Abstract The aim of this study was to characterize phenotypically and genotypically 27 mecApositive Staphylococcus aureus strains with oxacillin MICs of ≤2 g/ml by Vitek 2, isolated indifferent regions of Uruguay. Susceptibility to oxacillin and cefoxitin was studied by gradient dif-fusion, disk diffusion to cefoxitin, and Phoenix and MicroScan systems. PBP2a was determined.SCCmec typing was performed and the isolates were compared by PFGE. Twenty-six isolateswere susceptible to oxacillin; one strain was susceptible to cefoxitin by disk diffusion and 3strains by gradient diffusion. Phoenix and MicroScan panels detected methicillin resistance in25 and 27 strains, respectively. Twenty-six strains tested positive for PBP2a. Twenty-six strainscarried SCCmec V and 24 belonged to pulsotype A. One strain carried SCCmec IV and did notbelong to pulsotype A. Cefoxitin disk diffusion test and PBP2a detection correctly identified 26of these 27 strains as MRSA. PFGE results suggest the dissemination of a cluster of MRSA carryingSCCmec V.

Resumen El objetivo de este estudio fue caracterizar fenotípicamente y genotípicamente 27 cepas de Staphylococcus aureus positivas para mecA y con CIM de oxacilina <2 pg/ml según Vitek 2, obtenidas en diferentes regiones del país. La sensibilidad frente a la oxacilina y la cefoxitina se estudió por difusión en gradiente, por disco-difusión (cefoxitina) y por los sistemas Phoenix y MicroScan. Se analizó la portación de PBP2a, se realizó la tipificación de SCCmec y las cepas se compararon mediante PFGE. Resultaron sensibles a oxacilina por difusión en gradiente 26 cepas; una fue sensible a cefoxitina por disco-difusión y 3 lo fueron por difusión en gradiente. Los sistemas Phoenix y MicroScan detectaron resistencia a meticilina en 25 y 27 cepas, respectivamente. Asimismo, 26 cepas portaban PBP2a y 26 cepas mostraron presencia de SCCmec V, 24 correspondieron al pulsotipo A. Una portaba SCCmec IV y no perteneció al pulsotipo A. La prueba de disco-difusión con cefoxitina y la detección de PBP2a identificaron 26 de 27 cepas como MRSA. La PFGE sugiere la diseminación de un grupo MRSA con SCCmec V. © 2022 Asociación Argentina de Microbiología. Publicado por Elsevier Espana, S.L.U. Este es un artículo Open Access bajo la licencia CC BY-NC-ND (https://creativecommons.org/licenses/by-nc-nd/4.0/).

ABSTRACT The aim of this study was to describe the microbiological characteristics and profile of genes encoding enterotoxins in 95 Staphylococcus aureus isolates obtained between April 2011 and December 2014 from foodstuffs, persons and surfaces of retail food stores. After microbiological identification and antimicrobial susceptibility testing, polymerase chain reactions (PCR) were performed, targeting sea, seb, sec, sed and see genes that code for classical enterotoxins (ET) A-E, and three additional genes: seg , seh and sei , coding for so-called “new enterotoxins” G, H and I. The isolates were characterized by Pulsed Field Gel Electrophoresis (PFGE), and five selected isolates were further analyzed through Multi Locus Sequence Typing (MLST). It is noteworthy that 54.7% of the examined isolates harbored one or more of the investigated ET gene types. Most positive isolates carried more than one ET gene up to five types; seg was the most frequent ET gene, followed by sei. Five enterotoxin-coding isolates also coded for some antimicrobial resistance genes. Two of them, and four additional non-enterotoxic isolates carried erm genes expressing inducible clindamycin resistance. PFGE-types were numerous and diverse, even among enterotoxin-coding strains, because most isolates did not belong to known foodborne outbreaks and the sampling period was long. MLST profiles were also varied, and a new ST 3840 was described within this species. ST 88 and ST 72 enterotoxin-coding isolates have been identified in other regions in association with foodborne outbreaks. This manuscript reports the first systematic investigation of enterotoxin genes in S. aureus isolates obtained from foodstuffs and infected people in Uruguay.

