Antibiotics, Vol. 11, Pages 1725: Variability in Adaptive Resistance of Salmonella Typhimurium to Sublethal Levels of Antibiotics

Figure 1. Antibiotic susceptibilities of Salmonella Typhimurium ATCC 19585 (STATCC); (AD) and S. Typhimurium CCARM 8009 (STCCARM: EH) exposed to a half minimum inhibitory concentration (MIC) of cefotaxime (CEF1/2; A,E), chloramphenicol (CHL1/2; B,F), gentamicin (GEN1/2; C,G), and polymyxin B (POL1/2; E,H) for 0 (control; ○, ○) and 3 (●, ●) days. The optical density (OD) of STATCC and the STCCARM untreated control and after exposure to CEF1/2, CHL1/2, GEN1/2, and POL1/2 for 3 days was measured after incubating at 37 °C for 18 h.

Figure 1. Antibiotic susceptibilities of Salmonella Typhimurium ATCC 19585 (STATCC); (AD) and S. Typhimurium CCARM 8009 (STCCARM: EH) exposed to a half minimum inhibitory concentration (MIC) of cefotaxime (CEF1/2; A,E), chloramphenicol (CHL1/2; B,F), gentamicin (GEN1/2; C,G), and polymyxin B (POL1/2; E,H) for 0 (control; ○, ○) and 3 (●, ●) days. The optical density (OD) of STATCC and the STCCARM untreated control and after exposure to CEF1/2, CHL1/2, GEN1/2, and POL1/2 for 3 days was measured after incubating at 37 °C for 18 h.

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Figure 2. Frequencies of persistence (■, ■) and resistance (■, ■) in Salmonella Typhimurium ATCC 19585 (STATCC; A) and S. Typhimurium CCARM 8009 (STCCARM: B) exposed to a half minimum inhibitory concentration (MIC) of cefotaxime (CEF1/2), chloramphenicol (CHL1/2), gentamicin (GEN1/2), and polymyxin B (POL1/2). Different letters (a–c) on the bars show significant differences among treatments within persistence at p < 0.05, and different letters (x–z) on the bars show significant difference among treatments within resistance at p < 0.05. nd represents not determined.

Figure 2. Frequencies of persistence (■, ■) and resistance (■, ■) in Salmonella Typhimurium ATCC 19585 (STATCC; A) and S. Typhimurium CCARM 8009 (STCCARM: B) exposed to a half minimum inhibitory concentration (MIC) of cefotaxime (CEF1/2), chloramphenicol (CHL1/2), gentamicin (GEN1/2), and polymyxin B (POL1/2). Different letters (a–c) on the bars show significant differences among treatments within persistence at p < 0.05, and different letters (x–z) on the bars show significant difference among treatments within resistance at p < 0.05. nd represents not determined.

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Figure 3. Cross-resistance of Salmonella Typhimurium ATCC 19585 (STATCC; AD) and S. Typhimurium CCARM 8009 (STCCARM: EH) exposed to a half minimum inhibitory concentration (MIC) of cefotaxime (CEF1/2), chloramphenicol (CHL1/2), gentamicin (GEN1/2), and polymyxin B (POL1/2) to cefotaxime (A,E), chloramphenicol (B,F), gentamicin (C,G), and polymyxin B (D,H). The dotted lines represent untreated STATCC and STCCARM. ns indicates no significant difference and *, **, and *** denote significance differences at p < 0.05, p < 0.01, and p < 0.001, respectively.

Figure 3. Cross-resistance of Salmonella Typhimurium ATCC 19585 (STATCC; AD) and S. Typhimurium CCARM 8009 (STCCARM: EH) exposed to a half minimum inhibitory concentration (MIC) of cefotaxime (CEF1/2), chloramphenicol (CHL1/2), gentamicin (GEN1/2), and polymyxin B (POL1/2) to cefotaxime (A,E), chloramphenicol (B,F), gentamicin (C,G), and polymyxin B (D,H). The dotted lines represent untreated STATCC and STCCARM. ns indicates no significant difference and *, **, and *** denote significance differences at p < 0.05, p < 0.01, and p < 0.001, respectively.

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Figure 4. Relative fitness of Salmonella Typhimurium ATCC 19585 (STATCC; ■) and S. Typhimurium CCARM 8009 (STCCARM; ■) exposed to a half minimum inhibitory concentration (MIC) of cefotaxime (CEF1/2), chloramphenicol (CHL1/2), gentamicin (GEN1/2), and polymyxin B (POL1/2). Different letters (a–c) on the bars show significant differences among treatments within persistence at p < 0.05, and different letters (x–z) on the bars show significant differences among treatments within resistance at p < 0.05.

Figure 4. Relative fitness of Salmonella Typhimurium ATCC 19585 (STATCC; ■) and S. Typhimurium CCARM 8009 (STCCARM; ■) exposed to a half minimum inhibitory concentration (MIC) of cefotaxime (CEF1/2), chloramphenicol (CHL1/2), gentamicin (GEN1/2), and polymyxin B (POL1/2). Different letters (a–c) on the bars show significant differences among treatments within persistence at p < 0.05, and different letters (x–z) on the bars show significant differences among treatments within resistance at p < 0.05.

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Table 1. Antimicrobial property of antibiotics used in this study.

Table 1. Antimicrobial property of antibiotics used in this study.

ClassAntibioticSpectrumActivityAffinityInhibitory MechanismsCephemsCefotaximeBroadCidalHydrophilicCell wall synthesisAminoglycosidesGentamicinNarrowCidalHydrophilicProtein synthesis (30S)GlycopeptidesPolymyxin BNarrowCidalHydrophilicMembrane permeabilityPhenicolsChloramphenicolBroadStaticHydrophobicProtein synthesis (50S)

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