eighty-four percent of isolates were cagA-positive without statistically significant difference in prevalence between patients with UD or NUD. Genotype vacA-s1m1 was predominant, although unlike other South American regions, subtype s1am1 occurrence was higher than s1b. The multivariate model used to estimate the predictive value of cagA and vacA status for UD development disclosed infection with vacA-s1am1 isolates as the only variable that increased the risk of UD onset. ureAB fingerprinting showed considerable genetic divergence among isolates, however, confirmed that certain DNA banding profiles are conserved worldwide.

Capsule expression by bovine isolates of Staphylococcus aureus from Argentina: genetic and epidemiologic analyses.

Staphylococcus aureus is an important cause of bovine mastitis worldwide, and effective preventive or therapeutic modalities are lacking. Although most human S. aureus isolates produce capsular polysaccharides (CPs), few reports have described the prevalence of capsules on bovine isolates. This information is important for the rational design of a vaccine for the prevention of staphylococcal mastitis. We serotyped 195 S. aureus strains isolated between 1989 and 1997 from the milk of mastitic cows in Argentina. Only 14 (7.1%) of the strains were serotype 5, and all were recovered between 1989 and 1992. Thirteen serotype 8 strains were identified, and 12 of these were isolated between 1991 and 1994. The remaining 168 isolates were nonreactive (NR) with CP serotype 5 (CP5)- or CP8-specific antibodies. Hybridization studies performed with genomic DNA from eight NR strains revealed that only three of them carried the capsule genes. Pulsed-field gel electrophoresis (PFGE) performed with 127 of the 195 S. aureus isolates revealed that most (86%) strains belonged to one of four major PFGE groups. Although 8 of 14 CP5 isolates showed a common PFGE pattern (arbitrarily defined as A1), 31 other A1 isolates from the same time period (1989 to 1992) were not CP5 positive. In contrast, only nine PFGE type B3 isolates were recovered between 1990 and 1994, and eight of these were positive for CP8 (P < 0.0003). The results of this study underscore the variability in capsule expression by S. aureus strains isolated from different geographical regions and cast doubt on the roles of CP5 and CP8 in the pathogenesis and immunoprophylaxis of bovine mastitis in Argentina.

[Epidemiologic consistency of polymerase chain reaction (PCR) based methods for the study of Acinotobacter baumannii infections]. / Concordancia epidemiológica de los métodos basados en la reacción en cadena de la polimerasa (PCR) para la investigación de las infecciones por Acinetobacter baumannii.

Acinetobacter baumannii is one of the most frequent causative agents of nosocomial infections outbreaks. Consequently, a rapid and specific typing method that can identify epidemic strains is important in preventing their dissemination. To evaluate PCR (polymerase chain reaction)-based methods as epidemiological markers, epidemiologic concordance (EC) and the discriminatory power (D) of two of those methods: 1) arbitrary primed-PCR (AP-PCR), and 2) repetitive extragenic palindrome sequence-based PCR (REP-PCR), were analyzed. The results were compared with that of ribotyping using EcoRI, BglII and ClaI as restriction enzymes. These methods were applied to 69 A. baumannii isolates that included: 15 epidemiological unrelated isolates, 31 recovered from two outbreaks, and 23 obtained from endemic infections. Considering the unrelated isolates, D of ribotyping, AP-PCR and REP-PCR were 0.915, 0.904 and 0.847, respectively. The three methods showed the same EC with respect to the two analyzed outbreaks (100% and 83%, respectively), and the epidemic strains were uniformi differentiated from the co-transferred ones. Ribotyping classified the 23 isolates recovered from endemic infections in 4 different strains, while AP-PCR and REP-PCR identified 3 of them. Although, the 3 methods identified the most frequent disseminated strain. The mayor advantages of REP-PCR versus AP-PCR were reproducibility, and easier optimization. These advantages, in addition to the similar EC of the 3 methods, confirm REP-PCR as an appropriate marker to be used when rapid information about epidemiological A. baumannii infection analysis is required.

