RESUMO
ABSTRACT: Methicillin resistance in the Staphylococcus intermedius group (SIG) has emerged in small animal practice. Methicillin-resistant SIG (MRSIG) members have been implicated as causes of infections in both companion animals and humans. Staphylococcal cassette chromosome mec (SCCmec) elements carry the mecA/C genes, which encode for the transpeptidase PBP2a (PBP2') responsible for β-lactam antibiotic resistance in staphylococci. This study examined the SCCmec types of MRSIG isolates from different clinical specimens of dogs that exhibited methicillin MIC ≥ 0.5 μg/mL by an automated identification and susceptibility system in a Center for Veterinary Diagnostics in São Paulo, Brazil. Susceptibility to methicillin was determined by broth microdilution testing, and Oxoid® M.I.C.Evaluator® strips. PBP2a production was detected using a latex agglutination assay. SCCmec typing was performed according to the International Working Group on the Classification of Staphylococcal Cassette Chromosome Elements (IWG-SCC) guidelines. SCCmec type II (2A), SCCmec type III (3A), composite SCC structures consisting of a class A mec gene complex in addition to multiple ccr gene complexes, and non-typable SCCmec elements were reported in these MRSIG isolates. SCCmec type variants differing from those so far acknowledged by IWG-SCC were found, indicating new rearrangements in the genetic context of mecA in these canine MRSIG isolates.
RESUMO: A resistência à meticilina no grupo Staphylococcus intermedius (GSI) tem aumentado na clínica de pequenos animais. Membros GSI resistentes à meticilina (GSIRM) têm sido causas de infecções tanto em animais de companhia e humanos. Cassetes cromossômicos estafilocócicos mec (SCCmec) carregam os genes mecA/C, que codificam a transpeptidase PBP2a (PBP2') responsável pela resistência aos antibióticos β-lactâmicos em estafilococos. Nosso objetivo foi investigar os elementos SCCmec de GSIRM isolados de diferentes amostras clínicas de cães que exibiram CIM de meticilina ≥ 0,5 μg/mL por meio de um sistema automatizado em um Centro Veterinário de Diagnósticos em São Paulo, Brasil. A sensibilidade à meticilina foi determinada por meio do teste de microdiluição em caldo e fitas Oxoid® M.I.C.Evaluator®. A produção de PBP2a foi detectada usando um ensaio de aglutinação de látex. A tipagem dos elementos SCCmec foi realizada de acordo com as diretrizes do International Working Group on the Classification of Staphylococcal Cassette Chromosome Elements (IWG-SCC). SCCmec tipo II (2A), SCCmec tipo III (3A), SCC compostos de um complexo mec de classe A com múltiplos complexos ccr, e elementos SCCmec não tipáveis foram encontrados nesses isolados GSIRM. Variantes que diferem dos elementos SCCmec reconhecidos até o momento pelo IWG-SCC foram encontradas, indicando novos rearranjos no contexto genético de mecA nesses isolados GSIRM caninos.
RESUMO
Fifty-two Staphylococcus aureus recovered from papillary ostium and milk samples collected from cows with subclinical mastitis and milking environments in three small dairy herds located in southeastern Brazil were subjected to PCR identification based on the thermonuclease (nuc) gene. All the strains were submitted to in vitro antimicrobial susceptibility testing, and we investigated the sequence types (STs), agr groups (I-IV), virulence genes encoding for Microbial Surface Components Recognizing Adhesive Matrix Molecules (MSCRAMMs), biofilm-associated proteins, bi-component toxins, pyrogenic toxin superantigens, and enterotoxins. Screening for oxacillin resistance (2-6 µg/ml oxacillin), beta-lactamase activity assays, and PCR for the mecA/mecC genes detected 26 methicillin-susceptible S. aureus(MSSA) and 26 mec-independent oxacillin-nonsusceptible S. aureus (MIONSA). While MSSA isolates were found to be susceptible to all antimicrobial agents tested, or only resistant to penicillin and ampicillin, MIONSA isolates were multidrug-resistant. ST126-agr group II MSSA isolates were prevalent in milk (n=14) and carried a broad set of virulence genes (clfA, clfB, eno, fnbA, fiB, icaA, icaD, lukED, hla, and hlb), as well as the ST126-agr group II MIONSA isolated from milking liners (n=1), which also carried the eta gene. ST1-agr group III MIONSA isolates (n=4) were found in papillary ostium and milk, but most MIONSA isolates (n=21), which were identified in both papillary ostium and milking liners, were agr-negative and assigned to ST126. The agr-negative and agr group III lineages showed a low potential for virulence. Studies on the characterization of bovine-associated MSSA/MIONSA are essential to reduce S. aureus mastitis to prevent economic losses in dairy production and also to monitor the zoonotic potential of these pathogens associated with invasive infections and treatment failures in healthcare.
