Genotypic virulence profiles and associations in Salmonella isolated from meat samples in wet markets and abattoirs of Metro Manila, Philippines

Abstract

Background Salmonella are pathogenic foodborne bacteria with complex pathogenicity from numerous virulence genes housed in Salmonella pathogenicity islands (SPIs), plasmids, and other gene cassettes. However, Salmonella virulence gene distributions and mechanisms remain unestablished. In the Philippines, studies mainly report Salmonella incidences and antimicrobial resistance, but little to none on virulence profiles, their associations to animal sources, collection sites and Salmonella serogroups. Hence, a total of 799 Salmonella isolates, previously obtained from pig, cow, and chicken meat samples in wet markets and abattoirs (wet markets: 124 chicken, 151 cow, and 352 pig meat isolates; abattoirs: 172 pig tonsil and jejunum isolates) in Metro Manila, Philippines, were revived and confirmed as Salmonella through invA gene polymerase chain reaction (PCR). Isolates were then screened for eight virulence genes, namely avrA, hilA, sseC, mgtC, spi4R, pipB, spvC and spvR, by optimized multiplex PCR and significant pair associations between virulence genes were determined through Fisher’s exact test. Gene frequency patterns were also determined. Salmonella serogroups in addition to animal sources and location types were also used to predict virulence genes prevalence using binary logistic regression. Results High frequencies (64 to 98%) of SPI virulence genes were detected among 799 Salmonella isolates namely mgtC, pipB, avrA, hilA, spi4R and sseC, from most to least. However, only one isolate was positive for plasmid-borne virulence genes, spvC and spvR. Diversity in virulence genes across Salmonella serogroups for 587 Salmonella isolates (O:3 = 250, O:4 = 133, O:6,7 = 99, O:8 = 93, O:9 = 12) was also demonstrated through statistical predictions, particularly for avrA, hilA, sseC, and mgtC. mgtC, the most frequent virulence gene, was predicted by serogroup O:9, while sseC, the least frequent, was predicted by serogroup O:4 and chicken animal source. The highest virulence gene pattern involved SPIs 1-5 genes which suggests the wide distribution and high pathogenic potential of Salmonella. Statistical analyses showed five virulence gene pair associations, namely avrA and hilA, avrA and spi4R, hilA and spi4R, sseC and spi4R, and mgtC and pipB. The animal sources predicted the presence of virulence genes, sseC and pipB, whereas location type for hilA and spi4R, suggesting that these factors may contribute to the type and pathogenicity of Salmonella present. Conclusion The high prevalence of virulence genes among Salmonella in the study suggests the high pathogenic potential of Salmonella from abattoirs and wet markets of Metro Manila, Philippines which poses food safety and public health concerns and threatens the Philippine food animal industry. Statistical associations between virulence genes and prediction analyses across Salmonella serogroups and external factors such as animal source and location type and presence of virulence genes suggest the diversity of Salmonella virulence and illustrate determining factors to Salmonella pathogenicity. This study recommends relevant agencies in the Philippines to improve standards in food animal industries and increase efforts in monitoring of foodborne pathogens.

Molecular characterization of virulence and resistance genes in Salmonella strains isolated from chickens sold at the informal chicken market in Gauteng Province, South Africa

“…The frequency of virulence genes varied significantly across the townships or locations of the outlets studied except for gene pefC . This finding reflects the types and serovars of the infecting Salmonella and the practices that could have been affected by the types of farms, types of chickens, and their distribution across the townships, similar to the findings of others (Mthembu et al, 2019; Pavon et al, 2022).…”

“…All the isolates were carriers of at least one virulence gene using assays (SPI, plasmids, flagellin, CS54 island, and fimbriae), while 114 (42.5%) possessed one or more of the seven (38.9%) of the 18 AMR genes detected, Kumar et al (2021), in a similar study conducted on 'pluck shops'-processed poultry in Trinidad and Tobago, reported that of the 46 Salmonella isolates recovered, all were positive for one or more of the detected 12 (92.3%) of the 13 virulence genes tested while only 4 (33.3%) of the 12 AMR genes tested were detected. Variable frequencies of virulence and AMR genes have been reported for Salmonella isolates recovered from samples from the 'wet markets' elsewhere by others (Long et al, 2022;Pavon et al, 2022;Siddiky et al, 2022). The differences in the frequencies of virulence and resistance genes across the 'wet market' outlets in several countries may reflect the sample size, prevalence of Salmonella, types of genes tested for, and the types and use of antimicrobial agents in the poultry industry.…”

“…Virulence genes encoded in SPI-1 to SPI-5, detection frequency, and their activities in the pathogenicity of Salmonella spp. recovered from chickens or cases of human salmonellosis have been well documented in the literature (Kumar et al, 2021;Pavon et al, 2022;Zishiri et al, 2016). The frequency and types of virulence genes in Salmonella isolated from poultry are variable across countries (Kumar et al, 2021;Lozano-Villegas et al, 2023;Zishiri et al, 2016).…”

Physiological characteristics and virulence gene composition of selected serovars of seafood-borne Salmonella enterica

“…The avrA gene, which encodes an effector protein, is primarily involved in the enteritis pathway [33] and was detected only in four of the test isolates of this study. In a similar observation, the avrA gene was found in 30%-80% of the Salmonella isolates from food and food animal environments [34][35][36]. Genetic rearrangements within the pathogenicity islands result in variations within SPIs.…”

Resistencia antibiótica de cepas de Salmonella enterica aisladas de canales de cuyes en un mercado de Lima, 2021

“…DISCUSIÓN El 28.9 ± 4.5% (111/384) de cepas positivas a Salmonella enterica aislados en esta investigación difiere de lo reportado por Soriano (2020), quién utilizando la misma metodología de muestreo en el mismo lugar de estudio aisló solo 5.1 ± 2.2% (20/393) de cepas positivas en la canal externa e interna de El incremento en el número de muestras positivas en esta investigación sugiere como posibles causas: el faenamiento de animales infectados, el pobre manejo de la higiene, limpieza y desinfección del área de faenamiento, errores durante la etapa de evisceración y deficiencia de los programas de vigilancia y control que limiten la contaminación de las canales en los mercados de abasto. Sin embargo, el aislamiento de Salmonella enterica en órganos de cuyes aparentemente sanos y enfermos reportada por otros autores demuestra que existe mayor probabilidad de exposición a la infección previo al proceso de manufactura (Salvatierra et Se reconoce como principal nicho de la Salmonella al tracto intestinal, por lo que la fuente de contaminación de estas canales sería de tipo fecal, donde la eliminación de esta bacteria puede ser intermitente, esporádica o constante, producto de la relación de las diferentes cepas de Salmonella y los diferentes hospedadores que infectan (Andino y Hanning, 2015; Crump et al, 2015), mostrando amplias variaciones de prevalencias de serotipos en diferentes animales de consumo, ubicación, y otras variables externas al serovar de Salmonella en estudio (Pavon et al, 2022).…”