Resumen: Staphylococcus aureus es un patógeno humano reconocido capaz de adquirir mecanismos de resistencia para distintos antibióticos. La resistencia a oxacilina se debe principalmente al producto de los genes mecA o mecC que determinan una concentración inhibitoria mínima (CIM) de oxacilina ³4 mg/L. La expresión de estos genes es variable y se han descrito aislamientos portadores del gen mecA con CIM de oxacilina ³2 mg/L (fenotípicamente susceptibles) denominadas OS-MRSA. A partir de una niña cursando una infección articular se obtuvieron aislamientos bacterianos de S. aureus del líquido articular y de hemocultivo. El aislamiento de hemocultivo fue clasificado como resistente a meticilina (MRSA), mientras que el de líquido articular fue sensible a meticilina (MSSA) utilizando el sistema automatizado Vitek 2. Ambos mostraron halos de inhibición para oxacilina >15 mm y para cefoxitina de 19 y 17 mm, respectivamente. En los dos aislamientos se demostró la presencia de los genes mecA, sea, seb y el SCCmec tipo V. La comparación genética por SmaI-PFGE mostró perfiles idénticos para ambos cultivos, sugiriendo que se trataba de la misma cepa. Este reporte informa la detección de un aislamiento de OS-MRSA en Uruguay y destaca las limitaciones de algunos procedimientos de laboratorio para identificar correctamente fenotipos de resistencia asociados al gen mecA en aislamientos clínicos de S. aureus.

Abstract: Staphylococcus aureusis a common human pathogen that is able to acquire resistance mechanisms for different antibiotics. Oxaxicillin resistance mainly results from mecA or mecC genes which determine an oxacillin minimum inhibitory concentration (MIC) ³4 mg/L. Expression of these genes is variable and the isolation of mecA gen with oxacillin MIC ³2 mg/L (phenotypically susceptible) have been described carriers has been described, having been named OS-MRSA. S. aureus bacteria was isolated from the synovial fluid and blood culture in a girl with a joint infection. Isolation of the blood culture was classified as methicillin resistant (MRSA) while thet of the synovial fluid was methicillin sensitive (MSSA), by using the automatized Vitek 2 system. Both of them present oxacillin inhibition halos > 15 mm, and inhibition halos of 19 and 17 mm for cefoxitin, respectively. Both isolations proved mecA, sea, seb and type V SCCmec genes were present. Genetic comparison by SmaI-PFGE showed identical profiles for both cultures, suggesting it was the same strain. These report informs the identification of an OS-MRSA isolation in Uruguay and points out the limitation of a few laboratory procedures to correctly identify resistant phenotypes associated to mecA gene in clinical isolations of S. aureus.

Resumo: O Staphylococcus aureus é um agente patogênico humano conhecido capaz de adquirir mecanismos de resistência para distintos antibióticos. A resistência a oxacilina é devida principalmente ao produto dos genes mecA ou mecC que determinam uma concentração inibitória mínima (CIM) de oxacilina ³4 mg/L. A expressão destes genes é variável e isolamentos portadores del gen mecA com CIM de oxacilina ³2 mg/L (fenotipicamente susceptíveis) denominadas OS-MRSA foram descritos. Com material extraído de um menina com infecção articular foram obtidos isolamentos bacterianos de S. aureus do líquido articular e de hemocultura. O isolamento da hemocultura foi classificado como resistente a meticilina (MRSA) e o do líquido articular foi sensível a meticilina (MSSA) utilizando o sistema automatizado Vitek 2. Ambos mostraram halos de inibição para oxacilina >15 mm e para cefoxitina de 19 e 17 mm, respectivamente. Nos 2 isolamentos a presença dos genes mecA, sea, seb e o SCCmec tipo V foi demonstrada. A comparação genética por SmaI-PFGE mostrou perfis idênticos para ambos cultivos, sugerindo que se tratava da mesma cepa. Este artigo descreve a detecção de um isolamento de OS-MRSA no Uruguai e destaca as limitações de alguns procedimentos de laboratório para identificar corretamente fenótipos de resistência associados ao gen mecA em isolamentos clínicos de S. aureus.