Survival of Acinetobacter baumannii on bed rails during an outbreak and during sporadic cases.

Genotypic methods showed Acinetobacter baumannii biotype 9 genotype I to be the epidemic strain on an outbreak in an intensive care unit (ICU) which lasted from January to April of 1996. A cohort was established during March in which hospital personnel were assigned exclusively to A. baumannii infected or colonized patients. New patients were not admitted to the ICU until the last infected patient was discharged. However, strain I was isolated during April and vectors other than human carriage were suspected. The ICU comprised four sections; patients and beds were moved within them according the severity of diseases. Strain I was isolated from a bed rail nine days after the infected patient was discharged. This dry vector may explain the transmission of the epidemic strain between sections. The following July, four new infected patients were identified and three different strains, including the epidemic one, were recovered. The two other strains were also isolated from a bed rail. Although this environmental source does not explain by itself the transmission of an epidemic strain, it illustrates that dry vectors can be secondary reservoirs where A. baumannii can survive.

Concordancia epidemiológica de los métodos basados en la reacción en cadena de la polimerasa (PCR) para la investigación de las infecciones por Acinetobacter baumannii. / [Epidemiologic consistency of polymerase chain reaction (PCR) based methods for the study of Acinotobacter baumannii infections]

Acinetobacter baumannii is one of the most frequent causative agents of nosocomial infections outbreaks. Consequently, a rapid and specific typing method that can identify epidemic strains is important in preventing their dissemination. To evaluate PCR (polymerase chain reaction)-based methods as epidemiological markers, epidemiologic concordance (EC) and the discriminatory power (D) of two of those methods: 1) arbitrary primed-PCR (AP-PCR), and 2) repetitive extragenic palindrome sequence-based PCR (REP-PCR), were analyzed. The results were compared with that of ribotyping using EcoRI, BglII and ClaI as restriction enzymes. These methods were applied to 69 A. baumannii isolates that included: 15 epidemiological unrelated isolates, 31 recovered from two outbreaks, and 23 obtained from endemic infections. Considering the unrelated isolates, D of ribotyping, AP-PCR and REP-PCR were 0.915, 0.904 and 0.847, respectively. The three methods showed the same EC with respect to the two analyzed outbreaks (100

and 83

, respectively), and the epidemic strains were uniformi differentiated from the co-transferred ones. Ribotyping classified the 23 isolates recovered from endemic infections in 4 different strains, while AP-PCR and REP-PCR identified 3 of them. Although, the 3 methods identified the most frequent disseminated strain. The mayor advantages of REP-PCR versus AP-PCR were reproducibility, and easier optimization. These advantages, in addition to the similar EC of the 3 methods, confirm REP-PCR as an appropriate marker to be used when rapid information about epidemiological A. baumannii infection analysis is required.

The use of plasmid profile analysis and ribotyping for typing Acinetobacter baumannii isolates.

Plasmid profiles were used to analyse 39 Acinetobacter baumannii isolates from 36 patients at three hospitals. The isolates were prevously classified by biotyping and rDNA fingerprinting. Ribotyping was useful to establish the lineage of isolates and to confirm genospecies identification. Thirty-seven isolates (94.9%) contained plasmids. The variable number of plasmids with different molecular weights in each isolate enabled the identification of 13 profiles without the need for endonuclease digestion. Fifteen A. baumannii biotype 2 isolates of similar ribotype and antibiotype contained identical plasmids over a two-month outbreak at one hospital. Plasmid typing discriminated these isolates from sporadic A. baumannii isolates of close ribotype obtained from different hospitals. A few isolates of different lineage, however, showed similar plasmid profile. Our results suggest that plasmid typing is a practical method to assist infection control of nosocomial A baumannii. A combination of plasmid typing and ribotyping is suggested to confirm genospecies classification and to identify strains against reference band profiles.

The emergence of resistance to amikacin in Serratia marcescens isolates from patients with nosocomial infection.

