Background: Salmonella enterica ser. Typhi and Salmonella enterica ser. Paratyphi are agents of typhoid fever, a severe systemic disease, which remains to be a public health concern in the Philippines. Infection due to non-typhoidal Salmonella (NTS), on the other hand, most often results in a self-limiting acute gastroenteritis but may result in invasive disease in some cases. There is scarcity of information on the Salmonella serotypes in the Philippines which limits understanding of the distribution, transmission and antimicrobial resistance of these bacteria. Objective: This study describes the serotype distribution and antimicrobial resistance of Salmonella in the Philippines over a 15-year period. Methodolgy: Salmonella isolates were collected through the Philippine Department of Health-Antimicrobial Resistance Surveillance Program (DOH-ARSP) from January 1, 2004 to December 31, 2018. The isolates were serotyped using Sven Gard method for slide agglutination using antigens from Denka Seiken (Japan), and S and A serotest (Thailand). Antigenic formula obtained were classified according to White-Kauffmann-LeMinor scheme. Antimicrobial susceptibility testing for ampicillin, ceftriaxone, cefotaxime, chloramphenicol, ciprofloxacin, and trimethoprim-sulfamethoxazole, were performed using both automated and conventional methods (Kirby Bauer disk diffusion and gradient diffusion method). Antimicrobial susceptibility results were interpreted using Clinical and Laboratory Standards Institute (CLSI) 2018 interpretive criteria (M100Ed28E). Results: A total of 2,387 isolates were collected from human specimens during the 15-year study period. There were 69 serotypes of Salmonella identified with the most common being Salmonella enterica ser. Typhi: n=1895 (79.39%), Salmonella enterica ser. Enteritidis: n=182 (7.62%), Salmonella enterica ser. Typhimurium: n=87 (3.64%), Salmonella enterica ser. Weltevreden: n=24 (1.00%), Salmonella enterica ser. Paratyphi A: n=17 (0.71%), Salmonella enterica ser. Stanley: n=17 (0.71%), Salmonella enterica ser. Anatum: n=13 (0.54%), Salmonella enterica ser. Heidelberg: n=12 (0.50%), Salmonella enterica ser. Choleraesuis var. Kunzendorf: n=9 (0.38%). The multidrug resistant Salmonella serotypes reported in this study were mostly resistant to ampicillin, cefotaxime, ciprofloxacin combinations. Conclusion This present study showed that prevailing Salmonella serotypes in the Philippines were similar with Salmonella serotypes reported from other Asian countries. Typhoidal isolates were high among 6-17 years old and were mostly from males. The antimicrobial resistance rates for typhoidal Salmonella isolates to ampicillin, chloramphenicol, trimethoprim-sulfamethoxazole, ciprofloxacin, ceftriaxone and cefotaxime were lower compared with the antimicrobial resistance rates for non-typhoidal Salmonella isolates. Multidrug resistance for both Salmonella Typhi and NTS were relatively low. Continued and enhanced surveillance is needed to monitor the rising levels of antimicrobial resistance, determine risk factors and exposures associated with Salmonella Typhi and NTS infection to guide prevention and control measures.
Salmonella typhi ; Drug Resistance, Multiple

Objective: The epidemiology of invasive non-typhoidal Salmonella (iNTS) in the Philippines is not well elaborated. The present study describes the serotype distribution and antimicrobial susceptibility patterns of iNTS in the Philippines from 2014 to 2018. Methods: Invasive NTS isolates were collected through the Department of Health’s Antimicrobial Resistance Surveillance Program (ARSP). The identification of the isolates was confirmed using automated (Vitek®, bioMérieux, Marcy l’Étoile, France) and conventional methods. The isolates were serotyped using the slide agglutination method, and susceptibility testing was performed using Clinical and Laboratory Standards Institute guidelines. Demographic data were collected from the ARSP database. Results: There were 138 isolates collected from human invasive specimens with 97.8% from blood samples. The most common serotypes were Salmonella Enteritidis (n = 84, 60.9%) and Salmonella Typhimurium (n = 18, 13.0%). Most of the isolates were from males (n = 88, 63.8%) and from the 0–5-year age group (n = 61, 44.2%). The proportions of iNTS isolates resistant to first-line antibiotics were as follows: ampicillin (23.2%), chloramphenicol (9.6%), ciprofloxacin (8.7%), ceftriaxone (2.2%) and trimethoprim-sulfamethoxazole (8.8%). The proportion of isolates with multi-drug resistance was 13.0% (18/138) with the most common resistance profile being resistance to ampicillin-chloramphenicol-ciprofloxacin from Salmonella Enteritidis isolates (n = 5). Discussion: Resistance to first-line antibiotics limits the therapeutic choices for Salmonella infection. Relevant local antimicrobial resistance data on iNTS may support appropriate empiric therapy among vulnerable populations.