Cinquenta e dois isolados de Staphylococcus aureus obtidos de amostras colhidas do óstio papilar, do leite de vacas com mastite subclínica e do ambiente de ordenha em três fazendas de rebanhos leiteiros localizadas no sudeste do Brasil foram identificados por PCR para o gene da termonuclease (nuc). Todos os isolados foram testados para sensibilidade a antimicrobianos e foram investigados os sequence types (STs), grupos agr (I-IV) e genes de virulência que codificam Microbial Surface Components Recognizing Adhesive Matrix Molecules (MSCRAMMs), proteínas associadas a biofilme, toxinas bi-componentes, toxinas pirogênicas com propriedades de superantígenos e enterotoxinas. Triagem para detecção de resistência à oxacilina (2-6 µg/ml oxacilina), ensaios de atividade de enzimas beta-lactamases e PCR para os genes mecA/mecC detectaram 26 estirpes de S. aureus sensíveis à meticilina (methicillin-susceptible S. aureus, MSSA) e 26 estirpes de S. aureus mec-negativas não sensíveis à meticilina (mec-independent oxacillin-nonsusceptible S. aureus, MIONSA). Enquanto os isolados MSSA foram sensíveis a todos os agentes antimicrobianos testados, ou apenas resistentes à penicilina e ampicilina, os isolados MIONSA foram multirresistentes. MSSA ST126-agr grupo II foram prevalentes no leite (n= 14) e apresentaram um amplo conjunto de genes de virulência (clfA, clfB, eno, fnbA, fiB, icaA, icaD, lukED, hla e hlb), assim como o isolado MIONSA ST126-agr grupo II proveniente de um insuflador (n= 1), o qual também apresentou o gene eta. MIONSA ST1-agr grupo III (n= 4) foram identificados no óstio papilar e leite, mas a maioria dos isolados MIONSA (n= 21), encontrados em óstios papilares e insufladores, foram agr-negativos e pertenceram ao ST126. As linhagens agr-negativas e agr grupo III apresentaram baixo potencial de virulência. Estudos sobre a caracterização de MSSA/MIONSA associados a bovinos são essenciais para a redução da mastite causada por S. aureus e de perdas econômicas na produção leiteira e, também, para o monitoramento do potencial zoonótico desses patógenos associados a infecções invasivas e falhas de tratamento em ambientes hospitalares.
Assuntos
Animais , Feminino , Bovinos , Staphylococcus aureus/isolamento & purificação , Mastite Bovina/microbiologia , Antibacterianos/farmacologia , Staphylococcus aureus/efeitos dos fármacos , Staphylococcus aureus/genética , Virulência , Testes de Sensibilidade Microbiana , Reação em Cadeia da PolimeraseRESUMO
Linezolida foi o primeiro fármaco da classe das oxazolidinonas a ser aprovado para o uso clínico. Esta nova oxazolidinona inibe a síntese protéica impedindo a formação do complexo de iniciação formado pelo mRNA, tRNA f-Met e a subunidade 50S do ribossomo bacteriano. Embora a resistência à linezolida possa ser mediada pelo produto do gene cfr ou por mutações nas proteínas ribossômicas L3, L4 e L22, o mecanismo de resistência mais comum envolve mutações no domínio V do gene rRNA 23S. Entre março de 2008 a dezembro de 2011, 38 cepas de estafilococos coagulase-negativos (SCNs) resistentes à linezolida (20 S. epidermidis, 14 S. haemolyticus, 3 S. hominis e 1 S. warneri) isoladas de hemoculturas e pontas de cateter de pacientes internados em dois hospitais terciários do Estado de São Paulo foram incluídas neste estudo para a determinação dos mecanismos de resistência e análise da estabilidade do fenótipo resistente. As cepas de SCNs apresentaram altos níveis de resistência à linezolida (CIMs de 16-128 µg/ml) e foram multi-resistentes, permanecendo sensíveis à vancomicina e teicoplanina. A mutação G2576T foi identificada no domínio V do gene rRNA 23S em todas as cepas de SCNs, exceto em uma cepa de S. haemolyticus. O gene cfr e mutações nas proteínas L4 e L22 não foram detectados. Em relação à proteína L3, todas as cepas de S. epidermidis do hospital A, incluindo a cepa controle sensível à linezolida, apresentaram a substituição Leu101Val, sugerindo que essa mutação seja um marcador clonal dessa população sem envolvimento com a resistência à linezolida. A única cepa proveniente do hospital B (S. epidermidis) foi selvagem para essa proteína ribossômica. Somente uma cepa de S. haemoyticus teve uma mutação no gene rplC, resultando na alteração Val154Leu. Em S. hominis, a mutação Phe147Ile foi identificada em uma cepa, enquanto a associação de Gly139Arg e Met156Thr foi observada nas outras duas cepas dessa espécie. A identificação dessas mutações na proteína L3 de...