Administration of either amikacin (1985) or gentamicin (1984, 1986-1991) as first-choice aminoglycoside did not decrease the high incidence of amikacin-resistant Serratia marcescens (ARSm) isolates responsible for nosocomial infections at the J.A. Fernández Hospital of Buenos Aires (42% in 1984, 31% in 1985 and 41% in 1987, differences not significant). In addition, a significant peak (P = 0.003) was detected in 1986, with an ARSm incidence of 70%. The incidence of ARSm decreased by 1988-1991 for reasons not related to aminoglycoside use. In the period 1984-1987 all S. marcescens isolates carried the 6'-aminoglycoside-acetyltransferase-Ic [aac(6')-Ic] gene, while in addition 20% of the isolates contained the plasmid-encoded 3'-aminoglycoside-phosphotransferase-VIa[aph(3')-VIa] and 2% the 6'-aminoglycoside-acetyltransferase-Ib [aac(6')-Ib] genes. From 1988 to 1992 resistance to amikacin was associated with only 4 ARSm isolates and correlated with the appearance of Tn1331-related sequences in these isolates. This transposon or related sequences, however, was not widely spread in the S. marcescens population under investigation. Combined use of restriction fragment length polymorphism (RFLP), ribotyping and plasmid profile analysis revealed that S. marcescens strains of the same genotype, including isolates either expressing or not the aac(6')-Ic gene, were involved in outbreaks occurring in May 1984, May 1985 and May 1986. Furthermore, these epidemiological tools permitted discrimination of different S. marcescens clones, each bearing a particular amikacin-resistance marker.

Pseudomonas aeruginosa ribotyping: stability and interpretation of ribosomal operon restriction patterns.

Fifty-one Pseudomonas aeruginosa isolates were differentiated into 21 types by ribotyping. Several enzyme combinations, including the best ones proposed in literature, were utilized and the highest discrimination was reached by individual digestion with PvuII, HindII, and EcoRI or BamHI. Clinical isolates from outbreaks were clonally related as identified by this molecular approach. Restriction rDNA profiles were composed of strong and weak bands. Using 6 micrograms DNA we were able to demonstrate that PvuII, HindIII, and BamHI weak bands were reproducible. These weak bands should be considered not only to accomplish the highest discrimination but also to correctly assign isolate clonality. Conversely, we found that EcoRI weak bands were not reproducible and, therefore, are not recommended for ribotype analysis. Finally, profiles differing in one single band actually represented isolates of different genotype, as confirmed by further analysis using other molecular methods. In this report on P. Aeruginosa ribotyping of clinical isolates, criteria for band pattern interpretation are established.

Comparative usefulness of ribotyping, exotoxin A genotyping, and SalI restriction fragment length polymorphism analysis for Pseudomonas aeruginosa lineage assessment.

Ribotyping, exotoxin A genotyping (EAGP), and restriction fragment length polymorphism (RFLP) analysis of total DNA with SalI (SalI RFLP) were compared for intraspecies discrimination of 93 Pseudomonas aeruginosa isolates. Type-ability of all methods was 100% and the results of typing with each method remained unchanged during laboratory manipulation. Clonal groups defined with each molecular method were largely coincident and, in those cases where inconsistencies were detected, isolates were analyzed by transverse alternating field gel electrophoresis (TAFE) and arbitrarily primed polymerase chain reaction (AP-PCR). SalI RFLP analysis was highly discriminative so as to distinguish unrelated isolates of close lineage. However, it was not a good method to identify isolates of unrelated lineage because SalI RFLP appeared to be subjected to convergent evolution. The index of discrimination suggested by Hunter and Gaston was determined to assess the discriminatory power of the molecular methods utilized either alone or in several combinations. Combined use of ribotyping and SalI RFLP analysis reached the highest index of discrimination (0.982) and proved to be a very valuable tool for epidemiological differentiation of P. aeruginosa isolates.