Linezolid was the first agent of the oxazolidinone class to be introduced clinically. This oxazolidinone inhibits protein biosynthesis by preventing the formation of the initiation complex that consists of the mRNA, the f-Met tRNA and the 50S subunit of the ribosome. Although linezolid resistance has been mediated by the cfr-encoded product or by ribosomal proteins (L3, L4 and L22), the most common mechanism of resistance involves mutations in the central loop of domain V of the 23S rRNA gene. From March 2008 to December 2011, 38 coagulase-negative staphylococci (CNS) strains (20 S. epidermidis, 14 S. haemolyticus, 3 S. hominis e 1 S. warneri) exhibiting resistance to linezolid were isolated from blood and catheter cultures from patients in two tertiary care hospitals in the State of São Paulo and were included in this study for the ascertainment of the resistance mechanisms to this antimicrobial agent and for the analysis of the stability of this resistance. The strains exhibited high-level resistance to linezolid (MICs 16-128 µg/ml) and all were multidrug resistant, remaining susceptible to vancomycin and teicoplanin. The G2576T mutation in domain V region of 23S rRNA was identified in all isolates, except in a linezolid-resistant S. haemolyticus strain. The cfr gene and mutations in ribosomal proteins L4 and L22 were not detected. Regarding L3 protein analysis, all S. epidermidis strains of hospital A, including the linezolid-susceptible control strain, showed the L3 Leu101Val mutation, suggesting that this alteration is probably not involved in linezolid resistance. The one strain from hospital B (S. epidermidis) was wild-type for this ribosomal protein. Only one S. haemolyticus strain had a mutation in the L3 protein, Val154Leu. Two S. hominis strains showed Gly139Arg/Met156Thr mutations whereas one strain had Phe147Ile in L3 protein. The identification of these mutations in L3 protein of the linezolid-resistant S. haemolyticus and S. hominis strains...
Assuntos
Antibacterianos/análise , Coagulase/análise , Mecanismos Moleculares de Ação Farmacológica , Estrutura Molecular , Oxazolidinonas , FenótipoRESUMO
Linezolid was the first agent of the oxazolidinone class to be introduced clinically. This oxazolidinone inhibits protein biosynthesis by preventing the formation of the initiation complex that consists of the mRNA, the f-Met tRNA and the 50S subunit of the ribosome. Although linezolid resistance has been mediated by the cfr-encoded product or by ribosomal proteins (L3, L4 and L22), the most common mechanism of resistance involves mutations in the central loop of domain V of the 23S rRNA gene. From March 2008 to December 2011, 38 coagulase-negative staphylococci (CNS) strains (20 S. epidermidis, 14 S. haemolyticus, 3 S. hominis e 1 S. warneri) exhibiting resistance to linezolid were isolated from blood and catheter cultures from patients in two tertiary care hospitals in the State of São Paulo and were included in this study for the ascertainment of the resistance mechanisms to this antimicrobial agent and for the analysis of the stability of this resistance. The strains exhibited high-level resistance to linezolid (MICs 16-128 µg/ml) and all were multidrug resistant, remaining susceptible to vancomycin and teicoplanin. The G2576T mutation in domain V region of 23S rRNA was identified in all isolates, except in a linezolid-resistant S. haemolyticus strain. The cfr gene and mutations in ribosomal proteins L4 and L22 were not detected. Regarding L3 protein analysis, all S. epidermidis strains of hospital A, including the linezolid-susceptible control strain, showed the L3 Leu101Val mutation, suggesting that this alteration is probably not involved in linezolid resistance. The one strain from hospital B (S. epidermidis) was wild-type for this ribosomal protein. Only one S. haemolyticus strain had a mutation in the L3 protein, Val154Leu. Two S. hominis strains showed Gly139Arg/Met156Thr mutations whereas one strain had Phe147Ile in L3 protein. The identification of these mutations in L3 protein of the linezolid-resistant S. haemolyticus and S. hominis strains strengthens the role of these sites in the acquisition of linezolid resistance in Staphylococcus spp. However, the presence of G2576T in the 23S rRNA gene makes difficult to determine exactly the role of L3 mutations in conferring elevated linezolid MIC values showed by these clinical strains. In the absence of antibiotic pressure, after 130 passages, linezolid resistance was stable in the clinical strains of this study, which did not have all copies of the 23S rRNA gene mutated, according to the restriction of the domain V fragment with NheI enzyme. Sequencing of the individual copies of the 23S rRNA gene in the serially passaged strains showed G2576T in all amplified copies by PCR: 4/4 and 5/5 in S. epidermidis and 3/3 in S. haemolyticus strains (MIC of 16-32 µg/ml). The stability of the mutant rRNA copy was also observed in the linezolid-susceptible S. epidermidis strain (MIC of 4 µg/ml). After the passages in antibiotic-free medium, the linezolid MIC of this strain fell to 1 µg/ml and the G2576T mutation persisted in one 23S rRNA gene copy. The clonal relatedness of the strains was determined by PFGE and revealed a clonal dissemination of different CNS species. Regarding MLST analysis, all S. epidermidis strains belonged to the sequence type ST2 (CC2). Most likely, the increased selective pressure has contributed to the selection of endemic linezolid-resistant CNS clones showing the G2576T mutation that have been disseminated in the institution A since 2008. Differently, the restricted use of linezolid in the institution B could explain the occurrence of a single resistant strain since 2005